14.4) Homeostasis

14.4) Homeostasis

Homeostasis: is the maintenance of a constant internal environment.


Homeostasis is the control of internal conditions within set limits:

  • Cells: change composition of blood as they remove nutrients and O2 and add wastes and CO2.
  • Heart: keeps blood pressure constant to deliver oxygen and nutrients around body.
  • Skin: to maintain heat exchange with external environment.
  • Kidneys: regulate water and salt levels (osmoregulation) and the removal of wastes like urea (excretion).
  • Lungs: regulate gas exchange Intestines: supply soluble nutrients and water to blood.
  • Liver: regulates blood solutes and removes toxins.


Negative feedback:

Homeostatic control is achieved using negative feedback mechanisms:

  • if the level of something rises, control systems reduce it again
  • if the level of something falls, control systems raise it again


Regulation of blood sugar:

  • Blood glucose levels are monitored and controlled by the pancreas
  • The pancreas produces and releases different hormones depending on the blood glucose level
  • Insulin is released when blood glucose levels are high – the liver stores excess glucose as glycogen
  • Glucagon is released when blood glucose levels are low – the liver converts stored glycogen into glucose and releases it into the blood



  • Diabetes is a condition in which the blood glucose levels remain too high.
  • It can be treated by injecting insulin.
  • The extra insulin causes the liver to convert glucose into glycogen, which reduces the blood glucose level. There are two types of diabetes – Type 1 and Type 2.


Type 1 diabetes is caused by the lack of insulin:

  • Symptoms: feeling tired, thirsty, frequent urination and weight loss.
  • Treatment: regular exercise, injecting insulin, and monitoring the diet.

Skin structure:

  • The basal layer and the cells above it constitute the epidermis.
  • There a specialised pigment cells in the basal layer and epidermis. These produce a black pigment, melanin, which gives the skin its colour.The more melanin, the darker the skin.
  • The dermis contains connective tissue with hair follicles, sebaceous glands, sweat glands, blood vessels and nerve endings.
  • There is a layer of adipose tissue (fat deposit) beneath the dermis.


Temperature regulation:

The human body is designed to function most efficiently at 37ºC. If you become too hot or too cold, there are ways in which your body temperature can be controlled.

  • Insulation: provided by fatty tissue retains heat. Hairs become erect to trap warm air by contracting erector muscles and vice versa.
  • Vasodilatation: when it is hot, arterioles, which supply blood to the skin surface capillaries, dilate (become wider) to allow more blood near to skin surface to increase heat loss (face redder)
  • Vasoconstriction: when it is cold, arterioles, which supply blood to the skin-surface capillaries, constrict (become smaller) to allow less blood near to skin surface to decrease heat loss
  • Sweating: the water evaporates giving a cooling effect
  • Skin receptors: sense heat and sensory neurons send impulses to the hypothalamus
  • Shivering: muscular activity generates heat
  • Thermoregulatory center: in the hypothalamus, it controls the use of corrective mechanisms (e.g. sweating and shivering).
No comments yet.

Leave a Reply