Digestion And Assimilation

Question 1

Review of the gastrointestinal tract

Answer 1

Digestive enzymes are released in the saliva, stomach, duodenum and pancreas
• Bile is secreted from the liver into the duodenum.
• Digestion (breakdown) of ingesta in carnivores happens in the proximal GIT
• Assimilation happens in the jejunum and ileum.

Question 2

Assimilation

Answer 2

the absorption and digestion of food or nutrients by the body or any biological system.

Question 3

Microvilli

Answer 3

Provide larger surface area

Apical surface of cells

Question 4

Trancellular

Answer 4

Through the cells
Thing come across the microvilli and into cells
Includes transportation such as simple diffusion, active transportat, facilitated diffusion and co-transport

Question 5

Paracellular

Answer 5

Between the cells

Through a space where the cells meet- lateral border of cell

Question 6

Baso lateral border

Answer 6

The border of the cell that is not the lateral or apical borders

Question 7

Tight junction

Answer 7

Permits water and ions to move via paracellular transportat

Question 8

Carbohydrate digestion

Answer 8

• Complex carbohydrates (starch, lactose, sucrose) from the diet are broken down enzymatically into monosaccharides glucose, fructose and galactose.

Question 9

Monosaccharide absorption

Answer 9

• Monosaccharides can be absorbed across the brush border
• Glucose and galactose are transported by the SGLUT-1 transporter
which employs co-transport of glucose and Na2+.
• Glucose and Na2+ re released into the cytoplasm of the enterocyte
• Na2+ and glucose is transported from the enterocyte to the blood by exchange with K+ through the GLUT-2 transporter establishing an osmotic gradient that promotes water absorption.
• Fructose enters the enterocyte by GLUT-5 transporter
• Relationship of glucose, Na2+ and water absorption has clinical significance for fluid therapy.

Question 10

brush border

Answer 10

A brush border (striated border or brush border membrane) is the microvilli-covered surface of simple cuboidal and simple columnar epithelium found in different parts of the body.

Question 11

enterocyte

Answer 11

a cell of the intestinal lining.

Question 12

Protein Digestion

Answer 12

Protein digestion begins in the stomach through the action of pepsin
• Proteins must be digested into smaller units, amino acids, di- or tri-peptides
• In most instances whole proteins cannot permeate the brush border because of tight junctions between the enterocytes
• One exception is the ability for the neonate to absorb immunoglobulins from colostrum to gain immunity post partum

Question 13

Describe the passage of protein through the body and its digestion

Answer 13

From the mouth it travels to the stomach where it meets HCL and pepsin
These denature and partially hydrolyse The protein
It then travels to the small intestine where it meets trypsin, chymotrypsin, aminopeptidase and carboxypeptidase
This breaker it down into small Pepsins and amino acids
In the intestinal lining the amino acids enter the blood via active transport

Question 14

Peptidases

Answer 14

are enzymes that cleave proteins
• There are different types of peptidases:
• Endopeptidases, e.g. pepsin, trypsin, elastase, they cleave internal peptide bonds
• Exopeptidases, e.g. carboxypeptidase and aminopeptidase, they cleave one amino acid from the end of the peptide

Question 15

Amino acid absorption

Answer 15

• Peptides are co-transported with Na2+ across the brush border of the small intestine into the enterocyte
• Na2+ uptake drives an osmotic gradient that aids absorption of water
• The transporter is specific to the charge of the amino acid
• Additional transporters are required to transfer amino acids from the enterocyte into the blood

Question 16

Absorption of di- and tri-peptides

Answer 16

• H+ co-transporter PepT1

* Di- and tri-peptides are digested within the enterocyte by cytoplasmic peptidases

Question 17

Fat Digestion

Answer 17

• Fat in the diet is typically neutral fat or triglyceride which are insoluble in water
• Bile emulsifies fat
• The fat lobules created by emulsification have a larger area for pancreatic lipases to act on
• Monoglycerides and fatty acids are produced and form micelles with bile acids.

Question 18

Lipid absorption

Answer 18

• Monoglycerides and fatty acids are produced and form micelles with bile acids. These can be absorbed into enterocytes by simple diffusion across the membrane or using a fatty acid transporter.
• The monoglycerides enter the endoplasmic reticulum and Golgi of the enterocyte and get packed into chylomicrons ( a complex of triglyceride, cholesterol and other lipids).
• From here vesicle are formed by the Golgi budding. These vesicles are exocytosed at the cell surface.
• Chylomicrons enter the lymph lacteal rather than entering the blood stream directly.

Question 19

Water absorption

Answer 19

Diffuse through enterocytes and between enterocytes due to osmotic gradient generated by movement of Na2+
• May be against a concentration gradient between the lumen of the intestine and the blood