Renal

Overview of the Urinary System

  • Components: Comprises two kidneys, two ureters, a urinary bladder, and urethra.

  • Functions:

    • Regulates blood volume and pressure.

    • Maintains electrolyte balance (sodium, potassium, chloride).

    • Stabilizes blood pH.

    • Conserves nutrients and removes toxins and excess substances.

Anatomy of the Kidney

  • Kidney Location:

    • Located at the lower edge of pleura, with the right kidney positioned slightly lower than the left due to the liver.

  • Major Structures:

    • Renal Cortex: Outer region.

    • Renal Medulla: Inner region, containing renal pyramids.

    • Renal Pelvis: Collects urine from major calyces.

    • Renal Artery/Vena: Supply and drain blood.

    • Hilum: Indentation where vessels and ureter enter/exit.

Nephron: The Functional Unit of the Kidney

  • Each kidney has approximately 1.2 million nephrons.

  • Main components include the renal corpuscle (Bowman capsule + glomerulus) and renal tubules (PCT, nephron loop, DCT, and collecting duct).

  • Two Types of Nephrons:

    • Cortical Nephrons: 85%, mainly in the cortex.

    • Juxtamedullary Nephrons: 15%, involved in producing concentrated urine.

Urine Formation Stages

  1. Glomerular Filtration: Blood is filtered through the glomerulus, creating a plasma-like filtrate in Bowman’s capsule.

  2. Tubular Reabsorption: Useful substances (e.g., water, ions, nutrients) are reabsorbed back into the bloodstream.

  3. Tubular Secretion: Waste substances are secreted from the blood into the renal tubule.

  4. Water Conservation: Water is reabsorbed along the nephron, especially in the collecting ducts.

Key Processes in Urine Formation

  • Glomerular Filtration Rate (GFR): Normal rate is approximately 125extmL/min125 ext{ mL/min}.

  • Filtration Membrane: Composed of fenestrated capillaries, a basement membrane, and podocytes. Blood pressures involved:

    • Blood Hydrostatic Pressure (BHP): 60extmmHg60 ext{ mm Hg}

    • Colloid Osmotic Pressure (COP): −32extmmHg-32 ext{ mm Hg}

    • Capsular Pressure (CP): −18extmmHg-18 ext{ mm Hg}

    • Net Filtration Pressure (NFP): 10extmmHgout10 ext{ mm Hg out}

Transport and Reabsorption Details

  • Proximal Convoluted Tubule (PCT): Reabsorbs about 65% of the filtered liquid, utilizing ATP.

  • Tubular Reabsorption Mechanisms: Driven by gradients created primarily from sodium ( ext{Na}^+) reabsorption, allowing water to follow by osmosis.

  • Transport Maximum: The reabsorption rate can be limited by transporter availability; excess solute, like glucose (greater than 220extmg/dL220 ext{ mg/dL}), appears in urine (glycosuria).

Hormonal Regulation in Nephron Processes

  • Distal Convoluted Tubule (DCT) and Collecting Duct: Regulated by hormones like aldosterone, antidiuretic hormone (ADH), and atrial natriuretic peptide (ANP) to control water and salt reabsorption.

  • Nephron Loop: Creates a gradient to facilitate water reabsorption in the collecting duct, promoting concentrated urine.

Waste Management in the Urinary System

  • Nitrogenous Wastes:

    • Urea: Formed from protein catabolism.

    • Uric Acid: Produced from nucleic acid breakdown.

    • Creatinine: Derived from creatine phosphate breakdown.

  • Metabolic Waste: Any substance that is either excess to the body's needs or deemed useless by the body.

  • Tubular Secretion: Key for regulating blood composition and removing excess substances, including drugs and metabolic wastes.