Chapter 5 (and a bit of Chp 4) Biology 25: Human Biology Prof. Gonsalves Los Angeles City College Loosely Based on Mader’s Human Biology, 7 th edition
Integumentary System Components: Hair, skin, and nails. Functions: n Protects the body from: Infection: Barrier to microbes. u Mechanical injury u Excessive heat or cold: Thermoregulation u Water loss u n Communication: Receives stimuli from environment u Gives out subtle signals (blushing, etc. ). u Homeostatic Role: u Helps maintain constant body temperature.
1. Digestive System Components: Mouth, salivary glands, throat, esophagus, stomach, intestines, liver, gallbladder, pancreas, rectum, and anus. Functions: Ingest and mechanically break down food. u Digest food: Stomach and small intestine mainly. u Absorb nutrients and water. u Eliminate waste. u Homeostatic Roles: Supplies energy for life’s activities. u Supplies building blocks for macromolecules u
Stages of Food Processing 1. Ingestion: The act of eating. Usually involves placing food in mouth or oral cavity. 2. Digestion: Macromolecules in food (fats, proteins, polysaccharides, etc. ) are too large to be absorbed by digestive system. Must be broken down into small molecules (amino acids, simple sugars, etc. ) so they can be absorbed and utilized by the body. Involves two processes: Mechanical: Chewing and churning. Chemical: Enzymatic breakdown of food.
Stages of Food Processing 3. Absorption: Cells lining the digestive cavity take up building blocks (simple sugars, amino acids, etc. ), which then enter the bloodstream. Circulatory system distributes nutrients in blood to cells throughout the body. 4. Elimination: Undigested food materials are discharged from body.
Stages of Food Processing
Parts of the Human Digestive System Alimentary canal: Long tube like structure. u Mouth u Tongue u Pharynx (throat) u Esophagus u Stomach u Small intestine u Large intestine u Rectum u Anus Digestive glands: Produce enzymes, bile, and other substances important for digestion. u Salivary glands u Pancreas u Liver and gallbladder
Human Digestive System Mouth: u u Ingest and mechanically break down food. Digestion: Saliva lubricates and starts to digest food. t u Starch is digested by salivary amylase Other enzymes in saliva kill bacteria.
Part of the Human Digestive System Pharynx (Throat): Throat opens into both the trachea (respiratory system) and esophagus (digestive system). u As food enters pharynx, swallowing reflex is triggered: t Esophageal sphincter relaxes t Epiglottis blocks tracheal opening t Food is directed towards esophagus Esophagus: u Muscular tube that conveys food to stomach. u Peristalsis: Wavelike involuntary muscle contractions squeeze food through alimentary canal (towards the stomach). u
Swallowing Reflex and Esophageal Peristalsis
Smooth Muscle Peristalsis Moves Food Along Alimentary Canal
Part of the Human Digestive System Stomach: Located on left side of abdominal cavity, right below diaphragm. u Stores food (can stretch to accommodate up to 2 liters of food and water), and breaks it down with acids and enzymes. u Gastric juice is secreted by stomach. Contains hydrochloric acid (HCl), enzymes (pepsin), and mucus. u Protein digestion starts in stomach with pepsin. u Food is churned in stomach with gastric juice to form chyme. u Food remains in stomach from 2 to 6 hours, after which it is released into the small intestine. u
Part of the Human Digestive System Small Intestine: u u u Huge surface area, about 300 square meters. Most digestion and absorption occurs here. Pancreas and liver empty digestive enzymes and bile into the small intestine. t Pancreatic amylase: Breaks down starch t Trypsin and Chymotrypsin: Break down proteins t Lipases: Break down fats t Peptidases: Break down proteins t Nucleases: Break down DNA and RNA t Bile: Helps fat digestion by emulsifying fats. Very large surface area for absorption due to: t Large circular folds (villi) t Tiny cell surface projections (microvilli). Capillaries drain nutrients from small intestine and then sends them to first to liver and then rest of body.
Small Intestine is Site Most Enzymatic Digestion
Human Digestive System Large Intestine (Colon): u u u 1. 5 m long and 5 cm wide (diameter) Most water absorption occurs here (up to 90%). Undigested remainder of food is converted into feces. Site of bacterial synthesis t Vitamin K t Folic acid t Biotin t Several B vitamins Appendix: Small fingerlike projection. Involved in immunity. Rectum: u Stores feces until ready to eliminate
Human Digestive System Digestive Glands -- Liver: n Structure u n Composed of 2 lobes made up of about 100, 000 lobules Functions u u u u u Removes bilirubin, a hemoglobin breakdown waste product, from the blood and incorporates it into bile. Produces bile which is stored in gallbladder. Bile is released into the small intestine after a meal. Bile contains no enzymes, but helps solubilize fat particles. Detoxifies blood by removing and metabolizing poisonous substances Stores iron and fat-soluable vitamins A, D, E, K, and B 12 Makes plasma proteins, such as albumins and fibrinogen, from amino acids Synthesizes and degrades glycogen to maintain homeostatic levels of glucose Produces urea after breaking down amino acids
Pancreas: Produces several digestive enzymes which are emptied into small intestine. u Enzymes digest starch (pancreatic amylase), protein (trypsin), fats (lipase), and nucleic acids (nucleases). u
Pancreatic Juice n Contain H 20 , HC 03 - and digestive enzymes. Enzyme Zymogen Activator Action Trypsinogen Enterokinase Cleaves internal peptide bonds Chymotrypsinogen Trypsin Cleaves internal peptide bonds Elastase Proelastase Trypsin Cleaves internal peptide bonds Carboxypeptidase Procarboxypeptidase Trypsin Cleaves last amino acid from carboxylterminal end of polypeptide Phospholipase Prophospholipase Trypsin Cleaves fatty acids from phospholipids such as lecithin Lipase None Cleaves fatty acids from glycerol Amylase None Digests starch to maltose and short chains of glucose molecules Cholesterase None Releases cholesterol from its bonds with other molecules Ribonuclease None Cleaves RNA to form short chains Deoxyribonuclease None Cleaves DNA to form short chains
Gallbladder n Liver produces about 1, 000 ml of bile a day with excess being stored in the gallbladder. n Gallbladder reabsorbs water making bile thick and mucuslike. n Gallstones may form due to precipitation of cholesterol.
Vitamins and Minerals n n Small organic molecules that serve as coenzymes in metabolic reactions or have highly specific functions. Must be obtained from the diet because the body does not produce them, or does so in insufficient amounts. Certain vitamins function as antioxidants. 2 classes of vitamins: u Fat-soluble u Water-soluble
Vitamins n n Water-soluble vitamins: u Serve as coenzymes in the metabolism of carbohydrates, lipids, and proteins. u May serve as antioxidants. Fat-soluble vitamins: u Serve as antioxidants. u Bind to nuclear receptors. u Involved in regulating fetal development. u Regulate Ca++ balance.
Minerals n Needed as cofactors for specific enzymes and other critical functions. n Trace elements: n Required in small amounts from 50 mg to 18 mg/day.
Free Radicals and Antioxidants n n n Electrons are located in orbitals. u Each orbital contains a maximum of 2 electrons. Free radical: u When an orbital has an unpaired electron. u Highly reactive in the body. u Oxidize other atoms or reduce other atoms. Major free radicals called: u Reactive oxygen or nitrogen species. t Oxygen or nitrogen as unpaired electron.
Free Radicals and Antioxidants n n n Functions of free radicals: u Help to destroy bacteria. u Produce vasodilation. t NO, superoxide radical, and hydroxy radical. Exert oxidative stress contributing to disease states. Antioxidants: u Protective mechanism against oxidative stress. u Can react with free radicals by picking up unpaired electrons. t Glutathione, vitamin C, and vitamin E.
Obesity n n n Obesity is often diagnosed by using a body mass index (BMI). BMI = w h 2 t W = weight in kilograms t H = height in meters Obesity in childhood is due to an increase in both the size and the # of adipocytes. Obesity defined as BMI > 30. Healthy weight as BMI between 19 – 25.