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By the end of this section, you will be able to:
  • Explain the mechanism of action of diuretics
  • Explain why the differential permeability or impermeability of specific sections of the nephron tubules is necessary for urine formation

The major hormones influencing total body water are ADH, aldosterone, and ANH. Circumstances that lead to fluid depletion in the body include blood loss and dehydration. Homeostasis requires that volume and osmolarity be preserved. Blood volume is important in maintaining sufficient blood pressure, and there are nonrenal mechanisms involved in its preservation, including vasoconstriction, which can act within seconds of a drop in pressure. Thirst mechanisms are also activated to promote the consumption of water lost through respiration, evaporation, or urination. Hormonal mechanisms are activated to recover volume while maintaining a normal osmotic environment. These mechanisms act principally on the kidney.

Volume-sensing mechanisms

The body cannot directly measure blood volume, but blood pressure can be measured. Blood pressure often reflects blood volume and is measured by baroreceptors in the aorta and carotid sinuses. When blood pressure increases, baroreceptors send more frequent action potentials to the central nervous system, leading to widespread vasodilation. Included in this vasodilation are the afferent arterioles supplying the glomerulus, resulting in increased GFR, and water loss by the kidneys. If pressure decreases, fewer action potentials travel to the central nervous system, resulting in more sympathetic stimulation-producing vasoconstriction, which will result in decreased filtration and GFR, and water loss.

Decreased blood pressure is also sensed by the granular cells in the afferent arteriole of the JGA. In response, the enzyme renin is released. You saw earlier in the chapter that renin activity leads to an almost immediate rise in blood pressure as activated angiotensin II produces vasoconstriction. The rise in pressure is sustained by the aldosterone effects initiated by angiotensin II; this includes an increase in Na + retention and water volume. As an aside, late in the menstrual cycle, progesterone has a modest influence on water retention. Due to its structural similarity to aldosterone, progesterone binds to the aldosterone receptor in the collecting duct of the kidney, causing the same, albeit weaker, effect on Na + and water retention.

Cardiomyocytes of the atria also respond to greater stretch (as blood pressure rises) by secreting ANH. ANH opposes the action of aldosterone by inhibiting the recovery of Na + by the DCT and collecting ducts. More Na + is lost, and as water follows, total blood volume and pressure decline. In low-pressure states, ANH does not seem to have much effect.

ADH is also called vasopressin. Early researchers found that in cases of unusually high secretion of ADH, the hormone caused vasoconstriction (vasopressor activity, hence the name). Only later were its antidiuretic properties identified. Synthetic ADH is still used occasionally to stem life-threatening esophagus bleeding in alcoholics.

Questions & Answers

thank you sooo much bro
Fatima Reply
Fatima hw a u
any one elaborate fr me foramens of the skull and features which they transmit
icant undrestand plz
zahruuzh Reply
try to read I hop you will understand
state and explain 20 radiology uses
what are chemicals in anatomy and physiology?
Mike Reply
what can I do to find it easy for me in anatomy and physiology course
study up on the basics of the periodic chart, learn bones and muscles attachments, and learn muscles. Those take the longest to memorize. After that it should be a little easier.
what are the two types of body cells
Jennifer Reply
what is malnutrition
malnutrition refers to faulty nutrition resulting from malabsorption,poor diet or overeating. Sometimes too these food do not contain all the six food nutrients in their right proportion.
thank you
Will u be malnourished?
What's the difference between radiology and radiology
Nothing! Radiology it means the study or using of radiation in medical science it can be 1.diagnose or treatment diagnosed radiology! x- ray. ultrasound. ct-scan. mammogram. MRI. 2. treatmen- radiation oncology, like Cobalt 60. and nuclear medicine
what is X-ray?
X-ray is type of light that make it possible to see inside any object. as human body
How the nervous system develops
ayiesher Reply
From the cells at the back of an embryo
breifly explain anatomy of thorax
Hadiza Reply
How many region the rib is divided
how many bon of human being
how to study for the skeletal system
and anatomy
I really need sources immediately
I printed out all the different bones. Put them in the see through protective sheaths and got dry erase markers. I could right on them and erase to help me learn to spell the names of markings and bones.
Or go to a book store, Barnes and Noble(doesn't have to be this) and they have coloring books for anatomy. $16. Really helpful.
okay thanks and are what study tools you use to study the materials and get a better understanding
*what are
I prefer diagrams, pictures that lay out each step with the information in each step. For Example: how action potential creates muscles to move. A pictured diagram gives me a better understanding of how each piece plays a role in each step of the process.
Also for basics, such as memorizing vocab. Flash cards are great. Don't become discouraged if you don't get them all right the first times through. The more you go through them, your brain will remember pieces of information from each and help you to pull out the information 😉
okay thanks
what is the functions of the lips in human
Momboi Reply
could I say sensation?
for protection
Lips assist in speech and eating
Too many easy questions. Which bones are the axial and appendicular? What are the abbreviations for TEE, TTE, AED, A-Mode, B-Mode, and LTH? What is the difference between hypothalamus and thalamus? Where is the parathyroid located? How many True Ribs do we have?
Sovilace Reply
Transesophageal echocardiography Transthoracic Echocardiography automated external defibrillator brightnees mode Los Hermanos Taverna
what is anatomy
okello Reply
anatomy is scientific study of body structures and how they relate to each other
Are there other functions of the nucleolus apart from synthesis of RNA and formation of ribosomes
Peninah Reply
plays a role in cell response to stress
what is angle of auscultation
Bryan Reply
Anatomy which is the study of the human body structure has a couple of reasons it is been studied It helps to discover genetic disease cytology And histology which is the study of tissues Physiology is the study of function of the human cells It helps to know how the different body part works Its helps to know how part of the brain works And lastly It gives the essential to understand more about anatomy
Stephen Reply
describe the external features of a spinal cord
okoche Reply
Spinal nerves emerge in pairs, one from each side of the spinal cord along its length. The cervical nerves form a plexus (a complex interwoven network of nerves—nerves converge and branch). The cervical enlargement is a widening in the upper part of the spinal cord (C 4–T 1). Nerves that extend in
Hormones regulate certain target cell responses. These can include which of the following?
Nazareth Reply
describe the external features of spinal cord

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