The Urinary System

Chapter Overview

• Focuses on the anatomy and physiology of the urinary system.

• Highlights the unity of form and function in the renal system.

Anatomy of the Urinary System

Figure 23.1: Overview of the Urinary System

• Anterior View:

  • Includes the diaphragm, adrenal glands, renal arteries, renal veins, kidneys, and urinary bladder.

• Posterior View:

  • Shows the location of the kidneys against the posterior abdominal wall.

Functions of the Kidneys

Key Functions (Slide 23.1a)

• Filtration and Excretion:

  • Remove toxic metabolic wastes from blood.

• Regulation:

  • Blood volume, pressure, and osmolarity.

  • Electrolytes and acid-base balance.

• Secretion:

  • Erythropoietin for red blood cell production.

  • Calcitriol for calcium regulation.

• Hormone Clearance:

  • Detoxification of free radicals.

• Glucose Synthesis:

  • In starvation, kidneys synthesize glucose from amino acids.

Nitrogenous Wastes

Waste Definitions (Slide 23.1b)

• Metabolic Waste:

  • Urea, uric acid, and creatinine.

• Blood Urea Nitrogen (BUN):

  • Reflects nitrogenous waste levels; normal 10-20 mg/dL.

  • High levels indicate potential renal insufficiency (azotemia).

  • Uremia: toxic syndrome due to waste accumulation requiring dialysis or transplant.

Types of Nitrogenous Wastes

• Urea:

  • Produced from protein catabolism.

• Uric Acid:

  • Byproduct of nucleic acid metabolism.

• Creatinine:

  • Result of creatine phosphate catabolism.

Excretion Processes (Slide 23.1c)

Systems Involved in Excretion

• Respiratory System:

  • Excretes CO2 and water.

• Integumentary System:

  • Eliminates water, salts, lactate, and urea in sweat.

• Digestive System:

  • Removes various metabolic wastes.

• Urinary System:

  • Excretes metabolic wastes, toxins, drugs, hormones, and salts.

Kidney Position & Structure

Kidney Position (Slide 23.2a)

• Located against the posterior abdominal wall (T12-L3).

• Right kidney lower due to liver.

• Surrounded by other anatomical structures and retroperitoneal.

Gross Anatomy of the Kidney (Slide 23.2b)

• Each kidney: ~150g and bar soap sized.

• Hilum: Slit for nerves, blood vessels, and ureters.

• Connective Tissue Coverings:

  • Renal fascia, perirenal fat capsule, and fibrous capsule for protection and support.

Renal Parenchyma (Slide 23.11)

• Cortex and Medulla:

  • Outer cortex and inner medulla with renal pyramids.

• Renal Columns:

  • Structures dividing the medulla into lobes.

Urine Formation

Urine Formation Process (Slide 23.3)

• Stages of Formation:

  1. Glomerular filtration

  2. Tubular reabsorption

  3. Tubular secretion

  4. Water conservation

• Fluid Forms:

  • Glomerular Filtrate: Fluid in capsular space.

  • Tubular Fluid: From PCT to DCT with adjustments by tubular cells.

  • Urine: In collecting duct, minimal alterations except water content.

The Filtration Membrane (Slide 23.3a)

• Composed of: fenestrated endothelium, basement membrane, and podocyte filtration slits.

• Allows passage of water and small solutes; prevents blood cells and proteins from passing.

Glomerular Filtration Rate (GFR)

• Measurement of filtrate produced per minute.

• High efficiency with 99% reabsorption; ~1-2 L of urine is excreted daily.

Regulation of Glomerular Filtration

Factors Affecting GFR (Slides 23.39 - 23.45)

• If GFR is too high:

  • Increased urine output, risk of dehydration.

• If GFR is too low:

  • Potential for azotemia.

• Regulatory Mechanisms:

  • Renal Autoregulation: Nephrons adjust blood flow and GFR independently.

  • Sympathetic Control: Reduces GFR during stress/exercise.

  • Hormonal Control (Renin-Angiotensin System): Responds to decreased blood pressure.

Nephron Structure and Function

Nephrons (Slides 23.18 - 23.28)

• Types of Nephrons:

  • Juxtamedullary Nephrons: Long loops vital for osmotic gradient maintenance.

  • Cortical Nephrons: Short loops, more numerous.

• Each nephron comprises:

  • Renal corpuscle: filters blood plasma.

  • Renal tubule: processes filtrate into urine.

Renal Tubule Segments

• Proximal Convoluted Tubule (PCT): Major site for reabsorption and secretion, substantial ATP use.

• Nephron Loop (Loop of Henle): Creates osmotic gradient for urine concentration.

• Distal Convoluted Tubule (DCT): Final adjustments to urine composition.

Collecting Duct Function (Slides 23.71 - 23.73)

• Concentrates urine through water reabsorption..

• Regulated by hormones such as ADH and aldosterone.

Urine and Renal Function Tests

Urinalysis & Urine Composition

• Appearance: Varies from clear to amber; cloudiness implies potential infection.

• Density and pH: Normal ranges influence diagnostic interpretation.

Abnormal Findings in Urine

• Presence of Glucose, Proteins, or Blood: Suggestive of various pathophysiological conditions.

Measuring Renal Function

• GFR measured to assess kidney function; best methods involve substances like inulin (non-reabsorbed).

Ureters, Bladder, and Urethra

Ureters and Bladder Structure

• Ureters: Muscular tubes with flap valves to prevent backflow.

• Bladder: Muscular sac with smooth muscle layers for urine storage and expulsion.

Urethral Anatomy

• Male Urethra: Long and divided into sections (prostatic, membranous, spongy).

• Female Urethra: Short and anterior to the vagina.

Kidney Stones and Urinary Tract Infections

Kidney Stones

Causes

• Hypercalcemia, dehydration, pH imbalances, frequent urinary tract infections, stones, or an enlarged prostate causing urine retention

Formed from various substances; can obstruct urinary flow.

Treatments

• Treatments vary from medication to surgical interventions.

• Large stones might block the renal pelvis or the ureter and can cause pressure buildup in the kidney which destroys nephrons, leading to kidney damage and potential loss of function if not addressed promptly.

• Prevention strategies include staying well-hydrated, maintaining a balanced diet, and avoiding excessive salt and oxalate intake.

Urinary Tract Infections (UTI)

• Common infection type, especially in females, with varying degrees of severity.