Secretion I Flashcards
Major flow in unstimulated
state comes from:
submandibular
Major flow in unstimulated
state comes from:
parotid
parotid VS sublingual VS submandibular VS minor salivary (% + type of secretion)
table slide 5!!!
salivary gland anatomy:
- Grape-like clusters of acini
- Serous acinar cells largely supply
proteinaceous components
(enzymes), whereas mucous
acinar cells secrete watery
mucus. - Saliva makes its way through the
acini, via intercalated and
intralobular ducts.
o Intercalated ducts are linked
directly to the acini
o Help to expel saliva and
prevent backflow
secretory products of acinar cells:
o Proteinaceous components
* Digestive enzymes
* Lysozymes, antibacterial peptides
* Lactoferrin sequesters iron
* Secretory IgA
* Growth factors
secretory products of mucous acinar cells:
o Mucin (glycoproteins, viscoelastic)
o Water (1ml/min/g of gland tissue)
secretory products of inorganic solutes:
Ca, Phosphates
- ioni composition = similar to:
- composition = modified by active transport:
- plasma (electrolytes + salt)
- because there is some additional reabsorption or secretion
Constituents of saliva and their functions:
table slide 8
Regulation of salivary secretion:
- Almost entirely mediated by neural pathways.
- Salivary glands are positively regulated by both the parasympathetic and
sympathetic branches (this contrast with the reciprocal roles of these
branches in other functions). - Parasympathetic has the predominant role on secretion and
composition of saliva (quantitatively important). - Sympathetic modifies composition but has little effect on volume
- GI hormones - not a major role on salivary secretion, but can influence
composition of saliva. Eg. aldosterone increases the ability of the salivary
ducts to absorb sodium ions.
parasympathetic VS sympathetic roles in secretory glands:
table slide 10
muscarinic receptor def:
Muscarinic receptors mediate parasympathetic nervous system responses, which are typically rest-and-digest activities (slowing heart rate, increasing digestion, constricting pupils, etc.).
They respond to the neurotransmitter acetylcholine, which is released by nerve endings to influence organ functions.
Receptor Types:
There are five subtypes of muscarinic receptors, labeled M1 to M5. Each subtype has different functions and locations in the body:
M1: Found mainly in the brain and some glands, involved in memory and cognitive functions.
M2: Primarily in the heart, slows down the heart rate.
M3: In smooth muscles and glands, involved in contracting smooth muscles and stimulating gland secretion.
M4 and M5: Mostly in the brain, involved in regulating various neural activities.
beta-adrenergic vs alpha def:
Beta-adrenergic receptors are a type of adrenergic receptor that respond to the neurotransmitters epinephrine (adrenaline) and norepinephrine (noradrenaline). These receptors are found in various tissues throughout the body and play a crucial role in the sympathetic nervous system (the “fight-or-flight” response).
- Alpha-adrenergic receptors:
Primarily found in smooth muscles of blood vessels, especially those in the skin, gastrointestinal system, kidneys, and brain.
Present in other tissues like the eye (influencing pupil dilation), and internal organs such as the bladder and prostate.
- Beta-adrenergic receptors:
Located primarily in the heart, lungs, blood vessels, skeletal muscles, and fat cells.
Different subtypes are found in specific locations: β1 in the heart, β2 in smooth muscles of the airways and blood vessels, and β3 in adipose (fat) tissue.
Control of Salivary Secretion-Neural:
slide 11
- the superior cervical ganglion = used during sympathetic to control (The SCG provides sympathetic innervation to many structures in the head and neck. Sympathetic innervation is responsible for the “fight-or-flight” responses, such as increasing heart rate, constricting blood vessels, and dilating pupils)
NE = norepinephrine
VIP, IP3, cAMP roles:
- VIP: (neurotrasnmitter/hormone) Vasodilation, smooth muscle relaxation, inhibits gastric acid secretion, stimulates intestinal secretion.
- IP3: (messenger) Triggers calcium release from the endoplasmic reticulum, regulates smooth muscle contraction, and secretion.
- cAMP: (messenger) Activates PKA, regulates metabolism, smooth muscle relaxation, heart rate increase, and gene expression.
Characteristics of saliva:
- Concentrations of
electrolytes vary with the
rate of secretion, but it is
always hypotonic. - Is always lower in sodium
and chloride than plasma. - Is always higher in
potassium than plasma. - Is rich in bicarbonate most
of the time . - At very high rates of
secretion its concentration
resembles plasma’s.
Two-Stage Mechanism of Saliva Secretion:
Primary Secretion:
Produced by acinar cells.
Composition similar to plasma (isotonic), rich in Na⁺, Cl⁻, K⁺, and HCO₃⁻.
Contains water, enzymes (like amylase), mucins, and electrolytes.
Modification:
Occurs in the ducts, mainly in the striated ducts.
Sodium (Na⁺) and chloride (Cl⁻) are reabsorbed.
Potassium (K⁺) and bicarbonate (HCO₃⁻) are secreted.
No water reabsorption, resulting in hypotonic saliva.
- summary:
(* Composition changes from acini to ducts
* In acini same as plasma
* Na+ and Cl- are extracted
* K and bicarbonate added
* Loss of NaCl renders saliva hypotonic
* When secretion rate increases, tonicity rises)
Digestion and absorption in the oral cavity:
- The salivary enzymes merely
serve to begin the process,
neither is essential to the
digestion of food. - Amylase: begins catalysis of
complex carbohydrates to
oligosaccharides - Lipase: begins the biochemical
breakdown of fat (important in
infants) - No absorption of food occurs in
the mouth.
o Therapeutic agents such as
nitroglycerin, etc. directly absorbed
Salivary pathophysiology:
- Xerostomia (absence of saliva, dry mouth)
- Sjogren’s syndrome (autoimmune - atrophy of the
glands). Primary (drug use) or secondary
development (radiation) - Tumors of the mouth and esophagus – excessive
salivation - Cysts, mucocele
- Parkinson’s disease – excessive salivation
- Impaired salivation decreases oral
pH - Tooth decay, esophageal erosions,
difficulty lubricating and
swallowing, poor nutrition,
infections
stomach functional regions (cardia, fundus, antrum roles):
o Cardia is 5% of the gastric
surface, with transitional cell zone
o Fundus and body contains approx
75% of the gastric glands- so-
called oxyntic glands.
o Antrum contains glands that
secrete gastrin. Fulfills motility
functions.
secretion in stomach - functions:
- Critical for absorption of Vit. B12 and
non-heme iron. - The most characteristic secretory
product of the stomach is hydrochloric
acid. - Acidity begins digestion via simple
hydrolysis. - The acid sterilizes the meal; maintains
sterility of intestine. - Protects mucosa
- Motility
gastric cell types:
slide 20
- pepsinogen = pepsin (enzyme for digestion) precursor
- EE cells ( secretes CCK) = digestion + motility + appetite
- ECL cells (secrete Histamine, stimulate acid secretion from parietal cells)
- G cells (gastrin) stimulates acid secretion + motility (après goes into blood stream)
Gastric cells, products & functions:
table slide 21
Mucosal protection:
- Throughout the stomach, the surface cells are covered with a layer of mucus.
- The stability of the layer is additionally enhanced by the activity of small peptides, known as trefoil factors.
- Bicarbonate ions are secreted into the base of the mucus layer that protects it from excessively low and potentially injurious pH.
Innervation:
- Vagal afferent conveys
information from the dorsal
vagal complex - It integrates with info coming
from hypothalamus, to set the
level of secretory function - Visceral inputs also contribute
to gastric regulation via vagus
Output of taste receptors to the brain region (NTS) regulate secretion
and other gastric functions
Activation of sympathetic nerves tends to oppose the parasympathetic
limb
ENS coordinates local reflexes and conveys to CNS
DVC integrates gastric secretory function inputs
Gastric sensory nerves containing neurotransmitter calcitonin gene –
related peptide (CGRP) participate in down regulation of acid secretion
ENS !!!! (little brain)!!!!!
The ENS consists of over 100 million neurons, organized into two main plexuses:
Myenteric Plexus (Auerbach’s Plexus): Located between the longitudinal and circular muscle layers of the gut wall, it primarily regulates motility (movement) of the intestines.
Submucosal Plexus (Meissner’s Plexus): Found in the submucosa, this plexus regulates glandular secretions and blood flow within the GI tract.
DVC:
The DVC is involved in regulating parasympathetic outflow to various organs, particularly those in the gastrointestinal tract, heart, and lungs. It helps maintain homeostasis by balancing the body’s stress responses with relaxation and restorative functions.
(pr GI tract: functions of secretion and motility)
Regulation of gastric secretion:
Neuronal reflexes contribute to both stimulation and inhibition of
secretion.
Two type of reflexes control secretion: short reflexes (entirely within the
ENS), and long reflexes (vago-vagal).
Acetylcholine mediates both short and long reflexes. Stimulates parietal,
chief and ECL cells.
Gastrin releasing peptide (GRP) released by enteric nerves in vicinity of
gastrin-containing G cells in the gastric antrum.
(slide 25)
