The Urinary System

Front 1

What is the function of the kidney?

Back 1

To regulate plasma and interstitial fluid by formation of urine.

Front 2

In the process of urine formation, what do kidneys regulate? (4 things)

Back 2

1. Volume of blood plasma (which contributes to blood pressure).
2. Waste products in plasma
3. Concentration of electrolytes
(Including Na+, K+, HCO3-, and others)
4. Plasma pH

Front 3

Where are the kidneys located?

Back 3

Paired kidneys are on either side of vertebral column below diaphragm.

Front 4

Starting with the kidneys, what organs does urine flow through when excreted from the body?

Back 4

Kidneys --> ureters --> bladder --> urethra

Front 5

What does the renal cortex consist of?

Back 5

Many capillaries and outer parts of nephrons

Front 6

What 2 main substructures does the renal medulla consist of?

Back 6

Renal pyramids separated by renal columns

Front 7

What do renal pyramids consist of?

Back 7

Minor calyces which unite to form a major calyx.

Front 8

What does the renal pelvis consist of and what function does it serve?

Back 8

It consists of conjoined major calyces and functions to conduction urine to ureters which empty into the bladder.

Front 9

What is micturition reflex?

Back 9

Urination.

Front 10

In micturition reflex, or urination, what causes spontaneous action potentials and contraction?

Back 10

The stretching of the bladder.

Front 11

Is the bladder controlled by sympathetic or parasympathetic nerves?

Back 11

parasympathetic

Front 12

What neurotransmitter receptors are targeted by drugs that deal with overactive bladders?

Back 12

Muscarinic ACh

Front 13

What creates the sense of urgency when one needs to urinate?

Back 13

Filling of bladder activates stretch receptors that send impulses to the micturition reflex center. This activates Parasympathetic neurons, causing contraction of detrusor muscle that relaxes the internal urethral sphincter, creating sense of urgency.

Front 14

When urination is consciously initiated, what physiological changes occur in order for urine to be expelled?

Back 14

When urination is consciously initiated, descending motor tracts to the micturition center inhibit somatic motor fibers of the external urethral sphincter and urine is expelled.

Front 15

What is the functional unit of the kidney? In general, what does it do? In general, what does it consist of?

Back 15

The nephron is the functional unit of the kidney. They are responsible for the formation of urine. It consists of small tubes and associated small blood vessels

Front 16

What blood vessel does blood enter the kidney through, and what are the subsequent blood vessels that blood travels through en route to the glomeruli?

Back 16

Enters through the renal artery.
Renal artery --> interlobar arteries --> arcuate arteries --> interlobular arteries -->afferent arterioles --> glomeruli.

Front 17

What are glomeruli?

Back 17

They are the mass of capillaries inside glomerular capsule that gives rise to filtrate that enters nephron tubule

Front 18

What drains blood from the glomerulus, and what pathway does it take back to the blood stream?

Back 18

Efferent arteriole drains glomerulus and delivers that blood to peritubular capillaries. Blood from peritubular capillaries enters interlobular veins.

Front 19

Describe the pathway of the nephron tubule system.

Back 19

Begins with glomerular capsule which transitions into proximal convoluted tubule (PCT), then to descthe ending and ascending limbs of Loop of Henle (LH), and finally the distal convoluted tubule (DCT) where it ends and empties into collecting duct (CD).

Front 20

Where is the glomerular (or Bowman's) capsule located, and what occurs there?

Back 20

This is where glomerular filtration occurs. The filtrate is then passes into the proximal convoluted tubule.

Front 21

What is the significance of microvilli on the walls of the proximal convoluted tubule?

Back 21

They increase surface area for reabsorption of salt, water, and other molecules needed by the body. They are transported from the lumen through the tubular cells and into surrounding peritubular capillaries.

Front 22

Differentiate between cortical and juxtamedullary nephrons.

Back 22

-Cortical nephrons originate in outer 2/3 of cortex
-Juxtamedullary nephrons originate in inner 1/3 of the cortex, have long Loops of Henly, and are important in producing concentrated urine.

Front 23

Glomerular Capillaries are fenestrated. What does this mean?

Back 23

This refers to the fact that g. capillaries have large pores between their endothelial cells, big enough to allow any plasma molecule to pass, making them 100-400x more permeable than other capillaries.

Front 24

What prevents most proteins from entering the filtrate?

Back 24

Two things. Their large size and the fact that they are negatively charged since the slit diaphragms through which the filtrate contents must pass through are also negatively charged.

Front 25

What protein normally enters the filtrate, only to be reabsorbed? By what means is it reabsorbed?

Back 25

Albumin is reabsorbed by receptor-mediated endocytosis.

Front 26

What is proteinuria? What causes this?

Back 26

Defects in the slit diaphragm results in massive leakage of proteinin the filtrate and thus appears in the urine.

Front 27

What is the Glomerular Filtration Rate (GFR)? What are the average rates for men and women? Per day?

Back 27

The GFR is the volume of filtrate produced by both kidneys/min. Women average 115 ml/min. Men average 125 ml/min.

Front 28

How is the GFR regulated?

Back 28

-both extrinsic and intrinsic (autoregulation) mechanisms
-vasoconstriction or dilation of afferent arterioles affects rate of blood flow to glomeruli and thus GFR

Front 29

What leads to vasoconstriction? What effect does vasoconstriction have on GFR and urine production?

Back 29

sypathetic activity. Vasoconstriction lowers GFR, which in turn lowers urine production.

Front 30

Define Renal Autoregulation. What two mechanisms are responsible for it?

Back 30

The ability of kidneys to maintain relatively constant GFR inspite of fluctuating Blood Pressure.

Mech 1: Myogenic constriction of afferent arteriole due to smooth muscle responding to an increase in arterial pressure.
Mech 2: GFR Is also maintained by negative feedback between afferent arterioles and volume of filtrate (tubuloglomerular feedback). An increased flow of filtrate sensed by macula densa (part of juxtaglomerular apparatus) in the thick ascending LH signals afferent arterioles to constrict.

Front 31

Where do molecules travel if they are being re-absorbed? When is water transported in the reabsorption process?

Back 31

Back into the blood. Water is NEVER transported. Only molecules are transported, and water simply follows by osmosis.

Front 32

Describe the mechanism of reabsorption in the proximal tubule.

Back 32

There is coupled transport of glucose and Na+ into the cytoplasm. Na+ is actively transported across the basolateral membrane by a Na+/K+ pump. Glucose is then transported out of the cell by facilitated diffusion and is reabsorbed into the blood.

Front 33

What constant percentage of Na+, Cl-, and H2O is reabsorbed early in the tubule? What percentage is reabsorbed variably?

Back 33

85% reabsorbed early (65% in the PCT and 20% in the loop of Henly)
The remaining 15% is dependent on the level of hydration.

Front 34

Compare the osmolality in the interstiatial fluid of the medulla and that of the cortex and plasma. What is the significance of this gradient, and what causes it?

Back 34

Osmolality of medulla interstitial fluid (1200-1400 mOsm) is 4X that of cortex and plasma (300 mOsm)
This concentration gradient results largely from loop of Henle which allows interaction between descending and ascending limbs

Front 35

Define countercurrent flow.

Back 35

flow in opposite direction

Front 36

In terms of permeability to water and ability to actively transport, differentiate between the ascending and descending limbs of the loop of Henle.

Back 36

The ascending limb is impermeable to water and can actively transport Na+, Cl-, and K+ out into the interstitial fluid.

The descending limb is permeable to water, and cannot transport of Na+, Cl-, or K+.

Front 37

Explain the flow of molecules and water throughout the loop of Henle due to the Countercurrent Multiplier System.

Back 37

Extrusion of NaCl from the ascending limb makes the surrounding interstitial fluid more concentrated. The high concentration in the interstitial area pulls more water out of the descending limb. Fluid in the descending limb therefore increases in concentration.
When this more concentrated fluid reaches the ascending limb, more salt will be extruded out.

Front 38

Describe the active transport involved in the the ascending limb of the loop of Henle in terms of what ions are involved.

Back 38

In the thick segment, Na+ and K+ together with 2 Cl- enter tubule cells. Na+ then actively transported out across the basolateral membrane into interstitial space and Cl- follows passively
K+ diffuses back into filtrate; some also enters interstitial space.

Front 39

What is the signficance of the Countercurrent Multiplier System?

Back 39

Countercurrent flow and proximity allow descending and ascending limbs of Loop of Henle to interact in way that causes osmolality to build in medulla due to a positive feedback mechanism. Osmolality reaches equilibrium at 1400 Osm.

Front 40

What is the vasa recta?

Back 40

In the blood supply of the kidney, the vasa recta renis (or straight arteries of kidney, or straight arterioles of kidney) form a series of straight capillaries (recta is from the Latin for "straight") in the medulla.They lie parallel to the loop of Henle.

Each of the vasa recta has a hairpin turn in the medulla and carries blood at a very slow rate, two factors crucial in the maintenance of countercurrent exchange that prevent washout of the concentration gradients established in the renal medulla.

The maintenance of this concentration gradient is one of the components responsible for the kidney's ability to produce concentrated urine.

On the descending portion of the vasa recta, NaCl and urea are reabsorbed into the blood, while water is secreted. On the ascending portion of the vasa recta, NaCl and urea are secreted into the interstitium, while water is reabsorbed.

Descending section has urea transporters
Ascending section has fenestrated capillaries

Front 41

What is the role of urea in urine concentration?

Back 41

Urea diffuses out of inner collection duct into interstitial fluid in the medulla. Urea then passes into the ascending limb such that it recirculates in interstitial fluid in the medulla.
Water is reabsorbed by osmosis from collection duct.

Front 42

What important roles does the collection duct play? What does its permeability to salt and water depend on.

Back 42

Water conservation. The collection duct is impermeable to salt. It's permeability to water depends on the levels of ADH. When ADH increases, so does water retention, and urine decreases.

Front 43

What causes the secretion of ADH and where is it secreted from?

Back 43

Dehydration causes the pituitary gland to secrete ADH.

Front 44

What does the secretion of ADH stimulate?

Back 44

Inseration of aquaporins into the plasma membrane of the collection duct, drawing out water from it which is reabsorbed by the vasa recta.

Front 45

What is secretion?

Back 45

The active transport of substances from the peritubular capillaries into the tubular fluid. It opposite in direction to reabsorption.

Barriers same as for reabsorption
Transport mechanisms same but opposite direction

Front 46

How are many drugs, toxins, and metabolites secreted?

Back 46

By membrane transporters in the Proximal Tubule. The Major group of transporters involved is organic anion transporter (OAT).

Front 47

What are 5 common substances that are secreted?

Back 47

Potassium, Hydrogen ions, Choline, Creatinine, Penicillin

Front 48

What is the excretion rate?

Back 48

Excretion rate = (filtration rate + secretion rate) - reabsorption rate

Front 49

Why is inulin a useful polymer for measuring GFR?

Back 49

it is neither reabsorbed or secreted

Rate at which a substance is filtered by the glomeruli can be calculated:
Quantity filtered = GFR x P
P = inulin concentration in plasma
Quantity excreted (mg/min) = V x U
V = rate of urine formation in ml/min; U = inulin concentration in urine in mg/ml
Amount filtered = amount excreted
GFR(ml/min) = V(ml/min) x U(mg/ml) / P(mg/ml)

Front 50

What is renal plasma clearance (RPC)?

Back 50

The volume of plasma from which a substance is completely removed/min by excretion in urine.

Front 51

When is RPC = GFR?
When is RPC > GFR?
When is RPC < GFR?

Back 51

If substance is filtered but not reabsorbed then all filtered will be excreted RPC = GFR
If substance is filtered and reabsorbed then RPC < GFR
If substance is filtered but also secreted and excreted then RPC will be > GFR (=120 ml/ min)

Front 52

What is the formula for renal plasma clearance (RPC)?

Back 52

RPC = V x U / P
Where
V= urine volume/min
U= concentration of substance in urine
P = concentration of substance in plasma

Front 53

Compare the RPC of urea w/ that of inulin. Then discuss the RPC of gluose.

Back 53

RPC of urea = (2ml/min)(7.5mg/ml)/(0.2mg/ml) = 75ml/min
This is less than the clearance of inulin (120 ml/min). Thus 40-60% of filtered urea is always reabsorbed

Glucose has a clearance of 0, because none of it is excreted.

Front 54

What is PAH?

Back 54

Para-aminohippuric acid, or PAH, is an exogenous molecule that can be infused into the blood and used to measure total renal blood flow since virtually all of it exits through the urine (versus re-entering the blood stream). This accounts for both red blood cells and plasma.

Front 55

At what rate are glucose and amino acids normally reabsorbed?

Back 55

100%

Front 56

Where and how does the reabsorption of glucose and amino acids occur?

Back 56

Occurs in Proximal Tubule by carrier-mediated cotransport with Na+

Front 57

What is hyperglycemia? When does diabetes mellitus occur?

Back 57

Hyperglycemia occurs when plasma glucose concentration is abnormally high. Diabetes mellitus occurs when glycosuria results from hyperglycemia.

Front 58

In general, how do kidneys regulate levels of Na+, K+, H+, HCO3-, Cl-, and PO4-3 ?

Back 58

By matching excretion to ingestion

Front 59

What is the physiological significance of regulating plasma Na+? K+?

Back 59

Control of plasma Na+ is important in regulation of blood volume and pressure.
Control of plasma of K+ is important in proper function of cardiac and skeletal muscles.

Front 60

What does aldosterone regulate and where?

Back 60

In the urinary system, 90% of filtered Na+ and K+ is reabsorbed before Distal Tubule. Aldosterone regulates the K+ secretion and Na+ reabsorption of the remaining 10% in the distal tubule. In the absence of aldosterone, 80% of the remaining Na+ is reabsorbed in the Distal Tubule and the cortical Collection Duct. When aldosterone is high all of the remaining Na+ is reabsorbed.

Additionally, K+ almost completely reabsorbed in proximal tubule. Under aldosterone stimulation secreted into cortical collection ducts, all K+ in urine from secretion rather than filtration.

Front 61

What is the specialized region in each nephron where the afferent arteriole comes in contact with the thick part of the ascending limb of the Loop of Henle?

Back 61

the Juxtaglomerular Apparatus (JGA)

Front 62

What does the Renin-Angiotensin-Aldosterone System regulate? Where do each of these hormones come from?

Back 62

Blood pressure and water balance.

The R-A-A system is activated by the release of renin from the afferent arteriole through the juxtaglomerular apparatus. Renin converts angiotensinogen (secreted from the liver) to angiotensin I, which is converted to angiotensin II by an angiotensin-converting enzyme (ACE) in lungs. Angiotensin II stimulates the release of aldosterone.

Front 63

What stimulates renin release?

Back 63

Low blood volume and renal blood flow.

Front 64

What is Atrial Natriuretic Peptide (ANP)?

Back 64

An aldosterone antagonist that is produced by atria due to stretching of walls. ANP stimulates salt and H2O excretion and acts as an endogenous diuretic.

Front 65

From where and how is acid added to the blood? Where does output from the blood go?

Back 65

Input of blood acid from diet (proteins and fats) and metabolism (CO2, lactic acid, ketoacids).

Out as H+ to the kidneys and CO2 to the lungs.

Front 66

Explain Renal Acid-Base Regulation

Back 66

Kidneys help regulate blood pH by excreting H+ and/or reabsorbing HCO3-. Most H+ secretion occurs across walls of Proximal Tubule in exchange for Na+ (Na+/H+ antiporter).

Front 67

Explain Reabsorption of HCO3- in the Proximal Convoluted Tubule.

Back 67

When urine is acidic, HCO3- combines with H+ to form H2CO3 (catalyzed by CA on apical membrane of PCT cells)
H2CO3 dissociates into CO2 + H2O
CO2 diffuses into PCT cell and forms H2CO3 (catalyzed by CA)
H2CO3 splits into HCO3- and H+ ; HCO3- diffuses into blood

Front 68

What makes up the urinary buffering systems?

Back 68

Buffering reactions

HPO4-2 + H+  H2PO4-

NH3 + H+  NH4+ (ammonium ion)

Front 69

What are diuretics? Give an example.

Back 69

Diuretics are used to lower blood volume because of hypertension, congestive heart failure, or edema. They increase the volume of urine by increasing the proportion of glomerular filtrate that is excreted.

Examples include:
Loop diuretics are the most powerful; they inhibit AT salt in the thick ascending limb of LH.

Thiazide diuretics inhibit NaCl reabsorption in 1st part of DCT.

Carbonic anhydrase inhibitors prevent H2O reabsorption in PCT when HCOs- is reabsorbed.

Osmotic diuretics increase osmotic pressure of filtrate.

Front 70

What is acute renal failure? What causes it?

Back 70

Impaired ability of kidneys to excrete wastes and regulate blood volume, pH, and electrolytes.

Caused by atherosclerosis, inflammation of tubules, kidney ischemia, or overuse of NSAIDs (aspirin, ibuprofen, and naproxen).

Front 71

What is glomerulonephritis?

Back 71

It is inflammation of glomeruli. This is signified by autoimmune attack against glomerular capillary basement membranes, causing leakage of protein into urine resulting in decreased colloid osmotic pressure and resulting edema.

Front 72

What is renal insufficiency?

Back 72

Destroyed nephrons as a result of a disease. Clinical manifestations include salt and H2O retention and uremia (high plasma urea levels).

Treatment includes hemodialysis where the patient's blood is passed through a dialysis machine which separates molecules on basis of ability to diffuse through selectively permeable membrane.