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Chapter 16 Lecture Notes page 1 alimentary canal (gut) + accessory organs A. functions 1. digestion - breaking down food into molecules small enough to be transported into the body a. enzymes break chemical bonds to make molecules smaller - these are secreted by the salivary glands, stomach glands, and pancreas (other enzymes are components of the intestinal epithelial cell membranes) ENZYME large molecule small molecule b. mechanical processing makes food particles smaller and provides a larger surface area for the enzymes to work on 2. absorption - moving molecules (food, water, ions, vitamins) from the lumen of the gut across the epithelial cells and into capillaries 3. excretion of undigested materials, dead cells and bacteria, and bilirubin BIOL 2404 Strong/Fall 2006 Chapter 16 Lecture Notes page 2 B. general histological structure 1. mucosa (mucous membrane) - modified to increase surface area or allow expansion a. epithelium - protects, secretes, absorbs b. lamina propria (c.t.) - contains capillaries and glands c. muscularis mucosae - moves mucosal folds and villi 2. submucosa - c.t. containing larger blood vessels, lymph vessels, nerve network 3. muscularis externa - layers of smooth muscle that mix and propel gut contents; contains nerve network and pacesetter cells a. peristalsis - wave of contraction that moves contents forwards b. segmentation - alternating contraction and relaxation that mixes contents 4. serosa (visceral peritoneum) covers stomach, small intestines, cecum and colon the other organs have a layer of c.t. called the adventitia that that attaches them to surrounding structures BIOL 2404 Strong/Fall 2006 Chapter 16 Lecture Notes page 3 C. mesenteries are double layers of peritoneum that suspend some abdominal organs inside the abdominal cavity mesenteries contain blood vessels, lymph vessels and nerves for these organs greater omentum - greater curvature of stomach to transverse colon D. mouth 1. oral or buccal cavity vestibule = area between cheeks or lips and teeth 2. tongue - attached posteriorly lingual frenulum attaches inferior surface of tongue to floor of mouth used in chewing, speech and swallowing 3. salivary glands saliva contains water, mucous, salivary amylase, antibodies, lysozyme a. parotid - anterior to ear, ducts open at 2nd upper molar b. sublingual - below tongue, ducts open lateral to lingual frenulum c. submandibular - inside lower mandible, ducts open lateral to lingual frenulum BIOL 2404 Strong/Fall 2006 Chapter 16 Lecture Notes page 4 4. teeth - 20 deciduous, 32 permanent 5. chewing / mastication = mechanical processing 6. swallowing / deglutition a. oral phase - tongue pushes food into pharynx b. pharyngeal phase - pressure receptors in pharynx signal medulla oblongata, which causes larynx to elevate and epiglottis to cover glottis, pharyngeal muscles push food into esophagus c. esophageal phase - peristalsis and relaxation of gastroesophageal sphincter E. esophagus - muscular tube that extends from pharynx to stomach; located posterior to trachea 1. sphincters a. upper – between pharynx and esophagus b. (lower) gastroesophageal or cardiac – between esophagus and stomach 2. esophageal hiatus - opening in diaphragm for esophagus (hiatal hernia) F. stomach - storage organ (1-1.5 liters) located inferior to diaphragm in left upper abdomen 1. divisions: a. cardia b. fundus c. body d. pylorus pyloric sphincter controls movement of food into duodenum BIOL 2404 Strong/Fall 2006 Chapter 16 Lecture Notes page 5 2. glands in the mucosa produce gastric juice a. HCl - activates pepsinogen b. pepsinogen - inactive protein-digesting enzyme c. intrinsic factor - binds to vitamin B12 3. rugae are folds of the mucosa that allow expansion 4. control a. ANS sympathetic - inhibits stomach activity parasympathetic - stimulates stomach activity b. hormones gastrin stimulates stomach activity intestinal hormones inhibit stomach activity c. enterogastric reflex (nerve signals from duodenum) inhibits stomach activity G. small intestine (5 hour residence time) 1. divisions a. duodenum - 25 cm long - between stomach and jejunum common bile duct and major pancreatic duct enter at duodenal papilla most digestion and absorption occurs here duodenal glands secrete alkaline mucous b. jejunum - 2.5 meters long - between duodenum and ileum c. ileum - 3.5 meters long - between jejunum and large intestine ileocecal valve prevents backflow from large intestine 2. histology a. columnar epithelial cells have microvilli on apical surface - increases surface area BIOL 2404 Strong/Fall 2006 Chapter 16 Lecture Notes page 6 b. mucosa has finger-like projections called villi - increases surface area villi contain large lymphatic capillaries called lacteals and also vascular capillaries; absorbed materials enter these capillaries c. mucosa and submucosa form circular folds (plicae circulares) increases surface area 3. segmentation mixes contents 4. control a. ANS sympathetic - inhibits activity parasympathetic - stimulates activity b. hormones H. pancreas - located posterior and inferior to stomach 1. exocrine pancreas consists of secretory units that make digestive enzymes a. amylase breaks down large carbohydrates b. protease breaks down proteins c. lipase breaks down triglycerides 2. duct enters duodenum 3. secretion controlled by ANS and hormones BIOL 2404 Strong/Fall 2006 Chapter 16 Lecture Notes page 7 I. liver - located in upper right abdominal cavity just below diaphragm 1. lobes a. b. c. d. right left caudate quadrate 2. lobes are divided into lobules a. hepatocytes secrete bile into bile ducts b. hepatic sinusoids carry blood from hepatic portal vein and hepatic artery past hepatocytes, which absorb materials from the blood c. blood from sinusoids enters central veins → hepatic veins → inferior vena cava 3. functions a. bile secretion b. storage of glucose, lipids, vitamins, iron c. detoxification of various molecules, inactivation of hormones d. synthesis of plasma proteins (including clotting factors) e. metabolic activities BIOL 2404 Strong/Fall 2006 Chapter 16 Lecture Notes page 8 J. gall bladder - located inferior to right lobe of liver 1. function - storage, dehydration and release of bile bile emulsifies fat, which increases the surface area for enzymatic activity and speeds up lipid digestion 2. control: ANS and hormones cholecystokinin (CCK) causes contraction of gall bladder 3. bile duct system right hepatic duct left hepatic duct common hepatic duct cystic duct common bile duct duodenum K. large intestine - 1.5 meters long 1. divisions a. cecum - inferior to ileocecal valve, vermiform appendix opens into cecum and is located posterior to it b. colon: ascending, transverse, descending, sigmoid haustra - pouches in wall of colon c. rectum opens into anal canal anus is inferior opening of gut internal anal sphincter smooth muscle controlled by reflex external anal sphincter is skeletal muscle and controlled voluntarily BIOL 2404 Strong/Fall 2006 Chapter 16 Lecture Notes page 9 2. functions a. absorption of water b. absorption of vitamins made by resident bacteria: K, biotin, B 5 c. storage of feces d. recycles bile salts 3. mass movements are peristaltic waves that move feces into the rectum stimulated by distention of stomach (gastrocolic reflex) and duodenum 4. defecation a. reflex initiated by stretch receptors in rectum causes contraction of colon and rectum b. voluntary relaxation of external anal sphincter L. digestion and absorption (figure 16-18) 1. carbohydrates salivary amylase pancreatic amylase intestinal epithelial enzymes absorbed through intestinal epithelial cells into vascular capillaries 2. proteins pepsin pancreatic proteases intestinal epithelial enzymes absorbed through intestinal epithelial cells into vascular capillaries BIOL 2404 Strong/Fall 2006 Chapter 16 Lecture Notes page 10 3. lipids emulsification by bile (this is not chemical digestion) pancreatic lipase triglycerides are resynthesized inside the intestinal epithelial cells and combined with proteins to make chylomicrons absorbed through into lacteals 4. water and electrolytes a. sodium and chloride are absorbed from the intestine b. water follows by osmosis c. iron absorption is carefully controlled to prevent toxicity 5. vitamins a. water soluble b. fat soluble (A, D, E, K) - absorbed along with lipids from food c. vitamin B12 - must be bound to intrinsic factor BIOL 2404 Strong/Fall 2006