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the secretory function of the GI tube

digestive enzymes to be secreted and secretion of mucus from mucus gland provide lubrication and protection

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the glandar sturcture of the secretory function of the GI tract

mucous Gland , glandular pits(TUBULAR) , tubular glands, Acinar aveolar

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single cell mucous gland

mucous cell( globlet cell) , it is found on the surface off the epithelium in the GI Tract, its function is to respond to irritation of the epithelium by the producing mucus, which acts as a protectant to the surface from excorination and digestion

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Glandular Pits(tubular )

this represents invagination of the epithelium into the submucosa , in the small intestine this pits is called the cryptes of lieberkihn

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Tubular Glands

In the stomach and upper duodenum

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Acinar(alveolar)

found in the salivary glands, pancreas, and liver, provided secretion for digestion or emulsificatin of food, In the GI tract these acini feed into a system that empty into the allimentary tract. this are exocrine glands

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Stimulation of the secretory Glands is by

presence of food, Autonomic nervous system, and hormones

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the presence of food in the gi tract activates

the enteric nervous system of the gut wall, there is tactile sensation, chemical irritation, and distention of the gut

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parasympathetic stimulation of gland

affects the rate of alimentary glandular secretion from the glands in the upper portion of the tract eg salivary gland, esophagus gastric glands, pancreas, brunner's gland( duodenum). this is innervated by the by the glossopharyngeal and vagus nerve

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sympathetic stimulation of the secretory glands

cause moderate secretion by local gland, also resulting in constriction of blood vessels that supply the gland

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dual effect of sympathetic stimulation

sympathetic stimulation will cause increase in secretion, but if parasympathetic or hormonal stimulation is in effect, then it will reduce stimulation

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Hormones and stimulation of secretory glands

it regulates the volume and character of the secretion
the hormone are release from the GI mucosa in response to the presence of food
hormones are then absorbed into the blood and carried to the gland that will release secretion.

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1 step of secretion of organic substance

1. materials needed for formation of secretion must diffuse or be actively transported by the blood in the capillaries into the base of the glandular cell via merocrine secretion

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2 step of secretion of organic substance

mitochondria located in the glandular cells near its base uses oxidative energy to form ATP

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3 step of secretion of organic substance

atp and appropriate substance provided by the nutrient is used to synthesize organic substance. this occurs in the ER and Golgi complex.

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4th step of secretion of organic substance

the secretory material are transported through the tubules of the ER to the vesicle of the Golgi

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5th step of secretion of organic substance

In the Golgi material are modified and discharged into the cytoplasm in from of secretory vesicle, which are stored at the apex of the cell until stimulated

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--------stimulation causes water and salt to pass through the glandular cells

nervous stimulation

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the mechanism for the movement or secretion of water and electrolyte through the cell is known as

apical flush out

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apical flush out mechanism step 1

nerve stimulation affects the basal portion of the cell causing an active transport of cl- into the cell

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apical flush out mechanism step 2

the cell becomes more negative thus allowing for Na+ ion to move into the cell

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apical flush out mechanism step 3

excess positive and negative ione causes water to enter the cell, increasing cell volume and hydrostatic pressure( the cell swells)

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apical flush out mechanism step 4

the pressure in the cell causes the opening of secretory border flushing water, electrolyte, and organic substance out of the secretory end of the secretory glandular cell

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name the salivary glands

Parotid, submandibular, and sublingual gland. There are also small buccal glands

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name the types of salivary glands

serous secretion that contain ptyalin ( alpha amylase)
mucous secretion that contains mucin for lubrication and protection the GI tract surface.

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parotid secretes

serous secretion

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submandibular and sublingual secretes

both serous and mucus

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buccal gland secretes

mucus

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neural control of the the salivary gland and secretion is through

the parasympathetic nervous system by the superior and inferior salivatory nuclei in the brain stem

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salivatory nuclei

it is in the brain stem, juncture between medulla and pons,and are excited by both tastes and tactile stimuli from the tongue and mouth and pharynx inhibits or stimulates via nervous signal of CNS

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the major secretion of the esophagus is

mucous and aid with swallowing

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the esophagus is lined with

many simple mucous glands

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compound mucous gland are found

at the gastric end and to a lesser extent in the initial portion of the the esophagus

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the mucus secreted by the compound gland in the upper esophagus prevents

mucosa excoriation by the newly entering food

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compound glands near the esophagogastric junction functions

as a protection from digestion by acid gastric juices

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in addition to mucus-secreting cells, the stomach mucosa has to important type of tubular glands

oxyntic gland and pyloric gland

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oxyntic gland also called gastric gland secrete

HCL, pepsinogen ,intrinsic factor and mucus

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The pyloric gland secretes

mainly mucus for the protection of the the pyloric mucosa and it also secrete gastrin

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The oxyntic (gastric) gland is made up four cells

1 mucous cell--- secretes mainly mucus
2 chief cells( zymogenic )--- secrets pepsinogen
3 parietal cells--- secretes intrinsic factors and HCL
4. ECL( entrochromaffin-like cells) secrete hormone like material histamine .

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step 1 mechanism of the HCL secretion

cl- is actively transported into the lumen of the canaliculus then sodium is also actively transported into cytoplasm. this causes the cell to become more negative in the canaliculus , thus cause K+ to enter the cell and Na +, thus kcl enter the enter the canaliculus

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step 2 of the secretion of HCL

water dissociate in the cytoplasm to H+ and OH- , the H+ is secreted into the canaliculus in exchange for K ion by H+ K+ atpase, Na+ is also pump out by a na pump , thus resulting in the formation of HCL in the canaliculus , then secreted into lumen of the gland.

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step 3 of the secretion of HCL

water enters into the canaliculus via osmosis and the final secretion is water HCL

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step 4 of the secretion of HCL

finally carbon combines under the influence of carbonic anhydrase with hydroxyl ion to form bicarbonate, diffuses through the cell cytoplasm into the ECF in exchange for chloride ions that enter through the ecf then is later secreted

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intrinsic factor is essential for

The absorption of vitamin B12 in the ileum and is secrete by the parietal cells

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control of the chief cells

1. ANS controls the chief cells through the vagus nerve ( 10)
2. affected by the intrinsic nervous system ( plexuses)
3. Ph of the stomach
4. acetylcholine

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control of the parietal gland

1. main control is PNS( innveration of the mucous wall)
2. gastrin has a direct effect
3. histamine has an indirect effect

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brunner's gland

it is found in the duodenum of the small intestine and it functions to product alkaline mucus