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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 :
- A pair of kidneys.
- A pair of ureters.
- A urinary bladder
- A urethra
2.0Location of Kidneys
- Mammalian kidneys are bean shaped; reddish brown coloured with a tough fibrous connective tissue covering called the 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
- 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.
- 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.
- 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.