Human nutrition

Question 1

Five processes of human digestion

Answer 1

ingestion
digestion
absorption
assimilation
egestion

Question 2

Mechanical digestion

Answer 2

Physical breaking down of food by processes such as chewing in the mouth and the churning of food in the stomach. Prepares food for chemical digestion by increasing the surface area for enzyme action

Question 3

Chemical digestion

Answer 3

Breaking down of food by the process of hydrolysis into smaller, soluble substances that can be absorbed into the bloodstream.

Question 4

Hydrolysis

Answer 4

Enzymes break bonds that join molecules together by ADDING water

Question 5

Alimentary canal

Answer 5

Muscular tube from the mouth to the anus

Question 6

Accessory organs

Answer 6

Help the canal to work efficiently. Tongue, salivary glands, liver, gallbladder, pancreas

Question 7

Salivary amylase

Answer 7

Breaks down starch into dextrose and maltose, depending on how long food stays in the mouth. Only carbohydrate digestion occurs in the mouth

Question 8

Mucin

Answer 8

Coats food to make it slippery and moist for swallowing

Question 9

Lysozyme

Answer 9

Keeps mouth free of bacteria

Question 10

Teeth

Answer 10

Used for chewing or mastication which increases the surface area for enzyme activity

Question 11

Tongue

Answer 11

Responsible for mixing food with saliva. It has taste buds for tasting and forms the soft moist bolus ready for swallowing

Question 12

Oesophagus

Answer 12

Transports food to the stomach in process called peristalsis

Question 13

Peristalsis

Answer 13

Circular and longitudinal muscles in the gut wall contract and relax antagonistically to push the food in one direction along the whole digestive tract. May help to mix the food

Question 14

Stomach

Answer 14

Food passes into stomach through the cardiac sphincter. As stomach wall stretches gastrin is released into the blood from specialized cells in the lining. Gastrin causes gastric juice to be released

Question 15

Gastric juice made of

Answer 15

• pepsinogen (inactive form of pepsin)
• hydrochloric acid which activates pepsinogen into pepsin
• mucin which protects lining of stomach from acid and pepsin
• babies younger than six months also produce prorennin which causes milk to curdle and forms solid lumps so that it stays in the stomach for longer

Question 16

Small intestine

Answer 16

Duodenum - most secretions occur from this region

jejunum - no hormones are released

Ileum - very long and thin to maximise surface area for absorption

Question 17

Small intestine functions

Answer 17

• digestion = carbs are digested into glucose, proteins are digested into amino acids and lipis are digested into glycerol and fatty acids
• absorption =digested nutrients are soluble and can be carried through blood to where they are needed into the cell.

Question 18

Acidic chyme hormones

Answer 18

secretin and CCK (cholecystokinin)

Question 19

Secretin

Answer 19

Released by specialised cells of duodenum and targets the liver and causes it to secrete bile, targeting the pancreas which then releases pancreatic juice

Question 20

CCK

Answer 20

Hormone plays role in digestion and satiety + is released by cells of the small intestines and neurons in the brain. Presence of fatty acids / certain amino acids in the chyme entering duodenum stimulates CCK release

Question 21

Liver functions

Answer 21

1. Stores glucose in the form of glycogen which is used for cellular respiration
2. Forms fat from excess glucose and cholesterol for fat transport to adipose tissue
3. Breaks down excess amino acids and removes nitrogen wastes from the blood, leading to urea that passes through kidneys and then leaves body in form of urine
4. Detoxifies the blood out of harmful substances such as alcohol, drugs etc

Question 21

Importance of bile

Answer 21

Bile salts emulsify fats (increases surface area for the action of enzymes and therefore speed up process of digestion). Alkaline to neutralise the acidic chyme. Also helps with fat absorption by combining with fatty acids as well as fat soluble vitamins (A,D,E,K)

Question 22

Pancreas

Answer 22

Endocrine gland (Secretes hormones insulin and glucagon) and an exocrine gland (secretes digestive enzymes into the pancreatic duct which leads into the duodenum)

Question 23

Pancreatic juice contains:

Answer 23

1. Sodium bicarbonate - alkaline to convert acidic chyme into an alkaline solution with a pH of 8.5 (necessary for the functioning of enzymes which only work in slightly alkaline solutions)
2. Enzymes - digest proteins secreted as precursors and when they reach duodenum inactive forms are converted into active enzymes when they come into contact with intestinal juice and continue digestion of proteins
3. Pancreatic amylase, pancreatic lipase and nucleases

Question 24

Absorption

Answer 24

Mainly takes place in small intestine

Question 25

Structure of small intestine that makes it good for absorption pt 1

Answer 25

• has numerous folds along length
• extremely narrow which forces food to come into contact with wall often
• surface area is increased by villi
• each villus has epithelium consisting of a single layer of columnar cells, allowing for rapid diffusion. Cells have many mitochondria in them to provide energy for active transport
• columnar epithelial lining the villi possess microvilli at their free surfaces