Other Functions of the Excretory System

1. Other Functions of the Excretory System Water – Salt Balance Blood Pressure pH Balance Section 7.6 pg. 353

2. Regulating Water-Salt Balance Q: Why is water-salt balance important?

3. It is important because it influences: • Osmotic Pressure (blood volume) • Blood Pressure • pH Balance

4. Osmotic Pressure • osmotic pressure – water pressure due to presence of solutes • High concentration of solutes = high osmotic pressure • Changes in osmotic pressure are detected by osmoreceptors in the hypothalamus • Signals pituitary gland to release antidiuretic hormone (ADH)

5. osmoreceptors in hypothalamus detect increased osmotic pressure  sends signals to pituitary gland

6. Osmotic Pressure • ADH acts on the kidneys to increase the permeability of the distal tubule and collecting duct  increases water reabsorption • Overall effect – dilutes solutes in blood • Q: What type of situation would cause increased osmotic pressure? • sweating / dehydration • What kind of homeostatic system is this?

7. Urine Output • more water in usually means more urine out • some liquids encourage increase in urine excretion – diuretics • frequency of urination dependent on hormonal signals • Q: Any ideas of substances you may consume that act as a diuretic?

8. Osmotic Pressure increased osmotic pressure osmoreceptors pituitary gland; release ADH decreased osmotic pressure increased sensation of thirst increased water reabsorption by kidney

9. ADH Activity The following animation will contain some terminology not covered. Animation

10. Blood Pressure • blood pressure – increase force of blood on blood vessels • How the kidneys influence blood pressure: • aldosterone – hormone which increases Na+reabsorption in the distal tubule • increased H2O in blood • increased blood pressure

11. Blood Pressure • aldosterone produced in adrenal gland, above kidney

12. Blood Pressure

13. Blood Pressure What part of the kidney would be affected by low blood pressure? • glomerulus; high blood pressure needed for filtration • decreased blood pressure detected by receptors in the juxtaglomerular apparatus • receptors next to the glomerulus

14. Blood Pressure • the enzyme renin, is released angiotensinogenangiotensin (a plasma protein) renin

15. Blood Pressure Two important functions of angiotensin: • causes blood vessel constriction • stimulates aldosterone release

16. Blood Pressure low blood pressure cells to release renin; produce angiotensin juxtaglomerular apparatus blood pressure increases constrict blood vessels induce aldosteronereleaseby adrenal gland; increase Na+reabsorption

17. pH Balance How do living systems regulate the amount of acid / base in their systems? • buffers – conjugate acid-base pairs H3PO4 H2PO4- + H+

18. carbonate ion carbonic acid pH Balance • conversion of CO2 to other compounds help regulate blood pH H2O + CO2 H2CO3 HCO3- + H+ • HCO3- is reabsorbed in the proximal and distal tubules, H+ is excreted (secreted) as needed in kidneys to maintain a normal pH