digestive system

Question 1

digestive system order

Answer 1

mouth -> oesophagus -> stomach -> small intestine -> large intestine -> rectum -> anus

Question 2

peristalsis

Answer 2

• circular smooth muscle causes the lumen to constrict
• longitudinal smooth muscle causes localised shortening of the gut
• contractions progress in wave like motions to push food along
• occurs along parts of the alimentary canal (oesophagus, small intestine and large intestine

Question 3

types of digestion

Answer 3

1. mechanical – teeth grinding, stomach churning

2. chemical – using bile and enzymes which are produced by specialised cells in glands and tissues in the gut lining

Question 4

enzymes and pH in digestion

Answer 4

• HCl in the stomach kills bacteria and provides the correct pH for the protease enzyme, pepsin, to digest protein
• Bile and pancreatic juice contain bicarbonate ions to neutralise the stomach acid when it enters the small intestine and provide the alkaline conditions needed by the enzymes present in the small intestine

Question 5

stomach acid

Answer 5

forms part of the innate immune system (killing pathogens)

Question 6

bile

Answer 6

• made in the liver
• stored in the gall bladder
• gall bladder secretes it into the small intestine when stomach contents arrive in the small intestine

Question 7

sections of the small intestine

Answer 7

• duodenum (1st section)
• jejunum (2nd section)
• ileum (3rd section)

Question 8

digestive enzymes

Answer 8

• amylase: starch -> maltose (produced by salivary glands, pancreas and SI)
• protease: protein -> amino acids (produced by stomach, pancreas and SI)
• lipase: fat -> fatty acids+glycerol (produced by pancreas and SI)
• maltase: maltose -> glucose (SI)

Question 9

bile functions

Answer 9

• emulsifies lipids to increase the surface area for lipases to work on -> rate of digestion is increased
• neutralises stomach acid because bile is alkaline

Question 10

chyme

Answer 10

digested food and HCl

Question 11

villi

Answer 11

• increases surface area of small intestine
• the walls of the villi are 1 cell thick so there is a smaller diffusion distance -> faster ROR
• glucose and amino acids pass through the gut wall and are absorbed into the blood through the capillaries
• glycerol and fatty acids pass through the gut wall and into the lymph system through the lacteal (before entering the blood too)

Question 12

why does starch, protein and lipids need to be digested?

Answer 12

they are large, insoluble molecules and cannot pass through the gut wall

Question 13

why can fibre not be digested and absorbed by humans?

Answer 13

the enzymes required are not present

Question 14

extracellular enzymes

Answer 14

they are secreted into the gut lumen to break down the large insoluble molecules in food by hydrolysis

Question 15

how long does digestion take?

Answer 15

12-24 hours

Question 16

how does the body use digested food

Answer 16

• enzymes make new macromolecules (e.g. carbohydrates, proteins, lipids) using condensation reactions
• glucose is used in aerobic respiration to produce ATP

Question 17

undigested food

Answer 17

• indigestible components of food, eg cellulose (fibre), from plant-based foods are passed on to the large intestine
• undigested waste matter is called faeces
• brown colour of the faeces is due to bile pigments
• faeces passes through the large intestine, into the rectum and is expelled through the anus in a process called egestion

Question 18

Why is it necessary to have an amylase in the mouth and another one secreted by the pancreas?

Answer 18

• the amylase secreted by the salivary glands works when the pH is 7
• this amylase enzyme denatures when the food enters the stomach due to the acidic pH
• another amylase is therefore secreted by the pancreas which works in the alkaline conditions of the small intestine (pH8)

Question 19

digestive sequence

Answer 19

Mouth: Begins digestion of carbohydrates (starch by amylase produced by the salivary glands). Chewing breaks up the food into smaller pieces for easier digestion
Oesophagus: Food pushed down by peristalsis
Stomach: Stores food to slow down its progression along the digestive system. Breaks food up by churning. Begins digestion of proteins by pepsin (a protease). Produces HCl to kill bacteria and allow pepsin to work.
Liver: Produces bile
Gall Bladder: Stores bile and releases it when needed
Pancreas: Produces digestive enzymes. Its secretions also help neutralise stomach acid
Duodenum: continues digestion of carbs and proteins, begins digestion of lipids
Ileum: completes digestion of carbs, proteins and lipids + absorption of digested food
Large intestine: Absorption of water from undigested food
Rectum: Storage of faeces

Question 20

Absorption of glucose in the villi

Answer 20

-active transport is used to maximise the amount of glucose we get out of our food

Question 21

glycogen storage

Answer 21

glucose is stored as glycogen in skeletal muscles and the liver

Question 22

liver main functions

Answer 22

• removal of glucose from the blood and converting it to glycogen
• production of bile
• synthesis of cholesterol
• breakdown of hormones

Question 23

stomach/gastric juice contents

Answer 23

• HCl
• protease (pepsin)
• lipase

Question 24

pancreatic juice contents

Answer 24

• protease
• amylase
• lipase

Question 25

glucose and starch

Answer 25

• glucose is a single molecule

- starch is a polymer of glucose, made up of 500-2000000 glucose molecules

Question 26

amylase

Answer 26

mouth - from salivary gland (starch -> maltose)
duodenum - from pancreas (starch -> maltose)
ileum - from wall of ileum (maltose -> glucose)

Question 27

protease

Answer 27

stomach - from stomach glands
duodenum - from pancreas
ileum - from ileum wall

Question 28

lipase

Answer 28

duodenum - from pancreas