A&P Ch.15: Urinary System
Terms
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- What are the components of the urinary system?
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-two kidneys
-two ureters
-one urinary bladder
-one urethra - What do the kidneys do?
- -make urine and carry out other vital functions
- What do the ureters do?
- -carry urine to the urinary bladder
- What does the urinary bladder do?
- -collects, stores, and releases urine
- What does the urethra do?
- -empties urine from the body
- What are 6 functions of the urinary system?
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-eliminating organic waste products, such as urea
-regulating blood volume and pressure
-regulating plasma concentrations of ions
-helping stabalize blood pH
-conserving nutrients
-assisting the liver in detoxifying poisons - How does the urinary system regulate blood volume and pressure?
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-adjusting the volume of water lost
-releasing erythropoietin and renin - How does the urinary system help stabilize blood pH?
- -by controlling loss of hydrogen ions and bicarbonate ions in urine
- What is the gross anatomy of kidney?
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-bean shaped
-smooth surface (except cattle) - What is the hilus of the kidney?
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-point of entry for renal artery and renal nerves
-point of exit for renal vein and ureter - How many renal pyramids are typically in each kidney?
- -6 to 18
- Where does the tip of each pyramid go and what are they called?
- -renal papilla project into minor calyces
- What are renal columns?
- -cortical tissue that passes between pyramids
- What is a renal lobe?
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Produces urine and consists of: -renal pyramid
-overlying area of renal cortex
-adjacent tissues of renal columns - What path does urine take to get to the bladder?
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-renal papilla
-minor calyx
-major calyx
-renal pelvis
-ureter - How much of cardiac output do the kidneys recieve?
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-20 to 25% of total cardiac output
-1200 mL of blood flows through kidneys each minute
-kidney recieves blood through renal artery - How does blood get from the renal artery to the renal vein?
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-renal artery
-segmental arteries
-interlobar arteries
-arcuate arteries
-interlobular arteries
-afferent arterioles
-nephrons
-venuoles
-interlobular veins
-arcuate veins
-interlobar veins
-renal veins - What is the functional unit of the kidney?
- -nephron
- What does the nephron consist of?
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-renal corpuscle
-renal tubule - What parts make up the renal tubule?
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-proximal convoluted tubule
-the loop of Henle
-distal convoluted tubule - What makes up the renal corpuscle?
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-Bowmans capsule
-glomerulus - What is Bowman's capsule?
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-forms the outer wall of the renal corpuscle
-encapsulates the glomerular capillaries - What is the glomerulus?
- -capillary network inside Bowmans capsule
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What are the two epitheliums that make up Bowman's capsule?
What is the space between them? -
-parietal
-vesceral
-capsular space - What is the perietal epithelium made of?
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-a simple squamous epithelium, forms the outer wall
-continuous with visceral epithelium - What does the visceral epithelium cover?
- -covers glomerular capillaries
- What does the visceral epithelium consist of?
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-large cells (podocytes)
-have complex processes or "feet" that wrap around specialized lamina densa of glomerular capillaries
-have filtration slits - What are filtration slits in visceral epithelium?
- -narrow gaps between adjacent pedicels
- What delivers blood to the glomerulus? From the glomerulus?
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-afferent arteriole
-efferent arteriole - Once blood leaves glomerulus through efferent arteriole, where does it go?
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-flows into peritubular capillaries
-drains into small venules - What type of capillaries are in the glomerulus and how many?
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-fenestrated capillaries
-50 intertwining capillaries - What is the proximal convoluted tubule?
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-first part of renal tubule nearest to Bowman's capsule
-follows a winding, convoluted course - What is the loop of Henle?
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Consists of:
-a descending limbs
-a sharp turn
-an ascending limb
-each limb contains a thick segment and a thin segment - Where is the distal convoluted tubule?
- -convoluted tubule beyond the loop of Henle
- What are the parts of the renal tubule?
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-proximal convoluted tubule
-loop of Henle
-distal convoluted tubule - What are collecting ducts for and where are they?
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-receive fluid from many nephrons
-begin in cortex, descend into medulla, carry fluid to papillary duct that drains into a minor calyx - Describe the cortical nephrons
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-85% of all nephrons
-located mostly within superficial cortex of kidney
-loop of Henle is relatively short
-efferent arteriole delivers blood to a network of peritubular capillaries (which surround entire renal tubule - Describe juxtamedullary nephrons
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-have long loops of Henle that extend deep into medulla
-peritubular capillaries connect to vasa recta (long, straight capillaries parallel with loop of Henle) - What is the goal of urine production?
- -maintain homeostasis by regulating volume and composition of blood including excretion of metabolic waste products
- What is urea?
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-the most abundant organic waste
-produced during the breakdown of amino acids - What is creatinine?
- -generated in skeletal muscle tissue by breakdown of high-energy compound, creatine phosphate
- What is uric acid?
- -formed by the recycling of nitrogenou sbases from RNA molecules
- What are the three basic processes of urine formation?
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-filtration
-reabsorption
-secretion - What causes filtration in urine formation?
- -blood pressure forces water and small solutes across membrane into capsular space.
- During reabsorption in urine formation, where do molecules go?
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-out of tubule and into the peritubular blood
*selective process - What is the difference between the secretion and reabsorption of molecules?
- -secretion moves molecules out of peritubular blood and into the tubule for excretion instead of into peritubular blood.
- What makes up the filtration membrane?
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-capillary endothelium
-lamina densa
-filtration slits - What forces move water through membrane pores?
- -hydrostatic pressure forces water through membrane pores
- What molecules can move through filtration pores?
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-metabolic wastes and excess ions
-glucose, free fatty acids, amino acids, and vitamins - What is glomerular filtration governed by?
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-glomerular hydrostatic pressure
-capsular hydrostatic pressure
-blood colloid osmotic pressure - What are the three filtration pressures?
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-glomerular filtration
-net hydrostatic pressure
-filtration pressure - What is glomerular hydrostatic pressure?
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-45 to 55 mm Hg blood pressure
-significantly higher than capillary pressures in systemic circuit - What is capsular hydrostatic pressure
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-opposes GHP, approximately 15 mm Hg
-results from resistance to flow along nephron and conducting system - What is blood colloid osmotic pressure?
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-osmotic pressure resulting from presence of suspended proteins
- about 25 mm Hg - What is Net hydrostatic pressure?
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GHP-CsHP
-about 35 mm Hg - What is filtration pressure?
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NHP-BCOP
-about 10 mm Hg - What is the glomerular filtration rate?
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-GRF
-the amount of filtrate produced in the kidneys each minute
-about 125 mL per min in human
-any factor that alters the filtration pressure will change the GFR - At what blood pressure will kidney filtration cease?
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-when it drops by 20%
*very sensitive to changes in blood pressure - What are the three levels of GFR control?
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-autoregulation (local level)
-hormonal regulation (initiated by kidneys)
-autonomic regulation (by sympathetic divisions of ANS) - What is the purpose of autoregulation in GFR control?
- -maintains GFR despite changes in local blood pressure and blood flow
- What does reduced renal blood pressure trigger in autoregulation?
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-dilation of afferent arteriole
-dilation of glomerular capillaries
-constriction of efferent arterioles - What does a rise in renal blood pressure cause in autoregulation of GFR?
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-stretches walls of afferent arterioles
-causes smooth muscle cells to contract
-constricts afferent arterioles
-decreases glomerular blood flow - What are some hormonal regulations of GFR?
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-atrial natriuretic peptides
-renin-angiotensin system - What is atrial natriuretic peptides?
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-released by heart in response to stretching walls and due to increased blood volume or blood pressure
-trigger dilation of afferent arterioles and constriction of efferent arterioles
-elevates glomerular pressures and increases GFR - What is the renin-angiotensin system?
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-decline in blood pressure causes the juxtaglomerular apparatus to release renin
-renin stimulates production of angiotensin I and II (by liver) - What types of fibers mostly make up autonomic regulation?
- -sympathetic postganglionic fibers
- What does sympathetic activation cause in autonomic regulation?
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-constricts afferent arterioles
-decreases GFR
-slows filtrate production - How can changes in kidney blood flow due to sympathetic stimulation be opposed?
- -at local level by autoregulation
- How does the filtrate compare to blood plasma which is a result of glomerular filtration?
- -very similar but none (or very few) plasma proteins
- Where does reabsorption and secretion occur?
- -in every segment of nephron except in renal corpuscle
- Where do reabsorbed materials go?
- -enter peritubular fluid and diffuse into peritubular capillaries
- At the kidney level, what transport activities are there?
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-diffusion
-osmosis
-channel-mediated diffusion
-carrier-mediated transport - What is the renal threshold?
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-the plasma concentration where a specific compound or ion begins to appear in urine
-varies with the substance involved
-renal threshold for glucose approximately 180 mg/dl - Where does the most reabsorption and secretion occur in the kidneys?
- -proximal convoluted tubule
- What things are reabsorbed in the proximal convoluted tubule?
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-filtrate produced in the renal corpuscle (60-70%)
-glucose, a.a., other organic nutrients (99-100%)
-actively reabsorb ions (60-70%)
-passively reabsorb urea, Cl-, and lipid-soluble materials - What does the proximal convoluted tubule secrete?
- -H+, NH4+, creatinine, drugs, toxins
- What process reabsorbs fluid and molecules in the Loop of Henle?
- -countercurrent multiplication
- What does the descending limb of Henle's loop look like?
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-thin
-permeable to water
-impermeable to solutes - What does the ascending limb of Henle's loop look like?
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-impermeable to water
-active solute transport - How does the countercurrent multiplication and concentration of urine use a positive feedback loop?
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-pumps out Na and Cl to elevate osmotic conc. in peritubular fluid
-osmotic flow out of descending limb
-now highly conc soln moves into ascending limb accelerates transport of Na and Cl into peritubular fluid - What are two benefits of countercurrent multiplication?
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-efficiently reabsorbs solutes and water (before tubular fluid reaches DCT and collecting system)
-establishes concentration gradient (permits passice reabsorption of water from tubular fluid in collecting system) - How much of original filtrate volume reaches DCT?
- -15 to 20%
- What dictates reabsorption of water in DCT?
- -ADH stimulation
- What dictates reabsorption of Na+ in DCT?
- -aldosterone stimulation
- What is secreted at DCT?
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-H+
-NH4+
-creatinine
-drugs
-toxins - What does the collecting system secrete and why?
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-H+
-HCO3-
-controls body fluid pH - What is obligatory water reabsorption?
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-water absorption in teh proximal convoluted tubule and the descending limb of the loop of Henle
-can NOT be adjusted
-recovers 85% of filtrate - What is facultative water reabsorption?
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-the amount of water reabsorbed along the distal convoluted tubule and the collecting system
-can be precisely controlled (because segments are relatively impermeable to water except in the presence of ADH). - What are the two types of reabsorption methods in urine volume control?
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-obligatory water reabsorption
-facultative water reabsorption - What are the hormones that play a part in controlling urine volume?
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-ADH
-Aldosterone
-Atrial natriuretic hormones (ANH) - What does ADH do in urine control?
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-controls the permeability of the distal convoluted tubule and collecting system to water
-by increasing special water channels in the apical cell membranes - What does aldosterone do?
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-controls sodium ion pumps along most of the distal convoluted tubule and the proximal portion of the collecting system
-raise the sodium concentration of blood and thus promoting reabsorption of water - What does atrial natriuretic hormones do?
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-promotes loss of sodium via urine
-opposes aldosterone
-cause the kidney to reabsorb less water and thereby produce more urine - What is the vasa recta?
- -returns solutes and water reabsorbed in medulla to general circulation without disrupting the concentration gradient
- Describe acidemia.
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-pH of plasma falls below 7.35
-physiological state called acidosis - Describe alkalemia.
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-pH of plasma rises about 7.45
-physiological state result is called alkalosis - What are the limits of plasma pH where animals can't survive?
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-<6.8
->7.7 - What are the triple actions used to prevent abnormal pH developments
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-buffer system
-respiratory compensation
-renal compensation - What are the three parts of the buffer system?
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1) carbonic acid-bicarbonate buffer system
2) phosphate buffer system
3) protein buffer system - How does the respiratory compensation affect the carbonic acid-bicarbonate buffer system?
- -by the pulmonary ventilation
- What occurs with renal compensation?
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-kidneys excrete alkaline or acidic urine as needed
-vary rates of H+ secretion and HCO3- reabsorption (depending on the pH of the ECF) - What is the normal composition of urine?
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pH: 6
U.G: 1.003-1.030
osmolarity: 855-1335
water: 93-97%
volume: 1200 ml/day
color: clear yellow
odor: varies w/composition
bact content: sterile - What is urination called?
- micturition
- How do signals begin and travel as bladder fills?
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-stretch receptors stimulate sensory fibers in pelvic nerve
-afferent fibers to sacral spinal cord
-efferent fibers stimulate ganglionic neurons in wall of bladder
-postganglionic neuron in intramural ganglion stimulates detruscor muscle contraction
-interneuron relays sensation to thalamus
-projection fibers from thalamus deliver sensation to cerebral cortex - What is the last step of micturition?
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-voluntary relaxation of external urethral sphincter
-this causes relacation of internal urethral sphincter