Nutrition in Humans

Question 1

Oesophagus

Answer 1

It is a narrow, muscular tube that connects the mouth and stomach
(Muscles consist of a layer of longitudinal and a layer of circular muscles)

*circular muscle is the inner muscle while the longitudinal muscles is the exterior muscles

Question 2

What is peristalsis

Answer 2

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

Function: Enables food to be mixed with digestive juices and helps to push or propel food along the gut

Scenario 1: When the circular muscles contract and the longitudinal muscles relax, the gut becomes narrower and longer for food to be pushed forward.

Scenario 2: When the longitudinal muscles contract and the circular muscles relax, the gut become wider and shorter to allow food to enter the lumen

Question 3

Stomach

Answer 3

1. It has gastric glands which secrete gastric acids
2. It also contains a thick lining of mucus to protect itself from acid

Question 4

Small Intestines

Answer 4

1. Carries out most of the digestive processes
2. Absorbs water and nutrients from food

Question 5

Large Intestines

Answer 5

1. Absorbs remaining water and mineral salts from undigested food
2. Temporarily stores faeces in the rectum

Question 6

Liver

Answer 6

1. Produces and secretes bile which contain bile salts that emulsify fats

Question 7

Gall bladder

Answer 7

1. Bile produced by the liver is stored temporarily in the gall bladder

*When the gall bladder contracts, bile flows via the bile duct to the duodenum (part of the small intestine)

Question 8

Pancreas

Answer 8

1. Produces pancreatic juice which contain enzymes such as pancreatic amylase, pancreatic lipase and trypsin
2. Secretes insulin and glucagon to regulate blood glucose concentration in the blood

*The pancreas is connected to the duodenum via the pancreatic duct, where the bile duct joins the pancreatic ducts before it opens to the duodenum

Question 9

What are the types of digestion

Answer 9

1. Physical digestion
2. Chemical digestion

Question 10

Physical digestion

Answer 10

Involves the mechanical break-up of food into smaller pieces, increasing surface area-to-volume ratio of the food so that the enzymes can act on the food particles more effectively

Example: Chewing the the mouth, Churning in the stomach and Emulsification of fats by bile salts

Question 11

Chemical digestion

Answer 11

Involves the breaking down of large food molecules, such as proteins, starch and fats into small, soluble molecules that can be absorbed.

Example: Through enzymes

Question 12

Processes in the mouth

Answer 12

1. Salivary glands secrete saliva
2. Saliva mixes with the food and softens it
3. Salivary amylase in saliva digests starch to maltose at optimum pH 7
4. Food is further broken up into smaller pieces by chewing, increasing SATV ratio for salivary amylase to work on

Question 13

Processes in the stomach

Answer 13

1. Gastric glands secrete gastric juices
2. Churning breaks up the food and mixes the food with gastric juice
3. Gastric juice contains hydrochloric acid and pepsin
4. Hydrochloric acid
   - Stops the action of salivary amylase by denaturing it
   - Provides a low pH environment in the stomach for pepsin to digest proteins
   - kills microorganisms
5. Pepsin digests proteins into polypeptides

Question 14

Processes in the small intestines

Answer 14

1. When chyme enters the duodenum, the pancreas is stimulated to secrete pancreatic juice via the pancreatic duct
2. Pancreatic juice contains pancreatic amylase, pancreatic lipase and trypsin
3. Bile gladder releases bile into the duodenum via the bile duct.
   - Bile speeds up the digestion of fats by breaking up large fat molecule into smaller fat molecules
4. The small intestines produce enzymes maltase (breaks down maltose into glucose), intestinal protease and intestinal lipase

Question 15

Protein digestion

Answer 15

1. Protein digestion starts in the stomach where pepsin digests proteins into polypeptides
2. The undigested proteins enter the small intestines and are digested by trypsin into polypeptides
3. The polypeptides are digested into amino acids by intestinal protease

Question 16

Fat digestion

Answer 16

1. Bile salts emulsify fats by lowering its surface tension
2. The fats are then broken up into tiny fat droplets, increasing SATV ratio for lipase to work on
3. Emulsified fats are digested by lipase into fatty acids and glycerol in the small intestines

Question 17

What is absorption

Answer 17

The process whereby digested food is absorbed into the small intestines

Question 18

Adaptation of the small intestines for absorption

Answer 18

1. Inner surface has numerous finger-like projection called villi
   - Increases SATV for absorption
2. The epithelium (wall) of the villus is one cell thick
   - Provides a shorter diffusion distance for nutrients to pass through
3. The cells of the epithelium have many microvilli
   - Increases SATV for absorption
4. Each villus have many blood capillaries
   - Capillaries transport absorbed glucose and amino acids through the blood away from the villus, to maintain a steep diffusion gradient
5. Each villus has a lacteal
   - Lacteal transports absorbed fats away to maintain a steep diffusion gradient
6. The epithelial cells contain many mitochondria
   - Provides energy for the active transport of nutrients into the villi

Question 19

What is assimilation

Answer 19

The process whereby some of the absorbed nutrients are converted into new cytoplasm or used to provide energy

Question 20

What happens to glucose after absorption

Answer 20

1. The liver converts most absorbed glucose into glycogen and is stored
2. Some glucose is distributed around the body to be used for energy during cellular respiration
3. Excess glucose is transported back to the liver to be stored as glycogen for future use

Question 21

What happens to amino acids after absorption

Answer 21

1. Amino acids that enter the cells are converted into new cytoplasm that is used for growth and repair of worn-out parts of the body
2. Amino acids are used to form enzymes and hormones

Question 22

Function of the liver

Answer 22

1. Regulation of blood glucose concentraion
   - The islets of langerhan in the pancreas detect a change in blood glucose concentration and secrete insulin (high blood glucose concentraion) or glucagon (low blood glucose concentration)
2. Breakdown of Hormones
3. Detoxification
4. Secretion of bile

Question 23

Effects of alcohol on the digestive system

Answer 23

1. Alcohol stimulates acid secretion in the stomach, which can lead to gastric ulcers
2. Alcohol may lead to cirrhosis of the liver

Question 24

Effects of alcohol on the nervous system

Answer 24

1. Alcohol is a depressent that slows down some brain function
2. Alcohol causes reduced self-control in people
3. Alcohol affects peoples’ reaction time

Question 25

Long-term impacts of alcohol on the brain

Answer 25

1. Alcohol may cause wet brain
2. Alcohol may cause shrinkage of brain volume

Question 26

Social implications of alcohol

Answer 26

1. Addiction to alcohol, causing them to be unable to stop drinking until they are drunk
   - They may end up neglecting their work and families
   - They may exhibit violent behaviour
   - They are at a higher risk of committing a crime