Bài giảng Biology 25: Human Biology - Chapter 5: Integumentary System

Chapter 5 (and a bit of Chp 4)Biology 25: Human BiologyProf. GonsalvesLos Angeles City CollegeLoosely Based on Mader’s Human Biology,7th edition Integumentary SystemComponents: Hair, skin, and nails.Functions: Protects the body from:Infection: Barrier to microbes.Mechanical injuryExcessive heat or cold: ThermoregulationWater lossCommunication: Receives stimuli from environmentGives out subtle signals (blushing, etc.).Homeostatic Role:Helps maintain constant body temperature.1. Digestive SystemComponents: Mouth, salivary glands, throat, esophagus, stomach, intestines, liver, gallbladder, pancreas, rectum, and anus.Functions: Ingest and mechanically break down food.Digest food: Stomach and small intestine mainly.Absorb nutrients and water.Eliminate waste.Homeostatic Roles:Supplies energy for life’s activities.Supplies building blocks for macromolecules Stages of Food Processing1. 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 Processing3. 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 SystemAlimentary canal: Long tube like structure.Mouth TonguePharynx (throat)EsophagusStomachSmall intestineLarge intestineRectumAnusDigestive glands: Produce enzymes, bile, and other substances important for digestion.Salivary glands Pancreas Liver and gallbladderHuman Digestive SystemMouth: Ingest and mechanically break down food.Digestion: Saliva lubricates and starts to digest food.Starch is digested by salivary amylaseOther enzymes in saliva kill bacteria. Part of the Human Digestive SystemPharynx (Throat):Throat opens into both the trachea (respiratory system) and esophagus (digestive system).As food enters pharynx, swallowing reflex is triggered: Esophageal sphincter relaxes Epiglottis blocks tracheal opening Food is directed towards esophagusEsophagus:Muscular tube that conveys food to stomach.Peristalsis: Wavelike involuntary muscle contractions squeeze food through alimentary canal (towards the stomach). Swallowing Reflex and Esophageal PeristalsisSmooth Muscle Peristalsis Moves Food Along Alimentary CanalPart of the Human Digestive SystemStomach:Located on left side of abdominal cavity, right below diaphragm.Stores food (can stretch to accommodate up to 2 liters of food and water), and breaks it down with acids and enzymes.Gastric juice is secreted by stomach. Contains hydrochloric acid (HCl), enzymes (pepsin), and mucus.Protein digestion starts in stomach with pepsin.Food is churned in stomach with gastric juice to form chyme.Food remains in stomach from 2 to 6 hours, after which it is released into the small intestine.Part of the Human Digestive SystemSmall Intestine: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.Pancreatic amylase: Breaks down starchTrypsin and Chymotrypsin: Break down proteinsLipases: Break down fatsPeptidases: Break down proteinsNucleases: Break down DNA and RNABile: Helps fat digestion by emulsifying fats.Very large surface area for absorption due to: Large circular folds (villi) 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 DigestionHuman Digestive SystemLarge Intestine (Colon):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 synthesisVitamin KFolic acidBiotinSeveral B vitaminsAppendix: Small fingerlike projection. Involved in immunity. Rectum:Stores feces until ready to eliminateHuman Digestive SystemDigestive Glands -- Liver:StructureComposed of 2 lobes made up of about 100,000 lobulesFunctionsRemoves 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 substancesStores iron and fat-soluable vitamins A, D, E, K, and B12Makes plasma proteins, such as albumins and fibrinogen, from amino acidsSynthesizes and degrades glycogen to maintain homeostatic levels of glucoseProduces urea after breaking down amino acidsPancreas:Produces several digestive enzymes which are emptied into small intestine.Enzymes digest starch (pancreatic amylase), protein (trypsin), fats (lipase), and nucleic acids (nucleases).Contain H20 , HC03- and digestive enzymes. Pancreatic JuiceEnzyme Zymogen Activator ActionTrypsin Trypsinogen Enterokinase Cleaves internal peptide bondsChymotrypsin Chymotrypsinogen Trypsin Cleaves internal peptide bondsElastase Proelastase Trypsin Cleaves internal peptide bondsCarboxypeptidase Procarboxypeptidase Trypsin Cleaves last amino acid from carboxyl-terminal end of polypeptidePhospholipase Prophospholipase Trypsin Cleaves fatty acids from phospholipids such as lecithinLipase None None Cleaves fatty acids from glycerolAmylase None None Digests starch to maltose and short chains of glucose moleculesCholesterolesterase None None Releases cholesterol from its bonds with other moleculesRibonuclease None None Cleaves RNA to form short chainsDeoxyribonuclease None None Cleaves DNA to form short chains GallbladderLiver produces about 1,000 ml of bile a day with excess being stored in the gallbladder.Gallbladder reabsorbs water making bile thick and mucuslike. Gallstones may form due to precipitation of cholesterol.Vitamins and MineralsSmall 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:Fat-solubleWater-soluble VitaminsWater-soluble vitamins:Serve as coenzymes in the metabolism of carbohydrates, lipids, and proteins.May serve as antioxidants.Fat-soluble vitamins:Serve as antioxidants.Bind to nuclear receptors.Involved in regulating fetal development.Regulate Ca++ balance.MineralsNeeded as cofactors for specific enzymes and other critical functions.Trace elements:Required in small amounts from 50 mg to 18 mg/day.Free Radicals and AntioxidantsElectrons are located in orbitals.Each orbital contains a maximum of 2 electrons.Free radical:When an orbital has an unpaired electron.Highly reactive in the body.Oxidize other atoms or reduce other atoms.Major free radicals called:Reactive oxygen or nitrogen species.Oxygen or nitrogen as unpaired electron.Free Radicals and AntioxidantsFunctions of free radicals:Help to destroy bacteria.Produce vasodilation.NO, superoxide radical, and hydroxy radical.Exert oxidative stress contributing to disease states.Antioxidants:Protective mechanism against oxidative stress.Can react with free radicals by picking up unpaired electrons.Glutathione, vitamin C, and vitamin E.ObesityObesity is often diagnosed by using using a body mass index (BMI). BMI = w h 2W = weight in kilogramsH = height in metersObesity 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.