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What are the Urinary System Organs?

Kidneys, Urinary bladder, Ureter, and Urethra

What is an example of a major excretory organ?


What are kidney functions?

Removal of toxins, metabolic wastes, and excess ions from the blood, Regulation of blood volume, chemical composition, pH, Gluconeogenesis during prolonged fasting, Endocrine functions, and Activation of vitamin D

How do the kidneys regulate blood volume?

Determines how much filtrate it needs to put back in blood to equalize blood volume

How do the kidneys regulate chemical composition?

It determines what electrolytes to take up and how much to put back

How do the kidneys regulate pH?

By determining how much hydrogen needs to be taken up or put back to keep the bloods pH between 7.35-7.45

How do the kidneys regulate endocrine function?

by releasing Renin (regulation of blood pressure and kidney function) and Erythropoietin

Where in the body are the kidneys located?

Retroperitoneal, in the superior lumbar region; the right kidney is lower than the left

Describe how the kidney is shaped?

Convex lateral surface, concave medial surface

Ureters, renal blood vessels, lymphatics, and nerves enter and exit where?

At the hilum of the kidney

What is the renal cortex?

A granular superficial region

What is the renal medulla?

The cone shaped medullary (renal) pyramids separated by renal columns

What are the renal lobes?

A medullary pyramid and its surrounding cortical tissue

What are the renal papillae?

Tip of pyramid; releases urine into minor calyx

What is the renal pelvis?

The funnel-shaped tube within the renal sinus

What are the minor calyces of the kidney?

The branching channels of the renal pelvis that filter into the major calyces

What are the major calyces of the kidneys?

The branching channels of the renal pelvis that collects urine from minor calyces, and empties urine into the pelvis

How does urine flow from the collecting ducts?

Collecting duct → renal papillae →renal pyramids → minor calyces → major calyces → renal pelvis → ureters → bladder → urethra

How much blood flows into the kidneys via the renal artery each minute?

¼ of cardiac output or 1200 mL

How is the nerve supply delivered to the kidneys?

Via the sympathetic fibers from the renal plexus

State the sequence of blood flow through the kidney starting from the aorta?

Aorta → renal artery → segmental artery → interlobar artery → arcuate artery → cortical radiate artery →[afferent arteriole →glomerulus (capillaries) →efferent arteriole → peritubular capillaries and vasa recta](glomerulus blood filtration) → cortical radiate vein →arcuate vein → interlobar vein → renal vein → inferior vena cava

What is a nephron?

Structural and functional units that form urine

How many nephrons are there per kidney?

~1 million

What are the 2 main parts of a nephron?

Glomerulus and renal tubule

What is a glomerulus?

A tuft of capillaries that makes up part of a nephron

What is a renal corpuscle?

The glomerulus and its glomerular capsule (Bowman's capsule)

What is the purpose of having glomerulus composed of fenestrated glomerular endothelium?

Allows filtrate to pass from plasma into the glomerular capsule (Bowman's capsule)

What is a renal tubule?

Part of a nephron, that begins as a cup-shaped glomerular capsule (Bowman's capsule) surrounding the glomerulus and continues as the proximal convoluted tubule (PCT) and loop of henle, and finally distal convoluted tubule (DCT). This is where what is filtered out of the blood gets a chance to go back to blood or remain in tubules to turn into urine.

What is a proximal convoluted tubule (PCT)?

The tubule that is closest to the glomerulus; and composed of cuboidal cells with dense microvilli and large mitochondria. It is confined to the renal cortex.

What is the proximal convoluted tubules function?

Reabsorption and secretion

What is the loop of henle?

Ascending and descending limbs that connect the PCT and DCT.

What are the characteristics of the descending limb of the loop of henle?

It is composed of thin walls and is freely permeable to water but not solutes

What are the characteristics of the ascending limb of the loop of henle?

It is composed of a thick wall and is freely permeable to solutes but not water

What is the distal convoluted tubule (DCT)?

The tubule furthest from the glomerulus confined to the cortex.

What is the function of the distal convoluted tubule?

Functions more in secretion than absorption

What are collecting ducts?

A receiving chamber for many nephrons; that deliver urine from the nephrons through the papillae to be passed through the kidney and excreted.

What is the intercalated cells function?

Function in maintaining the acid-base balance of the body

What is the function of principal cells?

Help maintain the body's water and salt balance

What are the different types of nephrons?

Cortical and juxtamedullary

What are cortical nephrons?

Nephrons that almost entirely remain in the renal cortex therefore the reabsorption is occurring in the peritubular capillaries. Makes up the majority of nephrons (85%)

What are juxtamedullary nephrons?

Nephrons that consist of a long Loop of Henle that deeply invades the renal medulla; therefore reabsorption is occurring in the vasa recta

What are peritubular capillaries?

Capillaries that arise from efferent arteriole in cortical nephrons that cling to adjacent tubules

What are vasa recta?

Vessels that arise from efferent arterioles of juxtamedullary nephrons that are parallel to the long loops of henle.

What is the function of the vasa recta?

Formation of concentrated urine.

Explain the how the blood flow and filtration in the glomerulus is possible.

The blood enters the glomerulus via afferent arteriole and exits at the efferent arterioles. The movement is essential in creating backpressure in the glomerulus due to the size of the afferent (smaller) and efferent arterioles. The afferent arteriole gives rise to the glomerular capillaries where the high pressure forces the plasma (minus proteins) into the Bowman's capsule for filtration. The RBC's and protein continue out the efferent arterioles into the peritubular capillaries where many "lanes" open up reducing pressure.

What is the juxtaglomerular Apparatus?

The area where the cells of the DCT that touch the back of the glomerulus. Regulatory cells that controls flow rate of blood through the glomerular capillaries hence the rate of filtration. One per nephron.

How does the juxtaglomerular apparatus work?

Via granular cells in the afferent arteriole, macula densa cells in the DCT and extraglomerular mesangial cells.

What are granular cells?

Granular cells (juxtaglomerular/JG cells) in the arteriole changes vessel diameter by produce renin to by sensing the blood pressure in the kidneys

What are macula densa cells?

Macula densa cells in the DCT sense changes in sodium chloride content in filtrate, in order to adjust filtration rate.

What are extraglomerular mesangial cells?

Extraglomerular mesangial cells are communicator cells for the granular and macula densa cells.

Why is the juxtaglomerular apparatus important?

Regulation of filtrate formation and blood pressure

There is a lot of resistance in the afferent and efferent arterioles which cause blood pressure to do what?

Decline from 95 mm Hg to 8 mm Hg in the kidneys.

Why do we want the resistance in afferent arterioles?

Afferent: We don't want to blow out the capillaries in the glomerulus.

Why do we want the resistance in efferent arterioles?

Maintains high glomerular pressure, and reduces hydrostatic pressure in peritubular capillaries

What would happen to the glomerular capillaries if a person has chronic high blood pressure and what might be a sign of this?

Capillaries would burst, blood might be seen in the urine (blood in urine can mean many other things)

What is the filtration membrane?

The porous membrane between the blood and the capsular space that allows the passage of water and solutes smaller than most plasma membranes

What does the filtration membrane consist of?

Fenestrated endothelium of the glomerular capillaries, podocytes with foot processes and filtration slits), and gel-like basement membrane

How does the filtration membrane keep proteins and RBC from passing through?

Fenestrations prevent filtration of blood cells, basement membrane is negatively charged so it repels the proteins (large anions), and slit diaphragms also help to repel macromolecules

What are glomerular mesangial cells?

Cells in the filtration membrane that engulf and degrade macromolecules, they can also contract to change the total surface area available for filtration.

What membrane does the podocytes make up?

Visceral membrane of the glomerular capsule

How many times a day does the kidney filter the body's entire plasma volume?

60 times

What is filtrate?

Blood plasma minus proteins

What is urine?

Composed of less than 1% of total filtrate; contains metabolic wastes and unneeded substances.

What are the mechanisms of urine formation?

Glomerular filtration, tubular reabsorption, and tubular secretion

What is glomerular filtration?

A passive mechanical process driven by hydrostatic pressure that separates filtrate from blood, non-specifically. The molecules that are not filtered and move to efferent arteriole and maintains colloid osmotic pressure of the blood

Why is the glomerular filtration very efficient?

Because it has a large surface area.

What is glomerular blood pressure?

55 mm Hg

What is net filtration pressure (NFP)?

The pressure responsible for filtrate formation, it is simply the difference between the pressure in the capillaries in the glomerulus and the pressure in the filtrate. (10 mm Hg)

How is net filtration pressure determined?

NFP = HPg - (OPg + HPc)

What is the glomerular hydrostatic pressure (HPg)?

Pressure against inside of capillary walls (55 mm Hg)

What is the colloid osmotic pressure (Opg)?

Pressure put on filtrate water to want to go in and dilute out proteins due to intracellular proteins and electrolytes (30 mm Hg)

What is capsular hydrostatic pressure (HPc)?

Pressure exerted by filtrate on capillary wall that puts water back into capillaries (15 mm Hg)

What is glomerular filtration rate (GFR)?

Volume of filtrate formed per minute by the kidneys (120-125 mL/min)

What is glomerular filtration rate governed by (GFR)?

Total surface area available for filtration, filtration membrane permeability, and net filtration pressure

How is glomerular filtration regulated?

By Intrinsic controls and extrinsic controls

What are the intrinsic controls controlling glomerular filtration?

Renal autoregulation; act locally with the kidney. Regulated by smooth muscle in response to stretch. Has to do with myogenic mechanisms and tubuloglomerular feedback mechanism.

What would you expect to see in GFR as a result of myogenic mechanism?

If you increase the diameter of the afferent arteriole - more blood flows into glomerular capillaries increasing hydrostatic pressure therefore increasing GFR (b/c less time for reabsorption). If you decrease the arteriole diameter - less blood would flows into glomerular capillaries which decreases hydrostatic pressure and therefore decrease GFR (b/c more time for reabsorption).

What would you expect to see in GFR as a result of the tubuloglomerular feedback mechanism?

Juxtaglomerular apparatus looks at systemic blood pressure and sodium chloride levels and decides how to regulate glomerular filtration.

If the sodium chloride is high in filtrate and the GFR is high, the tubules don't have enough time to absorb it, so the juxtamedullary apparatus slows filtration. How does this happen?

Macula densa cells of the JGA respond to high sodium chloride by releasing a vasoconstricting chemical that acts on the afferent arteriole constricts the blood coming in and slows down flow rate allowing for more time for absorption.

If blood pressure was to increase what would you expect to see as a result of myogenic mechanism?

Constriction of afferent arterioles to help maintain glomerular filtration rate and protect glomeruli from damaging high BP

If blood pressure was to decrease what would you expect to see as a result of myogenic mechanism?

Dilation of afferent arterioles helps maintain glomerular filtration rate

What are the extrinsic controls controlling glomerular filtration?


What extrinsic controls are in charge under normal conditions at rest?

Renal blood vessels are dilated and renal autoregulation mechanisms prevail

What extrinsic controls are in charge when under extreme stress?

Norepinephrine and epinephrine are released, causing vasoconstriction (which reduces urinary output) and triggers the release of renin (which triggers the renin-angiotensin mechanism)

What is the renin-angiotensin mechanism?

Renin to angiotensinogen to angiotensin I which is catalyzed by ACE into angiotensin II

What are the effects of angiotensin II?

Triggers the release ofaldosterone, and ADH . Activates the thirst center, Constricts efferent arterioles, increases fluid reabsorption, and causes glomerular mesangial cells to contract, decreasing the surface area available for filtration

What are the other factors affecting GFR?

Prostaglandin E2, Intrarenal angiotensin II, and adenosine

How does prostaglandin E2 affect GFR?

Vasodilator that counteracts vasoconstriction by norepinephrine and angiotensin II. It prevents renal damage when peripheral resistance is increased

How does Intrarenal angiotensin II affect GFR?

Reinforces the effects of hormonal angiotensin II

How does adenosine affect GFR?

Vasoconstricts afferent arteriole

What is tubular reabsorption?

The return of almost all of the filtrate (99%) to the peritubular capillaries by a selective transepithelial process, and hormonal regulation. Includes active and passive process.

What are the 2 routes of tubular reabsorption?

Transcellular and Paracellular

What is the transcellular route in tubular reabsorption?

Transport takes place through the cell plasma membranes. Can transport through luminal membranes, diffuses through the cytosol, and across the basolateral membrane of tubule cells, into the interstitial fluid and into the peritubular capillary

What is the paracellular route in tubular reabsorption?

Transport takes place between cells and is limited to water movement and reabsorption of calcium, magnesium, phosphate, and some sodium in the PCT where tight junctions are leaky.

What if a substance cannot travel via transcellular or paracellular?

By transport proteins in the plasma membrane of the luminal wall that are going to actively transport them into the cell and then sometimes when they get in the cell the mechanism is diffusion and sometimes there are transport mechanisms that will take them further.4

Sodium is the most abundant active cation in the filtrate. How is it reabsorbed?

Primary active transport out of the tubule cell by the sodium-potassium ATPase pump. Secondary active transport or facilitated diffusion mechanisms through the luminal membrane. Meaning that once these cells expend some energy (Active transport) getting sodium from the filtrate through the wall of the tubule into the interstitial fluid and on in to the capillary you have created an ion gradient. By means of water and other solutes, water usually carries lots of solutes with it including sodium, waters going to follow salt and bring a lot of electrolytes with it (Passive transport).

What kind of pressure do you want to aid in reabsorption of sodium?

You want low hydrostatic pressure and high osmotic pressure in the peritubular capillaries to promote bulk flow of water and solutes.

How are organic nutrients reabsorbed?

Secondary active transport

What is the function of the PCT?

Site of most reabsorption. Reabsorbs 65% of sodium and water, all nutrients, ions, and small proteins.

What is reabsorbed in the descending loop of henle?

Water is reabsorbed from the tubule into the peritubular capillaries

What is the body reabsorbing in the ascending loop of henle?

Sodium, potassium, and chloride is reabsorbed from the tubule into the peritubular capillaries

What is reabsorbed in the DCT and collecting ducts?

All reabsorption is hormonally regulated. Calcium is absorbed by the hormone PTH, water is reabsorbed by the hormone ADH, and sodium is reabsorbed by the hormone aldosterone and ANP.

Where is aldosterone secreted?

Aldosterone is secreted by the granular cells in the juxtaglomerular apparatus in response to low sodium content or low blood pressure. If both of these exist you take in sodium and water follows transports more water into blood stream to increase blood pressure and sodium will follow increasing sodium content.

What are tubular secretions?

Reverse of reabsorption: selective addition to urine (capillaries to urine). At the end of the renal tubules sensory cells determine if there is an imbalance of potassium, hydrogen, ammonia, creatinine, and organic acids and fix it by putting it back in the urine. Also plasma proteins that are transporting things around in the blood and they need to get rid of it will secrete it back into filtrate. Eliminates undesirable substances that have been passively reabsorbed. Rids the body of excess potassium, and controls blood pH by altering amount of hydrogen or bicarbonate in the urine

How is Urine concentration and volume regulated?

Sensory cells in the JGA look at osmolality. High salt concentration in filtrate will cause the afferent arteriole to dilate increasing volume. The opposite for low concentration.

How does the countercurrent mechanism works and what it is useful for?

The countercurrent mechanism, in the loop of henle, establishes the osmotic gradient is to allow the nephron to form more concentrated urine by allowing for maximal water reabsorbing. The Descending loop is only permeable to water, therefore as move water leaves the filtrate causing sodium concentration to increase (increased osmalarity). The ascending loop is only permeable to NaCl, which wants to leave its area of high concentration and go into the interstitial space which because of the descending loop has higher water content. The result is decreased solute concentration (decrease in osmalarity) in the ascending limb. When the water moves into the space surrounding the nephron, this attracts the NaCl from the ascending limb into that space. And when the NaCl from the ascending limb moves into the space it encourages water from the descending limb to follow, therefore they work together to create this gradient.

Where is filtrate diluted?

Ascending loop of henle

Where is diluted filtrate travel in the absence of ADH?

In the absence of ADH, dilute filtrate continues into the renal pelvis as dilute urine, but you realize if ADH is present ADH is going to stimulate the uptake of sodium and water follows.

How is concentrated urine formed?

Depends on the medullary osmotic gradient and ADH; which triggers reabsorption of water in the collecting ducts

What is facultative water reabsorption?

Water reabsorption that depends on the presence of ADH 99% of water in filtrate is reabsorbed

What are diuretics?

Chemicals that enhance urinary output

What are osmotic diuretics?

Substances not reabsorbed (high glucose in diabetes patients)

What is renal clearance?

Volume of plasma "cleared" of a particular substance in a given time

What is renal clearance tests used for?

Determine GFR, Detect glomerular damage, or follow the progress of renal diseases.

How would you calculate renal clearance?

RC (renal clearance rate- mL/min) = U (concentration of the substance in urine mg/mL) x V (flow rate of urine formation- ml/min) all divided by P (concentration of the same substance in plasma. RC = (U x V)/P

What is the normal value for renal clearance?

125 mL/min

What does a renal clearance less than 125 mL/min signify?

The substance was reabsorbed

What does a renal clearance of 0 signify?

The substance is completely reabsorbed

What does a renal clearance higher than 125 signify?

The substance is secreted

What is the normal color and transparency of urine?

Clear, pale to deep yellow (due to urochrome)

What can alter the color of urine?

Drugs, vitamin supplements, and diet can alter the color

What can cloudy urine indicate?

Urinary tract infection

What is the odor of urine?

Slightly aromatic when fresh

What develops upon standing urine?

Ammonia odor

What may alter the odor of urine?

Some drugs and vegetables (asparagus)

What is the pH of urine?

Slightly acidic ~pH 6, range is 4.5 to 8.0

What can alter the pH of urine?

Diet prolonged vomiting, or UTI

What is the specific gravity of urine?

1.001 to 1.035, depending on solute concentration

What is the function of ureters?

Ureters transport urine from the kidneys to the bladder

What is the anatomical position of the ureters?

Retroperitoneal; they enter the base of the bladder through the posterior wall

How do the ureters prevent backflow?

As bladder pressure increases, distal ends of the ureters close

What are the three walls of the ureter?

Lining of transitional epithelium, smooth muscle muscularis (contracts in response to stretch), and outer adventitia of fibrous connective tissue.

What are renal calculi?

Kidney stones form in renal pelvis

Why are kidney stones formed of?

Crystalized calcium, magnesium, or uric acid salts

What can occur when there are large kidney stones present?

Block ureter, cause pressure and pain in kidneys

What are factors that can cause Kidney stones?

Chronic bacterial infection, urine retention, ↑calcium in blood, or ↑pH of urine

What is the function of the urinary bladder?

Urinary bladder is a muscular sac for temporary storage reservoir for urine

What is the anatomical position of the bladder?

Retroperitoneal, on pelvic floor, posterior to pubic symphysis: On males the prostate gland surrounds the neck inferiorly, and on females it is anterior to the vagina and uterus

What is the trigone?

Smooth triangular area outlined by the openings for the ureters and the urethra. This area is where infections tend to persist.

What are the 3 layers of the bladder wall?

Transitional epithelial mucosa, thick detrusor (3 layers of smooth muscle), and fibrous adventitia (peritoneum on superior surface only)

When does the urinary bladder collapse?

When empty, rugae appear

In what direction and when does the urinary bladder expand?

Expands and rises superiorly during filling without a significant rise in internal pressure

What is the function of the urethra?

Urethra is a muscular tube that transports urine out of the body

What is the lining of the urethra?

Mostly psuedostratified columnar epithelium, except transitional epithelia near bladder, and stratified squamous epithelia near external urethral orifice

What are the urethra sphincters?

Internal urethral sphincter and external urethral sphincter

What is the internal urethra sphincter?

Involuntary smooth muscle at bladder-urethra junction that contracts to open

What is the external urethra sphincter?

Voluntary skeletal muscle surrounding the urethra as it passes through the pelvic floor

Describe the female urethra.

3-4 cm in length tightly bound to the anterior vaginal wall. External urethra orifice is anterior to the vaginal opening, posterior to the clitoris

Describe the male urethra.

Carries both semen and urine and is composed of three regions the prostatic urethra, the membranous urethra, and the spongy urethra

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