1 HOMEOSTASIS Dr MUNAZA KHATTAK ASISTANT PROFESSOR PHYSIOLOGY

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HOMEOSTASIS Dr. MUNAZA KHATTAK ASISTANT PROFESSOR PHYSIOLOGY DEPARTMENT PMC

HOMEOSTASIS � Greek word for ‘same’ and ‘steady’ � Any process that living things use to actively maintain fairly stable conditions necessary for survival.

Homeostasis � Maintenance of nearly constant conditions of internal environment � Maintenance of environment compatible with life � Essential for survival of each cell � Each cell contribute its part in homeostasis

The Internal Environment � The internal environment or milieu interieur -Blood plasma -Intracellular fluid -Extracellular fluid � The maintenance of a steady state in these fluids is essential to living things

Homeostasis : Terms ◦ Set point �Expected value of regulated variable �Examples �Core body temperature = 37º C �Blood glucose (sugar) = 100 mg/d. L �Blood p. H = 7. 4 ◦ Error signal �Difference between value of set point and regulated variable

Homeostasis: Components q. Structures enabling homeostasis q. Components include q. Receptors(sensors that detect stimuli) q Thermoreceptors q Chemoreceptors q Baroreceptors q. Integrating Centers q. Effectors(Responsible for body responses) q Muscles (smooth, striated, and cardiac) q Glands q. Signals

◦ Signals �Allow components to communicate �Input signal is from a receptor to an integrating center �Output signal is from an integrating center to an effector �Signals are chemical or via neurons

Examples of Homeostasis � Body water regulation by osmoreceptors and kidneys � Excretion of waste products by kidneys and respiration � Temperature regulation � Blood glucose regulation � Constant supply of nutrients � Maintenance of p. H

� Osmoreceptors, pressure. sense change in osmotic � When the osmotic pressure of blood changes (i. e. it is more or less dilute), water diffusion into and out of the osmoreceptor cells changes. ◦ That is, they expand when the blood plasma is more dilute and contract with higher concentration. � This causes an afferent neural signal to be sent to the hypothalamus, which increases or decreases vasopressin (ADH) secretion from the posterior pituitary to return blood concentration to normal.

REGULATORY MECHANISM � Intrinsic (local)controls Built in or inherent to an organ e. g CO 2 in exercising muscles increase blood flow in the muscle � Extrinsic controls Initiated outside the organ Nervous system Endocrine system

� Action can be voluntary 1. Drink when thirsty 2. Eat when hungry 3. Put on clothing when cold 4. Open a window when one is too warm � Action can be Involuntary 1. Shivering 2. Sweating

SECTIONS OF HOMEOSTASIS � External environment � The Internal environment � Control system

� � Control Systems have two components: Sensor which detects the change Effector which corrects the change Most physiological systems in the body use feedback to maintain the body's internal environment exactly balanced

Control of homeostasis � Feedback Systems in Homeostasis 1. Negative feed back system 2. Positive feed back system

Regulatory Mechanism � Negative feed back control Change in controlled variable triggers a response opposite to the change. Positive feed back control Change in controlled variable continues to move in the direction of the change enhancing the change

Positive feedback loops cause a rapid change in a variable.

Homeostasis: Thermoregulation ◦ Core body temperature �Humans: 37º C (98. 6º F) �Hypothermia = decrease in body temperature �Hyperthermia = increase in body temperature �Above 41º C is dangerous �Above 43º C is deadly

◦ Mechanisms of heat transfer between body and external environment ◦ Radiation—thermal energy as electromagnetic waves. ◦ Conduction—thermal energy through contact. ◦ Evaporation—heat loss through evaporation of water �Insensible water loss �Sweating ◦ Convection—heat transfer by movement of fluid or air

Thermoregulation: Components ◦ Receptors = thermoreceptors �Central: found in CNS (hypothalamus) �Peripheral: found in PNS (mainly skin) ◦ Effectors �Glands: sweat glands �Muscles: skeletal muscles, and smooth muscle of cutaneous blood vessels

Thermoregulation: Components ◦ Integrating center �Thermoregulatory center in hypothalamus ◦ Signals �Nerve impulses via neurons �Chemicals via hormones

Thermoneutral Zone ◦ Range of outside temperature where alterations in blood flow alone regulates body temperature— 25 -30ºC ◦ Body temperature increase �Blood flow to skin increases ◦ Body temperature decrease �Blood flow to skin decreases

Negative feedback control of body temperature

Thermoregulation

FEVER ◦ Rise in core body temperature ◦ Accompanies infection ◦ White blood cells secrete pyrogens ◦ Body temperature set point increases ◦ Fever enhances immune response

Feedback Systems in Homeostasis �Negative feedback ◦ Used by most of the body's systems ◦ The response caused by the feedback is opposite to the change (stimulus). ◦ ↑ Thyroxin → → ↓ TSH → ↓ Thyroxin ◦ ↓ Thyroxin → → ↑ TSH → ↑ Thyroxin

-ve feed back control of thyroxin

Feedback Systems in Homeostasis �Positive �Control feedback is used in some cases. ◦ The response caused by the feedback is in the direction of the change (stimulus). ◦ Input increases or accelerates the response.

�Labor ◦ Oxytocin →↑ uterine contraction →↑Oxytocin

Pathophysiology Disruption of Homeostasis Disease Failure of homeostasis Death

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