Gastric physiology 2 Flashcards
Most abundant substance in chyme? % of water reabsorption in small intestine? Which portion absorbs the most? % of fluid reabsorbed?
Water
80%
Jejunum
98%- 2% excreted in stools
Most abundant solute in chyme? Actively transported from lumen in cell membranes where?
Sodium
Of the ileum and jejunum
Method of K+ reabsorption? Diarrhoea can result in loss of K+ known as what? Contents in colon are what?
Passive diffusion
Hypokalaemia
Iso-osmotic
Method for Cl- reabsorption?
Cl- is actively reabsorbed in exchange for bicarbonate resulting in intestinal contents becoming more alkaline
What is the absorptive state? What is post absorptive state?
Ingested nutrients enter the blood from the GI tract. Some provide energy requirements and remainder added to body’s energy stores
GI tract is empty- body’s stores must provide energy
3 main important fatty acids? Lipids in ingested food aggregate into what in the upper portion of the stomach? Converted into small droplets via what process?
Palmitic(most abundant,) stearic and oleic acid.
Large lipid droplets
Emulsification
What 2 things are needed for emulsification?
1) Mechanical disruption of large into small droplets- provided by GI motility
2) Emulsifying agent- phospholipids in food and bile salts in bile
Bile salts and phospholipids are what? Non-polar portion associated with what in lipid droplet? Polar portions go where?
Amphipathic
Non-polar interior of lipid droplet
Exposed at water surface- repel other lipid droplets coated in agents
Coating of lipid droplets in emulsifying agents impairs accessibility of what? Pancreas secretes what protein to overcome this? This binds to what?
Droplet for lipase
Colipase- binds to lipid droplet surface and lipase too
What are the small lipid droplets called? These consist of what?
Micelles
Bile salts with fat soluble vitamins and cholesterol, fatty acids, monoglycerides and phospholipids clustered together with polar ends outwards and non-polar ends inwards
It is not the micelle which is absorbed but what is? Fatty acids and monoglycerides recombined where in intestinal epithelial cells? Decreases fatty acid concentration where?
The individual lipid molecules from the micelles
SER
In cytoplasm- diffusion gradient for molecules into cell from intestinal lumen
Fat droplets in epithelial cells processed at what organelle into what? Fuse with membrane and enter interstitial fluid how? Enter where?
Golgi apparatus– chylomicrons
By exocytosis
Lacteals- empties into systemic veins
Fatty acids of chylomicrons are released where? Diffuse into where and combine with what?
Within adipose-tissue capillaries by endothelial lipoprotein lipase
Into adipocytes and combine with alpha-glycerol phosphate to form triglycerides
Why is glucose essential for triglyceride synthesis in adipocytes?
Don’t have enzyme for phosphorylation of glycerol to alpha glycerol- only produced by reducing dihydroxyacetone phosphate from glycolysis
3 main sources of fatty acids for triglyceride synthesis? 2) and 3) require what enzyme to released fatty acids from circulating triglycerides?
1) Glucose entering adipose tissue and is broken down
2) Glucose used in liver to form VLDL triglycerides- transported in blood and taken up by adipocytes
3) Ingested triglycerides transported in chylomicrons and taken up by adipocytes
Lipoprotein lipase
Examples of fat-soluble vitamins? Follows pathway for what absorption? Where does this occur?
Vitamins A, D, E and K
Fat absorption
In the ileum
Examples of water soluble vitamins? Absorbed by what 2 ways and where?
Vitamin C and B
Diffusion/ mediated transport in the jejunum.
How is vitamin B-12 absorbed? It is needed for what and what is it?
It is bound to the protein intrinsic factor– bind to specific sites on epithelial cells in lower portion of the ileum– absorbed via endocytosis.
It’s large and charged- needed for erythrocyte formation
Where does digestion of protein mainly occur? Amount needed by adult per day? Only what form of protein is found in the proteins we utilise?
In the duodenum
40-50g
L-forms
Chief cells in stomach release what which is activated by the low luminal pH? Pepsinogen I found only where? Pepsinogen II found where?
Pepsinogen activated into pepsin
In HCl secreting region (mainly in body)
In the pyloric region
Pepsins hydrolyse the bonds between what? pH in duodenal cap? pH in rest of the duodenum?
Aromatic amino acid and a second amino acid
2-4
6.5
Smaller peptides further fragmented by what in small intestine? Final digestion occurs where?
Endopeptidases and exopeptidase
In intestinal lumen, brush border and within the cell
Only what form of carbohydrate is used in metabolism? Starch first degraded by what in the mouth? Enzyme catalysing starch digestion in SI?
The D-isomers.
Ptyalin- the alpha amylase of saliva
Pancreatic alpha amylase
End products of carbohydrate digestion?
Disaccharide maltose, trisaccharide maltotriose, larger polymers of glucose with alpha 1-4 bonds and alpha-limit dextrin- branched polymers of around 8 units.
Oligosaccharidases at outer portion of membrane of microvilli? Hexoses and pentoses rapidly enter capillaries into where?
Maltase, lactase, sucrase, alpha-limit dextrinase.
Hepatic portal vein
Glucose and sodium share the same what in the intestine? What glucose isomer is transported from the lumen by the SGLT?
Sodium-glucose co transporter (SGLT).
Galactose
Fructose uses what carrier in the intestine? Transported by what method? These monosaccharides leave epithelial cells and enter where by how?
Glucose transporter (GLUT) Facilitated diffusion Leave the epithelial cells and enter interstitial fluid by facilitated diffusion via GLUT proteins in basolateral membranes of epithelial cells
Where do carbs go once absorbed? Liver can convert glucose into what also? Also occurs where too?
Enter hepatic portal vein and liver- converted into glucose. Broken down by skeletal muscle in absorptive phase/ converted into glycogen to be stored in liver/ muscle
Alpha-glycerol phosphate and fatty acids- used to make triglycerides
Adipose-Tissue cells (adipocytes)
Most of fat made from glucose in liver is packaged into what? Synthesis of this similar to that of what by intestinal mucosal cells? VDLs hydrolysed mainly to what?
Lipoproteins- VLDL’s
Chylomicrons
Monoglycerides and fatty acids by lipoprotein lipase as them being big mean they don’t readily penetrate capillary walls
Lipoprotein lipase is located where? Fatty acids from lipoprotein lipase go where? Some of monoglycerides go where?
On the blood-facing surface of capillary endothelial cells- especially those in adipose tissue
From capillaries into adipocytes- combine with alpha glycerol phosphate to form triglycerides
Taken up by adipocytes where enzymes reattach fatty acids to two available carbon atoms/ some go to liver to be metabolised
Glycogen stores sufficient to last for how long? Lipid stores to last for how long? Tissue protein only significant in times of what?
12 hours
3 months
Prolonged starvation
Fuels used by the brain? By muscle? Used by the liver? Why can’t the liver use ketone bodies?
Ketone bodies and glucose
Glucose, ketone bodies, triacylglycerol and branched chain amino acids
Amino acids, fatty acids, glucose and alcohol.
Extrahepatic tissue doesn’t have enzyme thiolase
Fuels sued by the kidneys? Used by the small intestine? Used by the large intestine?
Glucose, ketone bodies(cortex) and only glucose(medulla)
Ketone bodies, glutamine
Short-chain fatty acids, glutamine
Where is vitamin A stored? Functions of it? Sources?
In Ito cells in the space of Disse of the liver.
Cellular growth, vision, healthy skin, reproduction, embryonic development, maintenance of mucous membranes used in lymphocyte production
Liver, dairy products, oily fish, margarine
Deficiency in Vitamin A leads to what?
Night blindness, xerophthalmia, growth retardation, impaired hearing, taste and smell, prone to infection
Functions of vitamin C? Sources? Deficiency leads to what?
Synthesis of collagen, neurotransmitters and carnitine, antioxidant ability and absorption of non-harm iron
Citrus fruits, green veg, potatoes, kidney
Initial signs= non-specific, weakness, bleeding gum, hyperkeratosis, scurvy signs
Function of B vitamins? Found where? Deficiency leads to what?
Important in cell metabolism and energy production
Fish, poultry, meat and eggs
Pernicious anaemia
Liver storage prevents vitamin D deficiency for how long? How is vitamin D3 formed? Vitamin D2 from where?
3-4 months
Action of UV from cholesterol on cholesterol derivative in skin
From plants
How is vitamin D metabolised? Functions of this active hormonal form?
Hydroxyl groups are added first in liver, then in certain kidney cells– 1,25-(OH)2D
Stimulate intestinal absorption of Ca2+ and phosphate
Consequences of vitamin D deficiency?
Decreased intestinal and plasma Ca2+– parathyroid hormone released by parathyroid glands– resorption of bone osteoclasts= osteoporosis
Increases Ca2+ reabsorption in kidneys– decreased excretion
Decreases reabsorption of phosphate ions in kidneys
Main function of vitamin E? Main function of vitamin K?
Antioxidant
Needed for clotting factor production (10,9,7 and 2) in liver
What is giardiasis?
Infection which causes villi to atrophy reducing absorption capacity
What is coeliac disease? Leads to what?
Auto-immune condition whereby gluten is partially degraded causes immune system to attack villi and microvilli resulting in loss of brush border– decreases nutrient absorption
Prevent vitamin D absorption– less Ca2+– osteoporosis
Cystic fibrosis is autosomal recessive mutation in what protein?
Cystic fibrosis transmembrane conductance regulator (CFTR)
The exocrine portion of the pancreas secrete what? Into where?
HCO3- and a number of digestive enzymes e.g. lipase, colipase and alpha amylase
Into ducts that converge into pancreatic duct which joins common bile duct from liver before entering duodenum at duodenal papillae
What are pancreatic enzymes released by? HCO3- released by what? H+ from H2CO2 dissociation exchanged for what?
Gland cells at pancreatic end of duct system
Epithelial cells lining ducts through Cl-/HCO3- exchanger
Na+ on basolateral side of cell
Energy for HCO3- secretion from pancreas comes from where? Why don’t Cl- accumulate?
Na+/ K+ and ATPase pumps on basolateral membrane
These ions are recycled into lumen through the CFTR
What 2 things move into pancreatic ducts due to electrochemical gradient by CL- movement through CFTR? What builds up in gland cells in cystic fibrosis?
Na+ and H2O
CL- because CFTR is faulty- less HCO3- moves into duct and small intestine, so at low pH from stomach enzymes aren’t active– less digestion and absorption
In cystic fibrosis, lack of normal water movement leads to what?
A thickening of pancreatic secretion– clogging of pancreatic ducts.
Pancreatic enzymes begin clogged in ducts– unable to produce them eventually
What are cystic fibrosis sufferers given?
Pancreatic enzyme replacements to aid their digestion and absorption
