Human Physiology

Question 1

list the digestive system components

Answer 1

• mouth
• esophagus
• stomach
• small intestine
• pancreas
• liver
• gallbladder
• large intestine

Question 2

function of mouth

Answer 2

• voluntary control of eating and swallowing
• mechanical digestion by chewing and mixing with saliva
• saliva contains lubricants and enzymes that start starch digestion

Question 3

function of esophagus

Answer 3

movement of food by peristalsis from mouth to stomach

Question 4

function of stomach

Answer 4

• churning and mixing with secreted water and acid to kill pathogens in food
• initial stages of protein digestion

Question 5

function of small intestine

Answer 5

• final stages of digestion of lipids, carbohydrates, proteins, and nucleic acids
• neutralising stomach acid
• absorption of nutrients

Question 6

function of pancreas

Answer 6

secretion of lipase, amylase, and protease

Question 7

function of liver

Answer 7

secretion of surfactants in bile to break up lipid droplets

Question 8

function of gallbladder

Answer 8

storage and regulated release of bile

Question 9

function of large intestine

Answer 9

• reabsorption of water
• further digestion (especially of carbohydrates by symbiotic bacteria)
• formation and storage of feces

Question 10

define peristalsis

Answer 10

• the contraction of circular and longitudinal muscle layers of the small intestine
• which mixes food with enzymes and moves it along the gut

Question 11

structure of the small intestine’s wall

Answer 11

from outer to inner layer

• serosa: outer coat
• muscle layers: longitudinal muscle, and inside it, circular muscle
• sub-mucosa: tissue layer containing blood and lymph vessels
• mucosa: lining of small intestine with epithelium that absorbs nutrients on its inner surface

Question 12

types of gland tissue in pancreas

Answer 12

• one type secretes insulin and glucagon into the blood
• the other type synthesises and secretes digestive hormones into the gut in response to eating a meal (mediated by hormones synthesised and secreted in the stomach)

Question 13

digestive enzymes in pancreatic juice

Answer 13

• amylase: to digest starch
• lipase: to digest triglycerides and phospholipids
• protease: to digest proteins and peptides

Question 14

function of amylase

Answer 14

starch -> maltose

Question 15

function of lipase

Answer 15

triglycerides -> fatty acids and glycerol

Question 16

function of phospholipase

Answer 16

phospholipids -> fatty acids, glycerol, and phosphate

Question 17

function of protease

Answer 17

proteins/polypeptides -> shorter peptides

Question 18

enzymes produced by small intestine

Answer 18

• nuclease
• maltase
• lactase
• sucrose
• exopeptidase
• dipeptidase

Question 19

characteristics of small intestine enzymes

Answer 19

• some are secreted into intestinal juice

- but most are immobilised in the plasma membrane of epithelium cells

Question 20

function of nuclease

Answer 20

DNA/RNA -> nucleotides

Question 21

function of maltase

Answer 21

maltose -> glucose

Question 22

function of lactase

Answer 22

lactose -> glucose & galactose

Question 23

function of sucrase

Answer 23

sucrose -> glucose and fructose

Question 24

what is exopeptidase

Answer 24

• proteases that digest peptides
• by removing single amino acids either from the carboxy or amino terminal of the chain
• until only a dipeptide is left

Question 25

dipeptidase

Answer 25

dipeptide -> amino acid

Question 26

substances absorbed by villus cells

Answer 26

• monosaccharides: glucose, fructose, galactose…
• any of the 20 amino acids used to make proteins
• fatty acids, monoglycerides, glycerol
• bases from digestion of nucleotides
• mineral ions: calcium, potassium, sodium…
• vitamins

Question 27

what if harmful substances are absorbed by villus cells?

Answer 27

• sometimes harmful substances pass through the epithelium
• but they are subsequently removed from the blood and detoxified by the liver
• other absorbed unwanted (but harmless) substances pass out as urine
• some pathogens may be absorbed but are quickly removed by phagocytes in the liver

Question 28

methods of absorption: triglyceride example

Answer 28

• triglycerides are digested into fatty acids and monoglycerides, which can be absorbed into villus epithelium cells via simple diffusion (they can pass through phospholipids in the membrane)
• fatty acids can also be absorbed via facilitated diffusion through fatty acid transporter proteins in microvilli membrane
• inside epithelium cells, fatty acids + monoglycerides -> triglycerides again, and cannot diffuse back out into the lumen
• triglycerides coalesce with cholesterol to form droplets of 0.2 microns in diameter, which become coated in phospholipids and protein
• these lipoprotein particles are release via exocytosis on the inner side of villus epithelium cells
• they either enter the lacteal to be carried away in the lymph, or they enter the blood capillaries in the villi

Question 29

methods of absorption: glucose example

Answer 29

• glucose can’t pass through the membrane via simple diffusion as it’s polar (hydrophilic)
• sodium-potassium pumps in the inward-facing part of the plasma membrane pump sodium ions via active transport from cytoplasm to spaces inside the villus, and potassium in the opposite direction
• creating low conc of sodium in the villus epithelium cells
• sodium-glucose co-transporter proteins in the microvilli transfer a sodium ion and glucose molecule together from the intestinal lumen to the cytoplasm of the epithelium cells via a passive facilitated diffusion
• glucose channels allow the glucose to move via facilitated diffusion from cytoplasm to spaces inside the villus and into blood capillaries in the villus