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29 Cards in this Set

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2 Functions of GI tract secretions:
1. Production of digestive enzymes
2. Production of mucus
4 main types of secreting glands:
1. Unicell Goblet mucous glands
2. Crypts of Lieberkuhn
3. Tubular glands
4. Complex glands
What are Goblet cells?
Unicellular cells that excrete mucus in response to irritation or damage along epithelial tract surface most of the gut length.
Function of the mucus secreted by goblet cell mucous glands:
lubricant
What are Crypts of Lieberkuhn?
Pits in the GI tract surface that contain specialized cells.
What/where are tubular glands?
Glands mostly in the stomach and upper duodenum that secrete cell-specific secretions.
Example of a tubular gland:
Oxyntic glands - secrete acid and pepsinogen
3 types of complex glands:
-Salivary
-Liver
-Pancreatic
What is the function of secretions of complex glands?
Digestion and emulsification of food.
Main stimulus for release of mucus from GI tract:
Presence of food in contact with epithelium - causes release of mucus in that local vicinity and adjacent regions.
2 Ways that physical stimulus causes secretion:
-Direct contact with epithelium
-Reflex stimulus of ENS to both surface and deep glands
3 types of physical stimuli for gland secretions:
-Tactile
-Chemical irritation
-Gut wall distention
3 total ways to stimulate gland secretions:
-Physical stimulus
-Autonomic - PNS/SNS
-Hormonal
Effect of PNS on secretion:
-Increases rate of secretion especially in upper portions.
What nerves carry PNS fibers for secretion?
9 and 10
What nerves innervate the distal part of the large intestine?
Pelvic sympathetics - S2-S4
What is the effect of SNS on secretion?
DUAL:
-Can increase secretion
-But causes vasoconstriction of vessels to glands so decrease.
When does the SNS increase secretions?
When acting alone
When does the SNS decrease secretions?
When the PNS or hormones are already active
What stimulates the release of hormones from the stomach and intestine?
Presence of food in gut - different types
What do hormones then do?
Stimulate secretions
1st step in secretion mechanism of glandular cells:
Deliver substrate to make secretion - by active transport and pinocytosis from capillaries.
What do gland cells need to do to form secretions?
-Make ATP via mitochondria
-Use ATP for synthesis
Where do the cells make their secretions?
In rough ER and Golgi
How are secretions secreted?
After packaging into secretory vesicles Calcium influx causes exocytosis.
What gets secreted along with secretions? Why?
Water and electrolytes - to wash the secretions through the secretory border of cells.
Mechanism for excretion of water and electrolytes with secretions:
1. Nerve stimulates basal cell membane -> AT of Cl into cell
2. Cell hyperpolarizes ~15 mV to result in Na influx
3. Increased osmolarity; water follows into cell
4. Cell swells and hydrostatic pressure incr causes small ruptures of secretory border - releases water / electrolytes
What is Mucus made of?
-Water
-Electrolytes
-Glycoproteins
Functions/qualities of Mucus:
-Lubricant/protectant/buffer
-Adheres to surfaces
-Coats particles
-Low resistance
-Aggregates fecal particles