1. Components of the Renal System

The renal system consists of four main types of organ: 

–Kidneys (2) 
–Ureters (2) 
–Urinary bladder 
–Urethra

 
2. Kidneys 
Location 
Retroperitoneal (behind the peritoneum) 
On either side of the vertebral column 
Right kidney slightly lower than left (due to liver) 
Extend from T12 to L3 vertebrae

External Features 
Bean-shaped organs 
Length: ~11–12 cm

Hilum (medial indentation) allows passage of: 
Renal artery 
Renal vein 
Renal pelvis → ureter

Internal Structure of the Kidney: 

A. Renal Cortex 
Outer granular layer 
Contains: 
Renal corpuscles (glomeruli + Bowman’s capsule) 
Proximal & distal convoluted tubules 

B. Renal Medulla 
Inner striated region 
Made of renal pyramids 
Pyramids end in renal papillae 

C. Collecting System 
Minor calyces → Major calyces → Renal pelvis → Ureter 
 
3. Nephron (Functional Unit of Kidney)

A nephron is the tiny, essential filtering unit within each kidney, responsible for filtering blood, reabsorbing necessary substances, and excreting waste to form urine, maintaining the body’s fluid balance and homeostasis.

Each normal kidney has about 1 million nephrons.


 


Parts of a Nephron:

a. Renal corpuscle comprising of:
Glomerulus 
Bowman’s capsule
– Important for filtration.

b. Renal Tubules comprising of:
Proximal convoluted tubule (PCT) 
Loop of Henle 
Descending limb 
Ascending limb 
Distal convoluted tubule (DCT) 
(final) Collecting duct 
– Important for reabsorption and secretion of waste

Types of Nephrons 
Cortical nephrons (85%) 
Juxtamedullary nephrons (15%) – important for urine concentration

4. Blood Supply of the Kidney 
Renal artery 
Segmental arteries 
Interlobar arteries 
Arcuate arteries 
Interlobular arteries 
Afferent arteriole 
Glomerular capillaries 
Efferent arteriole 
Peritubular capillaries / Vasa recta 
Renal vein

5. Ureters 
Muscular tubes ~25–30 cm long 
Carry urine from kidneys to bladder 
Lined by transitional epithelium 
Enter bladder obliquely (prevents backflow)

6. Urinary Bladder 
Hollow muscular organ 
Located in pelvis 
Stores urine (≈500 mL capacity) 
Detrusor muscle in the wall 
Trigone: triangular area between ureteric openings and urethra

7. Urethra 
Conveys urine from bladder to exterior 
Length 
Male: ~20 cm 
Female: ~4 cm 
Sphincters 
Internal urethral sphincter (involuntary) 
External urethral sphincter (voluntary)

8. Layers of the Urinary Tract 
Mucosa (transitional epithelium/urothelium) 
Submucosa 
Muscular layer 
Adventitia / Serosa

Cross Section of a bladder: