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Lecture

Anatomy Chapter 14.docx

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Department
Biological Sciences
Course
BIOB33H3
Professor
Connie Soros
Semester
Winter

Description
Chapter 14 Urinary System • The Kidney is the major functional organ, other organs carry urine out of the body - basic functions 1. water balance and osmolarity 2. electrolyte (ion) balance 3. maintain plasma volume, long term regulation of blood pressure 4. acid/base balance 5. excrete wastes (urea, uric acid, creatinine) and foreign materials 6. secrete erythropoietin + 7. secrete renin (Na balance) 8. converts vitamin D to its active form - nephron is the functional unit of the kidney 1. arrangement forms cortex and medulla 2. glomerulus a. tuft of capillaries that filters blood b. renal artery branches to form afferent and efferent arteriole for each nephron (1) efferent arteriole divides to form peritubular capillaries (supply renal tissue with blood) 3. tubule a. Bowman's capsule surrounds glomerulus and collects filtrate b. proximal convoluted tubule (PCT) c. loop of Henle d. distal convoluted tubule (DCT) e. collecting duct/tubule - drains fluid from several nephrons to renal pelvis 4. juxtaglomerular apparatus a. regulates kidney function b. macula densa - specialized cells of DCT as it passes by glomerulus c. granular cells (juxtaglomerular cells or JG cells) are specialized smooth muscle cells of arterioles 5. 2 types of nephrons a. cortical - lie mainly in cortex (80%) b. juxtamedullary - loops dip to end of medulla (important in urine concentration/conserving water) (1) vasa recta are blood vessels that run near long loop - 3 renal processes 1. glomerular filtration a. about 20% of plasma entering glomerulus is filtered b. entire plasma volume filtered 65 times/day c. nonselective process - everything but cells and plasma proteins are filtered 2. tubular reabsorption a. selective recovery of filtered substances 3. tubular secretion a. selective transfer of materials from plasma in peritubular capillaries to filtrate • Glomerular Filtration - filtered substances pass through highly permeable filtration membrane 1. glomerular capillaries are 100x more permeable than other capillaries 2. basement membrane (collagen for strength and glycoproteins with a negative charge that repels plasma proteins) 3. inner layer of Bowman's capsule a. podocytes wrap around capillaries and form filtration slits - glomerular capillary blood pressure forces fluid through filtration membrane 1. higher than in other capillaries a. diameter of afferent arteriole larger than efferent arteriole, blood dams up and filtration occurs throughout glomerulus 2. glomerular filtration rate (GFR) a. GFR = K x net filtration pressure f (K= filtration coefficient, collective properties of filtration membrane) f b. autoregulation (1) allows GFR to remain constant despite changes in BP (vasoconstriction/dilation of afferent arteriole) (2) myogenic mechanism - arteriolar smooth muscle constricts when stretched, relaxes with decreased pressure (3) tubuloglomerular feedback mechanism - macula densa detects changes in rate of filtrate flow or osmotic changes and signals granular cells to release vasoactive substances increased flow  vasoconstriction  decreased GFR decreased flow  vasodilation  increased GFR (4) sufficient in MAP 80-180 mmHg range c. extrinsic sympathetic control (1) GFR changed based on need (override autoregulation to reg BP) (2) baroreceptor reflex decreased plasma volume  generalized vasoconstriction, including afferent arteriole  decreased GFR  conservation of fluids increased BP  vasodilation  increased GFR  eliminate more fluids (3) can alter f by closing off part of capillaries and filtration slits • Tubular Reabsorption - typically nephrons reabsorb 99% of the water, 100% of the sugar, 99.5% of the salt that is filtered - different portions of tubule specialize in particular substances - most substances pass through tubule cells (transepithelial transport) - can be active or passive 1. if any step is active, reabsorption of that substance is considered active - Na reabsorption 1. occurs via Na -K ATPase in the basolateral membrane a. creates gradients for diffusion b. tied to reabsorption of other substances (glucose, amino acids, water, Cl , urea) c. occurs in PCT and loop - automatically reabsorb most Na (92%) d. DCT and collecting tubule - hormonal control, reabsorption according to need 2. renin-angiotensin-aldosterone system a. in response to decreased NaCl/dec. ECF volume/dec. BP, macula densa signals granular cells to release
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