Chapter 6 Nutrition in Humans

Question 1

What is nutrition?

Answer 1

Nutrition is the process whereby organisms obtain food and energy for growth of new cells, repair of worn out cells, and for maintenance of the body.

Question 2

Name the processes involved in nutrition.

Answer 2

Ingestion, digestion, absorption, assimilation, egestion

Question 3

Explain digestion, absorption and assimilation, and egestion.

Answer 3

Digestion: Large, complex, insoluble food molecules are broken down into smaller, soluble molecules that can be absorbed by body cells

A&A: Digested food molecules are absorbed into the cells. These molecules are converted into new protoplasm or used to provide energy via assimilation.

Egestion: The process where undigested food is being removed from the body as waste

Question 4

Name all the parts of the alimentary canal and associated organs. [6] [4]

Answer 4

Mouth, pharynx, oesophagus, stomach, small intestine, large intestine

Salivary glands, liver, gallbladder, pancreas

Question 5

Explain what happens in the mouth.

Answer 5

Digestion of food begins in the mouth by the teeth and tongue, followed by salivary amylase

Question 6

Explain what happens in the pharynx.

Answer 6

The pharynx connects the buccal cavity/ the mouth to the oesophagus and larynx (voice box)
Also leads to the the trachea (windpipe), which in turn lead to the lungs
Part of both the respiratory and digestive systems

Question 7

Explain what happens in the oesophagus.

Answer 7

Long and narrow muscular tube that extends to the stomach
The wall of the oesophagus is made up of two layers of muscles that are antagonistic, the longitudinal muscles and the circular muscles

Question 8

Explain what happens in the stomach.

Answer 8

It is a distensible (stretchable) muscle bag
Food in the stomach is digested by gastric juice, released by the gastric glands in the gastric pits.

Question 9

Explain the small intestine.

Answer 9

Consists of the duodenum*, jejunum and ileum

Question 10

Explain the large intestine.

Answer 10

Consists of colon and rectum

Question 11

Explain what the salivary glands do.

Answer 11

Secrete saliva

Question 12

Explain what the liver does.

Answer 12

Liver cells secrete bile and help to detoxify harmful substances into non-harmful substances

Question 13

Explain what the gallbladder does.

Answer 13

Helps to store bile temporarily from the liver before releasing the bile into the duodenum

Question 14

Explain what the pancreas does.

Answer 14

Secretes pancreatic juice into the small intestine which helps to digest food.

Question 15

What happens during breathing?

Answer 15

The larynx has a slit-like opening called the glottis, which is covered by a flap-like tissue called the epiglottis.
During breathing, air passes through the trachea, the larynx moves downwards and the glottis is opened to allow air to go to the lungs for respiration

Question 16

What happens during swallowing?

Answer 16

During swallowing, the larynx moves upwards and pushes the epiglottis over the opening of the trachea and therefore covering the glottis. This prevents food from entering the trachea to prevent you from choking

Question 17

Define peristalsis.

Answer 17

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

Question 18

What does peristalsis help?

Answer 18

It helps the movement of food along the alimentary canal. It also enables food to be mixed with digestive juices. Peristalsis occurs in the oesophagus, stomach, small intestine, large intestine and rectum.

Question 19

What are antagonistic muscles?

Answer 19

Antagonistic muscles are a pair of muscles whose movements oppose each other

Question 20

What is digestion?

Answer 20

Digestion is the breakdown of large, complex and insoluble nutrient molecules into smaller, simple and soluble nutrient molecules.

Question 21

Explain what happens in digestion IN THE MOUTH.

Answer 21

1. The chewing action of the teeth, also known as mastication, breaks up lagre pieces of food into smaller pieces with a larger SAVR
2. The tongue will roll the food into small, round, slippery masses of food called boli (singular term is bolus)
3. The salivary glands in the mouth will secrete saliva; contains salivary amylase and mucin; which is mixed into the food by the tongue
4. The mucin will soften the food
5. The salivary amylase will catalyse the breakdown/ digestion of starch into maltose

Question 22

What happens during digestion in the oesophagus?

Answer 22

Peristalsis in the walls of the oesophagus will push the bolus into the stomach
Usually no chemical or physical digestion takes place here. There is, but in very small amounts

Question 23

What happens during digestion in the stomach?

Answer 23

Entry of the bolus into the stomach will stimulate the secretion and release of gastric juice by the gastric glands, through the gastric pit on the inner wall of the stomach
Peristalsis mixes the food with gastric juice
Churning of the stomach also breaks down large substances into smaller substances

Question 24

What happens during digestion in the stomach?

Answer 24

Entry of the bolus into the stomach will stimulate the secretion and release of gastric juice by the gastric glands, through the gastric pit on the inner wall of the stomach
Peristalsis mixes the food with gastric juice
Churning of the stomach also breaks down large substances into smaller substances

Question 25

What role does gastric juice play in digestion?

Answer 25

It is a dilute solution of hydrochloric acid, mucus and the enzyme called pepsin
Pepsin catalyses the digestion of proteins into polypeptides
The hydrochloric acid:
Denatures salivary amylase to stop its action in the stomach
Converts inactive pepsinogen into active pepsin.
Provides an acidic environment for the action of pepsin and for it to function optimally.
Kills harmful microorganisms and bacteria in food.

Question 26

What happens during digestion in the small intestine?

Answer 26

Chyme or partially digested food will enter the duodenum and stimulate the release of:
Pancreatic juice by the pancreas
Bile by the gallbladder
Intestinal juice by the small intestine
All these fluids are alkali and will neutralise the acidic chyme.

The alkaline medium is needed for the action and optimal function of pancreatic and intestinal enzymes to digest the chyme.

The gallbladder releases its stored bile; that is made from the cells in the liver;. The bile passes through the bile duct into the duodenum

The pancreas secretes pancreatic juice which contains enzymes such as pancreatic amylase, pancreatic lipase and trypsin

The intestinal juice is secreted by the intestinal glands. It contains the enzymes, maltase, sucrase, lactase, peptidases and intestinal lipase

Question 27

What enzymes and reaction happen from saliva?

Answer 27

Starch —salivary amylase—> maltose

Question 28

What enzymes and reaction happen from gastric juice?

Answer 28

Proteins —pepsin—> polypeptides

Question 29

What occurs from bile released from the liver?

Answer 29

Bile emulsifies fats.
Bile breaks down the fats into small fat droplets that are suspended in water.
Emulsification of fats helps to increase SAVR of the fat molecules for faster rate of chemical digestion catalysed by lipase

Question 30

What enzymes and reaction happen from pancreatic juice?

Answer 30

1. Starch —pancreatic amylase—> maltose
2. Proteins —trypsin—> polypeptides
3. Fats —pancreatic lipase—> fatty acids and glycerol

Question 31

What enzymes and reaction happen from intestinal juice?

Answer 31

Trypsinogen —enterokinase—> trypsin
Polypeptides —peptidase—> amino acids
Maltose —maltase—> glucose
Lactose —lactase—> glucose and galactose
Sucrose —sucrase—> glucose and fructose
Fats —intestinal lipase—> fatty acids and glycerol

Question 32

List the adaptations of the small intestine for absorption. [3]

Answer 32

Large surface area to volume ratio
Thin separating membrane
Steep concentration gradient

Question 33

Explain large SA2V ratio

Answer 33

The surface area to volume ratio is increased for faster rate of absorption. The surface area is increased by the numerous folds in the small intestine’s inner wall. The inner walls contain villi, which possess microvilli on the epithelium. These finger-like projections also increase the surface area to volume ratio to increase the rate of absorption of nutrients into the walls of the small intestine.

Question 34

Explain thin separating membrane

Answer 34

The one cell thick walls of the villi make it easier for nutrients to pass through into the bloodstream. The length of the small intestine (~6m) increases the time for absorption.

Question 35

Steep concentration gradient

Answer 35

Many capillaries are present to carry away the absorbed nutrients quickly, maintaining a constant concentration gradient. The Blood capillaries network helps to carry amino acids and glucose to the body. The lacteal/ lymphatic capillary helps to transport fats to the body.

Question 36

Why do each villus have a lacteal and numerous blood capps?

Answer 36

This is to facilitate the transport of fats, amino acids and glucose to the liver via the hepatic portal vein before it is taken to other parts of the body.

Lymphatic capillary of the villi will transport fats., glycerol and fatty acids will diffuse into the epithelium and recombine to form fat globules

The blood capillaries transport sugars and amino acids

This constant continual transport of digested foods maintains a steep concentration gradient which ensures the rapid diffusion of digested nutrient molecules into the blood

Question 37

Why is villus wall one cell thick?

Answer 37

TO reduce the diffusion distance, to allow for a faster rate of absorption of digested nutrient molecules into the bloodstream.

Question 38

Name the functions of the liver

Answer 38

1. Regulation of blood glucose concentration
2. Amino acid metabolism and formation of urea
3. Regulation of glucose and amino acids concentration to maintain blood osmotic potential
4. Production of bile
5. Storage of iron (used to synthesise new red blood cells)
6. Detoxification

Question 39

What are the effects of excessive alcohol consumption?

Answer 39

1. Liver cirrhosis (scarring of liver tissue)
2. Diminished ability to process surroundings
3. Increased reaction time (time needed to react to something)