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Digestive System
Anatomy Exam 4
| Term | Definition |
|---|---|
| Digestive System: | is essentially a "disassembly line". Organ system that processes foods, extracts nutrients from it, & absorbs the nutrients. It can breakdown nutrients into usable form then absorb nutrients. |
| Ingestion: | selective intake of food. |
| Digestion: | mechanical & chemical breakdown of food into a usable form by the body. |
| Absorption: | uptake of nutrient molecules into the epithelial cells of digestive tract then into blood and lymph. |
| Compaction: "making poop" | absorbing water and consolidating in digestible residue into feces. |
| Defecation: | eliminating feces. |
| Mechanical digestion: | physical breakdown of food into smaller particles "grinding of food". |
| Chemical Digestion: | series of hydrolysis reaction that breakdown dietary macromolecules to monomers (residue) |
| How? (chemical digestion): | Chemical enzymes - salivary glands, stomach enzymes, pancreatic enzymes, enzymes in small intestine. |
| Some nutrients: | are present in a usable form in ingested food. They can be absorbed without being digested. Examples: (vitamins, minerals, amino acids, cholesterol, & water). |
| Digestive Tract: (alimentary canal) | mouth, pharynx, esophagus, stomach, small intestine, and large intestine. |
| Accessory Organs: | teeth, tongue, salivary glands, liver, gallbladder, and pancreas. |
| Digestive Tract: | is open to the environment at both ends. Absorption by epithelial cell of digestive tract & material is external until you get absorption. (defecated food residue was never in the body). |
| Mucosa: | |
| Submucosa: | |
| Muscularis Externa: | |
| Serosa: | |
| Enteric Nervous System: | a nervous network in the esophagus, stomach, and intestines that regulated digestive tract motility, secretion, and blood flow. |
| Composed of two networks of neurons (enteric nervous system): | 1. Submucosal (meissner) plexus 2. Myenteric (auerbach) plexus |
| Submucosal (meissner) plexus: | in submucosa, controls glandular secretion of mucosa & movements of muscularis mucosa |
| Myenteric (auerbach) plexus: | parasympathetic ganglia and nerve fibers between two layers of the muscularis externa. It controls peristalsis and other contractions of the muscularis externa. |
| Enteric Nervous System: | contains sensory neurons that monitor tension in gut wall and conditions in lumen. |
| Short (myenteric) reflexes: | stretch or chemical stimulation acts through myenteric plexus (stimulates peristaltic contractions of swallowing. |
| Long (vagovagal) reflexes: | parasympathetic stimulation of digestive motility and secretion. |
| Hormones: | chemical messengers that travel long distance. |
| Paracrine secretions: (prostaglandins, histamines) | travel short distance through tissue fluid to nearby target cells (chemical messengers) |
| Tongue: | muscular, bulky, but remarkably agile and sensitive organ (manipulates food between teeth). |
| Mouth: | ingestion |
| Other sensory responses to food (mouth): | chewing and chemical digestion. swallowing, speech, and respiration. |
| Functions of cheeks and lips: | (1)retain food & pushing between teeth for chewing (2)articulation (3)suckling and blowing action |
| Mastication: | chewing your food - first step in mechanical digestion, food stimulates oral receptors that trigger an involuntary chewing refulx |
| Tongue, buccinator, and orbicularis oris: | manipulate food. |
| Masseter and temporalis: | elevate the teeth to crush food. |
| Medial & lateral pterygoids and masseter: | swing teeth in side-to-side grinding action of molars. |
| Function of Saliva: | (1)To moisten the mouth (2)Begin starch & fat digestion (3)Cleanse teeth (4)Inhibit bacterial growth (5)Dissolve molecules to stimulate taste buds (6)Moistens food and binds it together into bolus. |
| Salivary amylase: | enzyme that begins starch digestion in mouth. |
| Lingual Phase: | enzyme that is activated by stomach acid (digests fat after food is swallowed). |
| Mucus: | will bind and lubricate the masticated food. |
| Lysozyme: | enzyme that can kill bacteria. |
| Immunoglobulin A (IgA): | antibody that inhibits bacterial growth. |
| Electrolytes: | Na+, K+, Cl-, phosphate and bicarbonate |
| pH of Saliva: | 6.8 to 7.0 |
| Intrinsic Salivary Glands: | secrete a small amount of saliva at a constant rate (during eating or not) rate is the same. Example -> lingual glands - produces lingual lipase |
| Extrinsic Salivary Glands: | connected to oral cavity by ducts. Example -> parotid glans, submandibular glands, sublingual glands. |
| Pharynx: | a muscular funnel that connects oral cavity to esophagus and allows entrance of air from nasal cavity to larynx. |
| Pharyngeal Constrictors (esophageal sphincters): superior, middle, and inferior | circular muscles that force food downward during swallowing. When not swallowing, the inferior constrictor remains contracted to exclude air from the esophagus. |
| Esophagus: | a straight muscular tube, begins at level between C6 and cricoid cartilage. |
| Lower esophageal sphincter: | food pauses at this point because of this constriction. |
| Esophageal glands in submucosa: | secrete mucus, deeply folded into longitudinal ridges when empty. |
| Swallowing center: | pair of nuclei in medulla oblongata that coordinates swallowing. Communications with muscles of the pharynx and esophagus by way of trigeminal, facial, glossopharyngeal, and hypoglossal nerves. |
| Swallowing occurs in two phases: | buccal phase and pharyngoesophageal phase |
| Buccal Phase: | Tongue collects food, presses it against the palate forming a bolus, and pushes it posteriorly. Food accumulates in oropharynx in front of the 'blade' of the epiglottis. |
| Buccal Phase (cont): | Epiglottis tips posteriorly and food bolus slides around it through the laryngeal opening. Bolus enters laryngopharynx and stimulates tactile receptors and activates next phase. |
| Pharyngoesophageal Phase: | Food bolus is driven downward by constriction of the upper, then middle, and lower pharyngeal constrictors. Bolus enters esophagus, stretches it, & stimulates peristalsis. |
| Pharyngoesophageal Phase (cont): | When it reaches lower end of esophagus, the lower esophageal sphincter relaxes to let food pass into the stomach. |
| Stomach: | food storage organ, mechanically breaks up food particles, liquefies the food, and begins chemical digestion of protein and fat. |
| Chyme: | soupy/pasty mixture of semi-digested food in the stomach. |
| Most digestion occurs: | after the chyme passes on to the small intestine. [duodenum] - first part of small intestine. |
| Pyloric Valve (sphincter): | regulates the amount of chyme entering the small intestine. [stomach --> duodenum] |
| Stomach receives: | parasympathetic fibers from vagus, and sympathetic fibers from celiac ganglia. |
| Supplied with blood: | by branches of the celiac trunk. |
| All blood drained from stomach and intestines enters: | hepatic portal circulation and is filtered through liver before returning to heart. |
| Mucous cells: | located in gastric pit -> secrete mucous |
| Regenerative (stem) cells: | always being produced |
| Parietal cells: | secrete HCL, intrinsic factor, hunger hormone called (Ghrelin) |
| Chief cells: | most numerous, secrete gastric lipase & pepsinogen (precursor for peptin) -> breaks down protein |
| Enteroendocrine cells: | several class of cells that secrete hormones & paracrines. Example: G-cells: can secrete gastrin -> controls the release of acid in the stomach. |
| Gastric Juice: | 2-3 liters per day produced by the gastric glands. Mainly a mixture of water, hydrochloric acid, and pepsin. |
| Gastric juice: | has a high concentration of hydrochloric acid - very acidic (low pH) |
| Parietal cells: | produce HCI and contain carbonate anhydrase (CAH) |
| Hydrochloric acid slide: | *review this for reaction* |
| Functions of HCL: | (1)activates pepsin & lingual lipase (pepsin breaks down proteins) (2)breaks up connective tissue & plant cell walls (helps liquefy food & form chyme) |
| Functions of HCL: (cont) | (3)converts ingested ferric ions (Fe3+) to ferrous ions (Fe2+) -> absorbed & used for hemoglobin synthesis (4)contributes to nonspecific disease resistance by destroying most ingested pathogens. |
| Autocatalytic effect: | as some pepsin is formed, it converts more pepsinogen to pepsin. |
| Zymogens: | digestive enzymes secreted as inactive proteins. *Pepsinogen is a zymogens, when secreted -> pepsin. |
| Gastric Lipase: | produced by chief cells. |
| Gastic lipase and lingual lipase: | play a minor role in digesting dietary fats. |
| Majority digesting fats: | occurs in the small intestine. |
| Intrinsic Factor: | a glycoprotein secreted by parietal cells. It is essential to absorption of vitamin B12 by the small intestine. Binds to vitamin B12 & intestinal cells will absorb them by receptor mediated endocytosis. |
| Vitamin B12: | is needed to synthesize hemoglobin. |
| Secretion of intrinsic factor: | is the only indispensable function of the stomach. |
| Gastric and pyloric glands have eneroendocrine cells that produce chemical messengers: | hormones, paracrine secretions, peptides produced in both the digestive tract and the central nervous system. |
| Swallowing center of medulla oblongata: | signals stomach to relax - preparing the stomach to be able to receive food. |
| Food stretches stomach: | Activating a receptive-relaxation response. Soon stomach shows a rhythm of peristaltic contractions controlled by pacemaker cells in longitudinal layer of muscularis externa. |
| Peristaltic Contractions: | moves food along. *stronger contractions are at pyloric region. |
| Ripple Action: | mixes food with gastric juices -> promoting physical breakdown of food. |
| Salivary and gastric enzymes: | partially digest protein and lesser amounts of starch and fat in the stomach. |
| Most digestion and nearly all absorption: | occur after chyme has passed into the small intestine. |
| Stomach: | does not absorb any significant amount of nutrients. |
| Living stomach is protected in three ways from the harsh acidic and enzymatic environment it creates: | mucous coat, tight junctions, epithelial cell replacement |
| Breakdown of the 3 measures: | can result in inflammation and/or peptic ulcers. |
| Nervous and endocrine systems collaborate: | increase gastric secretion and motility when food is eaten, suppresses them when the stomach empties. |
| Gastric is divided into three phases: | cephalic phase, gastric phase, intestinal phase |
| Cephalic phase: | stomach is being controlled by the brain |
| Gastric phase: | stomach is controlling itself |
| Intestinal phase: | stomach is being controlled by the small intestine |
| *these phases: | overlap & can occur simultaneously (at the same time). |
| Cephalic Phase: | Stomach responds to site, smell, taste, or thought of food. Sensory and mental inputs converge on the hypothalamus. Vagus nerve fibers from medulla oblongata stimulate the enteric nervous system of stomach, in turn stimualtes gastric secretion |
| *Gastric Phase: | period in which swallowed food and semi-digested protein activates gastric activity. |
| Ingested food stimulates gastric activity in two ways: | by stretching the stomach, by increasing the pH of its contents. |
| Gastric secretion is stimulated by three chemicals: | acetylcholine (ACh), histamine, gastrin |
| Intestinal Phase: | stage in which the duodenum responds to arriving chyme and moderates gastric activity through hormones and nervous reflexes. Duodenum enhances gastric secretion, but soon inhibits it. |
| Intestinal Phase: (cont) | stretching of the duodenum accentuates vagovagal reflex that stimulates the stomach. peptides and amino acids in chyme stimulate G cells of the duodenum to secrete more gastrin which further stimulates the stomach. |
| Small intestine: | receives chyme from stomach. |
| Secretions from liver and pancreas: | enter digestive tract near the junction of stomach and small intestine. |
| Secretions: | are so important to the digestive process of the small intestine. |
| Functions of Hepatocytes: | after a meal, the hepatocytes absorb from the blood - glucose, amino acids, iron, vitamins, & other nutrients for metabolism or storage. |
| Hepatocytes removes and degrades: | hormones, toxins, bile pigments, and drugs. |
| Hepatocytes secrete into the blood: | albumin, lipoproteins, clotting factors, angiotensinogen, and other products. |
| Between meals: | hepatocytes breaks down stored glycogen and releases glucose into the blood. |
| Gallbladder function: | stores and concentrates the bile. |
| Liver: | makes the bile. |
| Bile: | yellow/greenish fluid that contains minerals, cholesterol, phospholipids, bile pigments, bile acids, neutral fats. Bile breaks down fats. |
| Pancreatic duct: | Runs lengthwise through the middle of the gland. -> joins the bile duct at the hepatopancreatic ampulla & hepatopancreatic sphincter controls release of broth bile & pancreatic juice into the duodenum. |
| Accessory pancreatic duct: | smaller duct that branches from the main pancreatic duct. -> opens independently into the duodenum, & bypasses the sphincter and allows pancreatic juice to be released into the duodenum even when bile is not. |
| Pancreatic juice: | alkaline mixture of water, enzymes, zymogens, sodium bicarbonate, and other electrolytes. |
| Acini secrete: | the enzymes and zymogens |
| Ducts secrete: | bicarbonate (bicarbonate buffers HCI arriving from the stomach). |
| Pancreatic zymogens are: | trypsinogen, chymotrypsinogen, procarboxypeptidase |
| Other pancreatic enzymes: | pancreatic amylase, pancreatic lipase, ribonuclease and deoxyribonuclease |
| Three stimuli are chiefly responsible for the release of pancreatic juice and bile: | Acetylcholine (ACh), cholecystokinin (CCK), and secretin |
| Small intestine: | nearly all chemical digestion and nutrient absorption occurs in small intestine. |
| Tissue Layers: | have modifications for nutrient digestion and absorption - large internal surface area for effective digestion and absorption. |
| Three types of internal folds or projections: | 1.circular folds (plicae circulares) 2.villi 3.microvilli |
| Microvilli: | fuzzy border of microvilli on apical surface of each absorptive cell. -the brush border increases absorptive surface area |
| Brush border enzymes: | contained in the plasma membrane of microvilli. |
| Functions: | (1)carry out some of the final stages of enzymatic digestion (2)contact digestion-the chyme must contact the brush border for digestion to occur (3)intestinal churning of chyme insures contact with the mucosa. |
| Intestinal crypts: | numerous pores that open into tubular glands on the floor of the small intestine between the bases of the villi. -similar to gastric glands, in upper half have enterocytes & goblet cells like the villi, in lower half dominated by dividing stem cells. |
| Intestinal crypts: (cont) | a few Paneth cells are clustered at the base of each crypt, they secrete lysozyme, phospholipase, and defensins. |
| Duodenal glands: | in submucosa of duodenum - secrete an abundance of bicarbonate-rich mucus, neutralizes stomach acid and shields the mucosa from its erosive effects. |
| Large population of defensive lymphocytes: | throughout the submucosa of small intestine to fight any potential pathogens. |
| Goblet cells: | secrete mucous. |
| Intestinal Crypts: | secrete 1 to 2 Liters of intestinal juice per day - in response to acid, hypertonic chyme, and distention of the intestines. |
| Intestinal Crypts: | pH of 7.4 to 7.8 and contains water, mucus, and little enzyme. |
| Most enzymes that function in the small intestine are in: | brush border, and pancreatic juice. |
| Contractions of small intestine serve three functions: | 1.to mix chyme with intestinal juice, bile, and pancreatic juice 2.to churn chyme and bring it in contact with the mucosa for contact digestion and nutrient absorption 3.to move residue toward large intestine |
| Segmentation: | purpose is to mix and churn not to move material along as in peristalsis. |
| Peristalsis: | purpose is to move materials along (pushing). |
| Pacemaker cells: | in the muscularis externa sets rhythm of segmentation. |
| Starch: | the most digestible carbohydrate. |
| Starch is digested to: | oligosaccharides, then into the disaccharide maltose, finally to glucose which is absorbed by the small intestine. |
| Process begins in the mouth: | salivary amylase hydrolyzes starch into oligosaccharides. |
| Amino acids absorbed by the small intestine come from: | (1)Dietary proteins (2)Digestive enzymes digested by wach other (3)Sloughed epithelial cells digested by enzymes |
| Protease (peptidases): | enzymes that digest proteins. They begin their work in the stomach in optimum pH of 1.5 to 3.5 |
| Pepsin: | hydrolyzes any peptide bond between tyrosine and phenylalanine. - pepsin digests 10-15% of dietary protein into shorter peptides and some free amino acids. |
| Proteins: | digested in the small intestine. -pepsin inactivated when it passes into the duodenum and mixes with the alkaline pancreatic juice (pH 8): lots of bicarbonate ions are in it, pancreatic enzymes trypsin and chymotrypsin take over the process |
| Proteins: | then it hydrolyzes polypeptides into even shorter oligopeptides, and oligopeptides are taken apart one amino acid at a time by three more enzymes |
| carboxypeptidase: | will remove amino acids from the COOH end of the chain. |
| aminopeptidase: | removes amino acids from the amino end (NH2-amine) |
| dipeptidase: | splits dipeptides in the middle & release 2 free amino acids |
| Carboxypeptidase: | is a pancreatic secretion |
| Aminopeptidase & dipeptidase: | are brush border enzymes. |
| *Large intestine receives about: | 500 mL of indigestible residue per day , reduces it to about 150 mL of feces by absorbing water and salts -> eliminates feces by defecation. |
| *Large intestine takes about: | 12 to 24 hours to reduce the residue of a meal to feces |
| *Feces consist of: | 75% water and 25% solids |
| Haustral contractions occur: | every 30 minutes - this kind of colonic motility is a form of segmentation & distension of a haustrum stimulates it to contract |
| Mass movements occur: | 1 to 3 times a day - it is triggered by gastrocolic and duodenocolic reflexes. |
| Neural Control of Defecation: | 1.filling of the rectum 2.reflex contraction of rectum and relaxation of internal anal sphincter 3.voluntary relaxation of external sphincter |
Created by:
mr209368