Lipid-Digestion & Absorption

Question 1

What increases surface area for absorption?

Answer 1

• Crypt
• Villi
• Microvilli

Question 2

Stem Cells of crypt

Answer 2

• produce new absorptive epithelial cells to replace lost cells

Question 3

Lacteal

Answer 3

transport fat to lymph

Question 4

What can lead to malabsorption of lipids?

Answer 4

• Bile deficiency
• Pancreatic Insufficiency

Question 5

Digestion and absorption of lipids

Answer 5

• 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

Question 6

Triglycerides are digested by and into?

Answer 6

• Lipase/colipase
• Monoglycerides
• free fatty acids

Question 7

Key enzymes in lipid digestion

Answer 7

Lipase

Colipase

Prophospholipase-A2

Cholesterol Esterase

Question 8

Bile Salts

Answer 8

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

Question 9

Digestion & Absorption of Fats: Steps

Answer 9

• 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

Question 10

Re-esterification of digested lipids by enterocytes

Answer 10

*

Question 11

What is olestra: Olestra

Answer 11

• 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

Question 12

Malabsorption of Fat causes

Answer 12

• 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)

Question 13

Fat Soluble Vitamin Deficiency

Answer 13

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

Question 14

Phases of Food Processing by GI tract

Answer 14

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

Question 15

Cephalic Phase

Answer 15

• 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

Question 16

Gastric Phase: fxn

Answer 16

• 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

Question 17

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

Answer 17

Gastric phase=food in stomach

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

Question 18

Intestinal Phase

Answer 18

• 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

Question 19

Transit time for a meal through the GI tract

Answer 19

• 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