# Thermoregulation and the Kidneys
Homeostasis is the regulation of internal conditions to maintain optimal functioning. Key examples include body temperature control and water balance.
1. Thermoregulation
Body temperature monitored by the thermoregulatory centre in the brain (hypothalamus). Optimum: 37°C (for enzymes).
Too Hot
- Blood vessels dilate (vasodilation) → more blood near skin → more heat lost
- Sweat glands produce sweat → evaporation cools skin
- Hairs lie flat
Too Cold
- Blood vessels constrict (vasoconstriction) → less blood near skin → less heat lost
- Shivering → muscle contractions generate heat
- Hairs stand up (erector muscles) → trap insulating air layer
This is negative feedback — the response opposes the change.
2. The Kidneys
The kidneys filter blood to remove waste and regulate water/ion balance.
Three Processes
- Filtration: blood filtered in glomerulus; small molecules (water, glucose, urea, ions) enter Bowman's capsule
- Selective reabsorption: useful substances reabsorbed in tubules
- All glucose reabsorbed
- Some water and ions reabsorbed (depending on need)
- Excretion: remaining fluid = urine (water, urea, excess ions)
3. Water Balance and ADH
ADH (antidiuretic hormone) controls water reabsorption in kidney tubules.
| Condition | ADH Level | Effect on Kidney | Urine |
|---|---|---|---|
| Dehydrated | High | More water reabsorbed | Small volume, concentrated |
| Over-hydrated | Low | Less water reabsorbed | Large volume, dilute |
ADH is released by the pituitary gland, controlled by negative feedback.
4. Kidney Failure Treatments
| Treatment | How It Works | Advantages | Disadvantages |
|---|---|---|---|
| Dialysis | Blood filtered by machine through partially permeable membrane | Available; no surgery | Time-consuming (3× per week); diet restrictions |
| Transplant | Healthy kidney from donor | Long-term solution; normal life | Donor needed; risk of rejection; immunosuppressants |
5. Practice Questions
- Describe two responses of the body when too hot.
- Explain the role of ADH in water balance.
- What is filtered from the blood in the kidneys?
- Why is all glucose reabsorbed by the kidneys?
- Compare dialysis and kidney transplant as treatments for kidney failure.
Want to check your answers and get step-by-step solutions?
Summary
- Thermoregulation: vasodilation/sweating (hot); vasoconstriction/shivering (cold)
- Kidneys: filtration → selective reabsorption → excretion
- ADH: more ADH = more water reabsorbed = concentrated urine
- Kidney failure: dialysis or transplant