Exam 3

• The organs that compose the urinary system include the kidneys, and the urinary tract, which includes the ureters, urinary bladder, and urethra.
• Kidney: paired organs that produce urine
• Urinary tract: eliminated urine
• Ureteres: Paired tubes
• Urinary Bladder: muscular sac
• Urethra: Exit tube
• The urinary system has three main functions: Excretion, Elimination, and homeostatic regulation of volume and concentration of blood.
• Excretion: the removal of metabolic waste from body fluids
• Elimination is the discharge of wastes from the body
• Kidneys are located on either side of the vertebral column. The left kidney is slightly superior to the right kidney due to the presence of the liver.
• Kidneys are protected and stabilized by three layers, the fibrous capsule, the perinephric fat, and the renal fascia.
• Perinephric fat is a thick layer of adipose tissue that surrounds the fibrous capsule.
• Renal Fascia is a dense fibrous outer layer that anchors the kidneys to the surrounding structure.
• Fibrous Capsule is a layer of collagen fibers that covers the outer surface of the entire organ.
• Nephrons: microscopic functional units of the kidneys. Each consists of a renal corpuscle and renal tubule. Each renal tubule empties into the collecting system.
• Podocytes: Large cells of the visceral layer. Contains complex foot processes, pedicels, that wrap around glomerular capillaries. Filtration slits are the narrow gaps between adjacent foot processes.
• The Distal Convoluted Tubule is the third segment of the renal tubule. The initial portion passes between afferent and efferent arterioles. Has a smaller luminal diameter than PCT. Epithelial cells lack microvilli. The primary function is to reabsorb water and selected ions. Actively secretes undesirable substances.
• The goal of urine production is to maintain homeostasis through regulating the volume and composition of blood. Involves the excretion of metabolic wastes. Three metabolic wastes, Urea, the most abundant organic waste; Creatinine, from the breakdown of creatine phosphate; and uric acid from the recycling of nitrogenous bases. Organic wastes dissolve in the bloodstream, eliminated only when dissolved in urine. Removal is accompanied by water loss.
• Basic processes of urine formation: Filtration, blood pressure forces water and solutes across walls of glomerular capillaries. Reabsorption, is the movement of water and solutes from filtrate to peritubular fluid. Secretion: transport of solutes from peritubular fluid to tubular fluid.
• Angiotensin is converted to angiotensin II by angiotensin-converting enzyme, ACE.
• Angiotensin II contracts vascular smooth muscle in peripheral capillary beds. Increases aldosterone secretion by adrenal glands and increases Na+ retention. Increases arterial pressures and stimulates thirst centers. Increases the production of ADH (antidiuretic hormone). Overall, angiotensin II increases systemic blood pressure and blood volume and restoration of normal GFR.
• Reabsorption and secretion by kidneys involve, diffusion, osmosis, leak channels or channel mediated diffusion, and carrier mediated transport.
• There are four types of carrier mediated transport. Facilitated diffusion, active transport, cotransport, and counter transport.
• Carrier-mediated transport is when a specific substrate binds to a carrier protein that facilitates movement across membrane. A given carrier protein typically works in one direction only. Distribution of carrier proteins can vary in a different region of cell surfaces. The membrane of a single tubular cell contains many types of carrier proteins
• The function of PCT: Reabsorption of organic nutrients, active reabsorption of ions, reabsorption of water, passive reabsorption of ions and secretion.
• Descending Limb of nephron loop: Freely permeable to water but not to solutes. Descending thin limb reabsorbs sodium and chloride ions from tubular fluid.
• Ascending Limb of nephron loop: Impermeable to water, Passively and actively removes sodium and chloride ions from tubular fluid. Very long in juxtamedullary nephrons creating high solute concentrations in peritubular fluid.
• Aldosterone is a hormone produced by adrenal cortex. Stimulates synthesis and incorporation of Na+ pumps and channels in plasma membranes along DCT and collecting duct. Reduces Na+ lost in urine.
• Parathyroid hormone in the kidneys regulates calcium ion reabsorption at DCT.
• Hydrogen Ion secretion: hydrogen ions generated by dissociation of carbonic acid are secreted by sodium ion linked counter transport in exchange for Na+ in tubular fluid.
• Hydrogen ion secretion acidifies tubular fluid, elevates blood pH and accelerates when blood pH falls.
• Pyelogram is an image of the urinary system. Obtained by taking an X-Ray after radiopaque dye has been administered intravenously.
• bladder is lined by transtitional epithelium
• Male urethra extends from the neck of urinary bladder to tip of the penis, about 18-20 cm. Composed of three parts. Prostatic urethra which passes through center of prostate. Membranous urethra includes the short segment that penetrates deep transverse perineal muscle. Spongy urethra extends from distal border of deep transverse perineal muscle to the external urethral orifice at tip of the penis.
•  In both sexes, the external urethral sphincter is a circular band of skeletal muscle. Acts as a valve under voluntary control via perineal branch of pudendal nerve. Has a resting muscle tone meaning it is always contracted. Voluntary relaxation of this muscle permits urination.
• The primary hormones that regulate fluid and electrolyte balance include antidiuretic hormone, aldosterone, and natriuretic peptides.
• ADH/antidiuretic hormone stimulated water conservation at kidneys reducing urinary water loss and concentrating urine. Stimulates hypothalamic thirst center. Promotes fluid intake. ADH production and release via osmoreceptors in hypothalamus. Monitors osmotic concentration of ECF. Axons of osmoreceptor neurons in hypothalamus that release ADH near fenestrated capillaries in posterior lobe of pituitary gland. Higher osmotic concentration increases ADH release.
• Aldosterone: secreted by adrenal cortex in response to the rising of K+ (potassium) or falling Na+ (potassium) levels in blood and the activation of renin-angiotensin-aldosterone system. Determines rate of Na+ reabsorption and K+ loss in kidneys. High aldosterone plasma concentration causes kidneys to conserve Na+. Also stimulates water retention.
• Natriuretic peptides. Include Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP). Released by cardiac muscle cells in response to abnormal stretching of heart walls. Reduces thirst and blocks the release of ADH and aldosterone. Causes diuresis/fluid loss by kidneys. Also lowers blood pressure and plasma volume.
• Dehydration: water depletion. Develops when water losses are greater than gains. If water is lost but electrolytes are retained, ECF osmotic concentration rises. Water moves from ICF to ECF. Because of large volume, net change in ICF Is small. Severe water loss may result from excessive perspiration, inadequate water consumption, or due to symptoms of illness such as repeated vomiting and diarrhea.