Homeostasis

Originally, homeostasis was defined as a state of reasonably stable balance between physiological variables. Maintenance of a relatively stable internal environment is termed homeostasis, Body systems maintain homeostasis, a dynamic steady state in internal environment.

Homeostatic Control Systems

All The activities of cells, tissues, and organs must be regulated and integrated with each other so that any change in the extracellular fluid initiates a reaction to correct the change.

Factors are regulated in the human body

  • Concentration of O2 and CO2
  • pH of the internal environment
  • Concentration of nutrients
  • Concentration of waste products
  • Concentrations of water, salt and other electrolytes
  • Volume and pressure of extracellular fluid
  • Temperature
  • …

Regulation of body functions

  • Nervous Regulation
  • Humoral Regulation
  • Autoregulation

Nervous regulation

Reflex: a reflex is a rapid, involuntary response to a stimulus, Reflex is the basic form of nervous regulation.

Characteristic: fast, precise

Reflex Arc:

Receptor

Afferent (sensory) nerve

Reflex center (brain or spinal cord)

Efferent (motor) nerve / endocrine cell

Effector

Figure 1. knee jerk reflex

Humoral regulation

In the majority of cases intercellular communication is performed by chemical messengers. There are three categories of such messengers: hormones, neurotransmitters, and paracrine or autocrine substances.

Characteristic: slow, persistent, wide

  • Endocrine action: the hormone is distributed in blood and binds to distant target cells
  • Paracrine action: the hormone acts locally by diffusing from its source to target cells in the neighborhood
  • Autocrine action: the hormone acts on the same cell that produced it
  • Neuroendocrine: descriptive of cells that release a hormone into the circulating blood in response to a neural stimulus

Figure 2. The Role of Intercellular Chemical Messengers in Homeostasis

Non automatic control system:

Non automatic control system is Open-loop which seldom seen under physiological conditions

Example: Stress

Figure 3. non automatic control system

Feedback control system

Feedback control system closed-loop which is Automatic control.

Negative feedback

A change in a condition leads to responses from the effectors which counteracts that change. which is way more common.

Examples:

  • Regulation of blood pressure,
  • Regulation of body temperature,
  • Regulation of hormone release…

Positive feedback

A change in a condition leads to responses from the effectors which amplifies that change.

Examples:

  • Child birth
  • Micturition
  • Blood coagulation
  • Vicious circle under pathophysiological conditions…

Fig 4. positive feedback control

Feedforward control

Feedforward control often seen in nervous system which is rapid

Examples:

  • some muscle contraction
  • conditioned reflex

 

Join Art of Medics

Become Part of Art of Medics for further scientific purposes