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The Urinary System · Chapter 4 of 7
Filtration is deliberately blind and wasteful; the tubule does the sorting. This chapter reads the tubule under the microscope segment by segment, follows what each one reclaims and dumps, works renal clearance and transport maximum, and sets Stina’s chemistries beside Mr. Wu’s to prove where each kidney was failing.
The question you will answer
Her albuminA plasma protein that helps maintain osmotic pressure and transport substances. pours out while her glucoseA simple sugar that is the main source of energy for cells., electrolytes and creatinine hold. Are her tubules failing too, or are they the proof the failure is upstream?
Opener · The Pack-Rat Tubule · about 2¾ minutes
The opener is the same narrated animation you will watch in Scene 2.
Watch the opener first. It sets the question; the chapter answers it.
1
Read the chart
Patient chart · Stina
2025 · age 50
Labs
Glucose negative in urineThe liquid waste excreted by the kidneys.. Serum sodium(Na⁺): Major ECF cation; important for fluid balance, nerve function. 139, potassium(K⁺): Major ICF cation; essential for muscle and nerve function. 4.1, bicarbonate(HCO₃⁻) – A crucial buffer in blood that helps maintain pH balance; formed when carbon dioxide react 24. Creatinine 0.8 mg/dL; estimated GFR normal. Urine specific gravityA measure of urine concentration that compares the density of urine to water. 1.020.
Beside it
24-hour urine protein in the nephrotic range, albumin-rich.
For contrast
Mr. Wu (the site’s case): oliguria 18 mL/h, glucose 200 mg/dL in urine, serum potassium 6.1, BUN 120, creatinine 3.2, specific gravity 1.050, osmolarityA measure of solute concentration in fluid; affects fluid movement between compartments. 2100.
Told
“Your kidney function is normal.” (It was — the part they measured.)
Chart clues this module: 1 · A little protein · 2 · Normal scan · 3 · The barrier · 4 · this chapter
Before you go on · your prediction
Albumin pouring out; glucose, electrolytes and creatinine normal. Her tubules are…
Open the one you lean toward. Nothing is recorded and nothing is revealed — you come back to it at the end.
Failing too — a nephron leaking protein is a nephron dying, top to bottom
Ask what a failing proximalCloser to the point of attachment or origin. tubule spills first, and whether her urine shows it. Mr. Wu is on the same page for a reason.
Intact — the leak is glomerular and the tubule is doing its job perfectly
Ask which labs actually read the tubule (glucose, potassium, bicarbonate, specific gravity) and what “kidney function is normal” measured.
Unknowable without a biopsy — chemistries cannot separate filter from tubule
Renal clearance and transport maximum exist to answer this before a biopsy. Watch for glucose and creatinine.
2
The story
Three short movements: the case, the anatomyThe study of the structure of the human body. and physiologyThe study of how the body functions., then the tie back to Stina. Each links to the scene where you’ll see it move.
I · Kidney function is normal
Her creatinine was 0.8 and her estimated filtrationThe process by which fluid moves out of capillaries into surrounding tissues due to hydrostatic pres rate was normal, so the phrase went on the chart: kidney function is normal. Her glucose was negative in the urine. Her sodium, potassium and bicarbonate held their tight ranges. Her specific gravity was ordinary. And beside those reassuring numbers, a 24-hour collection full of albumin. On the site’s other renal case, Mr. Wu, everything went the other way: almost no urine, glucose spilling, potassium climbing, BUN and creatinine soaring. Two kidneys, two reports, and the difference between them is the whole of this chapter.
See it move: Scene 5 · Two Kidneys, One Page
II · The tubule, segment by segment
Filtration separates by size, not need; the tubule takes back what the body wants. The proximal convoluted tubuleThe first part of the nephron tubule where most reabsorption of water, ions, and nutrients occurs. — simple cuboidal cellsThe basic structural and functional units of life. crowded with villiFinger-like projections in the small intestine that increase surface area for absorption., like the small intestine — reabsorbs sodium, calcium, glucose, amino acids, fatty acids, pretty much anything worth keeping, and secretes almost nothing but hydrogen ionsCharged atoms or molecules.: the pack rat arguing with the glomerulusA network of capillaries in the nephron where blood filtration occurs., “how can you throw this away?” The descending nephronThe functional unit of the kidney that filters blood and produces urine. loop — cuboidal without villi, then simple squamous at the bottom — reabsorbs waterThe universal solvent essential for life. into the vasa rectaCapillaries surrounding the loop of Henle in juxtamedullary nephrons that help maintain the medullar or peritubular capillary, more the deeper it dips, so the filtrateThe fluid that is filtered from the blood into the nephron and will eventually become urine. arrives at the bend concentrated. The ascending loopThe portion of the nephron loop that actively transports sodium and chloride out, making the medulla, thin squamous then thick cuboidal, reclaims sodium with a transporter that carries one sodium, one potassium and two chlorides at once — then hands the potassium back — and has no aquaporins at all, so water cannot follow: the filtrate leaves dilute. The distal convoluted tubuleThe part of the nephron where final adjustments to ion and water balance occur under hormonal contro, wider, cuboidal with fewer villi, is the last chance for everything but water: glucose back, excess potassium out, hydrogen and bicarbonate adjusted, and, under ADH and aldosteroneA hormone that increases sodium and water reabsorption in the kidneys, helping regulate blood pressu, aquaporins and sodium-potassium pumps inserted. The collecting ductA duct in the nephron that collects urine from multiple nephrons and adjusts water reabsorption., widest of all because it serves many nephrons, has principal cells that answer ADH and aldosterone and intercalated cells that secrete hydrogen — but only in trade for a reabsorbed potassium, undoing some of the DCT’s good work — and descends the pyramid to weep urine at the papilla. Alongside reabsorptionThe process of fluid moving back into capillaries from surrounding tissues due to colloid osmotic pr runs secretionThe process of moving substances from the blood into the nephron tubule to be excreted in urine.: the kidney’s second chance to dump the large things — toxins, drugs, hydrogen, potassium — that filtration could not. Renal clearance measures how much plasmaThe liquid component of blood. is cleared of a substance per minute; compare it to GFR and a substance reads as reabsorbed (clearance lower) or secreted (clearance higher). Creatinine estimates GFR but is partly secreted; inulin, from garlic and artichokes, is the honest marker. Transport maximum is the ceiling: below it every filtered glucose molecule is reclaimed, and above it — an entire cheesecake, uncontrolled diabetes, or an SGLT2 inhibitor blocking the transporter — glucose spills and its clearance jumps from zero.
See it move: Scene 1 · The Tubule Under the Microscope · Scene 2 · The Pack-Rat Tubule · Scene 3 · Water Never Moves Itself · Scene 4 · Clearance and the Ceiling
III · Two kidneys, one page
Mr. Wu’s chemistries read like a tubule that has stopped: glucose spilling below its transport maximum, potassium unsecreted, wastes uncleared, water gone to his ankles. Stina’s read like a tubule at work: every reclaimable thing reclaimed, every secretable thing secreted, clearance normal. The only thing wrong with her urine is the one thing the tubule never handles — albumin, which a healthy filter should never have sent it. A competent tubule beside a leaking glomerulus is not a contradiction. It is the localization.
See it move: Scene 5 · Two Kidneys, One Page
3
Watch · explore · think · check
5 scenes. Each one has a short animation or a slide, something to explore, a true/false spot-check of your thinking, and a quick check. Every scene gives you an evidence card for your board.
How to read the scenes
- Animation (dark teal) — a short animated explainer, one idea each
- Slide (dark teal) — a still to study: a micrograph, a diagram or a map
- Explore (purple) — something to push on while you watch
- Game (purple) — a quick challenge
- Think (gold) — reason it out, then spot-check yourself with a few true/false questions; not graded
- Check (gold) — a quick H5P that scores itself
Scene 1 of 5
The Tubule Under the Microscope
Villi, diameter, and two cell shapes.
Slide · a still to study
Tubules at 40×, PAS and H&E
Name the segment
- PCT: simple cuboidal cells with lots of villi, so the lumenThe inside space of a hollow organ or structure. looks fuzzy.
- DCT: cuboidal, with a wider, cleaner lumen and fewer villi.
- Nephron loop: the thick segmentsThe subdivisions of lung lobes, supplied by tertiary bronchi. are cuboidal; the thin segments are simple squamous.
- Collecting duct: the largest circles, with two cell populations, principal and intercalated cells.
Size, villi and cell shape name every segment. The game below tries them on a PAS-stained field from slide 210.
Prefer the full lecture? Anatomy of the Renal Tubule (original video on the site) · histology page: Renal Tubule
Game
Name the circle
Name each tubule from three clues: diameter, villi and cell shape. Then try it on a real slide.
Text description of this game
Step 1: five drawn cross-sections, drawn to the same scale, labelled A to E. A: a medium ring of tall cuboidal cells whose dense villi almost fill a small lumen. B: a slightly larger ring of cuboidal cells with a clean, wide lumen and a sparse fringe. C: a smaller ring of cuboidal cells with no fringe. D: a tiny ring of flat cells. E: the largest ring, cuboidal cells mostly pale with a few darker ones around a very wide lumen. For each, name the segment (PCT, DCT, thick loop, thin loop or collecting duct) and the one clue that decided it. Step 2: seven pins on a real PAS-stained slide from the site, to name as PCT, DCT, nephron loop or collecting duct. Step 3: predict which segment would look most changed on a slide from Mr. Wu.
Think · not graded
The PCT and the small intestine both grow villi. What do the two have in common that makes surface area worth the cost — and what would a PCT without villi leave in your urine?
Spot-check your thinking: true or false?
Check · Flip Cards
Tubule cells on a slide.
Evidence card 1
Add it to your evidence board
Each segment has its own cells for its own job; the slide tells you which is which.
Scene 2 of 5
The Pack-Rat Tubule
How can you throw this away? We need sodium.
Animation · narrated, with captions
The Pack-Rat Tubule
Module 19 · 19.4 · Opener and Scene 2 · 7 scenes · 2¾ minutes · narrated. Press Play to start; the words appear in the caption box under the picture.
Scene 1
Paused
Keyboard: when the picture has focus, Space plays or pauses, the left/right arrow keys move between scenes, and M mutes or unmutes.
Text description and full narration
Seven-scene narrated animation with captions, built on BioRender’s stretched-out nephron and a cuboidal-epithelium figure; drawn outlines, arrows and cards mark each station.
Scene 1 · The pack rat (0:00–0:25)
On screen: A nephron stretched out across the top: glomerulus at the left, the winding proximal tubule, the loop dipping down, the winding distal tubule and the collecting duct at the right. A speech bubble from the tubule: “How can you throw this away? We need sodium! We need glucose!” Chip: “filtration sorts by size, not by need”.
Narration: Filtration is a process that separates things by size, not by need, and in fact, filtration throws away everything small, including things that you might actually want. But the tubule takes all of those things back, and it does so kind of like a pack rat arguing with the glomerulus. How can you throw this away? This is awesome! We need sodium! We need glucose!
Scene 2 · Proximal tubule (0:25–0:55)
On screen: The proximal tubule is outlined in teal, a red capillary runs beneath it, and teal arrows carry things back into the blood. A card: “Proximal convoluted tubule — simple cuboidal cells crowded with villi. Reabsorbs: sodium, glucose, amino acids, fatty acids, calcium, and the water that follows — most of the filtrate. Secretes: almost nothing but hydrogen ions.” An orange arrow carries H⁺ into the tubule.
Narration: The proximal convoluted tubule is where most of that take-back gets done. Its cells are simple, cuboidal, crowded with villi like the lining of the small intestine, and they reabsorb sodium, glucose, amino acids, fatty acids, calcium, and all the water that follows. Most of the filtrate right there, they secrete almost nothing except for hydrogen ions.
Scene 3 · Descending loop (0:55–1:14)
On screen: The descending limb is outlined in blue; blue water arrows leave it into a saltier medulla. Card: “Descending loop — reabsorbs water; the medulla grows saltier as it dips; filtrate arrives at the bend concentrated.”
Narration: The descending loop, it reabsorbs water. The medulla around it grows really salty as the loop dips down into the medulla, and so water leaves, and the filtrate arrives at the bend in the loop, being very concentrated.
Scene 4 · Ascending loop (1:14–1:38)
On screen: The ascending limb is outlined in purple; purple arrows carry salt out. Card: “Ascending loop — one Na⁺ + one K⁺ + two Cl⁻ per transporter, the K⁺ handed back; no aquaporins, so water cannot follow; filtrate leaves dilute.”
Narration: The ascending loop does the reverse. Its transporters carry one sodium and one potassium and two chloride ions at once, and then it kind of like hands the potassium back. And it has no aquaporins at all, so water can't follow the salt. The filtrate leaves the loop very, very dilute.
Scene 5 · Distal tubule (1:38–1:58)
On screen: The distal tubule is outlined in green. Card: “Distal convoluted tubule — the last chance for everything except water: glucose back, excess K⁺ out, H⁺ and HCO₃⁻ adjusted.” Two stamps: ADH and aldosterone.
Narration: The distal convoluted tubule is kind of like the last chance for everything except water. Any glucose still left can come back into the blood. Any excess potassium gets excreted. Hydrogen and bicarbonate are adjusted, and this is where ADH and aldosterone kind of give their orders.
Scene 6 · Collecting duct (1:58–2:25)
On screen: The collecting duct is outlined in gold. Card: “Collecting duct — serves many nephrons, the widest tube on the slide. Principal cells: answer ADH and aldosterone. Intercalated cells: secrete H⁺, only in trade for K⁺.”
Narration: The collecting duct actually serves many nephrons, so it's the widest tube on the slide. Its principal cells answer ADH and aldosterone, like the DCT. Its intercalated cells secrete hydrogen, but only as a trade for potassium, so they kind of like undo some of the DCT's work.
Scene 7 · Secretion — and no station for albumin (2:25–2:48)
On screen: Orange secretion arrows appear along the whole tubule: “secretion: the second chance — toxins, drugs, H⁺, antibiotics, K⁺”. Final line beneath an empty station marker: “No station for albumin.”
Narration: And running alongside all of it is secretion, the kidney's second chance to dump the things filtration missed, toxins, drugs, hydrogen, antibiotics, potassium. Notice what has no station anywhere on this line. Albumin.
Prefer the full lecture? Urine Formation 3: Reabsorption and Secretion (original video on the site)
Game
The recycling plant
Decide what each station pulls back or adds, then shut one down and predict which of Mr. Wu’s numbers appear.
Text description of this game
A conveyor of filtrate runs past five stations: the PCT, the descending loop, the ascending loop, the DCT and the collecting duct. Step 1: for six cargo cards (most of the sodium and all the glucose; water but no salt; salt but no water; a little sodium, fine-tuned by aldosterone; water, only when ADH says so; drugs and hydrogen ions added to the filtrate), choose the station that does it. Step 2: a switch shuts the PCT station. Predict what the urine and blood will show, then run it; a readout lists urine glucose, small proteins, serum potassium, urine volume and serum bicarbonate.
Think · not graded
Secretion exists to dump large things that filtration could not. If the filter has started passing large things on its own, what does that do to the tubule’s job — and can the tubule reclaim albumin?
Spot-check your thinking: true or false?
Check · Single Choice
Which tubule segment does the bulk of reabsorption?
Evidence card 2
Add it to your evidence board
The tubule reclaims the small and dumps the large; it has no station for albumin.
Scene 3 of 5
Water Never Moves Itself
Pump the salt and the water follows — except going up.
Animation · narrated, with captions
Water Never Moves Itself
Module 19 · 19.4 · Scene 3 · 5 scenes · 2 minutes · narrated. Press Play to start; the words appear in the caption box under the picture.
Scene 1
Paused
Keyboard: when the picture has focus, Space plays or pauses, the left/right arrow keys move between scenes, and M mutes or unmutes.
Text description and full narration
Five-scene narrated animation with captions. A drawn nephron loop dips into a medulla shaded darker with depth; BioRender water-channel and water-molecule icons, drawn salt pumps and coloured filtrate show where water and salt move.
Scene 1 · The rule (0:00–0:24)
On screen: Two compartments separated by a membrane. A pump in the membrane moves salt into the right-hand side, and water molecules drift through a water channel after it. Chips: “water is never transported actively”, “no pumps for water — only pumps for solutes”, and finally “water follows salt”.
Narration: Here’s a rule the kidney kind of runs on. Water is never, ever, ever, ever transported actively. The cells of the nephron, they have no pumps for water. What they have are pumps for solutes. And by making one place saltier than another, they kind of decide where the water goes. Water follows salt.
Scene 2 · Down the loop: water leaves (0:24–0:48)
On screen: A nephron loop dipping into the medulla, drawn as a band that grows darker (saltier) toward the bottom. The descending limb carries water channels but no salt pumps; water leaves it into the medulla, and the filtrate inside darkens as it descends. At the bend: “most concentrated”.
Narration: Watch the loop. The medulla around it grows saltier as you get deeper toward the papilla. The descending limb has no salt pumps, but it does have water channels. So as the filtrate dips into that salty medulla, water leaves it. By the time we get to the bend, the filtrate is at its most concentrated.
Scene 3 · Up the loop: salt leaves, water can’t (0:48–1:12)
On screen: On the ascending limb, salt pumps move one Na⁺, one K⁺ and two Cl⁻ out (the K⁺ handed back). The wall has no water channels — crossed-out water — so water cannot follow, and the filtrate inside grows paler as it rises.
Narration: And then the ascending loop turns the rule exactly around. Its cells pump salt out. Remember, one sodium, one potassium, and two chlorides in each transporter with the potassium kind of handed back. And they have no water channels at all. Water cannot follow the salt out in the ascending loop.
Scene 4 · Dilute out, saltier medulla (1:12–1:31)
On screen: Filtrate leaving the top of the loop is paler than the filtrate that entered: “more dilute than when it entered”. The medulla band darkens: “and the medulla it passed through is saltier”. Chip: “the asymmetry is deliberate — the next chapter shows what it sets up”.
Narration: So the filtrate that leaves the top of the loop is way more dilute than the filtrate that entered it. And the medulla, it passed through, is saltier. That asymmetry, it's deliberate. And the next chapter, it will show what that stuff sets up.
Scene 5 · Doors on orders (1:31–1:56)
On screen: A collecting duct beside the loop. An “ADH” tag arrives and water channels (aquaporin doors) appear in the duct wall; water leaves. Text: “no aquaporins, no water”. Final line: “The kidney does not move water. It moves salt, and opens doors.”
Narration: But for now, the last two stations, the distal tubule and the collecting duct, they can reabsorb water. But they can only do it when a hormone, ADH, has told them to insert aquaporins. No aquaporins, no water reabsorption. The kidney does not move water. It moves salt, and it opens doors.
Prefer the full lecture? Water Management (original video on the site)
Explore
The ion ledger
Keep the ledger for one pass through the loop: what crosses each limb, and what the filtrate reads at the bend and the top.
Text description of this explore
An accountant’s ledger beside a drawing of one nephron loop. Step 1: for sodium, potassium, chloride and water, choose whether it leaves through the descending limb, the ascending limb, both or neither. Step 2: predict the filtrate’s concentration at the bend (300, 600 or 1200 mOsm) and at the top of the ascending limb (100, 300 or 600 mOsm), then commit. Step 3: a switch removes the aquaporins from the descending limb by mistake; predict what changes, then run it. A readout lists water and salt movement, the concentration at the bend and the top, and the strength of the medullary gradient.
Think · not graded
The ascending loop pulls out salt and refuses water. Why would a kidney deliberately make its filtrate dilute halfway through — what does that set up downstream?
Spot-check your thinking: true or false?
Check · Drag the Words
Sort the descending and ascending limbs.
Evidence card 3
Add it to your evidence board
Water follows salt; the loop’s asymmetry is deliberate.
Scene 4 of 5
Clearance and the Ceiling
Creatinine, inulin, and an entire cheesecake.
Slide · a still to study
Renal Clearance and Transport Maximum
Clearance
- Renal clearance is the volume of plasma cleared of a substance per minute.
- Compare it with the GFR: lower means the substance is reabsorbed; higher means it is secreted.
- Creatinine estimates the GFR, but a little is secreted, so it reads slightly high.
- Inulin (not insulin; it comes from garlic and artichokes) is filtered and nothing else, so its clearance equals the GFR.
The ceiling
- Transport maximum: the glucose carriersMembrane proteins that transport substances across a cell membrane. top out at about 375 mg a minute.
- Renal thresholdThe minimum voltage needed to trigger an action potential.: the plasma level at which the carriers saturate and glucose first appears in the urine.
- Uncontrolled diabetes pushes the filtered load past the ceiling. An SGLT2 inhibitor blocks the carrier on purpose. GLP-1 drugs keep the load under it.
Stina’s urine glucose was negative and her creatinine was 0.8. Her tubules were keeping up.
Prefer the full lecture? Renal Clearance and Transport Max (original video on the site)
Explore
The cheesecake test
Raise blood glucose slice by slice and predict when glucose reaches the urine. Then try two drugs.
Text description of this explore
A dessert counter beside a blood-glucose gauge and a row of ten glucose transporters in the PCT. A slider sets blood glucose from 80 to 400 mg/dL and a selector sets the drug: none, a GLP-1 agonist or an SGLT2 inhibitor, which blocks most of the transporters. Before each run you predict whether glucose reaches the urine. A readout lists blood glucose, the drug, the spill threshold and whether glucose is in the urine. Step 2 asks which drug causes glycosuria at a normal blood sugar. Step 3 asks whether creatinine or inulin overstates GFR, and why.
Think · not graded
A patient with a very low GFR can still have a nearly normal creatinine clearance. What does that tell you about creatinine — and which patient on this page would it fool?
Spot-check your thinking: true or false?
Check · Multiple Choice
Why does glucose appear in the urine after an entire cheesecake?
Evidence card 4
Add it to your evidence board
Clearance and transport maximum read the tubule’s work without a biopsy.
Scene 5 of 5
Two Kidneys, One Page
Mr. Wu’s tubule stopped; Stina’s never did.
Slide · a still to study
Stina Beside Mr. Wu
Mr. Wu’s blood pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. fell to 45/30 in surgery, and his tubules died. Stina’s values are from her 2025 chart.
Stina (2025) beside Mr. Wu
- Urine volume: Mr. Wu, 18 mL an hour (oliguria).
- Urine glucose: Stina, negative · Mr. Wu, 200 mg/dL.
- Urine specific gravity: Stina, 1.020 · Mr. Wu, 1.050.
- Urine osmolarity: Mr. Wu, 2100 mOsm/L.
- Urine protein: Stina, nephrotic range and albumin-rich.
- Serum sodium: Stina, 139 mEq/L.
- Serum potassium: Stina, 4.1 mEq/L · Mr. Wu, 6.1 mEq/L.
- Serum bicarbonate: Stina, 24 mEq/L.
- Blood pHA measure of hydrogen ion concentration in a solution.: Mr. Wu, 7.20.
- BUN: Mr. Wu, 30 rising to 120 mg/dL.
- Serum creatinine: Stina, 0.8 mg/dL · Mr. Wu, 3.2 mg/dL.
Mr. Wu’s values are from the site’s Urinary Case Study.
Mr. Wu’s numbers read like a tubule that has stopped. Stina’s read like a tubule at work, beside a filter that leaks.
Prefer the full lecture? Renal Clearance and Transport Max (original video on the site)
Explore
The localization desk
Two patients’ abnormal values, one nephron map. Pin each value on the station it blames.
Text description of this explore
A localization desk with two patient charts and a nephron map of five stations: the glomerulus, the PCT, the DCT and collecting duct, the whole tubule, and a station not on the map. Mr. Wu’s values: glucose in urine at a normal blood sugar, potassium 6.1, BUN 120, oliguria. Stina’s values: albumin in the urine, low serum albumin, edema. For each value, choose the station it blames. Step 2 asks which patient had “normal kidney function”, and what that phrase measured.
Think · not graded
Mr. Wu’s urine was ridiculously concentrated and that was bad news. Stina’s specific gravity was ordinary and that was good news. How can the same number mean opposite things — what else do you need beside it?
Spot-check your thinking: true or false?
Check · Fill in the Blanks
Distinguish obligatory from facultative water reabsorption.
Evidence card 5
Add it to your evidence board
Every tubular lab reads normal beside a heavy albumin leak — the failure is upstream.
4
Your evidence board
Every scene gave you an evidence card, and the chart adds more. Sort each card into the column it supports: The tubule is intact; the failure is at the filter, Neither on its own, or The tubule is failing too. Some cards can honestly go in more than one place — that’s allowed, and the feedback tells you which cards decide the case.
5
Your verdict
Time to decide. Look back at your bet, then build your verdict from statements that hold up — no writing needed.
Look back at your prediction
Albumin pouring out; glucose, electrolytes and creatinine normal — her tubules are…
Find the one you chose at the top. Does the evidence support it, refute it, or revise it?
- Failing too — a nephron leaking protein is a nephron dying, top to bottom
- Intact — the leak is glomerular and the tubule is doing its job perfectly
- Unknowable without a biopsy — chemistries cannot separate filter from tubule
Build your verdict · no writing
Choose the statement that holds in each set. The ones you keep become your argument.
6
The finding
Sign · intact tubular function beside a glomerular leak
Normal Kidney Function, Except the Part Nobody Measured
Glucose absent from the urine, potassium and bicarbonate in range, creatinine 0.8 with a normal clearance, an ordinary specific gravity — every reading that comes from the tubule reads as a tubule at work — beside a 24-hour collection full of albumin, the one substance the tubule has no station for. Mr. Wu’s chart shows what a failed tubule looks like; hers is its opposite. Chart entry: a competent tubule beside a leaking glomerulus — the contrast that localizes her disease to the filter, and the reason “kidney function is normal” was true and incomplete.
Next · Chapter 5
Master Regulator, and the Road Out
The kidney is not a drain. It sets your blood volume and pressure through hormones, and it hands its urine to a road of stretchy epithelium and two sphincters — one of which, in Stina, has not listened since a car crash.
Reliable information on rare diseases
NORD · NIH GARD · Orphanet · MedlinePlus Genetics: FMF · FMF & AID Global Association · Autoinflammatory Alliance · Global Genes · Amyloidosis Foundation
Stina has one rare disease. In the United States, about 1 in 10 people live with one of the more than 7,000 known rare diseases. These organizations are where patients, families and clinicians go for trustworthy information.
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All pages for Module 19 — The Urinary System
19.0 Module Overview
19.1 A Little Protein in the Urine
19.2 The Kidney from the Outside In
19.3 The Nephron and the Filtration Barrier
19.4 Reabsorption, Secretion, and How Urine Is Made
19.5 Master Regulator, and the Road Out
19.6 When the Filter Breaks
19.7 Not a Trace, an Alarm
19.8 Conclusion and Assessment
19.9 Evidence Behind the Case
All Modules
- Anatomical Language, Membranes & Homeostasis
- Just Enough Chemistry
- The Cell & Its Transport
- Making Cells & Proteins
- The Integumentary System
- The Skeletal System
- The Muscular System
- Nervous Tissue & the Senses
- The Spinal Cord
- The Brain & the Blood–Brain Barrier
- The Autonomic Nervous System
- Special Senses (in developmentThe process of growth and differentiation.)
- The Endocrine System
- Blood
- The Heart
- Blood Vessels
- The Digestive System
- The Respiratory System
- The Urinary System
- Fluids, Electrolytes & Acid–Base Balance
- The Reproductive System
- The Immune System
List of terms
- albumin
- glucose
- urine
- sodium
- potassium
- bicarbonate
- specific gravity
- osmolarity
- proximal
- anatomy
- physiology
- filtration
- proximal convoluted tubule
- cells
- villi
- ions
- glomerulus
- nephron
- water
- vasa recta
- filtrate
- ascending loop
- distal convoluted tubule
- aldosterone
- collecting duct
- reabsorption
- secretion
- plasma
- lumen
- segments
- carriers
- threshold
- pressure
- pH
- development