6+-+Renal+Function

Renal Function

Overview

  • Renal function refers to the processes and structures involved in maintaining homeostasis through filtration, reabsorption, and secretion in the kidneys.

Gross Anatomy of the Kidney

  • Kidney Structures:

    • Interlobular arteries and veins: supply blood to the renal cortex.

    • Renal cortex: outer part of the kidney where urine formation begins.

    • Arcuate arteries and veins: arch over the base of the renal pyramids.

    • Renal medulla: inner area containing the renal pyramids.

    • Interlobar arteries and veins: run between the pyramids to supply blood.

    • Renal pelvis: funnel-shaped structure that collects urine.

    • Renal artery/vein: major blood vessels that supply and drain the kidneys.

    • Ureter: tube that carries urine from the kidney to the bladder.

Functional Structures of the Kidney

Nephron Components

  • Glomerulus: filtration unit (capillary bed).

  • Bowman's Capsule: surrounds glomerulus, collecting filtrate.

  • Proximal Convoluted Tubule (PCT): site for solute reabsorption (like Na+).

  • Loop of Henle: critical for concentrating urine.

    • Descending limb: reabsorbs H2O.

    • Ascending limb: reabsorbs Na+ and Cl-.

  • Distal Convoluted Tubule (DCT): further adjusts urine content.

  • Collecting Duct: leading to renal pelvis; adjusts urine concentration based on hydration state.

Renal Physiology

Basic Renal Processes

  1. Glomerular Filtration: filtering blood to form urine.

  2. Tubular Reabsorption: reclaiming essential substances from filtrate back into the blood.

  3. Tubular Secretion: removing waste products from blood into urine.

Renal Blood Flow

  • Average renal blood flow: 1200 - 1500 mL/min.

  • Plasma flow: 600-700 mL/min, varying with body size.

  • GFR (Glomerular Filtration Rate): key measure of kidney function.

Glomerular Filtration

Mechanism

  • Filtration through glomerulus:

    • Comprised of a tuft of capillaries.

    • Permeability: selective for molecules < 70,000 Da.

  • Filtration layers:

    • Capillary wall, basement membrane, podocytes of Bowman’s capsule.

Pressures Affecting Filtration

  • Hydrostatic Pressure: from smaller size of efferent arteriole, enhancing filtration.

  • Oncotic Pressure: due to plasma proteins like albumin, opposes filtration.

Renin-Angiotensin-Aldosterone System (RAAS)

Function

  • Regulates blood flow and pressure in the kidneys.

    • Decreased blood volume, sodium, or pressure prompts renin secretion.

  • Renin converts angiotensinogen to angiotensin I, which is converted to angiotensin II, causing:

    1. Vasoconstriction.

    2. Sodium reabsorption in PCT.

    3. Aldosterone release, promoting Na+ retention in DCT.

Hormonal Regulation of Kidney Function

ADH (Antidiuretic Hormone)

  • Control over water reabsorption in DCT and collecting duct.

  • Increased ADH production: leads to more concentrated urine.

Mechanisms of Tubular Transport

Active Transport

  • Requires carrier proteins; happens in:

    • PCT: glucose, amino acids, salts.

    • Ascending Loop: reabsorption of chloride.

    • DCT: sodium reabsorption.

Passive Transport

  • Facilitated by concentration gradients:

    • Water reabsorption happens in all parts except ascending loop.

    • Electrolytes like sodium reabsorbed in loop of Henle.

Clearance Calculations

Creatinine Clearance

  • Derived from urine and plasma creatinine levels.

  • Normal values:

    • Male: 97 - 137 mL/min

    • Female: 88 - 128 mL/min

Laboratory Evaluation of Renal Function

  • Assess different types of renal injuries and monitor treatment effectiveness.

Summary of Clinical Tests for Renal Disease

  • Prerenal Azotemia: high BUN, high creatinine, low free water clearance.

  • Chronic Glomerular Injury: marked proteinuria, low serum albumin.

  • Acute Tubular Necrosis: increased BUN and creatinine, granular casts.

Clinical Cases and Calculations

  • Examples of calculating creatinine clearance based on lab results given urine and serum parameters.