Kidney Anatomy, Renal Physiology, and Abdominal Wall Muscles

Kidney Anatomy and Structure

The kidneys are bean-shaped organs featuring:

• Superior pole: With adrenal gland.
• Inferior pole: Anterior and posterior convex outer edge, inner edge concave with hilum.

Renal Structure

Wrapped in a smooth fibrous capsule, the kidney consists of:

• Cortex
• Medulla
• Columns of Bertin
• Renal pelvis
• Renal lobe

Microscopic Structure of the Kidneys

The kidney consists of a million nephrons, comprising:

• Renal corpuscle: Glomerulus and Bowman's capsule.
• Vascular tubules: Proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting ducts.

Vascularization

• Renal Artery: Branches of the abdominal aorta; the right is longer and more vertical. It is located between the vein and the renal pelvis at the hilum.
• Renal Veins: Drain into the inferior vena cava; the left renal vein crosses in front of the aorta.

Renal Functions

The kidneys contribute to maintaining normal blood composition through urine production, including the excretion of water, protein metabolism waste products, salts, and drugs. They also regulate blood pressure and perform erythropoietic functions.

Urine Production Mechanisms

1. Filtration: Occurs in renal corpuscles.
2. Resorption: Water and dissolved substances (97-99% of the filtrate), mainly in the loop of Henle and the collecting tubule.
3. Discharge: Active process of secreting H+, K+, ammonia, and certain drugs, especially in convoluted tubules.

The Ureter

The renal duct collects urine produced by the kidney and leads to the urinary bladder.

Anatomical Parts

• Renal Pelvis: Connects to the ureter.
• Abdominal Portion: Extends from the renal pelvis to the pelvic brim, resting on the psoas muscle and crossing in front of the iliac artery and vein.
• Pelvic Portion: Passes inside the internal iliac, crosses under the uterine artery or vas deferens, and empties into the back of the bladder through ureteral orifices (anti-reflux mechanism).

Ureter Structure

• External Fibrous Layer: Facilitates sliding against adjacent organs; rich in blood vessels.
• Muscle Layer: Smooth fibers arranged in a lattice, producing 4 to 6 peristaltic waves per minute.
• Mucosa: Urothelium with large cap-shaped cells that flatten under strain to waterproof the wall.

Muscles of the Abdominal Wall

The abdominal wall consists of three layers with different fiber directions:

• External Oblique: From ribs V-XII to the midline of the abdomen (rectus sheath), pubis, and anterior iliac crest. Fibers run forward and downward, forming the inguinal ligament (Poupart's ligament).
• Internal Oblique: From the iliac crest to the midline of the abdomen and ribs. Fibers run forward and upward.
• Transverse Abdominis: Fibers run almost horizontally.
• Rectus Abdominis: Located on either side of the linea alba, extending from the xiphoid process to the pubis.