High-Level Summary

The kidneys are bean-shaped organs protected by three outer layers and organized internally into the cortex, medulla, and renal pelvis. Nephrons in the cortex filter blood supplied by a highly branched vascular network that enters and exits through the renal hilum. Urine formed by nephrons flows through the renal pyramids into calyces, then the renal pelvis, and finally the ureter. Each kidney contains over one million nephrons, which are either cortical or juxtamedullary, depending on their position relative to the medulla.

Study Notes: Kidney Structure 1. External Kidney Structure

The kidney is surrounded by three protective layers (outer → inner):

• Renal fascia Tough connective tissue Anchors kidney to surrounding structures

• Perirenal fat capsule Cushions and stabilizes the kidney

• Renal capsule Thin, tough layer directly covering kidney surface

• Internal Kidney Regions

The kidney has three main internal regions:

Renal Cortex (outer region) Granular appearance Contains nephrons (functional units of the kidney) Site of blood filtration

Renal Medulla (middle region) Made of renal pyramids (cone-shaped tissue masses) Each kidney has ~8 pyramids Renal columns lie between pyramids and carry blood , vessels Pyramid tips = renal papillae, which point toward the , pelvis

Renal Pelvis (inner region) Located at the hilum Funnel-shaped urine collection area Drains urine into the ureter

1. Hilum of the Kidney

2. Concave region of the kidney

3. Entry/exit point for: Renal arteries Renal veins Nerves

4. Exit point for the ureter

5. Urine Flow Pathway

6. Minor calyces → Major calyces → Renal pelvis → Ureter → Urinary bladder

7. Renal Lobes

8. A renal lobe = one renal pyramid + surrounding cortical tissue

9. Functional subdivision of the kidney

Blood Supply of the Kidney (In Order) 1. Aorta 2. Renal arteries 3. Segmental arteries 4. Interlobar arteries (run through renal columns) 5. Arcuate arteries (arch at cortex–medulla boundary) 6. Cortical radiate arteries 7. Afferent arterioles 8. Glomerular capillaries (nephrons)

Venous return: Veins follow the same path in reverse. Same names as arteries except no segmental veins. Drain into the inferior vena cava.

Nephrons (Functional Units) Each kidney contains >1 million nephrons Located mainly in the renal cortex

Types of Nephrons Cortical nephrons (≈85%) Located deep in cortex Short loops of Henle Juxtamedullary nephrons Located near cortex–medulla boundary Long loops of Henle Important for urine concentration

Parts of a Nephron Renal corpuscle Renal tubule Associated capillary network