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Anatomy of the Genitourinary System I: Kidneys and Ureters

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The upper urinary system includes two kidneys and two ureters.

The kidneys are a pair of organs shaped like a bean in the retroperitoneal space.

Each kidney is wrapped in a tough, protective layer called the renal capsule, which is cushioned with fat to help keep it in place and shield it from injury.

There are two main parts inside: the outer cortex, which contains nephrons, and the inner medulla, which consists of renal pyramids directing filtered substances toward the renal pelvis.

Within the cortex, each nephron starts with the glomerulus, a network of tiny blood vessels surrounded by a Bowman's capsule. It is followed by a proximal convoluted tubule, a loop of Henle, and a distal convoluted tubule before reaching a collecting duct.

Finally, the ureters are long, slender tubes that transfer urine from the kidneys to the bladder. Each ureter is about 25 to 30 centimeters long and has three layers: an innermost mucosa, a middle muscular layer, and an outer adventitia.

Overview

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The upper urinary system comprises two kidneys and two ureters, which are crucial in filtering blood and forming urine.

Kidneys

Location and Structure:

The kidneys are two bean-shaped organs positioned behind the peritoneum on either side of the spine.
Kidneys are between the 12th thoracic (T12) and the 3rd lumbar (L3) vertebrae.
The position of the liver causes the right kidney to sit slightly lower than the left.

Protective Layers:

Each kidney is enveloped in a tough, fibrous membrane called the renal capsule, which provides protection and support.
A thick layer of fat surrounds each kidney, cushioning it against physical trauma and helping to keep it in place.
The renal fascia, a connective tissue layer, also anchors the kidneys to the surrounding structures.

Internal Structure:

The kidney's interior is divided into two regions: the outer cortex and the inner medulla.

Cortex: Contains the nephrons, the functional units responsible for filtering blood.
Medulla: Consists of cone-shaped structures called renal pyramids, which direct urine into the renal pelvis.

Functional Units – Nephrons:

Each kidney contains approximately one million nephrons. Nephrons are composed of:

Glomerulus: A network of capillaries where blood filtration begins.
Bowman's Capsule: Surrounds the glomerulus and collects the filtrate.
Proximal Convoluted Tubule (PCT): The first part of the nephron tubule that reabsorbs water, ions, and nutrients.
Loop of Henle: Descending and ascending limbs involved in concentrating urine.
Distal Convoluted Tubule (DCT): Further adjusts the composition of the filtrate.
Collecting Ducts: Receive urine from multiple nephrons and channel it to the renal pelvis.

Ureters

Structure and Function:

Ureters are long, slender tubes measuring about 25-30 cm long.
They transport urine from the kidneys to the urinary bladder.

Anatomy of the Ureter Wall:

Innermost Layer (Mucosa): Lined with transitional epithelium, preventing urine reabsorption.
Middle Muscular Layer: Comprises circular and longitudinal smooth muscles that create peristaltic waves, propelling urine toward the bladder.
Outer Layer (Adventitia): Composed of fibrous connective tissue, providing structural support.

Transcript

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Ureter Structure

Nephron Function

Glomerulus Filtration

Bowman s Capsule

Proximal Tubule

Collecting Ducts