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Urinary System Overview

Presented by Dr. Gholamreza Hassanzadeh, Professor of Anatomy, Tehran University of Medical Sciences.

Anatomy of Kidneys

  • Kidneys: Bean-shaped structures, located retroperitoneally in the posterior abdominal region.

  • Position: Lateral to the vertebral column, within extraperitoneal connective tissue.

Kidney Location and Structure

  • Kidney Positioning:

    • Upper part located at vertebral level T12; lower part at L3.

    • The urinary system comprises two kidneys, two ureters, one urinary bladder, and one urethra.

  • Kidney Dimensions:

    • Size: Approximately 11-12 cm in length and 5 cm in transverse diameter.

  • Kidney Surfaces:

    • Each kidney features:

      • Anterior and posterior surfaces.

      • Medial (concave) and lateral (convex) borders.

      • Superior and inferior poles.

  • Related Structures:

    • Superior pole is associated with the suprarenal (adrenal) gland.

    • Medial concave border contains the hilum for blood vessels entry and urinary pelvis exit.

Kidney Positioning Details

  • Supine Position:

    • Extend from T12 (superiorly) to L3 (inferiorly).

    • Right kidney typically lower than left due to liver positioning.

    • Left kidney: longer and slenderer compared to the right, closer to the midline.

Anterior Surface Relations (Right Kidney)

  • Right Kidney Relations:

    • Superior pole partly covered by right suprarenal gland.

    • Anterior surface related to liver, separated by peritoneum.

    • Medial: Descending part of the duodenum contacts the kidney.

    • Inferior pole relates to right colic flexure and intraperitoneal small intestine.

Anterior Surface Relations (Left Kidney)

  • Left Kidney Relationships:

    • Superior part related to adrenal gland.

    • Inferior part interacts with the spleen with anterior connections to the tail of the pancreas.

    • Inferiorly: jejunum (medially) and left colic flexure (laterally).

    • Triangular Area: Area between adrenal gland, pancreas tail, and spleen possibly affecting the stomach bed.

Left Kidney Structural Relations

  • The Left Kidney's Anterior Surface:

    • Covered by left suprarenal gland at superior pole.

    • Inferior, covered by stomach (intraperitoneal) and pancreas (retroperitoneal).

    • Medial and lateral relations involve jejunum and descending colon.

Posterior Relations of Kidneys

  • Muscle Relationships:

    • Posterior structures common for right and left kidneys:

      • Superiorly: diaphragm.

      • Inferiorly and moving laterally: psoas major, quadratus lumborum, transversus abdominis muscles.

Costodiaphragmatic Recess

  • Posterior Kidney Relationships:

    • Right kidney anterior to rib 12; left kidney anterior to ribs 11 and 12.

    • Posterior aspect features:

      • Subcostal vessels and nerves, iliohypogastric and ilioinguinal nerves run behind the kidneys.

Renal Fat and Fascia

  • Renal Protection:

    • Kidneys are surrounded by a unique arrangement of fascia and fat.

    • Perinephric Fat: Accumulation of extraperitoneal fat surrounding each kidney.

Renal Fascia

  • Fascia Arrangement:

    • Renal fascia ensheathes perinephric fat.

    • Encloses suprarenal glands, typically separated by a thin septum.

Renal Capsule and Support Structures

  • Kidney Encapsulation:

    • Renal Capsule composed of dense irregular connective tissue, providing structural support and protection.

    • Perirenal Fat: Surrounds the renal capsule and acts as an additional cushion.

    • Renal Fascia: Comprises anterior and posterior layers attaching superiorly to the kidney, contributing to stability.

    • Infection Spread: Infections may spread between kidneys and pelvis due to renal fascia's connections.

Renal Fascia Attachments

  • Renal Fascia Fusion:

    • Anterior and posterior layers fuse at lateral margins of each kidney.

    • Connects with transversalis fascia on the lateral abdominal wall.

    • Above suprarenal glands, these layers blend with diaphragmatic fascia.

Medial Fusion of Anterior Layer

  • Medial Layer Fusion:

    • The anterior layer of renal fascia fuses with connective tissue around aorta and inferior vena cava.

    • Some cases show crossing midline with companion layers, influencing renal mobility.

Posterior Layer Fusion

  • Posterior Layer Functions:

    • Passes medially between kidney and fascia of quadratus lumborum muscle to fuse with fascia over psoas major muscle.

    • Encloses ureters inferiorly, providing a protective layer.

Pararenal Fat

  • Supportive Structures:

    • Pararenal fat located posteriorly to kidneys.

    • Works alongside perinephric fat and renal fascia for added support, and acts as insulation against trauma.

Kidney Structure Overview

  • Kidney Surfaces:

    • Smooth anterior/posterior surfaces covered by fibrous capsule enhancing protection.

    • Hilum (Hilus): Deep vertical slit on medial margin for vessels, lymphatics, and nerves entry/exit.

Kidney Layers

  • Perinephric Fat Role:

    • Continues into hilum and surrounds internal structures.

    • Each kidney has an outer renal cortex and inner renal medulla.

Renal Medulla and Columns

  • Cortex and Medulla:

    • Renal cortex: pale tissue band enveloping renal medulla, responsible for filtration and blood processing.

    • Renal columns extend into kidney dividing the medulla into triangular renal pyramids, facilitating urine collection.

Renal Sinus and Pyramids

  • Renal Structures:

    • Renal Sinus: Area housing renal pelvis, arteries, and nerves.

    • Kidney Parenchyma: Cortex and medulla containing 15-20 pyramids, with bases towards cortex and apices into renal sinus allowing efficient urine drainage.

Papillary Ducts and Minor Calyces

  • Papillary Duct Function:

    • Collect urine from nephrons at renal papilla, surrounded by minor calyx.

    • Urine drainage begins at minor calyces leading to major calyx and then renal pelvis, emphasizing the kidney's role in filtration.

Urine Collection Pathways

  • Minor and Major Calyces:

    • Minor calyces gather urine, merge into major calyx, which forms renal pelvis (superior end of ureters) allowing urine transport to bladder.

Renal Vasculature Overview

  • Renal Arteries:

    • Supplied by a large renal artery from abdominal aorta, branching near L1/L2.

    • Left renal artery positioned higher than right; right crosses behind inferior vena cava, impacting blood flow dynamics.

Renal Artery Characteristics

  • Length and Hemodynamics:

    • Right renal artery is longer, causing higher resistance in flow and a potential risk for hypertension.

    • Bifurcation Angles: 85° on the left, 54° on the right influencing perfusion efficiency.

Imbalances in Blood Flow

  • High Blood Pressure Risks:

    • Turbulence at left renal artery origin may cause narrowing with age, risking hypertension from unequal kidney blood volumes and varying filtration capabilities.

Renal Artery Summary

  • Renal Artery Traits:

    • Branch from abdominal aorta at L1/L2 with similar dimensions.

    • Right renal artery longer with similar diameter (5mm) to the left, influencing renal function and response.

Arrangement of Renal Vessels

  • Position and Relationships:

    • Right renal vein shorter than the left, with left renal vein receiving left testicular/ovarian veins and crossing midline anterior to abdominal aorta for optimal drainage.

Accessory Renal Arteries

  • Accessory Artery Characteristics:

    • Often seen entering hilum or directly into kidney; called extrahilar arteries for branched structures near renal poles, potentially affecting kidney perfusion.

Kidney Development

  • Embryology:

    • Kidneys and adrenal glands develop in different initial locations, with kidneys ascending to their final position while adrenal glands remain higher.

    • Accessory renal arteries can persist post-development, affecting vascular supply.

Renal Vein and Compression

  • Left Renal Vein:

    • Longer artery crossing midline risks compression due to abdominal aorta and superior mesenteric artery aneurysm, potentially causing venous drainage issues.

Lymphatic Drainage of Kidneys

  • Lymphatic Connections:

    • Drains to lateral aortic (lumbar) nodes around renal artery origin, aiding fluid balance and immune response.

Ureters Introduction

  • Ureter Functions:

    • Tubes transporting urine from kidneys to bladder, continuous with renal pelvis, ensuring effective urine flow.

Ureter Structure

  • Ureter Composition:

    • Approximately 30 cm long; divided into abdominal and pelvic portions, with key anatomical relationships to psoas major and blood vessels.

Ureteropelvic Junction

  • Junction Profile:

    • Renal pelvis narrows at ureteropelvic junction leading to bladder entry is a critical point, susceptible to obstructions.

Ureter Course

  • Pelvic Inlet Entry:

    • Ureters cross pelvic inlet and join bladder base; significant anatomical relationships differ in sex (ductus deferens in males vs. uterine artery in females), impacting surgical approaches.

Ureter Functionality

  • Ureter Structure:

    • Enters bladder obliquely, positioned closer at the base within the pelvis, ensuring a one-way valve effect to prevent backflow.

Ureter Constrictions

  • Constriction Points:

    • Three notable constricted areas:

      1. Ureteropelvic junction

      2. Pelvic brim

      3. Bladder entry

    • These sites are common areas for kidney stones to become lodged.

Ureteric Vasculature

  • Blood Supply Sources:

    • Receives branches from renal, abdominal aorta, testicular, and internal iliac arteries ensuring sufficient blood supply along its course.

Lymphatic Drainage of Ureters

  • Drainage Pathways:

    • Lymph drains into lumbar nodes, common iliac lymph nodes, and iliac vessels-based nodes to maintain lymphatic flow and prevent infection.

Ureteric Innervation

  • Nerve Supply:

    • Innervation from renal, aortic, and hypogastric plexuses; involved in both sympathetic and parasympathetic input, regulating peristalsis and sensation.

Pain Referral in Ureters

  • Pain and Sensation:

    • Ureteric pain may refer to cutaneous areas supplied by spinal levels T11 to L2, influencing various body regions, making diagnosis challenging.

Urinary Bladder Overview

  • Anatomy of Bladder:

    • Anterior part of pelvic cavity, expands upwards as it fills, shaped like a tipped pyramid when empty to optimize space.

Urinary Bladder Characteristics

  • Bladder Structure:

    • Apex directed toward pubic symphysis with median umbilical ligament connected to umbilicus, helping maintain bladder position.

    • Relationships with various pelvic structures allow for expansion.

Bladder Base and Trigone

  • Base Shape:

    • Inverted triangular base with ureters entering at upper corners; urethra originating from lower corner.

    • Trigone: Smooth area of mucosa at bladder base, acting as a funnel for urine flow into the urethra.

Inferolateral Surface Support

  • Inferolateral Relations:

    • Surrounded by pelvic diaphragm and obturator internus muscles, providing muscular support; superior surface domes as bladder fills, enhancing capacity.

Urinary Bladder's Neck

  • Neck Functionality:

    • Fixed and inferior part around urethra origin; ligaments secure its position (pubovesical in women, puboprostatic in men), preventing displacement during movement or pressure changes.

Bladder Position in Children

  • Developmental Consideration:

    • Bladder positioned higher in children; location shifts with growth as abdominal organs develop and mature.

Urethra Structure Differences

  • Urethra in Men vs. Women:

    • Male urethra: 18-20 cm, curved to facilitate passage of semen as well as urine;

    • Female urethra: 3-4 cm, straight, directly leading to the external environment due to functional differences.

Female Urethra Details

  • Urethra Pathway in Women:

    • Short, slightly curved; opens in vestibule between labia minora, emphasizing differences in urinary structure and function compared to men.

Male Urethra Details

  • Urethra Length and Course:

    • Long, bends twice; begins at bladder neck, traverses prostate, perineal pouch, and penis root, impacting susceptibility to urological issues.

Internal Urethral Sphincter

  • Muscle Functions:

    • Smooth muscle surrounds the urethra at bladder neck, preventing retrograde ejaculation during sexual function and aiding in urinary control.

Prostatic Urethra

  • Glandular Influences:

    • Surrounded by prostate; features prostatic sinus and seminal colliculus which play roles in reproductive and urinary health.

Sexual Health Considerations

  • Prostate Issues:

    • Prostatitis and benign prostatic hyperplasia common in older men; cancer prevalence noted, underscoring the importance of regular screening.

Summary of Key Learnings

  • Important Points:

    • Turbulence and blood supply in renal circulation can have health implications, particularly for different organs in the urinary system, influencing overall function and disease susceptibility.