Homeostasis

Maintenance of steady states in body by coordinated physiologic mechanisms. 

1: Extracellular fluid: Internal environment in body in which the cells live and the fluid outside the cell 

Divisions of ECF

• Plasma: Part of ECF present in blood constitute ¼ OF ECF 
• Interstitial fluid: Part of ECF present in spaces between cells constitute ¾ of ECF. 

2: Intracellular fluid: Fluid inside the cells 

Average 70 kg adult has approximately 40 liters of water. Around 2/3 is ICF 

• Total body water= 0.6 x bodyweight 
• ECF 0.2X Body weight 
• ICF 0.4X Body weight 

Electrolytes distribution in ECF and ICF

Operating mechanism for homeostasis:

1: Negative feedback:

• Components: Regulated variable, Sensor, Controller, and Effector. 
• A regulated variable is sensed, information is fed back to the controller, and the effector acts to oppose change (hence the term negative) Control most systems of body.” 
• Examples:  Osmoregulation, regulation of blood, pressure, temperature regulation, regulation of CO2 in ECF. 

2: Positive feedback:

Promotes changes in one direction leading amplified effect. Cause vicious cycle and death, sometimes it can be useful. 

Examples: 

• Childbirth (During labor): The release of oxytocin from the posterior gland during childbirth and labor
• Blood clotting.
• Generation of nerve signals.
• Sensation of needing to urinate.
• Follicular phase of menstrual cycle