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Digestive System Anatomy and FunctionProcesses of the Digestive System1. Secretion- endocrine: hormones into blood- exocrine: enzymes into lumen2. Digestion- mechanical/chemical- most in small intest*3. Motility - coordinated muscle contractions along the gastro tract- too fast? diarhea- too slow? constipation4. Absorption- nutrients from food (lumen) --> cells (transcellular) --> blood- most in small intest* (fig 11.0)(fig 11.1)Mouth- no absorption- mechanical digest begins & digest of carbs- saliva secreted by 3 exocrine glands- saliva contains proteins and ions(fig 11.2)Salivary Glands1. Parotid gland: watery liquid & salivary amylase (carb digest)2. Submanibular gland: thicker liquid, mucus & amylase3. Sublingual gland: more mucus & less amylase Stages of Swallowing1. Voluntary Stage- chewing - only voluntary stage*2. Pharyngeal Stage- food --> pharynx- involuntary*3. Esophageal Stage- food down esophagus --> stomach- involuntary*Mastication- mechanical manipulation of food into a bolus- chemical digestion --> salivary amylase- lingual lipase secreted in mouth but not activated*Summary of MouthSecretion- saliva (varying composition)- enzymes: salivary amylase & lingual lipase (inactive)Digestion- mechanical & chemical - salivary amylase --> carb digestMotility- mouth=mastication (voluntary)- esophagus=peristalsis(involuntary)Absorption- nonePeristalsis- bolus down esophagus via coordiated contractions & relaxations- circular & longitudinal muscles- medulla oblongata- secondary peristalsis if food lodged in esophagusThe Stomachfig11.3
Exocrine Cells of the Stomach1. Mucus Neck Cells- secrete mucus and bicarbonate (neutralizes acid)2. Chief Cells - secrete pepsinogen (protein digest) & gastric lipase (fat breakdown)- pepsinogen=inactive. activated to pepsin with acidic environment3. Parietal Cells (aka oxyntic cells)- intrinsic factor, H and Cl (HCl)- intrinsic factor absorbs vitamin B12Enteroendocrine Cells1. G Cells- secrete gastrin (hormone) --> HCl production by parietal cells- occurs when food iis in stomach (mostly protein)insert box chart
Layers of the Stomach1. Mucosa (veggies)- inner stomach - blood vessels & capillaries- folds & rugae stretch- single layer of epithelial cells secrete enzymes, H20 and bicarbonate- epithelial cells vary in function along the digest tract (ie. chief cells, parietal cells)2. Submucosa (sauce)- connective layer (like glue)- larger blood vessels- layer of neuron cell bodies (enteric NS)3. Smooth Muscle (muscularis externa) (meat)- involuntary contraction/relaxation- circular muscles: - contract=dec. diameter - relax=inc. diameter- longitudinal muscles: - contract=dec. length - relax=inc. length4. Serosa (bread)- outermost layer- connective tissue
Digestion in the Stomach- bolus to chyme1. Mechanical Digestion- 1st gentle mixing of bolus & releasing of gastric juices- propelled towards pyloric sphincter- some chyme enters the duodenum but most returns to stomach body for mixing - pyloric stenosis: sphincter wont open at birth 2. Chemical Digestion- protein digest begins in stomach (HCL secretion --> pepsin production)- carb digest STOPS (salivary amylase inactive)*- lipid digest begins in stomach (acid activates lingual lipase)* through activation of lingual lipase and activity of gastric lipase- 10% lipid digest in stomach
Functions of Acid in the Stomach1. Activates lingual lipase*- pH specific enzyme- secreted in mouth- activated in stomach when in contact w/ acid- lipid digestion2. Activates pepsin* (from pepsinogen)- cleving pepsinogen to activate pepsin form- remains inactive (pepsinogen)- activated by acid3. Inactivates salivary amylase*- acid turns it off- carb digest is paused4, Kills microbes5. Denatures proteins- unfolding6. Stims secretion of hormones- activates G-cells --> hormone release
Summary of StomachSecretion - exocrine & enteroendocrine- mucus, bicarbonate, pepsinogen, gastric lipase, intrinsic factor, HCL, gastrinDigestion- mechanical: mixing- chemical: enzymes activated by acid - lingual lipase - pepsin - gastric lipaseMotility- mixing waves --> toward pylorus- pyloric sphincter lets small amount of chyme into small intest (gastric emtying)- most pushed back into stomach for mixingAbsorption- food particles not absorbed - medical & alch are
--------------------------------------------------------------------------------------------------------------------------------------Small Intestine- most digestion- most absorptionRegions of the Small Intestine1. Duodenum- regulates digest & absorpt- endocrine cells release hormones to assist digest & absorpt- hormones=how speed of digest, motility, absorpt (alike capillaries)2. Jejunum- most nutrient absorption here*- b/c of # and length of microvilli inc. SA for absorption3. Ileum- less nutrient absorption (less villi)- absorbs leftover nurients
Layers of the Small Intestine1. Mucosa- epithelial layer absorbs* (different than stomach which only secretes)- connective tissur, blood vessels, lacteals (absorb fat)- villi & crypts- villi: finger like & maximize absorption2. Submucosa- tells epithelial cells to secrete3. Muscularis- longitudinal & circular muscles (alike stomach)4. Serosa- connective layer
Segmentation- allows mixing & absorpt- small intest only*- localized mixing --> inc. interactions of particles w/ absorptive cells in intestinal mucosaPeristalsis- contents in one direction*- towards large intest - allows for next meal
Cell Types of the Intestinal Wall1. absorptive cells (epithelial cells)- absprptive epithelium w/ microvilli- chyme --> blood vessels/lacteals2. goblet cells- secrete mucus to reduce friction (for motility)3. intestinal gland cells- watery mucus lubricates4. paneth cells- lysozyme (exocrine)- destroys bacteria in chyme5. S cells (secretin: hormone)- secretin: secreted into blood vessels - travel to body- release of secretin stim by acid --> pancrease release bicarb --> neutralize small intest6. CCK cells (cholesystokinin) - hormone- tells gall bladder to contract when fat present--> release bile into small intest- tells pancreas to release digest enzymes- released in presence of partially digested proteins7. K cells - glucose insulinotropic peptide (GIP)- GIP regulated insulin release- insulin release: cck goes to pancreas & tells Beta cells to make insulin to absorb nutients
Microvilli (AKA brush borders)- crypts & villi inc. SA for absorpt in small intest- microvilli further inc. SA- microvilli break down food into small units to be absorbed (ie. amino acids)
Brush Border Enzymes1. Lactase- lactose --> glucose + galactose2. Sucrase- sucrose --> glucose + fructose3. Maltase- maltose --> glucose + glucoseAminopeptidase: breaks down proteins (polypeptide chains)- cuts aa from end of protein strandDipeptidase- cuts aa stuck together into single aaNote: - disacharides cannot be absorbed (ie. maltose, lactose)- monosacharides can be absorbed (ie. glucose, fructose, galactose)- lastose intolerant? cannot make lactase
Small Intestine SummarySecretion- mucus, lysosome, secretin, GIP, CCKDigestion- hormones affect- protiens --> trypsin- fats --> pancreatic lipase- carbs --> brush bordersMotility- segmentation (mixing)- peristalsis (propelling forward)Absorption- carbs, proteins, fats- most in jejunum
-----------------------------------------------------------------------------------------Large IntestineMain functions:- finish process of absorption- unidirectional- absorb water- digest things that werent absorbed (breakdown by fermentation)
Accessory Organs of the Digestive SystemPancreas- endocrine & exocrine - 2 ducts connect pancreas to duodenum- endocrine cells: surrounded by blood vesels (islets of langerhans- exocrine cells: secrete water, enzymes (Acinar cells)Pancreas - Exocrine Secretions1.* Bacarbonate- made by duct cells- buffer & protect small intest from acid2. *Pancreatic Amylase- digests carbs in small intest3. ***Pancreatic Lipase- digest fats in small intest- most important lipase**4. *Trypsinogen --> trypsin- digests proteins - enteropeptidase in brush border activates trypsin5. Chymotrypsinogen --> chymotrypsin- protein digester enzyme6. Procarboxypeptidase --> carboxypeptidase- digest protein7. Procolipase --> colipase- digest fat8. Prophospholipase --> phospholipase- digest phosphillipidsNote : 4-8 are zymogens and therefore inactive until cleaved
Pancreas Endocrine Secretions- islets of langerhans --> blood1. Insulin- released when eating a meal- takes nutrients and stores it - fat cells & skeletal muscles store glucose/nutrients2. Glucagon- released when hungry- releases nutrients fom fat and skeletal muscle3. Somatostatin- inhibits insulin & glucagon- "gate keeper"Liver- liver makes bileGall Bladder- stores bile- you can live w/o- no gallbladd=less effective fat reabsorption bc no splurge of bile to take care of high fat meal
----------------------------------------------------------------------------------------------------------------Regulation of Gastric Motility & SecretionsCephalic (brain) Phase Regulation- stim --> thinking, smelling, seeing, tasting food- neural control: medulla oblangata --> act. of enteric NS (can act on its own) - inc. saliva secretion - inc. secretions in stomach & small intest - inc. motility of stomach & small intestGastric Phase- stim: distension of stomach by food (& proteins)- stomach neural reflexes (not involving brain) activated, & hormone regulation (gastrin) - inc. exocrine secretions of stomach & endocrine secretions - inc. gastric motility & gastric emptyingIntestinal Phase- stim: presence of chyme in small intest- neuronal reflex & hormonal control (secretin, CCK, GIP) - inhibition of gastric motility & delays of gastric emptying - inhibition of acid production in stomach - promotes local intestinal motility (stagmentation & peristalsis)Alcohol: - absorbed better on an empty stomach - males/females metabolize alcohol differently. - females=less of metabolic enzyme - males= more of metabolic enzyme- always eat fatty food so there isnt a spike in blood alcohol
Nutrient AbsorptionSources of CarbsSimple Carbs: - monosaccharides (glucose, fructose, galactose- disaccharides (lactose, maltose, sucrose)Complex carbs:- starches (plant storage of glucose)Note: plants are composed of different numbers of simple, complex carbs and fiber - fiber keeps you regular & satisfied
Sources of Protein- amino acids - nonessential & essential - dipeptides, tripeptides and polypeptidesSources of Fat - triglycerides --> glycerol w/ 3 fatty acids- fatty acids: 4 to 24 carbons long (18 most common)- saturated (solid) --> single bonds - ie. butter- unsaturated (liquid) --> multiple bonds - ie. olive oil-------------------------------------------------------------------------------------------------
Metabolism and Adaptations to Metabolism Cellular Respiration1. Glycolysis - ten step rxn (enzymes)- one glucose is converted into pyruvate (makes ATP)2. Pyruvate is converted into Acetyl CoA3. Citric Acid Cycle- Acetyl CoA broken down to produce ATP & high energy electron carriers4. Electron Transport System- high energy electron carriers converted to ATP----------------------------------------------------------------------------------------------------------
Fates of Glucose & Glucose UptakeATP production- cellular respirationAA Synthesis- if missing an aa (protein anambolism
Glycogenesis- ST storage- certain cells (liver, skeletal muscle) have a large capacity to store gloucose as glycogen- brain cannot store glucoseGlycogenolysis- breakdown of glycogen to glucose-6-phosphate for energy use (glycolysis)- liver cells are unique and convert glucose-6-phosphate back to glucose
Gluconeogenesis- liver creates new glucose when glycogen stores are depleted- this can come from NON-CARB sources - aa from proteins - glycerol (from fat) - lactic acid- hopefully a limited production or willl over work liver
Fates of Lipids- stored in adipose tissue as fat deposits - oxidized to produce ATP- formation of structural molecules - phospholipids, myelin sheaths- triglyceride storage is unlimitedLipolysis- breakdown of triglycerides into glycerol and fatty acids to be used to make glucose & ATPLipogenesis- storing fats- liver & adipose cells can synthesize lipids from glucose/aaKetogenesis- liver cells (hepatocytes) can make ketone bodies (ecetoacetic acid)- ketone bodies diffuse into blood & use as alternative energy than glucose- **some cells (heart muscles & cortex of kidney) prefer ketone bodies over glucose-----------------------------------------------------------------------------------------------------------------------ProteinProtein Anabolism- cells use aa to generate proteins- necessary since most components of our cells are made up of proteins- **excessive dietary protein does not inc. mucle/bone massProtein Catabolism- aa from proteins can be converted to other aa- liver cells: aa--> fatty acids, ketone bodies or glucose
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