Flashcards in Ward: Gastric physiology of digestion Deck (49):
Two primary types of secretion
Type of gland: located in the epithelium, found in most parts of the GI tract, respond to local stimulation of the epithelium by extruding their mucus onto the epithelial surface to act as a lubricant and to protect the epithelial surface
single cell mucous glands
In the small intestine, invaginations of the epithelium into the submucosa
Crypts of Leiberkuhn
Located in the stomach and upper duodenum, often secrete acid and pepsinogen.
More complex glands with a primary function to provide secretions for digestion and emulsification of food
salivary glands, pancreas, and liver
Briefly discuss the mechanism of secretion by glandular cells.
Capillaries transport nutrients into the glandular cell
Secretory substances synthesized in ER/Gogli
Transported into Golgi where modification occurs
Discharged into cytoplasm as secretory vesicles which are stored in the apical ends of cells until the cell gets a signal to empty its contents
Briefly describe water and electrolyte secretion
1. nerve stimulation moves Cl- ions into cell
2. Na+ follows into cell
3. Water follows and creates hydrostatic pressure
4. Ruptures secretory border
Local stimulation can occur in two ways
How does the parasympathetic ANS stimulate secretion?
increases the rates of glandular secretions, especially the glands of the upper GI tract, also glands of the distal large intestine
How does the sympathetic ANS stimulate secretion?
If parasympathetic innervation is low, sympathetic stimulation will increase secretion. If parasympathetic stimulation is high, it will reduce secretion.
Hormones in the stomach and intestine are liberated from the mucosa in response to what?
the presence of food in the lumen
Constituents of saliva
Binding glycoprotein for IgA
What is saliva composed of?
Electrolytes, glycoproteins, and water
Properties of mucus (ABDAS)
Adherent so it tightly binds to particles
Barrier to mucosa
Strongly resistant to digestion
Four types of salivary glands
How are all the salivary glands drained?
By a single major excretory duct
Lie outside the wall of the GI tract and are connected via ducts that empty into the GI tract itself
Involved with directing fluids into the oral cavity.
Contractile cells involved in helping move serous and mucous secretions into ducts.
What happens to Na, Cl, and K+ levels in the saliva during maximal saliva secretion?
Concentrations of these ions begin to reach the level found in the plasma, because reabsorption cannot occur quick enough relative to the marked increase in saliva production. Na+ and Cl- increase, and K+ decreases
Things that activate salivary nucleus of the medulla
Things that inhibit salivary nucleus of the medulla
Secretion is increased by contractions of these cells, which are innervated by the parasympathetic system
What is released in response to parasympathetic stimulation? What does this produce? What does this result in?
Vasodilation and growth of salivary glands
Pathophysiology: Associated with chronic ulcerations of the buccal mucosa and with dental caries.
Xerostomia (dry mouth)
Pathophysiology: Absence of saliva
Pathophysiology: Atrophy of the glands and decreased saliva production
Pathophysiology: Na+ concentrations increased
Pathophysiology: Na+ concentrations decreased
Pathophysiology: Causes excessive salivation
Four constituents of gastric juice
1. intrinsic factor
2. H+ ions
secretes acid, pepsinogen, mucus and intrinsic factor and is located on the proximal 80% of the stomach.
Oxyntic gland area
The distal 20% of the stomach, which synthesizes and secretes the hormone gastrin and mucus.
Pyloric gland area
Gastric mucosa made up of two areas
Oxyntic gland area
Pyloric gland area
Contain the acid-producing parietal cells and the peptic or chief cells, which secrete the enzyme precursor pepsinogen
What do parietal cells produce?
What is the pH created by HCl secretion of parietal glands?
Between meals the cytoplasm of the parietal cell is dominated by numerous (blank)
The cell also possesses an intracellular (blank) that is continuous with the lumen of the oxyntic gland. During acid secretion the tubulovesicles become microvilli and project into the (blank). This increases the (blank) of the cell.
canaliculus; canaliculus; surface area
The activities of what two enzymes increases during HCl secretion?
Summarize the mechanism of HCl secretion by parietal cells.
How does H+ get pumped out?
Where does the supply of H+ come from?
H+ pumped out of APICAL cell membrane by H+/K+ ATPase if adequate supply of K+ outside cell
(H+ comes from dissociation of H20
Carbonic acid is formed from Co2 and H20 in a rxn catalyzed by carbonic anhydrase)
BASOLATERAL membrane exchanges Cl- for bicarb
What things occur when parasympathetic stimulation of salivary glands?
Myoepithelial cell contraction
Sympathetic activation of salivary glands increases (blank), while parasympathetic stimulation increases (blank) and (blank)
cAMP; IP3; Ca+
Component of gastric secretion; required for the absorption of vitamin B12 by the ileal mucosa (released from Parietal cells).
Component of gastric secretion; necessary for the conversion of pepsinogen to pepsin; also kills bacteria
Component of gastric secretion; begins the breakdown of protein; released from chief cells
Component of gastric secretion; protects the mucosa lining of the stomach, lubricates and neutralizes a small amount of acid
The gastric glands lie deep in the stomach wall and receive these two things.
rich blood supply