The kidney and the nephron
Introduced| English | Meaning |
|---|---|
| nephron/ˈnefrɒn/ | A microscopic kidney unit that filters blood plasma and modifies the resulting fluid through reabsorption and secretion. |
| cortex/ˈkɔːteks/ | The outer region of an organ, such as the kidney or cerebrum. |
| medulla/ˈmedʌlə/ | The inner region of an organ, such as the kidney region containing loops of Henle and collecting ducts. |
| glomerulus/ˈɡlɒmərjʊləs/ | A network of capillaries in a kidney nephron where blood is filtered into Bowman's capsule. |
| Bowman's capsule/ˈbəʊmənz ˈkæpsjuːl/ | The cup-shaped structure around a kidney glomerulus that receives fluid filtered from its capillaries. |
| ultrafiltration/ˌʊltrəfɪlˈtreɪʃn/ | The pressure-driven separation of water and small solutes from larger molecules across a filtration barrier. |
| selective reabsorption/sɪˈlektɪv riːbˈsɔːpʃn/ | The return of useful substances from kidney filtrate to the blood according to the body's needs. |
| microvilli/ˈmaɪkrəʊvɪlaɪ/ | Tiny projections of a cell's surface that increase its area for absorption or other exchange. |
The body's filter
- The kidney cleans the blood and controls its water content.
- It does this in about a million tiny tubes called nephrons 肾单位.
- Urine is made in two key steps.
The nephron is:
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Each kidney has about a million nephrons; each makes urine by filtration and reabsorption.
Ultrafiltration happens at the ______ — the knot of capillaries inside the Bowman's capsule.
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High blood pressure in the glomerulus forces small molecules out into the capsule.
Kidney and nephron parts
- The kidney has an outer cortex 皮质, an inner medulla 髓质, and a central renal pelvis (collects urine); the ureter carries urine to the bladder.
- Along a nephron: the glomerulus 肾小球 (a knot of capillaries) in the Bowman's capsule 鲍曼囊, then the proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.
A section through the kidney: the outer cortex, inner medulla and central renal pelvis
A nephron: ultrafiltration 超滤 and selective reabsorption 选择性重吸收
Explore the nephron
Tap each part. Filtration happens at the top; the long tubule then reabsorbs what the body needs, leaving urine.
Step 1: Ultrafiltration
- Happens in the Bowman's capsule.
- Blood in the glomerulus is under high pressure, pushing water and small molecules (glucose, ions, urea) out to form the filtrate.
- Blood cells and large proteins are too big to pass, so they stay in the blood.
During ultrafiltration in the Bowman's capsule:
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High pressure forces small molecules into the capsule; blood cells and large proteins are too big to pass.
Match each part of the nephron to its job.
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Filter at the capsule, reabsorb glucose at the proximal tubule, concentrate using the loop, and adjust water at the collecting duct.
During ultrafiltration, blood cells and large proteins are too big to pass into the nephron.
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Only small molecules (water, glucose, ions, urea) are filtered out; cells and proteins stay in the blood.
Step 2: Selective reabsorption
- Happens in the proximal convoluted tubule.
- Useful substances are taken back into the blood — all the glucose, and much of the water and ions.
- The tubule cells have microvilli 微绒毛 (large surface area) and many mitochondria (to power active transport).
In selective reabsorption at the proximal convoluted tubule:
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The proximal tubule reabsorbs all the glucose plus much water and ions back into the blood.
The proximal tubule cells are well suited to reabsorption because they have:
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Microvilli increase the surface area and the many mitochondria provide ATP for active transport.
You've got it
- the nephron is the kidney's working unit (~1 million per kidney)
- ultrafiltration (Bowman's capsule): high pressure pushes out small molecules; cells & proteins stay
- selective reabsorption (proximal tubule): all glucose + water + ions taken back
- tubule cells: microvilli (surface area) + mitochondria (active transport)