Controlling Internal Conditions
Homeostasis is the process in the body that helps to maintain a constant internal environment.
- Carbon dioxide - waste product of cellular respiration, excreted through lungs; air breathed in contains only 0.04% CO2 but air breathed out contains about 4% CO2
- Excess amino acids that are broken down are converted into urea (poisonous) by the liver and excreted by kidneys in urine (stored in the bladder)
- Water (lost through breathing, sweating and in urine) and ion (lost through sweat and in urine) content of cells must be carefully controlled, if not, too much or too little water may move in and out of cells by osmosis
Controlling Body Temperature
The thermoregulatory centre of the brain and receptors in the skin detect changes in temperature. The thermoregulatory centre controls the body's response to a change in internal temperature.
If core temperature rises:
- Blood vessels near the surface of skin dilate allowing more blood to flow through the skin capillaries; heat is lost by radiation
- Sweat glands produce more sweat which evaporates from skin's surface cooling the body
If core temperature falls:
- Blood vessels near the surface of skin constrict and less blood flows through the skin capillaries; less heat is radiated
- Shivering makes the muscles contract quickly; requires respiration and some of the energy produced is released as heat
Hairs on skin trap more warmth if they are standing up and less if they are lying flat. Tiny muscles in the skin can quickly pull hairs upright to reduce heat loss, or lay them down flat to increase heat loss.
Controlling Blood Sugar
The pancreas monitors and controls the level of sugar in our blood. When blood glucose concentration falls below the ideal range, the pancreas secretes glucagon which makes the liver break down glycogen, converting it back into glucose. If there is too much sugar in the blood the pancreas produces insulin (hormone) that results in the excess sugar being stored in the liver as glycogen.
Diabetes is the pancreas is not producing enough insulin, it can be controlled by diet or the person may need insulin injections. Injected insulin allows glucose to be taken into the body cells and converted into glycogen in the liver stopping the concentration of glucose in the blood from getting too high. As the blood glucose levels fall, natural glucagon makes sure glycogen is converted back to glucose.