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.
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.
- 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.
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).