alimentary canal 2.27, 2.28, 2.29, 2.30, 2.31, 2.32

Question 1

what happens to food in the alimentary canal?

Answer 1

food is:
- ingested
- digested
- absorbed
- egested
for the purpose that food can be assimilated

Question 2

name of organs involved in the alimentary canal:

Answer 2

• mouth
• oesophagus
• liver
• stomach
• pancreas
• duodenum & ileum (together these are the small intestine)
• colon & anus (together these are the large intestine)

Question 3

what does ingestion mean?

Answer 3

taking food in through the mouth and swallowing

Question 4

what does digestion mean?

Answer 4

breaking down large insoluble molecules in food into smaller pieces (physical digestion) and smaller, soluble molecules (chemical digestion)

Question 5

what does absorption mean?

Answer 5

movement of small soluble molecules out of the gut and into the blood by diffusion and active transport

Question 6

what does egestion mean?

Answer 6

passing out undigested food through the anus

Question 7

what does assimilation mean?

Answer 7

building larger biological molecules from the smaller soluble molecules in all cells

Question 8

what is the first structure in the alimentary canal and what’s its role?

Answer 8

mouth
where ingestion takes place = digestion, breakdown of large insoluble molecules into small soluble molecules

Question 9

what two types of digestion take place in the mouth?

Answer 9

mechanical digestion - food is broken up into smaller pieces via chewing, increasing the surface area for enzymes and prevent discomfort when swallowing

chemical digestion - saliva is released into the mouth by the salivary glands, making the food easier to swallow and it also contains the enzyme amylase, which breaks down starch to maltose

Question 10

what does amylase break starch into?

Answer 10

maltose
works best at neutral pH so is denatured when reaching stomach and stops working

Question 11

what is the role of swallowing?

Answer 11

before swallowing the food is shaped into a ball by the tongue and moved towards the back of the mouth
this ball is called BOLUS
there is a flap called EPIGLOTTIS which blocks the food from entering the trachea

Question 12

what is the role of the oesophagus?

Answer 12

the oesophagus is a long tube that connects the mouth to the stomach
food is pushed down by peristalsis
two sets of muscles push the food down:
- circular muscles contract behind the bolus pushing it along
- longitudinal muscles contract making the oesophagus wider

Question 13

how does the stomach begin the process of digestion?

Answer 13

the gastric glands in the stomach wall secrete the enzyme pepsin, which begins the process of digesting proteins into peptides (shorter chain of amino acids)

Question 14

what does pepsin break down proteins into?

Answer 14

peptide
pepsin’s optimum conditions are an acidic pH
the conditions in the stomach are acidic due to the release of hydrochloric acid by the gastric glands

Question 15

how does the contraction of the stomach wall aid digestion?

Answer 15

causes mixing of the contents of the stomach, maximising contact between the enzymes and food

Question 16

what stops the low pH of the stomach from burning through the stomach walls?

Answer 16

has a very low pH and would burn through stomach if it wasn’t for the mucus lining

Question 17

as well as hydrochloric acid aiding the optimum conditions for pepsin, what other roles does it perform?

Answer 17

kills bacteria and fungi which may be present in the food we eat

Question 18

what happens in the small intestine?

Answer 18

both digestion and absorption

digestion happens in the first section = duodenum

Question 19

what enzymes does the duodenum release to aid digestion?

Answer 19

finial site of chemical digestion

the pancreas makes several enzymes and secretes them into the duodenum:
trypsin, amylase and lipase

duodenum wall contains glands that make enzymes and secrete them into the duodenum:
maltase, peptidase

Question 20

duodenum and enzymes aiding digestion released from pancreas:
trypsin

Answer 20

protein > (trypsin) > peptide

Question 21

duodenum and enzymes aiding digestion released from pancreas:
amylase

Answer 21

starch > (amylase) > maltose

Question 22

duodenum and enzymes aiding digestion released from pancreas:
lipase

Answer 22

lipid (fat) > lipase > glycerol + 3 fatty acids

Question 23

duodenum and enzymes aiding digestion released from duodenum walls:
maltase

Answer 23

maltose > (maltase) > glucose

Question 24

duodenum and enzymes aiding digestion released from duodenum walls:
peptidase

Answer 24

peptide > (peptidase) > amino acids

Question 25

where is bile produced from?

Answer 25

produced by the liver and stored in the gall bladder, before being released into the duodenum through the bile duct

Question 26

what are the two functions of bile?

Answer 26

• neutralises the stomach acid = enzymes in the duodenum work best at pH 7-8
• emulsifiers lipids = breaking down large droplets into smaller droplets, increasing surface area for lipase to digest fats

Question 27

what happens once food enters the ileum?

Answer 27

digestion is over and absorption begins

Question 28

how is the ileum adapted for absorption?

Answer 28

ileum has many folds and is covered in finger-like projections called villi:
- small soluble molecules are absorbed
- some are absorbed via diffusion
- some are absorbed by active transport

Question 29

how is the rate of diffusion increased in the ileum?

Answer 29

• large surface area = folding of the ileum, villi and microvilli
• short diffusion distance = the villi are one cell thick
• high concentration gradient = provided by capillary network and lacteals removing absorbed molecules

Question 30

what is the large intestine made of?

Answer 30

the colon and rectum
colon - the site of reabsorption of water
rectum - where faeces are stored and egested from the anus