Renal System Overview

Renal System Components

• The urinary system comprises two kidneys, ureters, a bladder, and urethra.
• The kidneys are responsible for blood filtration and waste excretion.
• The ureters transport urinary waste from kidneys to the bladder.
• The bladder stores and expels urine.
• The urethra is the final passageway for urine excretion.

Kidney Location and Movement

• Kidneys are reddish-brown, bean-shaped organs situated on each side of the vertebral column.
• Their retroperitoneal positioning means they develop outside the peritoneum.
• The left kidney is generally positioned at vertebral levels T12, L1, and L2, while the right kidney sits slightly lower at L1, L2, and L3.
• The right kidney's lower position is due to the presence of the right liver lobe.
• The upper part of each kidney is protected by the 11th and 12th ribs (right kidney is protected by the 12th rib only).
• Kidneys have limited vertical movement (~3 cm) due to their fascial coverings.

Kidney Fascial Coverings

• Four layers of fascia surround the kidneys, from outer to inner: Pararenal fat, Renal fascia, Perirenal fat, and Fibrous capsule.

Pararenal Fat

• A layer of extraperitoneal fat in the lumbar region, being thicker posteriorly and laterally to the kidney.

Renal Fascia

• A condensed connective tissue (C.T.) membrane surrounding the kidney, perirenal fat, and suprarenal gland.

• It often sends a thin septum.

• Divided into anterior and posterior layers, each with distinct attachments:

• Posterior layer: extends medially, fusing with the psoas major muscle fascia and the lateral aspect of the vertebral bodies.

• Anterior layer: runs anterior to the kidney, positioned in front of the abdominal aorta and inferior vena cava, fusing with the opposing side's anterior fascia.

• Laterally, both layers merge and connect to the transversalis fascia.

• The renal fascia defines the boundaries of the kidney:

• Laterally: continuous with the transversalis fascia.

• Medially: merges with the adventitia of renal vessels and the psoas fascia.

• Superiorly: two layers enclose the kidney, fusing at the upper pole and then splitting to enclose the suprarenal gland. They continue with the diaphragmatic fascia, forming the main attachment point for the suprarenal gland (suspensory ligament).

• Inferiorly: the fascia extends along the ureter without attachment, allowing limited kidney mobility.

• Clinically, these attachments are essential for understanding perirenal abscesses and nephroptosis.

• In such cases, the direction of pus or blood follows the renal fascia attachments.

• For instance, within the pelvis, pus or blood is channeled between the anterior and posterior layers of the renal fascia.

Perirenal Fat

• Surrounds both the kidney and the suprarenal gland, separating them.
• It extends into the renal sinus among the renal vessels.

Fibrous Capsule

• A dense irregular connective tissue layer, forming the outermost layer of the kidney.

Kidney External Anatomy

• The outer layer (cortex) is divided into two zones: the cortical zone and the juxtamedullary zone.

• The inner medulla consists of renal pyramids (approximately 8-18).

• Two projections extend from the medulla into the cortex:

• Renal columns: extensions of the cortex that separate the pyramids.

• Medullary rays (radiated area): striated projections from the bases of the renal pyramids into the cortex.

Kidney Internal Anatomy

• Kidney internal anatomy includes:

• Outer layer (cortex)

• Inner medulla

• Renal pyramids (8-18)

• Renal columns

• Medullary rays

Nephron: The Functional Unit

• Nephrons, the functional units of the kidney, are responsible for blood filtration and urine production.
• Each kidney contains approximately 1 million nephrons, a relatively constant number throughout life.
• A nephron is composed of:

Renal Corpuscle

• Located in the cortex, responsible for blood filtration and urine formation.

• Consists of:

• Glomerulus: a network of capillaries.

• Glomerular (Bowman's) capsule: A double-walled cup lined with simple squamous epithelium.

• • Visceral wall: directly surrounds the capillaries.
• • Parietal wall: continues with the renal tubules.

Renal Tubule

• The renal tubule is comprised of several segments:

• Proximal convoluted tubule (PCT): located in the cortex.

• Loop of Henle: extends into both the cortex and medulla, with descending and ascending limbs.

• Distal convoluted tubule (DCT): located in the cortex, draining into the collecting duct.

• Collecting ducts: larger tubules that receive DCTs from multiple nephrons.

• • Each collecting duct, along with the nephrons draining into it, comprises a Renal Lobule.

• Papillary ducts: large ducts resulting from the union of collecting ducts.

• Located at the apex of renal pyramids (renal papilla), they drain into the minor calyx.

Nephron Types

• Cortical nephrons: constitute 80-85% of nephrons, with glomeruli located in the outer cortex and possessing short loops of Henle.
• Juxtamedullary nephrons: have glomeruli deep in the cortex and long loops of Henle that penetrate deeply into the medulla.

Renal Drainage System

• The drainage system in the kidney starts with collecting ducts within each pyramid, converging to form the Papillary ducts of Bellini (approximately 20).
• These ducts drain through the renal papilla (apex of the pyramid) into the minor calyx (8-18 per kidney).
• Multiple minor calyces merge to form major calyces (2-3 per kidney).
• Major calyces eventually join to form the renal pelvis.
• The renal pelvis then connects to the ureter.

Kidney Blood Supply: Arterial

• The kidney receives arterial blood mainly through the renal arteries.

• These arteries originate at the level of the intervertebral disc between L1 and L2.

• The right renal artery passes posterior to the inferior vena cava.

• At the hilum, each renal artery divides into a large anterior and a smaller posterior branch, giving rise to five segmental arteries.

• These segmental arteries, located within the renal sinus, are named based on their location:

• Superior (Apical) segmental artery 1

• Anterosuperior segmental artery 2

• Anteroinferior segmental artery 3

• Inferior segmental artery 4

• Posterior segmental artery 5 (continuation of a branch of the renal artery)

• Blood flow continues through a hierarchical network of arteries:

• Lobar arteries: one for each pyramid

• Interlobar arteries: pass through the renal lobes

• Arcuate arteries: located over the bases of the pyramids, arching between the medulla and cortex

• Interlobular arteries: run between the lobules of the kidney

Kidney Blood Supply: Venous

• Renal veins generally lie anterior to the renal arteries.

• The left renal vein is distinguished by its length and its crossing of the midline.

• It receives blood from:

• Left gonadal vein

• Left suprarenal vein

• Left inferior phrenic vein

• As it crosses the midline, the left renal vein traverses a sharp angle between the superior mesenteric artery (SMA) and the abdominal aorta (AA).

Renal Vein Entrapment Syndrome

• Also known as Nutcracker Syndrome, involves compression of the left renal vein between the superior mesenteric artery and the abdominal aorta.
• This can lead to various symptoms related to impaired blood flow.

Other Important Points

• The Transpyloric plane passes through the hilum of the left kidney at the level of L1.

• The renal hilum is the area where structures enter or leave the kidney, also known as the root of the kidney.

• The hilum opens into the renal sinus.

• Structures within the hilum are arranged anteroposteriorly (A → P):

• Renal vein: the most anterior structure, with the left vein being longer than the right.

• Renal artery: the right artery is longer than the left.

• Ureter: the most posterior structure.

Kidney Relations

• The right and left kidneys have distinct anatomical relationships with surrounding organs.

• For right kidney:

• Superior:

• • Liver (right lobe)
• • Suprarenal gland

• Anterior:

• • Right colic flexure
• • 2nd part of duodenum
• • Right lobe of the liver

• Posterior:

• • Diaphragm
• • Psoas major
• • Quadratus lumborum

• For left kidney:

• Superior:

• • Spleen
• • Suprarenal gland

• Anterior:

• • Pancreas
• • Left colic flexure

• Posterior:

• • Diaphragm
• • Psoas major
• • Quadratus lumborum

Test your knowledge of the renal system components, including the structure and function of kidneys, ureters, bladder, and urethra. This quiz also covers the anatomical positioning of the kidneys and their movement within the body. Prepare to dive into the essentials of urinary anatomy!