Physiology 3120 Lecture Notes - Salivary Gland, Enteric Nervous System, Acinus

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26 Nov 2011
Human Physiology
Friday, March 19, 2010
“Gastrointestinal I”
Gastrointestinal (GI) Tract
Contributes to and is impacted by all the previous systems; therefore is incredibly important
Receives 1/3 of the total cardiac output
Produces acids and bases, so it contributes to overall body pH
Receives major nerves (i.e. vagus); also has its own nervous system, called the enteric nervous
Produces some biologically active hormones
Performs 3 or 4 things
Salivary glands
In the neonate, the salivary glands are important; important for creating a
connection between the mouth and the mother’s nipple
Provide lubrication in oral cavity for moist mouth
Important for speech, chewing, swallowing, etc.
3 major salivary glands: parotid, submandibular, and submalingual
A converging duct system
oStart with many primary units that each drain into their own individual
ducts (small diameter), which fuse into larger and larger ducts, which form
one main excretory duct
oAlso seen in the pancreas
Examine a single primary unit called the salivon (so named because it moves
fluid, just like the nephron)
oClosed-off end (acinus) made of acinar cells; pressure is lower than
vascular pressure, so fluid moves through its semi-permeable membrane
by plasma filtration; the fluid should be isotonic to plasma (just like the
The source of most organic components to saliva, including (I)
enzyme called amylase, which breaks down amylose/starch, (II)
muco- and glycoproteins
oPart of duct closest to acinus is the intercalated duct (ID) (seems to
contain acinar cells)
oThe distal portion of the duct (striated duct [SD]) contains epithelial cells
that contain microvilli on basolateral surface; these cells have a lot of
mitochondria (for active transport)
oCells that line the duct in the ECF; have all the characteristics of epithelial
cells, but have actin and myosin (imparts contractile ability); squeeze the
duct to move fluid along toward the mouth; myoepithelial (ME) cells
oFluid moves down the salivon by its pressure gradient (even with ME
cells) through the ID duct; in the SD duct, there is a Na/K ATPase (3Na
out/2K in) that makes the fluid hypotonic to plasma; water DOES NOT
follow because SD not permeable to water
oFlow relationships determined at point X as you go from no stimulation to
maximum stimulation
As flow rate increases, Na has less time exposed to the pump, so
fewer Na’s can be extracted from the lumen; it plateau’s at the
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