3.3.2: Absorption of products of digestion

Question 1

what is the name of the inner lining of the ileum

Answer 1

mucosa

Question 2

describe the structure of the mucosa

Answer 2

there are folds in the mucosal tissue called villi, there are further folds in the epithelial cell membrane which are called the microvilli.

Question 3

how do the villi and microvilli increase absorption efficiency in the ileum

Answer 3

Increased surface area

Question 4

how does circulating blood in the ileum increase absorption efficiency in the ileum

Answer 4

maintains a diffusion gradient

Question 5

how do muscle layers in the ileum increase absorption efficiency in the ileum

Answer 5

maintains a diffusion gradient (ensures molecules stay in contact with villi)

Question 6

How does a thin gut wall in the ileum increase absorption efficiency in the ileum

Answer 6

short diffusion pathway and so increased rate of absorption

Question 7

Where do the products of protein and carbohydrate digestion go into when absorbed into the ileum lumen

Answer 7

capillary network

Question 8

Where do the products of lipid digestion go into when absorbed into the ileum lumen

Answer 8

lacteal

Question 9

List 3 mechanisms involved in the absorption of the products of digestion in the ileum

Answer 9

diffusion
active transport
osmosis

Question 10

Describe and explain the 5 steps of lipid absorption in the ileum

Answer 10

1 - Fatty acids and monoglycerides leave micelles and enter epithelial cells of mucosa by simple diffusion
2 - Fatty acids and monoglycerides form back into triglycerides
3 - In the Golgi, triglycerides combine with protein to form chylomicrons - these are soluble in water
4 - Chylomicrons are released from epithelial cells by exocytosis and enter the lacteal
5 - Chylomicrons in the lymph are transported to the thoracic duct and enter the bloodstream

Question 11

Describe and explain the 4 steps of glucose/amino acid absorption in the ileum

Answer 11

1 - Sodium and Potassium ion pump actively transports sodium ions out of the epithelial cell into the blood to create a steep concentration gradient. Potassium ions are actively transported into the cell via antiporter
2 - As there is a low conc. of sodium ions in the epithelial cell compared to the ileum lumen, a conc. gradient is created
3 - Sodium ions diffuse into epithelial cell from ileum lumen down conc. gradient pulling glucose molecules in with it (indirect active transport) via symporter
4 - As there is a high conc. of glucose now in the epithelial cell, facilitated diffusion of glucose occurs out of epithelial cell into blood down conc gradient via glucose uniporter

Question 12

Describe the process of assimilation of glucose from the ileum to the liver

Answer 12

when there is excess amino acids in the ileum, the hepatic portal vein transports glucose from ileum to liver. Excess glucose converted into glycogen and stored in the liver. Some glucose is also transported to other tissues from the liver

Question 13

Describe the process of assimilation of amino acids from the ileum to the liver and the deamination of amino acids in the liver

Answer 13

like glucose, excess amino acids in the ileum are transported into the liver via the hepatic portal vein. In the liver, the amine group and a hydrogen atom (ammonia) is removed from the amino acid and converted into urea. The leftover carbohydrate is used for respiration and is in excess is stored as fat

Question 14

Why can’t excess amino acids as ammonia be stored in the liver

Answer 14

because ammonia is toxic to cells