Urinary 1

Anatomy & Physiology II - Chapter 25: Urinary System

Introduction

  • Functions for Homeostasis:
      - Cleanses blood
      - Removes nitrogenous wastes
      - Regulates blood pH
      - Regulates blood pressure (BP)
      - Regulates concentration of solutes
      - Regulates concentration of red blood cells (RBCs)
      - Produces erythropoietin (EPO)
      - Involved in vitamin D production

Glomeruli & Urine

  • Glomeruli:
      - Specialized capillaries used to filter blood.
      - Serve as the beginning of the nephron.
  • Urine Color Changes:
      - Influenced by water intake.
      - Affected by exercise levels.
      - Can change with temperature variations.
      - Influenced by nutrient intake.

Urinalysis

  • Purpose: Can detect renal disease.
  • Urochrome: Yellow pigment found in urine.
  • Possible Problems in Urine:
      - Protein:
        - Indicates glomeruli damage.
      - Blood:
        - Possible indicators of kidney stones or cancer.
      - Dark/Brown Urine:
        - Can indicate liver disease or obstruction of bile flow.
      - Dark/Ammonia Smell:
        - Suggests dehydration.

Kidney Output

  • Urine Volume Variations:
      - Normal kidney output: 400-500 mL per day.
      - Oliguria: Below normal output.
      - Anuria: Absence of urine production.
      - Polyuria: Above normal output.

Urine Characteristics – 1

  • pH Variations:
      - Can vary with diet, typically within a range of 4.5-8.0.
      - Chronically high pH may lead to kidney stones and osteomalacia.
  • Specific Gravity:
      - Measures solutes per volume of solution.
      - Water is equal to 1; thus specific gravity > 1 indicates the presence of solutes.
      - Labs now directly measure urine osmolarity, with a range from 50 mOsmol/L to 1200 mOsmol/L.

Urine Characteristics – 2

  • Urine Components:
      - Leukocyte Esterase: Indicates leukocytes are present, suggesting infection.
      - Proteins: Presence indicates damaged glomeruli.
      - Ketones: Suggests body is utilizing fat for energy, often seen in diabetes.
      - Nitrite: Associated with bacterial infections.

Gross Anatomy

  • Kidneys:
      - Right kidney is typically lower than the left due to displacement by the liver.
      - Hilum: Exit site for vessels.
      - Nephron is the functional unit of the kidney.
  • Ureters:
      - Involved in peristalsis.
  • Urinary Bladder:
      - Collects and stores urine.
  • Urethra:
      - Transports urine out of the body.

Urethra – 1

  • Function: Transports urine from the bladder to the outside of the body.
  • Differences Between Males and Females:
      - Runs behind the pubic symphysis.
      - Proximal urethra: transitional epithelium.
      - In males only: pseudostratified columnar between proximal and distal regions.
      - Distal urethra: nonkeratinized stratified squamous epithelium.

Urethra – 2

  • Trigone: Region at the base of the bladder.
  • Micturition: The voiding of the bladder.
      - Internal Urinary Sphincter: Composed of smooth muscle.
      - External Urinary Sphincter: Composed of skeletal muscle.
      - Glands secrete alkaline substances to neutralize the acidity of urine.

Urethra – 3

  • In Males:
      - Urethra is longer, resulting in less incidence of urinary tract infections (UTIs).
      - Passes through prostate.
  • Urethral Regions:
      - Preprostatic: Very short, near bladder.
      - Prostatic: Located in the prostate, receives sperm.
      - Membranous: Receives mucus from Bulbourethral glands.
      - Spongy (Penile): Passes through corpus spongiosum and exits at the external urethral orifice.

Urinary Bladder

  • Function: Collects and stores urine.
  • In Females: Micturition frequency increases as the fetus expands above the bladder, reducing its capacity.
  • In Males: The presence of the prostate affects bladder function.
  • Detrusor Muscle: Smooth muscle of the bladder with crisscrossing fibers.
  • Transitional Epithelium: Lines the bladder.

Full Bladder Function

  • When Bladder is Full:
      - The parasympathetic system stimulates detrusor contraction, pushing urine out.
      - Micturition is controlled by the autonomic system. Smooth muscle contracts while the external sphincter remains relaxed.
  • When Bladder is Empty:
      - The sympathetic system relaxes the detrusor muscle, allowing the bladder to store urine.

Micturition Reflex – 1

  • Micturition: Technical term for urination or voiding.
  • Resulting from internal and external urethral sphincters working together.
  • Incontinence: Occurs due to the failure of voluntary constraint or external urethral sphincter control.
  • Bladder Volume Indicators:
      - 150 mL: Urge to micturate.
      - 300-400 mL: Failure of voluntary constraint and onset of incontinence.

Micturition Reflex – 2

  • Autonomic Nervous System: Control over micturition
      - Parasympathetic NS: Contracts detrusor and relaxes the internal urethral sphincter.
      - Stretch Receptors: Provide sensory input to trigger micturition impulses.
      - Motor Pathway: Contracts detrusor muscle and relaxes skeletal muscle of the external urethral sphincter.
      - Childhood Training: Children learn to override this reflex during potty training; catheters may be used when voluntary relaxation fails.

Micturition Reflex – 3

  • Nerves Controlling Micturition:
      - Includes hypogastric, pelvic, and pudendal nerves.
      - Sacral Micturition Center:
        - Involved in voluntary control using pudendal nerve, assuming no damage to the spinal cord.
      - Sympathetic NS: Suppresses contraction of detrusor muscle while bladder fills.
      - Parasympathetic NS: Triggers contractions for emptying the bladder.

Ureters

  • Pathway of Urine:
      - Formed urine passes through the minor calyx, major calyx, renal pelvis, hilum, ureter, and finally the bladder.
  • Physiological Sphincters:
      - The ureters function as one-way valves preventing the reflux of urine.
  • Transitional Epithelium & Goblet Cells: Present in ureter linings.
  • Peristalsis: Initiated at the renal pelvis to facilitate urine transport.

Kidneys – 1

  • Orientation:
      - The right kidney is slightly lower, displaced by the liver.
  • Fibrous Capsule: Dense irregular connective tissue protecting the kidney.
  • Renal Fat Pad: Offers further protection.
  • Adrenal Glands: Positioned superior to the kidneys; the adrenal cortex regulates sodium (Na+) reabsorption through aldosterone production.

Kidneys – 2

  • Kidney Regions:
      - Hilum
      - Capsule
      - Cortex
      - Medulla
      - Columns
      - Pyramids
      - Papillae lead to calyces, which lead to the renal pelvis, where veins and arteries are also located.

Arteries → Arterioles

  • Blood Flow Pathway:
      - Renal artery → segmental arteries → interlobar arteries → arcuate arteries → cortical radiate arteries → afferent arterioles → nephron.

Nephron – 1

  • Nephron: Functional unit of the kidney, responsible for:
      - Filtering larger solutes out of the blood.
      - Reabsorbing water.
      - Secreting waste products.
  • Secondary Functions:
      - Hormonal production: EPO (Erythropoietin for RBC production), renin (blood pressure regulation), and calcium absorption.

Nephron – 2

  • Nephron Pathway:
      - Afferent arteriole → glomerulus → nephron.
  • Renal Corpuscle:
      - Comprised of Bowman’s capsule and glomerulus.
      - Bowman’s Capsule: Encloses the glomerulus.
      - Glomerulus: Network of capillaries filtering blood based on particle size.
  • Functions:
      - Cleanses blood, balances blood constituents, and reabsorbs water.

Nephron – 3

  • Sequential Flow:
      - From Glomerulus in Bowman’s Capsule → Proximal Convoluted Tubule (PCT) → Nephron Loop → Distal Convoluted Tubule (DCT).
  • Capillary Function:
      - Recovery of solutes and water takes place through associated capillaries:
        - Efferent arterioles lead to peritubular capillaries in cortical nephr