This lesson explains how the body detects changes in blood pressure and adjusts water and sodium handling to preserve blood volume. It also introduces diuretics, which increase urine output and can be used to lower blood pressure.
The body does not directly measure blood volume. Instead, it uses blood pressure as an indicator because changes in blood volume often change pressure. Baroreceptors in the aorta and carotid sinuses detect pressure changes and send signals to the central nervous system.
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How does the renin–angiotensin–aldosterone response help when blood pressure falls?
Low pressure prompts granular cells in the afferent arteriole to release renin. Angiotensin II causes vasoconstriction and stimulates aldosterone, which promotes sodium retention; water follows sodium and helps restore volume.
What are two effects of ADH when blood volume falls?
ADH causes vasoconstriction and increases water reabsorption by activating aquaporin channels in the collecting ducts.
How do aldosterone and ANH affect sodium balance in opposite ways?
Aldosterone promotes sodium reabsorption in the DCT and collecting ducts. ANH reduces sodium reabsorption there, increasing sodium and water excretion.
How do buffers, the lungs, and kidneys contribute to acid–base regulation?
Buffers bind or release hydrogen ions rapidly. The lungs adjust carbon dioxide over seconds to minutes, while the kidneys regulate acid or base more slowly but with substantial capacity.
How can water-soluble drugs be eliminated by the kidneys?
They may be eliminated through glomerular filtration or tubular secretion, or returned to the blood through tubular reabsorption.
Quiz questions
When blood calcium falls, which set of renal and hormonal responses is associated with parathyroid hormone (PTH)?Answer: More calcium is reabsorbed, more phosphate is excreted, and calcitriol production is stimulated.
How can the lungs help respond to excess acid in the body?Answer: Bicarbonate can be converted to carbon dioxide, which is then exhaled.
Why does the liver convert most ammonia into urea?Answer: Ammonia is extremely toxic, whereas urea is the principal nitrogenous waste in human urine.
Why are large molecules such as heparin, and drugs bound to plasma proteins, not readily removed by glomerular filtration?Answer: They do not readily pass through the glomerular filter.
When aldosterone promotes sodium reabsorption, what happens to potassium handling in the nephron?Answer: The resulting electrical gradient favors potassium secretion into the tubular lumen.
Based on Anatomy and Physiology 2e by J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.