The Renin-Angiotensin-Aldosterone System (RAAS)
作用機制：
血管收縮素原(angiotensinogen) --(腎素(酶))–> 血管收縮素
- 近腎小球細胞分泌腎素如果：
- 近腎小球細胞偵測到血壓下降
- 緻密班偵測
濃度下降
血管收縮素依作用位置的反應：
- 一級反應
- 下視丘->口渴
- 腎上腺皮質->醛固酮分泌
- 近曲小管->
再吸收 - 腦垂腺後葉->(下視丘產生)釋出血管加壓素(Vasopressin)/抗利尿激素(Antidiuretic Hormone, ADH)分泌
- 血管收縮
- 交感神經作用
- 二級反應
- 水(血量)保存
- 喝水
再吸收(遠曲小管) - 抗利尿激素增加水的再吸收(遠曲小管/集尿管)
- 血壓回升
->恢復恆定
當滲透壓增加
- 受到神經與激素的控制
- 滲透壓增加->刺激下視丘滲透壓受器->口渴感(開源)
- 滲透壓增加->刺激下視丘滲透壓受器->腦垂腺後葉釋出抗利尿激素->增加遠曲小管/集尿管水的通透性(增加水通道蛋白的數量)->增加水分在腎臟的再吸收->排出濃尿
- 酒精->抑制ADH分泌->尿量增加->輕微脫水->刺激下視丘滲透壓受器->口渴感
腎結構
Per nephron
juxtaglomerular apparatus
JG cells (juxtaglomerular cells) store and secrete renin
- Renin is an enzyme that converts angiotensinogen -> angiotensin I
- Angiotensin I is converted to angiotensin II by angiotensin-converting enzyme (ACE) in the lungs
Angiotensin II
Direct effects
- Vasoconstriction
- Increase blood pressure
- At glomerulus
- Constrict the efferent arteriole(入球小動脈)
- Increase gfr and filtration pressure
- Proximal convoluted tubule
- Stimulate the sodium-hydrogen exchanger -> increase Na+ reabsorption/ H+ secretion -> more HCO3- reabsorption
Indirect effects
- Stimulate the adrenal cortex to secrete aldosterone
- Increase Na+ reabsorption/Potassium secretion(Principle cells)
- Increase ATPase activity/H+ secretion(alpha-intercalated cells)
- Stimulate the anti-diuretic hormone (ADH) secretion
- Increase water reabsorption
- Stimulate the hypothalamus to increase thirst
Overall effects
RAAS:
- Arterial pressure increase
- GFR increase and filtration pressure increase
- Na+/H2O reabsorption increase
- K+ secretion increase
- Contraction of alkalosis
Stimulated by:
- Low arterial pressure
Fast: Constrict -> increase pressure
Slow: Reabsorbs sodium and water -> increase blood volume -> increase pressure - Low NaCl delivery to macula densa
- Increased sympathetic tone
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