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SECRETIONSECRETION
The process of elaborating a specificThe process of elaborating a specificproduct as a result of the activity of aproduct as a result of the activity of agland which may range from separating agland which may range from separating aspecific substance of the blood to thespecific substance of the blood to theelaboration of a new chemical substance.elaboration of a new chemical substance.
Glands are those organs or tissues inGlands are those organs or tissues inwhich there are cells encaged in thewhich there are cells encaged in the
synthesis , storage & discharge ofsynthesis , storage & discharge ofsecretory products . There are two majorsecretory products . There are two majorcategories of gland in the body .categories of gland in the body .
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ENDOCRINE GLANDSENDOCRINE GLANDS
Synthesize hormones & secrete them intoSynthesize hormones & secrete them into
extracellular spaces from they enters theextracellular spaces from they enters the
blood stream or lymphatic system .blood stream or lymphatic system .
They do not possess a duct system & theThey do not possess a duct system & thesecretion enters the blood stream rapidlysecretion enters the blood stream rapidly
& it does not leave the body until it is& it does not leave the body until it is
ultimately metabolized or excreted .ultimately metabolized or excreted .
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EXOCRINE GLANDSEXOCRINE GLANDS
Their secretions are discharged from theTheir secretions are discharged from the
secretory cells onto a surface & not intosecretory cells onto a surface & not into
the extra cellular spaces .the extra cellular spaces .
The secretion passes through a system ofThe secretion passes through a system ofducts ( which may be a passive transportducts ( which may be a passive transport
system or may modify the secretion )system or may modify the secretion )
which may transport it to the surface orwhich may transport it to the surface or
the site of discharge . The secretion maythe site of discharge . The secretion maybe on body surface or on to an internalbe on body surface or on to an internal
surface like the intestine .surface like the intestine .
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MODEMODE OF SECRETIONOF SECRETION
Holocrine secretionHolocrine secretionHOLOCRINEHOLOCRINE = Wholly secreted ; denoting= Wholly secreted ; denoting
that type of glandular secretion in whichthat type of glandular secretion in which
the entire secreting cell, along with itsthe entire secreting cell, along with its
accumulated secretion , forms theaccumulated secretion , forms the
secreted matter of the gland .secreted matter of the gland .
The secretion from a gland consists ofThe secretion from a gland consists ofcomplete , usually degenerate cells likecomplete , usually degenerate cells like
the sebaceous glands of the skinthe sebaceous glands of the skin ..
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ApocrineApocrinesecretionsecretion
APOCRINEAPOCRINE = Denoting that type of= Denoting that type ofglandular secretion in which the free endglandular secretion in which the free endor apical portion of the secreting cell isor apical portion of the secreting cell iscast off along with the secretory productscast off along with the secretory products
that have accumulated therein .that have accumulated therein . InIn apocrine glands , a variable butapocrine glands , a variable but
substantial amount of cytoplasm issubstantial amount of cytoplasm issupposed to be lost during secretion .supposed to be lost during secretion .
It is now known that , in mammary gland &It is now known that , in mammary gland &axillary sweat glands , very little or evenaxillary sweat glands , very little or evenno cytoplasmic ground substance is lostno cytoplasmic ground substance is lostwhen the secretion leaves the cell .when the secretion leaves the cell .
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Merocrine secretionMerocrine secretion
MEROCRINEMEROCRINE = Partly secreted ; denoting= Partly secreted ; denoting
the type of glandular secretion in whichthe type of glandular secretion in which
the secreting cell remains intactthe secreting cell remains intact
throughout the process of formation &throughout the process of formation &discharge of the secretory products as indischarge of the secretory products as in
the salivary & pancreatic glands .the salivary & pancreatic glands .
The secretory product diffused from theThe secretory product diffused from the
cell so that no cellular contents are lostcell so that no cellular contents are lost ..
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TYPES OF SECRETIONTYPES OF SECRETION
SerousSerous : is clear , low viscosity fluid: is clear , low viscosity fluid
containing proteins .containing proteins .
MucousMucous
: is opaque high viscosity: is opaque high viscosity
fluid containing high proportion offluid containing high proportion of
glycoprotein.glycoprotein.
MixedMixed
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THE SECRETORY PROCESSTHE SECRETORY PROCESS
1.1. Transport of water & raw materials intoTransport of water & raw materials into
the cell from plasma .the cell from plasma .
2.2. Their movement through the cytoplasmTheir movement through the cytoplasm
together with synthesis & storage .together with synthesis & storage .3.3. The extrusion of the product into:The extrusion of the product into:
A. a lumen in case of exocrine, orA. a lumen in case of exocrine, or
B. into plasma of blood in case of endocrineB. into plasma of blood in case of endocrinegland .gland .
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MOVEMENT OF WATER &MOVEMENT OF WATER &
SOLUTE THROUGHSOLUTE THROUGH
MEMBRANESMEMBRANES Pressure gradients across the membranePressure gradients across the membranecreated by hydrostatic or osmotic forcescreated by hydrostatic or osmotic forcesmoves the water across the membrane .moves the water across the membrane .
Some solute passively transferred bySome solute passively transferred byhydrostatic & osmotic forces , but this ishydrostatic & osmotic forces , but this islimited by water & lipid solubility & thelimited by water & lipid solubility & thecharge , size & shape of the molecules .charge , size & shape of the molecules .
In some glands , the secreted fluidIn some glands , the secreted fluidcontains one or more constituents incontains one or more constituents inhigher concentration than in plasma ,higher concentration than in plasma ,exerts an osmotic pull on fluid across theexerts an osmotic pull on fluid across thecell into the secretion .cell into the secretion .
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Short feedback
Loop
eg. LH, ACTH,
GH
Regulation of secretionRegulation of secretionHigher centres
Hypothalamus
Pituitary
Hormone
Pituitary hormone
Releasing hormone
Long feedback
Loop
eg. Thyroxine,CortisolTarget gland
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Hypothalamus regulates secretion of hormones fromHypothalamus regulates secretion of hormones from
anterior and posterior pituitary ,ANS regulatesanterior and posterior pituitary ,ANS regulates
secretion of hormones from adrenal medulla andsecretion of hormones from adrenal medulla andpancreaspancreas
Sympathetic nerves stimulate the secretion ofSympathetic nerves stimulate the secretion of
adrenal medullaadrenal medulla
Parasympathetic nerves stimulate the secretion ofParasympathetic nerves stimulate the secretion of
pancreatic isletspancreatic islets
sex hormones from gonads regulate thesex hormones from gonads regulate thehypothalamushypothalamus
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