PHYSIO

Urinary System: Overview

  • Maintains body's fluid and solute balance.

  • Regulates blood pressure and blood volume.

  • Maintains stable blood pH.

  • Importance: Ensures healthy internal environment, prevents dehydration or excessive hydration.

Objectives

  • Explain the function of:

    • Antidiuretic Hormone (ADH)

    • Aldosterone

    • Atrial Natriuretic Peptide (ANP)

    • Brain Natriuretic Peptide (BNP)

  • Role of kidneys in maintaining blood pH.

  • Define the bicarbonate buffering system of the blood.

Urinary System Functions

  • Balances water, salts, and waste products.

  • Controls fluid and solute balance to maintain homeostasis.

Water–Salt Balance in Urine

  • Osmolarity affects urine concentration:

    • Initial filtered fluid is similar to blood composition.

    • Changes based on body's needs for dilute or concentrated urine.

  • Dilute Urine: Excretes excess water, fewer solutes, less concentrated than blood plasma.

  • Concentrated Urine: Conserves water, reabsorbs water in nephron, higher concentration when needed.

Antidiuretic Hormone (ADH)

  • Produced by hypothalamus, released by posterior pituitary.

  • Regulates water balance by controlling reabsorption in kidneys.

  • Feedback system:

    1. Detects high blood salinity due to low water.

    2. Hypothalamus signals ADH release.

    3. Kidneys reabsorb more water, reducing urine volume.

    4. Balance restored; ADH release stops.

  • Increased ADH: More reabsorption, less urine, concentrated.

  • Decreased ADH: Less reabsorption, more urine, diluted.

Hormones Influencing Salt Balance

  • Aldosterone: Produced by adrenal glands, regulates sodium and water; triggered by low blood pressure or sodium.

  • ANP and BNP: Vasodilators that decrease blood volume and regulate pressure.

  • Caffeine and Alcohol: Decrease ADH production; increase urine output.

Kidneys and Blood pH Maintenance

  • Kidneys regulate blood pH (7.35 - 7.45) by balancing acids and bases.

  • Importance: Optimal cellular function, stability of proteins, and biochemistry.

Bicarbonate Buffering System

  • Most efficient buffering system in blood.

  • Interacts with body systems, responds rapidly to pH changes.

Renal Regulation

  • CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-

  • HCO3- (Bicarbonate): neutralizes excess acids, reabsorbs or excretes based on blood acidity.

Blood pH Homeostasis

  • Disruptions in homeostasis lead to:

    • Decrease in blood pH (too acidic): kidneys excrete H+.

    • Increase in blood pH (too basic): kidneys excrete HCO3-.

References

  • NCI Dictionary of Cancer Terms

  • WebMD on Antidiuretic Hormone

  • "Visualizing Human Biology" by Ireland, K. A.

  • Acidosis and Alkalosis MADE EASY [YouTube]

  • Bicarbonate Buffer System Equation (Study.com)

Conclusion

  • The urinary system is crucial for maintaining fluid balance, regulating pH, and ensuring efficient body function.