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urinary – Chemistry

question

What organs comprise the urinary system?
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kidneys, urinary bladder, ureters, urethra
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Identify the functions of the urinary system.
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gluconeogenesis (during fasting)
produing hormones renin and erythropoietin
metabolize vitamin D to its active form
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Describe the location and external anatomy of a kidney.
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Bean shaped in retroperitoneal position in superior lumbar from t12 to L3. Lateral surface is convex and medial concave with a surface called renal hilum. Each kidney has an adrenal gland on top. The three layers are renal fascia, perirenal fat capsule, and fibrous capsule.
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Identify and describe the three layers of tissue that surround the kidney.
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renal fascia- outer layer of dense fibrous connective tissue that anchors the kidney and adrenal gland to surround structures 

perirenal fat capsule- a fatty mass that surrounds the kidney and cushions it against blows
fibrous capsule- a transparent capsule that prevents infections in surrounding regions from spreading to the kidney

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What is the primary neural innervation of the kidney?
How does the NS help regulate renal function?
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The renal plexus provides nerve supply to the kidney and ureter. Supplied by sympathetic fibers, which regulate renal blood flow by adjusting the diameter of renal arterioles and influencing the urine forming role of the nephrons.
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What are the two main parts of the nephron?
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glomerulus and renal tubule
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Name the vessels that carry blood into and out of a glomerulus.
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The efferent and afferent arteriole
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Describe the structure of the renal corpuscle.
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the glomerular capsule and the enclosed glomerulus. The glomerular casule is also called the bowman’s capsule and is double layered around the glomerulus (parietal and visceral layer) with capuslar space in between
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Identify the regions of the renal tubule and describe the histological characteristics of each.
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PCT- simple cuboidal ET, brush border, many mitochondria
Loop of Henle- thick segment (cuboidal or low columnar et) or thin segment (Squamous ET)
distal convoluted tube- cuboidal but little microvilli
question

Trace the tubular system of a nephron from the Bowman’s capusle to the renal pelvis
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Bowman’s Capsule ; Fenestrated Membrane ; Basement membrane ; Pedicels ; Proximal Convoluted Tubule ; Descending Thick Limb of Loop of Henle ; Descending Thin Limb of Loop of Henle ; Ascending Thin Limb of Loop of Henle ; Ascending Thick Limb of Loop of Henle ; Distal Convoluted Tubule ; Collecting Duct ; Minor Calyx ; Major Calyx ; Renal Pelvis
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Trace the circulatory pathway of a kidney from the renal artery to the renal vein.
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Aorta-renal artery- segmental artery-interlobar artery- arcuate artery- cortical radiate artery- afferent arteriole-glomerulus (capillaries)- efferent arteriole- peritubular carillaires and vasa recta- cortical radiate vein-arctuate vein- interlobar vein- renal vein- IVC
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Describe the location and function of the peritubular capillaries and the vasa recta.
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peritubular capillaries arise from the efferent arterioles draining glomeruli. low pressure, porous capillaries that readily absorb solutes and water from the tubule cells as these substances are reclaiming from the filtrate

vasa recta- bundles of long straight vessels that extend deep into the medulla paralleling the longest loops of henle, concentrate urine.

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Based on location and structure, what are the two types of nephrons.
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cortical nephrons (85%)- entirely located in cortex, has short loop of henle and glomerulus is further from corticomedullary junction, efferent arteriole supplies peritubular capillaries

juxtamedually nephon- originate close to cortex-medulla junction, impt role in kidneys ability to produce concentrated urine., get into medulla because of long loop of henle, efferent artieriole supples vasa recta

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Which type of nephron is most numerous? why type plays the most important role in regulating urine concentration? which type performs most of the reabsorptive and secretory functions of they kidney?
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cortical is most numerous, juxtamedullary nephron concentrates urine, cortical nephrons reabsorb and secrete;
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Describe the location and general function of the juxtaglomerular apparatus (JGA).
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JGA is located at point where DCT lies;against;the afferent aretiole of its own nephron. Important in regulating rate of filtrate formation and systemic blood pressure.
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Where are the macula densa cells located? what is their function?
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Macula densa cells are in the ascending limb of the loop of Henle adjacent to granular cells. They are chemoreceptors that respond to changes in the NaCl content of filtrate.
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Where are the juxtaglomerular cells located? What is their function?
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Juxtaglomerular cells are in the afferent arteriole wall and act as mechanoreceptors that sense blood pressure in afferent arteriole. They are smooth muscle cells that secrete renin.
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Identify and define the three steps involved in urine formation.
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glomerular filtration- the kidneys dump cell and protein free blood into the renal tubules and collecting ducts.
tubular reabsorption-kidney reclaims everything the body needs to keep (glucose, a.a., water, salt)
tubular secretion-adding stuff to the contained to be secreted (fine tuning the bodie’s chemical balance.
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Describe the filtration membrane.
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The filtration membrane lies between the blood and capsular space and consists of the glomerular capillary endothelium, the basement membrane, and the visceral membrane of the glomerular capsule. Allows only small solutes to pass through and water.
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How does the structure of the filtration membrane contribute to the process of glomerular filtration?
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The structure is pourous and has fenestrations. Most proteins are negatively charged which repels the negative charge plasma proteins.
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What factors promote glomerular filtration? what factors oppose glomerular filtration?
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Glomerular hydrostatic pressure promotes glomerular filtration, while colloid osmostic pressure of glomerular blood and capsular hydrostatic pressure oppose it.
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Why is net filtration pressure so much higher in the glomerulus than in the systemic capillaries?
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1) greater relative permeability of the filtration membrane
2)glomerular capillaries present in a large surface area
3) glomerular blood pressure is higher.
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How does NFP affect the glomerular filtration rate?
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NFP and glomerular filtration rate are directly proportional. 
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What effect does a change in glomerular hydrostatic have on GFR?
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An increase in glomerular hydrostatic pressure increases NFP, which then increases GFR.
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What is the effect on GFR or vasocontriction/vasodilation of the afferent arterioles? the efferent arterioles?
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Vasoconstriction of afferent arterioles descreases GFR, vasodilation increases GFR

Vasodilation of efferent arterioles decreases GFR, vasoconstriction of efferent arterioles increases GFR

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What effect does a change in colloid osmotic pressure have on GFR?
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Increased colloid osmotic pressure decreases GFR
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To what does the term renal autoregulation refer?
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intrinsic control of the kidneys
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Describe the composition osmolarity of glomerular filtrate.
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The osmolarity of glomerular filtrate is everything found in blood plasma except proteins. It is high in osmolarity?
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describe the myogenic mechanism and tell how it promotes a stable GFR.
answer

Increasing systemic blood pressure cause afferent arteriole to constrict so the blood flow in the glomerulus will not reach damaging levels. The contrary is true. This keeps GFR in normal limits.
question

Describe the roles of the macula densa and the JG cells in the tubuloglomerular feedback mechanism.
answer

When GFR increases, there is not enough time for reabsoprtion and the concentration of NaCl in the filtrate remains high. This causes macula densa cells to release vasoconstrictor chemical (maybe ATP) that causes constriction of afferent arteriole. Same for the contrary. Slowing down GFR allows more time for filtrate processing.
question

What cells release renin?
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juxtaglomerular cells
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Describe the steps in the reaction cascade triggered by renin.
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When renin is released, it converts angiotensinogen (liver) to angiotensin 1, which is converted into angiotensin 2 by angiotensin converting enzyme

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What is the end product of the renin-angiotensin cascade and what are its affects?
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angiotensin II
– activates smooth muscle of arterioles throughout the body raising mean arterial blood pressure
-angiotensis II stimulates reabsoprtion of Na+, by triggering the release of aldosterone from adrenal cortex and by acting on renal tubules
-stimulates hypothalamus to release antidiuretic hormon and activates he hypothalamus thirst center
-increases fluid reabsorption by decreasing peritubular capillary hydrostatic pressure 
-makes mesangial cells to contract, decreasing surgace area available for filtration
question

What factors trigger renin release?
answer

When systemic blood pressure decreases, granular cells of juxtaglomerular apparatus of kidney secretes renin. (below 80 mmhg)

Direct stimulation of granular cells via b1 adrenergic receptors by renal sympathetic nerves

stimulation of the granular cells by input from activated macula densa cells (Decreased release of ATP)

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What is the effect of angiotensin II on GFR?
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It reduces GFR
question

how is the release of atrial natriuretic peptide stimulated? what are the effects of anp?
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When there is an increased stretch of the atria, ANP is secreted by atrial cells. The effects of ANP are increased GFR, decreased NA+ reabsorption, decreased secretion of ADH, aldosterone, renin.
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under what conditions would the sympathetic division of the ANS override renal autoregulation and decrease GFR?
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if mean arterial pressure is above 180mmhg then autoregulation ceases.
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What is renal clearance?
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Renal clearance is the volume of plasma that is cleared of a certain solute in a given amount of time (usually a minute)
question

What characteristics of inulin and creatinine make them useful in determining clearance and GFR.
answer

Inulin is freely filtered across the glomerulus and is neither reabsorbed or secreted and has a RC of 125 ml/min

Creatinine has an RC of 140ml/min and is freely filtered but also secreted in small amounts.

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Why is plasma creatinine the more useful index for GFR in clinical situations?
answer

Since creatinine clearance reflects the rate at which kidneys filters blood, it is a good indicator of GFR. Bad filtration means creatinine levels rise.
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What is the maximal clearance value in a normal kidney?
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The normal maximal clearance value is 625 mmHg
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why is the clearance value for PAH an index of renal blood flow
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since PAH is completely secreted by the kidney, it  can be used to determine blood flow.
question

Why is the normal glucose clearance equal to 0ml/min??
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Since we need glucose in the body, we need to reabsorb it all or it is not filtered.
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If you were given measures of plasma creatinine, urine concentration of creatinine and urine volume, how would you calculate GFR?
answer

question

 Describe what happens during tubular reabsorption? ie h20 and solutes from __to__)
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H20 and solutes move from the tubule lumen into the blood of the peritubular capillaries or vasa recta.
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Describe what happens during tubular secretion (solutes are moved from __ to __)
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materials are moved from the blood into the filtrate (so unwanted materials are moved from blood)
question

Why is the active reabsorption of NA + so important to the overall process of tubular reabsorption?
answer

It provides the means by which many other solutes and water are absorbed (requires ATP). As it is actively transported into peritubular capillilaries from the tubule cell, this makes the tubule cell have a net negative charge, so positive ions will want to go in.
question

What is transport maximum? what happens when a solute in the filtrate exceeds renal threshold?
answer

Transport maximum is when the carriers are fully saturated (working at fastest rate). When the filtrate exceeds renal threshold the solute will show up in the urine. This also disrupts water reabsorption since the solutes will stay in tubule and exert osmotic pressure.
question

Generally describe the reabsorption and secretion activities in the various regions on the renal tubule.
answer

PCT- mostly reabsorption
Loop of Henle descending limb- water leaves via osmosis
ascending- water cant leave , but NA+, K+, 2Cl- can be rebasorbed; no secretion
DCT- regulated by hormones and can reabsorb na+cl+, water
question

Where is the Na+/K+/2cl- symporter located? Why is it important?
answer

It is located in the thick segment of the ascending limb. It is important because it is the main means of na+ entry at the luminal surface of the thick segment. It maintains K+ gradient. 
question

Describe the contransport process involved in the reabsoprtion of glucose.
answer

Glucose is reabsorbed by secondary active transport via na+k+ atpase pump present on the basolateral membrane. Na+ is transported by primary active transport. This energy is used to pump glucose into the tubule cell. Also from the electrochemical gradient since K+ leaks back out into interstitial fluid.
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Describe the process by which bicarbonate ions are reabsorbed in the PCT. What role do Na+/H+ antiporters play in this process?
answer

Hco3- does secondary active transport linked to H+ secretion and Na+ reabsorption by paracellular diffusion driven by electrochemical gradient for Cl. 

dissociation of carbonic acid liberates hc03- as well as H+. Hc03- leaves tubule cell either accompanied by na+ or in exchange for Cl-. So HCo3- reabsorption depends on active secretion of H+, mostly by NA+ H+ aniporter, but also by H+atpase.

question

What process is involved in water reabsorption?
answer

Osmosis occurs (obligatory water reabsorption in places where there re a lot of aquaporins like in the PCT). This is driven by solute reabsoprtion.
question

In what part of the tubule is the greatest amount of water reabsorbed? in what part of the tubule is water reabsorption regulated by ADH?
answer

The PCT is where most water is reabsorbed, and the distal portions of the tubule is where ADH regulates water reabsorption. If there is not ADH, then no aquaporin 2. 
question

How does aldosterone help regulate reabsorption in the distal convoluted tubule?
answer

Aldosterone acts on principal cells to NA+ reabsorption and K+ secretion. So very little urinary Na+ excretion.
question

What factors trigger aldosterone release?
answer

1) decreased blood volume or BP
2) hyponatremia- low Na
3) hyperkalemia- too much K+
4)the renin angiotensin system
question

Describe the osmotic gradient in the interstitial fluid of the renal cortex and medulla.
answer

The cortex has an mOsm/kg or 300 and then slowly increases to 1200 in the deepest part of the medulla.
question

How does the countercurrent mechanism help establish and maintain the renal osmotic gradient?
answer

The interaction between the flow of filtrate through ascending and descending limbs of the long loops of Henle of juxtamedullary nephrons and the flow of blood through the ascending and descending portions of the vasa recta blood vessels.
question

What role does the vasa recta play in  maintaining the medullary osmotic gradient?
answer

The vasa recta helps to protect the system by preventing rapid removal of salt from the medullary interstitial space, and by removing reabsorbed water. Essentially preserves the medullary gradient.
question

How does urea recycling help to establish the medullary osmotic gradient and promote water reabsorption? In what segment of the tubule is urea rebabsorbed?
answer

Urea enters the ascending limb via facilitated diffusion. Water is reabsorbed but urea is left behind. When filtrate reaches the collecting duct in the deep medullary region, it is highly concentrated and sent into interstitial fluid via facilitated diffusion of medulla, which is recycled back into the thin loop of henle. This contribues to high osmolality in medulla.
question

How does the medullary osmotic gradient promote the formation of a concentrated urine?
answer

The medullary osmotic gradient is responsible for moving water out of the collecting duct into the interstitial fluid, making the urine more concentrated. This depends on the presence of ADH.
question

Compare the osmolarity (tonicity) of the following solutions: body fluids (ie. the blood and interstitial fluid), glomerular filtrate, filtrate in the proximal convoluted tubule (PCT), filtrate at the deepest part of the loop of Henle (juxtamedullary nephrons), filtrate in the DCT, urine at the beginning of the collecting tubule, urine at the end of the collecting tubule.
answer

blood plasma is 300mOsm
urine at the beginning of the collecting tubule 100mOsm
urine at the end of the collecting duct= more concentrated than beginning of tubule
filtrate at the deepest part of the loop of Henle is 1200 mOsm
filtrate in DCT- gets more diluted as it goes up
filtrate in PCT- more concentrated as it goes down
glomerular filtrate- about 300 mOsm
question

What is the effect of ADH on urine volume and concentration?
answer

ADH makes urine volume decrease and concentration increase.
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Explain the physiologic mechanisms involved in maintaining homeostasis when the osmolarity of body fluids increases. what happens when the osmolarity decreases?
answer

When osmolarity of body fluids increase, the body needs to secrete more urine–diuretics increase urine production.

When osmolarity decreases ADH is released from posterior pituitary, which increases number of aquaporin 2 channels in apical membrane of distal tubule.  This promotes water reabsorption into the blood of the peritubular capillaries.

question

How do changes in blood pressure affect urine volume?
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higher blood pressure, higher urine volume. Lower blood pressure, lower urine volume.
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Describe the composition and pH of urine.
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95% water, nitrogenous wastes (urea, creatinine, uric acid), electrolytes, drugs, excess water soluble vitamins). pH is approx 6 (but range is 4.5-8)
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What are the metabolic sources of urea, uric acid, and creatinine?
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urea comes from excess nitrogen or from ammonia, uric acid comes from amino acids, and creatinine comes from muscle metabolism
question

Trace the flow of urine from the collecting tubules to the point where it leaves the body.
answer

collecting ducts–>minor calyx–>major calyx–>renal pelvis–>ureter–>kidneys–>bladder–> out of body
question

Describe the structure of the ureter.
answer

Slender tube that convey urine from the kidneys to the bladder. Has 3 tissue layers-mucosa, muscularis, adventia. No valves.
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How is urine propelled through the ureter to the urinary bladder?
answer

The weight of the bladder as it fills compresses ureters at the ureter bladder junction, prevent backflow of urine (nooo valve)
question

What is the detrusor muscle? What does it do?
answer

The detrusor muscle is in the muscularis of the urinary bladder. It stretches and thins allowing the bladder to store more urine without significant rise in internal pressure.
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Compare and contrast the male and female urethras
answer

female- 3-4 cm in length, lies directly posterior to the pubic symphysis, tightly bound to the anterior vaginal wall by fibrous CT, external urethral orifice lies anterior to the vaginal opening

male- about 20 cm, passes through prostate gland, urogenital diaphragm and the penis (3 parts- prostatic, membranous, penile/spongy urethra), serve as conduit for semen and urine

question

Describe the micturition reflex
answer

a reflex arc involving parasympathetic motor fibers from s2 and s2 level. causes rhythmic contractions of destrusor muscle and inhibits contraction internal urethral sphincter, helps us decide whether or not to urinate (impulses up cord to pons, and prefrontal region of cerebral cortex.