Chapter 6 - Nutrition in Man

Question 1

Define nutrition. [1]

Answer 1

Process by which organisms obtain food and energy for growth, repair and maintenance of the body [1]

Question 2

Define physical digestion. [3]

Answer 2

Involves mechanical break-up of food into smaller pieces [1]

By chewing, peristalsis, churning, action of bile [1]

Increases S.A to vol. ratio of food particles so enzymes can work on them faster [1]

Question 3

Define chemical digestion. [2]

Answer 3

Involves breakdown of large molecules in food into smaller, soluble molecules that can be absorbed by body cells [1]

Involves hydrolytic reactions catalysed by digestive enzymes [1]

Question 4

Describe the physical and chemical digestion that takes place in the mouth. [5]

Answer 4

P: Teeth physically breaks food into smaller pieces to increase S.A to vol ratio for digestive enzymes to work efficiently [1]. Tongue rolls small pieces of food into boli for easier swallowing and helps to mix saliva with food [1]

C: Salivary glands secrete saliva through salivary ducts [1], containing mucin to soften food [1] and salivary amylase that catalyses breakdown of starch to maltose [1]

Question 5

What is the oesophagus? [2]

Answer 5

Oesophagus is a narrow muscular tube that extends to the stomach [1]

The walls are made up of two layers of antagonistic muscles (movements oppose each other): longitudinal and circular that produce contractions [1]

Question 6

Define peristalsis. [1]

Answer 6

Peristalsis refers to 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. [1]

Question 7

What is the stomach? [2]

Answer 7

Stomach is a distensible muscular bag with thick and well-developed muscular bag [1].

Stomach walls form deep pits that contain gastric glands that secrete mucus to protect stomach walls and gastric juice, stimulated to be secreted when bolus enters stomach. [1]

Question 8

What is the function of hydrochloric acid in gastric juice? [4]

Answer 8

Hydrochloric acid in gastric juice denatures salivary amylase from mouth and stops its activity [1], activates inactive pepsinogen and converts it to active pepsin [1], provides an acidic medium for action of pepsin [1], kills harmful microorganisms [1]

Question 9

Describe the physical and chemical digestion in the stomach. [3]

Answer 9

P: Peristalsis in the walls of the stomach mixes food with gastric juice by churning. [1]

C: Pepsin catalyses breakdown of protein to polypeptides [1], partially digested food is liquefied to form chyme [1]

Question 10

Describe the chemical digestion in the small intestine. [9]

Answer 10

Carbohydrate digestion:
Starch is digested to maltose by pancreatic amylase [1], maltose digested to glucose + glucose by maltase [1]

Sucrose digested to glucose + fructose by sucrase [1]

Lactose digested to glucose + galactose by lactase [1]

Protein digestion:
Protein is digested to polypeptides by trypsin [1], which is activated by enterokinase [1] from inactive trypsinogen [1]. Polypeptides digested to amino acids by peptidases/erepsin [1].

Fat digestion:
Fat digested to 3 fatty acids + glycerol by intestinal/pancreatic lipase [1]

Question 11

Describe how the liver, pancreas and intestinal glands help in digestion. [15]

Answer 11

Liver:
Produces bile that is stored in the gallbladder [1], secreted into duodenum via bile ducts [1], emulsifies fats to increase S.A to volume ratio for lipases to work on and speed up fat digestion [1]

Pancreas:
Secretes pancreatic juice [1] containing inactive trypsinogen [1], pancreatic amylase [1], and pancreatic lipase [1]

Intestinal Glands:
Secretes intestinal juice [1] containing maltase [1], sucrase [1], lactase [1], peptidases [1], intestinal lipase [1], enterokinase [1], erepsin [1]

Question 12

What is the function of the large intestine? [3]

Answer 12

Absorb water and mineral salts from undigested food material [1], move undigested waste to the rectum via peristalsis [1], rectum stores faeces temporarily and expels through the anus [1]

Question 13

Define absorption. What is it influenced by? [4]

Answer 13

Absorption is the process where digested food substances are absorbed into body cells. [1]

Influenced by SA [1], thickness of epithelium of villi [1], conc. gradient [1] (more SA, less thickness, steeper conc gradient = higher rate of absorption)

Question 14

What adaptations do the small intestine / villi have for absorption? [5]

Answer 14

Folds, villi, microvilli in the walls of small intestine increases SA to vol ratio for faster absorption of nutrients [1]

Walls of villi are one-cell thick to make it easier for nutrients to pass into bloodstream faster [1], long length of small intestine increases time allowed for absorption [1], dense network of blood capillaries to carry away absorbed sugars and amino acids fast to maintain steep conc gradient [1], a lacteal/lymphatic capillary present in each villus to transport fats away from intestine [1]

Question 15

Define assimilation of absorbed nutrients. [1]

Answer 15

Process where absorbed food substances are converted into new protoplasm or used to release energy by respiration. [1]

Question 16

What is the function of the hepatic portal vein?

Answer 16

Transport of blood rich in absorbed nutrients from the small intestine to the liver [1]

Question 17

Describe how glucose, amino acids and fats are used. [6]

Answer 17

Glucose:
Respiration to release energy [1]

Amino Acids:
Converted to new protoplasm [1] to be used for growth and repair [1], synthesis of proteins [1]

Fats:
Used to build protoplasm if glucose is sufficient [1], used to provide energy if glucose is insufficient [1]

Question 18

Describe the 5 main functions of the liver. [5] [4] [3] [4] [4]

Answer 18

Regulation of Blood Glucose Concentration [1]

• When there is too much glucose, liver secrets insulin [1] to stimulate liver cells to convert excess glucose to glycogen to reduce blood glucose conc [1] by Islets of Langerhans.
• When there is too little glucose, liver secretes glucagon [1] to stimulate liver cells to convert excess glycogen to glucose to raise blood glucose conc [1]

Production of bile / Fat metabolism [1]
- Produces bile that emulsifies fat into smaller fat droplets [1], oxidises fat to produce energy [1], converts excess carbs and proteins to fatty acids and glycerol which are exported and stored as fatty tissue [1]

Deamination of amino acids / Protein metabolism [1]
- Removal of amino group, amino group converted to ammonia, then urea [1], carbon residues of amino groups are converted to glucose [1]

Storage of Iron / Breakdown of Red Blood Cells [1]
- Worn out red blood cells are destroyed in spleen [1], haemoglobin from these cells are transported to liver to be broken down [1], iron released from breakdown of haemoglobin stored in liver and synthesise new RBC [1]

Detoxification of Alcohol [1]
- Liver cells contain alcohol dehydrogenase [1], which converts alcohol to acetaldehyde [1]. Detoxification refers to the process where harmful substances are converted into harmless substances [1]

Question 19

Describe the impacts of excessive alcohol consumption. [9]

Answer 19

Reduced self-control [1], depressant [1], increased reaction times [1], neglect social responsibilities [1], inflammation and ulcers [1], scarring and destruction of liver cells [1] –> liver cirrhosis when liver cells are destroyed [1] –> liver failure [1], addiction [1]