topic 6.1- digestion and absorption

Question 1

what is peristalsis ?

Answer 1

peristalsis is the contraction of circular and longitudinal muscle layers

Question 2

what is the function of peristalsis in the small intestine?

Answer 2

to mix the food with enzymes and move it along the gut.

Question 3

what is the function of the pancreas?

Answer 3

to secrete enzymes into the lumen of the small intestine.

Question 4

what are the main enzymes present in pancreatic juice?

Answer 4

amylase, lipase, endopeptidase

Question 5

amylase

Answer 5

starch->maltose

Question 6

lipase

Answer 6

triglycerides-> fatty acids + glycerol
or
triglycerides-> fatty acids + monoglycerides

Question 7

nucleases

Answer 7

DNA and RNA -> nucleotides

Question 8

maltase

Answer 8

maltose -> glucose

Question 9

lactase

Answer 9

lactose -> glucose + galactose

Question 10

sucrase

Answer 10

sucrose -> glucose + fructose

Question 11

proteases/peptidases

Answer 11

proteins/polypeptides -> shorter peptides

Question 12

dipeptidases

Answer 12

dipeptides -> amino acids

Question 13

what do enzymes do?

Answer 13

they digest most macromolecules in food into monomers in the small intestine.

Question 14

describe the path of digestive enzymes from the pancreas to the small intestine

Answer 14

1. synthesised in pancreatic gland cells on ribosomes on the rER
2. processed in the Golgi apparatus
3. secreted by exocytosis
4. flow through pancreatic duct and into small intestine

Question 15

what type of reactions are macromolecules->monomers

Answer 15

hydrolysis

Question 16

what are the two functions of the villi in the small intestine?

Answer 16

• to increase the surface area of epithelium over which absorption is carried out
• to absorb monomers formed by digestion as well as minerals and vitamins

Question 17

draw out a labelled diagram of a villus

Answer 17

check

Question 18

list 6 substances absorbed by the villi in the small intestine

Answer 18

• glucose, fructose, galactose and other monosaccharides
• amino acids
• fatty acids, monoglycerides, glycerol
• bases (from nucleotides)
• mineral ions (eg Ca, K, Na)
• vitamins

Question 19

to be absorbed into the body, nutrients must pass from the —– of the small intestine to the ——- or ——- in the villi

Answer 19

lumen; capillaries; lacteals

Question 20

what happens before nutrients pass into the lacteal/capillaries of the villi?

Answer 20

they must first be absorbed into epithelium cells

Question 21

why can glucose not pass through the plasma membrane of the villus epithelium via simple diffusion?

Answer 21

because it is polar and therefore hydrophilic

Question 22

describe how triglycerides are absorbed from the small intestine into the villi.

Answer 22

1. triglycerides are digested into fatty acids and monoglycerides
2. monoglycerides are absorbed into villus epithelium cells by simple diffusion
3. fatty acids are absorbed by facilitated diffusion (via fatty acid transporters)
4. inside the epithelium cells, fatty acids + monoglycerides form triglycerides, which cannot diffuse back out.
5. triglycerides + cholesterol + phospholipids + protein -> lipoprotein particles
6. these are released into the interstitial spaces of the villus by exocytosis

Question 23

describe how glucose is absorbed from the small intestine into the villi

Answer 23

1. Na-K pumps in the inwards-facing part of the plasma membrane pump Na ions by active transport from the cytoplasm to the interstitial spaces inside the villus and K ions in the opposite direction
2. there is a low concentration of Na ions inside villus epithelium cells
3. sodium-glucose co-transporter proteins in the microvilli transfer a Na ion and glucose molecule together from the intestinal lumen to the cytoplasm of the epithelial cell (facilitated diffusion).
4. glucose channels allow the glucose to move from the cytoplasm to the interstitial spaces inside the villus and into the blood capillaries.

Question 24

mouth

Answer 24

• mechanical digestion of food by chewing and mixing with saliva (contains lubricants and enzymes)

Question 25

oesophagus

Answer 25

• movement of food by peristalsis from the mouth to the stomach

Question 26

stomach

Answer 26

• churning and mixing with secreted water + acid which kills foreign pathogens in food
• initial stages of protein digestion

Question 27

small intestine

Answer 27

• digestion of lipids, carbs, proteins, nucleic acids
• neutralisation of stomach acid
• absorption of nutrients

Question 28

pancreas

Answer 28

secretion of lipase, amylase, and protease

Question 29

liver

Answer 29

secretion of surfactants in bile to break up liquid droplets

Question 30

gall bladder

Answer 30

storage and regulated release of bile

Question 31

large intestine

Answer 31

• re-absorption of water
• further digestion by symbiotic bacteria (especially of carbs)
• formation and storage of faces

Question 32

describe the 4 layers of the wall of the small intestine

Answer 32

• serosa (outer coat)
• muscle layers (longitudinal muscle and inside it circular muscle)
• sub-mucosa (tissue layer containing blood and lymph vessels)
• mucosa (lining of SI, with epithelium that absorbs nutrients)

Question 33

describe the processs of starch digestion

Answer 33

Starch can exist in one of two forms – amylose (linear, only 1,4) or amylopectin (branched, 1,4+1,6)

The digestion of starch is initiated by salivary amylase in the mouth and continued by pancreatic amylase in the intestines

Amylase digests amylose into maltose subunits (disaccharide) and digests amylopectin into branched chains called dextrins (it cannot break 1,6 bonds)

Both maltose and dextrin are digested by enzymes (maltase) which are fixed to the epithelial lining of the small intestine

Question 34

how and why are the products of the digestion of starch transported to the liver?

Answer 34

via the hepatic portal vein; excess glucose is absorbed by liver cells and converted to glycogen for storage