3 IntroductionDigestion is the mechanical and chemical breakdown of food into forms that cells can absorb.Mechanical Digestion – breaks down food into smaller piecesChemical Digestion – decomposes food into smaller moleculesAdd these terms to vocabulary list…The digestive system consists of:The alimentary canal – extends from mouth to anusAccessory glands –secrete chemicals into the alimentary canal.
4 Human digestive system After chewing and swallowing, it takes 5 to 10 seconds for food to pass down the esophagus to the stomach, where it spends 2 to 6 hours being partially digested.Final digestion and nutrient absorption occur in the small intestine over a period of 5 to 6 hours.In 12 to 24 hours, any undigested material passes through the large intestine, and feces are expelled through the anus.
5 The Alimentary CanalIf stretched out, the alimentary canal is about 8 meters long.That’s 26 feet!
6 Structure of the wall Mucosa – mucous membrane Epithelial tissues on a bed of connective tissueThis layer absorb nutrients, secrete chemicals, and protect the underlying layers.Submucosa – Beneath the mucosaLoose connective tissueBlood vessels, nerves, and lymphatic vesselsThis layer nourishes the surrounding tissues, and carries away nutrients.Muscular –Decrease and increase the diameter of the A.C. to push food throughSerosa – serous membraneSecretes serous fluid, which lubricates the A.C.
7 Movements of the Alimentary Canal Muscles of the A.C. provide two basic movements:Segmentation – mixing movementSmooth muscles contract and relax, mixing foods with digestive juicesPeristalsis – propelling movementSmooth muscles contract in a wave-like motion pushing food through the alimentary canal
8 The Mouth (ORAL CAVITY) Receives foodMechanically breaks up solid particles using TEETH & TONGUEChemically digest food using saliva.This action is called masticationMakes a BOLUS (wet ball of food)The mouth also functions as an organ of speech, and sensory reception.
9 Salivary Glands Secrete saliva Saliva moistens the food, and begins the digestion of carbohydratesThree pairs of major salivary glands, include:Parotid glandsSubmandibularSublingual
10 SALIVA = water + mucus + amylase Salivary GlandsSALIVA = water + mucus + amylaseParotid glandsSecrete clear watery fluidRich in salivary amylase – begins the chemical digestion of carbohydratesSubmandibular glandsSecretes a mixed saliva with both watery fluid and mucusSublingual glandsSecrete primarily mucus
11 The palate and uvula The palate forms the roof of the oral cavity Hard Palate - bony roof of the mouthFormed by the palatine bones and portions of the maxillaSoft Palate - Muscular archUvula – cone-shaped projectionDuring swallowing, muscles draw the soft palate and the uvula upward preventing food from entering the nasal cavity.
12 The teeth Teeth are the hardest structures in the body primary (deciduous) teeth numbering 20Usually erupt through the gums from age of 6 months to 2 yearssecondary (permanent) teeth numbering 32Usually begin to erupt at 6 years3rd molars = wisdom teeth, which may erupt between years of age
13 Types of teeth Incisors- blade shaped teeth that bite or cut off large pieces of foodAdult – 8Child – 8Canines-cone shaped teeth that grasp and tear foodAdult – 4Child – 4Premolars –flattened surface for grinding foodAdult – 8Child – 0Molars –flattened surface for grinding foodAdult – 12Child – 8
14 The tongue Thick, muscular organ Manipulate foods and aids in swallowingMucous MembraneFrenulumRootAnchored to the hyoid bone.Covered with lingual tonsilsPapillae – projections on the surface of the tongue.Some provide friction, others house taste buds.
15 PharynxThe back of the throat.Deglutition (swallowing)3 parts
16 Swallowing Epiglottis flap of cartilage closes trachea (windpipe) when swallowingfood travels down esophagus
17 esophagus Peristalsis involuntary muscle contractions to move food alongEsophageal Hiatus – opening in the diaphragm, passage for esophagusHiatal hernia – part of the stomach protrudes through the hiatus.
18 Stomach 2 sphincters (valves) 3 layers of muscle Secretes gastric juices(enzymes + HCl)Mechanically and chemically breaks down food
19 stomach Fundus = top portion Pyloris = funnel-shaped lower portion Rugae – gastric folds line the stomach
20 Gastric Juice Acidic (pH 1.5-2.5) (HCl) Pepsin- an enzyme that breaks down large proteins into amino acids.HCl activates pepsinBOLUS + GASTRIC JUICE = chyme.
24 PancreasAn organ which secretes both digestive enzymes (exocrine) and hormones (endocrine)Pancreatic juice digests all major nutrient types.“ENZYME COCKTAIL” includes enzymes top break down all compounds: proteins, lipids and carbohydratesAlkaline (base) neutralizes acidic chyme coming from stomach.
27 Liver FunctionsThe liver carries on many important metabolic activities, including:Glycogenesis: producing glycogen from glucoseGlycolysis: breakdown of glycogen into glucoseGluconeogenesis: converts non-carbohydrates to glucoseOxidizes fatty acidsSynthesizes phospholipids and cholesterolForms ureaSynthesizes plasma proteinsStores glycogen, iron, and vitamins A, D, and B12Phagocytosis of worn out RBCs and foreign substancesRemoves toxins such as alcohol and certain drugs from the blood
28 LiverFunction: produces bileBILE breaks up fats
29 GALL BLADDER It stores bile between meals It concentrates bile by reabsorbing waterThe gall bladder itself does not produce bileBile duct –a long tube that carries BILEConnects the liver, pancreas, and gall bladder to the duodenum (small intestine)
31 GALLSTONESGALLSTONES – an accumulation of hardened cholesterol and/or calcium deposits in the gallbladderCan either be “passed” (OUCH!!) or surgically removed
32 Small intestine Function Structure chemical digestion major organ of digestion & absorptionabsorption through liningover 6 meters!small intestine has huge surface area = 300m2 (~size of tennis court)Structure3 sectionsduodenum = most digestionjejunum = absorption of nutrients & waterileum = absorption of nutrients & waterAbout every 20 seconds, the stomach contents are mixed by the churning action of smooth muscles.As a result of mixing and enzyme action, what begins in the stomach as a recently swallowed meal becomes a nutrient-rich broth known as acid chyme.At the opening from the stomach to the small intestine is the pyloric sphincter, which helps regulate the passage of chyme into the intestine.A squirt at a time, it takes about 2 to 6 hours after a meal for the stomach to empty.
33 Duodenum pancreas liver gall bladder 1st section of small intestines acid food from stomachmixes with digestive juices from:pancreaslivergall bladder
34 Absorption in the SIMuch absorption is thought to occur directly through the wall without the need for special adaptationsAlmost 90% of our daily fluid intake is absorbed in the small intestine.Villi - increase the surface area of the small intestines, thus providing better absorption of materials
35 Villi increase surface area. More surface area = More absorption
37 appendicitis inflammation of the appendix due to infection Common treatment is removal of the appendix via surgery
38 The Large IntestineThe large intestine is named because of its diameterIt has four parts:Cecum – blind pouchIleocecal sphincterThe appendix projects from the cecum.Colon(ascending, transverse, descending, sigmoid)Rectum - straightAnal canalThe anus – is guarded by two sphincter musclesexternal anal sphincter – composed of skeletal muscleinternal anal sphincter – composed of smooth muscle
39 Large intestines (colon) Functionre-absorb wateruse ~9 liters of water every day in digestive juices> 90% of water reabsorbed
40 Large Intestine Solid materials pass through the large intestine. These are undigestible solids (fibers).Water is absorbed.Vitamins K and B are reabsorbed with the water.Rectum- solid wastes exit the body.
41 feces Poop, excrement, solid waste, etc… Feces is composed of materials not digested or absorbed, and include: Water, Electrolytes, Mucus, Bacteria, and Bile pigmentsApproximately 1/3 of the dry weight of feces is bacteria.The color of feces is provided by bile pigments altered by bacteria.
42 diarrheaa gastrointestinal disturbance characterized by decreased water absorption and increased peristaltic activity of the large intestine.This results in increased, multiple, watery feces.This condition may result in severe dehydration, especially in infants
43 constipationa condition in which the large intestine is emptied with difficulty.Too much water is reabsorbedSolid waste hardens
44 Bacterial flora Escherichia coli (E. coli) Living in the large intestine is a community of helpful bacteriaEscherichia coli (E. coli)produce vitaminsvitamin K; B vitaminsgenerate gasesby-product of bacterial metabolismmethane, hydrogen sulfide
45 Rectum undigested materials Last section of colon (large intestines) eliminate fecesundigested materialsextracellular wastemainly cellulose from plantsroughage or fibermasses of bacteria
46 Anal Canal / Anus… Last Stop Exit or opening for solid wastesRegulated by anal sphincter (valve)Anal sphincter surrounded by musclesElimination aided by abdominal muscles
47 HemorrhoidsVery common, especially during pregnancy and after childbirth.Result from increased pressure in the veins of the anus. The pressure causes the veins to bulge and expand, making them painful, particularly when you are sitting..SymptomsAnal itchingAnal ache or pain,especially while sittingBright red blood ontoilet tissue, stool, orin the toilet bowlPain during bowelmovementsOne or more hard tender lumps near the anus