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Urinary System (Role of Hormones (Angiotensin-initially Angiotensinogen…
Urinary System
Role of Hormones
Angiotensin-initially Angiotensinogen produced by the liver powerful vasoconstrictor of systemic arterioles that increases peripheral resistance which increases BP. Also stimulates the release of Aldosterone
renin- is produced by the kidney. When BP drops it stimulates JG cells to release renin. Renin also catalyzes the reaction that creates Angiotensin II
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Aldosterone-increases sodium reabsorption by the tubules with water following this increases blood volume thus increasing BP. Produced by the adrenal glands
ADH- produced in Hypothalamus decreases urine output by decreasing the elimination of sodium. This causes H2O to come out of DCT and collecting duct and Na+ to come out of nephron in Loop of Henle. This raises BP
ANP- Decreases BP by raising the Glomular filtration rate decreasing sodium and H2O reabsorption and inhibiting the release of Aldosterone, ADH and Renin. Produced by arterial cells in the heart.
Renin-angiotensin-aldosterone Hormonal Mechanism Angiotensinogen+Renin--->Angiotensin I with help of ACE---> Angiotensin II This is catalyze
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Nephron Physiology
Glomerular Filtration- happens in the renal capsule and is where the formation of urine begins by filtering the blood plasma.The afferent arteriole is bigger around moving blood into Glomerulus the efferent arteriole is smaller and moves blood away. Difference in size causes GHP that moves blood plasma from glomerulus into Bowman's capsule. Only 20% of blood plasma is filtered in the glomerulus the rest continues out the efferent arteriole.
Tubular Reabsorption- begins when filtrate moves into PCT. Most substances get reabsorbed in the PCT. Sodium is the highest quantity in filtrate and allows reabsorption to continually occur. Negatively charged ions move across being pulled by the sodium like Cl- & K-. Descending Loop of Henle only permeable to H2O. Ascending Loop not permeable to H2O but will allow ions across. DCT reabsorbs some H20 Na+ & Cl-. Collecting Duct Reabsorbs Bicarb, Cl-, Na+ and H2O.
Secretion-gets rid of unwanted solutes including reabsorbed ones and helps control blood pH by secreting H+ ions into the tubular system from the blood. Most active in the PCT but is still active in DCT and collecting duct.
Excretion- After urine is formed through the tubules it enters the collecting ducts. It then travels to the minor calyx to the major calyx and then to the renal pelvis. The renal pelvis has smooth muscle which moves the urine through peristalsis into the ureters. The ureters empty into the bladder through openings in an area called the trigone. From bladder urine flows through the urethra and out of the body.
Filtration Membrane- 1. Capillary Endothelium-lines glomerular capillaries and contains fenestrations which are large pores that allow most substances into tubular system. 2. Glomerular Basement membrane- made up of collagen fibrils and structural proteins that keep out proteins. It also has a negative charge that helps keep out proteins.
3. Filtration Slits-made up of epithelial cells called podocytes that wrap around the basement membrane like fingers spread apart creating slits only allowing certain substances through
Glomerular Filtration Rate- total amount of filtrate formed per minute which is normally 120mL/min or 170 L/day. If GFR is too low most substances are reabsorbed including wastes if GFR is too high then needed substances aren't getting absorbed back into blood stream. This is regulated by vasodilation and vasoconstriction. GFR is directly proportional to net filtration pressure