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    Related Topics

    From Urinary System

    Renal Pyramids
    Cone-shaped tissues in the medulla.
    Kidneys
    Primary organs for filtration, fluid balance, and excretion.
    Peritubular Capillaries
    Surround cortical nephrons.
    Perirenal Fat
    Cushions and protects kidneys.
    Membranous Urethra
    Shortest male urethra segment.
    Renal Fascia
    Connective tissue anchoring kidney.
    Bladder Neck
    Region surrounding internal urethral orifice.
    Renal Artery
    Supplies oxygenated blood to kidney.
    Ureteral Openings
    Where ureters drain into bladder.
    Urethra
    Carries urine out of the body.
    Ureteropelvic Junction
    Where renal pelvis becomes ureter.
    Renal Papilla
    Apex of pyramid draining urine into minor calyx.
    External Urethral Meatus
    External urethral opening.
    Renal Medulla
    Inner region of kidney containing renal pyramids.
    Loop of Henle
    Creates osmotic gradient in medulla.
    Arcuate Arteries
    Arch over the base of pyramids.
    Interlobar Arteries
    Run between renal pyramids.
    Efferent Arteriole
    Drains from glomerulus.
    Pelvic Floor Muscles
    Support bladder and urethra.
    Median Umbilical Ligament
    Remnant of embryonic urachus.
    Proximal Convoluted Tubule
    Reabsorbs water, ions, and nutrients.
    External Urethral Sphincter
    Voluntary control of urination.
    Collecting Duct
    Final site for water reabsorption.
    Detrusor Muscle
    Smooth muscle for bladder contraction.
    Renal Columns
    Tissue between pyramids extending into medulla.

    Afferent Arteriole

    Reviewed by our medical team

    Leads into glomerulus.

    1. Overview

    The afferent arteriole is a small arterial vessel in the kidney that plays a key role in regulating blood flow to the glomerulus, the initial site of filtration in the nephron. As its name implies, it “brings in” blood—delivering it from the interlobular artery to the glomerular capillary bed. The afferent arteriole is critical in controlling glomerular filtration rate (GFR), renal blood pressure, and kidney perfusion.

    2. Location

    The afferent arteriole is located in the renal cortex, specifically within the vascular pole of the renal corpuscle. It branches from the interlobular arteries, which are derived from the arcuate arteries located along the corticomedullary junction. Each afferent arteriole supplies a single glomerulus within a nephron. After passing through the glomerulus, blood exits via the efferent arteriole, making the renal corpuscle the only capillary bed in the body between two arterioles.

    3. Structure

    The afferent arteriole has the typical structure of a small artery but with specialized features:

    • Endothelium: Lined by simple squamous endothelial cells that are fenestrated to allow fluid exchange in the glomerulus.

    • Vascular Smooth Muscle: The walls contain concentric layers of smooth muscle that allow vasoconstriction and vasodilation.

    • Juxtaglomerular Cells (JG Cells): Modified smooth muscle cells in the wall near the glomerulus that synthesize, store, and secrete renin.

    • Nerve Supply: Sympathetic innervation that modulates vasomotor tone and renin release.

    Its diameter is typically wider than that of the efferent arteriole, helping generate sufficient glomerular hydrostatic pressure for filtration.

    4. Function

    The afferent arteriole serves several core functions in renal physiology:

    • Blood Delivery: Delivers systemic blood to the glomerulus for filtration.

    • Regulation of Glomerular Pressure: Controls glomerular capillary hydrostatic pressure via vasomotor changes.

    • Filtration Rate Control: Affects GFR by modulating blood inflow into the glomerulus.

    • Renin Secretion: Through juxtaglomerular cells, initiates the renin-angiotensin-aldosterone system (RAAS).

    5. Physiological Role(s)

    The afferent arteriole plays several critical physiological roles:

    • Autoregulation of Renal Blood Flow: Through mechanisms like:

      • Myogenic response: Vascular smooth muscle contracts in response to stretch to maintain constant flow.

      • Tubuloglomerular feedback: Signals from the macula densa adjust afferent tone in response to sodium levels.

    • Systemic Blood Pressure Regulation: By releasing renin, it helps regulate blood volume and vascular tone via the RAAS cascade.

    • Maintaining Glomerular Integrity: Prevents overfiltration and damage by adjusting flow under changing systemic pressures.

    6. Clinical Significance

    Hypertension

    Abnormal constriction of afferent arterioles (e.g., due to excessive sympathetic activity or RAAS activation) can contribute to elevated glomerular pressure and systemic hypertension. Chronic hypertension may eventually damage glomerular capillaries.

    Acute Kidney Injury (AKI)

    In conditions like shock, sepsis, or volume depletion, afferent vasoconstriction can critically reduce renal perfusion, leading to decreased GFR and AKI.

    Use of NSAIDs

    Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit prostaglandin synthesis, which normally dilates afferent arterioles. NSAID use may thus reduce renal perfusion and precipitate AKI, especially in patients with compromised circulation (e.g., heart failure, dehydration).

    Glomerular Hyperfiltration

    In early diabetic nephropathy, afferent dilation combined with efferent constriction causes elevated glomerular pressure and hyperfiltration, leading to long-term glomerular damage and proteinuria.

    Renin-Secreting Tumors (Juxtaglomerular Cell Tumor)

    Rare neoplasms arising from juxtaglomerular cells can cause secondary hyperaldosteronism, leading to severe hypertension, hypokalemia, and high plasma renin activity.

    Pharmacologic Modulation

    • ACE inhibitors / ARBs: Primarily affect the efferent arteriole but indirectly preserve afferent tone in glomerular diseases.

    • Calcium channel blockers: Relax afferent arterioles to improve renal perfusion.

    Did you know? The renal cortex is the outer portion of the kidneys and contains the nephron filtering units.