Please help me answer these questions am stuck. 1 .What are the forces that gove

Question

Please help me answer these questions am stuck.

1.What are the forces that govern Glomerular filtration? How does glomerular filtration pressure affect glomerular filtration rate? What are two intrinsic mechanisms that function normally to maintain a relatively constant rate of filtration at the glomerulus? (explain those mechanisms in some detail). How does the autonomic nervous system affect GFR and when might it be activated?

2.Hormonal regulation plays an important role in the long-term control of blood pressure and ECF osmolarity. Identify the hormones outlined in this section that play a role in these two homeostatic factors and how those hormones are regulated, and the mechanisms they use. (You should discuss ADH, Angiotensin II, Aldosterone & ANP.)

3.Draw a negative feedback loop indicating what happens in the kidneys in response to a significant drop in MAP.

Explanation / Answer

1. Fores governing glomerular filtration- Hydrostatic pressure inside the glomerular capillaries, Osmotic pressure in glomerular capillaries and opposite pressure created from fluid withing the capsule.

There are two intrinsic mechanisms that function normally to maintain a relatively constant rate of filtration at the glomerulus-

(A) Myogenic mechanism - Mogenic mechanism reflects a property of vascular smooth muscle, it contracts when stretched and relaxes when not stretched. Rise in systemic BP stretches the afferent arteriole, causing it to reflexively constrict, this decreases blood flow into the glomerulus and prevents glomerular BP from rising. Decline in systemic BP causes reflexive vasodilation of the afferent arteriole, this increases blood flow into the glomerulus, so the volume of blood in the capillaries keeps the glomerular hydrostatic pressure in the appropriate range
-both responses maintain normal NFP and GFR.

(B) Tubuloglomerular feedback mechanism - directed by the macula densa cells of juxtaglomerular complex, these cells respond to the concentration of NaCl in the filtrate, if high levels of NaCl are detected, the macula densa releases vasoconstrictor chemicals that act on the afferent arteriole, the constriction of the afferent arteriole reduces blood flow into the glomerulus, this slows the flow of the filtrate to allow sufficient time for filtrate processing.If low levels of NaCl are detected, release of vasoconstrictors by the macula densa is inhibited, the afferent arteriole dilates, increasing blood flow into the glomerulus, this speeds up the flow of the filtrate to bring NFP and GFR back to the normal range.

GFR is regulated by autonomic nervous system. The kidneys are innervated by the sympathetic neurons of the autonomic nervous system via the celiac plexus and splanchnic nerves. Reduction of sympathetic stimulation results in vasodilation and increased blood flow through the kidneys during resting conditions.When the frequency of action potentials increases, the arteriolar smooth muscle constricts, resulting in diminished glomerular flow, so less filtration occurs. Under conditions of stress, sympathetic nervous activity increases, resulting in the direct vasoconstriction of afferent arterioles as well as stimulation of the adrenal medulla. The adrenal medulla, in turn, produces a generalized vasoconstriction through the release of epinephrine. This includes vasoconstriction of the afferent arterioles, further reducing the volume of blood flowing through the kidneys. This process redirects blood to other organs with more immediate needs. If blood pressure falls, the sympathetic nerves will also stimulate the release of renin. Additional renin increases production of the powerful vasoconstrictor angiotensin II. Angiotensin II, as discussed above, will also stimulate aldosterone production to augment blood volume through retention of more Na+ and water. Only a 10 mm Hg pressure differential across the glomerulus is required for normal GFR, so very small changes in afferent arterial pressure significantly increase or decrease GFR.

Hormonal regulation- The hypothalamus monitors the amount of water in the body by sensing the concentration of electrolytes in the blood; a high concentration of electrolytes means that the level of water in the body is low, ADH produced by the hypothalamus and released by the posterior pituitary, causes more water to be retained by the kidneys when water levels in the body are low. ADH effects water retention by creating special channels for water, called aquaporins, inside the kidneys so that more water can be reabsorbed before it is excreted. Aldosterone, produced by the adrenal cortex, causes the retention of water in the body by increasing the levels of sodium and potassium ions in the blood, which causes the body to reabsorb more water. When blood pressure is low, the enzyme renin is released, which cleaves the protein angiotensinogen into angiotensin I, which is further converted into angiotensin II. Angiotensin II signals the adrenal cortex to release aldosterone, which then increases the retention of sodium ions, enhancing the secretion of postassium ions, resulting in water retention and an increase in blood pressure. ANP acts to reduce the water, sodium and adipose loads on the circulatory system, thereby reducing blood pressure. ANP has exactly the opposite function of the aldosterone secreted by the zona glomerulosa in regard to its effect on sodium in the kidney, so, aldosterone stimulates sodium retention and ANP generates sodium loss.

Drop in MAP is detected by arterial baroreceptors, which leads to sympathetic nervous system activation, afferent arteriole constriction, and decreased GFR.

MAP detected by carotid bireceptors

SNS activation (In put in to afferent atriole)

Decreased GFR

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