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Nursing Field Notes / Renal + Fluid · Anatomy & Physiology

Renal A&P 🫘

Renal Anatomy & Physiology — the nephron, top to bottom

NG-263 RENAL + FLUID ADHD-friendly visual edition

The kidneys work like 2 washing machines 🌀 — they wash the blood of waste by filtration, regulate fluid volume by reabsorption, and stimulate red blood cell production by making erythropoietin. Every renal disease on your exam is one of those three jobs breaking.

📄 Simple Nursing original — opens in Drive →

🌀 2 washing machinesFilter waste · balance fluid · build blood. Three jobs, one organ.
🧠 “FRE the PEE”Filtration · Reabsorption · Erythropoietin — plus Hydrogen, Urea, Creatinine.
🧪 GFR over 90>90 mL/min = normal. Creatinine >1.3 = bad kidney.
💧 ADH = “Add Da H₂O”ADH holds water back → less urine, more concentrated.
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ANATOMY

STEP 1 · THE PARTS

You cannot reason about renal failure until you can point to the piece that broke — so learn the map first.

🫘 The kidney, sliced in half — every part labeled

Blood comes in through the renal artery, gets scrubbed in the cortex, the waste water drains down the pyramids into the calyces and renal pelvis, and leaves as urine down the ureter. Cortex filters · medulla concentrates · pelvis collects.

KIDNEY · CORONAL SECTION outside = filter · inside = drain Renal ARTERY — dirty blood IN Renal VEIN — clean blood OUT Renal capsule tough outer wrap CORTEX where nephrons filter · makes EPO MEDULLA concentrates urine Renal pyramid 8–18 per kidney Renal column cortex between pyramids Papilla → MINOR calyx tip of pyramid drips urine in MAJOR calyx → renal PELVIS the collecting funnel HILUM the notch — artery, vein & ureter all pass here URETER → bladder 🔬 1 million NEPHRONS live here
🧠 “Cortex Cleans, Medulla Milks, Pelvis Pours.” Outside filters, the middle squeezes water back, the inside pours what's left into the ureter. Waste always travels outside → in → down.

🔬 The nephron is the functional unit

  • About 1 million nephrons per kidney.
  • Inside each one sits the glomerulus — a network of small blood vessels that filters the blood of waste.
  • Kidneys take about 20–25% of cardiac output — roughly 1,200 mL of blood every minute.
  • They make about 180 L of filtrate a day and give back ~99% of it — only 1–2 L leaves as urine.
🧠 180 in, 1.5 out. The kidney filters a bathtub and hands you back a soda bottle. That's how aggressive reabsorption is.

🩸 Follow the blood — artery to vein

Renal artery (dirty blood in)
▼
Afferent arteriole — Arrives, wide
▼
🫧 GLOMERULUS — filtration happens here
▼
Efferent arteriole — Exits, narrow
▼
Peritubular capillaries & vasa recta
▼
Renal vein (clean blood out)
🧠 A = Afferent = Arrives. E = Efferent = Exits. The exit hose is narrower than the entrance hose — that back-pressure is exactly what squeezes filtrate out.

⭐ The nephron — every segment and the one job it does

HIGH YIELD Learn this and you get diuretics, electrolytes and renal failure for free. Each segment moves a different thing, so each one has its own drug and its own lab.

THE NEPHRON · follow the filtrate ▶ AFFERENT (in · wide) EFFERENT (out · narrow) GLOMERULUS in BOWMAN'S CAPSULE PROXIMAL convoluted tubule 💧 water OUT 🧂 salt OUT (no water) 💧 ADH pulls water back JUXTAGLOMERULAR APPARATUS senses low flow / low BP → releases RENIN → starts RAAS → raises BP 1 · GLOMERULUS — FILTERS Pressure pushes water, Na, K, glucose, urea & creatinine OUT of the blood. RBCs & protein must stay IN. 2 · PROXIMAL TUBULE — TAKES BACK ~65–70% of Na⁺ & water, ALL glucose, amino acids & bicarb. Activates vitamin D. Glucose in urine = blood glucose too high 3 · DESCENDING LOOP — WATER ONLY Permeable to water, not salt. Filtrate gets thicker & more concentrated. 4 · ASCENDING LOOP — SALT ONLY Na-K-2Cl pump; water can't follow. 💊 LOOP DIURETICS work here 5 · DISTAL TUBULE — FINE TUNES Trims Na⁺/Cl⁻; PTH pulls Ca²⁺ back. 💊 THIAZIDE DIURETICS work here 6 · COLLECTING DUCT — LAST CALL ADH opens water channels → water back to blood. Aldosterone: Na⁺ IN, K⁺ OUT. 💊 K⁺-SPARING DIURETICS work here ↓ URINE
🧠 “Pee Down Any Damp Corridor.” Proximal → Descending → Ascending → Distal → Collecting duct. Then hang the drugs on it: Loop on the Ascending, Thiazide on the Distal, Spironolactone on the Collecting duct.

🚰 Where the urine goes once it leaves

1 · KIDNEY makes urine 2 · URETER peristalsis pushes it down 3 · BLADDER urge at ~250 mL · full ~500 mL 4 · URETHRA → out short in females → more UTIs MINIMUM OUTPUT 30 mL/hr or 0.5 mL/kg/hr — below = report
🧠 “Kidney, Ureter, Bladder, Urethra” = KUB — the same three letters as the abdominal X-ray that looks for stones. One acronym, whole plumbing.
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PHYSIOLOGY

STEP 2 · THE JOBS

Three phases make urine — and seven jobs make you alive. Say them out loud.

⭐ Three phases of urine formation HESI

Q: What are the three phases of urine formation? A: Filtration, reabsorption, and secretion.

🩸 BLOOD (capillary side) 🚿 TUBULE (urine side) 1 · FILTRATION blood → tubule 180 L/day pushed out 2 · REABSORPTION tubule → blood 99% given back (water, Na, glucose) 3 · SECRETION blood → tubule last chance dump: K⁺, H⁺, drugs Filtrate that survives all three = URINE 💛
🧠 “Filter it, Fetch it back, Flush the rest.” Three F's, in order. Secretion is the kidney's trash chute — it's how potassium, acid and most drugs actually leave you.

🧠 “FRE the PEE” — the source mnemonic, unpacked

  • F — Filtration of medications & waste
  • R — Reabsorption, run by ADH (Anti-Diuretic Hormone)
  • E — Erythropoietin (stimulates RBC production in bone marrow)

And the three things filtration is supposed to dump:

  • H — Hydrogen ions (too much = high acidity = metabolic acidosis)
  • U — Urea → the BUN (Blood Urea Nitrogen)
  • C — Creatinine (over 1.3 = bad kidney)
🧠 “FRE the PEE — but HUC it out.” Filter, Reabsorb, Erythropoietin. What gets hucked out: Hydrogen, Urea, Creatinine. If they stay in, the labs climb.

⭐ All 7 kidney jobs: A WET BED

  • A — Acid–base balance (dumps H⁺, keeps HCO₃⁻)
  • W — Water balance
  • E — Electrolytes (Na⁺, K⁺, Ca²⁺, PO₄³⁻, Mg²⁺)
  • T — Toxin & drug removal
  • B — Blood pressure control (renin → RAAS)
  • E — Erythropoietin → red blood cells
  • D — vitamin D activation → calcium absorption
🧠 Kidneys fail = “A WET BED.” Acidosis, water overload, high K⁺, drug toxicity, hypertension, anemia, low calcium/bone disease. Every complication of renal failure is one letter of this.

💧 ADH — “Add Da H₂O”

ADH is made in the hypothalamus, stored in the posterior pituitary, and works on the collecting duct. More ADH = more water pulled back into the blood = less urine, darker and more concentrated.

🔺 ADH HIGH SIADH · dehydration · pain · stress water doors OPEN 💧 water back to blood little · dark urine Spec. gravity ↑ 1.030 ↓ urine output ↓ serum sodium 🔻 ADH LOW Diabetes Insipidus · alcohol · diuretics water doors SHUT 💧 water runs straight out tons of pale urine Spec. gravity ↓ 1.003 ↑↑ urine output ↑ serum sodium
🧠 “Add Da H₂O.” ADH adds water to the blood, so it subtracts water from the urine. High ADH = small dark pee; no ADH (DI) = a firehose of clear pee.

🩸 Erythropoietin — why kidney patients are anemic

KIDNEY senses low O₂ EPO 🧪 BONE MARROW NEW RBCs 🩸 No kidney = no EPO = ANEMIA
🧠 EPO = “Every Person's Oxygen.” Dead kidneys make no EPO → no new red cells → chronic anemia, fatigue and pallor even though nothing is bleeding.

📈 Blood pressure: the RAAS chain

⬇️ Low BP / low renal blood flow
▼
RENIN released from the kidney
▼
Angiotensin I → (lungs, ACE) → Angiotensin II
▼
Vasoconstriction + ALDOSTERONE
▼
💧 Na⁺ & water held · K⁺ dumped · BP ↑

Why it matters: a failing kidney thinks it is dry even when the body is drowning, so it keeps firing RAAS — that's why renal patients are hypertensive and fluid-overloaded at the same time.

🧠 “Aldosterone = Save Salt, Sack K⁺.” Sodium in, potassium out. Every ACE inhibitor, ARB and spironolactone question is just this chain being blocked at a different link.

🦴 Vitamin D & calcium — the quiet job

  • The proximal tubule converts vitamin D to its active form (calcitriol).
  • Active vitamin D lets the gut absorb calcium.
  • Failing kidney → no activation → low calcium → parathyroid pulls calcium out of bone.
  • Failing kidney also can't dump phosphate → high phosphate, which drives calcium down further.
🧠 Calcium and phosphate are on a seesaw ⚖️ — one up, the other down. Renal failure sits on the phosphate end, so calcium flies up out of the bones. That's renal bone disease.
🧪

NUMBERS & NURSING

STEP 3 · WHAT THE LABS MEAN

Four numbers tell you how a kidney is doing. Learn the bars, not the paragraphs.

🧪 The four kidney numbers — low · normal · high

ADULT REFERENCE RANGES standard adult values — always confirm your facility's lab sheet GFR · Glomerular Filtration Rate (mL/min) <15 – 59 · KIDNEY DISEASE 60–89 mild ↓ 90 and OVER = NORMAL ✅ Stage 5 / end-stage = GFR under 15 → dialysis territory. GFR is the single best measure of kidney function. CREATININE, serum (mg/dL) — the specific one LOW · low muscle mass 0.6 – 1.2 NORMAL ✅ OVER 1.3 = BAD KIDNEY 🚨 Made by muscle at a steady rate and cleared only by the kidney — so it rises only when the kidney is failing. BUN · Blood Urea Nitrogen (mg/dL) — the sensitive one UNDER 10 · fluid overload 10 – 20 NORMAL ✅ OVER 20 · dry, bleeding, or failing BUN moves with dehydration, high protein, GI bleed and steroids too — so a high BUN with a NORMAL creatinine usually means DRY, not broken. URINE SPECIFIC GRAVITY 1.003 · LIQUIDY BODY 💧 1.005 – 1.030 NORMAL 1.030 · DRY BODY 🏜️ Source range: 1.003–1.030. Low = dilute = overloaded or DI. High = concentrated = dehydrated or SIADH. ⏱️ URINE OUTPUT — keep it at 30 mL/hr or more (0.5 mL/kg/hr). Under 30 mL/hr = report.
🧠 “BUN is a Big Unreliable Number; Creatinine is the Cold hard truth.” If both are up → kidney. If only BUN is up → think dehydration or GI bleed first.

🧪 What each lab is actually telling you

LabNormal (adult)If it's HIGH, think…
GFR>90 mL/minLOW is the bad direction — <60 for 3 months = CKD
Creatinine0.6–1.2 mg/dLKidney damage — >1.3 = bad kidney
BUN10–20 mg/dLDehydration, GI bleed, high protein, kidney
BUN : Creatinine10:1 – 20:1>20:1 = pre-renal (dry) 💧
Potassium3.5–5.0 mEq/LKidney can't excrete K⁺ → cardiac arrest risk 🚨
Urine output≥30 mL/hrLOW is bad — oliguria = kidneys in distress
🧠 Potassium is the killer. Of every renal lab, K⁺ is the one that stops a heart. When a renal question lists five abnormal labs, look at the potassium first.

⏳ Half-life — and why renal patients overdose

Half-life = the time it takes for half of the medication to be eliminated from the body.

100% 50% 25% 12.5% 6.25% drug left in the body · one half-life per bar ▶

Bad kidney = long half-life = drug stacks up. That is why renally-cleared drugs get dose reductions in CKD.

🧠 “Half gone, half stays.” It takes roughly 4–5 half-lives to clear a drug — or to reach steady state on a new one.

🚨 Nephrotoxic — protect the kidney you have

💉Aminoglycosidesgentamicin
🧴Vancomycincheck trough
🩻IV contrast dyehydrate first
💊NSAIDsibuprofen, naproxen
🧪ACE / ARBswatch creatinine + K⁺
🍄Amphotericin B“ampho-terrible”

Never give an NSAID to a client in acute kidney injury — it constricts the afferent arteriole and drops the GFR further.

✅ Do instead: hydrate before and after contrast, check creatinine & GFR before nephrotoxic drugs, monitor strict I&O and daily weights (1 kg = 1 L).

🧠 “A VaNilla Ice cream cone” — Aminoglycosides · Vancomycin · NSAIDs · IV contrast. Four cold hits to the kidney.

✅ Daily weight is the best fluid monitor

  • Same time, same scale, same clothes, after voiding.
  • 1 kg = 1 L = 2.2 lb of fluid.
  • New, sudden, rapid weight gain = fluid retention, not fat.
  • Report >1 kg (2.2 lb) gain in a day, or >2 kg in a week.
🧠 Weight beats I&O. Charts lie, scales don't — a client can drink from the sink, but they can't hide a kilogram.
⚡

QUICK RECALL

SAY IT OUT LOUD
🌀 3 phasesFiltration → Reabsorption → Secretion
🔬 Nephron= functional unit · glomerulus = the filter
🧪 GFR >90 · Cr >1.3normal filter · bad kidney
🛏️ A WET BEDAcid · Water · Electrolytes · Toxins · BP · EPO · vit D
🎯 Cover & check — 6 rapid-fire questions
Q1: Name the three phases of urine formation.
Filtration, reabsorption, and secretion.
Q2: What is the functional unit of the kidney, and what filters inside it?
The nephron — about 1 million per kidney. Inside it the glomerulus, a network of small blood vessels, filters waste out of the blood.
Q3: A normal GFR is what number?
Over 90 mL/min. Under 60 for 3 months = chronic kidney disease; under 15 = end stage.
Q4: BUN is 32 and creatinine is 1.0. Kidney failure or dehydration?
Dehydration (pre-renal). A high BUN with a normal creatinine and a ratio over 20:1 points to volume depletion, not kidney damage.
Q5: What does ADH do, and where?
“Add Da H₂O” — it opens water channels in the collecting duct so water goes back to the blood. Result: less urine, darker urine, higher specific gravity.
Q6: Why is a client with chronic kidney disease anemic?
The damaged kidney stops making erythropoietin, so the bone marrow stops producing red blood cells — anemia with no bleeding.
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STUDY SHEETS

FROM YOUR SAVED SET
The nephron drawn out end to end — filtration at the glomerulus, reabsorption along the tubule, and the six steps from blood in to urine out.
The nephron drawn out end to end — filtration at the glomerulus, reabsorption along the tubule, and the six steps from blood in to urine out. — swipe it sideways if it is cut off, or tap to open it full size.
Kidney anatomy with the A WET BED functions, the terms-to-know table (dysuria through proteinuria), and the four steps of urine formation.
Kidney anatomy with the A WET BED functions, the terms-to-know table (dysuria through proteinuria), and the four steps of urine formation. — swipe it sideways if it is cut off, or tap to open it full size.

Saved study graphics from your own collection. Each one is someone else’s work — check anything clinical against your course materials before you rely on it.