Urinary System Flashcards
What are the three things the kidneys are responsible for regulating and keeping in homeostatic conditions?
Regulate
1. total body water and osmolarity
2. Ion concentrations in the ECF
(Na+, K+, Ca2+)
3. Acid-base balnce (pH)
What do the kidneys do with vitamin D?
Convert to its active form calcitrol
What can the kidneys do during fasting or starvation?
Gluconeogenesis via taking other types of molecules (proteins, fatty acids, amino acids) and converting them to glucose.
What hormone and what enzyme do the kidneys produce?
- Enzyme: Renin
- Hormone: Erythropoietin
What does it mean to say that the kidney is in the retroperitoneal position?
Behind the peritoneal membrane that lones the digestive cavity
What does the kidney bean visually resemble?
A kidney bean with a hilum
What sits ontop of each kidney?
Adrenal gland
What are the three supportive layers in order from superficial to deep of the kidney?
- Renal Fascia
- Perirenal fat Capsule
- Fibrous capsule
What is the role of the renal fascia?
Hold the kidneys in roughly the same place
Describe the perirenal fat capsule
A big heavy-duty layer of fat that is protective.
Describe the fibrous capsule of the kidney and its role
It is very tighly bound to the surface of the kidney that is designed to sort of suran wrap the kidney with heavy duty layer of protective tissue.
Is the fibrous capsule of the kidney ment for friction free movement?
No
What are the prenchymal (functional) structures of the kidney?
Cortex - All Corpuscles
-Outer Layer = PCT
-Renal Columns = DCT
Medullary Pyramids = Nephron Loops
What are the collecting structures of the kidney?
-Minor Calyx
-Major Calyx
-Renal Pelvis
-Ureter
-Bladder
-Urethra
-Out
What is meant by a “lobe” in the kidney?
1 medullary pyramid and the renal cortex that overrises it
What is the correct order of arteries in the kidney starting at the Aorta and ending at the efferent arteriole?
Aorta
Renal a.
Segmental a.
Interlobar a.
Arcuate a.
Cortical radiate a.
Afferent arteriole
Glomerulus
Efferent arteriole
What is the order of veins returning to the heart from the kidneys starting at the efferent arteriole?
Efferent Arteriole
Peritubular capillaries & Vasa recta
Cortical radiate v.
Arcuate v. (Vasa recta also flows into here)
Interlobar v.
Renal v.
Inferior Vena Cava
What is the functional and structural unit of the kidney?
Nephron
How many nephrons does each kidney have?
1 million
What does each nephron consist of
A renal corpuscle and a renal tubule?
Does only one nephron or do many nephrons feed into a single collecting duct?
Many
What comprises the renal corpuscle?
-Glomerulus
-Glomerular corpuscle
Describe the capillaries of the glomerulus
They are a ball of fenestrated capillaries that allow for filtration of everything except blood cells to occur more rapidly.
What doesn’t the glomerulus filter?
Everything but cells and proteins to pass from blood to the filtrate.
What is filtrate?
Whatever is filtered out of the blood
Describe the glomerular capsule
it surrounds the glomerulus and is continuous with the tubule.
What are the layers of the glomerular capsule and what are the comprised of?
Parietal layer - simple squamous epithelium
Visceral layer - podocytes that wrap around the capillaries
How long is the renal tubule and how many regions does it have?
-3cm
-3 regions
What are the three regions of the renal tubule?
-Proximal Convoluted Tubule (PCT)
-Nephron Loop
-Distal Convoluted Tubule (DCT)
Describe the PCT
It is comprised of simple cuboidal epithelium with many mitochondria and microvilli
Why would the PCT have a lot of mitochondria and microvilli?
The large amount of mitochondria indicate a large amount of energy being utilized and the large amount of microvilli increase the surface area for reabsorption.
What kind of transport would be occurring at the PCT?
Active Transport
About what percentage of your bodies ATP is utilized by the PCT)?
6%
Describe a generic nephron loop
A long tube with descending and ascending limbs that have thick and thin segments.
Describe the thick segments of the nephron loop
Simple cuboidal epithelium that is not permeable to H2O
Describe the thin segments of the nephron loop
Simple squamous epithelium that is permeable to H2O
What does the ascending limb of the nephron loop connect to?
DCT
Describe the DCT
Comprised of simple cuboidal epithelium with no microvilli or mitochondria
Describe the collecting duct
It is comprised of cuboidal cells (2 types) and drains into the minor calyx.
What is obligatory reabsorption?
The things we must reabsorb.
What are the two classes of nephrons and what are the percentage of each in the kidneys?
Cortical Type - 85%
Juxtamedullary Type - 15%
Describe the cortical type of nephron
-They are almost entirely in the cortex
-They have short nephron loops
-They filter blood and form urine
-Are associated with the peritubular capillaries
Describe the juxtamedullary type of nephron?
-Originate near the cortex/medullary border
-Very long nephron loops
-Filter blood, make urine, and maintain a salinity gradient in the medulla so urine can be concentrated
-Associated with the vasa recta
What is the salinity gradient in the medulla so important?
It allows urine to be concentrated and for H2O to be conserved which allows us to live on land.
Should reabsorption occur in the glomerulus?
No
What about the A&P of the glomerulus specializes it for filtration?
It is fed and drained by the arterioles which keeps the pressure high and forces filtration.
Describe the peritubular capillaries
They wrap around the tubule and readily reabsorb water and solutes that we need to get back after filtration and are associated with the cortical type of nephron loop.
Describe the vasa recta
Very long, straight vessels that play a role in concentrating urine and are associated with the juxtamedullary type of nephron loop.
Where is the juxtamedullary complex at?
Point of contact where the distal ascending loop lies against the afferent and efferent arteriole
What is the role of the juxtamedullary complex?
To regulate the rate of filtration and systemic blood pressure.
What do the macula densa cells do?
They monitor the NaCl content of the filtrate to find out how fast the filtrate is still moving and to make an estimate of systemic blood pressure based on the speed of the filtrate.
What determines filtration?
BP
How can the macula densa cells determine BP based on the speed of the filtrate?
The faster the filtrate moves the less NaCl is reabsorbed into the body (so the higher the BP)
What are the two roles of the granular cells?
- they are mechanoreceptors that monitor BP directly
- Secrete renin
What is the role of the mesangial cells?
They fill in the spaces between all the pieces in the glomerulus and they contain gap junctions that allow for quick communication/ split second decisions.
What does high NaCl detection by the macula densa cells mean?
Fast moving filtrate which means high BP
What does low NaCl detection by the macula densa cells mean?
Slow moving filtrate which means low BP
Where are macula densa cells located?
Embedded in the wall of the tubule
How many liters of liquid are in the body?
40 - 50 L
How many mL of blood pass through the glomeruli per minute?
1,200 mL
How many liters of filtrate are made per day?
180 L
How many L of urine are made per day?
1.5 L
How much of the 180 L of filtrate is reabsorbed per day?
178.5 L
How do the kidneys determine what to reabsorb vs what is a waste product?
Waste products are anything your body doesn’t need at that exact time
How much liquid is in the body?
40-50 L
How much blood passes through the glomeruli per minute?
1,200 mL
How much filtrate is made each day, how much is reabsorbed, and how much urine is actually made?
Made - 180 L
Reabsorbed - 178.5 L
Urine - 1.5 L
In order, what are the four mechanisms of urine formation?
-Glomerular Filtration
-Tubular reabsorption
-Tubular Secretion
-Water conservation
What is the purpose of glomerular filtration in the process of urine formation?
Creates a plasma-like filtrate of the blood
What is the purpose of tubular secretion in the process of urine formation?
To get rid of waste
What is the purpose of tubular secretion in the process of urine formation?
Removers additional waste from the blood, adds them to the filtrate
What is the purpose of water conservation in the process of urine formation?
Removes water from the urine and returns it to the blood; concentrates urine
What determines if something is a waste product or not?
Whether your body needs it at that exact time
Is glomerular filtration exact or not exact?
Not exact - “If it fits it is filtered”
Is tubular secretion exact or not exact?
Exact
What is glomerular filtration?
A passive process in which the hydrostatic pressure of the blood forces fluid and the solutes through a membrane.
What are the three parts of the filtration membrane in the glomeruli?
-Fenestrated epithelium of the glomerular capillaries
-Basement membrane
-“Feet” of the podocytes
What are the three parts of the filtration membrane in the glomeruli?
-Fenestrated epithelium of the glomerular capillaries
-Basement membrane
-“Feet” of the podocytes
What is the relationship between size of the molecule and filtration?
Molecules smaller than 3 nm pass freely and molecules larger than 5nm are barred
What are the pressures acting on the filtrate in the glomeruli?
Blood hydrostatic Pressure (BHP) = 60 mmHg out
Colloid Osmotic Pressure (COP) = -32 mmHg In
Capsular Pressure (CP) = -18 mmHg in
Net Filtration pressure (NFP) = 10 mmHg out
What is the Glomerular Filtration Rate (GFR)
The volume of filtrate formed each minute by both kidneys
What are the three factors GFR is determined by?
-Net filtration pressure
-Surface area for filtration
-Filtration membrane permeability
What is the average amount of GFR per minute?
120 - 125 mL/min
Why is GFR tightly regulated?
To maintain extracellular homeostasis and maintain systemic blood pressure
What are the two intrinsic, kidney autoregulation so direct, controls of GFR and what is the range they keep ?
-Myogenic mechanism
-Tubular feedback mechanism
-Maintain between 90 -180 mm Hg
What are the extrinsic, not the kidney so indirect, controls of GFR and why is it indirect?
-Nervous and Endocrine sytems
-Indirect because they work by raising the overall blood pressure in the body.
Explain the Myogenic mechanism of autoregulation:
- There is low systemic blood pressure
Then - Blood pressure in afferent arterioles drops causing GFR to also drop
Then - Stretch receptors in the walls of the smooth muscle detects less stretch (preferred stimulus )of the afferent arterioles.
Then - Vasodilation of the afferent arterioles increases the volume of blood coming in and the GFR rises
Describe the tubuloglomerular mechanism of autoregulation:
- Systemic blood pressure drops causing GFR to decrease
Then - That causes a decrease in the filtrate flow and a decrease in NaCl eh ascending limb of the nephron loop
Then - Macula densa cells of the juxtamedullary complex detect this drop in NaCl causing the release of vasoactive chemical to be inhibited
Then - Vasodilation of afferent arterioles increases GFR
Describe the Hormonal (renin-angiotensin-aldosterone) mechanism:
- There is a drop in systemic blood pressure causing there to be less filtrate and the macula densa cells detect a drop in NaCl causing the granular cells to release Renin
Then - Angiotensin two is formed via the cascade initiated by renin and it causes aldosterone secretion by the adrenal cortex and vasoconstriction of systemic arterioles
Then - The increase of Na and H2O reabsorption raising the blood volume along with the increased peripheral resistance from the vasoconstriction causes an increase in Systemic blood pressure which will indirectly raise the GFR
Describe the neural controls of GFR)
Baroreceptors are inhibited by a decrease in systemic blood pressure causing the sympathetic nervous system to signal vasoconstriction and the granular cells of the juxtamedullary system to release renin resulting in the same thing as the hormonal mechanism.
How often is the total plasma volume filtered into the renal tubules?
Roughly every 22 minutes
What two things does the PCT have an abundance of to aid in reabsorption?
-Mitochondria to produce the energy needed for active transport
-Microvilli to increase surface area
How does obligatory water reabsorption work?
Water moves via osmosis through aquaporins
What are transport maximums?
Any solute that uses a transport protein has a maximum amount that can get reabsorbed.
What is glucoses transport maximum?
180mg/dL
What is the most important step of tubular reabsorption?
The most important step is active transport of sodium because primary transport our of the tubule cells drives secondary transport from the filtrate into the cells
What happen to most amino acids, glucose, ions, and vitamins?
They are co-transported into the tubule with sodium and out of the tubule via facilitated diffusion.
What does the PCT reabsorb?
- 65% of water
- All glucose and Amino acids
- Bulk of ions
What does the PCT reabsorb?
- 65% of water
- All glucose and Amino acids
- Bulk of ions
Describe the descending limb of the nephron loop and its relationship with solutes and water:
Permeable to water but not to solutes
Describe the ascending limb of the nephron loop and its relationship with solutes and water:
Permeable to solutes but no to water
What is the effect of antidiuretic hormone on the collecting ducts?
causes aquaporins to be inserted into the membranes
What is the effect of aldosterone?
Increases sodium reabsorption and increases secretion of K+
What is the effect of natriuretic peptide?
Inhibits sodium reabsorption
What is the effect of parathyroid hormone?
Increases reabsorption of calcium
Causes excretion of phosphates so it can’t bind to calcium
Is tubular secretion selective or no selective?
It is very selective in what and how much is secreted.
What all is secreted?
-Drugs and metabolites
-Urea and uric acid that have been passively absorbed
-Potassium Ions (because of aldosterone Na+ and K+ “trade places”)
Hydrogen ions and bicarbonate ions to control pH
What are three things about urine that can indicate a pathology or problem?
- Blood
- Pus
- It is cloudy
What pH can urine range from?
4.5 - 8
What is the technical name for urination?
Micturition
What three parts of your body are responsible for transport, storage, and elimination of your urine?
- Ureters
- Bladder
- Urethra
Describe the ureters:
They are muscular tubes that run from the renal pelvis to the bladder and use smooth muscle contractions in the wall, peristalsis, to move the urine being collected in the kidney down to the bladder every 4-5 minutes
What are the three layers of the ureter?
- Mucosa
- Muscularis
- Adventitia (Connective tissue that blends into the surrounding tissues
Describe the urinary bladder:
- It is retroperitoneal and posterior to the pubic symphysis
- 3 Layers: Mucosa, smooth muscle, adventitia
- Is moderately full at 500 mL and can hold up to 1000 mL
Describe the urethra:
- Thin walled muscular tube that drains the bladder
- Has internal and external urethral sphincters
- Male urethras are significantly longer
Describe the smooth muscle layer of the urinary bladder:
Well defined: 3 layers of muscle that’s going to allow it to really contract from multiples directions so that we can increase the pressure in the bladder in order to urinate.
What part of the spinal cord is involved in micturition?
sacral region
Explain the involuntary micturition reflex
- Stretch receptors detect filling of bladder and transmit afferent signals to the spinal cord
- Efferent Signals return to bladder from spinal cord segments S2 and S3 via parasympathetic fibers in pelvic nerve and excite the detrusor muscle while relaxing the internal urethral sphincter
- Urine is involuntarily voided if not inhibited by the brain.
Explain voluntary control over micturition when it is timely to urinate:
- The initial signal from the stretch receptor makes its way to the micturition center in the pons
- Once or if it is timely to urinate the pons sends signals to spinal interneurons that excite detrusor and relax internal urethral sphincter resulting in urine being voided
Explain voluntary control of micturition when it is untimely to urinate:
- If it is untimely to urinate, signal form the cerebrum excite spinal interneurons that keep external urethral sphincter contracted and urine is retained in the bladder.
- Once it is timely to urinate, signals from cerebrum inhibit sacral neurons that keep external sphincter closed. This relaxes the external urethral sphincter and urine is voided.
What determines the volume and concentration of urine?
The medullary osmotic (salt) gradient
What creates the medullary osmotic gradient and what preserves it?
Creates: Long Nephron Loop
Preserves: Vasa recta
What must the vasa recta do?
It must perfuse the tissue while preserving the gradient
What utilizes the gradient to concentrate urine?
Collecting ducts
Why is the medullary osmotic gradient important evolutionarily?
The osmotic gradient allows us to conserve water making it possible to be alive without being surrounded by H2O.
What occurs down the descending (thin) limb of the nephron loop?
Obligatory water return
( a lot of this water return directly to he blood)
What occurs up the ascending (thick) limb of the nephron loop?
Replacing NaCl so the water doesn’t affect the gradient and we are making sure the medulla stays saltier than the cortex
(consistently adding salt)
What’s the maximal concentration level the bottom of the nephron loop can get reach?
1200 milliosmoles
Without the gradient what is the most urine could get concentrated to?
300 milliosmoles which is isotonic to most ECF
Describe how the vasa recta remains isotonic to the conditions in the medulla?
Due to countercurrent exchange, the vasa recta absorbs NaCl and expels H2O going down and absorbs H2O going up while expelling NaCl going back up.
What is the basis of osmosis?
Water moves until equilibrium and then there is just passive movement (no net movement)
Explain the relationship between antidiuretic hormone, the collecting duct, and the osmotic gradient?
- Antidiuretic hormone causes a specific amount of aquaporins based on how much we need to reabsorb.
- H20 is constantly being pulled toward the osmotic gradient so as soon as aquaporins are inserted into the collecting duct the water molecules are drawn out of the collecting duct and concentrates the urine.
Describe the countercurrent multiplier
- Filtrate entering the nephron loop is isosmotic both blood plasma and cortical interstitial fluid
- Water moves out of the filtrate in the descending limb down its osmotic gradient. This concentrates the filtrate.
- Filtrate reaches its highest concentration at the bend of the loop
- Na+ and Cl - are pumped out of the filtrate. This increases the interstitial osmolality.
- Filtrate is at its most dilute as it leaves the nephron loop. At 100 milliosmoles, it is hypo-osmotic to the interstitial fluid.
