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sure increases and causing it to relax when blood pressure decreases. Tubuloglomerular feedback involves paracrine signaling at the JGA [juxtaglomerular apparatus] to cause vasoconstriction or vasodilation to maintain a steady rate of blood flow.
25.8 Endocrine Regulation of Kidney Function
Several hormones have specific, important roles in regulating kidney function. They act to stimulate or inhibit blood flow. Some of these are endocrine, acting from a distance, whereas others are paracrine, acting locally. Renin is an enzyme that is produced by the granular cells of the afferent arteriole at the JGA. It enzymatically converts angiotensino- gen (made by the liver, freely circulating) into angiotensin I. Its release is stimulated by prostaglandins and NO from the JGA in response to decreased extracellular fluid volume.
ACE is not a hormone but it is functionally important in regulating systemic blood pres- sure and kidney function. It is produced in the lungs but binds to the surfaces of endothe- lial cells in the afferent arterioles and glomerulus. It enzymatically converts inactive angio- tensin I into active angiotensin II. ACE is important in raising blood pressure. People with high blood pressure are sometimes prescribed ACE inhibitors to lower their blood pres- sure. Angiotensin II is a potent vasoconstrictor that plays an immediate role in the regula- tion of blood pressure. It acts systemically to cause vasoconstriction as well as constriction of both the afferent and efferent arterioles of the glomerulus. Diuretics are drugs that can increase water loss by interfering with the recapture of solutes and water from the forming urine. They are often prescribed to lower blood pressure.
Coffee, tea, and alcoholic beverages are familiar diuretics. ADH, a 9-amino acid peptide released by the posterior pituitary, works to do the exact opposite. It promotes the recov- ery of water, decreases urine volume, and maintains plasma osmolarity and blood pres- sure. Endothelins are elevated in cases of diabetic kidney disease.
25.9 Regulation of Fluid Volume and Composition
The major hormones regulating body fluids are ADH, aldosterone and ANH. Progesterone is similar in structure to aldosterone and can bind to and weakly stimulate aldosterone re- ceptors, providing a similar but diminished response. Blood pressure is a reflection of blood volume and is monitored by baroreceptors in the aortic arch and carotid sinuses.
When blood pressure increases, more action potentials are sent to the central nervous sys- tem, resulting in greater vasodilation, greater GFR, and more water lost in the urine. ANH is released by the cardiomyocytes when blood pressure increases, causing Na+ and water loss. ADH at high levels causes vasoconstriction in addition to its action on the collecting ducts to recover more water. Diuretics increase urine volume.
25.10 The Urinary System and Homeostasis
The effects of failure of parts of the urinary system may range from inconvenient (inconti- nence) to fatal (loss of filtration and many others). The kidneys catalyze the final reaction in the synthesis of active vitamin D that in turn helps regulate Ca++.
The kidney hormone EPO stimulates erythrocyte development and promotes adequate O2 transport. The kidneys help regulate blood pressure through Na+ and water retention and loss. The kidneys work with the adrenal cortex, lungs, and liver in the renin–angiotens- in–aldosterone system to regulate blood pressure.
They regulate osmolarity of the blood by regulating both solutes and water. Three electro- lytes are more
closely regu-
lated than oth-
ers: Na+, Ca++, and K+. The kidneys share pH regu- lation with the lungs and plasma buff- ers, so that proteins can preserve their three- dimensional conformation and thus their function.
25.8 OBJECTIVES
1. Name and define the roles of other hormones that regulate kidney control
25.10 OBJECTIVES
1. Explain the mechanism of action of diuretics
25.9 OBJECTIVES
1. Explain the mechanism of action of diuretics
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State of Alaska EMS Education Primer - 2016
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