Chapter 6 - Nutrition In Humans

Question 1

What happens in the oesophagus?

Answer 1

Circular and longitudinal muscles contract and relax alternately to produce rhythmic, wave-like contractions known as peristalsis.

Question 2

Describe the physical digestion in the mouth. (3)

Answer 2

1) teeth chewing cuts and grinds food into smaller particles so as to increase surface area for faster digestion by salivary amylase
2) tongue rolls food into bolus and pushes it into the oesophagus.
3) mucus in saliva softens the food

Question 3

Describe the chemical digestion in the mouth. (1)

Answer 3

Salivary glands secrete saliva that contains salivary amylase that digests starch into maltose.

Question 4

Describe the physical digestion in the stomach.

Answer 4

The stomach is a distensible (can contract and relax) muscular bag. Peristalsis in the walls of the stomach churns the food to break them UP into smaller pieces and mix them with gastric juices.

Question 5

Define gastric juices.

Answer 5

Gastric juice is a dilute solution of hydrochloric acid and the enzyme pepsin.

Question 6

What are the 4 functions of HCL?

Answer 6

1) denatures salivary amylase
2) converts inactive PEPSINOGEN into active PEPSIN. Protease pepsin acts on proteins.
3) provides ACIDIC MEDIUM for actions of pepsin
4) kills harmful microorganisms in food

Question 7

How does chyme enter the small intestine?

Answer 7

It is passed through the duodenum when the pyloric sphincter relaxes.

Question 8

What is partially digested food called?

Answer 8

Chyme

Question 9

Describe the chemical digestion in the stomach. (2)

Answer 9

1) As bolus enters stomach, gastric glands are stimulated to secrete gastric juices containing HCL which converts inactive pepsinogen to active pepsin that digests proteins into polypeptides.
2) rennin converts soluble caeseinogen into insoluble casein (milk protein)

Question 10

Define antagonistic muscles and give an example.

Answer 10

They are a pair of muscles whose movements oppose each other. One example is the circular and longitudinal muscles of the oesophagus. When one muscle contracts, the other relaxes and vice versa.

Question 11

Define physical digestion.

Answer 11

It involves the mechanical break-UP of food into smaller particles.

Question 12

Define chemical digestion.

Answer 12

Breaking down bonds between molecules which involves enzymes.

Question 13

When chyme enters the duodenum, what does it stimulate (3) and what is their main function?

Answer 13

• pancreatic juices by pancreas
• bile by gall bladder
• intestinal juice by small intestine
  These alkali fluids neutralise the acidic chyme and creates an alkaline medium for action of intestinal and pancreatic enzymes.

Question 14

What is the function of the bile by gallbladder?

Answer 14

It emulsifies fats into small GLOBULES so as to increase surface area for faster digestion of fats by lipase.

Question 15

What does the 3 enzymes in the pancreatic juice digest?

Answer 15

1) lipase digests fat into fatty acids and glycerol
2) pancreatic amylase digests starch into maltose
3) trypsin digests protein into polypeptide

Question 16

What does the 6 enzymes in intestinal juices do?

Answer 16

1) lipase digests fats into fatty acids and glycerol
2) erepsin digests polypeptides into amino acids
3) maltase digests maltose into glucose
4) lactase digests lactose into galactose and glucose
5) sucrase digests sucrose into frutose and glucose
6) enterokinase converts inactive trypsinogen into active trypsin

Question 17

If both food and air must pass through the pharynx to enter the oesophagus and trachea, how is food prevented from entering the trachea when swallowing?

Answer 17

The glottis is covered by the epiglottis. During swallowing, the larynx moves upwards and the epiglottis covers the glottis, preventing food particles from entering the trachea.

Question 18

Define villi.

Answer 18

Villi are minute finger-like projections on the folds of the small intestines.

Question 19

How is the villus adapted to carry out its function?(3)

Answer 19

1) EPITHELIUM is one-cell thick to provide shorter distance for absorption of DIGESTED food materials.
2) richly supplied with blood capillaries and lacteal. Blood capillaries transport sugar and amino acids away. Lacteal transport fats. This continual transport of digested food substances MAINTAINS the concentration gradient for absorption to take place
3) presence of microvilli on EPITHELIAL CELLS (not epithelium) further increases surface area for absorption to take place.

Question 20

What does the rate of absorption depend on?

Answer 20

1) surface area
2) thickness of separating membrane
3) concentration gradient

Question 21

How are nutrients absorbed in the small and large intestines?(3)

Answer 21

• glucose and amino acids diffuse into the blood capillaries
• glycerol and fatty acids diffuse into the epithelium, and combine to form minute fat globules which enter the lymphatic capillary
• glucose and amino acids are absorbed by active transport when there is a lower concentration of the food substances in the small intestine than the blood capillaries

Question 22

What happens to the undigested and unabsorbed matter?

Answer 22

They are stored temporarily in the rectum and discharged as faeces through the anus, which is known as egestion.

Question 23

Name the function of the HEPATIC PORTAL VEIN.

Answer 23

transport sugars and amino acids to the liver from ileum

Question 24

What is the function of the HEPATIC VEIN?

Answer 24

Transport glucose and amino acids from liver to different parts of the body.

Question 25

How does the liver regulate blood glucose concentration? (Function of insulin)

Answer 25

Insulin stimulates the liver to convert EXCESS glucose to glycogen, and thus regulates the amount of glucose that enters the bloodstream.

Question 26

What are the amino acids distributed by the hepatic vein used for? (2)

Answer 26

1) growth and repair in cells

2) form enzymes and hormones

Question 27

What are the 5 functions of the liver?

Answer 27

1) detoxification where it breaks down harmful substances like alcohol into harmless substances
2) regulation of blood glucose concentration
3) produce bile which emulsify fats into smaller fat globules
4) breaks down haemoglobin and store as iron
5) excess amino acids transported to liver. Their amino groups are removed and converted to urea during deamination.

Question 28

How do insulin and glucagon control carbohydrate metabolism?(regulate blood glucose concentration)

Answer 28

• if there is too much glucose in the blood, the islets of Langerhans will secrete insulin. The liver is then stimulated to convert EXCESS glucose into glycogen, decreasing the blood glucose level.
• if there is too little glucose in the blood, the islets of Langerhans will secrete GLUCAGON. The liver is then stimulated to convert EXCESS glycogen into glucose, increasing the blood glucose level.

Question 29

How does the liver synthesis proteins? What are the proteins for?

Answer 29

The liver uses amino acids to synthesise proteins such as PROTHROMBIN and FIBRINOGEN which are essential for clotting of blood.

Question 30

Describe the fate of excess amino acids.

Answer 30

1) in deamination, the amino group of the amino acids are removed in the liver and first converted to ammonia, which is toxic to cells. Ammonia then combines with carbon dioxide to form urea, which is non-toxic. It is transported in the blood plasma to kidneys via the renal artery. Ultrafiltration in the kidney tubules filtered the urea from blood and excrete it in urine.
2) the carbon residues of amino acids from deamination are converted to glucose, then stored as glycogen in the liver and muscles.

Question 31

How is iron produced and stored?

Answer 31

When red blood cells are worn out, they are destroyed in the spleen and their haemoglobin is sent to the liver to be “recycled”. Breakdown of haemoglobin produces iron which is stored in the liver and used in the synthesis of new red blood cells.

Question 32

What does the breakdown of haemoglobin produce?

Answer 32

Bile and iron.

Question 33

Define detoxification.

Answer 33

It is the process of converting harmful substances into harmless products.

Question 34

List an example of detoxification.

Answer 34

Enzyme ALCOHOL DEHYDROGENASE converts alcohol into ACETALDEHYDE, which is used as a source of energy in cells.

Question 35

List 3 short term effects of excessive alcohol consumption.

Answer 35

1) caused symptoms of “drunkenness”
2) reduced self control
3) slow down brain functions: slower reaction rate and longer reaction time, blurred vision, poor muscle coordination

Question 36

List 3 long term effects of excessive alcohol consumption.

Answer 36

1) causes liver cirrhosis, leading to liver failure and death
2) increases risks of gastric ulcer as alcohol stimulates acid secretion in stomach
3) frequent intake may lead to addiction which leads to withdrawal symptoms

Question 37

What happens when the oesophagus walls constrict?

Answer 37

The circular muscles contract, and the longitudinal muscles relax, pushing the bolus forward.

Question 38

What happens when the oesophagus walls dilate?

Answer 38

The circular muscles relax, and the longitudinal muscles contract, widening the lumen for food to enter.

Question 39

Define absorption.

Answer 39

Products of digestion such as glucose and amino acids are taken into the bloodstream through the wall of the ileum by diffusion and active transport.