Urinary System Overview

Urinary System

• The urinary system consists of two kidneys, two ureters, one urinary bladder, and one urethra.
• The ureters are lined with transitional epithelium.

Functions of the Kidneys

• Excrete urine (approximately 1500-2000 ml/24 hours) containing metabolic waste products like urea, creatinine, and uric acid.
• Regulate water and electrolyte balance, maintaining acid-base balance.
• Produce renin hormone, which helps regulate blood pressure.
• Produce erythropoietin hormone, which stimulates erythrocyte production.
• Hydroxylate vitamin D3 to its active form.

Structure of the Kidney

• The kidney is divided into lobes and lobules, with a stroma consisting of a CT capsule, reticular fibers, and few collagenous bundles.
• The parenchyma is formed of urineferous tubules, comprising:
  • The cortex (outer) with a red color, containing Malpighian Renal Corpuscles.
  • The medulla (inner) with a light grey color, containing medullary rays and collecting tubules.

The Urineferous Tubule

• The urineferous tubule is formed of two parts: nephrons (active secretory part) and collecting tubules (excretory part).

The Nephron

• The nephron is the functional and structural unit of the kidney.
• Each nephron is formed of:
  • The Malpighian corpuscle.
  • The proximal and distal convoluted tubules.
  • The loop of Henle.

The Malpighian Renal Corpuscle

• The Malpighian renal corpuscles form the glomerular filtrate by the process of dialysis.
• Each corpuscle is formed of:
  • Bowman's Capsule.
  • Glomerular Capillaries.
  • Supporting Mesangial cells.
  • Afferent and Efferent arterioles.

Bowman's Capsule

• Bowman's capsule is a double-walled capsule surrounding the glomerular blood capillaries.
• It is formed of two continuous layers of epithelium separated by a capsular space:
  • Parietal layer (simple squamous epithelium).
  • Visceral layer (modified simple squamous cells, podocytes, with small foot-like processes, pedicles).

Mesangial Cells

• Mesangial cells are branched cells adherent to the surface of glomerular blood capillaries.
• They act as structural support to podocytes and vessels.

Juxtaglomerular Complex

• The Juxtaglomerular Complex is present under the distal convoluted tubule (DCT) and fits between the afferent and efferent arterioles.

Proximal Convoluted Tubules vs. Distal Convoluted Tubules

• Proximal convoluted tubules:
  • Have a large diameter.
  • Have more apical microvilli.
  • Reabsorb water, NaCl, Ca, phosphate, glucose, amino acids, and plasma proteins.
  • Excrete creatinine, iodine, and penicillin.
• Distal convoluted tubules:
  • Have a small diameter.
  • Have less apical microvilli.
  • Reabsorb water and sodium.
  • Excrete sodium, potassium, and ammonium.

Urinary System

• The urinary system consists of two kidneys, two ureters, one urinary bladder, and one urethra.
• The ureters are lined with transitional epithelium.

Functions of the Kidneys

• Excrete urine (approximately 1500-2000 ml/24 hours) containing metabolic waste products like urea, creatinine, and uric acid.
• Regulate water and electrolyte balance, maintaining acid-base balance.
• Produce renin hormone, which helps regulate blood pressure.
• Produce erythropoietin hormone, which stimulates erythrocyte production.
• Hydroxylate vitamin D3 to its active form.

Structure of the Kidney

• The kidney is divided into lobes and lobules, with a stroma consisting of a CT capsule, reticular fibers, and few collagenous bundles.
• The parenchyma is formed of urineferous tubules, comprising:
  • The cortex (outer) with a red color, containing Malpighian Renal Corpuscles.
  • The medulla (inner) with a light grey color, containing medullary rays and collecting tubules.

The Urineferous Tubule

• The urineferous tubule is formed of two parts: nephrons (active secretory part) and collecting tubules (excretory part).

The Nephron

• The nephron is the functional and structural unit of the kidney.
• Each nephron is formed of:
  • The Malpighian corpuscle.
  • The proximal and distal convoluted tubules.
  • The loop of Henle.

The Malpighian Renal Corpuscle

• The Malpighian renal corpuscles form the glomerular filtrate by the process of dialysis.
• Each corpuscle is formed of:
  • Bowman's Capsule.
  • Glomerular Capillaries.
  • Supporting Mesangial cells.
  • Afferent and Efferent arterioles.

Bowman's Capsule

• Bowman's capsule is a double-walled capsule surrounding the glomerular blood capillaries.
• It is formed of two continuous layers of epithelium separated by a capsular space:
  • Parietal layer (simple squamous epithelium).
  • Visceral layer (modified simple squamous cells, podocytes, with small foot-like processes, pedicles).

Mesangial Cells

• Mesangial cells are branched cells adherent to the surface of glomerular blood capillaries.
• They act as structural support to podocytes and vessels.

Juxtaglomerular Complex

• The Juxtaglomerular Complex is present under the distal convoluted tubule (DCT) and fits between the afferent and efferent arterioles.

Proximal Convoluted Tubules vs. Distal Convoluted Tubules

• Proximal convoluted tubules:
  • Have a large diameter.
  • Have more apical microvilli.
  • Reabsorb water, NaCl, Ca, phosphate, glucose, amino acids, and plasma proteins.
  • Excrete creatinine, iodine, and penicillin.
• Distal convoluted tubules:
  • Have a small diameter.
  • Have less apical microvilli.
  • Reabsorb water and sodium.
  • Excrete sodium, potassium, and ammonium.