3.3 Digestion And Absorption

Question 1

Oesophagus

Answer 1

Thin epithelial layer
No villi
Glands produce mucus - lubricate food
Thick muscular layer
Muscles propel food via peristalsis

Question 2

Duodenum

Answer 2

Pancreas - pancreatic juice - enzyme
Liver - bile - contains bile salts which aid lipid digestion and sodium hydrogen carbonate to neutralize acid
Low villi

Question 3

Illeum and jejunum

Answer 3

Mucosa and sub-mucosa contain glands which secrete enzymes mucus and alkali
Folding of mucosa, villa and micro villa increase SA
Peristalsis

Question 4

Large intestine

Answer 4

Caecum
Appendix
Colon
Rectum
Water absorbed forms semi solid faeces
Mucosa contain villi but no microvilli
Glands secrete mucus
Anal sphincter - releases faeces

Question 5

Carbohydrate digestion - amylase

Answer 5

Produced in salivary glands and pancreas
Secreted in duodenum and buccal cavity
Catalysts the break down of starch into disaccharides by hydrolises reactions which beak down alternative glyocosidic bonds

Question 6

Carbohydrate digestion - membrane bound disaccharidase

Answer 6

Enzymes attached to cell membranes of epithelial cells
Produced in the walls of the illeum
lining the ileum
Breaks disaccharides into monosaccharides

Question 7

Absorption of monosaccharides

Answer 7

1. Na+ actively transported out of epithelial cells into the blood via Na-K pump
2. High conc of Na+ in lumen than in epithelial cells
3. Na+ diffuse into epithelial cells down conc gradient coupled with a glucose or a-acid through a protein carrier (cotransporter)
4. Glucose passes into blood plasma via facilitated diffusion

Question 8

Protein digestion

Answer 8

Endopeptidase - hydrolyses peptide bonds within proteins
Pepsin, trypepsin, chymotrepsin

Exopeptidase - hydrolyses peptide bonds at the end of proteins

Dipeptidase - hydrolyses peptide bonds between 2 amino acids - cell membrane of epithelial cells

Question 9

Digestion of lipids

Answer 9

Bile salts - produced by liver, emulsification occurs in intestinal lumen
Emulsifies lipids to increase SA so lipase can digest faster
Pancreatic Lipase - prod by pancreas, secreted in s intestine
catalyses the breakdown of lipids in monoglycerides and fatty acids - hydrolyses of ester bonds- products attach to bile salts to form micelles - easier diffusion

Question 10

Absorption of lipids

Answer 10

Fatty acids and monoglycerides enter cell via diffusion
They resynthesise into triglycerides in the endoplasmic reticulum
The are repackaged with cholesterol and phospholipids in protein coated chylomicrons
These are Incapsuled in a vesicle which are released through the cell membrane via exocytosis in the lymphatic system