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26- Urinary
The Urinary System for A&P II
| Question | Answer |
|---|---|
| The functions of the kidneys | Regulation of blood ionic composition, Regulation of blood pH. Regulation of blood volume, Regulation of blood pressure, Maintenance of blood osmolarity, Production of hormones, Regulation of blood glucose level. Excretion of wastes and foreign substances |
| Osmolarity | A measure of the total number of dissolved particles per liter of solution |
| Retroperitoneal | Posterior to the peritoneum |
| The three layers of tissue that surround each kidney | renal capsule, adipose capsule, renal fascia |
| Renal capsule | a smooth, transparent sheet of dense irregular connective tissue that is continuous with the outer coat of the ureter |
| Adipose capsule | a mass of fatty tissue surrounding the renal capsule |
| Renal fascia | a thin layer of dense irregular connective tissue that anchors the kidney to the surrounding structures and to the abdominal wall |
| Path of blood flow | renal artery, segmental arteries, interlobar arteries, arcuate arteries, interlobular arteries, afferent arterioles, glomerular capillaries, efferent arterioles, peritubular capillaries, interlobular veins, arcuate veins, interlobar veins, renal vein |
| Nephron | The functional unit of the kidneys |
| Each nephron consists of two parts | renal corpuscle and renal tubule |
| Renal corpuscle | where blood plasma is filtered |
| Renal tubule | where filtered fluid passes |
| The two components of the renal corpuscle | glomerulus and the Bowman's capsule |
| Glomerulus | a rounded mass of nerves or blood vessels, especially the microscopic tuft of capillaries that is surrounded by the Bowman's capsule of each kidney tubule |
| Bowman's Capsule | a double-walled globe at the proximal end of a nephron that encloses the glomerular capillaries. Also called the glomerular capsule |
| Flow of fluid through a cortical nephron | Bowman's capsule, proximal convoluted tubule, descending limb of the loop of Henle, ascending limb of the loop of Henle, Distal convoluted tubule (which drains into collecting duct) |
| Flow of fluid through a juxtamedullary nephron | Bowman's capsule, proximal convoluted tubule, descending limb of the loop of Henle, Thin ascending limb of the loop of Henle, Thick ascending limb of the loop of Henle, distal convoluted tubule |
| Two types of nephrons | cortical nephrons and juxtamedullary nephrons |
| Cotrical nephrons | 80-85% of nephrons. Their renal corpuscles lie in the outer portion of the renal cortex, and they have a short loop of Henle that lie mainly in the cortex and penetrate only into the outer region of the renal medulla |
| Juxtamedullary nephrons | 15-20% of nephrons. Their renal corpuscles lie deep in the cortex, close to the medulla, and they have a long loop of Henle that extends into the deepest region of the medulla. |
| Podocytes | Modified simple squamous epithelial cells in the visceral layer of the glomerular capsule |
| Microvilli | increases surface area |
| Juxtaglomerular apparatus | helps regulate blood pressure in the kidneys |
| Macula densa | cells in the final part of the ascending loop of Henle |
| Juxtaglomerular cells | cells of afferent and efferent arterioles containing modified smooth muscle fibers |
| Principal cells | most of the cells in the distal convoluted tubule and collecting duct. Has receptors for ADH and aldosterone |
| Intercalated cells | play a role in the homeostasis of blood pH |
| The three basic processes of producing urine | glomerular filtration, tubular reabsorption, and tubular secretion |
| Glomerular filtration | Water and most solutes in blood plasma move across the wall of the glomerular capillaries into glomerular capsule and then renal tubule |
| Tubular reabsorption | return of most of the filtered water and many solutes to the bloodstream |
| Tubular secretion | transfer of material from blood into tubular fluid. helps control blood pH and eliminate substances from the body |
| Glomerular filtrate | fluid the enters capsular space |
| Filtration membrane | endothelial cells of glomerular capillaries and podocytes encircling capillaries. permits filtration of water and small solutes and prevents filtration of most plasma proteins, blood cells, and platelets |
| Net filtration pressure (NFP) | The total pressure that promotes filtration. NFP = GBHP - CHP - BCOP |
| Glomerular blood hydrostatic pressure | the blood pressure of the glomerular capillaries forcing water and solutes through filtration slits |
| Capsular hydrostatic pressure | the hydrostatic pressure exerted against the filtration membrane by fluid already in the capsular space. represents "back pressure" |
| Blood colloid osmotic pressure | due to presence of proteins in blood plasma. also opposes filtration |
| Glomerular filtration rate (GFR) | amount of filtrate formed in all the renal corpuscles of both kidneys each minute |
| Too high GFR | substances pass too quickly and are not reabsorbed |
| Too low GFR | nearly all substances are reabsorbed and some waste products not adequately excreted |
| Mechanisms regulating GFR | renal autoregulation, neural regulation, and hormonal regulation |
| Renal autoregulation | the kidneys themselves help maintain a constant renal blood flow and GFR, despite normal, everyday changes in blood pressure. Consists of two mechanisms- the myogenic mechanism and tubuloglomerular feedback |
| Myogenic mechanism | occurs when stretching triggers contraction of smooth muscle cells in afferent arterioles- reduces GFR |
| Tubuloglomerular mechanism | macula densa provides feedback to glomerulus, inhibits release of NO causing afferent arterioles to constrict and decrease GFR |
| Neural regulation | kidney blood vessels supplied by sympathetic ANS fibers that release norephinephrine causing vasoconstriction |
| Moersate stimulation | both afferent and efferent arterioles constrict to same degree and GFR decreases |
| Hormonal regulation- Angiotensin II | reduces GFR. potent vasoconstrictor of both afferent and efferent arterioles |
| Hormonal regulation- Atrial natriuretic peptide | increases GFR. stretching of atria causes release, increases capillary surface area for filtration |
| Renin Angiotensinogen System | triggered when the JG cells release renin. Renin acts on angiotensinogen to release angiotensin I. Angiotensin I is converted to angiotensin II in the lungs by ACE. As a result, both systemic and glomerular hydrostatic pressure rise |
| Renin release is triggered by | reduced stretch of the granular JG cells, stimulation of the JG cells by activated macula densa cells, direct stimulation of the JG cells via B1 adrenergic receptors by renal nerves, angiotensin II |
| Sympathetic Activation | produces powerful vasoconstriction of afferent arterioles, changes the regional pattern of blood flow, and stimulates release of renin by the juxtaglomerular apparatus |
| Reabsorption routes | paracellular reabsorption (between adjacent tubule cells) and transcellular reabsorption (through an individual cell) |
| Primary active transport | sodium-potassium pumps in basolateral membrane |
| Secondary active transport | the energy stored in an ion's electrochemical gradient drives another substance across a membrane. symporters, antiporters |
| Transport maximum | upper limit to how fast a transporter can work |
| Obligatory water reabsorption | water reabsorbed with solutes in tubular fluid is termed this because the water is obliged to follow the solutes when they are reabsorbed |
| Facultative water reabsorption | reabsorption of the final 10% of water that is regulated by ADH and occurs mainly in the collecting ducts |
| Most solute reabsorption involves | Sodium |
| Reabsorption & secretion in the proximal convoluted tubule | largest amount of solute and water reabsorption |
| Na+/H+ antiporter | causes Na+ to be reabsorbed and H+ to be secreted |
| Solute reabsorption | promotes osmosis which creates osmotic gradient |
| Reabsorption in the Loop of Henle | glucose, amino acides and other nutrients are reabsorbed, reabsorption of water and solutes are balances, Na+/K+/2Cl- symporters function in Na+ and Cl- reabsorption, and little of no water is reabsorbed in ascending limb (osmolarity decreases) |
| Reabsorption & secretion in the late distal convoluted tubule and collecting duct | 90-95% of filtered solutes and fluid have been returned by now Principal cells reabsorb Na+ and secrete K+ Intercalated cells reabsorb K+ and HCO3- and secrete H+ Amount of water reabsorption and solute reabsorption and secretion depends on body’s need |
| Angiotensin II | released when BV and pressure decrease, decreases GFR, enhances reabsorption of Na+, Cl-, and water in PCT, and stimulates aldosterone release by adrenal cortex |
| Parathyroid hormone | stimulates cells in distal convoluted tubule to reabsorb more Ca2+ |
| Antidiuretic hormone (ADH or vasopressin) | Increases water permeability of cells by inserting aquaporin-2 in last part of DCT and collecting duct |
| Atrial natriuretic peptide (ANP) | large increase in blood volume promotes release of ANP. decreases blood volume and pressure by inhibiting reabsorption of Na+ and water in PCT and collecting duct, suppresses secretion of ADH and aldosterone |
| Absent of low ADH | dilute urine |
| High levels of ADH | more concentrated urine through increase water reabsorption |
| Formation of dilute urine | Osmolarity of fluid increases as it goes down the descending loop of Henle Osmolarity decreases as it goes up the ascending limb Osmolarity decreases still more as it flows through the rest of the nephron and collecting duct |
| Contributing solutes to the formation of concentrated urine | Na+, Cl-, and urea |
| Countercurrent multiplication | process by which a progressively increasing osmotic gradient is formed as a result of countercurrent flow |
| Countercurrent Exchange | process by which solutes and water are passively exchanged between blood of the vasa recta and interstitial fluid of the renal medulla as a result of countercurrent flow |
| Urinalysis | analysis of the volume and physical, chemical, and microscopic properties of urine |
| Blood urea nitrogen | measures blood nitrogen that is part of the urea resulting from catabolism and deamination of amino acids |
| Renal plasma clearance | volume of blood cleared of a substance per unit time |
| Renal Clearance Equation | renal clearance rate (RC) = concentration of the substance in urine (U) * flow rate of urine formation (v) / concentration of the same substance in plasma (P) |
| Ureters | transport urine from renal pelvis of the kidneys to the bladder |
| Urinary bladder | hollow, distensible muscular organ |
| Micturition | discharge of urine from bladder |
| Urethra | small tube leading from internal urethral orifice in flow of bladder to exterior of the body |
| Micturition reflex | occurs via a combination of involuntary and voluntary muscle contractions. bladder stretch receptors signal micturition center in sacral spinal cord segments |
Created by:
ariellebtan
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