Renal_physiology_7001

Renal Physiology Overview

Body Fluid Distribution

• Total Body Mass (TBM) Distribution:

  • Female: 45% solids, 55% fluids

  • Male: 40% solids, 60% fluids

• Intracellular Fluid (ICF):

  • Comprises approximately 2/3 of body fluids, primarily located within cells.

• Extracellular Fluid (ECF):

  • Makes up about 1/3 of body fluids, including interstitial fluid that surrounds cells and blood plasma that circulates in the bloodstream.

Kidney Anatomy

• Major Structures:

  • Includes the diaphragm, adrenal gland, kidney, renal artery, renal vein, ureter, and urethra, all of which contribute to the function of the renal system.

• Internal Kidney Structure:

  • Cortex: The outer region containing the renal corpuscles and the proximal and distal convoluted tubules.

  • Medulla: The inner region, structured into pyramids containing the Loop of Henle and collecting ducts.

  • Renal Pelvis: A funnel-shaped cavity that collects urine from the major calyxes before it drains into the ureter.

  • Major/Minor Calyx: Structures that collect urine from the renal pyramids and funnel it into the renal pelvis.

Blood Flow through the Kidney

• Filtered Components:

  • Clean, filtered blood returns via the renal vein to the general circulation, while blood containing waste products enters the kidney from the renal artery.

• Waste Management:

  • Kidneys play a vital role in filtering blood to remove waste products and toxins, which are excreted as urine stored in the bladder prior to elimination from the body.

Kidney Function Mechanisms

• Urea Production:

  • Urea is created as a nitrogenous waste product from the breakdown of proteins.

  • Chemical formula: H2N-NH2; urea is less toxic than ammonia and is easily excreted by the kidneys.

• Nephron Function:

  • Nephrons, the functional units of the kidney, filter blood and regulate waste removal and electrolyte balance through three main processes:

    • Glomerular Filtration: Movement of water and solutes from blood into the Bowman's capsule.

    • Tubular Reabsorption: Reabsorption of essential substances into the bloodstream, including water, glucose, and salts.

    • Tubular Secretion: Active transport of additional waste products into the tubular fluid for excretion.

• Nephron Components:

  • Key parts of the nephron include the glomerulus, proximal convoluted tubule (PCT), distal convoluted tubule (DCT), Loop of Henle, and collecting duct.

Renal Physiology Mechanisms

• High-Pressure Blood Flow:

  • Blood pressure within the cortex facilitates the movement of small molecules through the capillary walls into the nephron tubules, driving the filtration process.

• Urine Formation Steps:

  1. Initial filtration of blood occurs in the glomerulus.

  2. Reabsorption phase wherein vital substances (water, sodium, essential salts, glucose, and amino acids) are reclaimed.

  3. Excretion phase where unwanted substances are expelled as urine.

• Glomerular Filtration Rate (GFR):

  • An important indicator of kidney function, GFR measures the rate at which blood is filtered by the glomeruli.

  • Importance of Blood Pressure:

    • Affects renal blood flow (RBF) and GFR; adequate blood pressure is crucial for maintaining normal kidney function and effective waste management.

Hormonal Regulation

• Antidiuretic Hormone (ADH):

  • Released from the posterior pituitary in response to dehydration; it promotes water reabsorption in the kidneys.

  • Mechanism of Action:

    • ADH targets the collecting ducts to increase water permeability, enhancing water retention in the body, and thus concentrating urine.

• Renin-Angiotensin System (RAS):

  • Mechanism: A drop in blood pressure triggers the secretion of renin from the kidneys, which acts on angiotensinogen (released by the liver) to form angiotensin I.

  • ACE (angiotensin-converting enzyme) from the lungs converts angiotensin I to angiotensin II, which is a potent vasoconstrictor.

    • Effects of Angiotensin II:

    • Stimulates adrenal glands to release aldosterone, which promotes the reabsorption of sodium and water in the kidneys, ultimately increasing blood pressure.

• Erythropoiesis Regulation:

  • The kidneys play a critical role in stimulating the production of red blood cells (RBCs) through the release of erythropoietin (EPO).

  • Triggers for Erythropoietin Release:

    • Low oxygen levels (hypoxia) in the bloodstream prompt the kidneys to produce more EPO, enhancing RBC production in the bone marrow to better oxygenate tissues.