Ch 25-26

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Ch 25-26
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2011-01-28 16:32:46
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Ch 25-26
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  1. Hepatic Lobes
  2. hepatocytes
  3. hepatic sinusoids
  4. hepatic macrophages (Kupffer cells)
  5. Functions of hepatocytes after a meal,
    absorb from the blood: glucose, amino acids, iron, vitamins, and other nutrients for metabolism or storage

    removes and degrades: hormones, toxins, bile pigment, and drugs

    secretes into the blood: albumin, lipoproteins, clotting factors, angiotensinogen, and other products
  6. Function of hepatocytes between meals
    break down stored glycogen and release glucose into the blood
  7. Hepatic lobe
    seperated by a sparse connective tissue-stroma
  8. Hepatic Triad
    two blood vessels and a bile duct, visible in the triangular areas where three or more lobules meet

    small branch of proper hepatic artery

    small branch of the hepatic portal vein

    • both supply blood to sinusoids which recieve a mixture of nutrient-laden venous blood from the intestines, and freshly oxygenated arterial blood from the celian trunk
    • after filtering through the sinusoids, the blood is collected in the central vein
    • ultimately flows into the right and left hepatic veins
  9. Gall Bladder
    a pear-shaped sac on the underside of the liver

    serves to store and concentrate bile by a factor of 20 by absorbing water and electrolytes

    about 10 cm long

    internally lined by highly folded mucosa with simple columnar epithelium

    fundus usually projects slightly beyond inferior margin of liver

    cervix leads into the cystic duct
  10. Bile
    yellow-green fluid containing minerals, cholesterol, neutral fats, phospholipids, bile pigments, and bile acids

    liver secretes about 500-1000mL of bile daily

    80% of bile acids are reabsorbed in the ileum and returned to the liver - hepatocytes absorb and resecrete them, enterohepatic circulation-this route secretion, reabsorption, and resecretion of bile acids teo or more times during digestion of an average meal

    20% of the bile acids are excreted in the feces - this the body's only way of eliminating excess cholesterol, liver synthesizes new bile acids from cholesterol to replace those lost in feces
  11. bilirubin
    principal pigment derived from the decomposition of hemoglobin

    metabolized with bacteria in large intestine to form urobilinogen - responsible fo rhte brown color of feces
  12. bile acids
    • (bile salts)
    • steroids synthesized from cholesterol
    • -bile acids and lecithin, a phospholipid, aid in fat digestion and absorption
  13. Gallstones
    form if bile becomes excessively concentrated

    bile gets in by first filling the bile duct then overflowing into the gallbladder
  14. Pancreas
    spongy retroperitoneal gland posterior to the greater curvature of the stomach

    measure 12 to 15 cm long and 25 cm thick

    has head encircled by duodenum, body, midportion, and a tail on the left

    endocrine and exocrine glands
  15. endocrine portion of pancreas
    pancreatic inlets that secrete insulin and glucagon
  16. Exocrine portion of pancreas
    • 99% of pancreas that secretes 1200 to 1500 mL of pancreatic juice per day
    • -secretory acini release their secreation into small ducts that converge on the main pancreatic duct
  17. Pancreatic Ducts
    • run lengthwise through the middle of the gland
    • -joins the bile duct at the hepatopancreatic ampulla
    • -hepatopancreatic sphincter controls release of both bile and pancreatic juice into the duodenum

    two ducts
  18. accessory pancreatic duct
    • smaller duct that branches from the main pancreatic duct
    • -opens independently intot he duodenum
    • -bypasses the sphincter and allows pancreatic juice to be released into the duodenum even when bile is not
  19. Pancreatic Juice
    • alkaline mixture of water, enzymes, zymogens, sodium bicarbonate, and other electrolytes
    • -acini secrete the enzymes and zymogens
    • -ducts secrete bicarbonate-bicarbonate buffers HCL arriving from the stomach
  20. Pancreatic Zymogens
    trypsinogen: secreted into intestinal lumen; converted to trypsin by enterokinase, and enzyme secreted by mucosa of small intestine; trypsin is autocatalytic-converts trypsinogen into still more trypsin

    chymotrypsinogen - converted to chymotrypsinogen by trypsin

    procarboxypeptidase-converted to carboxypeptidase by trypsin
  21. Pancreatic Enzymes
    pancreatic amylase-digest starch

    pancreatic lipase- digest fat

    ribonucleases and deoxyribonuclease- digest RNA and DNA respectively
  22. acetylcholine
    • (ACh)
    • stimulates release of pancreatic juice and bile from vagus and enteric nerves
    • -stimulates acini to secrete their enzymes during the cephalic phase of gastric control even before food is swallowed
  23. cholecystokinin
    • (CCK)
    • stimulates release of pancreatic juice and bile secreted by mucosa of duodenum in response to arrival of fats in small intestine
    • -stimulate pancreatic acini to seperate enzymes
    • -strongly stimulate gall bladder
    • -induces contractions of the gallbladder and relaxation of hepatopancreatic sphincter causing discharge of bile into the duodenum
  24. secretin
    • stimulates release of pancreatic juice and bile released from duodenum in response to acidic chyme arriving from the stomach
    • -stimulates ducts of both liver and pancreas to secrete more sodium bicarbonate
    • -raising pH to level pancreatic and intestinal digestive enzymes require
  25. Small Intestine
    nearly all chemical digestion and nutrient absorption occurs in small intestine

    • the longest part of the digestive tract
    • -2.7 to 4.5 m long in a living person
    • -4 to 8 m long in a cadaver where there is no muscle tone

    "small" refers to the diameter not length
  26. Three regions of the small intestine
    duodenum, jejunum, and ileum
  27. duodenum
    the first 25 cm of small intestine

    • begins at the pyloric valve
    • arches around the head of the pancreas
    • ends at a sharp bend called the duodenojejunal flexure
    • most is retoperitoneal
    • recieves stomach contents, pancreatic juice, and bile
    • stomach acid is neutralized here
    • fats are physically broken up (emulsified) by the bile acids
    • pepsin is inactivated by increased pH
    • pancreatic enzymes take over the job of chemical digestion
  28. jejunum
    first 40% of small intestine beyond duodenum

    • roughly 1 to 1.7 m in a living person
    • has large, tall, closely spaced circular folds
    • its wall is relatively thick and muscular
    • especially rich blood supply which gives it a red color
    • most digestion and nutrient absorption occurs here
  29. ileum
    forms the last 60% of the postduodenal small intestine

    • about 1.6 to 2.7m
    • thinner, less muscular, less vascular, and paler pink color
    • Peyer patches-prominent lymphatic nodules in clusters on the side opposite the mesenteric attachment-readily visible with the naked eye, become progressively larger approaching the large intestine
  30. ileocecal junction
    • the end of the small intestine
    • -where the ileum joins the cecum of the large intestine
  31. ileocecal valve
    • a sphincter formed by the thickened muscularis of the ileum
    • -protrudes into the cecum
    • -regulates passage of food residue into the large intestine

    both jejunum and ileum are intraperitoneal and covered with serosa
  32. Tissue layers have modifications for nutrient digestion and absorption..
    lumen lined with simple columnar epithelium

    muscularis externa is notable for a thick inner circular layer and a thinner outer longitudinal layer

    large internal surface area for effective digestion and absorption-great length and three types of internal folds or projections
  33. three types of internal folds
    circular folds (plicae circulares) - increase surface area by a factor of 2 to 3

    villi - increase surface area by a factor of 10

    microvilli - increase the surface area by a factor of 20
  34. circular folds
    • largest folds of intestinal wall
    • -up to 10mm high
    • -involve only mucosa and submucosa
    • -occur from the duodenum to the middle of hte ileum
    • -cause chyme flow in spiral path causing more contact with mucosa
    • -promotes more thorough mixing and nutrient absorption
    • -relatively small and sparse in ileum and not found in distal half-most nutrient absorption is completed by this point
  35. villi
    • fingerlike projections 0.5 to 1 mm tall
    • -make mucosa look fuzzy
    • -villus covered with two types of epithelial cells -absorptive cells(enterocytes), goblet cells(secrete mucus)
    • -epithelia joined by tight junctions that prevent digestive enzymes from seeping btwn them
    • -core of villus filled with areolar tissue of the lamina propria-embedded in this tissue are an arteriole, a capillary network, a venule, and a lymphatic capillary called a lacteal
  36. microvilli
    fuzzy border of microvilli on apical surface of each absorptive cell

    • about 1um high
    • the brush border enzymes-contained in the plasma membrane of microvilli
    • -carry out some of the final stages of enzymatic digestion
    • -not released into the lumen
    • -contact digestion-the chyme must contact the brush border for digestion to occur
    • -intestinal churning of chyme insures contact with the mucosa
  37. intestinal crypts
    • (crypts of Lieberkuhn)
    • 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 and goblet cells like the villi
    • -in lower half, dominated by dividing stem cells - life span of 3 to 6 days, new epithelial cells migrate up the crypt to the tip of the villus where it is sloughed off and digested
    • -a few Paneth cells are clustered at the base of each crypt - secrete lysozyme, phospholipase, and defensins-defensive proteins that resist bacterial invasion of the mucosa

    secrete 1 to 2 L of intestinal juice per day - inresponse to acid, hypertonic chyme, and distension of the intestines, pH of 7.4 to 7.8, contains water, mucus, and little enzyme
  38. duodenal glands
    • in submucosa of duodenum
    • -secrete an abundance of bicarbonate-rich mucus
    • -neutralizes stomach acid and shields the mucosa from its erosive effects
  39. Three functions of the small intestine contractions
    to mix chyme with intestinal juice, bile, and pancreatic juice - to neutralize acid, digest nutrients more effectively

    to churn chyme and bring it in contact with the mucosa for contact digestion and nutrient absorption

    to move residue toward large intestine
  40. segmentation
    the movement in which stationary ringlike constrictions appear in several places along the intestine

    they relax and new constructions form elsewhere

    most common kind of intestinal contraction

    pacemaker cells in muscularis externa set rhythm of segmentation - contractions about 12 times per minute in the duodenum, 8 to 9 times per minute in the ileum, when most nutrients have been absorbed and little remains but undigested residue, segmentation declines and peristalsis begins
  41. Peristalsis
    gradual movement of contents toward colon

    peristaltic wave begins in the duodenum, travels 10 to 70cm and dies out

    followed by another wave starting further down the tract

    migrating motor complex-successive, overlapping waves of contraction

    milk chyme toward colon over a period of two hours

    • ileocecal valve usually closed
    • -food in stomach triggers gastroileal reflex that enhances segmentation in the ileum and relaxes the valve
    • -ascecum fills with residue, pressure pinches the valve shut-prevents reflux of cecal contents into the ileum
  42. Starch
    the most digestible carbohydrate

    cellulose is indigestible

    • starch is first digested to
    • -oligosaccharides up to eight glucose residue long
    • -then into the disaccharide maltose
    • -finally to glucose which is absorbed by the small intestine
  43. Starch in the mouth
    salivary amylase hydrolyzes starch into oligosaccharides

    amylase works best at pH of 6.8 to 7 oral cavity

    amylase quickly denatured on contact with stomach acid and digested by pepsin

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