Lipid-Digestion & Absorption Flashcards Preview

week 46 > Lipid-Digestion & Absorption > Flashcards

Flashcards in Lipid-Digestion & Absorption Deck (19)
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1

What increases surface area for absorption?

  • Crypt
  • Villi
  • Microvilli

2

Stem Cells of crypt

  • produce new absorptive epithelial cells to replace lost cells

3

Lacteal

transport fat to lymph

4

What can lead to malabsorption of lipids?

  • Bile deficiency
  • Pancreatic Insufficiency

5

Digestion and absorption of lipids

  • Bile salts-emulsify fats
  • Pancreatic lipase-digest
    • Pancreatic co-lipase-facilitate digestion
  • Absorption in small intestins
  • Resynthesized as chylomicron
  • DOES NOT ENTER PORTAL VEin
    • enters lacteals-->lymphatics

6

Triglycerides are digested by and into?

  • Lipase/colipase
  • Monoglycerides
  • free fatty acids

7

Key enzymes in lipid digestion

Lipase

Colipase

Prophospholipase-A2

Cholesterol Esterase

8

Bile Salts

  • amphipathic molecules
    • Polar/hydrophilic-water
    • Nonpolar/Hydrophobic-Lipids
  • Coat lipids to emulsify

9

Digestion & Absorption of Fats: Steps

  • 1)Bile salts from liver coat fat droplets
  • 2)Pancreatic Lipase and colipase breakdown fats into monoglycerides and Fattyacids stored in micelles
  • 3a)Monoglycerides and FAs move out of micelle and enter cell by difusion
    • MVM-FABP
  • 3b) Cholesterol is transported into cells by a membrane transporter=NPC1L1 (inhibited by Ezetimibe)
  • 4) absorbed fats combine with cholesterol and proteins in the intestines to form chylomicrons
    • series of apolipoproteins
  • 5) Chylomicrons released into lymphatic system by exocytosis
  • EXCEPTION:
    • Chylomicron-mediated fat transport is for MCFA
      • water soluble 
      • pass through tight junction

10

Re-esterification of digested lipids by enterocytes

  •  

11

What is olestra: Olestra

  • Fat substitute
  • 6-8 fatty acids attached to sucrose
  • resistant to lipase digestion
  • too big to be reabsorbed
  • Food additivei n 1998

 

  • Original FDA warning label
    • abdominal cramping 
    • loose stools
    • inhibits the absorption of some vitamins and nutreints 
    • Vitamins A, D, E, and K have been added

 

  • Unabsorbed in small intestine--passes to colon
  • Colonic microflora metabolize
    • osmotic particles, intestinal gas, potential for diarrhea (anal leakage)
    • solution-diminish quantity ingested
  • Still forms micelles in GI Lumen
    • fat souble vitamins not absorbed
    • solution-supplement with extra fat soluble vitamins

12

Malabsorption of Fat causes

  • Bile salt deficiency
    • Fat soluble vitamin deficiency (A,D, E, K)
    • Steatorrhea
  • Obstruction of bile flow
    • cystic and bile ducts
  • Ileal resection
  • gallstones (Cholelithiasis)
  • Problems with:
    •  bile synethesis-hepatocytes
    • Enterohepatic circulation
  • Liver disease (Cirrhosis)

13

Fat Soluble Vitamin Deficiency

Deficiencies 

  • Vitamin A
    • night blindness
  • Vitamin D
    • decreased Ca2+ absorption 
    • osteoporosis
    • bone pain
    • fractures
  • Vitamin K
    • prolongs prothrombin time
    • purpura (bruising)
    • petechiae
      • red spots on skin
      • minute hemorrhage due to broken capillaries in the skin
  • Vitamin E
    • uncertain but may:
      • testicular atrophy
      • neurologic defects in children
      • antioxidant

14

Phases of Food Processing by GI tract

  • Cephalic Phase
  • Gastric Phase
  • Intestinal Phase (early and late)

15

Cephalic Phase

  • Chemical and mechanical digestion begins in the mouth 
    • mastication
  • Salivary Secretion 
    • autonomic control
    • softens and lubricates food
  • Chemical Digestion
    • salivary amylase
    • some lipase
  • Saliva contains protective agents
  • Deglutition(Swallowing( moves food from the mouth to the stomach
  • initiated by stimuli
    • activates PNS
    • small rise in plasma gastrin
  • neurohumoral factors increase:
    • salivary 
    • gastric
    • pancreatic secretions
  • Gallbladder contracts and sphincter of oddi relaxes
  • prepares stomach for food and digestion

16

Gastric Phase: fxn

  • Storage
    • stomach-stoes food and regulates passage into small intestine 
  • Digestion:
    • Stomach
      • secretion of acid, enzymes and signal molecules
      • chyme
  • Protection from bacterial invastion and autodigestion

17

What is the stimulus that initiates the gastric phase and cephalic phase

Gastric phase=food in stomach

Cephlaic-sight, smell, thought of food or food in the mouth

18

Intestinal Phase

  • Bicarb neutralizes gastric acid and inactivates remaining pepsin
  • Goblet cells
    • serete mucus
  • Bile
    • fat digestion
  • Digestive enzymes
    • Enteropeptidase (Aka enterokinase)
  • small intestine
    • most digestion
  • Large intestine:
    • reabsorbs salt and water
    • concentrates waste for excretion
    • Motility:
      • mass movment 
      • Defecatioin reflex
    • no digestion or absorption 

19

Transit time for a meal through the GI tract

  • Swallowing
    • seconds
  • Gastric passage
    • 1-4 hours
  • Small intesintal passage
    • 2-4 hours
  • Colonic motility
    • mixing by haustral contraction
  • Aboral movement @ 2-3 hr intervals by "mass movement
    •  or a few times a day
  • colonic passage
    • 48-72 hours