Urinary System Flashcards
What are the major functions of the kidneys?
- regulation of blood ions
- regulation of blood pH
- regulation of blood volume (water content)
- regulation of blood pressure
- maintenance of blood osmolarity
- production of hormones
- regulation of blood glucose levels
- excretion of wastes and foreign substances
What blood ions are regulated by the kidneys?
Ca, Na, K, Cl, HPO42
-primary is Ca.
What is the normal pH level of the blood?
7.35 - 7.45
How do the kidney’s regulate blood pressure?
the kidneys secrete Renin as part of the RAA system increasing blood pressure
What is the primary hormone in shock reduction?
Renin
What are the 2 main hormones the kidneys produce?
calcitriol and erythropoietin
What are the three external layers of the kidney?
- renal capsule
- adipose capsule
- renal fascia
Are the kidneys innervated by the PANS or the SANS?
the SANS (sympathetic autonomic nervous system)
How does the sympathetic nervous system regulate the renal arteries?
by causing vasodilation and vasoconstriction
What is the functional portion of the kidneys?
the nephrons
approximately how many nephrons/kidney?
1 million
Can you replace damaged or dead nephrons?
no
How much can one kidney take over if the other fails?
1 kidney is able to filter up to 80% of the rate of 2 kidneys
What kind of cells line the glomerular capsule?
simple squamous epithelium
What are the layers of the glomerulus?
the parietal layer and the visceral layer
What is the space between the parietal and visceral layer of the glomerulus called?
the capsular space
What is the renal tubule?
passageway for filtered fluid that runs from the glomerulus to the collecting ducts
What are the parts of the renal tubule?
- proximal convoluted tubule
- the loop of henle
- distal convoluted tubule
What are the two types of nephron loops?
- cortical nephrons
- JG nephrons
Define macula densa
densely compacted columnar cells in the ascending tubule cells
What are JG cells?
juxta-glomerular cells - smooth muscle fibers in the afferent arteriole
What is the juxta-glomerular apparatus?
a combination of the macula densa cells and JG cells; together they help regulate blood pressure in the kidneys
What are the two types of cells in the DCT and the collecting duct?
principal cells and intercalated cells
What is the purpose of principal cells?
they have receptors for ADH and aldosterone
What is the purpose of intercalated cells?
to provide homeostatic regulation of pH
What type of cells are in the renale tubule?
all cells in the renal tubule are simple cuboidal except in the descending limb and thin ascending limb are simple squamous cells
What is the flow through the nephron?
glomerular capsule - PCT - descending loop of Henle - ascending loop of Henle - DCT - collecting duct
What are the 3 layers of the ureters?
- mucosa - mostly transitional epithelium which allows lots of stretch
- musclaris - 2 layers of smooth muscle
- adventita - helps anchor the ureters to the wall of the peritoneum
Which part of the nervous system causes micturition?
parasympathetic nervous system
What is the blood flow through the kidneys starting at the aorta?
aorta - renal artery - segmental artery - interlobar artery - arcuate artery - cortical radiate artery - afferent arteriole - Glomerulus (capillaries) - efferent arteriole and vasa recta - peritubular capillaries - cortical radiate vein - arcuate vein - interlobar vein - renal vein - IVC
How is Renin a part of a negative feedback loop?
renin stops once aldosterone finishes its job because homeostasis is achieved.
What establishes the osmolarity gradient in the nephron?
the dilution - concentration - dilution of the loop of Henle
What is the hallmark of the PCT?
reabsorption
What is the hallmark of the LOH?
osmotic gradient
What is the hallmark of the DCT?
reabsorption with restrictions.
Which part of the nephron system responds to hormones?
the DCT only.
Where is the max H2O reabsorption in the nephron system?
in the DCT
What are the 3 main functions of the renal system?
- glomerular filtration
- tubular reabsorption
- tubular secretion
Define Glomerular filtrate
the fluid that enters the capsular space; approx 150-180 liters/day
How much the glomerular filtrate is reabsorbed?
99%
Define filtration fraction
the fraction of blood plasma that becomes the glomerular filtrate
What does the filtration membrane do?
permits the filtration of water and small solutes but NOT plasma proteins, blood cells and platelets
What is the filtration membrane made of?
- glomerular endothelial cells - contains large fenestrations that don’t allow passage of blood cells and platelets
- basal lamina - part of the basement membrane that prevents filtration of large negative proteins
- filtration slits - formed by podocytes’ projects caled pedicles; prevents passage of medium-sized proteins
What is the purpose of the net filtration pressure?
dictates how much will move in which direction
What does the NFP depend on?
- GBHP - glomerular blood hydrostatic pressure promotes filtration
- CHP - capsular hydrostatic pressure - opposes filtration
- BCOP - blood colloid osmotic pressure - opposes filtration
What is the formula for NFP?
NFP = GBHP - CHP - BCOP
=55-15-30
=10mmHg under normal circumstances
When will filtration stop?
if the GBHP drops below 45 mmHg because the opposing pressures equal 45 mmHg
What controls the GFR?
- renal autoregulation
- neural regulation
- hormonal regulation
What is renal autoregulation?
- myogenic mechanism (faster) - stretch receptors in afferent arterioles will respond to increase or decrease of blood pressure
- tubuloglomerular feedback (slower) - macula densa cells (of JGA) detect increase flow of Na, Cl an dwater and could inhibit release of NO (nitric oxide which is a vasodilator)
What is neural regulation?
sympathetic ANS fibers release norepinephrine to cause vasoconstriction of afferent arterioles during fight or flight
What is hormonal regulation?
- AG II (angiotensin II) - a vasoconstrictor that narrow afferent and efferent arterioles which lowers GFR
- ANP (atrial naturetic peptide) - secreted by heart cells; blood is atria stretches walls causing secretion of ANP which relaxes mesangial cells in glomerulus; this increase the surface area of glomerulus and increases GFR
What does ANP do?
gets rid of sodium and water
What is reabsorption in terms of the kidneys?
the return of most of the filtered water and many of the filtered solutes to the bloodstream
What is secretion in terms of the kidneys?
the transfer of materials from the blood and tubule cells into the glomerular filtrate
What are the 2 important outcomes of secretion?
- H+ secretion controls blood pH
2. it eliminates substances from the body
Define primary active transport
moves solute across membrane with a pump using ATP
ie. NA+/K+ pump
Define secondary active transport
an electrochemical gradient causes the movement of 2 ions across membrance; one ion movies with its gradient and one moves against its gradient
What is obligatory water reabsorption?
the fact that solute reabsorption drives water reabsorption via osmosis
Where does osmosis occur in the nephron?
in the PCT and the descending LOH
What is facultative water reabsorption?
the remaining 10% of water being reabsorbed.
Where is the majority of HCO3- reabsorped?
in the PCT
What is reabsorbed in the PCT?
- most of water, Na+ and K+ is reabsorbed
- also absorbs Cl-, Mg2+, Ca2+, HPO42-
- 80% of bicarbonate buffer
- all glucose and amino acids
What is secreted in the PCT?
- H+ is released into the lumen via Na+/K+ antiporters
- urea, NH3, and NH4
What is NH3?
amonia
What is NH4?
amonium
What reabsorption is happening in the LOH?
- 15% water in descending limb only
- little to no reabsorption of water in ascending limb
- 20-30% sodium and potassium in descending
- 35% of Cl- in descending
- some HCO2-, Ca2+ and Mg2+
What secretion is happening in the LOH?
variable to none
What reabsorption is happening in the early DCT?
-10-15% remaining water via osmosis
-5% of Na+ and Cl-
-PTH acts here to reabsorb Ca2+
(Ca2+ is the primary one to note)
What secretion in happening in the early DCT?
none
What reabsorption is happening in the late DCT?
- principal cells reabsorb Na+ and water
- intercalated cells reabsorb K+ and HCO3-
What secretion is happening in the late DCT?
- principal cells secrete K+ (because we are reabsorbing Na+)
- intercalated cells secrete H+
What are the hormones that affect the extent of Na+, Cl-, Ca2+ and water reabsorption and H+ secretion in the kidneys?
- RAA - renin-angiotensin-aldosterone system
- ADH - antidiuretic hormone
- ANP - atrial naturetic peptide
- PTH - parathyroid hormone
Why is RAA released?
due to a shock response (low BP and volume)
What does RAA do?
- decrease GFR via vasoconstriction of afferent arterioles
- increases reabsorption of Na+, Cl- and water via Na/K pumps in PCT
- stimulates adrenal cortex to release aldosterone with acts on principal cells to reabsorb more Na+, Cl-, water and secrete more K+
What does ADH do?
acts of principal cells to reabsorb more water via the formation of aquaporins.
What does low ADH do?
water goes into the urine so it dilutes urine
What does high ADH do?
water goes into the blood so it concentrates urine
Why is ADH released?
in response to low blood volume
Why is ANP released?
in response to high blood volume
What does ANP do?
inhibits reabsorption of Na+ and water as well as suppresses secretion of ADH and aldosterone
Why is PTH released?
in response to low levels of blood Ca2+
What does PTH target?
the DCT
What does PTH do?
increases reabsorption of Ca2+
When will you have dilute urine?
in the absence of ADH. the renal tubules will absorb more solutes than water
When will you have concentrated urine?
in the presence or excess of ADH. large amounts of water are reabsorbed from the tubular fluid into the interstitial fluid which increases solute concentration of the urine
What are the count current mechanisms?
- countercurrent multiplier
2. countercurrent exchange
What is the counter current multiplier?
the ascending and descending LOH establishes the osmotic gradient in the renal medulla which helps establish the osmotic gradient
What is the counter current exchange?
the process by which solutes and water are passively exchanged between the blood of the vasa recta and interstitial fluid of the renal medulla s a result of countercurrent flow. this helps maintain the osmotic gradient.
What do the kidneys develop from?
the intermediate mesoderm
What is the sequence the kidneys follow when developing?
- pronephros
- mesonephros
- metanephros
What happens to the kidneys with age?
- shrink in size
- have a decreased blood flow
- filter less blood
What two hormones contribute to regulation of GFR?
- angiotensin II - reduces GFR
- ANP - increases GFR
What is the myogenic mechanism?
occurs when stretching triggers contraction of smooth muscle cells in the walls of afferent arterioles.
