Major hormone regulator is renin-angiotensin-aldosterone system (RAAS) Renin releases is triggered by a decrease in blood pressure to afferent arterioles Renin helps to convert angiotensinogen to form angiotensin I. • Angiotensin-converting enzyme (ACE) is released from the lungs. • ACE acts on angiotensin I to form angiotensin Angiotensin I stimulates release of aldosterone and vasoconstriction of blood vessels. Reabsorption of water and sodium. Urine formation • Major function of nephron is urine formation. • 1. Filtering plasma at the glomerulus • Glomerular filtration • 2. Reabsorbing and secreting different substances along the tubular structures. • Proximal (convoluted) tubule • Loop of Henle and distal tubule • 3. Forming a filtrate of protein-free fluid • 4. Regulating the filtrate to maintain the body fluid volume, electrolyte composition, and pH with narrow limits. Balancing water & solute transport Excreting metabolic waste products Conserving nutrients Regulating acids-bases Secretes renin Erythropoietin Production Vitamin D3 Urine formation Nephron: functional unit of kidney Renal artery: supplies blood to kidney Afferent: blood arrives into glomerulus Efferent: blood exits glomerulus -Turns into peritubular capillaries Glomerular capillaries: blood to peritubular Distal tubule: Filtrate enters collecting tubules BUN, Creatinine, GFR Creatinine - freely filtered at the glomerulus • Normal is 0.7 - 1.2 mg/dL • Serum creatinine increases as GFR decreases Blood urea nitrogen (BUN) - urea is filtered at the glomerulus • Normal is 10 to 20 mg/dL • BUN increases as GFR decreases • Rise in states of dehydration and in renal failure Glomerular filtration rate (GFR) • Normal is > 60 ml/min • Best indicator of renal function • Damage to glomerular membrane or loss of nephrons leads to decrease in GFR Renal Corpuscle Glomerulus: Group of capillaries in renal cortex that loop into bowman’s capsule. Filters blood plasma Bowman (glomerular) capsule: surrounds glomerulus and empties filtrate into proximal tubule Kidneys : Maintains a stable internal environment for optimal cell & tissue metabolism GFR: Filtration of plasma per unit of time - Directly related to renal blood flow Blood pressure -Autoreg of intrarenal blood flow -BP afferent arteriole contracts -BP afferent arterioles dilate Kidneys are innervated by sympathetic nerve fibers Decreased systemic BP - release catecholamines Vasoconstriction - reduces RBF and GFR Increases renal tubular sodium and water reabsorption Increases systemic BP Increased systemic BP - opposite effect Renalase is released that promotes metabolism of catecholamines to reduce BP Collecting duct: releases urine into ureters Renal tubule: reabsorb & secrete Proximal tubule: reabsorbs water, glucose, Na, K. Ca, Cl. HCO3 -Will return back in to circulation Loop of Henle: entirely in medulla -Concentration of urine through reabsorption -Only water can flow out Hormones activated or synthesized by kidney Vitamin D - necessary for absorption of calcium and phosphate by small intestine • Vitamin D from sun and food are inactive and require two hydroxylations to become active (One from liver and second from kidney) • Renal hydroxylation is stimulated by secretion of parathyroid hormone •Erythropoietin - stimulates bone marrow to produce BC in response to hypoxia Renal vein: 99% of filtered blood is reabsorbed & circulated through vein, back to circulation .