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MODULE 19: THE URINARY SYSTEM
PART 3 OF 7
Stina’s quantified urine protein climbs over months from a trace into the heavy, nephrotic range — a leak pointing squarely at the glomerular filtration barrier this page dissects.
Slide 1 Transcript
PATIENT CHART
STINA
THIS PART
Age 51
PRESENTING WITH
Albumin-rich Proteinuria
TESTS ORDERED
Serum EPO, Renal Biopsy, 24-hour urineThe liquid waste excreted by the kidneys. protein
DIAGNOSIS
Renal Amyloid depositionThe process of bone matrix formation by osteoblasts.
CHART CLUES
COLLECTED AS YOU GO
Proteinuria History
Incidental Phlebolith
Albumin-Rich Glomerular Proteinuria
Intact Tubular Function Beside a Glomerular Leak
Neurogenic Bladder Rejoins + the EPO Thread
Biopsy-Confirmed Amyloid in Glomeruli
Renal Amyloid Deposition
Put your money down: Three thin layers stand between Stina’s blood and her urine. Which one, failing, lets albumin escape?
The glomerulusA network of capillaries in the nephron where blood filtration occurs. filters by size and by charge, and a healthy barrier keeps essentially all protein in the blood. Commit now: when albuminA plasma protein that helps maintain osmotic pressure and transport substances. starts appearing in Stina’s urine and climbing into the nephrotic range, is the filter being overwhelmed by pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. — or is the barrier itself being physically broken?
Pick the answer you believe now. We’ll come back to it later!
A Million Machines
The nephronThe functional unit of the kidney that filters blood and produces urine. is the kidney’s functional unit, about a million per kidney. Each begins as a tuft of capillariesThe smallest blood vessels where gas, nutrient, and waste exchange occurs between blood and tissues. — the glomerulus — cradled in Bowman’s capsule; together they form the renal corpuscleThe structure in the nephron that consists of the glomerulus and Bowman’s capsule, where filtration, where blood is filtered. The filtrateThe fluid that is filtered from the blood into the nephron and will eventually become urine. then runs a long, looping tubule — proximal convoluted tubuleThe first part of the nephron tubule where most reabsorption of water, ions, and nutrients occurs., loop of Henle diving into the medulla and back, distal convoluted tubuleThe part of the nephron where final adjustments to ion and water balance occur under hormonal contro, and collecting ductA duct in the nephron that collects urine from multiple nephrons and adjusts water reabsorption. — each segment editing the fluid before it becomes urine. Blood enters through an afferent arterioleThe small artery that carries blood into the glomerulus of the nephron. and leaves through a narrower efferent one, and that narrowing pressurizes the sieve.
A Million Filters
The kidney’s functional unit — filter plus tube.
Slide 2 Transcript
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Single Choice: What two parts make up a single nephron?
Corpuscle and Tubule
Where filtering ends and refining begins.
Slide 3 Transcript
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Fill in the Blanks: Order the tubule segmentsThe subdivisions of lung lobes, supplied by tertiary bronchi. from corpuscle to collecting duct.
Three Layers, Size and Charge
What makes the sieve trustworthy is its three-layer filtrationThe process by which fluid moves out of capillaries into surrounding tissues due to hydrostatic pres barrier. Plasma crossing into Bowman’s space passes, in order: the fenestrated capillaryCapillaries with pores (fenestrations) that allow rapid exchange of fluids and small solutes (found endotheliumThe innermost layer of blood vessels, composed of simple squamous epithelial cells, which reduces fr, whose pores stop blood cellsThe basic structural and functional units of life.; the glomerular basement membrane, a dense, negatively charged gel that is the main barrier to protein; and the filtration slits between the foot processes of the podocytesSpecialized cells in the glomerulus that form filtration slits, preventing large molecules from ente, octopus-like cells wrapping the capillaries. Together they filter by size and by charge — waterThe universal solvent essential for life. and small moleculesGroups of atoms bonded together. pass, while large, negatively charged proteinsLarge molecules made of amino acids with various functions in the body. like albumin are held back.
Under the Microscope
Reading the renal cortex — bull’s-eyes and brush borders.
Slide 4 Transcript
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Mark the Words: Mark the features that identify the cortex; leave medullary features unmarked.
Two Nephron Types
Shallow cortical versus deepAway from the surface of the body. juxtamedullaryRefers to nephrons or structures located near the boundary between the renal cortex and medulla. loops.
Slide 5 Transcript
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Multiple Choice: Which nephrons conserve the most water, and why?
The Message of the Leak
A healthy barrier keeps essentially all protein in the blood. So when protein appears in Stina’s urine and then climbs into the nephrotic range, the message is unambiguous: this three-layer barrier is failing — and specifically the glomerular basement membrane and podocyte slits, the structures amyloid attacks. The tubule downstream may be perfectly intact; the failure is here, at the filter. The next pages show what the healthy kidney does with the fluid that gets through — and then what was wrecking the barrier itself.
Three Layers
Filtering by size and by charge — albumin is the cutoff.
Slide 6 Transcript
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Drag the Words: Order the three layers a molecule crosses, endothelium to podocyte slit.
The Filtration Forces
One force pushes out; two push back.
Slide 6 Transcript
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Summary: Pick the true statement about net filtration pressure(NFP): The difference between hydrostatic and colloid osmotic pressures, determining whether fluid m and GFR.
When the Sieve Leaks
Stretch the holes and the macaroni slips through.
Slide 7 Transcript
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Multiple Choice: What kind of proteinuria signals a damaged glomerular filter?
FINDING!
Nephrotic-Range, Albumin-Rich Glomerular Proteinuria
Quantified over months, Stina’s protein climbs from a trace into the heavy, nephrotic range, and it is albumin-rich — the fingerprint of a damaged glomerular filtration barrier, not a tubular problem. Chart entry: a glomerular leak localizing the disease to the basement membrane and podocyte slits.
Confirm or refute your bet: Three thin layers stand between Stina’s blood and her urine. Which one, failing, lets albumin escape?
Now that you’ve dissected the three layers, return to the bet. Albumin escaping into the urine, climbing into the nephrotic range, means the barrier is being physically breached at the basement membrane and podocyte slits — not merely over-pressured. Chart entry: albumin-rich glomerular proteinuria pointing straight at the filter.
Slide 7 Transcript
NEXT PART
Filtration only makes raw filtrate — 180 liters a day of it. The kidney would empty Stina’s body in minutes if the tubule didn’t reclaim almost all of it. Next: reabsorptionThe process of fluid moving back into capillaries from surrounding tissues due to colloid osmotic pr and secretionThe process of moving substances from the blood into the nephron tubule to be excreted in urine..
QUICK QUESTIONS
QUICK QUESTIONS
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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 Glomerular Filtration Barrier
19.4 Reabsorption, Secretion, and How Urine Is Made
19.5 Master Regulator: Blood Volume, Pressure, and the Path of Urine
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
- urine
- deposition
- glomerulus
- albumin
- pressure
- nephron
- capillaries
- renal corpuscle
- filtrate
- proximal convoluted tubule
- distal convoluted tubule
- collecting duct
- afferent arteriole
- segments
- filtration
- fenestrated capillary
- endothelium
- cells
- podocytes
- water
- molecules
- proteins
- deep
- juxtamedullary
- net filtration pressure
- reabsorption
- secretion
- development