Nutrition In Humans

Question 1

Processes that take place in the mouth

Answer 1

1. Food in the mouth stimulates the salivary glands to secrete saliva
2. Saliva contains salivary amylase—>digest starch into maltose.
3. the saliva provides a neutral environment—>optimum pH for salivary amylase.
4. Chewing breaks food up into smaller pieces—>increases surface area to volume ratio—>faster rate of enzyme activity.
5. The tongue rolls the food into boli (singular:bolus)
6. The boli are swallowed and passed down into the oesophagus via the pharynx.

Question 2

What does the oesophagus/gullet consist of?

Answer 2

Contains 2 layers of muscles

• longitudinal muscles on the outer side of the gullet.
• circular muscles on the inner side of the gullet.

Question 3

What is peristalsis?

Answer 3

Peristalsis is the rhythmic, wave-like muscular contractions.

Question 4

Function of peristalsis

Answer 4

1. enables food to be mixed with the digestive juices.

2. Propels the food along the gut

Question 5

Action of peristalsis in the gullet

Answer 5

The circular muscles and the longitudinal muscles are antagonistic muscles( when one set of the muscles contracts, the other set relaxes)

1. When the circular muscles contract, the longitudinal muscles relax—>its size of lumen decreases—>food is squeezed and pushed forward towards the stomach.
2. When the longitudinal muscles contract, the circular muscles relax—>its lumen dilates—>allows food to enter.

Question 6

Functions of stomach

Answer 6

1. The stomach is a distensible muscular bag—>when it is fully distended—>send signals to the brain that it is sated.
2. the stomach walk has numerous pits—> contain gastric glands—>secretes gastric juice
3. Stores food temporarily

Question 7

Digestive processes in the stomach

Answer 7

1. The presence of food in the stomach stimulates the gastric glands to secrete gastric juices into the stomach cavity.
   2.Peristalsis in the stomach breaks up food into smaller pieces and mixes the food well with gastric juice.
   HCL:
   -stops the action of salivary amylase by denaturing it
   -changes the inactive form of enzyme pepsinogen into active form called pepsin
   -provide an acidic environment for pepsin
   -kills potential harm microorganisms in food
   -stores food for about 3-4hrs
   Pepsin:
   -digest proteins into polypeptides

Question 8

Function of liver

Answer 8

1. Secretes bile
   Bile contains bile salts and bile pigments
   Bile pigments—>give bile its colour (greenish-yellowish) —>waste product

Question 9

Function of bile

Answer 9

Bile:
1. Emulsify fats—>by breaking fats into smaller fat droplets—>increases surface area to volume ratio—>increase rate of enzyme activity

Question 10

Function of gallbladder

Answer 10

1. Temporarily stores bile—>bile flows into the small intestine via the bile duct.

Question 11

Function of pancreases

Answer 11

Produces enzymes:

1. pancreatic amylase
2. trypsin
3. pancreatic lipase

Question 12

Function of the large intestine

Answer 12

Colon:
1. Absorb water and mineral salts from undigested food materials not affected by levels of ADH
Rectum and Anus:
1. Excrement are stored temporarily in the rectum. When the rectum contracts, the excrement are expelled via the anus.

Question 13

Digestive processes in the small intestine

Answer 13

When chyme enters the small intestine, it stimulates:
1. Pancreas to secrete pancreatic juice—>enter via the pancreatic duct into the duodenum
2. Gall bladder to release bile—>bile enters the duodenum via the bile duct
3. Epithelial cells in the small intestine to secrete Maltase, peptidases and lipase
The alkalis(bile+pancreatic juice+intestinal juice):
-stops the action of pepsin by denaturing it
-provide alkaline pH to meet the optimum pH of enzymes

Enzymes present in the small intestine:
(Pancreatic amylase+trypsin+pancreatic lipase)-by pancreas
(Maltase+peptidases+lipase)-by small intestine

Question 14

How is the small intestine adapted for absorption?

Answer 14

1.Increasing surface area:
-The inner surface of the small intestine is folded
-The folds bear numerous villi
-The epithelial cells of the villi have numerous microvilli
2.The epithelium of the villi is one cell thick
3.The small intestine is long to provide sufficient time for absorption
4.In each villus is a lacteal/lymphatic capillary surrounded by blood capillaries—>lymphatic capillaries transport fats while the blood capillaries transport sugar and amino acids away from the intestine (this continual transport of digested food substances maintains a steep concentration gradient for faster rate of diffusion)
Note: Active transport may occur in the small intestine

Question 15

Where are insulin and glucagon produced

Answer 15

Secreted by the islets of Langerhans in the pancreas

Question 16

What happens to excess glucose?

Answer 16

1.Insulin produced by the islets of Langerhans stimulates the liver cells to convert excess glucose into glycogen.

Question 17

What happens when there’s not enough glucose in the blood?

Answer 17

Glucagon secreted by the islets of Langerhans stimulates the liver cells to convert glycogen into glucose to be released into the bloodstream.

Question 18

Function of hepatic portal vein

Answer 18

Transports blood rich in glucose and amino acids to the liver

Question 19

How are fats transported?

Answer 19

1. The lymphatic capillaries absorbs the fats

2. The lymphatic capillaries join to form larger lymphatic vessels to discharge fats into the bloodstream.

Question 20

How are fats utilized?

Answer 20

1. When there is sufficient supply of glucose, fats are not broken down, they are used to build protoplasm eg. Cell membranes
2. When glucose are in short supply, fats are broken down to provide the energy needed for vital activities
3. Excess fats are stored in adipose tissues—> protect organs by acting as shock absorbers.

Question 21

What happens to worn-out RBCs?

Answer 21

1. The RBCs are destroyed in the spleen
2. Their haemoglobin is brought to the liver
3. Liver breaks down the haemoglobin and stores the iron that is released in the process+ bile pigments formed from the breakdown of haemoglobin

Question 22

What is deamination?

Answer 22

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

Question 23

Deamination of amino acids

Answer 23

Excess amino acids are transported to the liver. Their amino groups are removed and the amino groups are converted into urea.

Question 24

Breakdown of alcohol

Answer 24

1. Liver cells contain an enzyme called alcohol dehydrogenase—> breaks down alcohol into acetaldehyde.
2. Acetaldehyde can be broken down further to compounds that can be used in respiration to release energy or cell activities.

Question 25

Effects of excessive alcohol consumption

Answer 25

1. Alcohol is a depressant by slowing down some brain functions
2. Alcohol reduces self-control
3. Increases reaction time
4. Prolonged alcohol abuse may lead of liver cirrhosis—>may lead to haemorrhage in the liver—>may cause liver failure and death.
5. Social implications:
   
   • Drink alcohol frequently—>may become an alcoholic—>may neglect their work and families—>may exhibit violent behaviors
   • Many crimes have been committed by people under the influence of alcohol