The Digestive System PDF

The Digestive System  Function of the Digestive System The main function of the digestive system is to break down food (large macromolecules, carbohydrates, proteins and fats) via hydrolysis into smaller molecules (glucose, amino acids and fatty acids) that can be used by the body’s cells.  Activi...

The Digestive System  Function of the Digestive System The main function of the digestive system is to break down food (large macromolecules, carbohydrates, proteins and fats) via hydrolysis into smaller molecules (glucose, amino acids and fatty acids) that can be used by the body’s cells.  Activities of the Digestive System 5 basic activities: 1. Ingestion: bringing food into the mouth 2. Peristalsis: pushing food along the digestive tract 3. Digestion: breakdown of food by mechanical and chemical mechanisms 4. Absorption: passage of digested food from the digestive tract into the circulatory and lymphatic systems for distribution to the body’s cells 5. Defecation: elimination from the body of those substances which cannot be digested and absorbed  Components of the Digestive System Gastrointestinal tract – Long continuous tube (from the mouth to the anus) – Mouth or oral cavity, pharynx, esophagus, stomach, small intestine, large intestine Accessory organs – Teeth, tongue, salivary glands, liver, gallbladder, pancreas  Components of the Digestive System Accessory Organs Teeth Major Subdivisions Mouth Mechanical digestion by chewing (mastication) Oral Cavity Tongue Mechanical processing, moistening, Assists mechanical digestion with mixing with salivary secretions teeth Pharynx Salivary Glands Muscular propulsion of materials Secretion of lubricating fluid into the esophagus containing enzymes that Esophagus break down carbohydrates Transport of materials to the Liver stomach Secretion of bile (important Stomach for lipid digestion), storage Chemical breakdown of materials via of nutrients acid and enzymes; mechanical processing (muscular contractions) Gallbladder Storage and concentration Small Intestine of bile Enzymatic digestion and absorption Pancreas water, organic substrates, vitamins, ions Exocrine cells secrete buffers and Large Intestine digestive enzymes; endocrine Dehydration and compaction of cells secrete hormones indigestible materials in preparation for elimination Anus Histology of the Digestive Tract It has the same general structure throughout most of its length, from esophagus to anus Four major tissue layers: – Tunica Mucosa Innermost layer – Tunica Submucosa – Tunica Muscularis – Tunica Serosa Outer layer  Tunica Mucosa Lines the luminal surface of digestive tract Highly folded surface greatly increases absorptive area Three layers of mucosa: – Epithelial tissue layer – Lamina propria (loose connective tissue) – Muscularis mucosa (smooth muscle)  Tunica Mucosa The mucosal surface is highly folded increasing the surface area for absorption Most folding in small intestine: maximum absorption Least folding in esophagus: non- absorption  Tunica Submucosa Thick layer of loose connective tissue Provides digestive tract with distensibility and elasticity Contains larger blood and lymph vessels Contains nerve network known as submucosal plexus  Tunica Muscularis Externa Skeletal muscle in the mouth, pharynx and the first part of the esophagus The rest of the tract consists of two layers of smooth muscle: – Circular layer Inner layer Contraction decreases diameter of lumen – Longitudinal layer Outer layer Contraction shortens the tube  Tunica Muscularis Externa Contractile activity produces propulsive and mixing movements Myenteric plexus (nerve network) – Lies between the two muscle layers  Tunica Serosa Outermost layer of the digestive tract Serous membrane made of connective and epithelial tissue Secretes a watery fluid (serous fluid), which lubricates and prevents friction between digestive organs and surrounding viscera  The Mouth or Oral Cavity Functions – Taste – Mechanical breakdown of food – Chemical digestion of carbohydrates Amylase  The Mouth or Oral Cavity Structure – Cavity lined with mucous membrane – Cavity floor formed by tongue – Cavity roof formed by hard and soft palate – Cavity sides formed by cheeks – Cavity opening guarded by lips  The Tongue - Forms floor of oral cavity - Composed of skeletal muscle - Movements aid in chewing and swallowing - Plays important role in speech - Taste buds What cranial nerve controls the tongue?? Hypoglossal nerve  The Salivary Glands Produced mainly by 3 pairs of salivary glands – Parotid, submandibular, sublingual Saliva – Is 99.5% water – The remaining 0.5% consists of the following solutes: - Amylase (enzyme), which digests carbohydrates - Bicarbonates and phosphates - Urea and uric acid (waste products) - Mucin which forms mucus to lubricate food - Lysozyme to destroy bacteria  The Teeth Responsible for chewing (mastication) First step in digestive process Functions of chewing: – Grind and break food into smaller pieces to make swallowing easier and increase food surface area on which salivary enzymes can act – Mix food with saliva – Stimulate taste buds  The Pharynx It is a common passageway for food, liquid, and air Divisions: Nasopharynx, oropharynx, laryngopharynx Function: begins swallowing (deglutition) Pharyngeal muscles involved in swallowing Voluntary stage of swallowing: food bolus is forced to the back of the mouth cavity and into the oropharynx Involuntary stage of swallowing: food bolus from the oropharynx passes through the laryngopharynx and enters the esophagus and finally the stomach  The Esophagus Hollow muscular tube from the pharynx region to the stomach It is 23 to 25 cm long and 2 cm in diameter Located posterior to the trachea Enters the peritoneal cavity by passing through the esophageal hiatus of the diaphragm  The Esophagus Sphincters at each end – Pharyngoesophageal sphincter (upper) Keeps entrance closed to prevent large volumes of air from entering esophagus and stomach during breathing – Gastroesophageal sphincter (lower) Controls passage of food into stomach Prevents reflux of gastric contents  The Esophagus Function: - Secretes mucus and transport food to the stomach - Food is pushed through the esophagus to stomach by smooth muscle contractions, called peristalsis - It does not produce any digestive enzymes and it does not absorb food  The Stomach J-shaped sac-like chamber lying between esophagus and small intestine Divided into 4 sections: – Cardia – Fundus – Body – Antrum Pyloric sphincter – Serves as barrier between stomach and upper part of small intestine  Anatomy of the Stomach Esophagus Fundus superior to the junction Musculature of the between the stomach and Stomach the esophagus Longitudinal muscle layer Anterior Cardia surface superior, medial portion of the Circular muscle layer stomach close to gastroesophageal junction. Oblique muscle layer Body between the fundus and Lesser curvature the pylorus. (medial surface) Pyloric Pyloris extends to the entrance to the sphincter Rugae duodenum. pyloric sphincter regulates Duodenum the into the duodenum. Greater curvature (lateral surface)  The Stomach The mucosa of the stomach has gastric glands that have 3 types of secreting cells: i) Zymogenic or chief cells which secrete the pepsinogen enzyme ii) Parietal cells which secrete HCL iii) Mucous cells which secrete mucus  The Stomach Three major functions: 1. Bulk storage of ingested food 2. Mechanical breakdown of ingested food 3. Chemical digestion of ingested food The end result is the production of chyme  The Small Intestine - Site where most digestion and absorption take place - Approximately 21 feet long/ 1 inch diameter in average, with 3 segments: 1. Duodenum 10 inches long; receives digestive enzymes from the pancreas, bile from the liver and gallbladder 2. Jejunum 8 feet long; most of the digestion and absorption occurs in the jejunum 3. Ileum 12 feet long; controls flow of materials into the cecum of large intestine (ileocecal valve or sphincter)  The Small Intestine The mucosa of the small intestine has glands (Crypts of Lieberkuhn) which secrete digestive enzymes The submucosa of the duodenum has Brunner’s glands which secrete alkaline mucus  The Small Intestine - Approximately 80% of all absorption of nutrients occurs in the small intestine - The anatomic structure of small intestine is highly specialized for the absorption Plicae: circular folds in the small intestine’s inner wall Villi: finger-like projections that protrude from the surface of the plicae site of nutrient absorption  The Small Intestine – The epithelial cells that cover the surface of the villus have brush border of microvilli – Microvilli increase absorption area – Villus contains arteriole, venule, capillary network, and lacteal  Small-Intestine Absorptive Surface Copyright © 2018 by Nelson Education Figure 15-20, p. 680 30 Ltd.  The Large Intestine - Approximately 5 feet in length, 2.5 inches in diameter - Divided into 4 regions: i) Cecum, the pouchlike first part ii) Colon (ascending, transverse, descending) which is the largest part iii) Rectum which terminates at the anus iv) Anus (anal canal)  The Large Intestine Functions Absorption of water Manufacture and absorption of vitamins Formation and expulsion of feces  The Pancreas - Elongated gland located behind and below the stomach - The pancreas consists of: Head: nearest the curvature of the duodenum Body: main part Tail: rounded end of the pancreas nearest the spleen Pancreatic duct: delivers secretions from the pancreas to the duodenum  The Pancreas -Mixture of exocrine and endocrine tissue - Endocrine function – Islets of Langerhans Found throughout pancreas Secrete hormones: insulin (beta cells) and glucagon (alpha cells), which enter the bloodstream to travel to target organs  The Pancreas Exocrine function - 3 pancreatic enzymes secreted by acinar cells and travel through the pancreatic duct to the small intestine Lipases: Digest lipids Carbohydrases: Digest carbohydrates Proteases: Digest protein - sodium bicarbonate solution actively secreted by duct cells that line pancreatic ducts Exocrine and Endocrine Portions of the Pancreas [[CATCH: C15-F13-HP4ce here, p. 668]] Figure 15-11, p. 668 Copyright © 2018 by Nelson Education Ltd.  The Liver – One of the largest organs of the digestive system which weights 4 pounds – It is divided into two lobes: Right lobe Left lobe – Falciform ligament separates the two lobes – The lobes of the liver are made up of numerous functional units called the lobules  The Liver Functions – Produces proteins such as heparin, prothrombin and thrombin – Phagocytosis of bacteria and old (white and red) blood cells – Stores excess carbohydrates (glycogen), minerals (iron and copper), and vitamins (A, D, E, K) – Converts toxins into less harmful substances – Produces bile which breaks down fats  The Gallbladder - Pear-shaped sac - Located in depression on surface of liver - The gallbladder is divided into three regions Fundus Body Neck - The cystic duct leads from the neck of the gallbladder to the common bile duct  The Gallbladder Stores and concentrates bile which is produced by the liver, until it is needed in the small intestine The bile enters duodenum (after meal) through the common bile duct  Pathology Mumps virus that infects the salivary glands affects children between the ages of 5 and 9 exposure stimulates antibody production resulting in permanent immunity an effective vaccine is available  Pathology Hiatal Hernia widening of the esophageal hiatus where the esophagus penetrates through the diaphragm muscle to connect with the stomach. results in a portion of the stomach protruding upward through the diaphragm occurs most often in adults, with 40% of the population affected major symptom is gastroesophageal reflux or acid reflux  Pathology Ulcers occur when the hydrochloric acid and digestive enzymes erode the layers of the stomach or duodenum. caused by either the excessive production of acid or the inadequate production of the alkaline mucus bacterium Helicobacter Pylori is associated with the development of 65% of ulcers  Pathology Hepatitis is inflammation of the liver caused by excessive alcohol consumption or by viral infection (HAV, HBV). Cirrhosis is a long-term degenerative disease of the liver in which the lobes are covered with fibrous connective tissue; can be caused by excessive alcohol consumption. Gallstones are caused when cholesterol which is secreted by the liver, precipitates in the gallbladder, it produces gallstones; affect 20% of the population over 40 years of age and are more prevalent in women than men; gallbladder has to be removed surgically to remove the buildup of the gallstones.  Pathology Appendicitis is inflammation of the vermiform appendix caused by an obstruction; more common in teenagers and young adults as well in males. Crohn’s disease is a chronic, inflammatory bowel disease of unknown origin; symptoms include frequent bouts of diarrhea, severe abdominal pain, fever, chills, nausea, weakness, anorexia, and weight loss; treatment aims at the symptoms  Pathology Pancreatitis (acute or chronic) is inflammation of the pancreas caused by the damage to the organ due to alcohol abuse, infectious disease or drugs. Symptoms: severe abdominal pain, nausea and vomiting, fever. Hemorrhoids caused by the inflammation and enlargement of rectal veins. Strain on defecation causes inflammation of these veins. High fiber diet helps produce softer stools, which results in less strain on defecation. The Respiratory System  Introduction The cells of the body need a continual supply of O2 to support their energy-generating chemical reactions The CO2 produced during these reactions must be eliminated from the body at the same rate as produced To prevent fluctuations in pH Respiration: The processes that cause passive movement of O2 from the atmosphere to the tissues, and the passive movement of CO2 from the tissues to the atmosphere.  Function of the Respiratory System General function is to obtain O2 for use by the body’s cells and to eliminate the CO2 the body cells produce Encompasses two separate but related processes: – External respiration Exchange of gases between lungs and blood – Internal respiration Exchange of gases between blood and body cells  Non-respiratory Functions of the Respiratory System Humidifies and warms the inspired air Enhances venous return Maintains normal acid-base balance by expelling CO2 Enables speech and other vocalizations Sense of smell Defends against inhaled foreign matter  The Respiratory System Functions in close association with the cardiovascular system When the respiratory and cardiovascular systems are examined together = “cardiorespiratory system” The oxygen transport system  The Cardiorespiratory System Responsible for: delivery of oxygen and nutrients to working muscles removal of carbon dioxide and waste products from the working muscles  Anatomy of the Respiratory System Anatomy consists of – Respiratory airways leading into the lungs – Lungs (airways and alveoli) – Structures of the thorax involved in producing movement of air through the airways into and out of the lungs  Airways Tubes that carry air between the atmosphere and the air sacs – Nasal passages (nose) External nares or nostrils: two openings on the undersurface of the external nose Internal nares or nostrils: two openings posteriorly, connect nose and pharynx Functions: warm and moisturize air, smell, speech tone Air enters the external nostrils, the internal nostrils and the nasopharynx  Airways – Pharynx which is also called a throat it is a tube, 13cm long 3 portions: i) Nasopharynx, the back of the nose area ii) Orophanynx, the back of the mouth area iii) Laryngopharynx, connects with the esophagus posteriorly and with the larynx anteriorly common passageway for respiratory and digestive systems  Airways – Larynx (voice box) Short passageway that connects the pharynx with the trachea Its walls are supported by cartilage Its epiglottis keeps food and drink out of the airway Its vocal folds or cords produce sound  Airways – Trachea (windpipe) Rigid tube ~12 cm long Anterior to esophagus Smooth muscle and connective tissue encircled by 16 to 20 incomplete C-shaped rings of cartilage which prevent collapse Tracheostomy done if object cannot be expelled – Usually done between second and third tracheal cartilages – Can be closed when blocking object removed  Airways – Trachea branches at inferior end into left primary bronchus (goes to the left lung) and right primary bronchus (goes to the right lung) – Primary bronchi branch into secondary bronchi – Secondary bronchi branch into tertiary bronchi  Airways – Tertiary bronchi branch into bronchioles – Bronchioles branch into terminal bronchioles  Airways – Bronchioles No cartilage to hold them open Walls contain smooth muscle innervated by autonomic nervous system Sensitive to certain hormones and local chemicals Alveoli (air sacs) are clustered at ends of terminal bronchioles  Airways Reflex mechanisms close off the trachea and larynx during swallowing, so food and drink don’t enter the lungs. The esophagus stays closed except during swallowing to keep air from entering the stomach while breathing. The trachea and bronchi are rigid tubes encircled by cartilage rings that prevent them from closing The bronchioles have no cartilage and contain smooth muscle that is innervated by the autonomic nervous system. The smooth muscle is also sensitive to hormones and local chemicals. Contractions of this smooth muscle regulate airflow to the lungs  Alveoli Respiratory bronchioles divide 2-11 alveolar ducts End in alveolar sacs Clusters of thin-walled, inflatable, grape-like sacs Lungs contain approximately 300 million alveoli Surface area of approx 75m2 (tennis court)  Alveoli They are composed of two types of epithelial cells: Type I and Type II Alveolar walls consist of a single layer of flattened Type I alveolar (epithelial) cells Type II alveolar (epithelial) cells secrete pulmonary surfactant (phospholipoprotein) which prevents alveolar collapse Pulmonary capillaries encircle each alveolus  Alveoli Alveolar macrophages protect against foreign agents (phagocytize bacteria in the alveoli) Pores of Kohn permit airflow between adjacent alveoli (collateral ventilation)  Alveoli At rest: Approximately 250 ml O2 /min leaves alveoli and enters the blood (0.25 L/min) Approximately 200 ml CO2 /min leaves the blood and enters the alveoli During heavy exercise: 25 times more O2 is transferred across the alveolar membrane (6.25 L/min or 6250 ml/min)  Alveolus and Respiratory Membrane Gas exchange at the alveoli Pulmonary arteries transport carbon dioxide to the alveolar capillaries Carbon dioxide leaves the capillaries and enters the alveolar sacs Oxygen leaves the alveolar sacs and enters the capillaries Oxygen enters the pulmonary veins and returns to the heart to be pumped to all parts of the body  The Lungs Found in the thoracic cavity Two lungs divided into several lobes, each supplied by one of the bronchi Lung consists of a series of highly branched airways, the alveoli, the pulmonary blood vessels, and large quantities of elastic connective tissue  The Lungs Lungs have a mass of approximately 1.3 kg The lungs occupy most of the volume of the chest cavity Protected by the ribs (which join the sternum anteriorly, and the thoracic vertebrae posteriorly) The diaphragm is immediately inferior to the lungs Separates the thoracic cavity from the abdominal cavity Sheet of muscle innervated by the phrenic nerve  The Chest Wall Chest wall (thoracic wall) – Formed by 12 pairs of ribs which join sternum (breastbone) anteriorly and thoracic vertebrae (backbone) posteriorly – The rib cage protects the lungs and heart – The chest wall contains the muscles involved in generating the pressure that causes airflow  The Chest Wall Internal Intercostal muscles - lie between the ribs - internal - innervated by intercostal nerves  The Chest Wall External intercostal muscles lie over the internal intercostal muscles and innervated by intercostal nerves  The Pleural Sac – Double-walled, closed sac that separates each lung from the thoracic wall – Parietal pleura: outer membrane which covers the inside lining of the thoracic wall – Visceral pleura: inner membrane which covers the outer surface of the lungs – Pleural cavity between these two membranes which is filled with pleural fluid Secreted by surfaces of the pleura Lubricates pleural surfaces Prevents friction between the two membranes  Pulmonary Ventilation Movement of air into and out of the lungs – breathing Reliant on differences in air pressure  Respiratory Mechanics Air tends to move from a region of high pressure to a region of low pressure, i.e., down a pressure gradient Recall the anatomy of the lungs: Atmosphere The pressure gradients across each space will determine if air is flowing into the lungs or out of the lungs  Respiratory Mechanics The pressures that are important for ventilation: Atmospheric pressure: The pressure exerted by the weight of the air At sea level = 760mmHg (1 atmosphere) Intra-alveolar pressure: The pressure within the alveoli Intrapleural pressure: The pressure within the pleural sac Exerted outside the lungs but in the thoracic cavity Approx 756mmHg at rest (Approx 4mmHg less than atmospheric pressure)  Respiratory Mechanics Air flows down a pressure gradient. When the pressure in the lungs (intra-alveolar) is less than the pressure of the atmosphere, air will rush into the lungs When the pressure in the lungs (intra-alveolar) is greater than the pressure of the atmosphere, air will be forced out of the lungs The pressure in the lungs changes when the volume of the lungs changes (caused by respiratory muscles) Boyle’s Law: The pressure of a given quantity of gas is inversely proportional to its volume (assuming a constant temperature).  Pulmonary Ventilation Boyle’s Law Changes in intra- alveolar pressure produce flow of air into and out of the lungs If this pressure is less than atmospheric pressure, air enters the lungs. If the opposite occurs, air exits from the lungs  Pulmonary Ventilation move air into and out of the lungs from the atmosphere Inspiration or Inhalation occurs when the pressure in the alveoli is less than atmospheric pressure. Expiration or Exhalation occurs when the pressure in the alveoli is greater than atmospheric pressure.  Quiet Inspiration The muscles involved in quiet inspiration are: The diaphragm The external intercostal muscles Contraction → thoracic volume increases → the thoracic (intra-alveolar) pressure decreases → air is drawn into the lungs The diaphragm: Innervated by the phrenic nerve At rest = dome shaped When it contracts, it flattens and descends Increasing the vertical dimension of the thoracic cavity Accounts for 50-75% of the enlargement of the thoracic cavity during quiet breathing The external intercostal muscles: Between ribs Contraction enlarges the thoracic cavity in the lateral and anteroposterior dimensions  Quiet Inspiration During quiet inspiration intra-alveolar pressure drops from 760 to 759mmHg, drawing air into the lungs (until intra-alveolar pressure returns to 760mmHg) During quiet inspiration intrapleural pressure drops to 754mmHg (due to the expansion of the chest cavity) ensuring that the lungs stretch and inflate  Deep Inspiration The muscles involved in deep inspiration are: The diaphragm The external intercostal muscles The accessory muscles In the neck Sternocleidomastoids Raise the sternum Scalenes Elevate the first 2 ribs  Quiet (Passive) Expiration Relaxation of the diaphragm and the external intercostal muscles The diaphragm assumes its original dome shape The elevated rib cage falls when external intercostals relax Relaxation of external intercostal muscles Relaxation of diaphragm Passive Expiration Return of diaphragm, ribs and sternum to resting position on relaxation of inspiratory muscles restores thoracic cavity to preinspiratory size The lungs passively recoil Thoracic (intra-alveolar) pressure increases to 761mmHg Air is forced out of the lungs until pressure reaches 760mmHg (equilibrates with atmospheric pressure)  Forced Expiration Expiration is forced during exercise, coughing or clearing the throat Expiratory muscles contract to further reduce the volume of the thoracic cavity Abdominal muscles (push the abdominal contents in and the diaphragm up) Internal intercostal muscles (pull the ribs down and in)  Respiratory Mechanics The flow of air into and out of the lungs also depends on the radius of the airways (although in a healthy person, the airways offer very little resistance to flow) F = ΔP R Where, F = airflow rate ΔP = Pressure gradient (intra-alveolar and atmospheric) R = Resistance of the airways (determined by radius)  Airway Resistance and Airflow Primary determinant of resistance to airflow is the radius of the conducting airway Autonomic nervous system controls contraction of smooth muscle in walls of bronchioles (changes the radius)  Airway Resistance and Airflow The lung is innervated by both branches of the autonomic nervous system: - Parasympathetic: acetylcholine (Ach) causes bronchoconstriction (smooth muscle contraction) - Sympathetic: norepinephrine (NE) and epinephrine causes bronchodilation (smooth muscle relaxation) 87  Measuring Lung Volumes and Capacities A spirometer consists of an air-filled drum floating in a water-filled chamber – Measures the volume of air breathed in and out  Lung Volumes and Capacities Tidal Volume (TV) The amount of air entering or leaving the lungs in a single breath At rest = approx 500mL Inspiratory Reserve Volume (IRV) The extra volume of air that can be maximally inspired over and above tidal volume Average value = approx 3000mL Inspiratory Capacity (IC) The maximum volume of air that can be inspired at the end of a normal quiet expiration (IC = IRV + TV) Average value = approx 3500mL  Lung Volumes and Capacities Expiratory Reserve Volume (ERV) The extra volume of air that can be actively expired (beyond passive expiration) by maximally contracting the expiratory muscles Average value = approx 1000mL Residual Volume (RV) The minimum volume of air remaining in the lungs even after a maximal expiration Average value = approx 1200mL  Lung Volumes and Capacities Functional Residual Capacity (FRC) The volume of air in the lungs at the end of a normal passive expiration (FRC = ERV + RV) Average value = approx 2200mL Vital Capacity (VC) The maximum volume of air that can be moved out during a single breath following a maximal inspiration (inspire maximally, then expire maximally) (VC = IRV + TV + ERV) Average value = approx 4500mL  Lung Volumes and Capacities Total Lung Capacity (TLC) The maximum volume of air that the lungs can hold at the end of maximum inspiration (TLC = VC + RV) Average value = approx 5700mL Forced Expiratory Volume in One Second (FEV1) The volume of air that can be expired during the first second of expiration in a vital capacity determination. Denotes maximal airflow rate Expressed as a ratio: FEV1/FVC Usually FEV1 is 80% of VC  Pulmonary Ventilation Minute ventilation Volume of air breathed in and out in one minute Pulmonary ventilation = tidal volume x respiratory rate (ml/min) (ml/breath) (breaths/min)  Alveolar Ventilation More important than pulmonary ventilation Volume of air exchanged between the atmosphere and the alveoli per minute Less than pulmonary ventilation due to anatomic dead space Volume of air in conducting airways that is useless for exchange Averages about 150 ml in adults Alveolar ventilation = (tidal volume – dead space) x respiratory rate Effect of Different Breathing Patterns on Alveolar Ventilation External and Internal Respiration External respiration Exchange of gases between lungs and blood Internal respiration Exchange of gases between blood and body cells  Gas Exchange At both pulmonary capillary and tissue capillary levels, gas exchange involves simple diffusion of O2 and CO2 down partial pressure gradients Partial pressure exerted by each gas in a mixture equals the total pressure multiplied by the fractional composition of this gas in the mixture  Partial Pressure partial pressure = % concentration x total pressure of gas mixture  Gas Diffusion Differences in PO2 and PCO2 drive gas exchange (diffusion) Gas diffuses from high partial pressure to low partial pressure  Oxygen Transport Oxygen is carried in the blood by: 1. plasma (1.5 %) 2. in combination with Hb (98.5%)  Carbon Dioxide Transport CO2 is transported to the lungs in one of three forms: 1. it may be carried as CO2 dissolved in plasma 2. as part of a compound formed by bonding to Hb 3. through bicarbonate  Pathology The common cold is a contagious infection of the upper respiratory tract caused by a form of the rhinovirus. Influenza or flu is a highly contagious viral infection of the respiratory tract caused by a myxovirus (3 strains: Type A, B, and C). Tuberculosis or TB is a chronic bacterial infection that usually affects the lungs and it is caused by the Mycobacterium tuberculosis.  Pathology Bronchitis is an inflammation of the bronchi leading to increased mucous production and a decrease in the diameter of the bronchial tubes, impairing breathing; can be caused by a bacterial/viral infection or develop from increased exposure to irritants like air pollutants or cigarette smoke. Emphysema is a degenerative disease with no cure caused by the destruction of the walls of the alveoli from prolonged exposure to respiratory irritants; decrease in gas exchange; symptoms include enlargement of the thoracic cavity and shortness of breath. Pneumonia refers to any infection in the lungs; most are caused by bacterial infections; symptoms include fever, chest pain, fluid in lungs, and difficulty in breathing.  Pathology Laryngitis is inflammation of the mucosal membrane lining of the larynx; symptoms include swelling of the vocal cords with accompanying symptoms of a cold; is caused by excessive use of the voice or by bacterial/viral infections Whooping cough, or pertussis, is caused by the bacterium Bordetella pertussis resulting in mucus accumulation and severe coughing; a childhood vaccine is available to prevent this disease  Pathology Cystic fibrosis an inherited disease that affects the secretory cells of the lungs caused by abnormal chloride ion secretions the mucus becomes thick resulting in difficulty breathing it was once fatal in childhood, but today individuals with the disease can live into early adulthood  Pathology Sudden infant death syndrome (SIDS) unexpected death of a healthy infant that happens during sleep when the child stops breathing most frequent cause of death in infants between 2 weeks and 1 year old the cause remains unknown and controversial abnormal development of the respiratory centers in the brain may be a factor other proposed causes are prolonged apnea, a defect in the respiratory mucosa, and immunoglobulin deficiencies No preventative treatments but infants should sleep on their backs or on their sides  Pathology Chronic obstructive pulmonary disease (COPD) a progressive disorder characterized by long-term obstruction of airflow the disease includes emphysema, asthma, and chronic bronchitis in most cases, COPD is preventable since smoking it is the most common cause other causes of COPD include exposure to dust and gases at the workplace, chronic air pollution, and pulmonary infections The Cardiovascular System The Cardiovascular System Includes: - heart - blood - blood vessels (arteries, veins capillaries) Functions of the Cardiovascular System The heart functions as a muscular pump that forces blood through the blood vessels The blood serves as a fluid for transporting O2, nutrients, hormones, and waste products The vessels serve to deliver the blood to all locations within the body, and to return the blood back to the heart  The Heart About the size of a clenched fist Average size: 12 cm long, 9 cm wide Average mass: 300 g Located within the thorax and rests upon the diaphragm  Covering of the Heart: The Pericardial Sac Heart is enclosed by pericardial sac Pericardial sac has two layers: – Fibrous pericardium (outer layer) tough, fibrous covering – Serous pericardium (inner layer) secretes pericardial fluid provides lubrication to prevent friction between pericardial layers Covering of the Heart: The Pericardial Sac 115  The Heart Walls Consist of three distinct layers: – Endocardium (endothelium) Thin inner tissue Epithelial tissue that lines entire circulatory system – Myocardium Middle layer Composed of cardiac muscle fibers Constitutes bulk of heart wall – Epicardium (visceral pericardium) Thin external layer that covers the heart 116  The Heart beats ~ 104,000 times per day (~72 beats/min) 4 chambers – 2 atria and 2 ventricles pumps blood into 2 circuits – Pulmonary circuit – Systemic circuit Circulatory System Pulmonary circulation – Closed loop of vessels carrying blood between heart and lungs Systemic circulation – Circuit of vessels carrying blood between heart and other body systems  The Heart is a Dual pump – Right and left sides of heart function as two separate pumps – Divided into right and left halves and has four chambers Atria (Atrium) Ventricles (Ventricle) – Septum Continuous muscular partition that prevents mixture of blood from the two sides of heart  Heart Champers Atria Upper chambers Receive blood returning to heart and transfer it to lower chambers Ventricles Lower chambers that pump blood from heart Thicker walls with more myocardium than atria  The Great Vessels of the Heart Superior vena cava – Receives blood from upper body Inferior vena cava – Receives blood from lower body  The Great Vessels of the Heart Pulmonary trunk: right and left pulmonary arteries – Carries deoxygenated blood to lungs Pulmonary veins (four): return oxygenated blood to heart (left atrium of the heart) Aorta: carries oxygenated blood out to body  The Valves of the Heart There are four valves in the heart Two atrioventricular valves (AV): Tricuspid valve (right) and Bicuspid or Mitral valve (left) Two semilunar valves: Aortic and pulmonary valves  Atrioventricular (AV) valves - Right and left AV valves are positioned between atrium and ventricle on right and left sides - Prevent backflow of blood from ventricles into atria during ventricular emptying Right AV valve: also called tricuspid valve Left AV valve: also called bicuspid valve or mitral valve  Semilunar valves – Aortic and pulmonary valves – They have three cusps (shallow half-moon-shaped pockets) – Lie at juncture where major arteries leave ventricles – Prevented from everting by anatomic structure and positioning of cusps Mechanism of Valve Action  Circuit of Blood Flow Blood returning from the systemic circulation enters the right atrium via - Superior vena cava (blood from the upper parts of the body; head, neck, arms to the heart) - Inferior vena cava (blood from the lower part of the body) Oxygen has been extracted from this blood. Carbon dioxide has been added to it. This blood is pumped from the right ventricle through the pulmonary artery to the lungs. Thus, the right side of the heart receives blood from the systemic circulation and pumps it to the pulmonary circulation.  Circuit of Blood Flow The lungs add oxygen to, and remove carbon dioxide from, the blood received from the right side of the heart. This blood flows through pulmonary veins to the left atrium of the heart. This oxygen rich blood is pumped from the left ventricle through the aorta, a large artery. Thus, the left side of the heart receives blood from the pulmonary circulation and pumps it to the systemic circulation. How is the proper directional flow of blood maintained? The valves of the heart; prevent back flowing of the blood  The Cardiac Cycle It is the sequence of events that occurs when the heart beats One complete sequence of contraction and relaxation of the heart It consists of alternate periods of systole (contraction and emptying) and diastole (relaxation and filling)  The Cardiac Cycle alternate periods of contraction & relaxation – Contraction is systole Blood is ejected into the ventricles Blood is ejected into the pulmonary trunk and the ascending aorta – Relaxation is diastole Chambers are filling with blood  The Cardiac Cycle During the cardiac cycle, the pressure within the chambers rises and falls Atrial systole - atria contract Atrial diastole - atria relax Ventricular systole - ventricles contract Ventricular diastole - ventricles relax  CARDIAC CYCLE ATRIA (SUMMARY) Relaxed atria  blood flows into (and through) atria  increased pressure in atria  atria contract (atrial systole)  blood flows into ventricles  atria relax (atrial diastole)  decreased pressure in atria  CARDIAC CYCLE VENTRICLES (SUMMARY) Ventricles fill with blood from contracting atria  Ventricles start to contract and pressure builds in ventricles (Isovolumetric contraction)  bicuspid and tricuspid valves close  Semilunar valves are forced open and blood flow from ventricles into arteries  Ventricles relax with bicuspid and tricuspid valves still closed (Isovolumetric relaxation)  Bicuspid and tricuspid valves open and blood flows from atria to ventricles For efficient cardiac function: 1. Atrial excitation and contraction should be completed before the onset of ventricular contraction. When blood returns to the heart, the AV valves are open, and blood entering the atria flows directly into the ventricles 80% of ventricular filling happens before atrial contraction The remaining 20% of ventricular filling happens when the atria contract and squeeze the blood into the ventricles Then the ventricles can contract and eject the blood they’ve received For efficient cardiac function: 2. The excitation of cardiac muscle fibers should be coordinated so that each chamber pumps as a unit. Random, uncoordinated excitation and contraction is known as fibrillation Ventricular fibrillation can be fatal 3. Both atria need to pump at the same time, and both ventricles need to pump at the same time. - Synchronized pumping of blood into the pulmonary and systemic circulation  Stroke Volume (SV) The volume of blood ejected from the ventricle with each beat (stroke) of the heart. Equals about 70 milliliters (ml) SV = EDV – ESV (e.g. 140ml-70ml=70ml)  Ejection Fraction (EF) The proportion of the blood pumped out of the left ventricle at any given beat. Reveals how much of the blood entering the ventricle is ejected during systole.  Cardiac Output Volume of blood ejected by each ventricle each minute Determined by heart rate times stroke volume 140  Cardiac Output Cardiac output (CO) = heart rate (HR) × stroke volume (SV) = 70 beats/min × 70 ml/beat = 4900 ml/min ~ 5 litres/min 141  HEART SOUNDS produced from the vibrations caused by valves closure “Lub, dub”  HEART SOUNDS 1st sound - S1: - occurs during ventricular contraction - when the tricuspid and bicuspid valves close 2nd sound – S2: - occurs during ventricular relaxation - when the pulmonary and aortic semilunar valves close  Intrinsic Control of Heart Rate Cardiac muscle generates its own electrical signal: autoconduction will contract without nervous stimulation 1% of cardiac muscle cells are specialized and spontaneously initiate contraction  Cardiac Muscle Cells Two specialized types of cardiac muscle cells: – Contractile cells – Autorhythmic cells  Contractile cells – 99 percent of cardiac muscle cells – Do mechanical work of pumping – Normally do not initiate own action potentials  Autorhythmic Cells 1% of the cardiac muscle cells – Do not contract – Specialized for initiating and conducting action potentials responsible for contraction of working cells  Autorhythmic Cells Autorhythmic cells are located in 4 specialized sites in the heart They generate and distribute the electrical impulses These electrical impulses stimulate the heart muscle to contract  Locations of autorhythmic cells 1. Sinoatrial node (SA node) Specialized region in right atrial wall near opening of superior vena cavae Pacemaker of the heart (fastest rate of autorhythmicity) 2. Atrioventricular node (AV node) Small bundle of specialized cardiac cells located at base of right atrium near septum  Locations of autorhythmic cells 3. Bundle of His (atrioventricular bundle) Cells originate at AV node and enters interventricular septum Divides to form right and left bundle branches which travel down septum, curve around tip of ventricular chambers, travel back toward atria along outer walls 4. Purkinje fibers Small, terminal fibers that extend from bundle branches and spread throughout ventricular myocardium Spread of Cardiac Excitation Measuring the Electrical Activity of the Heart ECG - electrocardiogram a recording of the electrical changes that occur in the myocardium (heart muscle) during a cardiac cycle correlates with contraction Electrocardiogram (ECG)  ECG Waveforms Different parts of ECG record can be correlated to specific cardiac events  Importance of ECG The ECG can be used to diagnose: Abnormal heart rate - Tachycardia (heart rate above 100 beats/min) - Bradycardia (heart rate below 60 beats/min)  Importance of ECG The ECG can be used to diagnose: abnormal heart rhythm - Ex. Ventricular fibrillation (ventricles exhibit uncoordinated, chaotic contractions) Cardiac myopathies (damage to the heart muscle) - Ex. Myocardial infarction (heart attack) (death of heart muscle due to blocked or ruptured blood supply)  Extrinsic Control This intrinsic rate of beating can be altered through “extrinsic” systems: 1. Parasympathetic NS 2. Sympathetic NS 3. Endocrine system  Extrinsic Control 1. Parasympathetic Nervous System – decreases the heart rate 2. Sympathetic Nervous System – increases the heart rate and also increases the force of contraction (stroke volume) 3. Endocrine System – adrenal gland secretes epinephrine which increases the heart rate and also increases the force of contraction (stroke volume)  Purpose of Cardiovascular System The cardiovascular system is responsible for controlling steady states or homeostasis within the body During exercise, the requirements of the muscle tissues during exercise can increase 15 to 25 times the resting levels Two major adjustments of blood flow are necessary Cardiovascular Adjustments 1) an increase in cardiac output which can be achieved by: i) increasing heart rate and/or ii) increasing stroke volume 2) redistribution of blood flow from the inactive organs to the working muscles  Cardiac Output Control Extrinsic control for the heart rate (controlled by the autonomic nervous system) Intrinsic and extrinsic control for the stroke volume  The Vascular Tree The systemic and pulmonary circulations each consist of a closed system of vessels The vascular tree consists of – Arteries Carry blood from heart to tissues – Arterioles Smaller branches of arteries  The Vascular Tree (cont’d) – Capillaries Smaller branches of arterioles Smallest of vessels across which all exchanges are made with surrounding cells – Venules Formed when capillaries rejoin Return blood to heart – Veins Formed when venules merge Return blood to heart  Structure of blood vessels Adventia Collagen fibres internal elastic membrane  Arteries Serve 2 main functions: 1. Serve as rapid-transit passageways for blood from heart to organs Their large radius offers little resistance to blood flow 2. Act as a pressure reservoir to provide driving force for blood when the heart is relaxing This reservoir action is possible since arterial connective tissue contains: - Collagen fibres which provide tensile strength - Elastin fibres which provide elasticity to arterial walls Arteries as a Pressure Reservoir  Arterial Pressure Blood pressure: the force exerted by blood against a vessel wall, depends on – Volume of blood contained within vessel – Compliance or distensibility of vessel walls  Arterial Pressure Systolic pressure – Peak pressure exerted by ejected blood against arterial walls during ventricular systole – Averages 120 mmHg Diastolic pressure – Minimum pressure in arteries when blood is draining off into vessels downstream during ventricular diastole – Averages 80 mmHg  Blood Pressure Can Be Measured Using a Sphygmomanometer Can be measured indirectly using a sphygmomanometer Korotkoff sounds – Sounds heard when determining blood pressure – Sounds are distinct from heart sounds associated with valve closure  Arterioles The major resistance vessels in the vascular tree Vasodilate and vasoconstrict to regulate blood flow to tissues Smooth muscle wall can alter the diameter of the arteriole  Capillaries Thin-walled, small-radius, extensively branched Sites of exchange between blood and surrounding tissue cells – Maximized surface area (large number of capillaries cover large surface area) and minimized diffusion distance (due to thin wall of capillaries)  Structure of Capillaries Basal lamina Endothelial cell Nucleus Continuous Fenestrated capillary capillary Endosomes Endosomes Fenestrations, or pores Boundary Boundary Basal between between Basal lamina endothelial lamina endothelial cells cells  Veins Venous system transports blood back to heart – Capillaries drain into venules – Venules converge to form small veins that exit organs  Veins – Smaller veins merge to form larger veins – Large radius offers little resistance to blood flow from the tissues to the heart – Also serve as blood reservoir, capacitance vessels (store more than 60% of blood at rest)  Veins Veins have a high storage capacity (Capacitance vessels) Thin walls Little amount of smooth muscle More collagen fibers than elastin fibers (easily distend and have little elastic recoil) At rest, veins act as a blood reservoir  Valves in Veins Valve closed Valve opens above contracting muscle Valve closed Valve closes below contracting muscle What happens if the valves don’t work?  Pathology Pericarditis: inflammation of the pericardium caused by viral or bacterial infection. Myocarditis: inflammation of the myocardium, which can cause a heart attack. Heart failure: progressive weakening of the myocardium and failure of the heart to pump adequate amounts of blood. Endocarditis: inflammation of the endocardium. Rheumatic heart disease: inflammation of the endocardium that usually occurs in children as a result of untreated infections of the bacterium Streptococcus affecting especially the bicuspid valve. Antibiotic treatments have reduced the frequency of this disease.  Pathology Atherosclerosis: a disease of the arteries in which cholesterol-containing masses called plaque accumulate on the inside of arterial walls. Hypertension: high blood pressure that can cause enlargement of the heart leading to heart failure. Arrhythmia: deviation from normal heartbeat rhythm. Bradycardia is a slow heartbeat rate of less than 60 b/min. Tachycardia is a fast heartbeat rate of more than 100 b/min that and can result from excessive sympathetic innervation, elevated body temperature, or drug interactions. Heart murmur: abnormal heart sound like a gentle blowing that is indicative of stenosis or incompetent heart valve.  Congenital heart disease Heart disease that is present at birth when the heart does not develop properly. Septal defect is a hole in the interatrial or interventricular septum between the left and right sides of the heart. This reduces the pumping effect of the heart. Stenosis of the heart valves is a narrowed opening through the valves causing backflow.  Coronary Heart Disease Ischemia (reduced blood flow) of the coronary arteries that causes a sensation of pain in the chest, left arm, and shoulder called angina pectoris. Coronary ischemia can cause an infarct (necrosis) of cardiac tissue leading to a heart attack, commonly referred to as a myocardial infarction. Degenerative changes in the coronary arteries cause the walls to be roughened with platelet aggregation, resulting in a blood clot in the vessel called coronary thrombosis. THE BLOOD Classification of Connective Tissue Connective Tissues can be divided into three types Connective Tissue Proper Fluid Connective Tissue Supporting Connective Tissue Loose Dense Blood Lymph Cartilage Bone Fibers create Fibers densely Contained in Contained Solid, rubbery Solid, loose, open packed cardiovascular in lymphatic matrix crystalline framework dense regular system system hyaline cartilage matrix areolar tissue dense elastic cartilage adipose tissue irregular fibrous cartilage reticular tissue elastic  Blood Basics Blood represents ~ 8% of total body weight Average volume – Males: 6 liters – Females: 5 liters ❖ Hypovolemic: low blood volume ❖ Normovolemic: normal blood volume ❖ Hypervolemic: excessive blood volume ❖ pH: 7.35–7.45  Functions of the Blood 1. Transport: gases (O2, CO2), nutrients (e.g. glucose), waste products (e.g. urea) 2. Regulation: body pH, body temperature, water content of the cells 3. Protection: - against foreign microbes and toxins through its white blood cells - from fluid loss due to damaged vessels and tissues via clotting mechanism  Blood Composition Blood consists of: Red Blood Cells RBCs (Erythrocytes) Important in O2 transport White Blood Cells WBCs(Leukocytes) Immune system’s mobile Suspended in defense units liquid (plasma) Platelets (Thrombocytes) Important in hemostasis (blood clotting) Blood Composition  Blood Composition Hematocrit: The percentage of packed cells in total blood volume Mostly red blood cells (but also includes white blood cells and platelets