Nutrition in Humans

Question 1

Describe the functions of the mouth.

Answer 1

[Physical digestion]

• The chewing action of the teeth mechanically breaks up larger pieces of food into small pieces.
• The tongue rolls the food into small, slippery round asses or boli.

Question 2

Describe the functions of the salivary glands.

Answer 2

[Chemical digestion]
-The salivary glands secrete saliva, which is mixed with the food by the tongue. The saliva contains mucin which softens the food. Salivary amylase digests starch into maltose.

Question 3

Describe the functions of the oesophagus.

Answer 3

Peristalsis in the walls of the oesophagus pushes the bolus into the stomach.

Question 4

Describe the functions of the stomach.

Answer 4

[Physical digestion]
-Peristalsis in the walls of the stomach mixes food with gastric juice.
[Chemical digestion]
-The pepsin in gastric juice digests proteins into polypeptides.

Question 5

Describe the functions of the duodenum.

Answer 5

[Physical digestion]
-Bile emulsifies large fat globules into smaller fat droplets (increase SA:VR).
[Chemical digestion]
-Pancreatic juice containing pancreatic amylase and pancreatic lipase catalyse the breakdown of starch and fats.
-Intestinal juice containing maltase, sucrase, lactase and intestinal lipase catalyse the breakdown of maltose, lactose, sucrose and fats.
-Trypsin catalyses the breakdown of protein to polypeptides.
-Peptidases catalyses the breakdown of polypeptides to amino acids.

Question 6

Describe the functions of the pancreas.

Answer 6

[Chemical digestion]
-The pancreas secretes pancreatic juice containing pancreatic amylase and pancreatic lipase that catalyse the breakdown of starch and fats in the duodenum.

Question 7

Describe the functions of the gall bladder.

Answer 7

The gall bladder stores bile, which is used to emulsify fats in the duodenum.

Question 8

Describe the functions of the liver.

Answer 8

• The liver regulates blood glucose concentrations.
• The liver produces bile.
• The liver synthesizes proteins such as albumins, globulins and fibrinogen.
• Excess amino acids undergo deamination in the liver.
• Iron is stored in the liver.
• The liver breaks down alcohol (detoxification).

Question 9

Describe the functions of the ileum.

Answer 9

-The ileum is the site of absorption of products of digestion such as simple sugars, amino acids, fatty acids and glycerol.

Question 10

Describe the functions of the colon (large intestine).

Answer 10

-The large intestine absorbs water and mineral salts from undigested food material.

Question 11

Describe the functions of the rectum.

Answer 11

-The rectum temporarily stores faeces before it expels it through the anus.

Question 12

Describe the functions of the anus.

Answer 12

Poopoo hole.

Question 13

Describe peristalsis.

Answer 13

Peristalsis is the rhythmic, wave-like contractions in the wall of the alimentary canal that enable food to be mixed with digestive juices and travel along the gut.

Question 14

Describe the functions of enzymes amylase, maltase, protease, lipase in digestion, listing the substrates and end-products.

Answer 14

• Amylase catalyses the breakdown of starch into maltose.
• Maltase catalyses the breakdown of maltose into glucose
• Protease catalyses the breakdown of proteins into polypeptides/amino acids.
• Lipase catalyses the breakdown of fats into fatty acids and glycerol.

Question 15

Describe the structure of a villus and its role, including the role of capillaries and lacteals in absorption.

Answer 15

• In each villus, there is a lacteal surrounded by blood capillaries that transport sugars and amino acids, away from the intestine.
• The thin walls of the villus that are one-cell thick make it easy for nutrients to pass through the bloodstream (faster)
• Dense networks of capillaries in the villus help carry away absorbed nutrients quickly (maintain steep concentration gradient for nutrient absorption)
• Glucose and amino acids diffuse into the capillaries. Glucose and amino acids are absorbed by active transport.
• Fatty acids and glycerol diffuse into the epithelium, combine to form minute fat globules which enter the lacteal.

Question 16

State the function of the hepatic portal vein.

Answer 16

The hepatic portal vein transports blood rich in sugars and amino acids from the small intestine to the liver.

Question 17

State the 6 roles of the liver.

Answer 17

• The liver regulates the blood glucose levels/concentration.
• The liver produces bile.
• The liver synthesizes proteins.
• The liver deaminates excess amino acids.
• The liver stores iron.
• The liver breaks down harmful substances (Detoxification) like alcohol and food preservatives,

Question 18

State the role of the liver in carbohydrate metabolism.

Answer 18

• The liver keeps the blood glucose concentration in the blood constant.
• When the glucose level in the blood is too high, the liver secretes insulin to stimulate liver cells to convert excess glucose to glycogen to reduce the blood glucose concentration.
• When the glucose level in the blood is too low, the liver secretes glucagon to stimulate liver cells to convert glycogen to glucose to raise the blood glucose concentration.

Question 19

State the role of the liver in fat digestion.

Answer 19

-The liver produces bile, which emulsifies (physical digestion) large fat globules into smaller fat droplets.

Question 20

State the role of the liver in the breakdown of red blood cells.

Answer 20

• When red blood cells are worn out, they are destroyed in the spleen. 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.
• Breakdown of haemoglobin in the liver also produces bile.

Question 21

State the role of the liver in the metabolism of amino acids and the formation of urea.

Answer 21

• Excess amino acids undergo deamination in the liver.
• The amino group is removed and converted to urea, which is removed from the body in the urine.
• The carbon residues of the amino acids are then converted to glucose.

Question 22

State the role of the liver in the breakdown of alcohol.

Answer 22

• Harmful substances are converted into harmless products by the liver cells in a process called detoxification.
• Liver cells contain the enzyme alcohol dehydrogenase that converts alcohol into acetaldehyde.

Question 23

Describe the effects of excessive consumption of alcohol.

Answer 23

• Reduced self-control
• Depressant (Slows down some brain functions)
• Increased reaction times
• Damage to liver (Causes liver cirrhosis, increased risk of stomach ulcer)
• Social implications (Alcohol addiction_

Question 24

Describe assimilation.

Answer 24

Assimilation is the process whereby some of the absorbed food substances are converted into new protoplasm or used to release energy (respiration).

Question 25

State the utilization of glucose in humans.

Answer 25

• Glucose is used for respiration to release energy for the cellular activities.
• [EXCESS] Converted into glycogen and stored in the liver and muscle cells.
• Regulated by the hormone insulin.

Question 26

State the utilization of amino acids in humans.

Answer 26

• Amino acids are converted into new protoplasm that is used for growth and repair of worn-out body cells.
• Synthesis of proteins such as enzymes and hormones.
• [EXCESS] Excess amino acids are deaminated in the liver.

Question 27

State the utilization of fats in humans.

Answer 27

• When there is sufficient supply of glucose, fats are used to build protoplasm (synthesis of cell membrane).
• When glucose is in short supply, fats are broken down to provide energy for the body’s activities.
• [EXCESS] Excess fats are stored in fat/adipose tissues.

Question 28

What is the difference between the hepatic vein and hepatic portal vein?

Answer 28

• The hepatic vein distributes remaining glucose and amino acids from the liver to the rest of the body.
• The hepatic portal vein transports amino acids and sugars from the intestines to the liver.

Question 29

What are the factors that affect the rate of absorption ?

Answer 29

1. Surface area
2. Thickness of separating material
3. Concentration gradient

Question 30

How is the small intestine adapted for absorption?

Answer 30

LARGE SURFACE AREA:
-Folds, villi and microvilli increase SA:VR for faster absorption of nutrients.
-Small intestine is very long (~6m long) which increases the time for absorption to take place.
THIN SEPARATING MATERIAL:
-Villi walls are one-cell thick to make it easy for nutrients to pass through into the bloodstream and faster.
STEEP CONCENTRATION GRADIENT:
-Dense network of capillaries help carry away absorbed nutrients quickly and maintain a steep concentration gradient.

Question 31

State the differences between physical digestion and chemical digestion.

Answer 31

PHYSICAL DIGESTION
-Involves mechanical break-up of food into smaller pieces.
-By chewing, peristalsis, churning, action of bile.
-Increases SA:VR of food particles so enzymes can work on them faster.
CHEMICAL DIGESTION
-Involves break-down of large food molecules into small soluble molecules that can be absorbed (into the blood).
-Involves hydrolytic reactions catalyzed by digestive enzymes.

Question 32

State all instances where physical digestion occurs in the human digestive system.

Answer 32

1. Chewing in the mouth breaks up large food pieces into small food pieces, which increases SA:VR for greater enzyme efficiency.
2. Churning in the stomach breaks up food into a semi-solid liquid called chyme that would be released into the duodenum.
3. Emulsification of fat droplets into smaller fat droplets by action of bile in the duodenum allows for increased SA:VR of fats, speeding up digestion by lipase.