BSC2086 1st Edition Lecture 21 Outline of Last Lecture I Stomach II Small intestine III Pancreas IV Liver V Gallbladder VI Coordination of secretion and absorption VII Large intestine Outline of Current Lecture I Urinary System Functions II Kidneys III Renal Tubule IV Nephron V Renal Corpuscle VI Collecting System Lecture Notes I Urinary System Functions a Three functions i excretion of organic wastes from body fluids ii eliminate waste products iii homeostatic regulation of blood plasma volume and solute concentration b Structures and functions i Kidneys 1 Organs that make urine II ii Urinary tract 1 Organs that eliminate urine 2 Ureters paired tubes 3 Urinary bladder muscular sac 4 Urethra exit tube iii Urination or micturition 1 Process of eliminating urine from the body 2 Urine forced through urethra and out of the body due to the contraction of the muscular urinary bladder c Homeostatic functions i Regulates blood volume and pressure 1 Adjust volume of water lost in urine 2 Release erythropoietin and renin ii Regulates the concentration of plasma ions 1 Control the quantities of sodium potassium and chloride ions lost in urine 2 Calcium ions through synthesis of calcitriol a Parathyroid hormones stimulates the release of calcitriol from the kidneys which increases the absorption of calcium 3 Stabilized blood pH by controlling loss of hydrogen ions and bicarbonate ions in the urine 4 Conserves valuable nutrients a Prevents their excretion which still excreting organic waste products 5 Helps liver in detoxifying poisins a Dying of starvation deaminates amino acids so other tissues can metabolize them Kidneys a Location i Found on either side of vertebral column ii Left kidney is superior to right kidney iii Adrenal gland caps their superior surfaces iv Position maintained by 1 Overlying peritoneum 2 Contact with adjacent visceral organs 3 Supportive connective tissues b Protection and Stabilization i Fibrous capsule 1 Innermost layer made of collagen fibers 2 Covers outer surface of the entire organ ii Perinephric fat capsule 1 Thick layer of adipose tissue that surrounds the renal capsule c d e f g h i j k l iii Renal fascia 1 Outermost layer 2 Anchors the kidneys to surrounding structure Hilum i Point of entry for renal artery and nerves ii Point of exit for renal vein and ureter Renal cortex i Top part of kidney in contact with renal capsule ii Reddish brown color and granular Renal pyramids i Made up of 16 18 distinct conical or triangular structures found in the renal medulla 1 Base abuts the cortex 2 Tip known as the renal papilla projects into the renal sinus Renal columns i Bands of cortical tissue separated by adjacent renal pyramids ii Extend into the medulla iii Have a distinct granular texture Renal lobe i Makes urine ii Made up of 1 Renal pyramid 2 Overlying area of renal cortex 3 Adjacent tissues of renal columns Renal papilla i Urine discharged by ducts into minor calyx a cup shaped drain Major calyx i Combination of 4 or 5 minor calyces Renal pelvis i Large funnel shaped chamber made of 2 or 3 major calyces ii Fills most of the renal sinus iii Connected to ureter which drains the kidney Nephrons i Functional unit of the kidney ii Microscopic tubular structure in the cortex of each renal lobe where urine production starts iii 1 25 million nephrons found in each kidney Blood supply i 20 25 of total cardiac output received by the kidneys ii 1200 mL of blood flows through kidneys each minute iii Kidneys gets blood through renal artery iv Blood flow from renal artery segmental arteries interlobar arteries arcuate arteries cortical radiate interlobular arteries afferent III arterioles glomerulus efferent arteriole peritubular capillaries venules cortical radiate interlobular veins arcuate veins interlobar veins renal vein m Renal nerves i Innervate the kidneys and the ureters ii Enter each kidney at the hilum and follow the tributaries of renal arteries to the individual nephrons iii Sympathetic innervation 1 Change blood flow and pressure at the nephron in order to adjust the rate of urine formation 2 Stimulates renin release to restrict loss of water and salt by urine 3 Stimulates reabsorption at nephron n The Nephron i Made of 1 Renal tubule a Spherical structure made of i Bowman s capsule glomerular capsule ii Cup shaped chamber iii Glomerulus capillary network 2 Renal corpuscle a Long tubular passageway that begins at the renal corpuscle o Glomerulus i Made of 50 intertwining capillaries ii Blood delivered via the afferent arteriole and leaves in the efferent arteriole 1 Then flows into peritubular capillaries which drains into small venules 2 Blood then returns to venous system p Filtration i Occurs in the renal corpuscle ii Blood pressure produces filtrate a protein free solution 1 Similar to blood plasma but lacks proteins iii Forces water and dissolved solutes out of the glomerular capillaries into capsular space Renal Tubule a Functions i Reabsorb useful organic nutrients that enter filtrate ii Reabsorb more than 90 of water in filtrate iii Secretes waste products that failed to enter the renal corpuscle through filtration at glomerulus b Segments i Located in cortex 1 Proximal convoluted tubeule PCT a First segment b Epithelial lining is simple cuboidal has microvilli on apical surfaces c Functions in reabsorption of i Organic nutrients 1 99 of glucose amino acids etc 2 Not all glucose is reabsorbed if glucose in blood is more than 180 mg dL a Glycosuria glucose in urine 3 After a protein rich meal amino acid common in urine a Aminoaciduria ii Ions Na K HCO3 iii H2O 1 By osmosis follows when solutes are reabsorbed d These reabsorbed substances enter the peritubular fluid IF around renal tubule and diffuse into the surrounding peritubular capillaries i PCT cells usually reabsorb 60 70 of the filtrate made in the renal corpuscle e There is some secretion of substances into tubular lumen i Active transport secretion of H ammonium ions drugs and toxins 2 Nephron loop Loop of Henle a U shaped tube b Extends partially in medulla i Nephron loop extends deeper in the medulla in juxtamedullary nephrons c Reabsorbs about of H2O and 2 3 of Na and Cl ions in tubular fluid d Very close parallel segments that are separated only by peritubular fluid i Very different permeability characteristics e Descending limb H2O reabsorption i Thin permeable to water but impermeable to solutes ii As tubular fluid flows through osmosis moves water into peritubular fluid leaving
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