Human Digestive System

Question 1

what is nutrition?

Answer 1

intake of food and the processes that convert food substances into living matter

Question 2

what does nutrition comprise of? (5 points)

Answer 2

ingestion: intake of food into body

digestion: large food molecules broken down/hydrolysed into smaller and soluble molecules

absorption: digested food molecules taken into body cells

assimilation: body cells make use of (assimilate) absorped food molecules

egestion: removal of undigested matter from body

Question 3

why is digestion necessary? (3 points)

Answer 3

food molecules are mostly insoluble in water

food molecules too large to pass through gut wall into bloodstream

helps break down large food molecules into smaller and soluble molecules

Question 4

why is the digestive system important?

Answer 4

enables us to use nutrients in food

Question 5

what is the physical digestion in the mouth? (2 points)

Answer 5

teeth cut and grind food (chewing), making it easier to swallow

increases surface area to volume ratio so enzymes can act on food more efficiently

Question 6

what is the chemical digestion in the mouth?

Answer 6

presence of food in mouth triggers a reflex that causes salivary glands to secrete saliva

Question 7

what are the constituents of saliva? (3 parts)

Answer 7

mucin (protein): protects soft lining of mouth from abrasion or and lubricates food for swallowing

antibacterial agents: kills many of the bacteria that enter the mouth with food

salivary amylase (enzyme): breaks down/digests starch to maltose

Question 8

what is the purpose of the pharynx?

Answer 8

connects buccal cavity to oesophagus and larynx

(also connects to trachea)

Question 9

what is the oesophagus?

Answer 9

long, narrow, muscular tube that extends to the stomach

Question 10

what is the purpose of the oesophagus?

Answer 10

conducts food from pharynx down to the stomach by peristalsis (no digestion occurs in oesophagus)

Question 11

what is the oesophagus made up of?

Answer 11

circular muscles (inner)
longitudinal muscle (outer)

^ antagonistic muscles (when one contracts, the other relaxes)

circular — contract, longitudinal — relax (wall constricts, inwards)
circular — relax, longitudinal — contract (wall dilates, outwards)

Question 12

what is peristalsis?

Answer 12

rhythmic, wave-like contractions (happens throughout alimentary canal)

2 sets of muscles work antagonistically (when one contracts, the other relaxes)

Question 13

what is the stomach lined with?

Answer 13

gastric glands that secrete gastric juices

Question 14

what is the physical digestion in the stomach?

Answer 14

churning action (peristalsis) by smooth muscles of stomach mixes food with gastric juice into chyme

Question 15

what does gastric juice contain?

Answer 15

dilute solution of hydrochloric acid (pH 2) and protease (pepsin)

Question 16

what happens with the gastric juice and food in the stomach? (4 points)

Answer 16

kills most harmful bacteria/microorganisms swallowed with food

provides acidic environment for enzymes (pepsinogen to pepsin) to work (optimum pH 2)

stops (denatures) action of salivary amylase (optimum pH 7)

protease breaks down/digests proteins into polypeptides

Question 17

why is the stomach protected by a layer of mucus?

Answer 17

prevents stomach lining from being damaged by acid

Question 18

what is the small intestine? (2 points)

Answer 18

consists of U-shaped duodenum and much-coiled ileum

where most digestion of large food molecules occur

Question 19

what is the process of digestion and absorption in the small intestine? (4 points)

Answer 19

chyme released from stomach into duodenum

intestinal glands secrete intestinal juice

pancreas secretes pancreatic juice

liver cells produce and secrete bile, stored in gallbladder, flows into duodenum via bile duct

Question 20

what is bile and its purpose?

Answer 20

alkaline greenish-yellow liquid produced by liver, an emulsifier (not enzyme, no optimum pH/temperature)

emulsifies fats by breaking up large fat droplets into tiny fat droplets so that surface area to volume ratio of fats increased to speed up digestion by pancreatic and intestinal lipases (emulsification)

(physical digestion)

Question 21

what does pancreatic juice contain? (3 enzymes)

Answer 21

pancreatic amylase (remaining starch —> maltose)
pancreatic lipase (lipids —> glycerol + fatty acids)
protease (proteins —> polypeptides)

Question 22

what does intestinal juice contain? (3 enzymes)

Answer 22

other carbohydrases (digests double sugars to single sugars), maltase (maltose —> glucose), sucrase (sucrose —> glucose + fructose)
other protease (polypeptides —> amino acids)
intestinal lipase (lipids —> glycerol + fatty acids)

Question 23

what is the fuction of the ileum?

Answer 23

absorps nutrients and water

Question 24

what are the functions of the large intestine? (2 points)

Answer 24

absorps water and mineral salts into blood

undigested matter temorarily stored in rectum, discharged through anus (egestion/defecation)

Question 25

what are villi? (3 points)

Answer 25

small intestine lined with many small finger-like projections to increase surface area for absorption of nutrients thin walls (1 cell thick) have many capillaries to transport absorped nutrients away

Question 26

how are absorped nutrients transported?

Answer 26

after absorption, blood capillaries rich in simple sugars and amino acids blood capillaries join into larger blood vessels larger blood vessels unite into hepatic portal vein (delivers nutrient-rich blood from gut to liver for assimilation)

Question 27

what is the use of glucose? (2 points)

Answer 27

substrate for cellular respiration excess stored as glycogen in liver and muscles of animals

Question 28

what is the use of amino acids? (2 points)

Answer 28

used in cells for synthesis of tissue proteins used in cells for sysnthesis of other substances such as enzymes and hormones

Question 29

what is the use of fats? (3 points)

Answer 29

formation of cell membranes excess stored in adipose tissue under skin or surrounding organs fats broken down to provide energy in certain conditions (starvation, fasting)

Question 30

why do diabetes occur?

Answer 30

body produces insufficient insulin (hormone that keeps blood sugar level balanced), or does not respond properly to insulin, resulting in high amount of sugar in the blood

Question 31

describe the 2 types of diabetes

Answer 31

type 1: inherited and cannot be prevented type 2: most common type, can be prevented

Question 32

how to prevent diabetes? (4 points)

Answer 32

eat in moderation (more fruits and vegetables, less sugar and saturated fat) at least 150min of physical activity weekly prevent weight gain (exercise regularly, control calorie intake) avoid smoking and reduce alcohol intake