Digestion Flashcards
exocrine glands
produce and secrete substances via a duct onto an epithelial surface on surface of body (sweat glands, sebaceous glands aka oil) and lumen of digestive tract / gut
digestive glands
- salivary glands (secrete saliva which contains amylase)
- gastric glands (secreted gastric juices which includes proteases that break down proteins)
- pancreatic glands (pancreatic juices which include lipase, proteases, and amylase)
- intestinal glands (secretes intestinal juices)
structure of exocrine gland
are composed of a cluster of secretory cells which collectively form an acinus
- acini are surrounded by a basement membrane and are held together by tight junctions between secretory cells
- secretory cells possess a highly developed ER and golgi network for material secretion and are rich in mitochondria
- exocrine products are released (via secretory vesicles) into a duct, which connects to an epithelial surface
secretion of digestive juices
controlled by nervous and hormonal mechanisms which control volume of secretions and specific content (enzymes, acids, etc.)
nervous mechanism
- The sight and smell of food triggers an immediate response by which gastric juice is secreted by the stomach pre-ingestion
- When food enters the stomach it causes distension, which is detected by stretch receptors in the stomach lining
- Signals are sent to the brain, which triggers the release of digestive hormones to achieve sustained gastric stimulation
hormonal mechanism
- Gastrin is secreted into the bloodstream from the gastric pits of the stomach and stimulates the release of stomach acids
- If stomach pH drops too low (becomes too acidic), gastrin secretion is inhibited by gut hormones (secretin and somatostatin)
- When digested food (chyme) passes into the small intestine, the duodenum also releases digestive hormones:
- Secretin and cholecystokinin (CCK) stimulate the pancreas and liver to release digestive juices
- Pancreatic juices contain bicarbonate ions which neutralize stomach acids, while the liver produces bile to emulsify fats
stomach acid
gastric glands that line the stomach wall secrete an acidic solution that creates a low pH environment within the stomach
- Assists in the digestion of food (by dissolving chemical bonds within food molecules)
- Activates stomach proteases (e.g. pepsin is activated when pepsinogen is proteolytically cleaved in acid conditions)
- Prevents pathogenic infection (stomach acids destroy microorganisms in ingested food)
stomach wall
lined by a layer of mucus, which protects stomach lining from being damaged by acid conditions
proton pumps
low pH environment is maintained by these in the partial cells of gastric pit
- they secrete H+ ions (via active transport), which combine with Cl- ions to form hydrochloric acid
proton pump inhibitors (PPIs)
drugs which irreversibly bind to proton pumps and prevent H+ ion secretion
- raises pH in the stomach to prevent gastric discomfort caused by high acidity (acid reflux)
villi
inner epithelial lining of the small intestine highly folded into finger-like projections. they protrude into intestinal lumen, greatly increasing available surface area for material absorption
features of villi
- microvilli: ruffling of epithelial membrane further increases surface area
- rich blood supply: dense capillary network rapidly transports absorbed products
- single layer epithelium: minimizes diffusion distance between lumen and blood
- lacteals: absorbs lipids from intestine into lymphatic system
- intestinal glands: exocrine pits release digestive juices
- membrane proteins: facilitates transport of digested materials into epithelial cells
features of epithelial villi
tight junctions:
- occulting associations between the plasma membrane of 2 adjacent cells, creating an impermeable barrier
- keep digestive fluids separated from tissues and maintain a concentration gradient by ensuring one-way movement
microvilli:
- borders significantly increase SA of plasma membrane, allowing for more absorption to occur
- membrane will be embedded with immobilized digestive enzymes,es and channel proteins to assist in material uptake
mitochondria:
- epithelial cells of intestinal villi will possess large numbers of mitochondria to provide ATP for active transport
- ATP may be required for primary active transport (against gradient), secondary active transport (co-transport), or pinocytosis
pinocytotic vesicles:
- pinocytosis (cell drinking) is the non-specific uptake of fluids and dissolved solutes
- materials will be injected via breaking and reforming of membrane and hence contained within vesicle
function of intestines
complete process of digestion and absorbed digested products into bloodstream
- small intestine absorbs usable food substances
- large intestine absorbs water and dissolved minerals from indigestible food residues
dietary fibre
indigestible portion of food derived principally from plans and fungi
- humans lack necessary enzymes to break down plant matter
- certain herbivores possess helpful bacteria in digestive tract that can break down indigestible plant matter
rate of transit of materials through large intestine
positively correlated with their fibre content:
- dietary fibre provides bulk in intestines to help keep materials moving through the gut
- also absorbs water, which keeps bowel movements soft and easy to pass
health benefits associated with diets rich in dietary fibre
- reduces frequency of constipation and lowers risk of colon and rectal cancer
- lowers blood cholesterol and regulates blood sugar levels (by slowing rate of absorption)
- aids in weight management (contributes few calories despite consisting a large volume of ingested material)
egestion
materials that are not absorbed by the small and large intestines are tested from the body as faeces
- bile pigments
- epithelial cells
- lignin
- cellulose
- human flora
stomach ulcer
inflamed and damaged areas in the stomach wall, typically caused by exposure to gastric acids
Helicobacter pylori
a bacterium that can survive the acid conditions in the stomach by penetrating the mucus lining
- H. pylori anchors to the epithelial lining of the stomach, underneath the mucus lining
- An inflammatory immune response damages the epithelial cells of the stomach – including the mucus-secreting goblet cells
- This results in the degradation of the protective mucus lining, exposing the stomach wall to gastric acids and causing ulcers
vibrio cholerae
bacterial pathogen that infects the intestines and causes acute diarrhoea and dehydration. releases a toxin that binds to ganglioside receptors on the surface of intestinal epithelium cells.
