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Unit I: Metabolism Digestive System

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1 Unit I: Metabolism Digestive System
Part II Chapter 21

2 Tissue Table Digestive Organ Epithelial Tissue Muscle Type pH
Oral Cavity Pharynx Esophagus Stomach Small Intestine Large Intestine Anal Canal

3 Small Intestine Segments Duodenum Jejunum Ileum Transverse colon (cut) Ascending colon Descending Sigmoid Cecum Rectum Longest part of the digestive tract and highly folded  lots of surface area to expose to chyme for absorption 6.6ft long in a living person (due to muscle tone); 19-23ft in cadaver 3 regions: duodenum, jejunum, and ileum Nearly all chemical digestion and nutrient absorption occurs in small intestine

4 Small Intestine Duodenum -10 in.
neutralizes stomach acids, emulsifies fats, pepsin inactivated by pH increase, pancreatic enzymes Jejunum - next 8 ft. Simple columnar Smooth muscle Ileum - last 12 ft. lymphatic nodules ileocecal junction Ileum Duodenum Jejunum Serosa Muscularis externa Submucosa Mucosa mucosae Circular folds Villi Peyer Patches curves around head of pancreas – name refers to length: 12 fingers receives stomach contents, pancreatic juice and bile emulsify – physically broken up – by bile acids; pancreatic enzymes take over chemical digestion 2.a. has large tall circular folds, walls are thick and muscular most digestion and nutrient absorption occur here  rich blood supply 3. Wall is thinner and less muscular and less vascular a. Peyer patches - remove pathogens b. ends at … with the large intestine (cecum)

5 Small Intestine - Surface Area
Circular folds Villi Small Intestine - Surface Area Circular folds - up to 10 mm tall chyme flows in spiral path Villi - 1 mm tall contain blood vessels and lymphatics (lacteal) nutrient absorption Microvilli 1 micron tall brush border enzymes Dextrinase Glucoamylase Maltase Sucrase, lactase Lacteal Columnar epithelial cell Mucous cell Nerve Capillary network Arteriole Lymphatic vessel Venule Muscularis mucosae Lamina propria Surface area is increased by (1) Long length (2) Surface elaborations: if it was flat – surface area=0.3m2; with surface elaborations=200m2 1.a. involve only mucosa and submucosa (transverse/spiral ridges) b. … slows progress  more contact, mixing, and absorption c. not in distal half of ileum  nutrient absorption done by then 2. Mucosa appears fuzzy due to villi. Fingerlike projections – largest in duodenum getting progressively smaller blood vessels absorb most nutrients lacteal (lymphatic capillaries) absorbs fat giving contents a milky appearance 3. Villi appear fuzzy due to microvilli – a. brush border of cells increase surface area; enzymes not released into lumen integral proteins of the plasma membrane b. some need contact for digestion which makes mixing in intestine so important. CONTACT DIGESTION

6 Intestinal Crypts absorptive cells, goblet cells and at base, rapidly dividing cells Brunner’s glands Secrete 1-2 L of intestinal juice/day pH Brunner’s Glands 1. Pores opening between villi lead to intestinal crypts - in mucosa: upper half  like villi (absorptive and goblet cells) bottom half  dividing stem cells (3-6 days: cells move up to tip of villus) a. Paneth cells - protect against bacterial infection - antibacterial secretions 2. in submucosa - secrete bicarbonate mucus - neutralize stomach acid 3. water and mucus, pH little enzymes  most enzymes on brush border or in pancreatic juice

7 Gross Anatomy of Large Intestine
500 ml of indigestible food residue/day 5 ft long and 2.5 inches in diameter in cadaver Appendix – columnar epithelium, goblet cells, WBC, and lymphocytes … reduces it to 150 ml of feces by absorbing water and salts  eliminates feces by defecation 3. Begins with cecum  appendix – columnar epithelium lines it, goblet cells, white blood cells similar to Peyer’s patches *no digestive function, no nutrient absorption - lymphocytes - significant source of immune cells 4. Colon – between ileocecal junction and rectum Ascending (right), transverse (horizontal), descending (left), ( form a 3- sided frame around small intestine) and sigmoid regions (S-shaped portion) 5. In pelvic cavity – large intestine straightens to form rectum. rectal valves – 3 internal folds enable to retain feces while passing gas

8 Microscopic Anatomy of Large Intestine
Aggregated lymphoid nodule Simple columnar epithelium Intestinal gland Mucous cells Muscularis mucosae Submucosa Muscularis Externa Circular layer Longitudinal layer Mucosa - simple columnar epithelium anal canal: non-keratinized stratified squamous Muscularis Externa – smooth muscle anal canal: skeletal No circular folds or villi Comparing large to small intestine 1. A. used for absorption and secretion. b. provides more resistance to abrasion from feces – protection 3. Intestinal crypts – deeper, more goblet cells for producing mucus only

9 Anatomy of Anal Canal 3 cm total length Anal columns Anal sinuses
Last 3 cm of large intestine terminates at the anus. Mucosa forms longitudinal ridges called anal columns separated by mucus secreting anal sinuses (depressions) between columns  lubricate canal during defecation Anus regulated by: Internal anal sphincter – smooth muscle; involuntary external anal sphincter – skeletal muscle; voluntary Hemorrhoids are permanently distended veins 3 cm total length Anal columns Anal sinuses Internal & External anal sphincters

10 Bacterial Flora and Intestinal Gas
Bacterial flora populate large intestine ferment cellulose and other undigested carbohydrates; synthesize vitamins B and K Flatus (gas) average person produces 500 mL per day most is swallowed air hydrogen sulfide, indole and skatole produce odor 800 species of bacteria in large intestine they digest cellulose, polysaccharides and we absorb the resulting sugars. some also: … vitamin K needed for blood clotting. everyone’s bacterial flora is different. 2. Intestinal gas a. reabsorbs the rest (7-10L of gas total) b. … but bacteria adds to it: flatus is composed of N, CO2, H, methane (CH4), hydrogen sulfide (H2S) and 2 amines: indole and skatole produce the odor of feces and gas; H gas is known to be combustible

11 Liver, Gallbladder and Pancreas
Accessory Organs: Liver, Gallbladder and Pancreas All release important secretions into small intestine to continue digestion

12 Gross Anatomy of Liver 3 lb. organ located inferior to the diaphragm
Simple cuboidal epithelium 4 lobes - falciform ligament round ligament 1. Body’s largest gland. GLANDS SECRETE fluids! And have simple cubiodal cells main function associated with digestion: secretion of bile no muscle! 2. right, left, quadrate (square) and caudate (tail like) a. … separates left and right – suspends it from the diaphragm. b. remnant of umbilical vein – carries blood from umbilical cord bypasses liver in fetus. 3. Gallbladder adheres to ventral surface between right and quadrate lobes

13 Microscopic Anatomy of Liver
Hepatocytes Hepatic sinusoids Bile duct Hepatic Portal vein Artery Hepatic Triad Tiny innumerable cylinders (functional units) called … Lobule consists of a central vein passing down its core, surrounded by sheets of cuboidal cells called hepatocytes. Sheets 1-2 cell layers thick 2. Spaces between sheets of hepatocytes are blood-filled channels called hepatic sinusoids. … fenestrated endothelium (thin layer of epithelial cells) – perforated with holes or slits. 3. Hepatic triad – two blood vessels and a bile ductule. a. Blood vessels are branches of hepatic artery and hepatic portal vein bring blood to liver. Hepatic lobules (2mm by 1mm) Sinusoids lined with fenestrated endothelium

14 Liver Function: Overview
Bile duct Branch of hepatic portal vein Branch of hepatic artery Blood enters the hepatic sinusoids from hepatic portal vein and hepatic artery. Hepatocytes regulate solute and nutrient levels and absorb or secrete molecules. Kupffer, phagocytic cells, engulf pathogens, cell debris, and damaged blood cells. Also responsible for storing iron, some lipids, and heavy metals (such as tin or mercury). Central vein  hepatic veins  inferior vena cava. Hepatocytes secrete bile into bile canaliculi Bile ductules  hepatic bile ducts in the nearest Triad Start …Roughly one-third of the blood supply to the liver is arterial blood from the hepatic artery. The rest is venous blood from the hepatic portal vein, which begins in the capillaries of the esophagus, stomach, small intestine, and most of the large intestine. Hepatocytes perform most functions. … After a meal, hepatocytes remove glucose, amino acids, vitamins, and nutrients for metabolism or storage. Removes and degrades hormones, toxins, bile pigments, drugs. Secretes albumin, lipoproteins, clotting factors, and angiotensin. Inbetween meals, release glucose back into bloodstream. Sinusoids  thru hepatocytes and Kupffer cells  central vein collects blood from the sinusoids of the lobule. The central veins of all the lobules ultimately merge to form the … … extend outward, away from the central vein. Bile canaliculi merge to form …

15 Ducts of Liver, Gallbladder, and Pancreas
Right and left hepatic ducts Round ligament Common hepatic duct Hepatic portal vein and hepatic artery Common bile duct Gallbladder Cystic duct Liver Duodenum Stomach Pancreas Pancreatic duct Hepatopancreatic sphincter Duodenal papilla Intestinal lumen 1. Bile passes from bile canaliculi between cells to bile ductules to right and left hepatic ducts 2. Right and left ducts join outside liver to form common hepatic duct 3. Cystic duct from gallbladder joins common hepatic duct to form bile duct ( through lesser omentum to near duodenum) 4. Pancreatic duct and bile duct combine (to form hepatopancreatic ampulla) emptying into duodenum at major duodenal papilla sphincter of Oddi (hepatopancreatic sphincter) regulates release of bile and pancreatic juice (closed between meals to prevent release of bile into intestine)

16 Gallbladder and Bile Gallbladder: 10 cm long
Bile: minerals, bile acids, cholesterol, bile pigments, fats and phospholipids bilirubin intestinal bacteria convert to urobilinogen = brown color bile acid (salts) enterohepatic circulation – hepatocytes liver small intestine Duodenum CCK Lipid droplet Bile salt The liver secretes bile continuously —roughly 1 liter per day. Between meals, bile becomes more concentrated. CCK triggers dilation of the hepatopancreatic sphincter and contraction of the gallbladder. Liver Start Sac on underside of liver made of folded mucosa and simple columnar epithelium – store bile smooth muscle to push bile out Picture: 1. Liver produces bile. Bile backs up into gallbladder from a filled bile duct. 2. between meals, water and electrolytes are absorbed from bile and concentrated. 3. Duodenum releases CCK … This ejects bile into duodenum through duodenal ampulla. 3. Yellow-green fluid containing … a. pigment from hemoglobin breakdown (bile pigments) gives bile its color i. … brown color of feces b. bile acids are steroids from cholesterol. Used for - Fat digestion and absorption; all other components of bile are destined for excretion. Increases surface area of fat globules for more efficient digestion by enzymes in small intestine ii. Circulation: 80% recycling of bile acids from ileum - bile acids are reabsorbed by small intestine ileum  returned to liver  resecreted by hepatocytes (2 or more times during digestion) The body’s only way of eliminating excess cholesterol. If built up they (cholesterol) form gallstones. Remove gallbladder  bile duct stores bile; functions as gallbladder

17 Gross Anatomy of Pancreas
Head of pancreas Body of Pancreatic lobules Pancreatic duct Common bile duct Accessory pancreatic duct (present in 3–10 percent of individuals) Duodenal papilla Duodenum Tail of Endocrine and exocrine gland secretes insulin and glucagon secretes 1500 mL pancreatic juice/day Pancreatic juice: Water, zymogens, enzymes, and sodium bicarbonate (Ventral side covered by peritoneum.) spongy, simple cuboidal epithelium (gland) no muscle! head (surrounded by duodenum), body and tail 2.a. Endocrine part is the pancreatic islets that secrete insulin … into the blood which affect carbohydrate metabolism (discussed w/ endocrine system) b. most (99%) is exocrine tissue. … into duodenum 3. Alkaline – to neutralize stomach HCl (pH = 8) b. Pancreatic juice consists of water, zymogens (enzyme precursor molecules), and enzymes secreted by acinar cells and sodium bicarbonate secreted by ducts.

18 Pancreatic Acinar Cells
duct Endocrine cells in pancreatic islet Cells of pancreatic acinus The exocrine pancreatic acini Zymogens  proteases Trypsinogen  trypsin Chymotrypsinogen  chymotrypsin Procarboxypeptidase  carboxypeptidase Other enzymes Amylase (starch) Lipase (fat) Ribonuclease (RNA) and deoxyribonuclease (DNA) Functional exocrine unit – acinus (pl. acini) Acinar cells – high density of rough ER  lots of ribosomes  enzymes Secrete: Proteases – splits proteins to smaller peptides large amount of protein production 1. Have a precursor (zymogens) so they don’t digest intracellular proteins. a. trypsinogen converted to trypsin in intestine by enterokinase  digests dietary protein and converts the other two. all “finished” enzymes are involved in protein digestion 2. A. carbohydrate digestion b. lipid digestion

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