Anatomy of the kidney

Question 1

Gross structure of the kidney
1. Outline the following:
*Poles
*Borders
*Segments

Answer 1

*Superior, inferior
*Lateral, medial
*Superior, inferior, anterior superior, anterior inferior, posterior

Has renal capsule which can be peeled off.

Question 2

Describe the anatomical location of the kidney.

Why is the right kidney slightly lower?

Answer 2

*The kidneys lie retroperitoneally (behind the peritoneum) in the abdomen, either side of the vertebral column.

*They typically extend from T12 to L3, although the right kidney is often situated slightly lower due to the presence of the liver.

*Liver: The liver is a large organ located on the right side of the abdominal cavity. The presence of the liver can displace the right kidney slightly downward. The right kidney is positioned below the liver, which can contribute to its lower placement compared to the left kidney.

Question 3

The kidneys are encased in complex layers of fascia and fat.

Arranged them from deep to superficial.

Answer 3

Renal capsule – tough fibrous capsule.

Perirenal fat – collection of extraperitoneal fat.

Renal fascia (also known as Gerota’s fascia or perirenal fascia) – encloses the kidneys and the suprarenal glands.

Pararenal fat – mainly located on the posterolateral aspect of the kidney.

Question 4

Describe the internal structure of the kidney.

Answer 4

The renal parenchyma can be divided into two main areas – the outer cortex and inner medulla.

The cortex extends into the medulla, dividing it into triangular shapes – these are known as renal pyramids.

The apex of a renal pyramid is called a renal papilla.

Each renal papilla is associated with a structure known as the minor calyx, which collects urine from the pyramids.

Several minor calices merge to form a major calyx.

Urine passes through the major calices into the renal pelvis, a flattened and funnel-shaped structure.

From the renal pelvis, urine drains into the ureter, which transports it to the bladder for storage.

The medial margin of each kidney is marked by a deep fissure, known as the renal hilum. This acts as a gateway to the kidney – normally the renal vessels and ureter enter/exit the kidney via this structure.

Question 5

Describe the blood supply to the kidney.

Answer 5

The kidneys are supplied with blood via the renal arteries, which arise directly from the abdominal aorta.

The renal artery enters the kidney via the renal hilum. At the hilum level, the renal artery forms an anterior and a posterior division.

Five segmental arteries originate from these two divisions.

Each segmental artery divides to form interlobar arteries. They are situated either side every renal pyramid.

These interlobar arteries undergo further division to form the arcuate arteries.

At 90 degrees to the arcuate arteries, the interlobular arteries arise.

The interlobular arteries pass through the cortex, dividing one last time to form afferent arterioles.

The afferent arterioles form a capillary network, the glomerulus, where filtration takes place. The capillaries come together to form the efferent arterioles.

In the outer two-thirds of the renal cortex, the efferent arterioles form what is a known as a peritubular network, supplying the nephron tubules with oxygen and nutrients.

The inner third of the cortex and the medulla are supplied by long, straight arteries called vasa recta.

Question 6

Describe the venous drainage of the kidneys.

Answer 6

The kidneys are drained of venous blood by the left and right renal veins.

They leave the renal hilum anteriorly to the renal arteries, and empty directly into the inferior vena cava.

As the vena cava lies slightly to the right, the left renal vein is longer, and travels anteriorly to the abdominal aorta below the origin of the superior mesenteric artery. The right renal artery lies posterior to the inferior vena cava.

Question 7

Describe the lymphatic supply of the kidneys.

Answer 7

Lymph from the kidney drains into the lateral aortic (or para-aortic) lymph nodes, which are located at the origin of the renal arteries.

Question 8

Describe the anatomy of the low urinary tract.

Answer 8

Places of Constriction (Ureteral Narrowing’s):

1. Pelvic Inlet and Outlet: The ureters cross the pelvic brim and pass over the pelvic brim (inlet) and the pelvic sidewall (outlet). These are potential areas of compression, especially in women, where the ureters can be affected by gynecological structures.
2. Crossing Blood Vessels: Ureters cross over the iliac vessels (common iliac artery and vein) in the pelvis, and compression can occur at these points.
3. Ureterovesical Junction (UVJ): This is the point where the ureters enter the bladder. The ureters pass through the bladder wall and traverse the detrusor muscle. The ureterovesical junction is a common site for constriction, and abnormalities here can lead to conditions like vesicoureteral reflux.

Bladder. This triangle-shaped, hollow organ is located in the lower abdomen.

It is held in place by ligaments that are attached to other organs and the pelvic bones.

Upon examination, specific “landmarks” are used to describe the location of any irregularities in the bladder. These are:

*Trigone: a triangle-shaped region near the junction of the urethra and the bladder

Right and left lateral walls: walls on either side of the trigone

Posterior wall: back wall

Dome: roof of the bladder

Diagram of the bladder layers

Two sphincter muscles. These circular muscles help keep urine from leaking by closing tightly like a rubber band around the opening of the bladder.

Urethra:
The urethra is a tube that connects the bladder to the external environment, allowing urine to be expelled from the body.

In males, the urethra serves a dual purpose, carrying urine from the bladder and also transporting semen during ejaculation from the reproductive system. It is longer in males and passes through the prostate gland.

In females, the urethra is shorter and is located between the clitoris and the vaginal opening.

There are two sphincters that control the flow of urine through the urethra:

*Internal Urethral Sphincter: This sphincter is involuntary and is located at the junction of the bladder and the urethra. It remains contracted to prevent urine leakage between voiding.

*External Urethral Sphincter: This sphincter is under voluntary control and is located where the urethra passes through the pelvic floor muscles. It allows for conscious control over the release of urine.