14 Feb Homeostasis

8/12/2019 14 Feb Homeostasis

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HOMEOSTASISCOMMUNIC TION

Prof. Hardi Darmawan, MD, MPH&TM.,FRSTM

Department of Physiology & Biophysic


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DEFINITION OF PHYSIOLOGY

Physiology is the study of how

things work

BASIC PRINCIPLE OFPHYSIOLOGY

Homeostasis is the basic principle

of physiology

Homeostasis is the maintenanceof a constant environment


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CHARACTERISTICS OF

HOMEOSTASIS

Effectors may have opposing

actions.

Negative feedback is the

process that prevent change.

Positive feedback is the

process that perpetuates

change.

Feed forward control is outside

stimuli that alter the normal

feedback response.


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COMMUNICATON IS AN

ESSENTIAL ELEMENT OF A

HOMEOSTATIC SYSTEM

Two languages of communication are

chemical and electrical.

Characteristics of communication aredistance, speed, distribution.

The sensor has to communicate with

the feedback controller and thefeedback controller has to communicate

with the effector. There are essentially

two languages of communication. One


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Communication has severalcharacteristics :

1. Distance : short vs long

2. Speed : fast vs slow

3. Distribution : focused vs diffuse


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Communication occurs overdistance as short as the

environment surrounding a single

cell. Cells can stimulate

themselves, called autocrine

stimulation,or their neighbor,

calledparacrine stimulation

through the release of chemicalagents.


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Communication can also occur

over long distance, such as a

nerve cell located in the spinalcord sending a process out to

the end of the finger to

stimulate a muscle cell.


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COMMUNICATION BETWEEN

CELLS figure 1.2

Cells communicate with eachother by mechanisms which

include endocrine, paracrineand neurocrine actions.

Endocrine communication isthrough secretion of chemicalsor hormones into the bloodstream which then circulates to

cells of target organs.


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Paracrine is a cell to cell or localcommunication by adjacentcells via secretions whichdiffuse into the interstitial fluid.This is mediated by receptors.

In neurocrine or synaptic

communication, the transmitterreleased at a nerve endingpasses through a synapse to thecommunicating or post-synaptic

cell.


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Intercellular CommunicationType Description` Means of

MessageTransmission

Local or

General

Examples

Autocrine Process by which

cell produces

subtance that

regulates that cellor neighboring

cells of same type

By diffusion in

interstitial fluid

Locally diffuse Prostaglandine

released by

uterine tissue

inducecontractions of

uterine smooth

muscle

Prostaglandins

released by

bronchiolarsmooth muscle

induce

vasodilation


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Endocrin

e

Process by

which cell

secretesregulatory

substance

directly into

blood stream,

which affectscells that

maybe some

distance away

By

circulating

blood

General Anterior pituitary

secretes prolactin,

which travels viabloodstream to

mammary glands to

stimulate milk

synthesis.

Pancreatic cells in

islets of Langerhans

secrete glucagon,

insulin, somatostatin,

and pancreatic

polypeptide (pancreas

has both exocrine and

endocrine function)


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Neurocri

ne

Process by

which neuron

releases

regulatory

substances

into blood

stream to

affect distant

cells

Axonal

transport

to

bloodstrea

m

Gener

al

Hypothalamus

releases

antidiuretic

hormone into

bloodstream

Paracrin

e

Process by

which cell

secretes

regulatory

substancethat diffuses

into ECF to

affect nearby

cells that are

different from

itself`

by diffusion

in

interstitial

fluid)

Locall

y

diffuse

Histamine

released from

cells in wall of

stomach

stimulates HCLsecretion by

parietal cells of

gastric gland.


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Process of Intracellular

Communication

Sequence Action

1 Agonist binds membrane receptor

2 G protein is activated by binding GTP

Amplification allows one agonist complex to

activate hundreds of effectors

3 Activated G protein interacts with effector

proteins to alter their activities

Effectors include enzymes, ion channels, and

phospholipases

4 Effector proteins affect activities of secondmessengers (cAMP, cGMP, DAG, IP3)


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5 Activity of second messenger alters activity

of second messenger-dependent protein

kinases (cAMP-dependent protein kinases,

cGMP-dependent protein kinases, protein

kinase C, calmodulin-dependent proteinkinase) or ion channels

6 Level of phosphorylation of enzyme or ionchannel is altered

7 Final cellular response

AGE SPLuRge Agonist, G Protein, Effector proteins, Second messengers,Protein kinases, level of phosphorylation, response

I t ll l M di t


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Intracellular MediatorsType Description / Example

Second Messenger

Cyclic Nucleotides

(cAMP, cGMP)Vision depends on cGMP-gated Na+ channels

present in plasma membranes of rods

When rhodopsin (receptor) is activated by light

(stimulus), rhodopsin interacts with the G

protein transducin

Activated transducin interacts with cGMP

phosphodiesterase, which increases cGMP and

causes closing of cGMP- activated Na+

channels and hyperpolarization of

photoreceptor cell


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IP3 and DAG G protein activates agonist receptor

complex, which then cleaves

phosphatidylinositol 4,5-bisphosphate

into IP3 and DAG

IP3 binds receptors on endoplasmic

reticulum, leading to release of Ca2+

into cytosol, which triggers cellular

response

Immunosuppressant drug

cyclosporine helps prevent transplant

rejection by blocking this pathway.

Ca2+ Ca2+ calmodulin complex activates

myosin light-chain kinase (a

calmodulin-dependent protein kinase),

which phosphorylates myosin, resulting

in smooth muscle contraction.


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Protein Kinases

Protein Kinase Enzyme activated by second messenger

thatphosphorylates proteins on serine or

threonine

residues (protein phosphatase is enzyme

that

dephosphorylates proteins).

cAMP-dependent protein kinase

phosphorylates

rate-determining enzymes in glycogen

metabolism

Ca2+ stimulates protein kinase C, which

stimulates

cell division and is involved in growth of

tumor

cells.


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G Proteins

Heterotrimeric Nucleotide regulatory protein that aids in

translation of signals between cells and helps

modulate intracellular concentrations of second

messengers.

In active state, acts as GTPase, hydrolyzing GTP

toGDP

Adenylyl cyclase (enzyme that aids synthesis of

cAMP) and cGMP phosphodiesterase (enzyme that

breaks down cGMP) are modulated by G proteins.Activation of phospholipase A2 by G protein leads

to production of arachidonic acid


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Monomeric Small G protein involved in protein

synthesis, cell

proliferation, neoplastic cell

transformation and

vesicle transport.

Ras like G protein regulate cell growth

anddifferentiation

Rab-like G protein help target vesicles to

membranes


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Intercellular Communication

By Chemical Mediators


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THANK YOU

FOR

YOUR

KIND

ATTENTION

THE END

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14 Feb Homeostasis

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