y3.1: human digestive system 🍣

Question 1

what is digestion?

Answer 1

digestion is the process that breaks down complex food substances into simple, soluble molecules that are small enough to be absorbed into the body cells

Question 2

what is physical digestion?

Answer 2

the mechanical breakdown of food into smaller particles to provide a large surface area to volume ratio for faster rate of digestion by digestive enzymes
- eg chewing, churning, emulsification of fats by bile

Question 3

what is chemical digestion?

Answer 3

the breakdown of large food molecules into small soluble molecules catalysed by digestive enzymes

Question 4

digestion in the mouth (pH 7)

Answer 4

physical: chewing (to increase SA:VR)
chemical: starch => maltose by salivary amylase

Question 5

what is peristalsis and how do the muscles contract?

Answer 5

peristalsis is the rhythmic, wave-like muscular contractions of alimentary canal wall

• circular inside, longitudinal outside (antagonistic)
• before and after the bolus, circular contracts
• at the bolus, longitudinal contracts

Question 6

digestion in the stomach (pH 2)

Answer 6

physical: churning to form chyme
chemical: protein => polypeptide by pepsin

Question 7

gastric juice components and uses

Answer 7

1) hydrochloric acid
- provides and acidic medium for optimum pH of pepsin
- kills bacteria in food
- changes inactive pepsinogen to active pepsin
2) pepsin
- digests protein to polypeptide by hydrolysis

Question 8

role of liver in digestion

Answer 8

liver produces bile

• bile emulsifies fats to physically break them down into fat droplets to increase SA:VR for faster digestion by lipase
• creates an alkaline environment (pH 8.5) for enzyme action and to neutralise hydrochloric acid from stomach

Question 9

role of gall bladder in digestion

Answer 9

stores bile

Question 10

role of pancreas in digestion

Answer 10

secretes pancreatic juice containing:

• pancreatic amylase
• pancreatic lipase
• trypsin

Question 11

digestion in the small intestine (pH 8.5)

Answer 11

physical: emulsification of fats into fat droplets by bile
chemical:
- starch => maltose by pancreatic amylase
- maltose / lactose / sucrose => glucose + galactose + fructose by maltase / lactase / sucrase
- fat droplets => 3 fatty acids + 1 glycerol by intestinal and pancreatic lipase
- protein => polypeptide by trypsin
- polypeptide => amino acids by peptidase

Question 12

how are glucose and amino acids absorbed in the small intestine?

Answer 12

glucose and amino acids diffuse through the epithelium and enter the blood capillaries in the villi via facilitated diffusion and active transport

Question 13

how are glycerol and fatty acids absorbed in the small intestine?

Answer 13

glycerol and fatty acids diffuse into epithelial cells, recombine to form fat globules and diffuse into the lacteal in the villi (simple diffusion)

Question 14

structural adaptations of the small intestine to its function

Answer 14

1) long
- provides sufficient time for absorption / diffusion to take place
2) walls of small intestine have villi, each villi have microvilli
- increase SA:VR => increase rate of diffusion => faster absorption
3) one cell thick epithelial cells
- reduce the distance for digested products to diffuse over
4) villi contains a dense network of blood capillaries and lacteal
- continuous transport of food substances away of the small intestine maintains a favourable concentrtaion gradient => increase rate of diffusion

Question 15

where do the glucose and amino acids go?

Answer 15

they are carried to the liver by the hepatic portal vein

Question 16

what is assimilation?

Answer 16

assimilation is the utilisation of absorbed nutrients and how the body deals with the excess nutrients

Question 17

how is excess glucose dealt with?

Answer 17

excess glucose is converted into glycogen by liver cells and stored, stimulated by insulin
- glycogen is converted back into glucose by liver cells, stimulated by glucagon

Question 18

how are excess amino acids dealt with?

Answer 18

excess amino acids are deaminated in the liver

• the amino group is removed and converted into urea
• the remaining carbon residue is converted into glucose

Question 19

how are excess lipids dealth with?

Answer 19

excess lipids are stored in cytoplasm of adipose cells, forming adipose tissues under the skin

Question 20

what is egestion 💩 ?

Answer 20

egestion is the elimination of faeces via the anus from the body

Question 21

functions of the liver

Answer 21

1) bile production
2) regulation of blood glucose concentration (w insulin and glucagon help)
3) protein synthesis of proteins in blood
4) deamination of excess amino acids
5) breakdown of red blood cells
6) detoxification

Question 22

how does the liver break down alcohol and hydrogen peroxide?

Answer 22

• the liver produces alcohol dehydrogenase which breaks down alocohol to acetaldehyde, which can be further broken down to glucose
• the liver breaks down hydrogen peroxide into water and oxygen by catalase