Lecture Notes on Kidney Anatomy and Function

Main Structures in the Kidney

• Pyramids
  • Upside-down pyramid shape
  • Apex (point) faces downward
• Cortex and Medulla
  • Cortex means crust; medulla means marrow
  • Cortex is external to the medulla
• Capsule
  • Outside of the cortex

Internal Structure

• Pyramids
  • Located within the medulla
  • Separated by renal columns
  • Tip of pyramid is called the papilla (nipple-shaped)
• Drainage System
  • Minor Calices: tubes where the pyramid apex drains
  • Major Calices: formed by fusion of minor calices
  • Renal Pelvis: drains into the ureter
  • Ureter: connects to urinary bladder, then to urethra
  • Hilum: entry/exit point for ureter, blood vessels, lymphatics, nerves

Parenchyma and Stroma

• Parenchyma: functional tissue (renal cortex and pyramids)
• Stroma: structural tissue (tubes, calyces)
• Nephron: functional unit, found in the pyramids

Numbers and Structure

• 8 to 18 renal pyramids
• Separated by renal columns

Kidneys in Transplant

• Donor kidney placed in pelvis of recipient
• Non-functioning kidney usually left in place unless cancerous
• Requires lifelong immunosuppressive drugs to prevent rejection

Nerve Supply and Function

• Extensive blood and nerve supply
• Kidney gets only sympathetic stimulation (no parasympathetic)
• Sympathetic stimulation controls urine production
  • High stimulation diverts blood to muscles (fight or flee)
  • Low stimulation allows active kidney function

Blood Supply

• Renal Artery: supplies blood
• Renal Vein: drains blood
• 25% of resting cardiac output goes to renal arteries
• Capillary Beds:
  • Glomerular Capillaries: filtration occurs here
  • Peritubular Capillaries: surround tubules of nephron, reabsorbs substances
  • Vasa Recta: supplies nutrients to medulla, maintains osmolarity

Types of Nephrons

• Cortical Nephron: mostly in the cortex, slightly dips into the pyramid
• Juxtamedullary Nephron: major loop in the pyramid, some parts atop the pyramid

Blood Flow in the Kidneys

• Flows through renal artery, series of arteries, afferent arterioles, glomerulus
• Efferent arteriole, peritubular capillaries for reabsorption, venules, veins, renal vein
• Extensive capillary network

Goals for Lecture

• List parts of the excretory system
• Describe macroscopic structure of the kidney
• Identify parts forming parenchyma and stroma
• Define terms like nephroptosis, afferent, efferent
• Explain sympathetic nervous system control of kidney
• Describe three capillary systems in the kidney
• Overview of kidney transplant process