6. Chyme pancreas & liver Flashcards Preview

ESA 3- GI system > 6. Chyme pancreas & liver > Flashcards

Flashcards in 6. Chyme pancreas & liver Deck (13)
Loading flashcards...
1
Q

describe and explain the osmotic and pH status of chyme as it enters duodenum

A
  1. hypertonic:
    • initial digestion of food creates solutes
    • stomach wall largely impermeable to water so water cannot move in to dilute chyme
  2. acidic: low pH due to gastric HCl secretion
2
Q

why must chyme release from stomach be regulated

A

Duodenum is relatively permeable to water so hypertonic chyme draws in water from ECF/circulation and becomes isotonic.

If chyme release not controlled, risk of overwhelming duodenum - would cause massive pull of water from ECF causing decreased blood volume and BP

3
Q

which hormones does the duodenum release in response to chyme presence and what is their effect

A

Duodenum secretes into blood:

  1. SECRETIN (in response to low chyme pH)
    - stimulates pancreas duct cells to release aqueous HCO3- component of pancreatic secretion… increases pH of chyme
  2. CCK (in response to hypertonicity, small peptides and fats in chyme)
    - stimulates pancreas acini to secrete digestive enzymes… continues digestion
    - stimulates gallbladder contraction and sphincter of Oddi relaxation… bile release… continues digestion
4
Q

why enzymes are released by pancreatic acini

A
  1. amylases (active)
  2. lipases (active)
  3. proteases (inactive) - only activated inside duodenum (by low pH and enteropeptidase) to prevent pancreatic auto-digestion
5
Q

which factors stimulate pancreatic exocrine secretion

A
  1. duodenal hormones: secretin and CCK

2. autonomics: sympathetics inihibit, parasympathetics (vagus n.) stimulate

6
Q

describe the arterial supply to the pancreas

A
  • branches of splenic a.

- branches of superior and inferior pancreatico-duodenal aa. (from gastroduodenal and superior mesenteric aa.)

7
Q

what is the main function of liver in digestion

A

secretes BILE (stored in liver) into duodenum - key role in emulsifying lipids so that they can be readily digested by pancreatic lipases

8
Q

hepatocytes in which acinar zones are more susceptible to toxic and ischaemic damage

A

Z1 - toxic

Z3 - ischaemic

9
Q

what are the 2 main components of bile

A
  1. alkaline juices - secreted by bile duct cells
  2. bile acids and pigments - hepatocytes produce bile acids which are then conjugated with amino acids (eg glycine) to form bile salts (as acids aren’t always soluble at duodenal pHs - functionally useless)
10
Q

what is the role of bile salts in lipid digestion

A
  1. bile salts (amphipathic structure allowing them to act at oil/water inferface) emulsify lipids into smaller units/droplets to increase surface area (instead of large globules)…
  2. allows lipases to catabolise lipids…
  3. bile salts then create micelles with products of lipid breakdown (cholesterol, monoglyerides, free fatty acids) to transport these towards enterocytes…
  4. lipids then diffuse into enterocytes whilst bile salts remain in gut
11
Q

what happens to bile acids after having transported lipid products

A

are reabsorbed in terminal ileum and returned to liver in portal blood (entero-hepatic circulation) for recycling

12
Q

what happens to lipid molecules inside enterocytes

A

i. are re-esterified back to TAGs, phospholipids and cholesterol, and packed with apoproteins to create chylomicrons…
ii. chylomicrons exocytosed from basolateral membrane into lacteals… enter lymphatic capillaries

13
Q

what is steatorrhoea

A

appearance of undigested fat in faeces (pale, floating, foul smelling) as a result of inadequate secretion of bile acids/salts or pancreatic lipases