Chapter 26 - The Urinary System
Glomerular capillaries
- unique among capillaries in the body because they are positioned between two arterioles (afferent and efferent), rather than between an arteriole and a venule -there are venules in the kidney, but they come later
Capsular hydrostatic pressure
-15 mmHg -exerted against the filtration membrane by fluid in the capsular space (opposes filtration)
Juxtamedullary nephrons
-15-20% of the nephrons -their renal corpuscles lie deep in the cortex, close to the medulla, and they have long loops of Henle that extend into the deepest region of the medulla -ascending limbs of their loops of Henle consist of both thin (simple squamous) and thick (simple cubodial) segments -receive their blood supply from the vasa recta that arise from peritubular capillaries before becoming peritubular venules
Blood osmotic (oncotic) pressure
-30 mmHg -the pressure of plasma proteins "pulling" on water (opposes filration) -normally very little protein escapes through the filtration membrane making capsular oncotic pressure a negligible force except in certain disease states
Blood hydrostatic pressure
-55mmHg -the main force that "pushes" water and solutes through the filtration membrane (promotes filtration)
Concentrated urine
-by the action of ADH on the DCT and collecting ducts of juxtamedullary nephrons -urine can be up to 4 times more concentrated than blood plasma -too concentrated=dehydrated
Bladder
-a hollow, distensible muscular organ with a capacity that averages 700-800mL -smooth muscles, transitional epithelium (distension=stretching)
Angiotensin II
-a potent vasoconstrictor of both afferent and efferent arteriole (reduces GFR = decreases urine output) -used when low BV
Urethra in females
-a small tube leading from the internal urethral orifice in the bladder floor to the exterior -4 cm -more likely to get bladder infections because bacteria can travel this short distance more easily -reproductive system is superior in the urinary system
Urethra in males
-a small tube leading from the internal urethral orifice in the bladder floor to the exterior -in males, it is also used to discharge semen -urine and ejaculation -due to valves -urinary system is superior to reproductive system
Angiotensin II
-active form of hormone -3 main effect: 1. vasoconstriction decreases GFR 2. increases blood volume by increasing reabsorption of water and electrolytes in the PCT (obligatory) 3. stimulates the adrenal cortex to release aldosterone
Juxtaglomerular cells (JG)
-alongside the macula dense, the wall of the afferent arteriole contains modified smooth muscle fibers -change pressure of blood going into nephron=changes filtration rate -increase filtration rate=increase urine output -decrease filtration rate=decrease urine output -together with the macula densa, they constitute the juxtaglomerular apparatus (JGA)
Urinalysis
-analyzes the physical, chemical and microscopic properties of urine -water accounts for 95% of total urine volume -solutes normally present in urine as filtered and secreted substances that are not reabsorbed -if disease alters metabolism or kidney function, traces of substances normally not present or normal constituents in abnormal amounts may appear -bacteria, albumin, protein (filtration not working), glucose (gluosuria), white blood cells, red blood cells (hematuria-blood in urine; kidney damage, tumor, on period)
Ureter
-approximately 25 cm long -originates near an indented area of each kidney called the hilum and travels to the base of the bladder -renal blood vessels also emerge from the hilum -hilum -point of entry and exit of an organ
Kidneys
-bean-shaped organs located just above the waist between the peritoneum and the posterior wall of the abdomen (in the retroperitoneal space) -partially protected by the eleventh and twelfth pairs of ribs -right one is slightly lower than the left
Trigone
-bottom region of the bladder -lacks rugae -allows all fluid to exit bladder
Yellow or amber
-color
Renal corpuscle
-composed of glomerular capillaries and glomerular capsule (bowman's capsule) - a double-walled epithelial cup that surrounds the glomerular capillaries
Renal Columns
-composed of lines of blood vessels and fibrous material which allows the cortex to be better anchored -between the pyramids to anchor them
Renal Pyramids
-consists of 8 to 18 conical subdivisions within the medulla that contain the kidneys secreting apparatus and tubules -portion of the medulla
Urinary System
-consists of the kidneys, ureters, bladder, and urethra, along with its associated nerves and blood vessels -regulates blood volume, pressure, pH, and concentration (osmolarity) of electrolytes -reabsorbing glucose and excreting wastes -releasing certain hormones like renin and EPO
Regulation of the GFR
-critical to maintaining homeostasis and is regulated by an assortment of local and systemic mechanism:
Facultative reabsorption of water
-describes variable water reabsorption, adapted to specific needs -regulated by hormones -regulated by effects of ADH and aldosterone on the principal cells of the renal tubules and collecting ducts -ADH puts in extra pores (aquaporins) into collecting ducts which allows more water to be absorbed into the system
Glomerulus
-each nephron receives one afferent arteriole, which divides into this tangled, ball-shaped capillary network -filters blood; fenestrated -has pores used to help substances exit -the ________ capillaries then reunite to form an efferent arteriole that carries blood out of the ___________ -efferent arteriole -wraps itself around nephron; peritubule capillaries, allows body to keep substances
Starling forces
-filtration is controlled by 2 opposing hydrostatic forces and 2 opposing osmotic forces at the glomerular membrane
Loop of Henle
-first part (descending limb) dips into the renal medulla -then makes a hairpin turn and returns to the renal cortex (ascending limb)
Bowman's space
-fluid filtered from the glomerular capillaries enters this space between the two layers of the glomerular capsule -which is the lumen of the urinary tube
Good Stuff of tubular reabsorption
-glucose, electrolytes, vitamins, water, amino acids, and any small proteins that might have inadvertently escaped from the blood into the filtrate -99% of the glomerular filtrate is reabsorbed
Renal Sinus
-hilum expands into this cavity within the kidney -space where all the tubes are found -contains part of the renal pelvis, the calyces, and branches of the renal blood vessels and nerves
Macula Densa
-in each nephron, the final part of the ascending limb of the loop of Henle makes contact with the afferent arteriole serving that renal corpuscle -because the columnar tubule cells in this region are crowed together, they are called ________________
Hormonal regulation
-involves angiotensin II and atrial natriuretic peptide (ANP)
Countercurrent flow
-kidney establishes this between the filtrate in the limbs of the Loops of Henle and the blood in the peritubular capillaries and Vasa Recta -in order to reabsorb all the nutrients and fluid needed while filtering out toxins
Urethra
-leaves the bladder and allows urine to be excreted -4 cm in length in women -24 cm in length in men
Juxtaglomerular Apparatus (JGA)
-macula densa and juxtaglomerular cells -helps regulate blood pressure within the kidneys -high BP=increase filtration=increase urine output -low BP (dehydrated)=decrease filtration=decrease urine output
Cortex of the kidney
-main function is filtration (of blood) to form urine
Medulla of the kidney
-main function is to collect and excrete urine
1. CO2 2. H+ and NH4+
-maintaining the body's proper pH requires cooperation mainly between the lungs and the kidneys 1. Lungs eliminate _____ -provides a Rapid response (minutes) 2. Kidneys eliminate _____ and ______ ions and concentrate bicarbonate -Slower response (hours-days) -the alimentary canal (digestive) and integumentary system (skin) provide minor contributions
Cortical nephrons
-make up about 80-85% of the 1 million microscopic nephrons that comprise each kidney -their renal corpuscles are located in the outer portion of the cortex, with short loops of Henle that penetrate only a small way into the medulla -ascending limbs of their loops of Henle consist of only a thick segment (simple cubodial), lacking any thin portions -receive their blood supply from peritubular capillaries that arise from efferent arterioles
Dilute urine
-mostly through obligatory reabsorption of water
1-2 L/d
-normal urine output; volume
Reabsorption of water
-obligatory or facultative -always moves by osmosis down its concentration gradient depending on the permeability of the tubule cells (which varies between the PCT, the different portions of the loop of Henle, DCT, and collecting ducts)
Obligatory reabsorption of water
-occurs when it follows the solutes as they are reabsorbed (to maintain the osmotic gradient) -in Loop of Henle
Renal autoregulation
-occurs when the kidneys themselves regulate GFR
Mildly aromatic
-odor
4.6-8.0; average 6.0
-pH
1. Renal artery and 2. renal vein
-pass into the substance of the kidney (the parenchyma) at the hilum 1. allows entrance of arterial blood -very large branches of the aorta, and up to a third of total cardiac output can pass through them to be filtered by the kidneys 2. allows exit of arterial blood
Renal Papilla
-point of the pyramid -collects urine
Festrations
-pores -formed by the epithelium of the visceral and parietal layers of the renal corpuscle -act as a filtration (dialysis) membrane -prevents filtration of blood cells but allows all components of blood plasma to pass through -Slit membrane between pedicels: prevents filtration of medium-sized proteins
Glomerular filtration
-pressure forces filtration of waste-laden blood in the glomerulus -the glomerular filtration rate (GFR) is the amount of filtrate formed in all the renal corpuscles of both kidneys each minute -deals with blood volume -the formation of a protein-free filtrate (ultra filtrate) of plasma across the glomerular membrane -the body's entire extracellular fluid volume is filtered about 12 times per day -the vast majority must be reclaimed, with just a small portion being excreted in the urine
Active and passive
-reabsorption of fluids, ions, and other substances occurs by both of these
Renin
-released by cells of the JGA -when blood volumes and blood pressure decrease or the sympathetic NS is stimulated, the walls of the afferent arterioles are stretched less caused the release of __________ -clips off a 10-amino-acid peptide called angiotensin I from angiotensinogen, which is synthesized by hepatocytes -by clipping off two more amino acids, angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II which is the active form of the hormone
ADH
-released by the posterior pituitary in response to low blood flow in this part of the brain -affects facultative water reabsorption by increasing the water permeability of principal cells in the last part of the distal convoluted tubule and throughout the collecting duct -in the absence, the apical membranes of principal cells are almost impermeable to water -increase H2O reabsorption in blood=decrease urine output
Atrial natriuretic peptide (ANP)
-released when a sudden large increase in BP stretches the cardiac atria -used when high BV -causes the glomerulus to relax, increasing the surface area for filtration -dilate -increase GFR = increase urine
Renal 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
1. Minor and 2. Major calyces
-renal papilla is the location where the medullary pyramids empty urine into cupcake structures called _______________ 1. singular tube, 8-18 2. two or more come together, 2-3 -receive urine from the papilla of one renal pyramid -one the filtrate enters the ______, it becomes urine because no further reabsorption can occur (no more changes can be made)
180-200 mg/dl
-renal threshold of glucose -when this level is exceeded (as in diabetes mellitus), the glucose is said to "spill" into the urine (meaning the substance which is not normally present in urine begins to appear)
around 1
-specific gravity
Aldosterone
-stimulates the principal cells in the collecting ducts to reabsorb more Na+ and Cl- and secrete more K+ -the osmotic consequence of reabsorbing more Na+ and Cl- is that more water is reabsorbed, which increase blood volume and blood pressure -acts on collecting duct by reabsorbing solutes causing H2O to follow
Renal threshold
-surpassed when there are higher than normal amounts of substances present in the filtrate -when that happens, the substance cannot be reabsorbed fast enough, and it will be excreted in the urine
Micturition
-the act of emptying the bladder -urination -requires a combination of voluntary and involuntary muscle contractions -when volume increases, stretch receptors send signals to a _________ center in the Spinal Cord triggering a spinal reflex - the _____________ reflex -in early childhood, we learn to initiate and stop the reflex voluntary
Nephron
-the functional unit of the kidney -it is a microscopic structure composed of blood vessels and tubes that collect the filtrate which will ultimately become urine -renal tubes=simple cubodial
Tubular secretion
-the movement of waste materials from the body, capillaries which surround the nephron, into the filtrate -regulate pH of the blood (H+) -taking H+ out of blood to filtrate -occurs at a site other than the filtration membrane (in the proximal convoluted tubule, distal convoluted tubule, and collecting ducts) by Active Transport
Countercurrent exchange
-the process by which solutes and water are passively exchanged between the blood of the vasa recta and interstitial fluid of the renal medulla as a result of countercurrent flow -this provides O2 and nutrients to the renal medulla without washing out or diminishing the gradient -reabsorption of fluid and electrolytes and the formation of concentrated urine
Tubular reabsorption
-the process of returning important substances from the filtrate back to the body -return to blood -fenestrated -the process of returning important substances ("good stuff") from the filtrate back into the renal interstitium, then into the renal blood vessels and back into the body
Ureters
-transport urine from the renal pelvis of the kidneys to the bladder using peristaltic waves, hydrostatic pressure (pressure of fluid) and gravity to move the urine -there is no anatomical valve at the opening of the ______ into the bladder -urine is constantly entering bladder (no valves)
Transparent
-turbidity
Renal Pelvis
-urine drains into this single large cavity after it leaves the major calyces -then urine flows out through the ureter (tube leading to ureter)
1. Glomerular Blood Hydrostatic Pressure 2. Capsular Hydrostatic Pressure 3. Blood Colloid Osmotic Pressure 4. Net Filtration Pressure
1. 55 mmHg 2. 15 mmHg 3. 30 mmHg 4. 10 mmHg
Blood plasma filtration through the nephron
1. Renal corpuscle: glomerular capillaries into the glomerular capsule 2. Filtered fluid passes into the renal tubule: -Proximal convoluted tubule (PCT) -loop of Henle -Distal convoluted tubule (DCT) : of many nephrons empty into a single... 3. Collecting duct: (makes final changes to urine); unite and converge into several hundred large... 4. Papillary ducts (papilla): which drain into the.... 5. Minor calyces, major calyces, renal pelvis, and ureters
Loop of Henle: 1. Descending limb 2. Ascending limb
1. composed of a simple squamous epithelium -impermeable to solutes but allows for the passage of water 2. may be either "thin" (composed of simple squamous epithelium) or "thick" (composed of simple caboodle to low columnar cells) -some nephrons contain both thin and thick -allows for passage of solutes but impermeable to water
Bowman's capsule 1. Visceral layer 2. Parietal layer
1. made of modified simple squamous epithelial cells called Podocytes. -the many foot-like projecitons of these cells (pedicels) wrap around the single layer of endothelial cells of the glomerular capillaries and form the inner wall of the capsule 2. a simple squamous epithelium and forms the outer wall of the capsule
1. Cortical nephron 2. Juxtamedullary nephron
1. short loop of Henle; stays in the cortex 2. long loop of Henle that goes into the medulla -enables kidneys to create a concentration gradient in the renal medulla and to excrete very dilute or very concentrated urine
Net filtration
Blood Hydrostatic Pressure - Blood Osmotic Pressure - Capsular Hydrostatic Pressure = ? 55-30-15 = 10 mmHg
