Digestion Flashcards

1
Q

exocrine glands

A

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

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2
Q

digestive glands

A
  • 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)
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3
Q

structure of exocrine gland

A

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

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4
Q

secretion of digestive juices

A

controlled by nervous and hormonal mechanisms which control volume of secretions and specific content (enzymes, acids, etc.)

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5
Q

nervous mechanism

A
  • 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
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6
Q

hormonal mechanism

A
  • 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
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7
Q

stomach acid

A

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)

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8
Q

stomach wall

A

lined by a layer of mucus, which protects stomach lining from being damaged by acid conditions

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9
Q

proton pumps

A

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

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10
Q

proton pump inhibitors (PPIs)

A

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)

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11
Q

villi

A

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

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12
Q

features of villi

A
  • 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
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13
Q

features of epithelial villi

A

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

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14
Q

function of intestines

A

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

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15
Q

dietary fibre

A

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

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16
Q

rate of transit of materials through large intestine

A

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

17
Q

health benefits associated with diets rich in dietary fibre

A
  • 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)
18
Q

egestion

A

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

19
Q

stomach ulcer

A

inflamed and damaged areas in the stomach wall, typically caused by exposure to gastric acids

20
Q

Helicobacter pylori

A

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

21
Q

vibrio cholerae

A

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.