Nephrons

What is the urinary system and why do we even care?

Think of your body like a city. Every building (cell) makes waste — and if you didn’t take out the trash, everything would fall apart.
👉 The urinary system is your body’s garbage collection + water balance + pH control system.

What’s in this system?

Part	What it does	Analogy
Kidneys	Main filter for blood	Giant water filter with sensors
Ureters	Tubes from kidneys to bladder	Water slide
Bladder	Holds urine	Storage tank
Urethra	Pee exit	Exit pipe
Sphincter	Muscle that controls pee	Tap valve or clamp

🏋‍♂️ THE KIDNEYS

• Your kidneys are the size of your fist and weigh about 150g each

• They filter 200 liters of blood every day 🩸💧

• They hold 25% of all your blood at once — crazy right?

🧠 Their job is to:

• Filter waste

• Control how much water you keep or lose

• Keep blood pH balanced

🧬 METABOLIC WASTE TABLE

Waste	Where it comes from	How you get rid of it
Ammonia	Liver breaks down protein (deamination)	Kidney pee
Urea	2 ammonia + CO₂ = urea (less toxic)	Kidney pee
Uric acid	Breakdown of DNA/RNA	Kidney pee
CO₂	Cellular respiration (breathing)	Lungs breathe it out
Lactic acid	When you work out without enough oxygen	Liver breaks it down

🔬 Kidneys mostly handle nitrogen waste (like ammonia, urea, uric acid), and lungs handle carbon waste (like CO₂). The liver helps clean up emergency waste (like lactic acid).

🧪 KIDNEY PARTS

Part	What it does	Analogy
Renal artery	Brings blood into the kidney	Water pipe in
Renal vein	Takes filtered blood out	Clean water out pipe
Renal cortex	Outer layer, has filtering parts	Shell of the avocado
Renal medulla	Inner layer, has loops + ducts	Pit of the avocado (does reabsorption)
Renal pelvis	Funnel that collects urine	Sink drain
Ureter	Tube to bladder	Pipe to tank

🧩 NEPHRON = The Main Unit

🧠 Think of a nephron like a factory assembly line inside the kidney:

• Filters blood

• Reabsorbs stuff you want to keep (like water, salt)

• Gets rid of stuff you don’t (waste, toxins)

Each kidney has about 1 million nephrons. They’re tiny but powerful.

PARTS OF A NEPHRON

1. Afferent Arteriole

• Brings blood INTO the nephron

• Comes from renal artery

🔁 Think of it like the delivery truck pulling up to the filter station

2. Glomerulus

• A round ball of capillaries (tiny blood vessels)

• Site of filtration — high pressure pushes out water, glucose, waste, etc.

💧 Like a high-pressure coffee filter

3. Bowman’s Capsule

• Cup-shaped part around glomerulus

• Catches the filtrate that leaks out (water + small stuff)

☕ Like the coffee pot collecting what passes through the filter

4. Proximal Tubule

• Tube right after Bowman’s

• Reabsorbs good stuff (water, glucose, ions)

🧠 Think of a smart scanner that puts good things back into the blood

5. Loop of Henle

• Long U-shaped section

• Reabsorbs water and salt

• Helps concentrate urine (so you're not peeing pure water)

🚰 Like a water recycling station

6. Distal Tubule

• Connects Loop of Henle to Collecting Duct

• Does secretion (adds extra waste into urine)

🧪 Like someone double-checking and adding last trash items before pickup

7. Collecting Duct

• Gets urine from many nephrons

• Sends it to the renal pelvis

🚽 Like the big pipe that gathers all the garbage bags and sends them out

8. Peritubular Capillaries

• Tiny blood vessels that wrap around the nephron

• Where reabsorbed stuff goes back into your blood

🧃 Like straw tubes sucking nutrients back out of the nephron and into blood

path of blood + urine

Afferent → Glomerulus → Bowman’s → Proximal → Loop → Distal → Collecting Duct → Ureter