Homeostasis and negative feedback

In a nutshell

Homeostasis is used to control internal levels of temperature, pH and glucose to keep cellular function at an optimum level. More than one negative feedback system is required to enable total control.

Homeostasis

Definition

Homeostasis is a process where a stable internal environment is maintained.

Homeostasis uses control systems that keep the internal environment stable. This is important for bodily functions to occur normally.

Example

Cell machinery is made mostly of proteins, their optimum temperature for function is $37\space \degree C$ . When the temperature drops cell machinery doesn't function as quickly and when the temperature rises the proteins in the cell machinery begin to denature. Cells cannot function properly without temperature being regulated by homeostasis.

Negative feedback

Definition

Homeostatic systems are always bringing their environment back to a base level. A system which returns a change back to a normal level is called a negative feedback system.

Receptors, effectors and communicators are involved in homeostatic systems. A receptor monitors a change in the environment and relays messages through the nervous system to effectors which return the environment back to the normal level.

Temperature

Biology; Control systems; KS5 Year 12; Homeostasis and negative feedback

1.	The internal temperature increases above $37\space \degree C$ and receptors detect the change and send messages to effectors through the nervous system.
2.	The effectors respond to the change by decreasing the internal temperature.
3.	The body temperature drops below $37\space \degree C$ and receptors detect the change and send messages to effectors through the nervous system.
4.	This process constantly repeats and the internal body temperature is kept within $0.5$ $\degree C$ of $37\space \degree C$ .

Negative feedback is only effective between small limits. If the change in internal environment is too great then effectors may not be able to effectively alter the change.

pH

The pH level, like temperature, is important for the proper functioning of every protein in the body. If the pH is too high or too low then cellular proteins and enzymes will become denatured. Hydrogen bonds, at different pH levels, are altered inducing shape changes to proteins.

Effectors, receptors and the nervous system work in a negative feedback loop to keep internal pH level the same. Cellular machinery works at optimum efficiency at around pH $7$ , therefore, homeostasis must keep pH at this level,

Glucose

Blood glucose concentration must be kept constant to provide enough energy for cellular function. Glucose is used in respiration to provide energy for all internal processes. If the blood glucose concentration drops below the optimum level, then normal cell function is prevented.

On the other hand, if blood glucose concentration increases above the optimum level it has severe consequences on the osmotic potential of cells. High blood glucose concentration causes water molecules to leave cells by osmosis, to balance the water potential. If enough water molecules exit the cell, then cell lysis is triggered.

Multiple feedback mechanisms

In reality, one negative feedback system doesn't enable adequate control. One feedback system only allows an effector to be turned on or off. Multiple feedback systems allow organisms to actively increase and decrease factors in the internal environment.

More than one negative feedback mechanism is required in organisms to keep the internal environment stable. One negative feedback mechanism provides only slow responses and less control.