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A&P Ch.15: Urinary System


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What are the components of the urinary system?
-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?
-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?
-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?
-bean shaped
-smooth surface (except cattle)
What is the hilus of the kidney?
-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?
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?
-renal papilla
-minor calyx
-major calyx
-renal pelvis
How much of cardiac output do the kidneys recieve?
-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?
-renal artery
-segmental arteries
-interlobar arteries
-arcuate arteries
-interlobular arteries
-afferent arterioles
-interlobular veins
-arcuate veins
-interlobar veins
-renal veins
What is the functional unit of the kidney?
What does the nephron consist of?
-renal corpuscle
-renal tubule
What parts make up the renal tubule?
-proximal convoluted tubule
-the loop of Henle
-distal convoluted tubule
What makes up the renal corpuscle?
-Bowmans capsule
What is Bowman's capsule?
-forms the outer wall of the renal corpuscle
-encapsulates the glomerular capillaries
What is the glomerulus?
-capillary network inside Bowmans capsule
What are the two epitheliums that make up Bowman's capsule?
What is the space between them?
-capsular space
What is the perietal epithelium made of?
-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?
-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?
-afferent arteriole
-efferent arteriole
Once blood leaves glomerulus through efferent arteriole, where does it go?
-flows into peritubular capillaries
-drains into small venules
What type of capillaries are in the glomerulus and how many?
-fenestrated capillaries
-50 intertwining capillaries
What is the proximal convoluted tubule?
-first part of renal tubule nearest to Bowman's capsule
-follows a winding, convoluted course
What is the loop of Henle?
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?
-proximal convoluted tubule
-loop of Henle
-distal convoluted tubule
What are collecting ducts for and where are they?
-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
-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
-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?
-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?
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?
-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?
-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?
-metabolic wastes and excess ions
-glucose, free fatty acids, amino acids, and vitamins
What is glomerular filtration governed by?
-glomerular hydrostatic pressure
-capsular hydrostatic pressure
-blood colloid osmotic pressure
What are the three filtration pressures?
-glomerular filtration
-net hydrostatic pressure
-filtration pressure
What is glomerular hydrostatic pressure?
-45 to 55 mm Hg blood pressure
-significantly higher than capillary pressures in systemic circuit
What is capsular hydrostatic pressure
-opposes GHP, approximately 15 mm Hg
-results from resistance to flow along nephron and conducting system
What is blood colloid osmotic pressure?
-osmotic pressure resulting from presence of suspended proteins
- about 25 mm Hg
What is Net hydrostatic pressure?
-about 35 mm Hg
What is filtration pressure?
-about 10 mm Hg
What is the glomerular filtration rate?
-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?
-when it drops by 20%
*very sensitive to changes in blood pressure
What are the three levels of GFR control?
-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?
-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?
-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?
-atrial natriuretic peptides
-renin-angiotensin system
What is atrial natriuretic peptides?
-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?
-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?
-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?
-channel-mediated diffusion
-carrier-mediated transport
What is the renal threshold?
-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?
-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?
-permeable to water
-impermeable to solutes
What does the ascending limb of Henle's loop look like?
-impermeable to water
-active solute transport
How does the countercurrent multiplication and concentration of urine use a positive feedback loop?
-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?
-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?
What does the collecting system secrete and why?
-controls body fluid pH
What is obligatory water reabsorption?
-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?
-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?
-obligatory water reabsorption
-facultative water reabsorption
What are the hormones that play a part in controlling urine volume?
-Atrial natriuretic hormones (ANH)
What does ADH do in urine control?
-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?
-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?
-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.
-pH of plasma falls below 7.35
-physiological state called acidosis
Describe alkalemia.
-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?
What are the triple actions used to prevent abnormal pH developments
-buffer system
-respiratory compensation
-renal compensation
What are the three parts of the buffer system?
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?
-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?
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?
How do signals begin and travel as bladder fills?
-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?
-voluntary relaxation of external urethral sphincter
-this causes relacation of internal urethral sphincter

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