physiology of secretion

8/14/2019 Physiology of Secretion

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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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physiology of secretion

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