Urinary system

🧠 P1 – General Functions of Urinary System

🔹 Big Picture (Homeostasis)

  • All systems work together:

    • Cardiovascular → transport (O₂, CO₂, nutrients, waste)

    • Respiratory → O₂ in, CO₂ out

    • Digestive → nutrients in

    • Urinary → waste out

👉 Cells need:

  • O₂ + nutrients → ATP

  • Produce:

  • CO₂ + metabolic waste → removed by urinary system

🔹 Key Functions of Urinary System

  • Filters blood

  • Removes:

    • metabolic waste

    • drugs/toxins

  • Conserves:

    • nutrients

  • Maintains:

    • homeostasis

🧠 P2 & P3 – Gross Anatomy

🔹 Organs

  • Kidneys

  • Ureters

  • Bladder

  • Urethra

🔹 Kidney Location

  • Retroperitoneal

  • Surrounded by:

    • Fibrous capsule

    • Perinephric fat

    • Renal fascia

🔹 Internal Structure

  • Cortex (outer)

  • Medulla (inner)

  • Renal pyramids

🔹 Urine Flow (VERY TESTABLE)

  1. Renal papilla

  2. Minor calyx

  3. Major calyx

  4. Renal pelvis

  5. Ureter

🧠 P2 – Nephrons (MOST IMPORTANT)

🔹 Definition

  • Functional unit of kidney

  • Millions per kidney

🔹 Types

  • Cortical nephron

  • Juxtamedullary nephron

🔹 Structure Flow

  1. Renal corpuscle (filtration)

  2. PCT

  3. Loop of Henle

  4. DCT

  5. Collecting duct

🔹 Renal Corpuscle

  • Afferent arteriole (in)

  • Glomerulus

  • Efferent arteriole (out)

  • Capsular space

🔹 Filtration Membrane

  • Fenestrated capillaries

  • Basement membrane

  • Podocytes

🧠 P4 – Urine Formation

🔹 3 Processes

  1. Filtration (glomerulus)

  2. Reabsorption (back to blood)

  3. Secretion (into tubule)

🔹 Substance Trends

Substance

Blood

Filtrate

Urine

Glucose

High

High

Low

Protein

High

None

None

Urea

Low

Low

High

🔥 Clinical

  • Glucose in urine → diabetes

  • Protein in urine → filtration damage

  • Urea in blood → kidney failure

🔹 GFR (VERY TESTABLE)

Equation:

NFP = GHP – (CHP + BCOP)

Forces:

  • GHP → pushes OUT

  • CHP → pushes IN

  • BCOP → pulls IN

🔥 Effects:

  • ↑ GHP → ↑ GFR

  • ↑ BCOP → ↓ GFR

  • ↑ CHP → ↓ GFR

🧠 P5 – JGA + BP Regulation

🔹 JGA Components

  • Macula densa → senses NaCl

  • Granular cells → release renin

  • Mesangial cells

🔹 Low BP / Low NaCl

→ activates RAAS:

  • Renin → Angiotensin II

  • ↑ Aldosterone

  • ↑ ADH

  • ↑ Thirst

  • ↑ Vasoconstriction

🔥 KEY:

  • Aldosterone = Na⁺ + water retention

  • Water follows Na⁺

🧠 Q1 – Fluid Compartments

🔹 Total Body Water

  • ~42 L

🔹 Compartments

  • ICF (inside cells)

  • ECF (outside cells)

🔹 ECF Breakdown

  • Interstitial fluid

  • Plasma

🔹 Barriers

  • Cell membrane → ICF vs ECF

  • Capillary wall → plasma vs IF

🔹 Movement

  • Osmosis

  • Diffusion

  • Aquaporins

🧠 Q2 – Osmolarity

🔹 Osmolarity = solute concentration

🔹 Tonicity

  • Isotonic → no change

  • Hypertonic → cells shrink

  • Hypotonic → cells swell

🔥 KEY:

Water moves toward higher solute

🧠 Q4 – Potassium Balance

🔹 Distribution

  • 98% in ICF

🔹 Regulation

  • Aldosterone:

    • ↑ Na⁺ reabsorption

    • ↑ K⁺ secretion

🔹 Clinical

  • Hyperkalemia → arrhythmias

  • Hypokalemia → muscle dysfunction

🧠 Q5 – Acid-Base

🔹 Normal pH

  • 7.35 – 7.45

🔹 CO₂ Relationship

  • ↑ CO₂ → ↑ H⁺ → ↓ pH (acidic)

  • ↓ CO₂ → ↓ H⁺ → ↑ pH

🔹 Buffer Systems

  • Bicarbonate (ECF)

  • Phosphate (ICF)

  • Protein buffers

  • Ammonia (kidney)