Urinary System Overview and Components

Urinary System Overview

• The urinary system is responsible for regulating plasma ion concentrations (Na+, K+, Cl-), blood volume and blood pressure, and blood pH.
• It also prevents the loss of valuable nutrients, eliminates organic matter/waste (like urea), synthesizes calcitriol (active form of vitamin D), and prevents dehydration.
• It aids the liver by detoxifying poisons

Urinary System Components

• Kidneys: Produce urine
• Ureters: Transport urine to the urinary bladder
• Urinary Bladder: Temporarily stores urine prior to elimination
• Urethra: Conducts urine to the exterior; in males, it also transports semen

Kidney Structure and Position

• Right Kidney: Located behind the liver, hepatic flexure, and duodenum.
• Left Kidney: Located behind the spleen, stomach, pancreas, splenic flexure, and jejunum; positioned slightly higher than the right kidney.
• Both kidneys are capped by the suprarenal glands.

Kidney Structure: Sectional Anatomy

• Cortex: Outer layer
• Medulla: Inner layer, contains renal pyramids.
• Renal Pyramids: Cone-shaped structures in the medulla.
• Renal Columns: Tissue extending inward from the cortex between the pyramids.
• Renal Papilla: Tip of the renal pyramid projecting into the minor calyx.
• Renal Pelvis: Funnel-shaped structure that receives urine from the major calyxes.
• Minor Calyx: Collect urine from the renal pyramids.
• Major Calyx: Collect urine from the minor calyxes.
• Renal Sinus: Cavity within the kidney containing the renal pelvis, calyxes, and blood vessels.

Kidney Blood Supply

• The renal artery supplies blood to the kidney. There are numerous branches leading to arterioles further into the kidney.
• Arterioles are a key part of how blood is filtered and processed in the renal corpuscles.
• The renal veins drain blood from the kidney.

Nephron Structure and Function

• The nephron is the basic structural and functional unit of the kidney
• Glomerulus: Intertwining capillaries inside the Bowman's capsule, performs filtration.
• Renal Tubule: Long tubular passageway that processes the filtrate.
  • Proximal Convoluted Tubule (PCT) - Reabsorbs water, ions, and most organic nutrients. This is important for re-absorption of valuable nutrients and water preventing dehydration.
  • Nephron Loop/Loop of Henle - Reabsorbs water and ions, crucial for creating a concentration gradient in the medulla. This is vital to establishing osmotic pressure and enabling high water reabsorption later. The thick ascending loop actively pumps sodium and chloride out.
    • Thin descending limb allows water to leave passively. The thick ascending limb actively transports sodium and chloride, making the medulla more concentrated in solutes. This is critical to the function of the nephrons.
  • Distal Convoluted Tubule (DCT) - Reabsorbs water, sodium, calcium, and secretes excess ions and waste products.

Renal Corpuscle Structure

• Glomerular Capsule (Bowman's Capsule):
  • Parietal Layer: Outer epithelial layer.
  • Visceral Layer: Inner epithelial layer made of podocytes. Podocytes have filtration slits to regulate what is passed into the Bowman's capsule (the initial filtrate collection space)
• Glomerular Capillaries (glomerulus): Fenestrated (with holes) capillaries, enabling filtration of small molecules but preventing filtration of larger molecules
• The renal corpuscle performs initial filtration.

Filtration in the Renal Corpuscle

• Filtration of fluid and solutes from the blood into the glomerular capsule/Bowman's capsule occurs through filtration membrane
• filtration membrane is a 3-layered structure of:
  • capillary endothelium
  • the basal lamina
  • podocyte epithelium

Juxtaglomerular Complex

• Macula Densa cells: Monitor electrolyte concentration (sodium and chloride) in the DCT.
• Juxtaglomerular cells: Secrete renin, regulating blood pressure and erythropoietin stimulating red blood cell production.

The Collecting System

• The collecting duct receives filtrate from several nephrons.
• Filtrate passes through the collecting ducts and papillary ducts, then the minor calyx, major calyx into the renal pelvis. This enables final adjustments to the concentration of the urine.

Urine Transport, Storage, and Elimination

• Ureters: Peristaltic contractions move urine to the urinary bladder.
• Urinary Bladder: Temporarily stores urine.
• Urethra: Conducts urine outside the body; external urethral sphincter in both sexes allows for voluntary control of urine flow

Additional information on the Male and Female differences in the Urinary System are included in the pages of the document.

Explore the essential functions and components of the urinary system, including kidneys, ureters, bladder, and urethra. This quiz will assess your understanding of how these structures work together to regulate important bodily functions. Test your knowledge on kidney anatomy and its role in detoxification.