Urinary System Flashcards
Functions of the kidneys
(Hint: 6 )
Structure of urinary system
Urine produced from the kidneys move from:
Kidney ➡️ renal pelvis ➡️ ureters ➡️ bladder ➡️ urethra
The kidney has two regions :
Cortex and Medulla
Arterial blood enters the kidney through which artery ?
Renal artery
The renal artery divides into ______________________ , then subdivides into numerous ____________________.
Interlobar arteries
Afferent arterioles
Which blood vessels deliver blood to the glomeruli
Afferent arterioles
What are glomeruli
Capillary networks that produce blood filtrate that enters the urinary tubules
(It filters the blood from the afferent arterioles, and that filtrate moves into the urinary tubules while the now filtered blood continues into the efferent arteriole.)
The blood remaining in the glomerulus leaves through an ________________________.
Efferent arteriole
The efferent arteriole delivers the blood to _________________.
Peritubular capillaries
Peritubular capillaries surround what structure ?
Renal tubules
Where does the blood from the Peritubular capillaries drain into
Veins and eventually leaves the kidney as a single RENAL VEIN
Renal circulation summary steps:
- Blood goes from Renal artery > interlobar arteries > afferent arteriole
- Afferent arterioles delivers blood into glomeruli
- Glomerulus filters the blood and the blood filtrate enters urinary tubules + the remaining filtered blood leaves through efferent arteriole
- The blood moves from efferent arteriole > peritubular capillaries > veins > renal vein
what is a nephron
Function unit of the kidney where urine is formed
How many nephrons in a kidney
About one million
Nephron blood circulation
Nephron filtrate flow in tubules
(After being filtered in the golmerulus , where does the filtrate go?)
Very important to know ALL these parts to understand the rest of the note
I know
3 main types of nephrons + how much each type makes up of total nephrons %
- Juxta-medullary (10%)
- Cortical nephrons (20%)
- Mid-cortical (70%)
Characteristics of juxta-medullary nephrons
- deep glomeruli (in cortex near medulla)
- long loops of Henle
- their peritubular capillaries are modified into VASA RECTA
What is vasa recta
Long hair-pin shaped blood vessels that surround the loop of Henle
(Modified peritubular capillaries in juxta-medullary nephrons)
What feature of the juxta-medullary nephron plays a role in concentrating urine (more water absorption) ?
Long loop of henle
Juxta-medullary nephrons play an important role in :
Concentration of urine
Vasa recta are modified ___________________________ for juxta-medullary nephrons .
Peritubular capillaries
Characteristics of cortical nephrons
- glomeruli in superficial cortex
- short loops of Henle
Characteristics of mid-cortical nephrons
- glomeruli in mid cortex
- loops of Henle are of intermediate length
Sympathetic stimulation effect on the kidney
(Important and easy)
- Contracts smooth muscles of major branches of renal artery + afferent arterioles + efferent arterioles = VASOCONSTRICTION
(Vasoconstriction > less blood flow > less blood filtration > ⬇️GFR)
- Acts on β adrenergic receptors in the juxtaglomerular apparatus to cause the release of RENIN (enzyme)
(Angiotensinogen ➡️ ٍRenin ➡️ Angiotensin 1)
(Angiotensin 1 ➡️ ACE ➡️ Angiotensin 2)
AND ANGIOTENSIN 2 IS A VASOCONSTRICTOR (so also ⬇️ GFR)
NOTE:
Renin and ACE are enzymes
- Acts on α adrenergic receptors in the collecting ducts to increase Na+ reabsorption
What converts angiotensinogen to angiotensin 1
Renin
Where is angiotensinogen produced
Liver
What produces Renin
Kidney (specifically juxtaglomerular apparatus)
What two cell types are present in the Juxtaglomerular apparatus
Granular cells
Macula dense
What happens to GFR when the sympathetic nervous system is activated and why
⬇️ GFR
Why?
- vasoconstriction
- renin (angiotensin 2 is vasoconstrictor)
Sympathetic stimulation effect on β adrenergic receptors
Release of renin from juxtaglomerular apparatus
Sympathetic stimulation effect on α adrenergic receptors in collecting duct
Increase Na+ reabsorption
What is renal blood flow
Blood volume delivered to the kidneys per unit time 
Unit of renal blood flow RBF
ml / min
L / min
Renal blood flow is _____ % of cardiac output
20%
If cardiac output if 5 L/min, then what is renal blood flow?
RBF is 20% of cardiac output so
20/100 x 5 = 1 L/min
What is renal plasma flow
Volume of plasma delivered to the kidneys every minute
Renal plasma flow depends on two things:
- Renal blood flow
- Hematocrit
Renal blood flow is regulated through three different ways:
- Autoregulation
- Neural regulation
- Humoral regulation
What is meant by renal autoregulation
Maintaining renal blood flow constant under changes in blood pressure in order to maintain constant GFR
(Meaning in order for the GFR to remain constant , the renal blood flow has to be constant as well , so that’s why we need autoregulation in case of changes in blood pressure) 
What is the blood flow formula
During autoregulation, which blood vessel is manipulated to control renal blood flow to kidneys?
Afferent arteriole
Describe what happens to the afferent arteriole during changes in blood pressure to keep the GFR constant !
BP ⬆️ = VASOCONSTRICTION = constant GFR
BP ⬇️ = VASODILATION = constant GFR
(We need to maintain blood flow to maintain constant GFR)
In autoregulation , increased blood pressure leads to ___________________ of afferent arteriole.
Vasoconstriction
In autoregulation , decreased blood pressure leads to ___________________ of afferent arteriole.
Vasodilation
In the absence of neural and hormonal factors, the kidney maintains renal blood flow and GFR ( through autoregulation) within what pressure range ?
80 to 200 mmHg
Neural regulation of renal blood flow is done by
Sympathetic noradrenergic (NE) nerve fibers
Humoral regulation of renal blood flow is done through
( you must know which causes vasoconstriction and vasodilation and which are involved in autoregulation)
Answer in the picture
Hints:
Vasoconstriction: AE
Vasodilation : NAP
Autoregulation: PEN
What is the first step in urine formation
Filtration
(Or glomerular filtration)
What occurs during filtration
Blood passes through the glomerulus and a fraction of it is filtered through the glomerular filtration barrier GFB
How much of plasma is filtered as blood passes through the glomerulus
20% of plasma
What is reabsorption
The retrieval of water and some solutes (NaCl, glucose, amino acids) from the tubule fluid back into the peritubular capillary blood
What is secretion
The addition of some substances from the peritubular capillary blood or from the tubule cells into the luminal fluid 
What is excretion
The solute and water eliminated in the urine are said to be excreted by the kidneys
What are the processes that occur along the nephron
Filtration
Reabsorption
Secretion
Excretion
How to calculate the amount excreted in the urine
Excreted = filtered - reabsorped + secreted
E = F - R + S
NOTE: NO BRACKETS IN THIS EQUATION
Filtration is due to __________ pressure in the glomerular capillaries
High
Difference between ultrafiltrate and plasma
They are similar BUT ultrafiltrate does NOT have:
- blood cells
- proteins
What is glomerular filtration rate
The volume of filtrate produced by BOTH kidneys every minute
Features of glomerular capillaries
Foot processes
Podocyte cell body
Pedicles
Three layers of the glomerular filtration barrier
- Fenestrated capillary endothelial cells
- Basement membrane
- Slit diaphragm between podocyte foot processes
ALL three layers of the GFB barrier are ________________ charged
Negatively
Effect of the nagetively charged GFB on different types of ions and neutral molecules
- ⬇️ filtration of anionic molecules (ex: albumin)
- ⬆️facilitates filtration of cationic molecules
- little impact on neutral molecules
NOTE:
Anion means negative ion
Cation means positive ion
True or false
The ultrafiltrate has very low amounts of plasma proteins 
True
Why does the ultrafiltrate have very low amounts of plasma proteins
- proteins are large in size
( GFB has small pore sizes) - proteins are negatively charged
(GFB is also negatively charged so they resell each other)
Effect of the GFB’s negative charge on small solutes (Na+, Ca2+, Cl-, HCO3-)
No effect at all (no repelling occurs)
They are freely filtered because they are verrry small
Filtration of solutes depend on
- Size
- Charge
The filtrate is formed under pressure called
Net filtration pressure
What are the different pressures involved in net filtration pressure
- PGC = hydrostatic pressure
- πGC = oncotic pressure
- PBS = hydrostatic pressure
- πBS = oncotic pressure
NOTE:
GC - glomerular capillary
BS - Bowman’s space
Which pressure favors filtration
PCG
Which pressures are against/oppose filtration
πGC
PBS
Which filtration pressure remains 0 in both afferent end and efferent end ? Why?
πBS
Because in normal conditions, there is no protein in the Bowman’s space that will pull the fluid and contribute to filtration.
What is glomerular hydrostatic pressure PCG
Pressure due to circulating blood in the capillary
This pressure FAVORS filtration 
What is glomerular oncotic pressure πGC
Pressure due to the presence of plasma proteins in the glomerular capillaries
This pressure is AGAINST filtration
What is interstitial hydrostatic pressure PBS
The pressure inside Bowman’s space
This pressure is AGAINST filtration
What is interstitial oncotic pressure πBS
Pressure due to the presence of proteins in Bowman’s space
USUALLY ZERO, because proteins are not filtered
Regulation of glomerular filtration rate GFR
- Constriction of afferent arteriole
(symmetric stimulation، Endothelin)
= ⬇️ renal blood flow = ⬇️ PCG = ⬇️GFR
- Dilation of efferent arteriole
( NO, ANP, Prostaglandins)
= ⬆️ renal blood flow = ⬆️ PCG = ⬆️ GFR
Understand how this mechanism works (easy)
- Low BP/Fight or flight/ Exercise = sympathetic stimulation
- Sympathetic stimulation causes:
- increased CO
- vasoconstriction of afferent
- increase in TPR (due to vasoconstriction) - Vasoconstriction of afferent causes :
low GFR = low urine production = high blood volume - Blood pressure is restored
ALSO NOTE:
high blood pressure ALSO causes sympathetic stimulation = vasoconstriction = to maintain constant GFR (autoregulation)
What is renal plasma clearance
The ability of the kidneys to remove molecules from the blood by excreting them into the urine
What is plasma clearance of a substance
The volume of plasma that was completely cleared of that substance per unit time
(Unit: ml/min)
Formula for clearance
NOTE: also know how to calculate excretion rate which is (Ux x V)
Effect of filtration, reabsorption, and secretion on clearance
Filtration = ⬆️ clearance
Reabsorption = ⬇️ clearance
Secretion = ⬆️ clearance
What is Inulin
- polymer of fructose
- exogenous (not produced by body)
- used to measure GFR
How is inulin clearance used to measure GFR
- inulin is administered intravenously
- inulin is ONLY filtered (not secreted or reabsorbed)
So
Amount filtered = Amount excreted
GFR = clearance of inulin
How to measure amount of inulin filtered (filtered load)?
How to measure amount of inulin excreted (excretion rate)?
Inulin filtered :
GFR x P(in)
Inulin excreted:
U(in) x V
Inulin was infused intravenously and the concentration in plasma was maintained at 0.5 mg/mL. Urine was collected and the following data were obtained.. 
Rate of urine formation is 2 ml/min
Concentration of inulin in urine was 30 mg/ml
Calculate GFR
Px = 0.5
Ux = 30
V = 2
GFR = (30 x 2) / 0.5 = 120 ml/min
Since this is inulin : GFR = clearance (that’s why we can use this formula)
Clearance of urea
Urea is both FILTERED and REABSORBED
It is filtered like inulin but 50% is reabsorption in proximal tubule
So….
Urea Clearance < GFR
Where is urea reabsorbed
Proximal tubule
Clearance of PAH
PAH is FILTERED and SECRETED
It is filtered like inulin and completely secreted in proximal tubule
So…
PAH clearance > GFR
What is PAH secretion used for ?
To estimate renal plasma flow RPF
Clearance of glucose
Glucose is FREELY FILTERED and COMPLETELY REABSORBED in proximal tubule
Glucose is reabsorbed by SGLT ( Na+ - glucose co-transport)
SGLTs are saturable so there is a maximum load of filtered glucose it can handle
This maximum load is called TRANSPORT MAXIMUM TM
TM = 375 mg/min
Glucose filtered load is = GFR x P(g)
BUT glucose excretion is NORMALLY = 0 (zero) !!
So plasma clearance = 0
What is responsible for the reabsorption of glucose in proximal tubule
SGLT
The maximum load SGLT can handle is called
Transport maximum
(Or tubular maximum)
How much is transport maximum for glucose
TM = 375 mg/min
Normally, how much is glucose excretion ?
ZERO
(Because normally for people with healthy diet , ALL of the glucose is reabsorbed back by SGLT so none is excreted)
If filtered glucose is higher than the TM, this condition is called
Hyperglycemia
(High amount of glucose in blood)
What is glucosuria
Excretion of glucose into the urine. This happens when the filtered glucose exceeds the transport maximum of SGLT

Excretion rate of glucose > zero
Clearance of glucose > zero
Plasma glucose concentration = 1 mg/mL
GFR = 120 ml/min
What is the filtered load of glucose
GFR x P(g) = 120 x 1 = 120 mg/min
Since 120 < 375 (TM)
Then ALL of the glucose is reabsorbed and none is excreted (zero)
If plasma glucose concentration = 4 mg/mL.
GFR = 120 mL/min

What is filtered load of glucose?
GFR x P(g) = 120 x 4 = 480
Since 480 > 375
Only 375 will be absorbed and the rest of the 480 will be excreted
Excreted glucose = 480 - 375 = 105 mg/min
_____% of filtrate is reabsorbed and _____% is excreted
99% reabsorbed
1% excreted
If 180 L is filtered a day, how many was excreted ?
180 x 1/100 = 1.8 L
Because only 1% of the filtrate is excreted , the rest of the 99% are reabsorbed
The minimum volume of water needed to excrete waste materials by the kidneys is called
Obligatory water loss (400 ml)
Where does water reabsorption occur and how does it happen
In PROXIMAL tubule by OSMOSIS
The proximal tubule reabsorbs _______% of the filtered Na+, water, and K+
67%
Normally, _______% of the glucose and amino acids and proteins filtered by the glomerulus are reabsorbed in the proximal tubule
100%
Two ways exchange of solutes between tubule and capillary can occur
- Paracellular pathway ( BETWEEN CELLS)
- Transcellular pathway (THROUGH CELLS)
Solute such as Na+ and Cl- are freely filtered, therefore there osmolarity of ultrafiltrate is similar to plasma which is about
300 mOsm/L
True or false
Osmolarity of ultrafiltrate is similar to plasma
True
Where is sodium reabsorbed
67% by proximal tubule
25% by thick ascending loop of Henle (TALH)
5-7% by distal tubule
3% By connecting segment and collecting duct
Where is water reabsorbed
67% by proximal tubule ✅
15% by thin descending loop of Henle ✅
0% NONE BY THE ASCENDING LOOP OR EARLY DISTAL TUBULE ❌
8-17% IN THE PRESENCE OF ADH ONLLLY⚠️
What is ADH
Antidiuretic hormone that is synthesized by the hypothalamus and stored in the posterior pituitary
Which part of the nephron is impermeable to water (does NOT reabsorb water)
Ascending loop of Henle AND early distal tubule
Water and solutes reabsorption in the proximal tubule
Water:
- passive transport : diffuses through tubular cells via aquaporin all the way into the capillary
Na+ :
- secondary active transport (when entering tubule) via SGLT2
- primary active transport (when leaving tubule into capillary) via ATPase
Glucose:
- secondary active transport (when entering tubule) via SGLT2
- passive (facilitated) diffusion (when leaving tubule into capillary) via GLUT2
Reabsorption of water is dependent on ______________
Solute reabsorption
Why?
Reabsorption of solutes creates osmotic pressure which causes water movement by osmosis from the lumen into the blood
Just like Na+, K+ is also reabsorbed in the _______________ and _______.

Proximal tubule and TALH
True or false
In a normal diet. potassium is secreted
True
Where is K+ secreted
Connecting segment and collecting duct
K+ is _____________ in a normal or high K+ diet.
K+ is ______________ in a low K+ diet
Secreted
Reabsorbed
Sodium reabsorption is regulated by:
- Angiotensin 2:
INCREASES NaCl reabsorption in proximal tubule - Aldosterone:
INCREASES NaCl reabsorption in connecting segment and collecting duct - ANP:
DECREASES Na+ and water reabsorption in collecting duct
INCREASES Na+ excretion (Natriuresis)
Effects of angiotensin 2 on sodium reabsorption
Increases NaCl reabsorption in proximal tubule 
Effect of aldosterone on sodium reabsorption
-Increases NaCl reabsorption in the connecting segment and collecting duct
- increases K+ secretion
True or false
aldosterone increases K+ secretion
True
Effect of ANP on sodium reabsorption
Decreases Na+ and water reabsorption
Increases Na+ excretion
What is natriuresis
Excretion of Na+ in urine
What regulates water reabsorption
- ADH
- increases water reabsorption in DISTAL tubule by increasing permeability of the collecting ducts to water ONLY - ⬆️ NaCl reabsorption = ⬆️ water reabsorption in PROXIMAL tubule
Which part of the nephron does ADH increase water reabsorption in
DISTAL tubule
True or false
ADH increases water and sodium reabsorption by increasing the permeability of collecting duct
False
ONLY water reabsorption (NOT sodium)
Easy summary diagram
Explanation:
1.Low sodium (either due to less intake or drinking too much water and diluting sodium) will lead to low sodium in the blood. This will trigger the hypothalamus and pituitary gland to decrease ADH to decrease water reabsorption.
- Decreasing water reabsorption will increase urine volume and lower blood volume.
- Low blood volume will stimulate the juxtaglomerular apparatus to secrete renin in order to increase angiotensin 2
- Angiotensin 2 will cause vasoconstriction to lower GFR AND to stimulate adrenal medulla to create more aldosterone
- Aldosterone will keep in sodium by increasing its reabsorption
- Sodium levels return to normal
Easy summary
Low water intake requires high ADH to increase water reabsorption and decrease urine secretion
High water intake requires low ADH to decrease water reabsorption and increase urine secretion
Renal function tests: What is an indicator of GFR
Inulin clearance
Renal function tests: what is an indicator of renal plasma/blood flow
PAH clearance
Renal function tests: what is an index of renal function
Plasma creatinine
(Creatinine is filtered and slightly secreted)
What is microalbuminuria
Increase in urine albumin meaning proteins are being filtered and excreted in the urine which normally shouldn’t happen because proteins are large and negative
List some kidney diseases
Acute renal failure
Glomerulonephritis
Renal insufficiency
