Which body process is dependent upon the presence of calcium in the body fluids Quizlet

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The best food sources of magnesium include:
a. legumes, whole grains, and chocolate.
b. milk, rice, and apples.
c. oranges, beef, and cheese.
d. oils, bananas, and pork.
e. pizza, potatoes, and tomatoes.

Supplement users are more likely to have excessive intakes of:
a. the B vitamins.
b. iron, zinc, vitamin A, and niacin.
c. vitamins A, D, E, and K.
d. calcium, iron, vitamin C, and thiamin.
e. folate, vitamin A, and vitamin C.

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As Na+, Cl-, and other ions are reabsorbed, water follows passively by osmosis

This figure summarizes this coupling of solute and water reabsorption.

(1) Na+ is transported from he tubular lumen to the interstitial fluid across the epithelial cells. Other solutes, such as glucose, amino acids, and HCO3-, whose reabsorption depends on Na+ transport, also contribute to osmosis.

(2) The removal of solutes from the tubular lumen decreases the local osmolarity of the tubular fluid adjacent to the cell (i.e., the local water concentration increases). At the same time, the appearance of solute in the interstitial fluid just outside the cell increases the local osmolarity (i.e., the local water concentration decreases).

(3) The difference in water concentration between lumen and inter- stitial fluid causes net diffusion of water from the lumen across the tubular cells' plasma membranes and/or tight junctions into the interstitial fluid.

(4) From there, water, Na+, and everything else dissolved in the interstitial fluid move together by bulk flow into peritubular capillaries as the final step in reabsorption.

One would think that as plasma with the usual osmolarity of 300 mOsm/L enters the highly concentrated environment of the medulla, there would be massive net diffusion of Na+ and Cl- into the capillaries and water out of them and, thus, the interstitial gradient would be "washed away."

However, the blood vessels in the medulla (vasa recta) form hairpin loops that run parallel to the loops of Henle and medullary collecting ducts.

blood enters the top of the vessel loop at an osmolarity of 300 mOsm/L, and as the blood flows down the loop deeper and deeper into the medulla, Na1 and Cl2 do indeed diffuse into—and water out of—the vessel. However, after the bend in the loop is reached, the blood then flows up the ascending vessel loop, where the process is almost completely reversed. Therefore, the hairpin-loop structure of the vasa recta minimizes excessive loss of solute from the interstitium by diffusion. At the same time, both the salt and water being reabsorbed from the loops of Henle and collecting ducts are carried away in equivalent amounts by bulk flow, as determined by the usual capillary Starling forces. This maintains the steady-state countercurrent gradient set up by the loops of Henle. Because of NaCl and water reabsorbed from the loop of Henle and collecting ducts, the amount of blood flow leaving the vasa recta is at least twofold higher than the blood flow entering the vasa recta. Finally, the total blood flow going through all of the vasa recta is a small percentage of the total renal blood flow. This helps to minimize the washout of the hypertonic interstitium of the medulla.

participates in the development of increased osmolarity in the renal medullary interstitium

As a result, there is increased water reabsorption from the lumen in the thin descending loop of Henle with a resultant increase in tubular fluid osmolarity even though vasopressin does not have a direct effect on the loop

the peak osmolarity in the loop of Henle is lower in the absence of vasopressin. This is because, as previously mentioned, vasopressin stimulates urea reabsorption in the medullary collecting ducts.

In the absence of this effect of vasopressin, urea concentration in the medulla decreases. Since urea is responsible for at least half of the solute in the medulla, the maximum osmolarity at the bottom of the loop of Henle (located in the medulla) is decreased.

the tubular fluid osmolarity decreases in the latter half of the loop of Henle under both conditions while there is no change in tubular fluid volume; this reflects the selective reabsorption of solutes from the tubular fluid in these water-impermeable segments of the nephron. Therefore, the ultimate determinant of the volume of urine excreted and the concentration of urine under any set of conditions is vasopressin.

In the absence of vasopressin, there is minimal water reabsorption in the collecting ducts so there is little decrease in the volume of the filtrate; this results in a diuresis and hypoosmotic urine. In the presence of maximum vasopressin during, for example, severe water restriction, most of the water is reabsorbed in the collecting ducts leading to a very small urine volume (antidi- uresis) and hypertonic urine. In reality, most humans with access to water have an intermediate vasopressin concentration in the blood.

responses that regulate urinary Na1 excretion are initiated mainly by various cardiovascular baro- receptors, such as the carotid sinus

baroreceptors respond to pres- sure changes within the circulatory system and initiate reflexes that rapidly regulate these pressures by acting on the heart, arte- rioles, and veins.

regulation of cardiovascular pressures by baroreceptors also simultaneously achieves regulation of total-body sodium.

The distribution of water between fluid compartments in the body depends in large part on the concentration of solute in the extracellular fluid. Na+ is the major extracellular solute constituting, along with associated anions, approximately 90% of these solutes.

Therefore, changes in total-body sodium result in similar changes in extracellular volume. Because extracellular volume comprises plasma volume and interstitial volume, plasma volume is also directly related to total-body sodium.

Thus, the chain linking total-body sodium to cardiovascular pressures is completed: Low total-body sodium leads to low plasma volume, which leads to a decrease in cardiovascular pressures. These lower pressures, via baroreceptors, initiate reflexes that influence the renal arterioles and tubules so as to decrease GFR and increase Na1 reabsorption. These latter events decrease Na1 excretion, thereby retaining Na1 (and therefore water) in the body and preventing further decreases in plasma volume and cardiovascular pressures. Increases in total- body sodium have the reverse reflex effects.

changes in total- body water with no corresponding change in total-body sodium are compensated for by altering water excretion without altering Na1 excretion.

changes in water alone, in contrast to Na1, have relatively little effect on extracellular volume. The reason is that water, unlike Na1, distributes throughout all the body fluid compartments, with about two-thirds entering the intracellular compartment rather than simply staying in the extracellular compartment, as Na1 does.

Therefore, cardiovascular pressures and baroreceptors are only slightly affected by pure water gains or losses. In contrast, the major effect of water loss or gain out of proportion to Na1 loss or gain is a change in the osmolarity of the body fluids.

This is a key point because, under conditions due pre- dominantly to water gain or loss, the sensory receptors that initiate the reflexes controlling vasopressin secretion are osmoreceptors in the hypothalamus.

The best understood of the other important controllers of vasopressin secretion.

A decreased extracellular fluid volume due, for example, to diarrhea or hemorrhage, elicits an increase in aldosterone release via activation of the renin-angiotensin system. However, the decreased extracellular volume also triggers an increase in vaso- pressin secretion. This increased vasopressin increases the water permeability of the collecting ducts. More water is passively reab- sorbed and less is excreted, so water is retained to help stabilize the extracellular volume.

This reflex is initiated by several baroreceptors in the cardiovascular system. The baroreceptors decrease their rate of firing when cardiovascular pressures decrease, as occurs when blood volume decreases. Therefore, the barorecep- tors transmit fewer impulses via afferent neurons and ascending pathways to the hypothalamus, and the result is increased vaso- pressin secretion. Conversely, increased cardiovascular pressures cause more firing by the baroreceptors, resulting in a decrease in vasopressin secretion.

The mechanism of this inverse relationship is an inhibitory neurotransmitter released by neurons in the affer- ent pathway.

The baroreceptor reflex for vasopressin, as just described, has a relatively high threshold—that is, there must be a sizable reduc- tion in cardiovascular pressures to trigger it. Therefore, this reflex, compared to the osmoreceptor reflex described earlier, has a lesser function under most physiological circumstances, but it can become very important in pathological states, such as hemorrhage.

When plasma calcium is low, the secretion of parathyroid hormone (PTH) from the parathyroid glands increases.

PTH stimulates the opening of calcium channels in these parts of the nephron, thereby increasing calcium ion reabsorption.

another important action of PTH in the kidneys is to increase the activity of the 1-hydroxylase enzyme, thus activating 25(OH)-D to 1,25-(OH)2D, which then goes on to increase calcium and phosphate ion absorption in the gastrointestinal tract.

Unlike calcium ion, phosphate ion reabsorption is decreased by PTH, thereby increasing the excretion of phosphate ion. Therefore, when plasma calcium is low, and PTH and calcium ion reabsorption are increased as a result, phosphate ion excretion is increased.

Which of the following body processes is not dependent upon the presence of calcium in the body fluids?

What role does calcium play in the body quizlet?

Where is calcium found in the body quizlet?

Where is the most calcium found in the body quizlet?