GIT Physiology and Metabolism - Lecture 6 Flashcards
How much crude protein should a 40kg pig growing 1kg/day eat?
0.25kg/day
How much starch/sugars should a 40kg pig growing 1kg/day eat?
0.75kg/day
How much fats/ oils should a 40kg pig growing 1kg/day eat?
0.15kg/day
How much water should a 40kg pig growing 1kg/day eat?
5L/day
How much food should a 40kg pig growing 1kg/day eat?
1.6kg DM/day
How much of a 1.6kg ration given to a 40kg pig is digested in the GIT?
1.3kg
How is ‘apparent digestibility calculated?
(amount ingested - amount excreted) divided by amount ingested x 100
Why is reabsorption of water and salts associated with secretory processes critical?
for the maintenance of water balance and systemic mineral and pH homeostasis
Which mineral anion is primarily responsible for blood and acid base balance and is potentially lost in large amounts in diarrhoea?
Bicarbonate
What secretions into the small intestine contain bicarbonate?
bile, pancreatic juice and intestinal juice
Why is reabsorbing digestive juices important?
failure to reabsorb could lead to diarrhoea and dehydration and would also waste the metabolites supplied in secretions
What are the sites of protein digestion?
Stomach, SI lumen and SI brush border
What happens when pepsinogen is exposed to HCL?
it is activated to pepsin
How to HCL and pepsin aid in the digestion of proteins?
HCL denatures them and pepsin hydrolyses them into large polypeptides
What is secreted by Pancreatic Acinar cells?
inactive forms of trypsin, chymotrypsin and carboxypeptidase
How is trypsinogen activated?
Enzymes in brush border of SI activates it, which also activates the other enzymes that hydrolyse proteins
What are the brush border enzymes?
aminopeptidase, carboxypeptidase, dipeptidase
What are the two types of bonds between sugar units in carbohydrates?
alpha and beta bonds
Why are some carbohydrates indigestible by mammals?
alpha bonds (all on same side) are able to be hydrolysed in the SI. beta bonds cannot be hydrolysed , but can be fermented by microbes.
Where can carbohydrates be digested?
mouth and stomach (pigs and humans only), SI lumen and SI brush border membrane
How are carbs digested in the mouth?
salivary glands release amylase in saliva which hydrolyse bonds between glucose units
How are carbs digested in the stomach?
salivary amylase continues to hydrolyse starch until it is inactivated by HCL
How are carbs digested in the small intestine?
Pancreatic acini cells secrete pancreatic juice containing amylase to hydrolyse starch and oligosaccharides
how are carbs digested in the small intestine brush border membrane?
brush border enzymes (anchored to cell membrane)
- Maltase hydrolyses maltose and maltotriose
- lactase hydrolyses lactose (in young animals only)
- sucrase/ sucrase-isomaltase and maltase-glucoamylase hydrolyse oligosaccharides
where is lactose digested in adult animals?
fermented in the large intestine, rather than the small intestine like young animals
Where do nutrients go once they are absorbed through the membrane in the small intestine?
diffuse across interstitial space and into capillaries, where they enter the superior mesenteric vein, then the hepatic portal vein and then the liver
Where are bile salts and B12 absorbed?
the ileum
What is absorbed in the jejunum?
amino acids, di and tripeptides, monosaccharides, B group vitamins
What happens when triacylglycerides are exposed to aqueous solutions?
they are insoluble, so they form droplets
How do bile salts affect fat droplets?
bile salts with polar and non-polar parts absorb onto the surface of fat droplets and promote emulsification into micelles in the SI lumen. This creates high SA to volume and increase efficiency of lipase on fat
What two routes can minerals be absorbed by?
- intracellular route
2. Paracellular route
What is the intracellular route of absorption?
absorbed directly through the cell
what is the paracellular route?
absorbed via gaps between cells
What minerals are absorbed via the intracellular route?
- Na+, K+, Cl- and bicarbonate.
- also Ca2+, Mg2+, Fe2+, PO4(3-) and SO3(2-)
What minerals are absorbed via the paracellular route?
- most of Ca2+ and Mg2+
What is the primary mechanism to achieve and control mineral homeostasis?
excretion via the kidneys
What regulates the uptake of Calcium?
Calcitriol (Vitamin D3)
where is iron absorbed?
duodenum
Why is the absorption of iron tightly controlled?
excess iron is toxic, especially to liver parenchymal cells
How is iron regulated when iron stores are saturated?
when plasma transferrin is saturated, less transferrin is produced by the liver. reduced iron (Fe2+) crosses the cell membrane and is bound to apoferritin as Fe3+ where it migrates to top of villus and is sloughed off
How is iron regulated when iron stores are depleted?
rreduced iron (Fe2+) crosses cell membrane and moves into blood capillaries where its bound to unsaturated transferrin which allows transport to tissues
How does infection with salmonella (salmonelliosis) affect digestion and absorption?
organism multiplies in enterocytes and invades lamina propria. damage to mucosa results in villous atrophy, malabsorption and osmotic and inflammatory diarrhoea. Once past lamina propria, can enter circulation and cause systemic infection
How does infection with Giardia (Giardiasis) affect digestion and absorption?
increases permeability of enterocytes and decreases activity of SI brush border enzymes, especially lipase, some proteases and disaccharidases. Decreases overall absorptive area in SI leading to impaired intake of water, electrolytes, etc. resulting in secretory and osmotic diarrhoea
