Unit 6 - Salivation and Gastric Function Flashcards Preview

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Flashcards in Unit 6 - Salivation and Gastric Function Deck (62)
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how do hormones get to GIT?

peptides released from endocrine cells of GIT
-secreted into portal circulation, pass thru liver, enter systemic circulation
-delivers hormones to target cells


how are paracrines related to GIT?

secreted by endocrine cells of GIT
-act locally in same tissue that secretes them


what is paracrine control of GIT exerted by? (3 factors)

1. serotonin - made by enterochromaffic cells (EC) in intestine in response to distension; indirectly excites ENS to increase motility and secretions
2. somatostatin - peptide made by D cells, and potent inhibitor of many processes (pancreatic/gastric secretions, motility)
-acts in endocrine and paracrine manner
3. histamine - made by EC-like cells in stomach, stimulating HCl secretion via H2 recceptors
-acts in paracrine fashion, but not a peptide


how are neurocrines related to GIT?

made in neurons in GIT, released following AP
-after release, diffuse across synaptic cleft to act on target cell
-ACh, NE, VIP, GRP, and substance P


location, relative amounts, and action of gastrin

secreted by antral mucosal cells via G-cells in response to food, distension, and vagus
-increase acid secretion by parietal cells
-stimulate growth of gastric mucosa
-tapers off in jejunum, no longer in ileum


location, relative amounts, and action of cholecystokinin

CCK; secreted by mucosa of intestine (I cells in duodenum and jejunum) in response to fats, PRO, peptides, AA
-increase GB contraction
-increase pancreatic enzyme and bicarbonate secretion (trypsin, chymotrypsin, lipase, amylase)
-inhibits gastric emptying
-tapers off in ileum


location, relative amounts, and action of secretin

secreted by mucosa of small intestine (S-cells in duodenum) in response to acidic chyme from stomach
-increases bicarbonate (HCO3-) and fluid secretion by pancreas
-decreases gastric acid secretion in stomach by decreasing gastrin
-inhibits gastric emptying
-tapers off in ileum


location, relative amounts, and action of motlin

secreted by mucosa of SI (M cells in duodenum and jejunum) during fasting period
-promotes contractions in distal stomach and intestines to 'clear" tract of indigestible materials (MMC)
-only in duodenum and jejunum


location, relative amounts, and action of glucose-dependent insulinomic peptide

secreted by mucosa of SI (K-cells in duodenum and jejunum) in response to fat and CHO
-acts on pancreas to stimulate insulin secretion
-inhibits HCl secretion by parietal cells
-only in duodenum and jejunum


what is membrane digestion?

complete digestion of CHO and PRO via enzymes on luminal surface of SI


when is digestion of PRO initiated?

in stomach via pepsins; continued in intestines via pancreatic enzymes


when is digestion of fat initiated?

in mouth via lingual lipase; continued with swallowed lingual lipase in stomach, and finished in intestines via pancreatic enzymes


what is the physiological secretory unit of salivary glands? how much is secreted? what are components of the salivary system?

salvion; similar in structure to pancreas
-1.5 L saliva secreted per day from parotid, submandicular, and sublingual glands (other glands dispersed thruout submucosa of oral cavity)


what kinds of saliva do acinar cells of parotid, sublingual, and submandibular glands secrete?

parotid: serous 9watery) substance rich in alpha-amylase (~25% of saliva/day)
sublingual (5%) and submandibular (70%) secrete sero-mucous product rich in mucin glycoPRO


what are saliva functions for

L: moistens mouth to prevent dehydration of oral mucosa, and lubricates food for swallowing
-depends on presence of mucous in saliva (sublingual and submandibular)
P: flows across teeth to clear bacteria and reduce bacterial growth (lysozyme, IgA-binding PRO)
D: amylase (ptyalin) that converts starch to sugar at optimum pH = 7 (denatured below 4 in stomach); lingual lipase hydrolyzes TG and secreted by small salivary glands on tongue


Sjogren syndrome

chronic and progressive autoimmune disease that destroys salivary and lacrimal glands



dry mouth; from inadequate saliva production
-typically leads to difficulty speaking due to poor lubrication
-dental carries, and halitosis from bacteria


how is the composition of saliva modified?

"primary secretion" contains amylase, Na, K, Cl, HCO3 like plasma
-at low flow rates, NaCl is absorbed and KHCO3 is secreted by duct cells of salivary glands
--creates K+ rich, hypotonic secretion at rest
--"tightness" of ductal epithelium inhibits paracellular water movement, contributing to hypotonic product
-at high flow rates, saliva is like plasma, b/c transport processes cannot handle increased load


what does high [HCO3-] do to fresh saliva?

makes it more alkaline than plasma, and functions to neutralize gastric acid that refluxes into esophagus, plus acid made by oral bacteria


what is the only humoral agent to activate salivation?

-stimulates Na+ reabsorption and K+ secretion by salivary glands


how is blood flow changed during salivary secretion?

blood flow to acinar cells is increased by PNS stimulation, and ultrafiltrate from plasma (mostly serous fluid) enters
-filtrate from cells enters lumen of acinar cells, mixing with secreted mucus and ptyalin, creating primary secretion
-lingual lipase (from Von Ebner's glands on tongue) is added in mouth


how do the GI hormones, PNS, and SNS control salivary secretion

unaffected by GI hormones
-PNS promotes increased and sustained salivary secretion, where flow is increased 10x over basal rate
-SNS causes lesser and more transient stimulation


what does activation of salivary glands cause?

release of kallikrein, causing production of vasodilator bradykinin from precursors
-vasodilation increases capillary hydrostatic pressure and capillary filtration, thus supplying fluid for secretion


where are the salivary nuclei and how are they excited?

near juncture of medulla and pons, and are excited by taste and tactle stimuli from tongue and other areas of mouth/pharynx


how can rate of salivation be changed by stimuli?

taste and tactile
-sour or smooth objects cause increased salivation
-rough causes less or inhibits
also occurs in response to reflexes from stomach and upper SI (irritating foods, or nausea; saliva removes irritating factor)


where are oxyntic glands and what do they secrete (from 3 types of cells)

acid-forming; on inside surfaces of body and fundus of stomach (proximal 80%); have 3 cell types
1. mucous neck cells secrete mainly mucus
2. peptic (chief) cells secrete pepsinogen and gastric lipase
3. parietal (oxyntic) cells secrete HCl and intrinsic factor


what happens when parietal cells are destroyed?

happens in chronic gastritis
-develop achlorhydria (lack of stomach acid secretion) and pernicious anemia (failure of RBC maturation in absence of B12 stimulation of bone marrow)


where are pyloric glands and what do they secrete?

in antrum (distal 20%), with deeper pits than oxyntic glands
-secrete mucus for protection of pyloric mucosa from stomach acid
-secrete gastrin (G-cells), and somatostatin (D cells)
-fewer peptic cells and no parietal cells compoared to oxyntic glands
-have mostly mucous cells


what are cardiac glands?

mucus secreting glands in limited area near esophageal orifice


what do pepsins digest in meat? what happens if there is a deficiency?

collagen of connective tissue; if lack it in stomach juices, digest meat poorly

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