D2 Flashcards
Where and how do exocrine glands produce and secrete substances?
- via duct on epithelial surface
- surface of body
- lumen of digestive tract/gut
What are examples of digestive glands? (4)
- 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)
What is the exocrine gland composed of? (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
How are exocrine products released?
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)
What is the nervous mechanism for the secretion of gastric juices? (3)
- 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
What is the hormonal mechanism to secretion fo gastric juices? (5)
- 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
What function does the acidic condition of the stomach serve? (3)
- 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)
What protects the stomach lining from being damages by acidic conditions?
Layer of mucus
How is low pH is stomach maintained? (3)
- 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
What do Proton pump inhibitors (PPI) do? (3)
- 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)
what are the features of villi? (6)
- 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
what do epithelial lining villi contain to optimise absorption capacity? (3)
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
why can humans not digest cellulose?
- cellulase
- ruminant animals possess bacteria
why does roughage positively correlate with the rate of transit of material in large intestine? (2)
- it provides bulk to keep food moving
- absorbs water which keeps bowel movements soft and easy to pass
what are the health benefits associated with diets rich with fibre? (3)
- reduces frequency of constipation lowers risk of colon and rectal cancer
- lowers cholesterol and regulates blood sugar levels
- aids weight management
