Human Urinary System

The human urinary system is a vital organ system responsible for removing waste products and excess substances from the body, maintaining the body's fluid and electrolyte balance, and regulating blood pressure. It plays a crucial role in filtering blood, forming urine, and excreting it from the body.

1.0Introduction

Human excretory system consists of :

1. A pair of kidneys.  
2. A pair of ureters.  
3. A urinary bladder        
4. A urethra

2.0Location Of Kidneys

• Mammalian kidneys are bean shaped; reddish brown coloured with a tough fibrous connective tissue covering called renal capsule.
• Kidneys are located laterally on either side of vertebral column levels between the last thoracic (T₁₂) and third lumbar (L₃) vertebrae close to the dorsal inner wall of the abdominal cavity.
• In humans, the right kidney is at a slightly lower level than the left kidney, because of the presence of the liver in the right side of the abdominal cavity.

• Towards the center of the inner concave surface of the kidney is a notch called Hilum (Hilus renalis). Through this, the renal artery and nerve enter while renal vein and ureter leave the kidney.
• Inner to the hilum is a broad funnel shaped space called the renal pelvis, with projections called calyces.

3.0Structure Of Kidneys

•  Inside the kidney, there are two zones, an outer cortex and an inner medulla.
• The medulla is divided into a few conical masses (medullary pyramids) (8 to 12 in humans) projecting into the calyces (sing.: calyx).
• The cortex extends in between the medullary pyramids as renal columns called columns of Bertini/Renal column.
• Each kidney has nearly one million complex tubular structures called Nephrons which are the functional units.

• Urine produced by each nephron empties into a collecting duct.
• The collecting duct passes through a papilla into the renal calyx (Pleural - calyces).
• The renal calyces drain urine in the central cavity of the renal pelvis.

4.0Post Renal Urinary Tract

1. Ureter 

• Urine passes from the renal pelvis into the ureter. 
• Both the ureters open through separate oblique openings into the urinary bladder. 
• The obliquity of the openings prevents the backflow of urine.

2. Urinary bladder 

• Externally, the bladder is lined by detrusor muscle. 
• It is involuntary in nature while internally the bladder is lined by transitional epithelium or urothelium.
• This epithelium has great capacity to expand so that a large volume of urine can be stored. 
• The opening of the urinary bladder is controlled by sphincters made of circular muscles. In humans two sphincters are present. 
• These normally remain contracted and during micturition these relax to release urine.

3. Urethra 

• The urinary bladder opens into a membranous duct called Urethra.
• The urethra leads to the end of the penis in males and into the vulva in females. 

5.0Function Of Kidneys 

• Excretion of metabolic waste and foreign chemicals.
• Regulation of body fluid osmolarity and electrolyte concentration.
• Regulation of acid base balance.
• Secretion of hormones like Erythropoietin and Renin.
•  Regulation of arterial pressure.