Bio Finals PDF

Rheyniel A. Escobel, LPT Course Code: PSC 201 Course Description: The course aims to provide the students with a broad understanding of the primary disciplines in the biological sciences, including molecular biology, genetics, cell biology, biochemistry, and physiology; Conceptual foundation in biology; critically evaluate scientific data and scientific literature, develop an appreciation for the scope, unity, and diversity of life in the biosphere, including the classification of plants, animals, and microbes; develop essential professional skills such as interpersonal skills, oral and written communication skills, and problem-solving skills including scientific inquiry, and apply technology for the purposes of problem-solving and reporting results. Course Intended Learning Outcomes (CILO): At the end of this course, the students should be able to: 1. Understand and appreciate the scope, unity, and diversity of life in the biosphere, including the classification of plants, animals, and microbes. 2. Students will develop essential professional skills such as interpersonal skills, oral and written communication skills, and problem-solving skills including scientific inquiry. 3. Students will be able to apply technology for the purposes of problem-solving and reporting results. 4. Develop an appreciation for the scope, unity, and diversity of life in the biosphere, including the classification of plants, animals, and microbes. 5. Develop essential professional skills such as interpersonal skills, oral and written communication skills, and problem-solving skills including scientific inquiry. 6. Apply technology for the purposes of problem-solving and reporting results. Course Requirements: Class Standing - 60% Major Exams - 40% Periodic Grade 100% Prelim Grade 60% Class Standing + 40% Prelim Exam Midterm Grade 30% Prelim Grade + 70% Midterm Grade (60% Class Standing + 40% Midterm Exam) Final Grade 30% Midterm Grade + 70% Final Grade (60% Class Standing + 40% Final Exam) 148 Table of Contents MODULE 12 The Respiratory System.............................................................. 154 Introduction................................................................................................. 154 Lesson 1: Anatomy of the Respiratory System................................................... 154 Lesson 2: The Process of Breathing and Transport of Gases.............................. 167 Lesson 3: Gas Exchange.................................................................................... 172 Assessment Tasks....................................................................................... 178 References:.................................................................................................. 181 MODULE 13 The Digestive System.................................................................. 182 Introduction................................................................................................. 182 Lesson 1: Anatomy of the Digestive System....................................................... 182 Lesson 2: Accessory Organs in Digestion........................................................... 194 Lesson 3: Digestive Processes............................................................................ 199 Lesson 4: Chemical Digestion and Absorption................................................... 201 Assessment Tasks....................................................................................... 207 References:.................................................................................................. 210 MODULE 14 The Endocrine System................................................................. 211 Introduction................................................................................................. 211 Lesson 1: Overview of the Endocrine System..................................................... 211 Lesson 2: Hormones.......................................................................................... 213 Lesson 3: The Endocrine Glands and other Hormones....................................... 215 Assessment Tasks....................................................................................... 219 References:.................................................................................................. 221 MODULE 15 The Excretory System................................................................. 222 Introduction................................................................................................. 222 Lesson 1: Anatomy of the Urinary System......................................................... 222 Lesson 2: Gross Anatomy of the Kidney and Urine Transport............................ 223 Lesson 3: Physical Characteristics of Urine....................................................... 229 Lesson 4: The Excretory System and Homeostasis............................................. 231 Assessment Tasks....................................................................................... 235 References:.................................................................................................. 238 MODULE 16 Introduction to Molecular Genetics............................................ 239 Introduction................................................................................................. 239 Lesson 1: Historical Basis.................................................................................. 239 149 Lesson 2: DNA Structure and Sequencing......................................................... 241 Lesson 3: DNA Replication................................................................................. 243 Lesson 4: Mutations and DNA Repair Mechanisms............................................ 247 Lesson 5: Transcription and Translation........................................................... 248 Lesson 5: Cellular Differentiation...................................................................... 252 Assessment Tasks....................................................................................... 254 References:.................................................................................................. 256 MODULE 17 Mendelian Genetics.................................................................... 257 Introduction................................................................................................. 257 Lesson 1: Mendel’s Experiments and the Laws of Probability............................. 257 Lesson 2: Pattern of Inheritance........................................................................ 260 Lesson 3: Law of Inheritance............................................................................. 273 Assessment Tasks....................................................................................... 277 References:.................................................................................................. 279 MODULE 18 Evolution and Origin of Species................................................... 280 Introduction................................................................................................. 280 Lesson 1: Overview and Understanding of Evolution......................................... 280 Lesson 2: Formation of New Species.................................................................. 286 Lesson 3: Population Evolution......................................................................... 290 Assessment Tasks....................................................................................... 294 References:.................................................................................................. 296 150 Table of Figures Figure 12. 1 The major respiratory structures......................................................... 155 Figure 12. 2 The external features of the nose......................................................... 156 Figure 12. 3 The skeletal features of the nose.......................................................... 157 Figure 12. 4 The upper respiratory tract.................................................................. 158 Figure 12. 5 The respiratory epithelium................................................................... 159 Figure 12. 6 The divisions of the pharynx................................................................ 159 Figure 12. 7 The anterior and right lateral view of the larynx................................... 161 Figure 12. 8 Vocal cords.......................................................................................... 162 Figure 12. 9 The tracheal tube................................................................................. 163 Figure 12. 10 The tracheal mucosa.......................................................................... 164 Figure 12. 11 Bronchioles........................................................................................ 164 Figure 12. 12 The alveoli.......................................................................................... 165 Figure 12. 13 The alveolar structures within lung tissue......................................... 166 Figure 12. 14 Gross anatomy of the lungs............................................................... 167 Figure 12. 15 Boyle’s Law........................................................................................ 168 Figure 12. 16 Intrapulmonary and intrapleural pressure relationships.................... 170 Figure 12. 17 Primary phases of pulmonary ventilation........................................... 171 Figure 12. 18 Partial and total pressures of a gas.................................................... 173 Figure 12. 19 External and Internal respiration....................................................... 174 Figure 12. 20 Erythrocyte and hemoglobin.............................................................. 175 Figure 12. 21 Hemoglobin Dissociation Curve.......................................................... 176 Figure 13. 1 The components of the digestive system............................................... 184 Figure 13. 2 Functions of several digestive organs................................................... 185 Figure 13. 3 Contribution of other Body Systems to the Digestive System............... 186 Figure 13. 4 The Mouth........................................................................................... 186 Figure 13. 5 The pharynx or throat.......................................................................... 188 Figure 13. 6 The esophagus..................................................................................... 189 Figure 13. 7 Deglutition........................................................................................... 190 Figure 13. 8 The stomach........................................................................................ 191 Figure 13. 9 The small intestine............................................................................... 192 Figure 13. 10 The large intestine............................................................................. 193 Figure 13. 11 The tongue......................................................................................... 194 Figure 13. 12 A typical tooth and surrounding structures....................................... 195 Figure 13. 13 Dentitions and times of eruptions (indicated in parentheses)............. 196 Figure 13. 14 The three major salivary glands......................................................... 197 Figure 13. 15 Relation of the pancreas to the liver, gallbladder, and duodenum...... 198 Figure 13. 16 The liver............................................................................................. 198 Figure 13. 17 The gallbladder.................................................................................. 199 Figure 13. 18 The six digestion processes................................................................ 200 Figure 13. 19 Digestion and absorption................................................................... 202 Figure 13. 20 Digestive enzymes.............................................................................. 203 Figure 13. 21 Absorption......................................................................................... 205 Figure 14. 1 Comparison of Control by the Nervous and Endocrine Systems........... 212 Figure 14. 2 The Structures of Endocrine System.................................................... 213 Figure 14. 3 The Endocrine System......................................................................... 215 151 Figure 14. 4 Hypothalamus–pituitary complex......................................................... 216 Figure 14. 5 Posterior pituitary................................................................................ 217 Figure 14. 6 Summary of the Principal Actions of Anterior Pituitary Hormones....... 218 Figure 15. 1 Sagittal section through the right kidney............................................. 224 Figure 15. 2 Frontal sections of the right kidney...................................................... 225 Figure 15. 3 The female and male urethras.............................................................. 226 Figure 15. 4 Sagittal section of female urethra......................................................... 227 Figure 15. 5 Sagittal section of male urethra........................................................... 228 Figure 15. 6 The bladder and ureter........................................................................ 229 Figure 15. 7 Urine Color.......................................................................................... 231 Figure 15. 8 Focus on Homeostasis: The Urinary System......................................... 234 Figure 16. 1 James Watson and Francis Crick with their DNA model...................... 240 Figure 16. 2 Rosalind Franklin................................................................................ 241 Figure 16. 3 The DNA Structure.............................................................................. 242 Figure 16. 4 Components of DNA (left) and DNA structure backbone (right)............. 242 Figure 16. 5 Suggested Models of DNA Replication.................................................. 244 Figure 16. 6 DNA Replication in Prokaryotes........................................................... 245 Figure 16. 7 xeroderma pigmentosum (left) and ataxia-telangiectasia (right)............ 248 Figure 16. 8 Transcription unit................................................................................ 249 Figure 16. 9 Three steps of transcription................................................................. 250 Figure 16. 10 The triplet code is translated into amino acids................................... 251 Figure 16. 11 The differences between translation vs transcription.......................... 252 Figure 16. 12 Cell Differentiation............................................................................. 253 Figure 17. 1 Gregor Mendel..................................................................................... 258 Figure 17. 2 The seven characteristics Mendel studied in pea plants....................... 259 Figure 17. 3 A gene.................................................................................................. 261 Figure 17. 4 Mendelian crosses................................................................................ 262 Figure 17. 5 Mendelian crosses................................................................................ 263 Figure 17. 6 Example of a test cross........................................................................ 265 Figure 17. 7 Incomplete dominance......................................................................... 266 Figure 17. 8 Example of multiple alleles for rabbit coat color................................... 267 Figure 17. 9 Wild-type Drosophila (left) and the Antennapedia mutant (right).......... 268 Figure 17. 10 Human male Karyotype...................................................................... 269 Figure 17. 11 X-linked trait in Drosophila (eye color)............................................... 270 Figure 17. 12 Punnett square analysis of Drosophila eye color: X-Linked Recessive Disorders in Humans and Recessive Carriers.......................................................... 271 Figure 17. 13 Color perception in different types of color blindness......................... 272 Figure 17. 14 X-linked disorders.............................................................................. 273 Figure 17. 15 The Law of Segregation...................................................................... 274 Figure 17. 16 Law of Independent Assortment......................................................... 274 Figure 17. 17 dihybrid cross of pea plants............................................................... 275 Figure 17. 18 Law of Dominance.............................................................................. 276 Figure 18. 1 Charles Darwin (a) and Alfred Wallace (b)............................................ 281 Figure 18. 2 Adaptive Radiation of Darwin’s Finches............................................... 283 152 Figure 18. 3 Flowering plants.................................................................................. 285 Figure 18. 4 Interbreeding in dogs........................................................................... 287 Figure 18. 5 Temporal isolation (a) and Habitat isolation (b).................................... 288 Figure 18. 6 The Evolution of Species...................................................................... 289 Figure 18. 7 The Evolution of Species...................................................................... 290 Figure 18. 8 Mutation and natural selection............................................................ 292 Figure 18. 9 Genetic drift and gene fixation............................................................. 293 153 MODULE 12 The Respiratory System Introduction All living things need to exchange materials like food, oxygen, and waste with their environment and circulate them within their bodies. Complex animals use respiratory systems to exchange gases (like oxygen and carbon dioxide) and circulatory systems (also called cardiovascular systems in animals with backbones) to transport nutrients and gases throughout their bodies (Kratz and Siegfried, 2010). Lesson 1: Anatomy of the Respiratory System According to Chruścik et al. (2021), the respiratory system's primary functions include removing carbon dioxide waste, supplying oxygen to bodily tissues for energy, and maintaining the body's acid-base balance. The respiratory system's components also assist with non- essential functions including speaking, breathing, and straining during birthing or coughing. 154 Figure 12. 1 The major respiratory structures The authors further explained that the respiratory system has two main parts: the conducting zone and the respiratory zone. The conducting zone includes the organs and structures that help move air but are not involved in gas exchange. The actual gas exchange happens in the respiratory zone. Conducting Zone The conducting zone serves three primary functions: air movement, dust and germ removal, and air heating and humidification. The conducting zone has extra purposes for certain of its components. For instance, the bronchial lining of the lungs can break down some hazardous compounds in the air, while the nasal passages aid in the detection of odors. The Nose and Its Adjacent Structures According to Chruścik et al. (2021), the respiratory system's primary entry and departure 155 points are through the nose. The nasal cavity (internal nose) and the external nose make up its two primary sections. Additionally, the visible components that determine the nose's appearance and functionality comprise the external nose. The space between the eyebrows is known as the root, and the bridge joins the root to the remainder of the nose. The tip, or apex, is where the dorsum nasi ends as it travels down the length of the nose. The cartilaginous structures known as alae form the nostrils, which are located on either side of the apex. The groove that runs from the tip of the nose to the upper lip is called the philtrum (Chruścik et al., 2021). Figure 12. 2 The external features of the nose Chruścik et al. (2021) stated that the nose's skeletal characteristics are visible beneath its skin. The nasal root and bridge are composed of bone, whereas the portion that protrudes is composed of cartilage. This explains why a skull lacks a nose. Beneath the root and bridge, the nasal bone joins the maxillary bones on either side with the frontal bone above. The nasal bone and flexible septal cartilage work together to generate the nose's length or dorsum nasi. The alar cartilage encircles the nostrils and forms the tip of the nose. 156 Figure 12. 3 The skeletal features of the nose The nasal septum divides the nasal cavity into left and right portions, and the nostrils (nares) lead into it. The ethmoid and vomer bones form the back of the septum, whereas the flexible cartilage that makes up its front is what you can feel. The superior, middle, and inferior nasal conchae are the three bony ridges that are located inside each side of the nasal cavity. Furthermore, conchae aid in expanding surface area and decreasing airflow, enabling the air to be heated and cleansed. Additionally, they aid in retaining moisture when exhaling. The palate, which consists of a soft palate in the rear (muscle) and a hard palate in the front (bone), makes up the floor of the nasal cavity. The nasal cavity's air leaves through the internal nares and moves into the pharynx (Chruścik et al., 2021). The authors further explained that several bones around the nasal cavity have air-filled spaces called sinuses. These sinuses warm and moisten the air you breathe. Each paranasal sinus is named after the bone it’s in frontal, maxillary, sphenoidal, and ethmoidal. They produce mucus and help make the skull lighter. Additionally, the front part of the nasal cavity and the nostrils are lined with mucous membranes that have glands (sebaceous) and hair follicles to catch large particles like dirt. 157 Deeper in the nasal cavity, there are special cells that detect smells which is known as the olfactory epithelium. Figure 12. 4 The upper respiratory tract The nasal cavity has a special lining called respiratory epithelium with tiny hair-like structures (cilia) and mucus-producing cells (goblet cells). The cilia move mucus and debris to the throat to be swallowed. Cold air can slow down the cilia, leading to a runny nose. This lining helps warm and humidify the air. Tiny blood vessels under the lining heat the air, and cells produce enzymes and proteins to fight bacteria. Immune cells in the tissue also help protect against infections (Chruścik et al., 2021). 158 Figure 12. 5 The respiratory epithelium Pharynx According to Chruścik et al. (2021), the pharynx is a muscle tube covered with a mucus lining that connects with the nasal cavities. It has three main parts: the nasopharynx, the oropharynx, and the laryngopharynx. Figure 12. 6 The divisions of the pharynx 159 According to Chruścik et al. (2021), the nasopharynx, located behind the nose, is mainly an airway. At the top, it has pharyngeal tonsils (or adenoids), which are clusters of lymph tissue that help trap and destroy pathogens. These tonsils are large in children but shrink with age. The uvula, a small teardrop-shaped structure, and the soft palate move upward during swallowing to block the nasal passage, preventing food from entering the nose. The nasopharynx also connects to the ears through the Eustachian (auditory) tubes, which is why ear infections can occur during a cold. Additionally, the oropharynx is a shared pathway for both air and food, located behind the mouth and below the nasopharynx. It connects to the oral cavity through an opening called the fauces. The lining here changes to a tougher tissue that can handle the friction from food. The oropharynx has two sets of tonsils: the palatine tonsils, located on the sides near the fauces, and the lingual tonsils at the base of the tongue. These tonsils are made of lymph tissue and help trap and destroy pathogens that enter through the mouth or nose. Chruścik et al. (2021) explained that positioned behind the larynx and beneath the oropharynx is the laryngopharynx. Food and air pass through it before entering the digestive and breathing systems. The same stiff tissue that lines the oropharynx also lines this area. The laryngopharynx is connected to the esophagus at the back (for food) and the larynx at the front (for air). 160 Larynx Figure 12. 7 The anterior and right lateral view of the larynx The larynx, located below the laryngopharynx, connects the throat to the trachea and controls airflow into the lungs. It’s made of several cartilage pieces, including the thyroid cartilage (front), epiglottis (top), and cricoid cartilage (bottom). The thyroid cartilage is the largest and includes the “Adam’s apple,” which is more visible in men. The cricoid cartilage forms a ring with a wider back and narrower front. Smaller paired cartilages (arytenoids, corniculates, and cuneiforms) are involved in moving the vocal cords for speech (Chruścik et al. 2021). 161 Figure 12. 8 Vocal cords The trachea is covered by a flexible flap called the epiglottis, which is affixed to the thyroid cartilage. The vestibular folds, or fake vocal cords, the genuine vocal cords, and the space between them make up the glottis when it is closed. The actual vocal cords are flexible white folds that vibrate to make sound, whereas the vestibular folds are mucous membranes. Males often have larger vocal cords, which results in deeper voices. The size of these cords varies, impacting voice pitch. The pharynx and larynx rise during swallowing, assisting the trachea closure mechanism of the epiglottis to keep food particles out of the airway. The upper part of the larynx is lined with tough stratified squamous epithelium, which changes into a mucus-producing lining with cilia as it continues downward. Like in the nasal cavity, this mucus traps debris and pathogens. The cilia move the mucus upward toward the laryngopharynx, where it can be swallowed into the esophagus. Trachea According to Chruścik et al. (2021), the trachea, or windpipe, extends from the larynx to the lungs and is made up of 16 to 20 C-shaped cartilage rings connected by dense tissue. The open part of the rings is at the back, filled by the tracheal muscle and elastic tissue, which together form a flexible membrane. This allows the trachea to stretch and expand during breathing, while the cartilage rings keep it from collapsing. The tracheal muscle can tighten to help push air out forcefully. The trachea is lined with ciliated epithelium that traps debris, and it 162 sits in front of the esophagus. Figure 12. 9 The tracheal tube Bronchial Tree Chruścik et al. (2021) explained that the carina, a delicate region where anything might enter and cause violent coughing, is where the trachea divides into the left and right primary bronchi. Like the trachea, these bronchi are lined with ciliated epithelium and cells that produce mucus. The bronchi are supported by cartilage rings to avoid collapse. The hilum is where the bronchi enter the lungs, along with blood, nerve, and lymphatic vessels. The bronchi then divide into smaller airways called the bronchial tree, which traps infections and debris while enabling airflow into and out of the lungs. 163 Figure 12. 10 The tracheal mucosa Respiratory Zone The respiratory zone, unlike the conducting zone, includes structures for gas exchange, starting from where terminal bronchioles connect to respiratory bronchioles and leading to alveolar ducts and alveoli (Chruścik et al., 2021). Figure 12. 11 Bronchioles 164 Alveoli Small, grape-like sacs called alveoli, which are used for gas exchange, are reached by an alveolar duct, a tube made of smooth muscle and connective tissue. A collection of these alveoli, each measuring 200 mm in diameter and featuring elastic walls to enhance gas exchange surface area, is called an alveolar sac. Pores that connect the alveoli aid in regulating the amount of air pressure in the lungs (Chruścik et al., 2021). Figure 12. 12 The alveoli Additionally, three main cell types make up the alveolar wall: alveolar macrophages, which remove debris and pathogens, type II alveolar cells, which release surfactant to lower surface tension, and type I alveolar cells, which cover the majority of the surface and are extremely thin and gas-permeable. Together, type I cells and capillary endothelial cells create a very thin respiratory membrane (about 0.5 mm) that facilitates CO2 release and oxygen intake by allowing gas exchange by simple diffusion. 165 Figure 12. 13 The alveolar structures within lung tissue The Lungs Both conducting and respiratory zone structures are present in each lung, which is a primary respiratory system organ. Its primary job is to exchange carbon dioxide and oxygen with the surrounding air over a surface area of roughly 70 square meters of extremely permeable epithelium (Chruścik et al., 2021). Gross Anatomy of the Lungs According to Chruścik et al. (2021), the lungs are pyramid-shaped, paired organs connected to the trachea by the right and left bronchi, and are bordered by the diaphragm at their base. They are enclosed by pleurae attached to the mediastinum. The right lung is shorter and wider than the left, which has a cardiac notch for the heart. The apex of each lung is the top part, the base is near the diaphragm, the costal surface faces the ribs, and the mediastinal surface faces the midline. 166 Figure 12. 14 Gross anatomy of the lungs Additionally, there are lobes within each lung, spaced apart by fissures. While the left lung contains two lobes (superior and inferior), the right lung has three (superior, middle, and inferior). There are several bronchopulmonary segments in each lobe, and each has its tertiary bronchus and artery. Certain segments may be affected by diseases, and in certain cases, removing one segment will have little effect on adjacent segments. The lungs' divisions known as pulmonary lobules are created when bronchi split into bronchioles, each of which receives a sizable bronchiole with several branches. These lobules are divided by connective tissue-based interlobular septa. Lesson 2: The Process of Breathing and Transport of Gases Chruścik et al. (2021) stated that pulmonary ventilation, or breathing, involves moving air into and out of the lungs. It is driven by three main pressures: atmospheric pressure (Patm), alveolar pressure (Palv) inside the alveoli, and intrapleural pressure (Pip) within the pleural cavity. 167 Mechanisms of Breathing Breathing depends on the atmospheric pressure and the air pressure within the lungs. While alveolar and intrapleural pressures are influenced by lung features, the process of air entering and leaving the lungs relies on the differences between atmospheric pressure and lung pressure (Chruścik et al., 2021). Pressure Relationships Chruścik et al. (2021) explained that inspiration and expiration depend on pressure differences between the atmosphere and the lungs. Pressure in gases is the force resulting from the movement of gas molecules within a confined space. Figure 12. 15 Boyle’s Law For instance, compared to the same number of molecules in a one-liter container, the gas molecules in a two-liter container press against the walls with less force as seen in Figure 12.15 above. As a result, the pressure in the one-liter container is higher and in the two-liter container is lower. Pressure varies with volume and the number of gas molecules at constant temperature. According to Boyle's law, a gas's pressure and volume at constant temperature are inversely related. Pressure falls with increasing volume and vice versa. A one-liter container, which has half the volume of a two-liter container, would, for instance, have twice the pressure 168 of the two-liter container (Chruścik et al., 2021). Boyle’s law is expressed by the following formula: 𝑷𝟏 𝑽𝟏 = 𝑷𝟐 𝑽𝟐 In Boyle’s law formula, 𝑷𝟏 𝑽𝟏 represent the initial pressure and volume, while 𝑷𝟐 𝑽𝟐 represent the final pressure and volume. If two containers with different volumes are connected, gases will move from the higher pressure (smaller volume) to the lower pressure (larger volume) when the volume of one container changes. Air pressure, intra-alveolar pressure (within the alveoli), and intrapleural pressure (inside the pleural cavity) are the three types of pressure that are necessary for pulmonary breathing. Atmospheric Pressure Atmospheric pressure is the force exerted by the air surrounding a surface, measured in atmospheres (atm) or millimeters of mercury (mm Hg). At sea level, 1 atm equals 760 mm Hg. In respiration, pressures are often described relative to atmospheric pressure: negative pressure is lower than atmospheric pressure, positive pressure is higher, and pressure equal to atmospheric pressure is considered zero (Chruścik et al., 2021). 169 Figure 12. 16 Intrapulmonary and intrapleural pressure relationships Intra-alveolar Pressure Intra-alveolar pressure is the pressure of air inside the alveoli and varies with the phases of breathing. Since the alveoli are connected to the atmosphere through the airways, the intra- alveolar pressure always equalizes with atmospheric pressure (Chruścik et al., 2021). Intrapleural Pressure The pressure that exists between the parietal and visceral pleurae inside the pleural cavity is known as intrapleural pressure. Although it fluctuates when breathing, it is always less than (negative) the intra-alveolar and atmospheric pressures. Throughout the breathing cycle, intrapleural pressure usually stays at –4 mm Hg, but it varies with inspiration and expiration. Additionally, breathing relies on muscle movements, mainly from the diaphragm and intercostal muscles, which create pressure changes to move air in and out of the lungs. The lungs themselves are passive and move with the thoracic wall due to pleural fluid. During inhalation, the chest expands, pulling the lungs outward, while during exhalation, the chest 170 contracts, pushing the lungs inward. Airway resistance, which increases with smaller airway diameters, affects how easily air flows through the lungs. This resistance can be understood with the formula F = ΔP / R, where F is airflow, ΔP is the pressure change, and R is resistance. Lastly, surface tension in the alveoli, caused by water, can inhibit their expansion. Pulmonary surfactant, secreted by type II alveolar cells, reduces this surface tension and prevents alveolar collapse. Thoracic wall compliance, or the ability of the thoracic wall to stretch under pressure, also affects breathing effort. Poor compliance makes it harder to expand the thorax and lungs during inspiration (Chruścik et al., 2021). Pulmonary Ventilation According to Chruścik et al. (2021), inspiration and expiration are the two primary phases of pulmonary breathing. Air enters the lungs during inspiration and leaves during expiration. One complete sequence of inhalation and expiration makes up a respiratory cycle. Figure 12. 17 Primary phases of pulmonary ventilation According to Chruścik et al. (2021), the diaphragm and external intercostal muscles are 171 the two primary muscle groups used during normal inspiration. The diaphragm expands the thoracic cavity and makes more room for the lungs when it contracts, moving downward. As the external intercostal muscles tighten, the rib cage and thoracic cavity expand even further as the ribs are lifted outward. The lungs stretch and expand as a result of this expansion, which is supported by the adhesive force of the pleural fluid. The pressure gradient that forces air into the lungs is caused by a reduction in intra-alveolar pressure as the volume of the thoracic cavity grows. Additionally, energy is not needed for the passive process of normal expiration. It depends on the flexibility of lung tissue, which, upon relaxation of the diaphragm and intercostal muscles, causes the lungs to rebound. The thoracic cavity and lungs' volume are reduced by this rebound, raising intra-alveolar pressure. The pressure gradient causes air to be forced out of the lungs when intra-alveolar pressure is higher than ambient pressure (Chruścik et al., 2021). Lesson 3: Gas Exchange According to Chruścik et al. (2021), understanding the fundamentals of gas behavior is essential to comprehending the mechanics underlying gas exchange in the lungs. In addition to Boyle's rule, several other gas laws provide light on the behavior of gases and aid in the understanding of the processes involved in respiration. Gas Laws and Air Composition Pressure is the force that gas molecules apply to the surfaces they come into contact with. Gases in natural systems are typically combinations of many molecular kinds. For example, atmospheric pressure is the total pressure exerted by the gases that make up the atmosphere, which includes nitrogen, carbon dioxide, oxygen, and other gases (Chruścik et al., 2021). Partial pressure - refers to the pressure exerted by a single type of gas in a mixture. For example, in the atmosphere, oxygen has its partial pressure, separate from the partial pressure of nitrogen. Total pressure - The total pressure of a gas mixture is the sum of all the partial pressures of the individual gases. 172 Figure 12. 18 Partial and total pressures of a gas Dalton’s Law - The behavior of nonreactive gases in a combination is explained by Dalton's law. According to this, the total pressure is the sum of the partial pressures of all the gases in the mixture, and each gas in the mixture exerts its pressure independently. Henry’s Law - Gases react differently from liquids, such as blood, according to Henry's law. It asserts that the solubility and partial pressure of a gas are closely correlated with its concentration in a liquid. More gas molecules will dissolve in the liquid the greater the gas's partial pressure. The solubility of the gas in that particular liquid also affects the concentration. Gas Exchange According to Chruścik et al. (2021), gas exchange in the body occurs at two sites: in the lungs (external respiration) and in the tissues (internal respiration). The alveoli are the site of external respiration, where carbon dioxide is exhaled and oxygen is taken in. Body tissues go through an internal respiration process during which carbon dioxide is taken up and oxygen is supplied. Energy is not needed for gas exchange because it is based on simple diffusion that is 173 fueled by pressure gradients. The respiratory membrane's high gas permeability, thinness, and huge surface area for gas exchange all work together to optimize this diffusion in the lungs. External Respiration The partial pressure differentials of carbon dioxide and oxygen between the blood in the pulmonary capillaries and the alveoli are what allow for external respiration. The flow of oxygen from the alveoli into the blood and carbon dioxide from the blood into the alveoli is propelled by the pressure gradients that are created by these variations (Chruścik et al., 2021). Internal Respiration Similar to external respiration, internal respiration is the gas exchange that takes place at the tissue level and is propelled by partial pressure gradients. In contrast to those at the respiratory membrane, the gradients are, nevertheless, inverted. Because cells constantly use oxygen for breathing, the partial pressure of oxygen in bodily tissues is low (around 40 mm Hg). As a result of a gradient created by the blood's considerably greater partial pressure of oxygen (about 100 mm Hg), oxygen diffuses out of hemoglobin, crosses the interstitial space, and enters the tissues. The blood returns to the heart a deeper burgundy color as hemoglobin loses oxygen (Chruścik et al., 2021). Figure 12. 19 External and Internal respiration 174 Oxygen Transport in the Blood Chruścik et al. (2021) explained that despite being carried by blood, oxygen has a low solubility in liquids. In the bloodstream, only 1.5% of oxygen dissolves immediately. The majority of oxygen is transported by red blood cells, or erythrocytes, from the lungs to the tissues. Hemoglobin, a metalloprotein found in erythrocytes, binds oxygen molecules to facilitate effective oxygen transport throughout the body. Additionally, the heme groups found in hemoglobin are rich in iron and are in charge of binding oxygen. Because each hemoglobin molecule has several heme groups, it can carry up to four oxygen atoms. Oxygen penetrates red blood cells and attaches itself to the heme groups in hemoglobin as it diffuses from the alveoli to the capillaries through the respiratory membrane. Figure 12. 20 Erythrocyte and hemoglobin Hemoglobin binds oxygen at heme sites that contain iron. It is a four-subunit protein. More oxygen can attach more easily when one oxygen molecule binds. Until all four locations are occupied, this procedure is repeated. More oxygen can be released more easily when more oxygen is released. The proportion of heme sites that are oxygen-bound is known as hemoglobin saturation. While 95–99% saturation is typical in healthy people, 100% saturation indicates that every site is occupied (Chruścik et al., 2021). Oxygen Dissociation from Hemoglobin Chruścik et al. (2021) described that the oxygen-hemoglobin dissociation curve shows how oxygen binds to and releases from hemoglobin based on the partial pressure of oxygen. As the partial pressure of oxygen increases, more oxygen molecules bind to hemoglobin. Conversely, when the partial pressure of oxygen decreases, fewer oxygen molecules are bound. 175 This curve illustrates that the partial pressure of oxygen significantly affects how much oxygen binds to hemoglobin in the lungs and how much is released in the tissues. Figure 12. 21 Hemoglobin Dissociation Curve Furthermore, the oxygen-hemoglobin dissociation curve helps adjust oxygen delivery based on tissue needs. Active tissues like muscles use oxygen quickly, lowering their oxygen levels and creating a big difference with the higher oxygen levels in capillaries. This difference causes more oxygen to be released from hemoglobin and enters these tissues. Tissues with lower activity, like fat, keep higher oxygen levels, so less oxygen is released. Even deoxygenated blood still carries some oxygen, providing a reserve for tissues that might need extra oxygen suddenly. The authors also pointed out that several factors influence how oxygen binds to and dissociates from hemoglobin: Temperature: Higher temperatures cause hemoglobin to release oxygen more easily, which is beneficial for active tissues that generate heat. Hormones: Certain hormones, like adrenaline and thyroid hormones, increase the production of 2,3-bisphosphoglycerate (BPG) in red blood cells. BPG promotes the release of oxygen from hemoglobin. 176 pH Levels: The Bohr effect describes how blood pH affects oxygen binding. Lower (more acidic) pH levels lead to more oxygen being released from hemoglobin, while higher (more basic) pH levels make hemoglobin hold onto oxygen more tightly. Increased carbon dioxide in the blood lowers pH, enhancing oxygen release. 177 Assessment Tasks Part 1: Crossword Puzzle. Use the clues to fill in the crossword puzzle. Each number in the grid corresponds to a word either across or down. 178 Part 2: Short Answer. Briefly discuss the following statements. 1. Explain the primary functions of the respiratory system. 2. Describe the difference between the conducting and respiratory zones in the respiratory system. 3. Define pulmonary ventilation and explain how Boyle’s Law applies to the process of breathing. Part 3. Essay Discuss the process of gas exchange in the lungs and the role of partial pressure in this process. How does Henry’s Law explain the solubility of gases in the bloodstream? 179 180 References: Basehore, B. et. al. 2023. General Biology l - Laboratory Manual. Harrisburg Area Community College Chruścik, A., Kauter, K., Windus, L., & Whiteside, E. (2021). Fundamentals of Anatomy and Physiology. http://eprints.usq.edu.au/43908/ iStock. (n.d.). Gas exchange. External and internal respiration stock illustration. Retrieved August 23, 2024, from https://www.istockphoto.com/vector/gas-exchange- external-and-internal-respiration-gm1255908994-367556466 Jabilles, A. B., Illahi, M. N., & Tormes, J. N. (2013.). Study Guide in Biological Science: A Simplified Approach. ISBN 978-971-0412-42-6 Kratz, R. F., & Siegfried, D. R. (2010). Biology for Dummies 2nd Edition. https://ci.nii.ac.jp/ncid/BB02888032 Lecturio. (2024). Pharynx: Anatomy. Retrieved August 23, 2024, from https://www.lecturio.com/concepts/pharynx/ Lumen Learning. (n.d.). Organs and Structures of the Respiratory System. Retrieved August 23, 204, from https://courses.lumenlearning.com/suny-ap2/chapter/organs-and- structures-of-the-respiratory-system/ NCERT (2021). Biology Textbook for Class XI. ISBN 81-7450-496-6 Nursing Hero. (n.d.) Gas Exchange. Retrieved August 23, 2024, from https://www.nursinghero.com/study-guides/boundless-ap/gas-exchange SigmaAlrich.com. (n.d.). Hemoglobin & Erythrocytes. Retrieved August 23, 2024, from https://www.sigmaaldrich.com/PH/en/technical-documents/technical-article/ clinical-testing-and-diagnostics-manufacturing/hematology/hemoglobin-heme-products Wikimedia. (n.d.). Structures of the Respiratory Zone-a.jpg. Retrieved August 23, 2024, from https://commons.wikimedia.org/wiki/File:2310_Structures_of_the_ Respiratory_Zone-a.jpg Wikimedia. (n.d.). Boyles Law.jpg. Retrieved August 23, 2024, from https://commons.wikimedia.org/wiki/File:2314_Boyles_Law.jpg 181 MODULE 13 The Digestive System Introduction Without much conscious thought, the digestive tract processes food in the background. For instance, you may appreciate the flavor of an apple while you're chewing it, but you probably don't realize the intricate process your body goes through afterward. Your stomach and intestines are working hard to break down and absorb the nutrients from the apple while you go about your day or go to sleep. Your body has absorbed every nutrient it can by the time it releases any waste. The organs of the digestive system carry out these functions with ease, making sure you receive the nutrition and energy you require from your diet even when you are not aware of it (Chruścik et al., 2021). Lesson 1: Anatomy of the Digestive System According to Tortora and Derrickson (2009), by converting food into nutrients that the body's cells may use for energy, growth, and repair, the digestive system is essential to maintaining homeostasis. It draws waste materials out of the body and absorbs necessary materials like water, vitamins, and minerals. This guarantees that the body gets what it requires to maintain equilibrium and function correctly. Additionally, the nutrients found in food are essential for maintaining and mending bodily tissues as well as supplying the chemical energy needed to sustain life. These nutrients are typically found in big molecules, though, which the body's cells cannot directly utilize. Digestion, or the process of reducing food into smaller, more useful molecules, is therefore crucial. This breakdown occurs in the digestive tract, a tube structure that runs from the mouth to the anus. It has a huge surface area that engages in interactions with the outside world and is intimately related to the cardiovascular system. For the body to metabolize food and absorb nutrients, this design is essential. 182 Tortora and Derrickson (2009) stated that the gastrointestinal (GI) tract and the accessory digestive organs are the two primary organ groupings that make up the digestive system. The gastrointestinal tract, sometimes referred to as the alimentary canal, is a continuous tube that passes through the thoracic and abdominopelvic cavities on its way from the mouth to the anus. The mouth, throat, esophagus, stomach, small intestine, and large intestine are all included. The GI tract is around 5 to 7 meters (16.5 to 23 ft) long in a living individual, but because the muscles that ordinarily maintain it constricted are relaxed in a corpse, the GI tract is longer (7 to 9 meters, or 23 to 29.5 feet). The tongue, teeth, pancreas, liver, gallbladder, and salivary glands are examples of auxiliary (accessory) digestive organs. The tongue facilitates chewing and swallowing, whereas the teeth assist in the physical breakdown of food. The other accessory organs help in the chemical digestion of food by producing or storing secretions that enter the GI system through ducts, even though they don't come into contact with the food. 183 Figure 13. 1 The components of the digestive system 184 \ Figure 13. 2 Functions of several digestive organs Chruścik et al. (2021) pointed out that other bodily systems and the digestive system are closely interdependent. The circulatory system removes waste from the body and supplies nutrients and oxygen to the digestive organs. Before returning to the heart, blood from the digestive organs is processed by the liver to provide nutrients. The nutrients required for the heart and blood vessels are also supplied by the digestive system. The nutrients from digestion power the endocrine system's operations, and hormones from the endocrine system aid in controlling digestion. 185 Figure 13. 3 Contribution of other Body Systems to the Digestive System The Mouth The tongue, hard and soft palates, and cheeks make up the mouth, often known as the oral or buccal cavity. The sidewalls of the oral cavity are formed by the cheeks. They are lined with a mucous membrane composed of nonkeratinized stratified squamous epithelium on the inside and skin on the exterior. The buccinator muscles and connective tissue lie between the epidermis and the mucous membranes of the cheeks. The lips merge with the front edges of the cheeks (Chruścik et al., 2021). Figure 13. 4 The Mouth 186 Lips (Labia) - Fleshy folds around the mouth's opening, made of the orbicularis oris muscle. They have skin on the outside and a mucous membrane on the inside. Each lip is attached to the gums by a midline fold called the labial frenulum. These muscles help keep food between the teeth and assist in speech. Oral Vestibule - The space between the cheeks and lips on the outside and the gums and teeth on the inside. Oral Cavity Proper - The space from the gums and teeth to the fauces, which is the opening between the mouth and the throat. Palate - The structure that separates the mouth from the nasal cavity. It allows for chewing and breathing at the same time. o Hard Palate - The bony front part of the roof of the mouth, formed by the maxillae and palatine bones. o Soft Palate - The muscular back part of the roof of the mouth, forming an arch between the mouth and the throat. Uvula - A small, conical structure hanging from the soft palate. It helps close off the nasal cavity when swallowing to prevent food from entering the nose. Palatoglossal and Palatopharyngeal Arches - Muscular folds that run from the soft palate to the sides of the tongue and pharynx. They help form the boundaries of the throat area where the palatine tonsils and lingual tonsils are located. The mouth connects to the oropharynx through the fauces at the back of the soft palate. The Pharynx Chruścik et al. (2021) explained that the respiratory and digestive systems both use the pharynx or throat. Food and air from the mouth and nasal cavities are given to it. Involuntary muscular contractions restrict the airways to keep food from getting into the respiratory passages when it enters the pharynx. The pharynx (throat) is a short tube of skeletal muscle lined with mucous membrane that extends from the back of the mouth and nasal cavities to the openings of the esophagus and larynx. It has three parts: Nasopharynx - Located at the top, it is involved only in breathing and speech. Oropharynx - Located below the nasopharynx, it serves both breathing and digestion. 187 Laryngopharynx - The lowest part, connecting to the esophagus and larynx, allowing air to flow to the bronchial tree and food to enter the esophagus. The uvula and soft palate rise during swallowing to seal off the nasopharynx. To stop food from getting into the airways, the larynx rises and the epiglottis folds down to cover the glottis. Coughing aids in the expulsion of food that unintentionally gets into the trachea. Figure 13. 5 The pharynx or throat The Esophagus Chruścik et al. (2021) described that behind the trachea is the esophagus, a flexible muscular tube that measures around 25 cm (10 in.). It begins at the base of the laryngopharynx, travels through the mediastinum, the chest cavity in front of the spine, and then links to the upper 188 portion of the stomach through the esophageal hiatus, a gap in the diaphragm (Tortora and Derrickson, 2009). Furthermore, food entry into the esophagus is regulated by the upper esophageal sphincter, which is attached to the bottom portion of the throat. Both smooth and skeletal muscle make up the esophagus; smooth muscle makes up the lower third and skeletal muscle the top two-thirds. Food is moved toward the stomach via peristalsis, a wave-like contraction of the muscles. The mucus is secreted by the esophagus to help lubricate meals. Lastly, the lower esophageal sphincter, sometimes referred to as the gastroesophageal or cardiac sphincter, allows food to pass into the stomach. Similar to a valve, this sphincter relaxes to allow food to enter the stomach and contracts to prevent stomach acids from reentering the esophagus. When not swallowing, the diaphragm surrounding the sphincter aids in keeping it closed. Acid reflux can result in heartburn or gastroesophageal reflux disease (GERD) if the sphincter is unable to seal properly. Figure 13. 6 The esophagus Deglutition Swallowing, or deglutition, moves food from the mouth to the stomach. This process involves the mouth, pharynx, and esophagus and is assisted by saliva and mucus. Although it seems quick and easy, swallowing involves complex muscle actions and is supported by mucus 189 and saliva. There are three stages: Voluntary Stage - In the voluntary phase of swallowing (or the oral phase), you control when to swallow. After chewing, the tongue pushes the food (bolus) to the back of the mouth and into the oropharynx. Muscles keep the mouth closed to prevent food from falling out. This starts the two involuntary phases of swallowing. Pharyngeal Stage - In the pharyngeal phase of swallowing, receptors in the oropharynx send signals to the swallowing center in the brain. This causes the uvula and soft palate to move upward and close off the nasopharynx, while laryngeal muscles contract to prevent food from entering the trachea. Breathing briefly stops (deglutition apnea). The pharyngeal constrictor muscles then push the food through the pharynx, and the upper esophageal sphincter relaxes to let the food enter the esophagus. Esophageal Stage - In the esophageal phase of swallowing, the food enters the esophagus and peristalsis begins. Controlled by the medulla oblongata, peristalsis involves a series of muscle contractions that move the food toward the stomach. The circular muscles contract to push the food forward, while the longitudinal muscles contract to shorten the esophagus and make room for the food. As the food approaches the stomach, the esophagus stretches and triggers the lower esophageal sphincter to relax, allowing the food to enter the stomach. During this phase, mucus is secreted to lubricate the food and reduce friction. Figure 13. 7 Deglutition 190 The Stomach According to Tortora and Derrickson (2009), underneath the diaphragm in the upper abdomen, the stomach is a J-shaped organ. It joins the duodenum, the first segment of the small intestine, to the esophagus. Food is mixed and held in the stomach until it is digested and then progressively released in small amounts into the small intestine. Breathing causes its size and position to alter; it expands when it is full and contracts when it is empty. The stomach breaks down carbohydrates, begins breaking down proteins and fats, transforms food into a liquid, and absorbs certain chemicals. Figure 13. 8 The stomach The Small and Large Intestines According to Tortora and Derrickson (2009), the term "intestine" comes from a Latin word meaning "internal." The intestines, which include the small and large bowel, occupy most of the abdominal cavity. Together, they make up the longest and most significant part of the digestive system and handle almost all digestive functions, except for the initial ingestion of food. 191 Small Intestine The small intestine is where most digestion and nutrient absorption take place. In a living individual, the small intestine is a lengthy, coiled tube that is around 3 meters (10 feet) long; in a cadaver, it is 6.5 meters (21 feet) long. It joins the large intestine at the beginning of the stomach. Its inner surface features small projections and folds that aid in the absorption of nutrients and aid in digestion (Tortora and Derrickson, 2009). The authors further explained that the small intestine has three parts: the duodenum, jejunum, and ileum. The duodenum, the shortest section, starts at the stomach and is about 25 cm (10 in.) long. It connects to the jejunum, which is about 1 meter (3 ft) long. The ileum, the longest part at around 2 meters (6 ft), connects to the large intestine through the ileocecal sphincter. Figure 13. 9 The small intestine Large Intestine The last segment of the digestive system is the large intestine. Its primary duties include producing specific vitamins, finishing the process of absorbing nutrients and water, forming feces, and eliminating excrement from the body (Chruścik et al., 2021). 192 The large intestine has four main parts: the cecum, colon, rectum, and anus. The ileocecal valve controls the flow of chyme from the small intestine into the large intestine. Cecum - This sac-like structure, located below the ileocecal valve, is about 6 cm long and continues the absorption of water and salts. It has the appendix attached, which, despite being considered vestigial, may help repopulate beneficial bacteria during illnesses. Colon -The colon begins at the cecum and is divided into four segments: o Ascending Colon -Moves up the right side of the abdomen. o Transverse Colon - Runs across the abdomen from right to left. o Descending Colon - Travels down the left side of the abdomen. o Sigmoid Colon - Curves into the pelvis and connects to the rectum. The colon is anchored to the posterior abdominal wall by the mesocolon. Rectum - This 20.3 cm long section follows the contour of the sacrum and coccyx and features transverse folds called rectal valves that help separate feces from gas. Anal Canal - The final part of the large intestine, located in the perineum, opens to the exterior at the anus. It has two sphincters: o Internal Anal Sphincter - Made of smooth muscle and controlled involuntarily. o External Anal Sphincter - Made of skeletal muscle and under voluntary control. Figure 13. 10 The large intestine 193 Lesson 2: Accessory Organs in Digestion Accessory digestive organs include the tongue, teeth, salivary glands, pancreas, liver, and gallbladder. While the teeth aid in the actual breakdown of food, the tongue makes chewing and swallowing easier. Despite not coming into touch with the food, the other auxiliary organs aid in the chemical digestion of food by creating or storing secretions that enter the GI system through the ducts body (Chruścik et al., 2021). The Tongue According to Tortora and Derrickson (2009), the tongue is a skeletal muscle-covered mucous membrane auxiliary digestive organ. A median septum divides it into two symmetrical halves and creates the floor of the oral cavity. The mandible, the styloid process of the temporal bone, and the hyoid bone are where the tongue is attached. The muscles on either side of the tongue are the same, both intrinsic and extrinsic. Figure 13. 11 The tongue 194 The Teeth The mandible and maxilla's alveolar processes house the teeth, or dentes, which are auxiliary digestive organs. The gingivae, or gums, cover these sockets and reach somewhat into each one. The periodontal ligament, a thick band of fibrous connective tissue that lines the sockets and holds the teeth in place, is located within them (Tortora and Derrickson, 2009). In a normal tooth, the crown, root, and neck are its three primary sections. The area visible above the gums is called the crown. The tooth is secured in place by the implanted root(s) in the socket. The neck is the little space, close to the gum line, where the crown and root converge. Figure 13. 12 A typical tooth and surrounding structures Types of Teeth Chruścik et al. (2021) pointed out that over our lifetime, we develop two sets of teeth, known as dentitions. The first set includes 20 deciduous teeth (baby teeth), which begin appearing around 6 months of age. Between ages 6 and 12, these are replaced by 32 permanent teeth. From the center of the mouth outward: 195 Incisors (8 total) - Four on top and four on the bottom, used for biting food. Cuspids (or canines, 4 total) - Located next to the incisors, with pointed edges for tearing food. Premolars (or bicuspids, 8 total) - Positioned behind the cuspids, with flatter surfaces for mashing food. Additionally, the largest teeth in the back are the 12 molars, each with several cusps designed to crush food before swallowing. The third molars, also known as wisdom teeth, usually emerge in early adulthood. However, wisdom teeth often remain impacted (stuck beneath the gums), requiring surgical removal. Figure 13. 13 Dentitions and times of eruptions (indicated in parentheses) The Salivary Glands Tortora and Derrickson (2009) explained that saliva is released into the mouth by salivary glands. They typically secrete enough saliva to maintain a moist and clean mouth and throat. Saliva production rises in the presence of food, though, to lubricate, dissolve, and initiate the chemical breakdown of food. 196 Small salivary glands in the mouth and tongue release saliva into the oral cavity directly or through tiny ducts. These include the salivary glands found in the lips, cheeks, palate, and tongue, which produce saliva in minute amounts. They are also known as the buccal, palatal, lingual, and labial glands. The parotid, submandibular, and sublingual glands are the three pairs of primary salivary glands that produce the majority of saliva. The authors further explained that salivary glands are divided into three major glands: Parotid glands - The parotid glands are located near the ears and release saliva into the mouth through ducts that open near the upper molars. Submandibular glands - The submandibular glands, found beneath the jaw, have ducts that run along the floor of the mouth and open near the base of the tongue. Sublingual glands - The sublingual glands are situated under the tongue and release saliva through several ducts on the floor of the mouth. Figure 13. 14 The three major salivary glands The Pancreas The pancreas is a soft, elongated gland located behind the stomach in the retroperitoneum. Its head fits snugly into the C-shaped curve of the duodenum, while its body extends leftward about 15 cm, tapering into a tail that reaches the hilum of the spleen. The 197 pancreas performs both exocrine functions by secreting digestive enzymes and endocrine functions by releasing hormones into the bloodstream (Chruścik et al., 2021) Figure 13. 15 Relation of the pancreas to the liver, gallbladder, and duodenum The Liver According to Chruścik et al. (2021) the largest gland in the body, the liver weighs roughly three pounds (1.4 kg) in adults and is essential for metabolism, digestion, and control. It is shielded by the ribs and situated in the right upper quadrant of the abdominal cavity, directly below the diaphragm. Figure 13. 16 The liver 198 Located in the right upper abdomen under the diaphragm and protected by the ribs, it has two main lobes: a large right lobe and a smaller left lobe. It is held in place by five ligaments: the falciform, coronary, two lateral ligaments, and the ligamentum teres hepatis, which are remnants of the umbilical vein. The lesser omentum connects the liver to the stomach. The Gallbladder Situated on the rear of the right lobe of the liver, the gallbladder is a muscular sac that is around 8-10 cm in length. When necessary, it releases the concentrated and stored bile through the common bile duct into the duodenum. The fundus, which is the largest portion of the gallbladder, the body, and the neck, which joins to the cystic duct, are its three main sections. Bile can then move from the liver to the gallbladder and ultimately to the small intestine thanks to the cystic duct's connection to the hepatic duct (Chruścik et al., 2021). Figure 13. 17 The gallbladder Lesson 3: Digestive Processes Chruścik et al. (2021) and Tortora and Derrickson (2009) explained that the processes of digestion include six activities: ingestion, propulsion, mechanical or physical digestion, chemical digestion, absorption, and defecation. 199 Ingestion - This is the act of taking in food through the mouth, where it is chewed and mixed with saliva. Saliva contains enzymes that start breaking down carbohydrates and some fats. Propulsion - This involves moving food through the digestive tract, starting with swallowing (voluntary) and followed by peristalsis (involuntary), which are wave-like muscle contractions that push food along the digestive system. Mechanical Digestion - This process physically breaks down food into smaller pieces, increasing surface area. It includes chewing in the mouth, stomach-churning, and segmentation in the intestines, where food is mixed and broken down further. Chemical Digestion - In this step, enzymes break down complex food molecules into their basic chemical components, like turning proteins into amino acids. This starts in the mouth and continues through the stomach and small intestine. Absorption - Nutrients are absorbed mainly in the small intestine, where they enter the bloodstream. Fats are absorbed into the lymphatic system before entering the bloodstream. Defecation - This final step involves the elimination of indigestible waste from the body as feces. Figure 13. 18 The six digestion processes 200 Mechanical and Chemical Digestion in the Mouth According to Tortora and Derrickson (2009), mechanical digestion in the mouth occurs through chewing (mastication), where food is mixed with saliva, broken down by teeth, and shaped into a soft mass called a bolus. This process helps dissolve food molecules, allowing enzymes to begin breaking them down. Two enzymes play a role in chemical digestion: salivary amylase starts breaking down starches, and lingual lipase begins fat digestion. Salivary amylase, an enzyme from the salivary glands, starts breaking down starches in food into smaller sugars like maltose and maltotriose. This process begins in the mouth but continues for about an hour after swallowing before stomach acids stop it. Lingual lipase is an enzyme released by tongue glands and found in saliva. It begins to break down dietary triglycerides into fatty acids and diglycerides (glycerol connected to two fatty acids) but only when food enters the stomach's acidic environment. Lesson 4: Chemical Digestion and Absorption Chruścik et al. (2021) explained that contrary to chemical digestion, which is more sophisticated and breaks food down into its chemical components for absorption and sustenance, mechanical digestion physically breaks down food without altering its chemical composition. 201 Figure 13. 19 Digestion and absorption Chemical Digestion According to Chruścik et al. (2021), large food molecules like proteins, lipids, nucleic acids, and starches are broken down into smaller subunits that can be absorbed by the gastrointestinal tract. This breakdown is achieved by enzymes through a process called hydrolysis. The various enzymes involved in chemical digestion are summarized in Figure 13.20. 202 Figure 13. 20 Digestive enzymes Carbohydrate Digestion - About half of our diet is carbs, which include simple sugars (like glucose) and complex sugars (like starch). Simple sugars are absorbed directly. Disaccharides (sucrose, lactose) and polysaccharides (starch) are broken down into simple sugars. Fibrous carbs like cellulose aren’t digested but help with digestion. Protein Digestion - Proteins, which make up 15–25% of our diet, are broken down into smaller pieces in the stomach and then further broken down into amino acids in the small intestine. These amino acids are absorbed into the blood. 203 Lipid Digestion - Fats should make up about 35% of our diet, mainly as triglycerides (glycerol and fatty acids). Most fat digestion happens in the small intestine with pancreatic lipase breaking fats into fatty acids and monoglycerides. Nucleic Acid Digestion - DNA and RNA from foods are digested in the small intestine. Pancreatic enzymes break them down into nucleotides, which are then further split into simpler parts (sugars, phosphates, and bases) and absorbed. Absorption Food is broken down by the digestive system into tiny molecules that the intestines can absorb. It can process up to 10 liters of food, drinks, and secretions per day, but only approximately 1 liter makes it to the large intestine. The small intestine is where most absorption takes place: 90% of water, 80% of electrolytes, and almost all food are absorbed there. Proteins and carbohydrates are mostly absorbed in the jejunum, whereas bile salts and vitamin B12 are absorbed in the terminal ileum. Most of the chyme consists of water, bacteria, and indigestible waste by the time it reaches the large intestine (Chruścik et al., 2021). The authors further explained that absorption can occur through five mechanisms: (1) active transport, (2) passive diffusion, (3) facilitated diffusion, (4) co-transport (or secondary active transport), and (5) endocytosis. 204 Figure 13. 21 Absorption Carbohydrates Absorption - Absorbed as monosaccharides in the small intestine, with glucose and galactose using sodium to enter cells, and fructose using facilitated diffusion. Proteins Absorption - Mostly absorbed as amino acids in the small intestine. Some small peptides are absorbed but broken down into amino acids inside cells before entering the bloodstream. Lipids Absorption - About 95% are absorbed in the small intestine. Short-chain fatty acids enter cells directly, while long-chain fatty acids are absorbed via micelles and then recombined into triglycerides to form chylomicrons. Chylomicrons enter lymph vessels, then the bloodstream, where they are broken down by lipoprotein lipase. Nucleic Acids Absorption - Digested into sugars, bases, and phosphates, which are absorbed by active transport. 205 Minerals Absorption - Most are absorbed regardless of need, but iron and calcium are regulated. Iron is stored as ferritin, and calcium absorption is controlled by blood levels and vitamin D. Vitamins Absorption - Fat-soluble vitamins (A, D, E, K) are absorbed with fats, while most water-soluble vitamins are absorbed directly. Vitamin B12 requires an intrinsic factor for absorption. Water Absorption - About 90% of water entering the small intestine is absorbed, driven by water concentration gradients. The small intestine is where most of the breakdown of food and nutrient absorption happens. Enzymes from the pancreas and the intestine split large food molecules into smaller ones. Fats are broken down with the help of bile, forming micelles that deliver fats to the intestine cells. These fats are then turned into chylomicrons, which enter lymph vessels and eventually the bloodstream. Other nutrients go directly into the blood and are carried to the liver. 206 Assessment Tasks Part 1. Multiple Choice Questions. Choose the BEST answer. _________ 1. Which of the following is the primary site for nutrient absorption in the digestive system? A. Stomach C. Small intestine B. Large intestine D. Esophagus _________ 2. Which organ produces bile, which aids in the digestion of fats? A. Gallbladder C. Liver B. Pancreas D. Stomach _________ 3. Chemical digestion of proteins begins in the: A. Mouth C. Small intestine B. Stomach D. Large intestine _________ 4. The process of peristalsis is: ______________________ A. The breakdown of food by enzymes B. The wave-like muscle contractions that move food through the digestive tract C. The absorption of nutrients D. The release of digestive enzymes _________ 5. Which of the following is NOT an accessory organ in digestion? A. Liver C. Stomach B. Pancreas D. Gallbladder _________ 6. Which of the following is not a component of saliva? A. Water C. Amylase B. Mucus D. Hydrochloric acid _________ 7. Which of the following is not a part of the small intestine? A. Duodenum C. Jejunum B. Ileum D. Colon _________ 8. What is the role of villi and microvilli in the small intestine? A. To secrete digestive enzymes C. To transport nutrients to the liver B. To increase surface area for absorption D. To store excess nutrients _________ 9. Bile is produced by which organ and stored in the gallbladder until needed for digestion? A. Stomach C. Liver 207 B. Pancreas D. Small intestine _________ 10. Digestion”, alone, refers to the (very specific answer) A. absorption of nutrients in the gut. B. progressive dehydration of indigestible residue. C. input of food into the digestive tract. D. chemical/mechanical breakdown of food. Part 2: Essay. Discuss the given statement below in two to three paragraphs. Explain the process of chemical digestion and absorption of carbohydrates, fats, and proteins in the small intestine. What role do enzymes play in these processes? 208 Part 3: Labelling the parts. 209 References: Basehore, B. et. al. 2023. General Biology l - Laboratory Manual. Harrisburg Area Community College Chruścik, A., Kauter, K., Windus, L., & Whiteside, E. (2021). Fundamentals of Anatomy and Physiology. http://eprints.usq.edu.au/43908/ Crousillac (2024). Human Anatomy and Physiology I Copyright © 2024 by LOUIS: The Louisiana Library Network Jabilles, A. B., Illahi, M. N., & Tormes, J. N. (2013.). Study Guide in Biological Science: A Simplified Approach. ISBN 978-971-0412-42-6 Ken Hub (n.d.). Tongue. Retrieved August 24, 2024, from, https://www.kenhub.com/en/library/anatomy/tongue Lybrate.com. (n.d.). Esophagus (Human Anatomy): Image, Function, Conditions, and More. Retrieved August 24, 2024, from https://www.lybrate.com/topic/esophagus-image NCERT (2021). Biology Textbook for Class XI. ISBN 81-7450-496-6 Nursing Hero. (n.d.). Digestive System Processes and Regulation. Retrieved August 24, 2024, from https://www.nursinghero.com/study-guides/cuny-kbcc-ap2/digestive-system- processes-and-regulation Nursing Hero. (n.d.). Digestive System. Retrieved August 24, 2024, from https://www.nursinghero.com/study-guides/pierce-nutritionmaster/digestive-system Pressbooks.pub. (n.d.). Chemical Digestion and Absorption. Retrieved August 24, 2024, from, https://usq.pressbooks.pub/anatomy/chapter/12-7-chemical-digestion-and- absorption-a-closer-look/ Tortora, G. J., & Derrickson, B. (2009). Principles of Anatomy and Physiology Twelfth Edition. http://repository.poltekkes-kaltim.ac.id/1158/ WisTech Open. (n.d.). Anatomy of the Digestive System. Retrieved August 24, 2024, from https://wtcs.pressbooks.pub/medterm/chapter/12-4-anatomy-of-the-digestive- system/ 210 MODULE 14 The Endocrine System Introduction During puberty, noticeable changes in physical appearance and behavior arise due to the endocrine system. In girls, estrogens lead to the development of breasts and hips, creating a more feminine shape. In boys, rising testosterone levels build muscle mass and deepen the voice. These hormonal changes are powerful examples of how the endocrine system influences the body. Additionally, hormones play a crucial role in maintaining daily balance by regulating muscle activity, metabolism, growth, reproduction, and circadian rhythms (Tortora and Derrickson, 2009). To manage and coordinate actions, the body uses communication to transfer signals from a sender to one or more receivers. The neurological and endocrine systems play a pivotal role in this "long-distance" communication, collaborating to maintain homeostasis—the stable, balanced state of the organism (Chruścik et al., 2021). Lesson 1: Overview of the Endocrine System Comparison of Control by the Nervous and Endocrine Systems Chruścik et al. (2021) and Tortora and Derrickson (2009) both explained that neurotransmitters and electrical signals are the two ways that the nervous system communicates. Neurotransmitters are produced upon the arrival of an electrical signal at a nerve terminal, where they bridge a gap and attach themselves to receptors on a target cell. This sets off a fast reaction, such as a signal or cell change. The quick start and quick finish of the process enable the nervous system to regulate quick actions such as sensation, movement, and thought. On the contrary, hormones are chemical messengers produced in the bloodstream by 211 glands of the endocrine system. These hormones travel to certain cells throughout the body, attaching themselves to receptors to cause an action. Because endocrine communication depends on blood circulation, it functions more slowly than nervous system communication. Certain hormones, such as adrenaline during a fight-or-flight response, respond quickly; other hormones, such as reproductive hormones, might take up to 48 hours to start acting. Generally speaking, endocrine signaling is less selective than neurological transmission because a given hormone might affect several processes based on the target cells. For example, oxytocin facilitates breastfeeding, aids in labor contractions, and may even affect a man's or woman's emotional bonding and sexual response. The endocrine system functions more slowly, concentrating on preserving the body's internal balance, managing reproduction, and guaranteeing long-term homeostasis, in contrast to the neurological system, which reacts quickly to changes in the external environment. Figure 14. 1 Comparison of Control by the Nervous and Endocrine Systems Structures of the Endocrine System According to Chruścik et al. (2021) and Tortora and Derrickson (2009), the body has two types of glands: exocrine and endocrine. Exocrine glands release their products into ducts that lead to body surfaces, cavities, or organ lumens. Examples include sweat, oil, mucus, and digestive glands. Endocrine glands, however, release hormones directly into the surrounding fluid, which then diffuse into the blood. The blood carries these hormones to target cells across the body. Since hormones are needed in small amounts, their circulating levels are usually low. The pituitary, thyroid, parathyroid, adrenal, and pineal glands are components of the endocrine system. Certain glands perform both exocrine and endocrine tasks. For example, the pancreas secretes glucagon and insulin, which regulate blood glucose levels and aid in digesting. Endocrine functions are also performed by the hypothalamus, thymus, heart, kidneys, 212 stomach, intestines, liver, skin, ovaries, and testes. Hormone production is observed in both bone and adipose tissue, underscoring the lesser-known endocrine activities of these tissues. Figure 14. 2 The Structures of Endocrine System Lesson 2: Hormones Chemical Classes of Hormones Tortora and Derrickson (2009) stated that there are two primary categories of hormones based on their chemical makeup: lipid-soluble and water-soluble. This difference matters because it affects how they function. Steroids and other lipid-soluble hormones are readily absorbed through cell membranes and interact with intracellular receptors. Water-soluble hormones, on the other hand, like peptides, attach to cell surface receptors and cause internal cell reactions. Lipid-soluble Hormones The lipid-soluble hormones include steroid hormones, thyroid hormones, and nitric oxide. Steroid Hormones - Made from cholesterol, these hormones have different chemical groups attached to a core structure, allowing them to perform a wide range of functions. Thyroid Hormones - T3 and T4 are made by adding iodine to the amino acid tyrosine. 213 Their structure makes them very lipid soluble. Nitric Oxide (NO) - This gas acts as both a hormone and a neurotransmitter. Its production is catalyzed by the enzyme nitric oxide synthase. Water-soluble Hormones The water-soluble hormones include amine hormones, peptide and protein hormones, and eicosanoid hormones. Amine Hormones - Made by modifying amino acids, like epinephrine and dopamine (from tyrosine), histamine (from histidine), and serotonin and melatonin (from tryptophan). Peptide and Protein Hormones - Chains of amino acids. Peptides are short chains (like oxytocin), while proteins are longer chains (like insulin). Some, like thyroid-stimulating hormones, also have carbohydrate groups. Eicosanoid Hormones - Made from arachidonic acid, these include prostaglandins and leukotrienes. They mostly act locally but can also circulate in the blood. Factors Affecting Cell Response Target cells must have specific receptors to respond to a hormone. If a hormone's concentration is high, cells may reduce the number of receptors in a process called downregulation to decrease sensitivity. Conversely, if hormone levels are low, cells may increase receptor numbers through upregulation to enhance sensitivity. Additionally, cells can adjust the sensitivity of their receptors to hormones. These processes help regulate how cells respond to varying hormone levels (Chruścik et al., 2021). Hormones can interact in several ways to influence cell responses: Permissive Effect - One hormone allows another hormone to act. For example, thyroid hormones enable certain reproductive hormones to function properly. A deficiency in thyroid hormones due to iodine lack can impact reproductive health. Synergistic Effect - Two hormones with similar effects work together to produce a stronger response or are both needed for a full response. For instance, follicle- 214 stimulating hormone (FSH) and estrogen both contribute to the maturation of female eggs. Antagonistic Effect - Two hormones have opposing effects. For example, insulin lowers blood glucose by promoting glucose storage, while glucagon increases blood glucose by stimulating glycogen breakdown. Lesson 3: The Endocrine Glands and other Hormones The endocrine system is a network of glands and organs that use hormones to regulate various body functions. It manages metabolism, energy levels, reproduction, growth, development, and responses to injury, stress, and mood. Figure 14. 3 The Endocrine System 215 The Hypothalamus and Pituitary Gland The endocrine system's "command center" is the hypothalamus-pituitary complex. It secretes hormones that control the synthesis of hormones by other glands and directly impact the target tissues. Additionally, it synchronizes signals between the neurological and endocrine systems, frequently converting nerve system inputs into hormone reactions (Chruścik et al., 2021). Figure 14. 4 Hypothalamus–pituitary complex Posterior Pituitary The posterior pituitary is an extension of hypothalamic neurons, specifically from the paraventricular and supraoptic nuclei. While the hypothalamus produces the hormones oxytocin and ADH, the posterior pituitary doesn't make these hormones but stores and releases them. The hormones travel through the hypothalamic–hypophyseal tract to the posterior pituitary, where they are released into the bloodstream in response to signals from the hypothalamus (Chruścik et al., 2021). Oxytocin - Oxytocin has an impact on the mother's uterus and breasts both during and 216 after childbirth. It intensifies the contractions of the uterus during birth and prompts the mammary glands to release milk (also known as "letdown") in reaction to the newborn sucking. The precise function of oxytocin in men and non-pregnant women is poorly understood. Research on animals indicates that it could impact brain processes associated with caring for parents and enhance sensations of sex. Antidiuretic Hormone - An antidiuretic hormone (ADH) reduces urine production by making the kidneys return more water to the blood, decreasing urine volume. Without ADH, urine output can increase dramatically, from 1-2 liters to about 20 liters a day. Alcohol inhibits ADH secretion, leading to frequent urination. ADH also reduces water loss through sweating and constricts blood vessels, which raises blood pressure. This blood pressure effect is why ADH is also known as vasopressin. Figure 14. 5 Posterior pituitary 217 Anterior Pituitary According to Chruścik et al. (2021), during development, the anterior pituitary gland travels from the digestive system toward the brain. The pars distalis (front), pars intermedia (next to the posterior pituitary), and pars tuberalis (around the infundibulum) are its three components. The anterior pituitary produces hormones, in contrast to the posterior pituitary, which solely stores them. The hypothalamus regulates its hormone release by sending messages that either encourage or inhibit its activity. The anterior pituitary produces seven hormones: growth hormone (GH), thyroid- stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), beta-endorphin, and prolactin. TSH, ACTH, FSH, and LH are known as tropic hormones because they regulate the activity of other endocrine glands. Figure 14. 6 Summary of the Principal Actions of Anterior Pituitary Hormones 218 Assessment Tasks Part 1: Case Analysis. Read the case carefully and explain the following statements below. Samantha, a 35-year-old woman, has been feeling increasingly fatigued, gaining weight despite eating less and experiencing cold intolerance. Upon visiting her doctor, blood tests reveal elevated TSH (Thyroid Stimulating Hormone) levels and low T3 and T4 (thyroid hormones). 1. Based on Samantha’s symptoms and test results, identify her likely endocrine condition. 2. Explain how the hypothalamic-pituitary-thyroid axis is disrupted in Samantha’s case. 3. What treatment options might be considered for her condition, and how do they help restore normal function? 219 4. Discuss the potential long-term effects of untreated hypothyroidism. Part 2: Labeling the parts.

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