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:
- 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).