Physiology Ch. 28: Osmolarity Regulation (Adh)

Front 1

Location of osmoreceptors. How are these stimulated?

Back 1

Anterior hypothalamus (AV3V) near the supraoptic nucleus.
Increased osmolarity causes the cells to shrink, causing them to fire an AP to the supraoptic nucleus

Front 2

Where in the kidney do ADH receptors increase water reabsorption?

Back 2

Distal collecting tubules, cortical collecting tubules and medullary collecting ducts.

Front 3

How is ADH released?

Back 3

Stimulation of the magnocellular neurons of the supraoptic and paraventricular nuclei, causes an AP and thus their membrane permeability to increase. Ca2+ enters the cell and ADH stored in secretory vesicles is released into the capillaries of the Posterior Pituitary.

Front 4

Lesions in what region cause multiple deficits in the control of ADH secretion, thirst, sodium appetite, and blood pressure.

Back 4

Anteroventral region of the third ventricle (AV3V)

Front 5

Send nerve signals to the supraoptic nucleus to control their firing and secretion of ADH

Back 5

osmoreceptors of the AV3V

Front 6

Median preoptic nucleus

Back 6

Multiple nerve connections with the two organs, the supraoptic nuclei, and the BP control centers of the medulla

Front 7

Location of median preoptic nucleus

Back 7

Between the subfornical organ and the organum vasculosum of the lamina terminalis

Front 8

Area whose vscular supplies lacks the typical blood-brain barrier. Why is this important?

Back 8

Subfornical organ and the organum vasculosum:
Allows ions and other solutes to pass between the blood and the interstitial fluid, allowing osmoreceptors to react rapidly.

Front 9

How does blood pressure and blood volume effect ADH secretion? Mechanism?

Back 9

Decreased BV and BP increase the release of ADH. This occurs via receptors in the high pressure aortic arch and carotid sinus, and the low pressure cardiac atria that sense the drops. This causes these areas to send Afferent signals through the vagus and glossopharyngeal nerves to the Nuc Solitarius, which relays the signals to the hypothalamus

Front 10

Is ADH secretion more sensitive to osmolarity or decreases in BV?

Back 10

It is much more sensitive to osmolarity. Decreased BV, however, greatly enhances the ADH response to increased osmolarity.

Front 11

How does nausea effect ADH secretion?

Back 11

Increases ADH

Front 12

Drugs that stimulate ADH release?
Inhibit?

Back 12

Increase: Morphine, Nicotine, cyclophosphamide
Decrease: Alcohol, Haloperidol, and Clonidine

Front 13

Fluid intake is regulated by what mechanism?

Back 13

Thirst, which acts together with the osmoreceptor-ADH mechanism

Front 14

Inability to produce or release ADH from the posterior pituitary. What mechanism keeps the body in homeostasis?

Back 14

Central diabetes insipidus
Thirst mechanism

Front 15

Where does desmopressin act?

Back 15

On V2 receptors of the epithelium of the kidney

Front 16

How does renal disease cause Diabetes Insipidus

Back 16

Damage to the renal medulla impairs the concentrating mechanism and thus the urine is unable to become hyperosmotic. This is a form of nephrogenic diabetes insipidus.

Front 17

Action of diuretics

Back 17

Inhibit electrolyte reabsorption in the loop of henle

Front 18

Regulation of extracellular fluid osmolarity is linked with what ion. Calculation of Plasma osmolarity?

Back 18

Na
Posm= 2.1 x plasma Na concentration

Front 19

Threshold for drinking

Back 19

When the osmolarity increases 2mEq/L above normal, the thirst mechanism is activated.

Front 20

Increased CSF osmolarity may activate the thirst mechanism via what area

Back 20

The organum vasculosum of the lamina terminalis

Front 21

Affects of angiotensin II and aldosterone on plasma osmolarity

Back 21

Because these hormones increase both sodium and water reabsorption, they have little effect on the sodium concentration, except under extreme conditions.

Front 22

During Addison's disease, how does the extracellular fluid environment become hypo-osmolaric?

Back 22

Loss of extreme amounts of Na, leads to decreased blood volume and pressure, which activates the cardiovascular reflexes. Once activated, the reflexes work to stimulate thirst, leading to further dilution of the plasma Na concentration.

Front 23

What stimuli drive the salt appetite?

Back 23

Decreased extracellular fluid Na concentration and decreased blood volume or pressure

Front 24

How does excess water effect ADH secretion and kidney permeability?

Back 24

Decreases ADH secretion, causing the distal tubules and collecting ducts to be impermeable to water.

Front 25

How does drinking large amounts of water affect the reabsorption of solutes?

Back 25

It doesnt

Front 26

Initial glomerular filtrate has an osmolarity equal to what?

Back 26

Plasma

Front 27

Fluid osmolarity in the proximal tubule. When does the tubular fluid first become hypertonic?

Back 27

Isotonic, this is because both solutes and water are reabsorbed.
As it passes down the descending loop of henle.

Front 28

As fluid reaches the renal medulla, what is its tonicity

Back 28

Hypertonic

Front 29

Is fluid leaving the early distal tubule hyper or hypo osmotic? Is this influenced by ADH

Back 29

Hypo-osmotic
NO!

Front 30

Most solutes are reabsorbed in what part of the kidney?

Back 30

Ascending limb of the loop of henle

Front 31

In healthy kidneys, where is fluid always dilute?

Back 31

In the ascending limb and early distal tubule

Front 32

Maximum urine osmolarity

Back 32

1200-1400 mOsm/L

Front 33

Basic requirements for forming a concentrated urine

Back 33

High level of ADH
High osmolarity of the renal medullary interstitial fluid. This provides the osmotic gradient necessary for water reabsorption.

Front 34

ADH increases the permeability of urea where?

Back 34

Inner medullary collecting duct

Front 35

Most important cause of high medullary interstitial osmolarity

Back 35

Active transport of solutes from the thick ascending loop of henle into the interstitium

Front 36

ADH increases urea reabsorption how?

Back 36

In the presence of ADH, water is reabsorbed creating a high urea tubular concentration. At the inner collecting medullary duct, ADH activates UT-AI urea transport receptors that work to rebasorb urea.

Front 37

Malnutritions effects on urine concentration

Back 37

When protein malnutrition occurs, there are low amounts of nitrogenous urea formed as protein waste. This hinders the ability of urine

Front 38

During dehydration how is urea reabsorbed?

Back 38

By passive diffusion due to presence of ADH

Front 39

How is urea concentration affected during kidney disease?

Back 39

A decreased GFR raises the plasma urea concentration, which allows for the continued excretion of urea despite a decreased GFR

Front 40

How do the vasa recta contribute to the medullary interstitial hyperosmolarity?

Back 40

They prevent it from being dissipated

Front 41

How does medullary blood flow affect the medullary osmolarity?

Back 41

Slow blood flow through the medulla minimizes solute loss

Front 42

How do vasodilators affect medullary osmolarity?

Back 42

They markedly increase medullary blood flow causing the an increase in absorption of solutes from the medullary interstitium. This decreases the urines concentrating ability