University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2019
Views:

266

Pages:

38
Author:

mostatxutw5

Liver, Gallbladder and Pancreas • Liver and Pancreas are vital accessory glands to the intestines. • Liver and Pancreas release important secretions into the duodenum. • Liver and Pancreas secretions continue the digestion process. Liver • 3 lb. organ with 4 lobes located right upper quadrant of abdomen • blood supply from hepatic portal vein and hepatic arteries • produces bile (stored in gall bladder) and plasma proteins (coagulation factors, albumen and many others) • liver cells store minerals, vitamins, glycogen that can be released into blood as needed • detoxifies blood from ammonia, plant toxins, poisons, alcohol and other drugs • Can regenerate after some diseases or surgical removal of part. Veins of Hepatic Portal System Microscopic Anatomy of Liver • Liver functional units are tiny cylinders called lobules (about 1mm diameter). • Blood, from portal vein and hepatic artery mixes and flows through capillaries over hepatocytes on way to central vein. • Hepatocytes secrete bile into tiny canaliculi that flow into bile ductules that flow toward the gall bladder. Ducts of Gallbladder, Liver, Pancreas • Hepatocytes secrete bile into bile canaliculi in between the hepatocytes. All the bile from the canaliculi eventually flows into the right and left hepatic ducts. • Right and left hepatic ducts join to form common hepatic duct. • Cystic duct from gallbladder joins common hepatic duct to form the common bile duct. • Pancreatic duct and common bile duct merge at the hepatopancreatic ampulla that empties into the duodenum at the major duodenal papilla – sphincter of Oddi (hepatopancreatic sphincter) regulates release of bile and pancreatic fluid (juice) Ducts of Liver, Gallbladder and Pancreas 1) left and right hepatic ducts merge to form a common hepatic duct 2) common hepatic duct and cystic duct merge to form a common bile duct 3) pancreatic duct merges with common bile duct at hepatopancreatic ampulla 4) bile and pancreatic fluid enter duodenum through major duodenal papilla Gallbladder and Bile • Liver produces about 500 to 1000 ml bile each day. • Gallbladder stores and concentrates bile – Bile backs up into the gallbladder between meals when the hepatopancreatic sphincter (sphincter of Oddi) is closed. – Between meals, bile is concentrated by 20 x by a highly folded mucosa. • Bile is a yellow-green fluid containing minerals, fats, bile pigments, and bile acids. – bile pigments are from the breakdown of hemoglobin from old RBCs destroyed by macrophages in the liver. Bilirubin is the primary pigment and is green-yellow in color. Bile pigments are excreted as waste. • intestinal bacteria convert bile pigments into the brown pigment, urobilinogen which gives a brown color to feces. In the absence of bile secretion, as in liver disease, feces are grayish white and streaked with undigested fat. – bile acids (bile salts) emulsify fats and aid in their digestion • enterohepatic circulation recycles 80% of the bile from the ileum – cholesterol, phospholipids, lecithin in the bile help make lipids more soluble in water. Fat Emulsification and Absorption 1) Fat globules are broken up into emulsification droplets by the lecithin and bile acids in the bile. 2) Emulsification droplets are hydrolyzed (digested) by pancreatic lipase into simpler fatty acids and smaller fat droplets coated with bile acids called micelles. 3) Micelles are absorbed through the brush border of intestinal absorptive cells. Intestinal cells resynthesize triglycerides and package them with cholesterol and phospholipids into chylomicrons. 4) The Golgi of intestinal cells packages chylomicrons into secretory vesicles that are release from their basal surface and then absorbed into lymphatic lacteals. Fat Emulsification Fat Digestion and Micelle Formation Fat Absorption Gross Anatomy of the Pancreas • Retroperitoneal gland posterior to stomach – head, body and tail regions • Contains Endocrine and Exocrine tissue – secretes insulin and glucagon into the blood – secretes 1500 ml exocrine fluid into duodenum per day that contains water, enzymes, and bicarbonate • Pancreatic Duct runs length of gland and opens at the major duodenal papilla when the hepatopancreatic sphincter relaxes – accessory duct (if present) opens independently in duodenum Pancreas Hormonal Control of the Liver and Pancreas • Cholecystokinin released from duodenum into blood in response to arrival of acid and fat – causes secretion of pancreatic enzymes, contraction of gallbladder, and relaxation of hepatopancreatic sphincter • Secretin released from duodenum into blood in response to acidic chyme – stimulates pancreatic ducts to secrete more bicarbonate • Gastrin released from stomach and duodenum into blood also stimulates gallbladder contraction and pancreatic enzyme secretion Pancreatic Acinar Cells • Acinar Cells release Zymogen Granules of: – trypsinogen – chymotrypsinogen – procarboxypeptidase – amylase – lipase – ribonuclease and deoxyribonuclease Acinar Cells Activation of Pancreatic Enzymes by the Brush Border of the Small Intestine Protein Digestion in Stomach • Pepsin has optimal pH of 1.5 to 3.5 and is inactivated when it passes into the duodenum and mixes with alkaline pancreatic fluid (pH 8) Protein Digestion and Absorption in Small Intestine Pancreatic enzymes (trypsin, chymotrypsin and carboxypeptidase) continue to digest proteins in the intestines by hydrolyzing polypeptides into shorter polypeptides Protein Digestion and Absorption in Small Intestine • Brush border enzymes (Peptidases) cleave small proteins into simple amino acids that are absorbed into the intestinal epithelial cells. • Cotransporters move amino acids into epithelial cells and facilitated diffusion moves amino acids into the blood stream. Carbohydrate Digestion in Small Intestine • Salivary amylase stops working in acidic stomach (at pH< 4.5) • Pancreatic amylase completes starch digestion in intestines. • Brush border enzymes break down polysaccharides including sucrose and lactose – Most humans produce less lactase after age 4 making lactose less digestible (lactose intolerance) CAPILLARY Monosaccharide Sugar Absorption • membrane transport proteins absorb monosaccharides from the intestines • Some transport proteins move sugars via sodiumglucose transporters (SGLT) • Some sugar is absorbed with water between cells Vitamins and Minerals • Vitamins are absorbed unchanged – A, D, E, K are absorbed with other lipids – B complex and Vitamin C are absorbed by simple diffusion – B12 is only absorbed if bound to intrinsic factor • Minerals are absorbed throughout the intestines. Intestinal Motility • Movement of intestines mixes chyme with intestinal secretions, bile and pancreatic fluid and increases contact with mucosa for absorption and digestion. – segmentation is random ring-like constrictions that mix and churn contents about 12 times per minute – peristaltic waves push chyme through small intestines towards colon. Takes about 2 hours • Food in stomach causes gastroileal reflex (relaxes ileocecal valve between small and large intestine) and may cause the urge to defecate as the colon fills. Segmentation in the Small Intestine Purpose of segmentation is to mix intestinal contents, not to move material along as in peristalsis. Peristalsis • Waves of contraction that gradually move contents towards the colon • Begin after absorption starts Gross Anatomy of Large Intestine Greater Omentum Gross Anatomy of Large Intestine • Large intestine is also called the colon • 5 feet long and 2.5 inches in diameter • Begins at cecum in lower right quadrant and leads to ascending, transverse, descending and sigmoid portions. • Sigmoid colon is S-shaped portion leading down to the rectum in the pelvis • Rectum is straight portion ending at anus • Lining of colon is smooth with only a few folds and no villi. • Muscularis Externa – longitudinal muscle fibers called teniae coli run the length of the colon – haustra coli are lateral pouches along the length of the colon Microscopic Anatomy of Large Intestine • Mucosa is simple columnar epithelium – epithelium consists of absorptive cells and goblet cells – epithelium transitions to a stratified squamous epithelium at the anus • Intestinal Glands produce mucus only Water Balance • Water is absorbed by osmosis through absorptive cells following a gradient established by the absorption of salts, vitamins and organic nutrients • Diarrhea occurs when too little water is absorbed from the feces. Diarrhea occurs when: – feces pass through too quickly when the mucosa is irritated. – feces may contain high concentrations of a solute, like lactose (from lactose intolerance) that osmotically keeps water in the feces. Bacterial and Intestinal Gas • Bacteria, including Escherichia coli and many others, live symbiotically in the large intestine. – synthesize vitamins B and K – ferment some cellulose and other undigested carbohydrates – average person produces 500 mL per day of gas (flatus) – most is swallowed air but it can contain gases produced by bacteria including odorless methane and odorous gasses including hydrogen sulfide, indole and skatole. Colon Absorption and Motility • Transit time is 12 to 24 hours – reabsorbs water and electrolytes • Feces consist of water and solids (bacteria, mucus, undigested fiber, fat, sloughed epithelial cells) • Contractions occur about every 30 minutes – distension of the colon stimulates it to contract • Mass movements usually occur 1 to 3 times a day Appendix Appendix • • • • • • • The appendix is a thin, closed tube attached to the cecum. The submucosa contains numerous lymphoid follicles that contain abundant lymphocytes that play a role in immunity. The appendix receives small amounts of processed food and can respond to dangerous antigens. Infection and inflammation of the mucosa of the appendix can lead to pain, swelling and possible rupture that could lead to peritonitis. The appendix contains a diverse population of intestinal bacteria, and many types are beneficial to human health. After severe, chronic diarrhea, as caused by diseases such as cholera or amoebic dysentery, the gut may be cleared of bacteria except in the appendix and those bacteria can help repopulate the colon with a normal flora faster than individuals without an appendix. http://www.dukemagazine.duke.edu/issues/030408/depqa.html Anatomy of the Rectum and Anus • Anal canal is about 3 cm total length • Anal columns are longitudinal ridges separated by mucus secreting anal sinuses • Hemorrhoids are distended veins in the lamina propria