AG

Module-1-and-2-Urinary (Physio 2)

Module 1: Urinary System Introduction

  • Overview of roles: regulation of arterial pressure, homeostasis, Glomerular Filtration Rate (GFR) and its autoregulation.

  • Learning Outcomes: Understanding flow of blood to/from kidneys, diagramming urinary system functions, discussing juxtaglomerular responses, and GFR autoregulation.

The Urinary System

  • Function: Cleans blood of unwanted substances.

  • Kidneys:

    • Major organs, bean-shaped in mammals.

    • Bilaterally located in retroperitoneal cavity.

    • Responsible for metabolism waste removal.

Functions of the Urinary System

  1. Balances water and electrolytes.

  2. Regulates plasma osmolality and arterial pressure.

  3. Maintains acid-base balance.

  4. Secretes hormones like Renin and erythropoietin.

  5. Aids in glucose production.

Nephrons

  • Functional units of kidneys; millions present per kidney.

  • Parts:

    1. Glomerulus: Responsible for filtration.

    2. Renal Tubules: Involved in reabsorption & secretion.

  • Structure:

    • Made of glomerular capillaries with fenestrae for filtration.

    • Two capillary groups: glomerular (high pressure) and peritubular (low pressure).

Filtration and GFR

  • Glomerular filtration occurs in the glomerular capillary membrane (3 layers: endothelial cells, basement membrane, epithelial cells/podocytes).

  • Glomerular Filtrate: Similar to blood plasma but protein-free and devoid of blood cells, consists mostly of salts.

  • GFR: Amount of filtrate per nephron, influenced by:

    1. Glomerular Hydrostatic Pressure: 60 mmHg

    2. Plasma Colloid Osmotic Pressure: 32 mmHg

    3. Bowman’s Capsule Pressure: 18 mmHg

    4. Bowman’s Capsule Osmotic Pressure: 10 mmHg

Systematic Circulation

  • Distributes blood via arterial tree; renal artery feeds kidneys.

  • Branches into smaller vessels (arcuate arteries → afferent arterioles → glomeruli).

  • Efferent arterioles collect blood to peritubular capillaries and vasa recta, then to arcuate veins.

Autoregulation of GFR

  • Self-regulation of GFR via blood flow and arterial pressure.

  • Mechanisms include:

    1. Afferent arteriolar: vasodilation/vasoconstriction.

    2. Efferent arteriolar: vasoconstriction/vasodilation.

  • Sympathetic nerve fibers can constrict arterioles, decreasing blood flow and GFR, influenced by Angiotensin II.

Juxtaglomerular Complex

  • Structures involved: macula densa, juxtaglomerular cells, mesangial cells.

  • Low sodium chloride in macula densa dilates arterioles, leading to Renin release, initiating angiotensin production and influencing arteriolar resistance.

Angiotensin II Functions

  • Restores blood pressure and volume via:

    1. Stimulating aldosterone secretion → increased sodium reabsorption.

    2. Vasoconstricting efferent arterioles → increased glomerular concentration and filtrate formation.

    3. Direct renal effects leading to increased sodium retention.

  • Higher sodium levels increase extracellular fluid osmolality, leading to release of ADH for water reabsorption.

Renal Tubules

  • Components:

    1. Proximal Tubule: receives filtrate.

    2. Descending Loop of Henle: water reabsorption.

    3. Ascending Loop of Henle: Na+, Cl-, K+, Ca++, HCO3- reabsorption.

    4. Distal Tubule: further filtration.

    5. Collecting Tubules (cortical & medullary).

    6. Renal Pelvis: urine exits into ureter.

Urine Formation

  • Urine is formed by processes of:

    1. Reabsorption: Substances move from tubules to extracellular fluid.

    2. Secretion: Substances move from extracellular fluid to tubules.

  • Urine quality is influenced by blood ECF composition.

Types of Urine

  1. Hypotonic Urine: Low salt, high water.

  2. Hypertonic Urine: High salt, low water.

  3. Dilute Urine: More water, less solutes.

  4. Concentrated Urine: More solutes, less solvent.

  5. Acidic Urine: More H+ ions, less HCO3-.

Hormonal Influence on Urine Formation

  • Vasopressin and vasotocin regulate urine concentration and dilution in mammals and birds respectively.

  • Sodium concentration affects urine quality and influences renin-angiotensin II mechanism, stimulating aldosterone release.

  • Acid-base balance controlled by intercalated cells affecting H+ and HCO3- transport.

Mammalian Urine Characteristics

  • Color: Pale yellow to yellow.

  • Odor: Generally odorless; influenced by diet.

  • Transparency: Clear (except horses).

  • pH: Varies with diet (carnivores = acidic; herbivores = alkaline).

  • Nitrogenous Waste: Primarily urea, formed from ammonia in amino acid metabolism.

Unique Urination Behaviors

  • Horses: Urinate while standing; cannot urinate lying down.

  • Oxen: Urine dribbles due to urethral canal curvature.

Learning Activity

  1. Watch video on nephron urine formation.

  2. Read assigned textbook sections.

  3. Complete tasks: create flowcharts on Juxtaglomerular complex responses, GFR autoregulation, and discuss urine concentration/dilution processes.

References

  • Cunningham, J.G. (2020), Guyton A.C. & Hall, J.E. (2006), Swenson M.J. & Reece, W.O. (1997), Rhodes, R.A. & Tanner, G.A. (1995).

Module 2: Avian Urinary Systems

  • Learning Outcomes: Explain avian urine modifications, compare avian and mammalian urinary systems.

The Avian Urinary System

  • Differences from Mammals:

    • Lobulated kidneys, lacking renal pelvis.

  • Different nephron types:

    • Reptilian Nephrons: Small glomeruli, no loop of Henle.

    • Mammalian Nephrons: Operate at higher filtration rates, capable of urine concentration.

  • Renal Portal System: Blood flow from hind limbs enters kidneys, mixing with afferent blood.

Uric Acid Formation

  • Birds excrete uric acid instead of urea for water conservation.

  • Post Ureteral Modification: During retrograde flow, urine interacts with cloaca and colon.

  • Uric acid crystallizes in renal tubules, forming colloidal particles for transport.

Avian Droppings

  • Composed of feces, urates (chalky white), and urine (clear).

  • Variations may indicate health issues.

Urinary Conditions Terms

  1. Incontinence: Frequent dribbling.

  2. Polyuria: Increased urine output.

  3. Oliguria: Decreased output.

  4. Anuria: No output.

  5. Dysuria: Painful urination.

  6. Stranguria: Painful, slow urine discharge.

Learning Activity

  1. Create diagrams on avian urine modifications.

  2. Tabular comparison of avian and mammalian structures.

  3. Discuss concentrated urine formation in birds.

References for Module 2

  • As per prior references.