BSC2086 1st Edition Lecture 21 Outline of Last Lecture I. StomachII. Small intestine III. Pancreas IV. LiverV. GallbladderVI. Coordination of secretion and absorption VII. Large intestineOutline of Current Lecture I. Urinary System FunctionsII. Kidneys III. Renal Tubule IV. Nephron V. Renal Corpuscle VI. Collecting SystemLecture Notes I. Urinary System Functionsa. Three functionsi. excretion of organic wastes from body fluidsii. eliminate waste productsiii. homeostatic regulation of blood plasma volume and solute concentration b. Structures and functionsi. Kidneys 1. Organs that make urineii. Urinary tract 1. Organs that eliminate urine 2. Ureters paired tubes3. Urinary bladder muscular sac4. Urethra exit tubeiii. Urination or micturition 1. Process of eliminating urine from the body2. 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 urine2. Release erythropoietin and reninii. Regulates the concentration of plasma ions 1. Control the quantities of sodium, potassium and chloride ions lost in urine2. Calcium ions through synthesis of calcitriola. Parathyroid hormones stimulates the release of calcitriol from the kidneys which increases the absorption of calcium3. Stabilized blood pH by controlling loss of hydrogen ions and bicarbonate ions in the urine4. Conserves valuable nutrientsa. Prevents their excretion which still excreting organic waste products5. Helps liver in detoxifying poisins a. Dying of starvation deaminates amino acids so other tissues can metabolize themII. Kidneys a. Locationi. Found on either side of vertebral columnii. Left kidney is superior to right kidneyiii. Adrenal gland caps their superior surfacesiv. Position maintained by 1. Overlying peritoneum2. Contact with adjacent visceral organs3. Supportive connective tissues b. Protection and Stabilizationi. Fibrous capsule1. Innermost layer made of collagen fibers2. Covers outer surface of the entire organii. Perinephric fat capsule1. Thick layer of adipose tissue that surrounds the renal capsuleiii. Renal fascia 1. Outermost layer2. Anchors the kidneys to surrounding structurec. Hilumi. Point of entry for renal artery and nervesii. Point of exit for renal vein and ureter d. Renal cortex i. Top part of kidney in contact with renal capsule ii. Reddish brown color and granulare. Renal pyramidsi. Made up of 16-18 distinct conical or triangular structures found in the renal medulla 1. Base abuts the cortex2. Tip, known as the renal papilla, projects into the renal sinus f. Renal columnsi. Bands of cortical tissue separated by adjacent renal pyramidsii. Extend into the medulla iii. Have a distinct granular texture g. Renal lobei. Makes urineii. Made up of1. Renal pyramid2. Overlying area of renal cortex3. Adjacent tissues of renal columnsh. Renal papillai. Urine discharged by ducts into minor calyx, a cup-shaped draini. Major calyxi. Combination of 4 or 5 minor calycesj. Renal pelvisi. Large funnel shaped chamber made of 2 or 3 major calycesii. Fills most of the renal sinusiii. Connected to ureter which drains the kidney k. Nephrons i. Functional unit of the kidneyii. Microscopic tubular structure in the cortex of each renal lobe where urineproduction startsiii. 1.25 million nephrons found in each kidney l. Blood supplyi. 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 → afferentarterioles → glomerulus efferent arteriole → peritubular capillaries → venules → cortical radiate (interlobular) veins → arcuate veins → interlobar veins → renal veinm. Renal nervesi. Innervate the kidneys and the uretersii. Enter each kidney at the hilum and follow the tributaries of renal arteries to the individual nephrons iii. Sympathetic innervation1. Change blood flow and pressure at the nephron in order to adjust the rate of urine formation2. Stimulates renin release to restrict loss of water and salt by urine 3. Stimulates reabsorption at nephron n. The Nephroni. Made of:1. Renal tubule a. Spherical structure made of i. Bowman’s capsule (glomerular capsule)ii. Cup shaped chamberiii. Glomerulus (capillary network)2. Renal corpuscle a. Long tubular passageway that begins at the renal corpuscleo. Glomerulus i. Made of 50 intertwining capillariesii. Blood delivered via the afferent arteriole and leaves in the efferent arteriole1. Then flows into peritubular capillaries which drains into small venules2. Blood then returns to venous systemp. Filtrationi. Occurs in the renal corpuscle ii. Blood pressure produces filtrate, a protein free solution1. Similar to blood plasma but lacks proteins iii. Forces water and dissolved solutes out of the glomerular capillaries into capsular space III. Renal Tubulea. Functions i. Reabsorb useful organic nutrients that enter filtrate ii. Reabsorb more than 90% of water in filtrateiii. Secretes waste products that failed to enter the renal corpuscle through filtration at glomerulus b. Segments i. Located in cortex1. Proximal convoluted tubeule (PCT)a. First segmentb. Epithelial lining is simple cuboidal, has microvilli on apical surfacesc. 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/dLa. 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 tubeb. Extends partially in medullai. Nephron loop extends deeper in the medulla in juxtamedullary nephronsc. Reabsorbs about ½ 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 characteristicse.
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