Nutrition in Humans

Question 1

What is peristalsis?

Answer 1

Peristalsis is the rhythmic, wave-like muscular contractions in the wall of the alimentary canal.

Question 2

How does peristalsis work?

Answer 2

The circular muscles and longitudinal muscles are antagonistic.
When the circular muscles contract, the longitudinal muscles relax. As a result, the wall of the gut constricts and food is pushed forward.
When the longitudinal muscles contract, the circular muscles relax. The wall of the gut dilates and allows food to enter.

Question 3

What digestive processes take place in the mouth?

Answer 3

Saliva is produced by the salivary glands.
The tongue rolls the food into small boli, which is swallowed and passed down to the oesophagus.
Peristalsis in the walls of the oesophagus pushes each bolus of food down to the stomach.

Question 4

What digestive processes take place in the stomach?

Answer 4

Gastric juice is produced by the gastric glands. It contains mucus, dilute hydrochloric acid and pepsin.
Pepsin digests proteins to polypeptides.
The partially digested food becomes chyme, which passes in small amounts into the duodenum.

Question 5

What is the function of saliva in the mouth?

Answer 5

Saliva contains mucus, which helps soften food, and salivary amylase which digests starch to maltose. It has a pH of around 7.

Question 6

What is the function of hydrochloric acid in the stomach?

Answer 6

Hydrochloric acid denatures salivary amylase, converts pepsinogen to pepsin and provides an acidic environment that is optimal for pepsin action. It also kills certain potentially harmful microorganisms in food.

Question 7

What digestive processes take place in the small intestine?

Answer 7

The pancreas secretes pancreatic juice into the duodenum. The gall bladder releases bile into the duodenum, and the epithelial cells in the small intestine produces maltase (maltose -> glucose), peptidase (polypeptides -> amino acids) and lipase (fats -> fatty acids + glycerol).

Question 8

What is the function of pancreatic juices in the small intestine?

Answer 8

Pancreatic juice contains pancreatic amylase (starch -> maltose), trypsin (proteins -> polypeptides) and pancreatic lipase (fats -> fatty acids + glycerol).

Question 9

What is the function of bile in the small intestine?

Answer 9

Bile does not participate in digestion, but it speeds up the digestion of fats by emulsifying them. They lower the surface tension of fats, causing them to break into tiny fat droplets. This results in an increased surface area to volume ratio of the fats.

Question 10

How is the small intestine adapted for absorption?

Answer 10

• Large surface area (folded inner surface, numerous finger-like projections called villi, numerous microvilli on epithelial cells) -> faster absorption
• Thin membrane (epithelium) between food substances and capillaries -> shorter time to pass through
• Concentration gradients (maintained by lacteal and blood capillaries)
• Thin wall on villi
• Long -> enough time for absorption

Question 11

How does absorption take place in the intestines?

Answer 11

Glucose and amino acids are absorbed by diffusion into the blood capillaries of the villi. They are also absorbed by active transport, when there is a lower concentration of digested food substances in the lumen than the blood capillaries.
Fatty acids and glycerol diffuse into the epithelium, where they combine to form minute fat globules which enter the lacteals.

Question 12

How is glucose transported and utilised in the human body?

Answer 12

Glucose is transported to the liver via the hepatic portal vein. It is assimilated and then oxidised during respiration to release energy. Excess glucose is returned to the liver, and insulin from the pancreas stimulates liver cells to convert glucose to glycogen.

Question 13

How are amino acids transported and utilised?

Answer 13

Amino acids which enter cells are converted to new protoplasm.
Excess amino acids are deaminated in the liver.

Question 14

How are fats transported and utilised?

Answer 14

Fats are absorbed into lymphatic capillaries, which join to form larger lymphatic vessels before discharging the fats into the bloodstream.
When there is sufficient glucose, fats are used to build protoplasm. When there is a short supply of glucose, fats are broken down as a replacement for energy. Excess fats are stored in adipose tissues beneath the skin and around the heart and kidneys. These adipose tissues protect the organs by acting as shock absorbers.

Question 15

What are the functions of the liver?

Answer 15

• Regulation of blood glucose concentration
• Production of bile (from destroyed red blood cells)
• Storage of iron (from destroyed red blood cells)
• Synthesis of proteins (prothrombin and fibrinogen)
• Deamination of amino acids
• Detoxification

Question 16

What is deamination?

Answer 16

Deamination is the process by which amino groups are removed from amino acids and converted to urea.

Question 17

What is detoxification?

Answer 17

Detoxification is the process of converting harmful substances into harmless ones.

Question 18

What are the effects of excess alcohol consumption on the digestive system?

Answer 18

Alcohol stimulates acid secretion in the stomach, increasing the risk of gastric ulcers. Prolonged alcohol abuse may lead to cirrhosis, in which the liver cells are destroyed and replaced with fibrous tissue. The patient may also have bleeding in the liver, and potentially liver failure and death.

Question 19

What are the effects of excess alcohol consumption on the nervous system?

Answer 19

Alcohol is a depressant which slows down some brain functions. It also reduces self control, increases reaction time, and causes blurred vision and poor muscular coordination.