Final Exam

Urinary System Study Guide

General Functions & Anatomy

Primary Functions of the Kidneys

The kidneys help maintain homeostasis by:

• Filtering wastes from the blood

• Removing toxins and drugs

• Regulating water balance

• Regulating electrolyte levels (Na⁺, K⁺, Ca²⁺)

• Maintaining blood pH

• Controlling blood pressure through renin

• Stimulating red blood cell production with erythropoietin (EPO)

• Activating vitamin D for calcium absorption

Major Parts of the Urinary System

1. Kidneys – filter blood and form urine

2. Ureters – transport urine to bladder

3. Urinary bladder – stores urine

4. Urethra – carries urine out of body

Main Structures of the Kidney

External Structures

• Renal capsule – protective covering

• Hilum – entry/exit for blood vessels and ureter

Internal Structures

• Renal cortex

  • Outer layer

  • Contains glomeruli and convoluted tubules

• Renal medulla

  • Inner region with renal pyramids

  • Helps concentrate urine

• Renal papilla

  • Drains urine into calyces

• Minor and major calyces

  • Collect urine

• Renal pelvis

  • Funnel-shaped structure leading to ureter

  • Blood Flow Through the Kidneys

    Route of Blood Flow

    Aorta → Renal artery → Segmental artery → Interlobar artery → Arcuate artery → Cortical radiate artery → Afferent arteriole → Glomerulus → Efferent arteriole → Peritubular capillaries/Vasa recta → Veins → Renal vein → Inferior vena cava

    Important Points

    • Afferent arteriole brings blood into glomerulus

    • Efferent arteriole carries blood away

    • Vasa recta helps maintain concentration gradient

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    The Nephron

    Definition

    A nephron is the functional unit of the kidney that filters blood and forms urine.

    Each kidney contains about 1 million nephrons.

1. Renal Corpuscle

Contains:

• Glomerulus – capillary network where filtration occurs

• Glomerular capsule (Bowman’s capsule) – surrounds glomerulus

2. Renal Tubule

Includes:

• Proximal convoluted tubule (PCT)

• Nephron loop (Loop of Henle)

• Distal convoluted tubule (DCT)

3. Collecting Duct

• Receives fluid from many nephrons

• Final site of water reabsorption

• Helps determine urine concentration

Functions of Renal Tubules

Proximal Convoluted Tubule (PCT)

• Reabsorbs:

  • Water

  • Glucose

  • Amino acids

  • Sodium

Loop of Henle

• Descending limb:

  • Water leaves

• Ascending limb:

  • Salt leaves

  • Water cannot follow

Distal Convoluted Tubule (DCT)

• Hormone-regulated ion balance

• Aldosterone increases sodium reabsorption

Collecting Duct

• ADH increases water reabsorption

• Produces concentrated urine

Urine Formation & GFR

Three Stages of Urine Formation

1. Glomerular Filtration

• Blood pressure forces water and small solutes out of blood into capsule

• Creates filtrate

• Proteins and blood cells remain in blood

Factors Affecting Filtration

• Blood pressure

• Capsular pressure

• Osmotic pressure

2. Tubular Reabsorption

• Useful substances return to blood

• Occurs mainly in PCT

Reabsorbed:

• Water

• Glucose

• Electrolytes

• Nutrients

3. Tubular Secretion

• Additional wastes move from blood into tubules

Secreted substances:

• H⁺

• K⁺

• Drugs

• Toxins

Purpose:

• Remove wastes

• Help regulate pH

Glomerular Filtration Rate (GFR)

Definition

GFR = amount of filtrate formed each minute by kidneys

Normal GFR:

• About 125 mL/min

Regulation of GFR

1. Renal Autoregulation

Kidneys adjust blood vessel diameter automatically.

2. Neural Regulation

Sympathetic nerves reduce GFR during stress/blood loss.

3. Hormonal Regulation

• Renin-Angiotensin-Aldosterone System (RAAS) increases blood pressure

• Atrial natriuretic peptide (ANP) lowers blood pressure and increases filtration

Urine Concentration & Characteristics

How Kidneys Produce Dilute or Concentrated Urine

Dilute Urine

• Less ADH released

• Less water reabsorbed

• More water lost in urine

Concentrated Urine

• More ADH released

• More water reabsorbed

• Less water lost

Medullary Osmotic Gradient

Definition

High salt concentration in renal medulla helps pull water out of filtrate.

Countercurrent Mechanism

• Loop of Henle creates gradient

• Vasa recta preserves it

Role of Urea

• Urea diffuses into medulla

• Increases osmotic concentration

• Helps kidneys conserve water

Normal Urine Characteristics

Normal Contents

• Water (95%)

• Urea

• Uric acid

• Creatinine

• Electrolytes

Normal Characteristics

• Clear to pale yellow

• Slight odor

• Sterile

• pH about 6

• Specific gravity: 1.001–1.035

Abnormal Findings

• Glucose → diabetes mellitus

• Protein → kidney damage

• Blood → infection or injury

• Ketones → starvation/diabetes

Urine Storage & Elimination

Ureters

• Muscular tubes carrying urine to bladder

• Use peristalsis to move urine

• Lined with transitional epithelium

Urinary Bladder

Functions

• Stores urine temporarily

Important Structures

• Trigone – triangular region between ureter openings and urethra

• Detrusor muscle – smooth muscle that contracts during urination

Urethra

Female Urethra

• Shorter

• Higher risk of UTIs

Male Urethra

• Longer

• Passes through prostate and penis

Micturition (Urination)

Process

1. Bladder fills with urine

2. Stretch receptors activated

3. Spinal cord reflex triggers detrusor contraction

4. Internal urethral sphincter relaxes

5. External urethral sphincter voluntarily relaxes

6. Urine exits body

Key Hormones to Know

Quick Review Questions

1. What are the 3 stages of urine formation?

2. What is the function of the Loop of Henle?

3. What does ADH do?

4. What is GFR?

5. Which nephron structure performs filtration?

6. What is the role of aldosterone?

7. Why is the medullary gradient important?

8. What is the function of the collecting duct?

9. What are normal components of urine?

10. What muscle contracts during urination?