A&P II Module 9: The Urinary System

Module 9: The Urinary System

Learning Outcomes

• State and describe the major organs of the urinary system.

• Describe the location, structure, blood supply and functions of the kidneys.

• Explain the role of the nephron unit in the formation of urine.

Overview of the Urinary System

• Functions:

  • Produces and excretes urine.

  • Cleanses blood and eliminates waste.

  • Regulates pH and blood pressure.

  • Determines solute concentration and levels of red blood cells.

• Main Components:

  • Kidneys: Major excretory organs.

  • Ureters: Transport urine from kidneys to urinary bladder.

  • Urinary Bladder: Temporary storage for urine.

  • Urethra: Transports urine out of the body.

In-Class Activity #1

Urinalysis is often used in the clinic to provide clues to renal disease. There are normal characteristics of urine and if a patients urine deviates significantly from these normal characteristics it is an indication that they may have a renal disease. The normal urine characteristics are shown in the table to the right.

If glucose is found in the urine, would this be concerning?

Yes, indicator of diabetes

If a large amount of proteins is found in the urine would this be concerning?

Yes, indicator of glomerulus damage

Kidneys: Structure and Function

• Location:

  • Retroperitoneal, in the superior lumbar region (T12 to L5).

  • The right kidney is lower than the left due to the liver.

• Anatomy:

  • Adrenal glands sit atop each kidney.

  • Surrounding layers:

  • Renal fascia: dense fibrous connective tissue.

  • Perirenal fat capsule: fatty cushion around the kidney.

  • Fibrous capsule: prevents infection spread.

• Internal Structure:

  • Renal Cortex: Granular-looking outer region.

  • Renal Medulla: Inner region with cone-shaped renal pyramids.

  • Renal Pelvis: Funnel shape collects urine before it moves to the ureters.

  • Collecting Ducts: Deliver urine through papillae into minor calyces.

Blood and Nerve Supply to the Kidneys

• Blood Supply:

  • Renal arteries deliver about 1200 ml (one-fourth) of cardiac output/minute.

  • Arterial flow: renal → segmental → interlobar → arcuate → cortical radiate (interlobular).

  • Venous flow: cortical radiate → arcuate → interlobar → renal veins.

• Nerve Supply:

  • Provided by sympathetic fibers from the renal plexus.

In-Class Activity #2

What is the name of the vessel that feeds blood into the glomerulus?

Afferent (enter) arteriole

What is the name of the vessel that sends blood out of the glomerulus?

Efferent (exit) arteriole

The Nephron: Structure and Function

• Definition: Nephrons are the functional units of the kidney essential for urine formation.

• Components:

  • Renal Corpuscle:

  • Glomerulus: Tuft of capillaries for filtration.

    • Fenestrated endothelium allows high filtration efficiency.

  • Bowman’s Capsule: Surrounds glomerulus, has parietal and visceral layers with filtration slits.

  • Renal Tubule: Divided into:

  • Proximal Convoluted Tubule (PCT): Reabsorbs nutrients and ions.

  • Nephron Loop (Loop of Henle):

    • Descending limb: permeable to water.

    • Ascending limb: impermeable to water, allows ion movement.

  • Distal Convoluted Tubule (DCT): Further reabsorption and secretion.

  • Collecting Duct: Receives filtrate from several nephrons, functions in urine formation.

Nephron Capillary Beds

• **Two Capillary Beds Associated: $

  • Glomerulus: Specialized for filtration.

  • Peritubular Capillaries: Adapted for absorption of water and solutes.

  • Vasa Recta: Associated with juxtamedullary nephrons; aid in concentration of urine.

In-Class Activity #3

Describe how the anatomy of the renal corpuscle structures allow for blood filtration.

Renal Corpsule = Glomerulus + Bowman’s Capsule

Physiology of Urine Formation

• Daily Processing: 180 L of fluid processed, producing 1.5 L of urine.

  • Filtrate is plasma minus proteins.

• Processes of Urine Formation:

  • Glomerular Filtration: Produces cell- and protein-free filtrate.

  • Tubular Reabsorption: Reclaims 99% of substances from filtrate back into blood; occurs mainly in PCT.

    • Nephron → Circulatory System

  • Tubular Secretion: Moves substances from blood into filtrate; important for regulating blood composition.

    • Peritubilar Capillaries → Nephron Tubules

Regulation of Urine Components

• **Hormonal Regulation: $

  • Antidiuretic Hormone (ADH): Increases water reabsorption in collecting ducts.

  • Aldosterone: Promotes Na+ reabsorption affecting blood volume and pressure.

  • Atrial Natriuretic Peptide: Decreases blood Na+ levels, leading to reduced blood volume.

  • Parathyroid Hormone: Increases Ca2+ reabsorption in the DCT.

In-Class Activity #4

Which region of the nephron plays the biggest role in reabsorption?
→ Proximal convoluted tubule (PCT)

Which region of the nephron plays the biggest role in the secretion?

→ Distal convoluted tubule (DCT)

Summary Points

1. The urinary system includes ureters, bladder, urethra, and kidneys, functioning to excrete urine.

2. Urine formation primarily occurs through blood filtration in the kidneys.

3. Nephrons are key to urine production via processes of glomerular filtration, tubular reabsorption, and secretion.

4. Each nephron consists of renal corpuscle (glomerulus + Bowman’s capsule) and renal tubule (PCT, nephron loop, DCT).