6. Human Physiology : 6.1 Digestion

Question 1

Explain the process of the digestive system.

Answer 1

1. Mouth : chew + saliva (enzymes)
2. Oesophagus: peristalsis
3. Stomach : digestion + acid
4. Small intestine:
   - food enters through duodenum
   - acid need to be neutralised so enzymes can function properly
   - digestion completed
   - absorbed by ileum
5. Large intestine:
   - liquid mixture of undigested substances
   - water, vitamins reabsorbed
   - faeces formed and stored in rectum

Question 2

What happens in peristalsis?

Answer 2

Peristalsis:

1. Longitudinal and circular muscles contract and relax in an opposite way
2. The longitudinal muscle contracts to widen the lumen of the alimentary canal while the circular muscle contracts to constrict the lumen

Definition: peristalsis is a wave of contraction and relaxation of the longitudinal and circular muscles of the alimentary canal to move the food contents along.

Question 3

What happens in the small intestine?

Answer 3

1. Food enters through duodenum
2. Acid passing needs to be neutralised so that enzymes that digest lipids and fats could function properly
3. At the end of the small intestine. digestion complete
4. Digested products have been absorbed by ileum
5. Where most absorption takes place

Question 4

What happens in the large intestine?

Answer 4

1. Liquid mixture of undigested material and digestive juices enter
2. Water, vitamins made by bacteria are reabsorbed
3. The anaerobic bacteria in the large intestine can stir up undigested polysaccharides to produce energy
4. Faeces is formed and stored in rectum

Question 5

What are the functions of pancreas, liver and the gallbladder?

Answer 5

Pancreas: secretes amylase, lipase and protease into small intestine

Liver: secretes bile to emulsify the liquids

Gallbladder: stores bile

Question 6

What are the three parts of the small intestine?

Answer 6

duodenum
jejunum
ileum

Question 7

What are the tissue layers of the small intestine? Explain.

Answer 7

Serosa: the outermost layer in contact with the body

Longitudinal muscles : peristalsis to move digested food forward

Circular muscles : same as above

Submucosa: connective tissue that supports the mucosa and contains large arteries and veins which give rise to capillary bed to mucosa

Mucosa: innermost layer of the tube forming a soft lining comprising of epithelium, connective tissue and smooth muscle

Question 8

What is the point of digestion?

Answer 8

1. Large food molecules are broken down into smaller units
2. Smaller units are broken down into monomers that can easily be absorbed, pancreas secrete enzymes into wall of intestine for this process

Question 9

What are the different types of enzymes produced in the pancreas and what do they do?

Answer 9

1. Amylase: breaks down starch into maltose
2. Endopeptidase: breaks down proteins into smaller polypeptides
3. Lipase, phospholipase: breaks down lipids and phospholipids into fatty acids and glycerol, for phospholipids, phosphate is also produced

Once these enzymes are produced, the pancreatic duct to the duodenum releases the enzymes into the lumen of small intestine

Question 10

But molecules are still too large, so more enzymes produced in the intestinal epithelial cells. What are these enzymes?

Answer 10

Nucleases: breaks down dna and rna

Maltase: breaks down maltose into glucose

Lactase: lactose into glucose and galactose

Exopeptidases: remove a single amino acid from the end of the polypeptides

Dipeptidases: break down a dipeptide into two amino acids

Question 11

What happens in the intestinal villi?

Answer 11

• Dense capillary network provides the villi with a good blood supply.
• This increases the efficiency of the removal of water-soluble products
• Lacteal: absorbs fat-soluble products, this prevents blood from being clogged with fats
  The nervous impulses from brain tells villus to sway the in the intestine and this causes the pushing of chyme along and better absorption

Question 12

What products are absorbed by the villi?

Answer 12

• fatty acids and glycerol
• monomers
• amino acids
• bases and phosphates from nucleic acid

Question 13

What are 4 methods of absorption?

Answer 13

1. Simple diffusion: molecules are small and hydrophobic
2. Facilitated diffusion: fructose, glucose and other hydrophilic monomers moving through a protein channel
3. Active transport: when concentrations are lower in lumen of intestine, movement needs to occur against a concentration gradient
4. Pinocytosis: takes in small droplets of liquid surrounded by a phospholipid membrane forming a vesicle

Question 14

How is amylase useful in the digestion process?

Answer 14

Amylase in saliva digests the starch in food.
Once the saliva and food mixed, amylase breaks it to alpha-1,4 glycosidic bonds
Glycosidic bonds connect the glucose monomers in amylose and amylopectin
End products: maltose, glucose connected by the alpha 1,4 bonds and maltotriose
Amylopectin also contains alpha-1,6 glycosidic bonds

Question 15

What is the dialysis tubing?

Answer 15

Dialysis tubing: is partially permeable cellulose tubing that contains microscopic pores
Allows water, small molecules and ions but not large molecules
Used in separation techniques that remove small molecules from macromolecules in solution

Question 16

How do molecules diffuse in the dialysis tubing process?

Answer 16

Because size of molecules are small inside tube, ti will diffuse from high concentration to low concentration: outside the tube. The reason for this observation is that starch molecules are too big to pass through the pores of the dialysis tubing. The same thing would occur inside the small intestine: starch and other complex undigested molecules are not absorbed.