Ability to maintain relatively stable internal conditions despite a changing external environment. Dynamic state of equilibrium, or balance.
- The body is said to be in homeostasis when its cellular needs are adequately met and functional activities are occurring smoothly.
- Virtually every organ system plays a role in maintaining the internal environment.
A homeostatic regulatory mechanism consists of 5 parts:
- Receptors: It act as a sensors/receiver that respond to a stimulus. It monitors change in control condition.
- Sensory Neurons: It send the input information/message to control center, means information from cell/tissue/organ etc to integrated system i.e brain and spinal cord.
- Integrated System: It analyze the incoming message received from the sensory neurons and sends out commands/messages. In the body there are hundred controlled conditions.
A few examples are heart rate, blood pressure, temperature and breathing rate.
- Motor Neurons: The output information/message from integrated center (brain and spinal cord) to cell/tissue/organ etc are travelled by motor neurons.
- Effectors: The cell/tissue/organ etc act as effector that responds according to output command of the control/integrated center
Receptors, control center and effectors maintain the homeostasis by two mechanisms
1. Negative Feedback
When the response of effectors opposes the original stimulus, it is called negative
feedback because it negates the stimulus.
- An example of negative feedback is the temperature thermostat in your home.
- Temperature sensors turn the air conditioner off and on to maintain air temperature within a specific, limited range.
- In the same way, the brain controls normal body-temperature homeostasis by negative feedback
Some stimulus (Stress) disrupts homeostasis (control condition) by an increase in body temperature.
Due to this condition thermoreceptors (temperature sensitive receptors) in the skin and brain activate and send input message via nerve impulse to control center.
Control center analyze the input message and send output message to effectors (skin).
2. Positive Feedback
The effector adds to the initial stimulus instead of negating it, speeding up the process
Labor contraction is the example of positive feedback system.
– Labor contractions force baby’s head or body into birth canal.
– It produces effect on control condition and increases distention of cervix of uterus.
– It activates the stretch receptors of cervix and send input message to control center via sensory nerve impulse.
– Control center activates the hypothalamus and pituitary gland and send the output message to increase oxytocin secretion in blood.
– Oxytocin produces their effect on to the effector (cervix of uterus) and cause distention of cervix of uterus than the normal value to push the baby further into birth canal.
– Birth of the baby decreases distention of cervix of uterus and interrupts positive feedback cycle
Water content of the body is divided into:
- Intracellular compartment (67%) – Inside the cell
- Extracellular compartment (33%) – Outside the cell
Intracellular Fluid (ICF)
- Comprises, 2/3 of the body water.
- If body has 60% water, ICF is about 40% of your weight.
- The ICF is primarily a solution of potassium and organic anions, proteins etc.
- The cell membranes and cellular metabolism control the constituents of this ICF
Extracellular compartment (ECF):
ECF is about 20% of the body weight.
The ECF is primarily a NaCl and NaHCO3 solution.
The ECF is further subdivided into three sub-compartments:
A. Interstitial Fluid (ISF).
C. Transcellular fluid