Human Kidney Structure and Function

Kidney Structure and Function

• Nephrons, tiny structures in renal pyramids, filter gallons of blood daily.
• Kidneys are retroperitoneal organs, located behind the peritoneum.
• The right kidney is slightly lower than the left kidney to accommodate the liver.

Urine Formation

• The 3 main steps of urine formation are: glomerular filtration, reabsorption, and secretion.
• The glomerulus is a network of capillaries surrounded by the glomerular capsule (or Bowman's capsule).

Urine Composition

• Nitrogenous wastes excreted in urine include urea, creatinine, ammonia, and uric acid.

Urination Process

• The internal sphincter is involuntary and surrounds the opening of the bladder to the urethra, relaxing to allow urine to pass.
• The external sphincter is voluntary and surrounds the urethra outside the bladder, requiring relaxation for urination to occur.

Functions of the Urinary System

Regulation of Blood Pressure

• Kidneys regulate blood pressure by controlling extracellular fluid volume and through the renin-angiotensin-aldosterone mechanism.

Hormones Secreted by Kidneys

• Erythropoietin
• Thrombopoietin
• Renin
• 1,25-dihydroxycholecalciferol (calcitriol)
• Prostaglandins

Regulation of Blood Glucose Level

• Kidneys use glutamine in gluconeogenesis, synthesizing new glucose molecules and releasing them into the blood to maintain a normal blood glucose level.

Maintenance of Acid-Base Balance

• Kidneys regulate acid-base balance along with the respiratory system, keeping blood pH at around 7.4 by excreting H+ and reabsorbing bicarbonate (HCO3-).