Homeostasis | Short notes

Introduction to Homeostasis

The composition of the internal environment is maintained within narrow limits, and this fairly constant state is called Homeostasis.

Or

When structures and functions are coordinated the body achieves a relative stability which is called as Homeostasis. (Staying the same), 

Homeostasis is also referred as body’s ability to maintain stable or unchanged body's internal environment.
When this balance is disturbed or lost, there is a serious risk to the health of the individual. 

The homeostasis process has three basic Components:-

• Detector
• Control Center
• Effector

The control center receives an input from the detector or sensors, and integrates the incoming information,
When the incoming signal indicates need of adjustments the control center responds,
Thus, its output to the effector is changed. This is a process that maintain Homeostasis.

The homeostasis process shows two types of feedback mechanisms,:-

• Positive Feedback Mechanism
• Negative Feedback Mechanism

Positive Feedback Mechanism

In Positive feedback mechanisms,the stimulus progressively increases the response,so that as long as the stimulus is continued the response is progressively being amplified.

Examples of Positive feedback mechanism-

• During Labour,contraction of the uterus force the baby's head into the cervix,also called as Ferguson Reflux.

Fig.Example of Positive feedback mechanism Uterine contractions during labour

- During labour, contraction of the uterus are stimulate by hormone oxytocin these force the baby's head into the cervix of the uterus stimulating stretch receptors there.

- This stimulation carried to hypothalamus and posterior pituitary gland via nerve impulses results in the increased release of oxytocin.

- In response to this, uterine contraction increases and maintaining labour.

- After the baby is born the stimulus is no longer present and release of oxytocin stops.

• Clotting of blood or coagulation

Fig.Example of Positive feedback mechanism Blood clotting

- In case of any injury to the living body starts bleeding and exposes sub-endothelial chemicals like collagen, von Willebrand factor and thrombin in blood at the site of injury.

- These chemicals stimulate/activate platelets in the blood.

- In response, the platelets starts forming plug by sticking to each other and to the side of wound.

- Then clotting factors triggers production of fibrin which is a thread like structure to form a fibrin clot that stop bleeding and keep clot stable.
- The clot remains till the injury get healed completely.
- After that platelets do not adhere to smoothen blood vessel lining. Also anticoagulants stops further coagulation.

Negative Feedback Mechanism

In negative feedback the effector response decreases or reduces the effect of the original stimulus, for restoring homeostasis.

Example of negative feedback mechanism -

• Body temperature regulation

- Body temperature is a physiological variable controlled by negative feedback mechanism body temperature falls below the normal level [98.6°F].

Fig.Example of negative feedback mechanism Temperature Regulation

- Temperature sensitive nerve endings presents on skin detects change  in body temperature and transmit the information as an stimulation to control system.
- Group of cells in hypothalamus of brain acts as control system interprets information and sends stimulation to effectors like skeletal muscles, blood vessels in the skin to reduce heat loss from peripheries . 
- When body temperature rises there is simultaneous inhibition of temperature sensitive cells to stop the stimulation of the detectors.
- To maintain the normal body temperature.

• Blood Pressure (B.P.) Regulation (Baroreflex)

- Blood pressure must remain normal for better blood circulation in the body.

Fig.Example of Negative Feedback Mechanism Blood Pressure Regulation 

- If the blood pressure is high or low with respect to normal blood pressure that is detected by detectors that are baroreceptors present on walls of arteries.
- Detectors sends chemical stimulation to brain via glossopharyngeal nerve then brain interprets information and stimulates the effectors accordingly.
- Effector that is Heart increases pumping rate in case of low blood pressure to rise it and in case of high blood pressure heart decreases pumping rate to fall it.
- This cycles is needed to regulate normal blood pressure.


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