The nephron and urea
| English | Chinese | Pinyin |
|---|---|---|
| nephrons | 肾单位 | shèn dān wèi |
| ultrafiltration | 超滤 | chāo lǜ |
| selective reabsorption | 选择性重吸收 | xuǎn zé xìng zhòng xī shōu |
| osmoregulation | 渗透调节 | shèn tòu tiáo jié |
Inside the kidney's filter
- Each kidney contains about a million tiny filtering units called nephrons 肾单位.
- They clean the blood, keep what's useful, and remove what's not.
During ultrafiltration in the nephron, which stays in the blood?
Large things (cells, proteins) are not filtered out.
The tiny filtering unit of the kidney is the ______.
Each kidney has about a million nephrons.
Filtration
- High blood pressure forces small molecules (water, glucose, salts, urea) out of the blood — ultrafiltration 超滤.
- Big things (blood cells, proteins) stay in the blood.
A nephron filters the blood, then reabsorbs the useful substances; what is left is urine
The nephron at work
Each nephron filters the blood, then takes back what the body needs — what is left becomes urine.
How much glucose is normally reabsorbed back into the blood?
Glucose is useful, so all of it is reabsorbed.
Selective reabsorption returns useful substances from the nephron to the blood.
Glucose and needed water are reabsorbed.
Reabsorption
- Useful substances are taken back into the blood — selective reabsorption 选择性重吸收.
- All the glucose, and as much water as the body needs, are reabsorbed.
The liver makes urea from excess amino acids; the kidneys excrete it
Urine is mainly made of:
Useful substances are reabsorbed; waste forms urine.
What's left is urine
- What remains — urea, excess water and salts — becomes urine.
- The amount of water reabsorbed adjusts to keep the body's water balance right (osmoregulation 渗透调节).
Worked example. Glucose is filtered out of the blood at the nephron, but it's useful — so all of it is reabsorbed. Finding glucose in someone's urine can be a sign of diabetes.
You've got it
- the nephron filters blood: ultrafiltration pushes out small molecules, keeps cells/proteins
- selective reabsorption returns useful substances (all glucose + needed water)
- what's left (urea, excess water/salts) is urine