Introduction to HomeostasisIntroduction to Homeostasis

Levels of OrganizationLevels of Organization• ChemicalChemical• CellularCellular• TissueTissue• OrgansOrgans• System LevelSystem Level• Organismic LevelOrganismic Level

Body SystemsBody Systems• Groups of organs that perform related Groups of organs that perform related

functions and interact to accomplish a functions and interact to accomplish a common activity essential to survival of the common activity essential to survival of the whole bodywhole body

• Do not act in isolation from one anotherDo not act in isolation from one another• Human body has 11 systemsHuman body has 11 systems

Body SystemsBody Systems

Body SystemsBody Systems

HomeostasisHomeostasis• Defined as maintenance of a relatively Defined as maintenance of a relatively

stable internal environmentstable internal environment• Does not mean that composition, Does not mean that composition,

temperature, and other characteristics are temperature, and other characteristics are absolutely unchangingabsolutely unchanging

• Homeostasis is essential for survival and Homeostasis is essential for survival and function of all cellsfunction of all cells

• Each cell contributes to maintenance of a Each cell contributes to maintenance of a relatively stable internal environmentrelatively stable internal environment

Basic Cell FunctionsBasic Cell Functions• Sensing and responding to changes in Sensing and responding to changes in

surrounding environmentsurrounding environment• Control exchange of materials between cell and Control exchange of materials between cell and

its surrounding environmentits surrounding environment• Obtain nutrients and oxygen from surrounding Obtain nutrients and oxygen from surrounding

environmentenvironment• Eliminate carbon dioxide and other wastes to Eliminate carbon dioxide and other wastes to

surrounding environmentsurrounding environment

• Perform chemical reactions that provide energy Perform chemical reactions that provide energy for the cellfor the cell

• Synthesize needed cellular componentsSynthesize needed cellular components

HomeostasisHomeostasis• Body cells are in contained in Body cells are in contained in

watery internal environment watery internal environment through which life-sustaining through which life-sustaining exchanges are madeexchanges are made

• Extracellular fluid (ECF) - Extracellular fluid (ECF) - Fluid environment in which Fluid environment in which the cells live (fluid outside the the cells live (fluid outside the cells)cells)

• Two components: Two components: • PlasmaPlasma• Interstitial fluidInterstitial fluid

• Intracellular fluid (ICF) - Fluid Intracellular fluid (ICF) - Fluid contained within all body cellscontained within all body cells

HomeostasisHomeostasis

Cells, the fundamental units of life, exchange nutrients and wastes with their surroundings:

The intracellular fluid is “conditioned by”… the interstitial fluid, which is “conditioned by” … the plasma, which is “conditioned by” … the organ systems it passes through.

Balancing the Internal and External Environment

ICF ISF plasma organs

external environment

internal environment

Homeostasis

• Homeostasis involves dynamic mechanisms that detect and respond to deviations in physiological variables from their “set point” values by initiating effector responses that restore the variables to the optimal physiological range.

• Two systems that maintain homeostasis are: Nervous system & Endocrine system

Maintenance of HomeostasisMaintenance of Homeostasis

• Nervous systemNervous system• Controls and coordinates bodily activities that require Controls and coordinates bodily activities that require

rapid responsesrapid responses• Detects and initiates reactions to changes in external Detects and initiates reactions to changes in external

environmentenvironment• Endocrine systemEndocrine system

• Secreting glands of endocrine regulate activities that Secreting glands of endocrine regulate activities that require duration rather than speedrequire duration rather than speed

• Controls concentration of nutrients and, by adjusting Controls concentration of nutrients and, by adjusting kidney function, controls internal environment’s kidney function, controls internal environment’s volume and electrolyte compositionvolume and electrolyte composition

HomeostasisHomeostasis

Factors homeostatically regulated includeFactors homeostatically regulated include• Concentration of nutrient moleculesConcentration of nutrient molecules• Concentration of water, salt, and other electrolytesConcentration of water, salt, and other electrolytes• Concentration of waste productsConcentration of waste products• Concentration of OConcentration of O2 2 = 100mmHg and CO = 100mmHg and CO2 2 = 40 = 40

mmHgmmHg• pH = 7.35pH = 7.35• Blood volume 4-6 L and pressure 120/80Blood volume 4-6 L and pressure 120/80• Temperature = 37Temperature = 37oo C C

Control of HomeostasisControl of Homeostasis

• Homeostasis is continually being Homeostasis is continually being disrupted bydisrupted by• External stimuli External stimuli

• heat, cold, lack of oxygen, heat, cold, lack of oxygen, pathogens, toxinspathogens, toxins

• Internal stimuliInternal stimuli• Body temperatureBody temperature• Blood pressureBlood pressure• Concentration of water, glucose, Concentration of water, glucose,

salts, oxygen, etc.salts, oxygen, etc.• Physical and psychological Physical and psychological

distressesdistresses• Disruptions can be mild to severeDisruptions can be mild to severe• If homeostasis is not maintained, If homeostasis is not maintained,

death may resultdeath may result

Control of HomeostasisControl of Homeostasis

Homeostatic Control SystemsHomeostatic Control Systems

• In order to maintain homeostasis, control In order to maintain homeostasis, control system must be able tosystem must be able to• Detect deviations from normal in the internal Detect deviations from normal in the internal

environment that need to be held within narrow environment that need to be held within narrow limitslimits

• Integrate this information with other relevant Integrate this information with other relevant informationinformation

• Make appropriate adjustments in order to Make appropriate adjustments in order to restore factor to its desired valuerestore factor to its desired value

Homeostatic Control SystemsHomeostatic Control Systems

• Control systems are grouped into two Control systems are grouped into two classesclasses• Intrinsic controlsIntrinsic controls

• Local controls that are inherent in an organLocal controls that are inherent in an organ

• Extrinsic controlsExtrinsic controls• Regulatory mechanisms initiated outside an organRegulatory mechanisms initiated outside an organ• Accomplished by nervous and endocrine systemsAccomplished by nervous and endocrine systems

Homeostatic Control SystemsHomeostatic Control Systems

• Feedforward - term used for responses Feedforward - term used for responses made in anticipation of a changemade in anticipation of a change

• Feedback - refers to responses made after Feedback - refers to responses made after change has been detectedchange has been detected• Types of feedback systemsTypes of feedback systems

• NegativeNegative• Positive Positive

Feedback Loops: TypesFeedback Loops: Types• Negative feedback loopNegative feedback loop

• original stimulus reversed original stimulus reversed • most feedback systems in the body are negativemost feedback systems in the body are negative• used for conditions that need frequent used for conditions that need frequent

adjustmentadjustment

• Positive feedback loopPositive feedback loop• original stimulus intensifiedoriginal stimulus intensified• seen during normal childbirthseen during normal childbirth

Negative Feedback LoopNegative Feedback Loop• Negative feed back loop consists of:Negative feed back loop consists of:• Receptor - structures that monitor a controlled condition and detect Receptor - structures that monitor a controlled condition and detect

changeschanges

• Control centre - determines next action Control centre - determines next action

• EffectorEffector• receives directions from the control centrereceives directions from the control centre• produces a response that restores the controlled conditionproduces a response that restores the controlled condition

Homeostatic Regulation of Body Temperature Homeostatic Regulation of Body Temperature through Negative Feedbackthrough Negative Feedback

Negative Feedback LoopNegative Feedback Loop

Negative Feedback LoopNegative Feedback Loop

Homeostasis – Negative Feedback LoopHomeostasis – Negative Feedback Loop• Blood glucose concentrations rise after a sugary meal (the Blood glucose concentrations rise after a sugary meal (the

stimulus), the hormone insulin is released and it speeds up the stimulus), the hormone insulin is released and it speeds up the transport of glucose out of the blood and into selected tissues (the transport of glucose out of the blood and into selected tissues (the response), so blood glucose concentrations decrease (thus response), so blood glucose concentrations decrease (thus decreasing the original stimulus). decreasing the original stimulus).

Homeostasis of Blood PressureHomeostasis of Blood Pressure

• Baroreceptors in walls of Baroreceptors in walls of blood vessels detect an blood vessels detect an increase in BPincrease in BP

• Brain receives input and Brain receives input and signals blood vessels and signals blood vessels and heartheart

• Blood vessels dilate, HR Blood vessels dilate, HR decreasesdecreases

• BP decreasesBP decreases

Positive Feedback during ChildbirthPositive Feedback during Childbirth• Stretch receptors in walls of uterus send signals Stretch receptors in walls of uterus send signals

to the brainto the brain• Brain induces release of hormone (oxytocin) into Brain induces release of hormone (oxytocin) into

bloodstreambloodstream• Uterine smooth muscle contracts more forcefullyUterine smooth muscle contracts more forcefully• More stretch, more hormone, more contraction More stretch, more hormone, more contraction

etc.etc.• Cycle ends with birth of the baby & decrease in Cycle ends with birth of the baby & decrease in

stretchstretch

+ Feedback + Feedback LoopLoop

Role of Body Systems in Role of Body Systems in HomeostasisHomeostasis