17. Digestion and Absorption of Lipids, Fluids and Electrolytes Flashcards
(24 cards)
Bile salts emulsify fats into what?
Colloidal form
Bile salts are known as what type of molecules?
Amphipathic
What is the function of pancreatic lipase?
Hydrolyse 1 & 3 bonds of TAG’s to yield monoglycerides and 2 FFA
What assists the function of pancreatic lipase?
Colipase
What molecules digest cholesterol esters and vitamin esters?
Pancreatic esterases
What is a micelle?
An aggregate of surfactant in a colloidal solution
How are micelle’s formed?
From substrates and products of fat formation and phospholipids
Stabilised by bile salts
What is the fate of micelles?
Diffuse slowly acrosse unstirred water layer ot enterocyte - present highly concentrated packets of fats to membrane
Where does absorption into enterocyte mainly occur?
Jejunum
How do lipid soluble contents of micelle cross membrane into cytosol?
Passive diffusion
What is the fate of bile salts after absorption of micelle contents?
Left outside the cell to form more micelles (95%)
Transport from terminal ileum, recycled to liver, gall bladder, “enterohepatic circulation”
How are short chain ionised FA’s absorbed?
Pass direct into bloodstream
What is the fate of most FFA’s and MG’s?
Re-esterified into TG’s in smooth ER, coated with phospholipids and protein in the Golgi to form chylomicrons
How do chylomicrons leave enterocytes?
Pinocytosis into lacteals to lymph and then eventually the bloodstream
Ho are TG’s cleared from the blood?
Lipoprotein on endothelial surface of capillaries; TG’s passively diffuse into cells like adipocytes
When are bile salts not absorbed?
Terminal ileum damaged or if resins given
What do drugs resemble, molecularly?
Weak acids or bases
What does the ratio of ionised and non ionised forms of drugs depend on?
pK and pH of environment
Henderson Hasselbach equation
How are non-ionised drugs absorbed?
Passive diffusion
Route for most drugs
How can water cross epithelial barriers? Where is this greatest?
Diffusion via transcellular and paracellular routes
Wherever villi biggest and epithelia leakiest (duodenum and upper jejunum)
Net flux = ?
Absorption - Secretion
How is sodium absorbed?
Passive diffusion (paracellular)
Cotransport with glucose and AA
Active transport
What are some common causes of diarrhoea?
Drugs
Toxins
Infectious agents
Foods/IBS
Anxiety
Explain osmotic factors role in in fluid accumulation of intestinal lumen
Faulty nutrient digestion and absorption
Cause increase in osmotic pressure and subsequent osmotic movement into lumen
