64. Physiology - ADH, Water Excretion, Renin-Angiotensin

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Questions and Answers

What is the primary trigger for the secretion of ADH during dehydration?

Decreased solute concentration

Decreased vascular volume

Increased arterial pressure

Increased plasma osmolality (correct)

How does arterial baroreceptor activity influence ADH secretion?

Low volume stimulates ADH secretion (correct)

High pressure causes increased ADH production

Low pressure leads to ADH inhibition

Increased stretch inhibits ADH release (correct)

When plasma osmolality rises above the normal threshold, what happens to ADH levels?

There is no change in ADH secretion

ADH secretion decreases sharply

ADH release is immediately inhibited

ADH secretion is progressively increased (correct)

Which of the following receptors do not respond to increases in plasma volume?

Blood glucose sensors Signup and view all the answers

In the event of significant hemorrhage, what effect will it have on ADH secretion?

ADH levels will drastically increase due to decreased blood volume Signup and view all the answers

What is the relationship between nerve activity and ADH secretion in the heart’s atria?

Decreased nerve activity increases ADH secretion Signup and view all the answers

What is the required percentage change in arterial pressure to initiate non-osmotic ADH stimulation?

10% change Signup and view all the answers

Which of the following accurately describes the mechanism by which increased pressure affects renin secretion?

Increased pressure leads to increased JG cell stretch, which increases intracellular calcium and consequently decreases renin secretion. Signup and view all the answers

What role do sympathetic nerve activities play in the regulation of renin secretion?

Decreased sympathetic nerve activity reduces the activation of beta receptors on JG cells and thus decreases renin secretion. Signup and view all the answers

How does the delivery of NaCl to the macula densa cells influence renin secretion?

Reduced delivery of NaCl to macula densa due to decreased blood pressure increases renin secretion. Signup and view all the answers

Which statement accurately describes the function of renin in the renin-angiotensin-aldosterone system?

Renin catalyzes the conversion of angiotensinogen to angiotensin I. Signup and view all the answers

What is the immediate effect of angiotensin II on the renal system?

Stimulates aldosterone secretion, promoting sodium reabsorption. Signup and view all the answers

What happens to the acetate channels in the collecting duct when ADH levels decrease?

Some AQP2 channels are sloughed out into the urine Signup and view all the answers

In central diabetes insipidus, what is the primary physiological defect?

Lack of ADH secretion from the posterior pituitary Signup and view all the answers

What occurs when AQP2 water channels are activated in the apical membrane?

Urine osmolality increases Signup and view all the answers

What is the physiological effect of drinking excessive amounts of water rapidly after intense exercise?

Stimulation of osmoreceptors in the hypothalamus Signup and view all the answers

What is one consequence of aquaporin 2 channel mutations in nephrogenic diabetes insipidus?

Inability to concentrate urine Signup and view all the answers

How does ADH mainly exert its effects on the kidneys?

By activating V2 receptors on collecting duct cells Signup and view all the answers

What is the result of water resorption through AQP3 and AQP4 channels?

Fluid enters the interstitial space and plasma compartment Signup and view all the answers

Which receptor type is primarily involved in ADH action on the kidneys?

V2 receptors Signup and view all the answers

What does the insertion of AQP2 channels into the apical membrane lead to?

Higher urine osmolality Signup and view all the answers

What can result from excessively rapid water intake after dehydration?

Brain edema Signup and view all the answers

What primary physiological factor decreases ADH secretion when increased?

Plasma osmolality Signup and view all the answers

Which of the following substances is known to inhibit ADH secretion?

Ethanol Signup and view all the answers

Under what condition would you expect the secretion of ADH to increase?

Dehydration Signup and view all the answers

Which receptor type is primarily responsible for sensing arterial pressure and influencing ADH levels?

Baroreceptors in the aortic arch Signup and view all the answers

What effect does hypoxia have on ADH secretion?

It causes ADH release Signup and view all the answers

What physiological change occurs in the kidneys as a result of increased ADH action?

Increased water reabsorption in collecting ducts Signup and view all the answers

Which neurotransmitter is discussed as a stimulant for ADH secretion?

Serotonin Signup and view all the answers

What happens to ADH levels when individuals experience excessive fluid intake?

ADH levels decrease Signup and view all the answers

What is the primary source of angiotensin II in the body?

Liver Signup and view all the answers

Which condition may lead to 'water intoxication' as a result of increased ADH?

Use of ecstasy Signup and view all the answers

What triggers the secretion of ADH in response to decreased blood pressure?

Decreased stretch in baroreceptors Signup and view all the answers

How does plasma osmolality affect ADH secretion when water content changes?

Decreased water content results in increased ADH release Signup and view all the answers

What is the primary role of baroreceptors in the regulation of ADH secretion?

To sense stretch related to blood pressure and volume Signup and view all the answers

Which of the following statements about ADH is incorrect?

ADH functions to decrease plasma osmolality Signup and view all the answers

What happens to ADH levels when both blood volume and blood pressure increase?

ADH levels decrease Signup and view all the answers

Which brain regions are primarily involved in the synthesis of ADH?

Supraoptic and paraventricular nuclei of the hypothalamus Signup and view all the answers

What effect does increased osmolality have on ADH secretion?

Increases ADH secretion Signup and view all the answers

Which of the following correctly describes the interaction between osmolality and baroreceptor signals on ADH secretion?

Osmolality regulates ADH independently but interactions may occur Signup and view all the answers

How does dehydration affect plasma osmolality and ADH secretion?

Plasma osmolality increases, and ADH secretion increases Signup and view all the answers

Study Notes

Learning Objectives

Distal tubule and collecting duct function, emphasizing water handling
- Vasopressin (ADH) role: source, location, characteristics, osmotic/non-osmotic forces influencing release, cellular mechanisms, role in water reabsorption (aquaporin 2)
- Principal cell identification and function in urinary concentration and dilution
- Collecting duct function in conjunction with the medullary gradient (loop of Henle)
- Range of urinary osmolalities in adults
Juxtaglomerular apparatus and renin-angiotensin-aldosterone system
- Components of the JGA, anatomic location, and function
- Components of the renin-angiotensin-aldosterone system, locations of enzymes/factors, and roles of components like angiotensin II and aldosterone in renal sodium and water handling
- Factors stimulating or inhibiting renin secretion
Integrating ADH, Ang II, and other neurohormones in a concerted renal response to challenges like hemorrhage.

Vasopressin (ADH)

Synthesized in hypothalamic neurons, released by posterior pituitary
Regulated by osmolality, pressure/volume, and neurotransmitters
Also known as arginine vasopressin (AVP)
Plasma osmolality increases when water evaporates and solutes remain; decreased water content increases plasma osmolality and ADH secretion
When water content is high, plasma osmolality decreases and ADH secretion decreases.
Baroreceptors (arterial and venous) sense pressure (stretch) and inhibit ADH secretion at normal pressure.
Low pressures/low blood volume stimulate ADH release.

Osmolarity Control

Normal plasma osmolality is ~285 mOsm/kg H₂O
ADH release progressively increases when plasma osmolality increases by 1%, and a substantial change (~10-20%) in blood volume/pressure is needed for baroreceptor-driven ADH release.

Other Stimuli for ADH Secretion

Hormones, neurotransmitters, and drugs (e.g., angiotensin II, nicotine, ethanol, catecholamines, endothelin, prostaglandins, dopamine, nitric oxide, serotonin, cannabanoids)
Hypoxia, low pO2, and hypercarbia (high pCO2)

ADH Action in the Kidney

ADH acts on V2 receptors on basolateral membranes
cAMP pathway activates protein kinase A, which phosphorylates aquaporin 2 (AQP2).
AQP2 insertion in the apical membrane allows water reabsorption, concentrating urine
ADH reduction causes AQP2 removal from the apical membrane.

Diabetes Insipidus

Characterized by copious urine output and low urine osmolality.
Can be central (lack of ADH secretion) or nephrogenic (ADH receptors or AQP2 channels defective)
Symptoms include extreme thirst and excessive urination.

Renin-Angiotensin-Aldosterone System (RAAS)

Juxtaglomerular apparatus (JGA)
- Macula densa cells sense NaCl delivery and trigger feedback to granular cells.
- Extraglomerular mesangial cells transduce signals.
- Granular cells (JG cells) secrete renin.
Three factors regulating renin secretion: perfusion pressure (stretch), sympathetic nerve activity, and NaCl delivery to the macula densa
Renin-catalyzes the conversion of angiotensinogen into angiotensin I
ACE converts angiotensin I to angiotensin II (Ang II)
Ang II: constricts blood vessels, stimulates aldosterone secretion, influences brain sites, etc.
Aldosterone acts on principal cells to increase Na reabsorption

Hemorrhagic Shock

Severe drop in blood pressure and volume trigger a neurohormonal response:
- Increased renin release.
- Increased ADH secretion.
- Vasoconstriction to maintain blood pressure; Reduced GFR.

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Description

Explore the intricate functions of the distal tubule and collecting duct in water handling, focusing on the role of vasopressin (ADH) and its impact on urinary concentration. This quiz covers the juxtaglomerular apparatus and the renin-angiotensin-aldosterone system, including the integration of neurohormones during physiological challenges. Test your understanding of these essential renal processes.