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오늘은 ' 근위세뇨관 [ proximal tubule ] '에 대해 알아보고 정리하겠습니다!
근위세뇨관
[ proximal tubule ]
정의
직경 약 60µm이고, 길이가 전체 세뇨관의 절반을 차지하는 관으로 세뇨관은 전체 길이가 약 4-5cm이며, 보우만캡슐에 직결되는 근위세뇨관은 근위곡세뇨관과 근위직세뇨관으로 나누어진다. 관벽은 한층의 상피세포로 이루어지지만, 그 구조는 소장의 상피세포와 매우 유사하고, 미세융모를 볼 수 있다. 또 세포기저면에 수직으로 미토콘드리아를 볼 수 있다.
이곳에서는 Na와 물의 재흡수가 전체의 2/3가 일어나고 글루고스와 아미노산은 100%, 칼륨은 약 65%, 요소는 50% 인산염은 80%가 일어난다. Na는 수동적으로 Na/K ATPase pump에 의해 일어나며 글루코스는 Na와 함께 cotranspoter에 의해 일어난다.
구조
기능
근위세뇨관 수송체 물질이동 기전
https://www.youtube.com/watch?v=trnTwFi28xg&t=191s
문제
A 47-year-old woman presents to a physician because of vomiting and diarrhea for 2 days. Her symptoms began following a company picnic a few days ago. Initially, she was unable to tolerate any solids or liquids by mouth but now she is able to drink sips of water. She had a mild headache, which was relieved with acetaminophen. The past medical history is unremarkable. She does not take any medications. Her blood pressure is 120/60 mm Hg and her heart rate is 60/min. On examination, the mucous membranes are dry and the eyes are slightly sunken. Where is most of the sodium reabsorbed in this patient’s kidneys?
| A. Collecting duct B. Distal tubule C. Descending limb of the loop of Henle D. Proximal tubule E. Ascending limb of the loop of Henle |
| Explanation: Correct answer D: Sodium uptake by the proximal tubules is obligatory and is unaffected by any changes in the sodium plasma concentration, and it is not under hormonal control. Approximately two-thirds of the filtered sodium is reabsorbed in the proximal tubule first, along with glucose and amino acids (secondary active transport). Sodium is then passively reabsorbed along the electrochemical gradient through sodium channels. Water and chloride follow sodium reabsorption via passive diffusion. The Na+/K+ ATPase pump on the basolateral membrane removes sodium from the tubular epithelial cells to help maintain the necessary gradient. Image: Na+/K+ ATPase pump. By: Phil Schatz. License: CC BY 4.0 Option A: While the collecting duct is only responsible for approximately 3% of normal sodium reabsorption, aldosterone increases the sodium reabsorption rate by the principal cells in this segment. The collecting duct regulates physiological sodium concentration. Option B: The distal tubule contains sodium chloride transporters that actively remove sodium chloride from the tubule against an electrochemical gradient. Normally, approximately 5% of the filtered sodium is reabsorbed in this segment. Option C: The descending limb of the loop of Henle is impermeable to sodium and other solutes. The loop of Henle is responsible for removing water from the tubule and serves as the concentrating segment of the nephron. Option E: The thick ascending limb of the loop of Henle is impermeable to water, and electrolytes are actively removed from the tubule by the Na+/K+/2Cl– (NKCC) cotransporter. The thick ascending limb of the loop of Henle is responsible for removing approximately 25% of sodium, and like the proximal tubule, it is not under hormonal control and is not dependent on plasma concentrations of sodium. Learning objective: Regardless of all other factors, including a dehydrated state, the proximal tubule is responsible for reabsorbing most of the filtered sodium from the renal tubule. |
| Related Videos: Proximal Tubule: Ion Transport06:55 min 0% Complete |
| Book References: First Aid for the USMLE Step 1 (2021, 31st ed): 609 First Aid for the USMLE Step 1 (2020, 30th ed): 585 First Aid for the USMLE Step 1 (2019, 29th ed): 573 First Aid for the USMLE Step 1 (2018, 28th ed): 569 First Aid for the USMLE Step 1 (2017, 27th ed): 555 |
참고자료
https://terms.naver.com/entry.naver?docId=2690835&cid=60261&categoryId=60261
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