Salivary, gastric and pancreatic secretions Flashcards
How is Salivary secretion stimulated
Overall, it is a reflex action set off by taste smell and touch.
Receptors in the mouth send impulses to SUBLINGUAL, SUBMANDIBULAR, PAROTID glands
The production of water saliva is elected by cholingeric, adrenergic and petidergenic stimulation.
PARASYMPATHETIC- chondalingual nerve-
increase oxygen consumption- salivation is not due hydrostatic pressure gradient from the blood to the saliva but rather an active process
increase in blood flow
marked fluid secretion ( atropine- blocks secretion but not blood flow)
SYMPATHETIC- vasoconstriction (then vasodilation)
produces protein rich secretion
Describe salivary glands
They are compound organs that secrete electrolytes and proteins as fluid into oral cavity.
Saliva formed by 2 stages- in which isotonic primary fluid is produced by the acinar cells ( which secrete protein and water via vascular and granular pathways) - THEN modified by striated duct system which reabsorbs Na+ and Cl- and secretes K+ and HCO3-
The fact that Cl- is being reabsorbed allows for water to move out as well by osmosis which allows for salivary flow
NB Vasculature is highly fenestrated therefore there’s a 5-10 fold increase in blood flow during neural stimulation which can then guarantee neural stimulation.
Saliva functions
Digestive- chewing, amylase + lipase, taste, swallowing
Additional- Speech, excretion, trophic, social interaction
Other- thermoregulation, affactory signals, grooming
Protective- healing, dilution, buffering, lubrications, antimicrobial actions
How does ageing impact on the salivary secretion
Causes gland atrophy
This cases salivary gland hypofucntion
which decreases salivary secretion
Submandibular glands
Found on the floor of the mouth inside the surface of the lower jaw- secretes more viscous fluid
Parotid gland
the largest of the major salivary glands
secretes watery clear fluid that is rich in salivary amylase
Sublinguinal gland
fond on the floor of the mouth, inferior to the tongue
Secretions which enter the mouth enter through many Rivumus’ ducts which are thick and stringy
Swallowing mechanism
1st stage- Voluntary- food is chewed and mixed with saliva and the tongue tools the mixture into a bolus
2nd Stage- food approaches the pharynx, stimulating rah sensory receptors around the pharyngeal opening
3rd stage-
1) Soft Palate raises which prevents the food form entering the nasal cavity
2) Hyphoid bone and larynx are elevated
3) Epiglotis closes the top of the trachea- food is less likely to enter
4) Tongue presses against the soft palate and uvula, sealing off the oral cavity from pharynx
5) The longitudinal muscles in the pharyngeal wall contacts pulling the pharynx upwards towards food
6) The lower portion of the inferior constrictor muscle relaxes- oesophageal opens
7) The superior constrictor muscles contracts stimulating the peristaltic wave in the other pharyngeal muscles, pushing food into oesophagus
Describe how gastric secretions are secreted
Secreted by stomach which secretes a large acid volume after a meal
- electrolytes- Na,Cl,K
- Pepsin- initiates protein digestion
Intrinsic factors- a glycoprotein that combines with B12 aiding its absorption into the ileum
Division of gastric mucosa
Cardiac Glands- mucous near oesophageal end
tubular, highly branched, coiled glands
Few/ No oxyntic cells
Secrete some electrolytes
Pyloric glands- secrete alkaline mucous juice
electrolytes ( Ca, PO4 3-, HCO3- , NaCl, KCl)
- deep gastric pits
- release by exocytosis into basal and lateral cell surfaces
Oxyntic glands- occupy fundus and body of stomach
- numerous gastric pits
- secretion HCl
i) Isthmus - parietal and mucous cells
ii) neck - parietal and mucous cells
iii) Base - chief cells, endocrine cell, G -cells
Phases of Gastric secretion
Cephalic- activated by sight smell taste chewing
- mediated by efferent impulses - stomach
Gastric- food enters the stomach
and distension and chemical composition of food factors
evokes gastric phase
Intestinal- food entering the intestine
- liver extract, peptone, aa mixture are effective stimulants of acid secretion
- Intestinal acid, fat, hyperosmolar solution inhibit acid secretion
This stimulates intestinal cells to release a hormone called intestinal gastrin- gastric gland secretion
But… as more food moves into the SI, sympathetic reflex triggered by acid in upper part of SI which decreases gastric juice
pH of contents increases when food mixes–>
gastrin secretion enhances—> pH = 3.0 —–> gastrin secretion decreases
For stomach to secrete HCl, H2 is removed, alkaline bicarbonate released. Following a meal, [HCO3-] blood increases
Mechanical action of the stomach
Propulsion- bolus is pushed towards the closed pylorus
Grinding- the antrum churns the trapped material
Retropulsion- Bolus is pushed back into the proximal stomach
Mucous cells -
secretes copious thin mucous- because pepsin can digest proteins of the stomach cells
Stem/ regenerative cells
repairing cells as cells are damaged/die
