ch5 bio310

Urinary System Overview

  • Course: BIO310 / Urinary / NHM

Lesson Outcomes

  • Students should be able to:

    • Describe and illustrate the external anatomy of the kidney.

    • Describe and illustrate the internal anatomy of the kidney.

    • Describe the general functions of the kidney.

    • Describe and illustrate the structure of the nephron.

    • Describe the functions of the ureter, urinary bladder, and urethra.

    • Describe the processes of glomerular formation, tubular reabsorption, and tubular secretion.

Structure and Functions of the Kidney

Kidney Function

  • Regulatory Roles:

    • Regulate volume of blood plasma.

    • Regulate concentration of wastes.

    • Regulate concentration of electrolytes.

    • Regulate pH of blood plasma.

    • Eliminate metabolic toxins.

Kidney Structure

  • Shape: Bean-shaped, located between the dorsal body wall and parietal peritoneum.

  • Urine production:

    • Urine forms in the kidneys, collects in the renal pelvis, moves to the ureter, and is stored in the urinary bladder before exiting through the urethra.

Kidney Anatomy

  • Regions:

    • Renal cortex: Outer region.

    • Renal medulla: Inner region with renal pyramids and columns where urine drains into minor calyx, major calyx, and finally the renal pelvis.

Renal Blood Vessels

  • Oxygenated Blood Flow: Renal artery → Interlobar artery → Arcuate artery → Interlobular artery.

  • Deoxygenated Blood Flow: Interlobular vein → Arcuate vein → Interlobar vein → Renal vein.

Components of the Nephron

  • Nephron: Functional unit of the kidney consisting of small tubules and associated blood vessels.

  • Each kidney contains over a million nephrons.

  • *Key Components:

    • Glomerulus.

    • Bowman's capsule.

    • Proximal tubule.

    • Loop of Henle (descending and ascending limbs).

    • Distal convoluted tubule.

    • Collecting duct.

Urine Production

  • Process:

    • Nephrons process approximately 180 L of filtrate daily, resulting in around 1.5 L of urine excreted.

    • The blood volume is filtered approximately 20-25 times each day.

Glomerular Filtration

  • Occurs in the renal corpuscle, where blood is filtered into Bowman's capsule.

  • Filtration Mechanism:

    • Non-selective, allowing small molecules (salts, glucose, nitrogenous wastes) to pass while preventing blood cells and large proteins from filtering through.

  • Net Filtration Pressure (NFP):

    • NFP = Glomerular capillary hydrostatic pressure (55 mm Hg) - Bowman’s capsule hydrostatic pressure (15 mm Hg) - Plasma-colloid osmotic pressure (30 mm Hg) = 10 mm Hg.

Nephron Functions

Filtration, Reabsorption, and Secretion

  • Filtration: Blood pressure forces fluid into Bowman's capsule, producing filtrate.

  • Reabsorption:

    • Begins at the proximal tubule where most solutes are reclaimed.

    • Loop of Henle plays a critical role in concentrating or diluting urine.

    • Mechanisms: Active and passive transport for sodium, water, and other nutrients.

  • Secretion: Reverse process of reabsorption, transporting K+, NH4+, H+, and pharmaceuticals from the blood to the lumen.

Types of Nephrons

  • Cortical Nephrons:

    • 80% of nephrons, renal corpuscles located in superficial cortex.

    • Shorter loops of Henle.

  • Juxtamedullary Nephrons:

    • 20% of nephrons, renal corpuscles located near the medulla.

    • Long loops for concentrated urine production.

Countercurrent Multiplication

  • Mechanism involving the loop of Henle and collecting duct to set osmotic gradients.

  • Water and Salts Transport:

    • Descending limb: Permeable to water, allowing reabsorption.

    • Ascending limb: Impermeable to water, actively pumps out salts to create concentration gradients.

Hormonal Regulation

  • Antidiuretic Hormone (ADH):

    • Increases water reabsorption in distal convoluted tubules and collecting ducts.

  • Aldosterone:

    • Plays a role in sodium reabsorption and potassium excretion.

Glomerular Filtration Rate (GFR)

  • Measurement of fluid volume filtered per minute from glomerular capillaries into Bowman's capsule.

  • Influenced by glomerular capillary pressure and the resistance in arteries.

Summary of Key Terms

  • Nephron: Basic functional unit of kidney.

  • Filtration: Movement of water and solutes through the glomerulus.

  • Reabsorption: Process returning essential substances from filtrate back into blood.

  • Secretion: Process of transferring materials from blood into nephron.

  • ADH: Hormone regulating water balance.

  • Osmoregulation: Regulation of water concentrations in the bloodstream.

ADH (Antidiuretic Hormone) primarily regulates water reabsorption in the kidneys, specifically in the distal convoluted tubules and collecting ducts, increasing water reabsorption to concentrate urine and reduce water loss.

  1. Aldosterone primarily regulates sodium reabsorption and potassium excretion in the kidneys. It increases sodium reabsorption, leading to water retention and potassium excretion to maintain blood pressure and electrolyte balance.