GIT Physiology and Metabolism - Lecture 6

Question 1

How much crude protein should a 40kg pig growing 1kg/day eat?

Answer 1

0.25kg/day

Question 2

How much starch/sugars should a 40kg pig growing 1kg/day eat?

Answer 2

0.75kg/day

Question 3

How much fats/ oils should a 40kg pig growing 1kg/day eat?

Answer 3

0.15kg/day

Question 4

How much water should a 40kg pig growing 1kg/day eat?

Answer 4

5L/day

Question 5

How much food should a 40kg pig growing 1kg/day eat?

Answer 5

1.6kg DM/day

Question 6

How much of a 1.6kg ration given to a 40kg pig is digested in the GIT?

Answer 6

1.3kg

Question 7

How is ‘apparent digestibility calculated?

Answer 7

(amount ingested - amount excreted) divided by amount ingested x 100

Question 8

Why is reabsorption of water and salts associated with secretory processes critical?

Answer 8

for the maintenance of water balance and systemic mineral and pH homeostasis

Question 9

Which mineral anion is primarily responsible for blood and acid base balance and is potentially lost in large amounts in diarrhoea?

Answer 9

Bicarbonate

Question 10

What secretions into the small intestine contain bicarbonate?

Answer 10

bile, pancreatic juice and intestinal juice

Question 11

Why is reabsorbing digestive juices important?

Answer 11

failure to reabsorb could lead to diarrhoea and dehydration and would also waste the metabolites supplied in secretions

Question 12

What are the sites of protein digestion?

Answer 12

Stomach, SI lumen and SI brush border

Question 13

What happens when pepsinogen is exposed to HCL?

Answer 13

it is activated to pepsin

Question 14

How to HCL and pepsin aid in the digestion of proteins?

Answer 14

HCL denatures them and pepsin hydrolyses them into large polypeptides

Question 15

What is secreted by Pancreatic Acinar cells?

Answer 15

inactive forms of trypsin, chymotrypsin and carboxypeptidase

Question 16

How is trypsinogen activated?

Answer 16

Enzymes in brush border of SI activates it, which also activates the other enzymes that hydrolyse proteins

Question 17

What are the brush border enzymes?

Answer 17

aminopeptidase, carboxypeptidase, dipeptidase

Question 18

What are the two types of bonds between sugar units in carbohydrates?

Answer 18

alpha and beta bonds

Question 19

Why are some carbohydrates indigestible by mammals?

Answer 19

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.

Question 20

Where can carbohydrates be digested?

Answer 20

mouth and stomach (pigs and humans only), SI lumen and SI brush border membrane

Question 21

How are carbs digested in the mouth?

Answer 21

salivary glands release amylase in saliva which hydrolyse bonds between glucose units

Question 22

How are carbs digested in the stomach?

Answer 22

salivary amylase continues to hydrolyse starch until it is inactivated by HCL

Question 23

How are carbs digested in the small intestine?

Answer 23

Pancreatic acini cells secrete pancreatic juice containing amylase to hydrolyse starch and oligosaccharides

Question 24

how are carbs digested in the small intestine brush border membrane?

Answer 24

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

Question 25

where is lactose digested in adult animals?

Answer 25

fermented in the large intestine, rather than the small intestine like young animals

Question 26

Where do nutrients go once they are absorbed through the membrane in the small intestine?

Answer 26

diffuse across interstitial space and into capillaries, where they enter the superior mesenteric vein, then the hepatic portal vein and then the liver

Question 27

Where are bile salts and B12 absorbed?

Answer 27

the ileum

Question 28

What is absorbed in the jejunum?

Answer 28

amino acids, di and tripeptides, monosaccharides, B group vitamins

Question 29

What happens when triacylglycerides are exposed to aqueous solutions?

Answer 29

they are insoluble, so they form droplets

Question 30

How do bile salts affect fat droplets?

Answer 30

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

Question 31

What two routes can minerals be absorbed by?

Answer 31

1. intracellular route | 2. Paracellular route

Question 32

What is the intracellular route of absorption?

Answer 32

absorbed directly through the cell

Question 33

what is the paracellular route?

Answer 33

absorbed via gaps between cells

Question 34

What minerals are absorbed via the intracellular route?

Answer 34

- Na+, K+, Cl- and bicarbonate. | - also Ca2+, Mg2+, Fe2+, PO4(3-) and SO3(2-)

Question 35

What minerals are absorbed via the paracellular route?

Answer 35

- most of Ca2+ and Mg2+

Question 36

What is the primary mechanism to achieve and control mineral homeostasis?

Answer 36

excretion via the kidneys

Question 37

What regulates the uptake of Calcium?

Answer 37

Calcitriol (Vitamin D3)

Question 38

where is iron absorbed?

Answer 38

duodenum

Question 39

Why is the absorption of iron tightly controlled?

Answer 39

excess iron is toxic, especially to liver parenchymal cells

Question 40

How is iron regulated when iron stores are saturated?

Answer 40

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

Question 41

How is iron regulated when iron stores are depleted?

Answer 41

rreduced iron (Fe2+) crosses cell membrane and moves into blood capillaries where its bound to unsaturated transferrin which allows transport to tissues

Question 42

How does infection with salmonella (salmonelliosis) affect digestion and absorption?

Answer 42

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

Question 43

How does infection with Giardia (Giardiasis) affect digestion and absorption?

Answer 43

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