Human Body: Digestive System

Human Body Systems

• The human digestive system analyzes large organic molecules in food, breaking them into smaller molecules.
• This process enables absorption through cell membranes, providing essential building blocks for the body.
• Amino acids build necessary proteins, while fatty acids, glycerol, and cholesterol are used to construct fats.

Components of the Digestive System

• Mouth
• Pharynx
• Esophagus
• Stomach
• Small intestine
• Large intestine

Digestion Process in the Mouth

• Mechanical digestion involves tearing and grinding food into smaller pieces using teeth and jaw muscles.
• The tongue mixes food with saliva.
• Chemical digestion breaks down complex organic materials with the amylase enzyme in saliva.

Functions of the Tongue

• Speech
• Food movement
• Taste perception

Taste Perception

• The tip detects sweet and salty tastes.
• Sides detect sour tastes.
• The end of the tongue recognizes bitter tastes.

Pharynx

• A short muscular tube with a dual role.
• It passes food from the mouth to the esophagus.
• Directs air from the nose and mouth to the larynx.

Epiglottis

• Flexible fibrocartilaginous tissue
• It covers the larynx, preventing food from entering the respiratory tract during swallowing

Esophagus

• After swallowing transports the food to the stomach through the cardiac sphincter, preventing reflux except during vomiting.
• Muscles in the esophagus create peristaltic movements.
• The relaxation in front of the bolus and contraction behind moves food toward the stomach.
• This process occurs throughout the digestive system.

Stomach Entry and Function

• The upper opening contains the cardiac sphincter, allowing food to enter
• It prevents backflow into the esophagus.
• The pyloric valve at the stomach’s end allows passage of chyme into the duodenum.
• Stomach walls consist of three muscle layers, enabling mixture of food with digestive juices, accelerating digestion.
• Internal walls have many folds with digestive enzyme-secreting glands and hydrochloric acid glands to increase the surface area.

Stomach Juice Composition

• Clear, yellowish fluid
• A mix of digestive enzymes and hydrochloric acid.

Components of Gastric Juices

• 97-99% water
• Hydrochloric acid (HCl) where pH = 1
• Pepsin and rennin enzymes are essential for protein digestion.
• Inorganic salts
• Lipase enzyme breaks down fats but has limited action

Hydrochloric Acid

• It activates pepsin, aiding in protein digestion, and eliminates ingested germs.
• The stomach wall produces a mucous substance, protecting its lining from secretions.

Pepsin

• Breaks specific peptide bonds, converting large protein chains into large polypeptides known as peptones.

Rennin

• Causes milk coagulation by altering casein in the presence of calcium ions.
• This is necessary for infants, preventing rapid milk transfer from the stomach to the intestines; adults don't commonly secrete the enzyme, which is used in cheese production.

Lipase

• Breaks down fats into an emulsion of small droplets, aiding in digestion in the duodenum and breaking down 30% of triglycerides in the stomach

Small Intestine Attributes and Function

• A convoluted muscular tube about 6 meters long completes digestion.
• It does so with secretions from its lining, liver, and pancreas.

Pancreas

• Secretes hydrogen carbonate ions
• These neutralize the acidic liquid coming from the stomach.

Pancreatic Enzymes

• Break down proteins, carbohydrates, and fats.

Liver

• Produces bile
• Stored in the gallbladder
• Aids fat digestion.

Glandular Cells

• In the small intestine lining
• Secrete enzymes like trypsin
• These enzymes complete protein digestion.

Intestinal Processes

• The large intestine contains E. coli bacteria.
• These produce vitamins K and B12.
• It absorbs most of the remaining water and salts.
• Turns the fluid chyme into semi-solid or solid feces which contains undigested food remnants, cellulose, plant fibers, bacteria, and shed cells.
• The rectum stores feces.
• Feces are eliminated through the anus.

Circulatory System

• Consists of the heart, blood vessels, and blood
• The heart is a muscular organ that pumps blood with self-generated contractions regulated by the nervous and hormonal systems, creating blood pressure.

Blood Vessels

• Arteries carry blood from the heart to the body's organs.
• Veins return blood to the heart.
• They contain valves to prevent backflow.
• Blood capillaries connect the blood to cells in various organs.
• Blood contains blood cells, plasma, and proteins while circulating throughout the body.

Internal Circulation

• Blood flows from all body areas except lungs.
• It flows through three major vena cavae.
• Blood flows from the upper part of the body, and from the lower parts, plus the coronary sinus which comes from the heart muscles.
• The right atrium fills, pushing blood to the right ventricle.
• The right ventricle contracts, sending blood to the lungs.
• Blood then returns through four pulmonary veins into the heart’s left atrium which contracts, pumping blood into the left ventricle.
• The left ventricle fills with blood and sends blood to the body via the aorta.
• The aorta divides supplying the heart and organs except the lungs.

Blood Circulation

• Two main circuits and a short circuit exist for the blood flow within the human heart.

Pulmonary Circulation

• Unoxygenated blood moves from the heart to the lungs.
• Oxygenated blood returns to the heart.
• Venous blood flows from the right ventricle into the pulmonary artery, branching into the lungs and then into capillaries around lung alveoli.
• Gas exchange occurs via carbon dioxide transfer from blood to alveoli and oxygen transfer to blood capillaries.
• Oxygenated blood returns to the heart’s left atrium via the pulmonary veins.
• Oxygenated blood is transferred from the left atrium to the left ventricle.

Systemic Circulation

• Transfers oxygenated blood from the left ventricle to all parts of the body via the aorta.
• Returns blood to the right atrium via the superior and inferior vena cava and coronary veins after passing through various arteries.

Lymphatic System

• Composed of lymph nodes in the groin, around the pharynx and armpit lymph vessels.
• Includes the thymus, tonsils, and spleen.
• Integral to the circulatory system
• Interstitial fluid surrounds body cells, similar in composition to blood plasma.
• The lymphatic vessels carry this fluid.

Lymph Function and Components

• 2.5-3 liters circulate body daily.
• Lymph is a medium between blood, tissue cells, & interstitial fluid.
• Transports proteins that cannot penetrate blood vessels.
• Lymph drains into the bloodstream via the thoracic duct.
• Absorbs fats from the intestines.

Lymphatic Tissues

• Provide defense via T cells and B cells.
• These produce plasma cells for antibody production, protecting against foreign substances.

Respiratory System Divisions

• Structurally, it contains the nose, pharynx, larynx, trachea, bronchi, and lungs.
• Functionally, it includes conducting zones and respiratory zones.

Conducting Zones

• The cavities and tubes transport air to the lungs.

Respiratory Zones

• Gas exchange happens in the respiratory bronchioles, alveolar ducts, and alveoli.

Nose

• The internal structure is specialized for three:
  • Warming, moistening, and filtering inhaled air.
  • Receiving olfactory stimuli.
  • Providing resonant chambers for speech.
• Air enters through the nostrils, lined with coarse hairs that filter out large particles.
• Air passes through the nasal cavity, divided by the nasal septum into two passages.
• Nasal cavities have three shelves extending from the lateral walls.
• This divides each cavity into a series of grooves.
• The olfactory receptors are in the lining of the upper nasal cavity.
• Columnar epithelium with goblet cells and blood vessels lines the nasal cavity.

Nasal Cavity Function

• Air is warmed as it passes between the shelves due to blood in the capillaries.
• Air is humidified with mucus from goblet cells.
• Mucus traps particles.
• Cilia propel the mucus and trapped particles toward the pharynx to be swallowed or spat out.

Pharynx (Throat)

• Funnel-shaped tube
• Extends from the end of the nasal cavity, to the top of the trachea.
• Located behind the nasal cavity, oral cavity, larynx, and cervical vertebrae.
• Made of skeletal muscles
• Lined with a mucous membrane
• Functions: - Air and food passage. - Resonates sound.

Three Regions of the Pharynx :

• Nasopharynx
• Oropharynx
• Laryngopharynx

Larynx (Voice Box)

• Short passage
• Connects the pharynx and trachea
• Lined with pseudostratified ciliated columnar epithelium containing goblet cells.
• Elastic cartilage structure, the epiglottis
• It prevents food from entering the larynx during swallowing.

Trachea

• Tubular passageway, in front of the esophagus.
• Extends into the thoracic cavity, dividing into the right and left bronchi.
• The lining is pseudostratified ciliated columnar epithelium and goblet cells.
• 16-20 incomplete hyaline cartilage rings
• Arranged horizontally
• Keeps the trachea open.
• The open part of the rings faces the esophagus
• Allows the esophagus to expand slightly during swallowing.
• The mucous membrane is sensitive and induces coughing.

Bronchi

• The trachea divides into a right main bronchus which enters the right lung.
• The left one enters the left lung.
• Lined with ciliated columnar epithelium within the lungs.
• They divide into smaller branches.

Types of Bronchi

• Primary Bronchi
• Secondary Bronchi
• Tertiary Bronchi
• Bronchioles
• Terminal Bronchioles

Lungs

• Cone-shaped organs in the thoracic cavity
• The mediastinum contains the heart between the lungs
• There are two layers of fibrous tissue known as the pleura.
• These envelop and protect each lung; the outer connects to the thoracic cavity wall