Chapter 25: Urinary system Flashcards
What are the four organs that make up this system?
Kidneys, ureters, urinary bladder, and urethra
What are the 7 functions of the urinary system?
1) maintain fluid and electrolyte balance
2) remove metabolic wastes
3) maintain acid - base balance
4) secretes renin to control BP
5) secretes erythropoietin (RBC synthesis)
6) carries out gluconeogenesis during prolonged fasting
7) activates vit D to regulate Ca absorption in DT
Briefly explain what gluconeogenesis is.
It is the production of glucose from non-carb substances like protein and fats
Where do blood, lymph, nerves, and ureters enter the kidneys?
at the hilium
Are the kidneys retroperitoneal?
yes
What are the three layers of supportive tissues for the kidneys. Briefly describe what their function is.
RENAL FASCIA: outer layer
- dense fibrous CT
function - anchors kidneys to body wall
ADIPOSE CAPSULE: middle layer
- perirenal fat
function - cushions and protects
RENAL (FIBROUS) CAPSULE: innermost
- attached to kidney surface
function - prevents spread of infection
What are the three regions of the kidney?
cortex (outer)
medulla (middle)
renal pelvis (inner)
Describe the cortex of the kidneys
- lighter in colour
- granular layer (b/c of gromeruli)
- contains most of the nephrons
Describe the medulla of the kidneys
consists of 8 lobes
each LOBE:
- contains a renal PYRAMID; these are collecting ducts which drain into papillae
- renal COLUMNS run between lobes and carry blood vessels
Describe the renal pelvis of the kidneys
funnel shaped structure that collects urine from the major calyces and drains into the ureter
What type of tissue makes up the walls of the renal pelvis, calyces, and ureter? What does this allow for?
smooth muscle to allow for peristalsis
Describe the flow of urine
nephrons -> collecting ducts -> papillae -> minor calyx -> major calyx -> renal pelvis -> ureter -> urinary bladder -> urethra -> into toilet (hopefully haha)
How much blood do the renal arteries supply the kidney per minute? What fraction of cardiac output does this represent?
about 1200 mL
1/4 of cardiac output
Describe the flow of blood through the kidneys.
aorta -> renal artery -> segmental arteries -> lobar arteries -> interlobar arteries -> arcuate arteries -> cortical radiate arteries -> afferent arteries -> glomeruli capillary loops -> efferent arteriole -> peritubular capillaries -> cortical radiate vein -> arcuate vein -> interlobar vein -> renal vein -> inferior vena cava
Describe the nerve supply for the kidneys.
by the renal fibers
innervated by SYMPATHETIC vasomotor fibers: regulate blood flow through the nephron by controlling renal arteriole diameter
What is a nephron? How many are there in each kidney?
it is the structural and functional unit of the kidney
approximately 1 million
What are the 2 major parts of a nephron and the structures that form them.
1) RENAL CORPUSCLE:
Glomerular (Bowman’s) capsule + glomerulus
2) RENAL TUBULE:
proximal convoluted tubule -> loop of henle -> distal convoluted tubule
What is a collecting duct in the kidneys?
it is a structure that collects urine from many different nephrons
Describe the structure of the glomerular capsule.
Consists of 2 different layers with a space in between them (space is where the filtrate forms).
Outer PARIETAL layer:
- simple squamous epithelium
Inner VISCERAL layer:
- cover gromerular capillaries
- lined with PODOCYTES have foot processes that form filtration slits
Describe the structure of the glomerulus.
it is a cluster of leaky capillaries
- endothelium is fenestrated: many pores to allow substances to pass
What is the driving force behind filtration in the kidneys?
hydrostatic pressure
Describe the structure of the proximal convoluted tubule.
Simple CUBOIDAL epithelium with microvilli
- contain many mitochondria to drive active transport
function:
- drains filtrate from cavity of gromerular capsule
- reabsorption and secretion
What part of the kidney are proximal convoluted tubules found?
in the cortex (low salt)
Describe the structure of the loop of henle
DSCENDING limb: thin segment
- simple squamous epithelium
ASCENDING limb: thick segment
- cuboidal epithelium
all extend into medulla, juxtamedullary extend very deep into medulla
Describe the structure of the distal convoluted tubule
made of cuboidal epithelium with few microvilli
- function is more secretion than reabsorption
confined to the renal cortex
What are the collecting ducts of the kidneys?
they are tubules that receive urine from many nephrons
fuse together to deliver urine through the papilla to minor calyx
What are the 2 different types of cells in the collecting ducts of the kidneys? What is their function
INTERCALATED cells: have microvilli
- acid-base balance
PRINCIPAL cells: no microvilli
- water and salt balance
What are the two possible locations of the nephrons?
CORTICAL: entirely in cortex except for loop of henle
85% of nephrons
role: excretion and regulation
JUXTAMEDULLARY: very close to junction of regions
15% of nephrons
role: concentration or dilution of urine
Describe the peritubular capillaries.
they are a capillary bed that receive blood from efferent arteriole and surround renal tubules
- are porous and low in pressure (facilitates absorption)
- absorb fluid and solutes from filtrate
- secrete some substances into filtrate
What are the vasa recta of the kidneys?
they are peritubular capillaries that surround juxtamedullary nephrons and extend deep into medulla
What is the juxtagromerular apparatus (JGA)?
a sensory structure located just outside the glomerulus where efferent and afferent arterioles and ascending limb of loop of henle meet.
What are the two types of cells in the juxtagromular apparatus (JGA)?
Granular JG cells
Macula densa cells
Describe the granular JG cells of the JGA including location and function
smooth muscle cells
- located in afferent arteriole
- act as mechanoreceptors: respond to dec in BP
- granules release renin to inc BP (REGULATION of systemic BP)
Describe the macula densa cells including location and function.
located in ascending limb of loop of henle
- act as osmoreceptors
low solute content or filtrate flow -> release of vasodilator -> inc blood flow -> inc GFR
FUNCTION: regulates rate of filtrate formation
What are the three processes involved in urine formation?
1) Glomerular filtration
2) Tubular reabsorption
3) Tubular secretion
How many times in a day do the kidneys filter the body’s entire plasma volume?
60 times
What does tubular reabsorption return?
all glucose and amino acids
99% of water
salt
and other components
How can blood pressure in the gromerulus be altered?
through vasoconstriction/dilation of the afferent arteriole
Describe the filtration membrane
consists of the visceral gromerular capsule layer (podocytes) with foot process
fenestrated endothelium of the gromerular capillaries
and the gel-like basement membrane that fuses the two
what is the function of the filtration membrane?
allow passage of: water and solutes smaller than most plasma proteins (< 5 nm)
prevent passage of: blood cells, plasma proteins, macromolecules
Ho much greater is gromerular blood pressure than in other capillaries
55 mm Hg
Why is it important that plasma proteins not be filtered out of the blood.
because they are vital to retain the blood’s high osmotic pressure and therefore the blood’s ability to reabsorb water
What does NFP stand for?
net filtration pressure
describe the pressure components that net filtration pressure is dependent upon
GROMERULAR hydrostatic pressure (HPg)
- main force that moves fluid from glomerulus into capsule
2 opposing forces: move back into glomerulus
COLLOID osmotic pressure of glomerular blood (OPg)
CAPSULAR hydrostatic pressure of filtrate (HPc)
there is a 4th force that is considered 0 since there should be no proteins in flitrate, but in abnormal conditions could change (ex diabetes insipidus)
OPc - colloid osmotic pressure of capillaries
How is net filtration pressure calculated?
NFP = HPg - (OPg + HPc)
Briefly explain what glomerular filtration rate (GFR) is and its relationship with NFP
it is total gromerular filtrate formed in mL/min
directly proportional to NFP
What is normal GFR?
120-125 ml/min
or
180 L/day
Why must a constant GFR be maintained despite systemic pressure? what happens if it is not
to ensure proper reabsorption from filtrate
too slow -> too much reabsorption (wastes will re-enter)
too fast -> too little reabsorbed (nutrients lost)
What are the two types of mechanisms that regulate gromerular filtration rate (GFR)?
INTRINSIC controls: renal autoregulation
EXTRINSIC controls: nervous and endocrine mechanisms that maintain blood pressure but affect kidney function
What are the two types of intrinsic (autoregulation) mechanisms for gromerular filtration rate (GFR)?
Myogenic mechanism
Tubulogromerular feedback mechanism
Describe the myogenic mechanism of autoregulation of gromerular filtration rate (GFR).
responds to changes in BP of the blood vessels
inc BP -> constriction of afferent arterioles
- maintains normal GFR, protects gromeruli from dmg from high pressure
dec BP -> dilation of afferent arterioles
- maintains normal GFR,
Describe the tubuloglomerular feedback mechanism of autoregulation of gromerular filtration rate (GFR).
MACULA DENSA cells: respond to change in flow or ion content of filtrate
inc GFR -> filtrate flow inc -> inc in NaCl concentration (less time to reabsorb) -> macula densa cells of the JGA respond by releasing vasoconstricting chem into the afferent arteriole -> dec GFR
if GFR dec then macula densa cells stop secreting vasoconstrictors
What are the two extrinsic controls for regulation of gromerular filtration rate (GFR)
SYMPATHETIC nervous control
HORMONAL control
Describe the sympathetic control of the GFR
- releases norepinephrine from its nerve fibers
- stimulates adrenal medulla to release epinephrine
these stimulate afferent arterioles to constrict strongly to shunt blood. Decreases GFR -> dec filtrate flow
What are the two routes of tubular reabsorption?
TRANSCELLULAR
PARACELLULAR
Which one route of tubular reabsorption is major (more common)
the transcelllular route
Describe the transcellular route of tubular reabsorption
occurs primarily in proximal convoluted tubule
filtrate -> luminal membrane of tubule cells -> through the cytosol of tubule cells -> through the basolateral membrane -> through the interstitial fluid -> through squamous ep cells -> into the capillary blood
Describe the paracellular route of tubular reabsorption.
occurs between cells
some limited water movement and reabsorption of some ions where tight junctions are leaky
Describe the process of tubular reabsorption of water and ions.
1) SODIUM reabsorption
- facilitated diffusion and cotransport into tubular cells
- primary active transport out of tubule cell into ISF (interstitial fluid)
- simple diffusion from ISF in to blood
2) anions follow created electrochemical gradient by sodium leaving
- Cl and HCO3 diffuse through to blood
3) water follows osmotic gradient created by ion movement
- called obligatory water reabsorption
Describe the process for absorption of organic nutrients (other than ions and water) from filtrate to the blood.
the absorption of sodium provides energy/mechanism to drive absorption by pushing Na out of the cell.
Organic nutrients are reabsorbed by secondary active transport (cotransport)
each substance requires a specific transport protein
Explain what transport maximum is.
mg/min of substance absorbed when all transporters are saturated
transporters for substances like glucose have a high TM
if filtrate exceeds TM, substances will be lost
Normally, there are no proteins in the filtrate. How are they reabsorbed if there are?
through endocytosis by tubular cells
then they are digested into amino acids -> diffuse into interstitial fluid (ISF) -> into blood
What are the three reasons why some substances are not reabsorbed?
1) lack carriers
2) not lipid soluble
3) too large to pass through the membrane
What are the most important substance to not be reabsorbed?
nitrogenous waste
Give a few examples of nitrogenous waste
urea, uric acid, creatinine
Which part of the kidney tubules perform the majority of reabsorption?
proximal convoluted tubule
Describe the characteristics of the filtrate content as it enters the distal convoluted tubule.
10% of the salt
25% of the water
that it had in the gromerular capsule
Describe how the proximal convoluted tubule absorbs substances.
uses active transport for Na, most nutrients, and proteins
passive transport of other cations, anions, water, urea, and lipid soluble molecules
What is the absorption in the distal convoluted tubule (DCT) and collecting duct dependent on and how is it controlled?
depends on the bodies needs
under hormonal control
What is the water absorption in the DCT and the collecting ducts called?
facultative water reabsorption
Describe what obligatory water reabsorption is.
it occurs in the PCT
- Na is absorbed by active transport
- anions follow this gradient created by Na (negative particles follow the positive Na)
- water follows by osmosis (goes from hypotonic to hypertonic)
What are the two hormones that control water absorption in the DCT and collecting ducts?
ADH - causes collecting ducts to become more permeable to water (direct control)
Aldosterone - causes the DCT and collecting ducts to inc Na absorption causing water to follow (indirect)
Describe the tubular secretion (third) process of urine formation.
Involves active transport of excessive or unwanted materials out of blood into filtrate
What are the 4 roles of tubular secretion?
1) disposes of unwanted substances in blood.
ex drugs, antibiotics
2) eliminates reabsorbed substances that are toxic
ex urea, uric acid
3) eliminates excess K
4) controls blood pH
What is osmolality?
number of solute particles dissolved in 1kg (1L) of H2O
What is osmolarity?
number of solute particles dissolved in 1L of solution.
Does osmolality or osmolarity indicate the ability to cause osmosis?
osmolality
How is osmolality expressed?
milliosmoles (mOsm)
What is the normal osmolality of the blood that is maintained by the kidneys?
about 300 mOsm
How do the kidneys maintain the osmolality of the blood plasma?
by countercurrent mechanisms
What are countercurrent mechanisms?
occur when fluid flows in opposite directions in adjacent sections of the same tube
–low conc———-high conc——>
<–low conc———-high conc—–
allows for greater gradients to be maintained
what is the osmolality of the renal cortex and medulla?
cortex 300 mOsm
- significant that it does not need to be high b/c there is a lot of low concentration filtrate in the tubes at this point
medulla 1200 mOsm
- significant b/c at this point there is less filtrate and higher filtrate conc
What are the two types of countercurrent mechanisms used by the kidneys?
Countercurrent MULTIPLIER: filtrate flow in the loop of Henle
- creates high salt content in the medulla that is used to adjust water content of the filtrate
Countercurrent EXCHANGER: blood flow in vasa recta
- maintains the concentration gradient of the medulla
Describe the counter current multiplier in the loop of henle.
DESCENDING LIMB:
- impermeable to NaCl, permeable to water
- water leaves via osmosis as it descends and approaches 1200 mOsm
ASCENDING LIMB:
- impermeable to water, permeable to salt
- NaCl reabsorped (passively in thin segment, actively in thick)
- filtrate approaches 100 mOsm
- filtrate is flowing in opposite directions in adjacent channels allowing greater conc gradient to be maintained
Describe the counter current exchange in the vasa recta
- maintains conc gradient by running parallel to loop of henle
- blood flows parallel to filtrate
- protects osmotic gradient by preventing rapid removal of salt and reabsorbing H2O
How does the counter current exchange in the vasa recta protect the osmotic gradient of the medulla?
in ascending vasa recta, salt comes out and is absorbed in the descending vasa vecta.
in descending vasa recta, H2O is released and absorbed in the ascending
prevents rapid removal of salt
removes absorbed water
What is the primary regulator of urine concentration and volume?
ADH
How does ADH act to control urine concentration?
makes the membrane of the collecting ducts permeable to water
if normal BP -> no ADH -> no facultative reabsorption -> dilute urine with normal volume
if low BP -> ADH secreted -> facultative reabsorption -> concentrated urine with small volume
What are two types of drugs that can affect urine output?
Antidiuretics -> dec urine output
Diuretics -> enhance urinary output
What are the two ways that diuretic drugs can increase urinary output?
1) block ADH (ex alcohol)
2) block Na reabsorption and therefore obligatory reabsorption in the PCT
What is an osmotic diuretic?
it is a substance that can cause diuresis by having a high concentration in the filtrate that increases its osmolality
ex High glucose from diabetes mellitus
What is renal clearance (RC)?
the rate at which something is removed from the blood by the kidneys
measured in mL/min
What is the formula for renal clearance?
RC = UV/P
U = concentration in urine V = volume of urine flow P = concentration in plasma
What is the normal color of urine, what contributes to this?
clear - pale yellow - deep yellow
urochrome is the pigment that causes the yellow color
- from hemoglobin breakdown
What happens to the odour of urine when it is left standing
begins to smell like ammonia due to bacterial action
What is the normal pH of the urine?
slightly acidic 4.5-8
approx. 6.0
What is the normal specific gravity of the urine?
1.001 - 1.035
What is the normal chemical composition of the urine?
95% water, 5% solute
nitrogenous waste:
urea from metabolism of amino acids
uric acid from metabolism of nucleic acids
creatine from skeletal muscle
electrolytes: Na, K, PO4, SO4, Ca, Mg, HCO3
list some abnormal substances that might be found in urine.
Glucose - diabetes mellitus
Ketones - Starvation or diabetes mellitus
high protein - infection
hemoglobin - indication of RBC lysis (transfusions)
RBCs - kidney dmg/renal hemorrhage
WBCs - infection
Bile pigments - jaundice
What is anuria?
abnormally low urine production
(virtually none)
less than 50 mL/day
What is polyuria
excessive urination
What is oliguria?
low urination
What is dysuria?
painful urination
What is the purpose of the ureters?
to convey urine from the kidneys to the urinary bladder
Are the ureters retroperitoneal?
yes
describe the three layers of the ureters?
Mucosa coat (inner) - transitional epithelial
Muscular coat (middle layer)
- smooth muscle in circular and longitudinal layers
- contracts in response to stretch
Fibrous layer (outer) - also called adventitia
explain what can cause kidney stones and what another name for it is.
Also called renal calculi
caused when concentration in urine is to high, solutes (Ca, Mg, or uric acid salts) crystalize out of solution
can block ureter, cause pressure and pain in kidneys
CAUSE:
infection, urine retention, inc Ca conc, inc pH of urine
When do rugae appear in the urinary bladder?
when it is deflated
what is the trigone of the urinary bladder?
triangular area outlined by openings for ureters and the urethra
What region of the urinary bladder do infections tend to occur?
in the trigone
What are the 4 layers of the urinary bladder?
MUCOUS coat
- transitional epithelium
SUB MUCOUS coat
- CT with many elastic fibers
MUSCULAR coat
- 3 layers in all directions
SEROUS coat
- parietal peritoneum on superior surface, inferior surface is adventitia
What is the detrusor muscle?
the muscle formed by the three layers of muscle in the muscular coat of the urinary bladder. (empty the bladder)
What is the urethra?
a muscular tube that conducts urine from bladder to exterior
Describe the mucosa of the urethra
Near urinary bladder: transitional
mostly pseudostratified columnar ep
stratified squamous ep near external opening
Describe the two sphincters of the urethra
INTERNAL sphincter: by bladder
- smooth muscle, autonomic,
- contracts to open
EXTERNAL sphincter: closer to external opening
- skeletal muscle
- voluntary control
- contracts to close
What is the process of voiding urine called?
micturition
Describe the process of micturition
- sensation stimulated by stretching
stretch receptors -> micturition centers in pons
pontine storage center: inhibits micturition
pontine micturition: promotes micturition
reflex is triggered by PS neurons in micturition center in spinal cord
sacral reflex center:
- stimulates contraction of detrusor by ANS
- opening of internal urethral sphincter by ANS
- opening of external urethral by somatic (relax)
emptying aided by abdominal and diaphragm contractions
