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BIO 2401 URINARY SYSTEM page 1 URINARY SYSTEM Location of Kidney 2 bean-shaped organs located on each side of the abdominal aorta and vertebrae (terminal thoracic and superior lumbar) under the 12 th rib in a retroperitoneal position, extending from the 12 th thoracic vertebra to 3 rd lumbar vertebra; thus is under floating ribs and is protected, somewhat, by rib cage right kidney is crowded by liver so is slightly lower than left liver Major Functions – regulates constancy of body fluids by filtering 200-500 l of fluid from blood daily 1. regulates water balance 2. eliminates nitrogenous wastes: urea, uric acid, creatinine in concentrated urine 3. regulates pH 4. regulates electrolytes; gets rid of excess ions 5. can take on a gluconeogenesis function when fasting for prolonged periods; supplies 20% of glucose that liver delivers 6. endocrine function – secretes renin and erythropoietin hormones renin is secreted by juxtaglomerular apparatus in response to low blood pressure/volume or changes in osmolarity (via elevated K + or depressed Na + ) cleaves off part of plasma protein angiotensionogen and triggers formation of angiotensin II that stimulates secretion of aldosterone from adrenal cortex stimulates retention of Na + ions, so water reabsorption is increased (via osmosis), and blood pressure is increased erythropoietin secreted by juxtaglomerular cells in response to reduced #’s of RBCs, reduced availability of oxygen, increased tissue need for oxygen stimulates bone marrow to produce more RBCs 7. metabolizes vitamin D to active form of calcitriol stimulated by parathormone from parathyroid gland Kidney Structure Three layers surround kidneys: 1. renal fascia – outermost; covers kidney and adrenal gland 2. adipose capsule – middle layer; attaches kidney to posterior body wall; cusions kidney 3. renal capsule – innermost layer; adheres directly to kidney surface (transparent); is barrier against spread of infection from surrounding tissues External anatomy: weighs ~150 gm (~5 oz) in adult ~12 cm long, 6 cm wiide, 3 cm thick lateral surface is convex
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BIO 2401 URINARY SYSTEM page 2 medial surface is concave with an indentation (renal hilus) hilus leads to renal sinus, which is entry point for ureter, blood vessels, nerves, lymphatics adrenal gland sits on each kidney Internal structure of kidney: cortex – outer region; lighter in color; granular; contains nephrons and proximal/distal tubules renal columns – cells and connecting tissue between renal pyramids medulla – inner region; darker, redish-brown in color renal pyramids - cone-shaped tissue masses (aka medullary pyramids); has striations due to
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