6.3. Function of the salivary glands and regulation of salivary secretion. Gastric secretion and its control. Flashcards
I. Basics
1. What are general principles of secretory functions of GI-tract?
- Exocrine glands (salivary glands, pancreas, liver)
- Glands of gut wall (crypts of Lieberkühn, Brunner’s gland)
- Intestinal mucosa
I. Basics
2. What are the 2 main functions of secretion?
- Protection (chemical, mechanical, immunological)
- Digestion + absorption (dilution + lubrication of chyme)
I. Basics
3A. What are the 2 types of products secreted?
- Inorganic
- Organic
I. Basics
3B. What are the secreted organic products?
- Water (essential for aqueous environment + dilution function)
- Electrolytes (HCl- = gastric acid, HCO3- = buffer acidic chyme, Na+ + Cl- for H2O secretion)
I. Basics
3C. What are the secreted inorganic products?
- Proteins
- Digestive enzymes: break down macromolecules into smaller molecules -> absorb them
- Mucin: lubrication for the chyme + is sticky, so it coats the inner surface of the gut wall -> inhibits direct contact between chyme + gut wall
- Immunoglobulins: protective (immunological) role - Humoral agents
- Bile acids/salts
I. Basics
4. What is the mechanism of secretion?
- Exocytosis: e.g. digestive enzymes released from vesicles by Ca2+/cAMP-signals
- H2O + electrolyte secretion via ion transport (mainly driven by Cl- - active transport)
I. Basics
5A. What are the 2 types of regulation of secretion?
- Local regulation
- Systemic regulation
I. Basics
5B. What are features of systemic regulation?
- SYM + PARA act via the ENS
- PARA: ↑ rate of secretion, in response to meals
- SYM: dual effects – sometimes inhibits/activates secretory functions
II. Salivary secretion
1. What is the amount of daily salivary secretion?
Daily secretion: 800 – 1500mL/day (90% of production during meals)
=> pH~7
II. Salivary secretion
2. What is the Composition of saliva?
H2O, electrolytes (Na+, K+, Ca2+, Mg2+, Cl-, HCO3-), salivary amylase, lingual lipase, IgA, lysozyme, mucin
II. Salivary secretion
3A. What are the functions of saliva
II. Salivary secretion
3B. Explain the Antimicrobial effect of saliva?
secretory IgA + lysozyme = enzyme which cleaves bacterial cell
wall
II. Salivary secretion
3C. Explain the Ca2+-binding proteins (trapped in mucins) function of saliva?
keeps the teeth healthy
- Excessive teeth brushing + washing will lead to removal of these proteins -> decay
III. Major salivary glands
1. What is the general structure of salivary glands?
- Tubuloalveolar structure
III. Major salivary glands
2. Give the classification of acinar portion
- Acinar portion of gland is classified into:
+) Serous: contains vesicles, zymogen granules
+) Mucous: produces mucin (glycoprotein)
III. Major salivary glands
3. How is salivary secretion drained?
Intralobular intercalated duct
-> Intralobular striated ducts
-> Interlobular ducts
-> Interlobular excretory ducts
-> Main excretory ducts
III. Major salivary glands
4. What are the features of extrinsic glands?
Extrinsic (lie outside the oral cavity) glands
- Parotid gland = serous gland
- Sublingual gland = mostly mucous
- Submandibular gland mixed
III. Major salivary glands
5. What are the features of Intrinsic glands?
Intrinsic (found within the oral cavity):
- buccal, labial, palatine glands (mucous glands)
=> intrinsic salivary glands constantly secrete saliva to keep oral cavity moist
IV. The two-stage model of salivary secretion
1A. What are the features of primary acinar secretion of saliva?
Primary secretion: PRIMARY ACINAR SECRETION
- proteins, water, electrolytes are produced by acinar cells
- isotonic + the [major ions] is similar to that in the plasma
- the primary-acinar-secretion transport ions to transport fluid (H2O)
=> secondary active Cl—transport
IV. The two-stage model of salivary secretion
1B. Make a schematic diagram of primary acinar secretion
IV. The two-stage model of salivary secretion
2A. What are the features of Secondary secretion?
Secondary secretion: DUCT CELL SECRETION/ABSORPTION
- Primary secretion is modified as it passes through ducts that absorb Na+ and Cl-, and secrete K+ and HCO3-
- Secondary secretion has both secretory and absorptive functions
- Since there are no aquaporins + the epithelium is tightly connected => H2O-impermeable epithelium
IV. The two-stage model of salivary secretion
2B. Make a schematic diagram of Secondary secretion?
IV. The two-stage model of salivary secretion
4. Explain the salivary flow rate
- Rate of secretion does affect the composition of saliva
- Saliva is hypotonic/hypoosmotic to plasma at all flow rates
- [HCO3-] in saliva exceeds that in plasma except at extremely low flow rates
- The duct epithelium is bound tightly together and lacks expression of aquaporin, and therefore H2O cannot follow the ions to maintain isotonicity at moderate or high flow rates
=> The higher the flow rate, the shorter time for ionic modifications by the duct cells -> resulting saliva will become like the 1st secretion
V. Regulation of salivary secretion
1. Regulation of salivary secretion is neural or hormonal?
EXCLUSIVELY NEURAL!
V. Regulation of salivary secretion
2. What are the 2 types of regulation of salivary secretion?
- Parasympathetic nervous system (PARA) - gets activated in response to meal
- Sympathetic nervous system (SYM) - ↑fluid secretion
V. Regulation of salivary secretion
3. Describe regulation of salivary secretion by Parasympathetic nervous system (PARA)
- Parasympathetic nervous system (PARA) – gets activated in response to meal
- VIP (acts on vessels in sal.glands)-Gs -> vasodilation -> fluid secretion↑↑
- ACh (acts on acinar cells) – M3-ACh-R (Gq) -> Ca2+-signal -> 2 effects:
1) Exocytosis ↑ (amylase/lipase can be excreted)
2) Constrict acinar cells -> gaps between them get bigger -> paracellular fluid movement ↑ -> fluid secretion↑
V. Regulation of salivary secretion
3. Describe regulation of salivary secretion by Sympathetic nervous system (SYM)
Sympathetic nervous system (SYM) - ↑fluid secretion
- NE -> β2-AR -> mucin secretion↑ ( -> content + volume↑)
- NE -> α1-AR (vessels) -> vasoconstriction -> fluid secretion↓
VI. Gastric secretion
1. What are general features of Gastric secretion?
- Gastric mucosa secretes gastric juice which is a mixture of secretory products of various cells
- Various cells parallelly secrete into the gastric lumen
- 1-1,5 L/day
- Composed of water, electrolytes (H+, Cl-), HCO3-, proteins (mucin, digestive enzymes)
VI. Gastric secretion
2. What is the amount of gastric secretion per day?
1-1,5 L/day
VI. Gastric secretion
3. What is gastric secretion composed of?
Composed of water, electrolytes (H+, Cl-), HCO3-, proteins (mucin, digestive enzymes)
VI. Gastric secretion
4. What are functions of gastric juice?
- H+ (proton) is important for digestion, killing microbes and disinfecting food
- Conversion of inactive pepsinogen to active pepsins -> chemical digestion of
proteins - Intrinsic factor – essential for absorption of vitamin B12 (if not present = severities!)
- Protection of mucosa, by HCO3- + mucin, against the acidic luminal environment (if not present = ulcer)
- H2O lubricates chyme, food etc.
VI. Gastric secretion
5. What is gastric pit?
opening of a duct into which gastric glands empty
VI. Gastric secretion
6. What are the types of cells in gastric glands?
Gastric glands have several types of cells that secrete unique substances:
- Parietal cells: HCl + intrinsic factor (B12)
- Chief cells: digestive enzymes (pepsinogen)
=> Surface epithelial cells: HCO3-, mucins -> protect mucosa from gastric acid