❤️Chapter 20- Urinary System

🧠Introduction to the Urinary System (pg. 572–573)

• Main Function: Filters and removes waste products from blood (urea (most abundant nitrogenous waste), excess salts, etc.).

  • waste products- urea, creatinine, uric acid, ammonia

• Organs Involved: 2 kidneys, 2 ureters, 1 bladder, 1 urethra.

• Key Point: Helps maintain fluid, electrolyte, and acid–base balance.

• Malfunction can cause uremia (dangerous waste buildup).

Location of the Kidneys (pg. 573)

• Found under the muscles of the back in the retroperitoneal space.

• The right kidney is lower than the left due to liver placement.

• Protected by the lower ribs and a renal fat pad.

🧫Gross Structure of the Kidney (pg. 573–574)

External Anatomy

• Hilum: Entry/exit point for arteries, veins, nerves, and ureter.

• Covered by a fibrous capsule.

Internal Anatomy

Important structures you should recognize from Figure 20-2:

1. Renal cortex – outer layer.

2. Renal medulla – inner layer.

3. Renal pyramids – triangle sections in the medulla; makes most medullary tissue

   1. Renal columns- connective tissue

4. Renal papilla – tip of pyramid; opens into calix, allowing urine to flow into the minor calyces before entering the major calyces.

5. Renal pelvis – collecting area that leads to ureter.

6. Calyx (calyces) – funnel-like areas that collect urine. (the plumbing system)

🔬 Microscopic Structure: The Nephron (pg. 574–575)

Each kidney has over 1 million nephrons!

Nephron components:

A. Renal Corpuscle

1. Glomerular capsule (Bowman capsule) – surrounds the glomerulus.

2. Glomerulus – capillary network where filtration begins, also part of circulatory system

B. Renal Tubule

1. Proximal Convoluted Tubule (PCT) – reabsorbs most of the filtered nutrients.

2. Nephron loop (Loop of Henle) – dips into medulla; has descending and ascending limbs. Important for concentrated or very diluted urine.

3. Distal Convoluted Tubule (DCT) – lead-s from loop to collecting duct.

4. Collecting Duct (CD) – collects from multiple nephrons, sends urine to calyces → renal pelvis → ureter.

🧠 Note the two nephron types:

• Cortical nephrons: mostly in the cortex. makes up 85%

• Juxtamedullary nephrons: loop dips deep into the medulla. important in concentrating urine

💧 Overview of Kidney Function (pg. 576–579)

🔄 Main Functions:

• Maintain homeostasis by adjusting fluid, electrolytes, and acid–base levels.

• Remove wastes (e.g., urea, ammonia, uric acid, and creatinine from the bloodstream through filtration.)

• Regulate blood volume/pressure, electrolytes, and pH.

• Produce erythropoietin (EPO) during low oxygen (stimulates RBC production).

💉 Juxtaglomerular (JG) Apparatus

• JG cells monitor blood pressure.

• When blood pressure or blood volume drops, they secrete renin, starting the renin–angiotensin–aldosterone system (RAAS) to raise BP.

  • constricts blood vessels

• Also involved in secreting EPO when oxygen is low.

🔄 Urine Formation (pg. 577–579)

The nephron forms urine in 3 main steps

1. Filtration – Occurs only in renal corpuscle.

   • Blood pressure forces water/solutes through glomerular-capsular membrane into the capsule.

   • Called glomerular filtrate (~180 L/day) at a rate of 125ml/min

   • glomerulus → bowman capsule

2. Reabsorption – Occurs in tubules, mainly PCT

   • Water (by osmosis), glucose, ions are reclaimed back into blood.

   • 99% of filtrate is reabsorbed!

   • when failed → glycosuria

3. Secretion – Occurs in DCT and CD.

   • Moves substances (e.g., drugs, H⁺, K⁺, NH₄⁺) from blood into tubule.

   • urine → blood

Key Concepts:

• Countercurrent mechanisms: Loop of Henle and surrounding vessels help concentrate urine by making medulla salty (hyperosmotic).

• Transport Maximum (Tm): Max amount of a substance the nephron can reabsorb. If too much (e.g., too much glucose), excess ends up in urine.

• Renal Threshold: Blood level beyond which the nephron cannot reabsorb all of a substance.

💡 Summary of Urine Formation (pg. 579)

📊Table 20-1 – Nephron Function

🧠 Helpful Breakdown:

• Filtration = Blood → Nephron
  Happens ONLY in the glomerulus/capsule.

• Reabsorption = Nephron → Blood
  Major site: PCT (2/3 of all reabsorption happens here!). Water, glucose, ions return to blood.

• Secretion = Blood → Nephron
  Mostly occurs in DCT & CD. Actively removes extra ions (H⁺, K⁺), toxins, and drugs.

Tie This into the Big Picture:

• The PCT is where the bulk of useful substances are reclaimed.

• The Loop of Henle sets up the medullary salt gradient for water reabsorption.

• The DCT & CD fine-tune urine concentration based on hormones like ADH and aldosterone.

• Filtration happens just once—but reabsorption and secretion happen continuously to maintain homeostasis.

💧Regulation of Urine Volume (pg. 580–581)

🔑 Hormones Involved:

1. Antidiuretic Hormone (ADH)

   • Released from: Posterior pituitary

   • Action: Makes collecting ducts permeable to water.

   • Effect: Decreases urine volume by reabsorbing water.

   • “Water-retaining” or “urine-decreasing” hormone.

2. Aldosterone

   • Released from: Adrenal cortex

   • Action: Stimulates tubules to reabsorb sodium → water follows.

   • Effect: Decreases urine volume.

   • “Salt- and water-retaining” hormone.

3. Atrial Natriuretic Hormone (ANH)

   • Released from: Heart’s atrial wall

   • Action: Inhibits ADH/aldosterone → increases sodium and water loss.

   • Effect: Increases urine volume.

   • “Water-losing” or “salt-secreting” hormone.

🔁

Renin–Angiotensin–Aldosterone System (RAAS)

Stimulated by: Low blood pressure or low plasma volume

Sequence:

1. JG cells detect ↓ BP → release renin

2. Renin converts angiotensinogen → angiotensin I

3. ACE converts angiotensin I → angiotensin II → high BP

4. Angiotensin II causes:

   • Vasoconstriction

   • Aldosterone release

5. Aldosterone increases Na⁺/water reabsorption → ↑ blood volume & pressure

🔎Urine Volume Conditions

• Anuria – No urine output

• Oliguria – Low urine output

• Polyuria – Excessive urine output

• pyuria- pus in the urine

• dysuria- painful urination

🚽 Elimination of Urine (Ureters, Bladder, Urethra) (pg. 581–583)

✏ Ureters

• Muscular tubes that move urine from kidneys to bladder

• Use peristalsis to move urine

• Renal colic = pain from kidney stones traveling down ureter

🫙Urinary Bladder

• Located behind pubic symphysis

• Transitional epithelium stretches with filling

• Rugae allow expansion when empty

• Trigone: triangular area with smooth lining (between ureter and urethral openings)

🧻Urethra

• Carries urine out of the body

• Lined with mucous membrane

• Female urethra ≈ 4 cm long (only urine)

• Male urethra ≈ 20 cm long (urine + semen)

💥 Micturition (Urination Process) (pg. 583)

🧠 Controlled by:

• Internal sphincter – involuntary smooth muscle

• External sphincter – voluntary skeletal muscle

📈 Reflex Arc:

• Bladder stretches → spinal reflex triggered → empties bladder unless overridden by brain

• Voiding reflex occurs ~150–300 mL; strong urge ~400 mL

💉Urinary Catheterization

• Insertion of sterile tube into urethra to drain urine

• Used for retention, surgery, infection risk

• Improper technique → risk for cystitis (bladder infection)

🚨 Abnormal Urine Output (pg. 583–584)

• Urinary retention = bladder can’t empty (even though kidneys make urine)

  • treated by urinary catheterization, allowing for drainage of the bladder and relief of discomfort.

• Urinary suppression = kidneys don’t produce urine

• Incontinence Types:

  • Stress – laughing/coughing

  • Urge – strong sudden urge

  • Overflow – bladder doesn’t empty completely

    • urinary retention and over distended bladder

      • men with enlarged prostate gland

  • Reflex – from neurological damage (e.g., spinal cord injury)

    • common in nervous system; stroke, parkinsonism, or spinal cord injury

Urinalysis (pg. 584–585)

🧪 Includes:

• Routine urinalysis – color, pH, odor, specific gravity

• Microscopic urinalysis – WBCs, bacteria, casts, crystals

⚖ Table 20-2 – Characteristics of Urine

Compounds in Normal Urine:

• Na⁺, Cl⁻, K⁺

• Urea, creatinine, uric acid

• Urochrome (yellow pigment from bilirubin metabolism)

🔬Proteinuria After Exercise

Proteinuria is the presence of plasma proteins—especially albumin—in urine. Normally, proteins are too large to pass through the nephron’s filtration membrane. However:

• After intense exercise, some temporary proteinuria can occur, even in healthy individuals.

• This postexercise proteinuria is not necessarily due to kidney damage.

• One theory is that hormonal changes during exercise increase permeability of the nephron’s filter.

• It typically resolves shortly after exercise and is considered acceptable unless persistent.

💡 Key Concept: While protein in the urine usually indicates kidney disease, short-term proteinuria after exercise can be normal and not a sign of pathology.

💢 Renal and Urinary Conditions

These are problems that disrupt the normal flow or function of the urinary system. Some are life-threatening, while others are chronic or obstructive.

🚫Obstructive Conditions

These block normal urine flow, causing urine backup and damaging the kidney.

Hydronephrosis

• Swelling of renal pelvis and calyces from urine buildup.

• Caused by stones, tumors, inflammation, or structural problems.

• If untreated, leads to permanent kidney damage.

Renal Calculi (Kidney Stones)

• Made of crystallized minerals (e.g., calcium, uric acid).

• Staghorn calculi are large and branched stones.

• Can cause renal colic—severe pain due to rhythmic ureter contractions.

• Small stones pass in urine; large stones may block flow and need removal

🦠Tumors

• Kidney and bladder tumors can block urine.

• Most kidney tumors are renal cell carcinomas (often in 1 kidney).

• Bladder cancers occur nearly as often.

• Can cause hematuria (blood in urine), pain, and urinary blockage.

• Diagnosed via cystoscopy—a procedure using a scope through the urethra.

📊 Clinical Application:

Removal of Kidney Stones with Ultrasound

• 1 in 1,000 people in the U.S. gets kidney stones.

• Ultrasound technique = lithotripsy.

• Breaks stones into fragments without surgery.

• Less risk, less pain, and faster recovery.

🧫

Urinalysis

A lab test that checks:

• Physical properties: color, clarity, smell.

• Chemical properties: pH, glucose, proteins.

• Microscopic elements: cells, bacteria, crystals.

Proteinuria detected here can suggest kidney damage but must be interpreted carefully (as above).

🧪 Health & Well-Being Tip Summary

• Proteinuria is not always bad.

• Can result from exercise, not necessarily disease.

• Must differentiate between transient and pathologic proteinuria.

🌡 Urinary Tract Infections (UTIs)

Most UTIs are caused by gram-negative bacteria, especially E. coli.

• 🦠Common Types of UTIs

  • ➤Urethritis

    • Inflammation of the urethra.

    • Often caused by STIs like gonorrhea or chlamydia.

    • Infant boys more likely to get it than older boys/men.

  • ➤Cystitis

    • Bladder infection

    • Common in women due to shorter urethra

    • Causes: Bacteria, stones, tumors

    • Symptoms: Pelvic pain, urgency, dysuria (painful urination), hematuria

    • Can become ulcerated or spread to kidneys if untreated

  • ➤Urethral Syndrome (nonbacterial cystitis)

    • Most common in young women

    • Symptoms: Dysuria, frequency, no bacteria in urine

    • Possibly autoimmune, related to lupus

  • ➤Overactive Bladder

    • Frequent urination of small amounts

    • Involves urgency, dysuria

    • Treated with nervous system drugs

  • ➤ Interstitial Cystitis

    • Chronic bladder pain without infection

    • Treated with bladder irrigation and drugs to expand capacity

🧬 Pyelonephritis

• Type of nephritis (inflammation of the kidney)

  • renal pelvis nephritis

• Usually caused by bacterial infection (can also be fungal or viral)

• 🧯Acute Pyelonephritis

  • Sudden onset: Fever, flank pain, nausea, urgency

  • Bacteria enter via urethra or bloodstream

• 🕰 Chronic Pyelonephritis

  • Long-term damage

  • May be from autoimmune cause

  • Often asymptomatic early, but leads to scarring & renal failure

• 🧫 Glomerular Conditions

  • 🔥Glomerulonephritis

    • Inflammation of glomeruli

    • Caused by autoimmunity, infection, or heredity

    • Damages filtration membrane → leads to proteinuria, hematuria

    • ACUTE → DELAYED IMMUNE RESPONSE TO A STRETOCOCCAL IN

    • CHRONIC→ LEADS TO RENAL FAILURE

💧 Nephrotic Syndrome

Collection of signs from glomerular damage:

1. Proteinuria – Albumin leaks into urine

2. Hypoalbuminemia – ↓ Albumin in blood

3. Edema – Water shifts into tissues due to low osmotic pressure

🧠 Albumin: Most abundant plasma protein; keeps water in vessels

🛑 Kidney Failure

• 🔴Acute Renal Failure (ARF)

  • Sudden ↓ in kidney function

  • Causes: Severe infection, glomerulonephritis, hypotension, hemorrhage, severe burns, obstruction of the lower urinary tract

  • Symptoms: Oliguria, high BUN (blood urea nitrogen)

  • Treat the cause → kidney function may fully recover

• 🟡Chronic Renal Failure (CRF)

  • Slow, irreversible decline in kidney function

  • Caused by: Diabetes, hypertension, glomerulonephritis, PKD

  • Progresses in stages → leads to uremia

• 🔴Stages of Chronic Renal Failure

  • 📊 Refer to Figure 20–16 (GFR & BUN changes):

  1. Stage 1: Compensated

     • Nephrons enlarge to take over lost ones

     • Function preserved for years

  2. Stage 2: Renal Insufficiency

     • Kidneys can’t keep up

     • BUN rises, kidneys can’t concentrate urine

     • Polyuria and dehydration may occur

  3. Stage 3: Uremia

     • Massive nephron loss

     • Waste buildup in blood

     • Requires dialysis or transplant

🧬 Polycystic Kidney Disease (PKD)

• Inherited; appears ~40 y/o

• Kidneys fill with fluid-filled cysts

• S/S: Flank pain, hematuria

• Cysts grow → kidney tissue destroyed → renal failure