2.77 - more

2.77 Understand that homeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis

Homeostasis: conditions are kept the same

Homeothermic organisms carry out thermoregulation where they maintain the same temperature no matter what the environmental temperature is. This is important because the body wants to be kept at an optimum tempreature for the highest rate of enzyme reactions.

Control of body temperature

Negative feedback loop – maintaining constant conditions

Stimuli (temperature of the body, more blood) à Receptor (hypothalamus in brain) à Co-ordinator (fixed point, e.g. 37°C) à Effector (skin) à Response (increase or decrease in body temperature) à Feedback à Stimuli

1) If the body temperature increases, hypothalamus responds and decreases body temperature. This is done through sweating, increase in blood flow to the surface, vasodilation (blood vessels dilate). They increase the exchange of heat e.g. radiation and evaporation. The body returns to normal level of temperature.

2) In a cold environment, the body temperature will fall. This feeds to the hypothalamus, which increases body temperature (shivering, vasoconstriction, hairs raised). The blood is forced to travel deeper and reduces foreign heat exchange. Temperature will go up and down.

Sweat glands and the capillary network are responsible for body temperature control. Efficiency is determined by the deviation between the raised/ lowered temperature and the fixed point.

Osmoregulation: Regulation of body water (plasma and tissue fluid) content

Stimuli (blood) à Receptor (hypothalamus) à Effector (kidneys, collecting duct) à Response (filtered blood) à Stimuli (NEGATIVE FEEDFBACK LOOP)

1) If blood becomes more concentrated (hypertonic), hypothalamus brings the concentration of blood back down to the isotonic point. This is done by ADH, which targets the collecting duct. The effect is the reabsoprtion of water into blood plasma.

2) If blood becomes more diluted (hypotonic), hypothalamus brings the concentration of blood back up to the isotonic point. Thi sis done by the inbition of ADH. This puts more water into the urine so it bceoms more dilute. We have reduced reabsoprtion of water.