K-35 BakulEndoIntroGenFunc.ppt

8/10/2019 K-35 BakulEndoIntroGenFunc.ppt

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Second level

Third level

Fourth level Fifth level

Physiology DepartmentMedical School, University of Sumatera Utara


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Second level

Third level


Body function controlled by endocrine and

nervous system

Both maintain the internal environment in a

state of homeostasis

It enable to alter in response to changes in

the external environment


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Second level

Third level


Endocrine

Endocrine system does this by means of

glands that secrete chemicals or hormones.

Endocrine refers to a gland that releases the

chemicals directly into the celluler

compartment and thence into blood stream


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Hormones :

DefinitionClassification

By origin

By site of action

By structure

Mechanisms of action

Lipid soluble hormones (cytoplasmic receptors)

Lipid insoluble hormones (cell-surface receptors)Endocrine systems :

Control of secretion

Feedback

Long-loop, short-loop


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Hormone - a substance secreted by specialized cells,

released in to the bloodstream, causing a response in

target cells elsewhere in the body.

Response is mediated by receptors that are specific to

the hormone.

Definition


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Functions of Hormone

Controlled behaviour and sexual function

Controlled salt and water balance

Maintain blood glucose Reproductive function

Involve and influence metabolic system

Lactation

Body respons to stress

Growth function

etc


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Endocrine glands


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Classif icat ion

Hormones can be classified by several properties

1. Classi f ic at ion by s ite of act ion .

Autocr ine secretion - substance released by cell that

affects the secreting cell itself

(e.g. norepinephrine is released by a neurosecretory cell in

the adrenal medulla, and norepinephrine itself inhibitsfurther release by that cell - this is also an example of

direct negative feedback)


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Paracrine secretion - substance released by cell that affects

neighboring cells. Not released into bloodstream(e.g. histamine released at site of injury to constrict blood

vessel walls and stop bleeding)

Endocr ine secretion - substance released by cell intobloodstream that affects distant cells.

(e.g. testosterone is secreted by Leydig cells in testis, makes

hair grow on your back)

Though hormones may also have autocrine or paracrine

actions, we're mainly concerned with endocrine actions


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Exocr ine secretion - substance released by cell into a duct

that leads to epithelial surface

(onto skin or into gut). Action doesntdepend on receptors intarget tissue. (e.g. sweat, saliva)

Endocrine and exocrine secretions are glandular

secret ions; they come from specialized secretory cells thatare clumped together to form a gland. Endocrine glands are

sometimes called ductless glands.

Note that a secretion may have several si tes o f act ion

simul taneously.Example of norepinephrine above - autocrine action causes

negative feedback on secretion. Simultaneously, endocrine

action causes respiration rate to , peripheral blood vessels

to contract, etc.


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Circulating & Local Hormones

Circulating

hormones act on distant targets

travel in blood

Local hormones act on neighboring

cells or same cell

that secreted them


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2. Classi f ic at ion by orig in.

Another set of terms, related to those just discussed, is

commonly used to classify secretions, based both on

or ig in and site of action

Neurohormones - endocrine, source = nerve

Glandu lar ho rmones - endocrine, source = gland

Local Hormones - paracrine (source may not be gland)

Pheromones - exocrine


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Chemical signaling by hormones: (a) Endocrine hormones are produced by cells of

endocrine glands and transported by the blood to target cells. (b) Some hormones are

released by neurosecretory cells, which function in both the nervous and endocrine

systems. (c) A few hormones are secreted over short distances through tissue fluid.


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3. Classi f icat ion by molecular struc ture.

Amines- small molecules derived from amino acids. Thecatecholamines are epinephrine and norepinephrine,

secreted by the adrenal medulla. Lipid insoluble

Prostaglandins - fatty acids. Lipid soluble.

Steroids - cyclic hydrocarbons derived from cholesterol. Lipid

soluble

Peptides and p roteins - large, complex, structure can differamong species due to amino acid substitutions. Lipid

insoluble.


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Steroids are fat soluble, so they bind to receptors in the

cytoplasm, either in the cytosol or directly in the nucleus.

When the steroid binds to the receptor, i t dis inh ibi ts a

DNA binding si te on the receptor.

The steroid-receptor complex then moves into the nucleus

and activates or suppresses specific genes. By altering

gene expression, steroids produce long-lasting effects.


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Action of Lipid-Soluble Hormones

Hormone diffuses

through phospholipid

bilayer & into cell

Binds to receptor

turning on/off specificgenes

Gene copies are

formed & direct

synthesis of newproteins

New protein alters

cells activity


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Action of Lipid-

insoluble Hormones


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The mechanism of peptide hormones(1) Peptide hormones are produced by an endocrine gland and carried by the blood. (2)

Receptors on the plasma membrane of a target cell bind with the hormone. The hormone

itself does not enter the cell. (3) An enzyme in the plasma membrane changes ATP to cyclic

AMP (cAMP). The cAMP molecule is the secondmessenger,carrying the hormonessignal

through the cell. (4) Enzymes are activated, triggering a series of reactions. (5) These

reactions bring about the changes controlled by the hormone.


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Effects o f hormones:

mechanisms of hormone act ion on target t issue

What does a hormone do when it arrives somewhere

via the blood?


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1. First level controlling action: target/non-target.

Hormones have their effects only on target t issues. Cells in

target tissue have receptors, molecules that bind

specifically to that hormone. In non-target tissue, cells have

no receptors and are not affected by the hormone no matter

how much of it is present.


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Hormone Receptors

Hormones only affect target cellswith specificmembrane proteins called receptors


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2. Second level controlling action: receptor densi ty.

Target cells vary in the number of receptors they hold. A cell

with many receptors is more strongly affected than one withfew receptors, when exposed to the same amount of

hormone.

Receptor density for a given tissue changes through time.

Down-regulat ion is a decrease in receptor density.

Up-regulat ion is an increase in receptor density.

Down and up-regulation commonly respond to the amount of

hormone in circulation over the long-term, as a damping

mechanism. If blood concentration of cortisol (a stresshormone from the cortex of the adrenal gland) is high for a

long time, receptor densities will decrease to modulate the

response.


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Mechanisms of Activation

Hormones can alter the rateof cellular activity

They do not alter the activity of the cell

Cellular activity is controlled by: changes in PM permeability

synthesis of regulatory molecules

enzyme activity/de-activity

induction of secretion

stimulation of mitosiscell division


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Hormonal Activation

Once bound to the cell will hormone affect the

cell by one of two mechanisms

Amino Acid based hormones and a second

messenger system, the second messenger thenbrings about the desired affect

Steroids diffuse into the cell and bind to

receptors this then activates protein synthesis


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Time Scale of Activation

The level of a given hormone in the blood

reflects the balance between release and

removal

The persistence of a given hormone in the bloodis called the Half Life

Unlike the nervous system which has a rapid

response which is short lived the endocrine

system takes longer to have an effect but the

effect last longer


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Hormone Release

Negative feed back loops

Endocrine gland stimulation

Humoral - Ca+levels and PTH/calcitonin

- Glucose and Insulin Neural - Fight or Flight

Hormonal - release is triggered by other hormones

Nervous system regulation


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Feedback loops


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Feedback loops

NEGATIVE FEEDBACK

Positive Feedback:

Hormones stimulate each

other, product of target cell

increases production ofinitial hormone which

causes even more

secretion of the target cell

product

Tend to be rareandshortlived because they

can quickly get out of

control!

Negative feedback:

Short- and long-loops.

Product inhibits further

production of self and of

stimulating hormone.

Can operate on multiple

levels.


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Negative

feed

backcontrol


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K-35 BakulEndoIntroGenFunc.ppt

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