D2

Question 1

Where and how do exocrine glands produce and secrete substances?

Answer 1

• via duct on epithelial surface
• surface of body
• lumen of digestive tract/gut

Question 2

What are examples of digestive glands? (4)

Answer 2

• salivary glands -> secrete saliva (contains amylase)
• gastric glands -> secrete gastric juices (contains hydrochloride acid and protease)
• pancreatic glands -> secrete pancreatic juices (contains lipids)
• intestinal glands -> secrete intestinal juices (via crypts of Lieberkuhn)

Question 3

What is the exocrine gland composed of? (3)

Answer 3

• cluster of secretory cells which form an acinus
• acini are surrounded by basement membrane and held together by tight junctions between secretory cells
• secretory cells have highly develop ER and golgi network for material secretion and rich in mitochondria

Question 4

How are exocrine products released?

Answer 4

Products released Via secretory vesicles into a duct which connect to epithelial surface
(Ducts may arise from a convergence of smaller ductules to enhance secretion)

Question 5

What is the nervous mechanism for the secretion of gastric juices? (3)

Answer 5

• sight and smell of food triggers immediate response by which gastric juice is secreted by stomach pre-ingestion
• food enters and causes distension which is detected by stretch receptors in stomach lining
• signals sent to brain which triggers release of digestive hormones to achieve sustained gastric stimulation

Question 6

What is the hormonal mechanism to secretion fo gastric juices? (5)

Answer 6

• gastrin is secreted in bloodstream from gastric puits of stomach and stimulates release of stomach acids
• if stomach pH drops too lows, gastric secretion is inhibited by git hormone (secretin and somatostatin)
• when chyme passes into small intestine, the duodenum releases digestive juices
  -> secretin and CCK stimulate pancreas and liver to release digestive juices
  -> pancreatic juices contain biocarbonate ions which neutralise stomach acids and liver produces bile to emulsify fats

Question 7

What function does the acidic condition of the stomach serve? (3)

Answer 7

• assists digestion (breaking bond in food molecules)
• activate stomach proteases (eg., pepsin action ate dinner when Pepsi oven is proteolytically cleaves in acidic conditions)
• prevents pathogenic infections (destroy microorganisms)

Question 8

What protects the stomach lining from being damages by acidic conditions?

Answer 8

Layer of mucus

Question 9

How is low pH is stomach maintained? (3)

Answer 9

• maintained by proton pumps in parental cells of gastric pit
• proton pumps secrete H+ which combine with Cl- to form hydrochloride acid
• medications and disease can increase secretion of H+ ions and lowers pH in stomach

Question 10

What do Proton pump inhibitors (PPI) do? (3)

Answer 10

• irreversibly bind to proton pumps and prevent H+ secretion
• raises pH in stomach to prevent gastric discomfort caused by high acidity
• taking PPI increases susceptibility to gastric infections (due to recused acid secretion)

Question 11

what are the features of villi? (6)

Answer 11

• microvilli - ruffling of epithelial membrane
• rich blood supply - dense capillary network
• single layer epithelium - minimise diffusion distance (lumen-> blood)
• lacteals - lipid from instine into lymphatic system
• intestinal glands - exocrine pits (crypts of lieberkuhn)
• membrane proteins - facilitate transport of digested material into epithelial cells

Question 12

what do epithelial lining villi contain to optimise absorption capacity? (3)

Answer 12

tight junctions
- occluding associations between plasma membrane and 2 adjacent cells (create impermeable barrier)
- separate digestive fluids and tissues to maintain concentration gradient
microvilli
- increase SA and many mitochondria for AT
- ATP required for primary AT, secondary AT and pinocytosis
pinocytotic vesicles
- non-specific uptake of fluids and dissolves solutes (fast)
- breaking and reforming of membrane

Question 13

why can humans not digest cellulose?

Answer 13

• cellulase
• ruminant animals possess bacteria

Question 14

why does roughage positively correlate with the rate of transit of material in large intestine? (2)

Answer 14

• it provides bulk to keep food moving
• absorbs water which keeps bowel movements soft and easy to pass

Question 15

what are the health benefits associated with diets rich with fibre? (3)

Answer 15

• reduces frequency of constipation lowers risk of colon and rectal cancer
• lowers cholesterol and regulates blood sugar levels
• aids weight management

Question 16

what is egestion?

Answer 16

materials not absorbed by small and large instestine

Question 17

what are materials which are egested? (4)

Answer 17

bile pigment
epithelial cells
lignin
cellulose
human flora

Question 18

what are stomach ulcers?

Answer 18

inflamed and damaged stomach wall due to exposure to gastric acid

Question 19

how does helicobacter pylori cause stomach ulcers? (4)

Answer 19

• anchors to epithelial lining of stomach under mucus lining
• triggers inflammatory immune response which damages epithelial cells (including mucus-secreting globlet cells)
• degradation of protective mucus lining
• stomach ulcer may lead to cancer

Question 20

how does v.cholerae infect intestines and cause diarrhoea and dehydration? (5)

Answer 20

• releases toxin that bind to ganglioside receptors on surface of intestinal epithelium cells
• the toxin is internalised by endocytosis and triggers production of cyclic AMP in cell
• cyclic AMP activates specific ion channels within cell membrane cause efflux of ions
• build up of ions in intsetinal lumen draws water out of cells and tissues via osmosis
• water is removed from body tissues and dehydration occurs