Dr. MUNAZA KHATTAK ASISTANT PROFESSOR PHYSIOLOGY DEPARTMENT PMC 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/dL Blood pH = 7.4 Error signal Difference between value of set point and regulated variable

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

Osmoreceptors, sense change in osmotic pressure. 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 CO2 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 Negative feed back system 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 feedback Control 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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