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Flashcards in Human Kidneys Deck (122):

What are the three layers on the outside of the kidneys?

- Renal Capsule
- Adipose Capsule
- Renal Fascia


What is the renal capsule and its function?

It is the outermost layer of the kidney, formed by connective tissue adhering to the outside of the kidney
It forms a physical barrier around the kidney, as well as maintaining the shape of the kidneys


What is the adipose capsule and its function?

It is padding surrounding the renal capsule, providing physical protection and maintaining the position of the kidneys in the body


What is the renal fascia and its function?

It is a connective tissue layer that anchors the kidney to surrounding structures


How does the kidney interact with blood?

It collects the fluid (filtration), and changes the composition of the fluid, selectively returning some substances to the blood, others to body fluid, and the rest into urine.


Why is the kidney multilobar?

It contains many lobes


What is the layer deep to the renal capsule?

The renal cortex


What are the renal columns?

Extensions of the cortex + fat, separating the medullary pyramids


What is the medulla?

The layer of the kidney deep to the renal cortex


What is the papilla?

The tip of the pyramid formed by the medullary pyramids. They are attached to the minor calyces


What forms a lobe within the kidney?

The medullary pyramid, its ortex and half of each renal column


How many lobes are there in the kidney?



What is interlobar?

The area between lobes of the kidney


How is the medulla broken up?

Into small cones- all together they look like bunches of flowers. These are called medullary pyramids


What is the functional unit of the kidney?

The nephron


How many nephrons are there in a kidney?

Approx. 1 million


Where do nephrons empty into?

The collecting duct


Where do collecting ducts empty into?

The papillary duct


Where is the papillary duct?

The tube within the papilla of the medullary pyramid


Where do papillary ducts empty into?

The minor calyces


Where do the minor calyces enter into?

The major calyces


Where do the major calyces enter into?

The pelvis


Where does the pelvis continue?

Through the ureter to the urinary bladder


What are lobules?

Miniature lobes within the renal cortex and medulla


Where are blood vessels in the kidneys?

The enter the renal artery and vein, the renal columns, the renal cortex and between lobules


What is the pathway of blood through the kidneys?

O2 blood---> Renal Artery --> Interlobar arteries --> arcuate arteries --> interlobular arteries --> Afferent Arterioles --> glomerular capillaries --> efferent arteriole --> (Descending vasa recta --> peritubular capillaries of the medulla --> Ascending vasa recta) OR )Peritubular capillaries of the cortex) ---> Interlobular vein --> arcuate vein --> interlobar vein --> Renal vein --> DeO2 blood


What is the renal hilum?

The region of the kidney where many blood vessels enter and exit


What defines a lobule?

The area between an interlobular artery and vein


What are the 2 pathways the blood in an efferent arteriole can take?

The vasa recta pathway, or go to the peritubular capillaries of the cortex


What is the function of the descending vasa recta?

Supports the tubular portion of the renal medulla with Oxygen


What is the function of the peritubular capillaries of the medulla?

Supplies the hoop of henle with Oxygen


What is the parenchyma?

The functional portion of the kidney


What are juxtamedullary nephrons?

Nephrons extending into both the cortex and the medulla


What is the progress of 'urine' from glomerular capsule to to minor calyx?

Glomerular capsule --> Proximal Convoluted tubule --> Thick descending loop of henle --> Thin descending loop of henle --> Thin ascending loop of henle--> thick ascending loop of henle --> Distal convoluted tubule --> collecting duct --> papillary duct --> minor calyx


What parts of the nephron are in the medulla vs. the cortex?

Cortex: Proximal convoluted tubule, renal corpuscle, distal convoluted tubule
Medulla: Thick and thin ascending and descending loops of henle, papillary duct
Both: Collecting duct


What makes up the renal corpuscle?

Glomerular capsule


What is the glomerulus?

A specialized know of capillaries, formed of endothelium. It is found inside the glomerular capsule


What is the glomerular capsule?

AKA bowman's capsule
Has 2 parts:
- Visceral: Podocytes
- Parietal: forms the outer wall of the capsule in simple squamous epithelium, continuous with the rest of the nephron


What are podocytes?

Specialized epithelial cells with interlocking foot processes. They are continuous with the parietal layer of the glomerular capsule


What is the hollow group of cells between the afferent and efferent arterioles?

The distal convoluted tubule, able to give feedback about filtrate composition. Its layer of cells closest to the renal corpuscle are the macula densa, the cells just beyond that are mesanglial cells, while a circle of cells surrounding the arterioles are the granular cells.


What is notable about the cells of the proximal convoluted tubule?

It contains cells with microvilli to increase the surface area available for the reabsorption of nutrients and electrolytes before they reach the loop of henle.


What makes up the filtration membrane of the renal corpuscle?

Fenestrations in glomerular (capillary) cells
Basal lamina between both
Slit membrane between pedicels


What are pedicels?

Foot-like processes of the podocytes that are interdigitated.


How does the fenestrated capillary membrane help filtration in the kidneys?

It permits all sizes of proteins through, but not cells


How does the basal lamina of the renal corpuscle help filtration in the kidneys?

It permits medium and small proteins through, but not large proteins.
It isn't uniform, and is formed by the combination of the basement membrane of the endothelium and podocytes


How does the slit membrane between the pedicels help filtration in the kidneys?

It allows small proteins through, but not medium proteins.


What is the overall purpose of the filtration membrane in the kidneys?

It allows gradation of filtrates, with only small proteins and molecules getting through into the filtrate. This allows much of the necessary plasma components to remain in the blood, while preventing clogging


What happens to the plasma components not allowed through the filtration membrane?

They make their way back into the blood.


What are the two most important functions of the kidneys?

- Regulation of water and electrolyte balance
- Regulation of arterial pressure


What are less important functions of the kidneys?

- Excretion of waste and foreign chemicals
- pH regulation
- Regulation of erythrocyte production
- Regulation of hormone production
- Regulation of blood glucose levels


What can happen if the kidneys malfunction?

They retain water, causing swelling --> high BP --> shortness of breath --> fatigues, nausea, poor blood pH


What are polycystic kidneys?

Fluid filled cysts that replace filtration


What is homeostasis?

The maintenance of a nearly constant internal environment


How much blood is usually diverted to the kidneys?

20% at rest


What is osmolality (and its difference to osmolarity)?

It is the measure of the effective gradient for water, assuming all solute is impermanent - a count of the number of dissolved particles per LITRE as opposed to per GRAM.
In other words; it measures the pressure exerted by a solution across a semi-permeable membrane in comparison to pure water


What needs to be remembered about osmolality?

When a compound dissociates, its osmolarity increases- eg. 150mOsmL of NaCl = 300mOsm/L in reality.


What is tonicity?

A functional term describing the tendency of a solution to resist expansion of intracellular volume.


What is the difference between isosmotic and isotonic?

Isosmotic solutions have the same number of dissolved particles per unit, regardless of water flow
Isotonic solutions cause no water movement across a membrane barrier, regardless of particle count.


Compared to a 300mM solution: A hyperosmotic solution is...

A solution with higher osmolarity that 300mM- eg. 600mM


Compared to a 300mM solution: An isosmotic solution is...

A solution with the same osmolarity- eg. 300mM


Compared to a 300mM solution: A hypotonic solution is...

A solution with less than 300mM- eg. 150mM


Hypertonic solutions make cells:

Shrink, as their water moves into the more concentrated fluid to dilute it


Isotonic solutions make cells:

No change


Hypotonic solutions make cells:

Swell, as water moves into them to concentrate the solution.


How can solutions be isosmotic and not isotonic?

Eg. 300mM solution of urea: urea is very permeable and would move into the cell down its concentration gradient, causing the ISF to become hypotonic, and the cell to swell.


What is osmosis?

The movement of water through a selectively permeable membrane from an area of low solute conc. to high solute conc. (high H2O to low H2O)


What is osmotic pressure?

The pressure required to stop H2O movement via osmosis.


What doesn't vs. does dissociate?

Urea and sucrose don't
NaCl does.


What proportion of body weight does water account for?

60% in males, 50% in females and 65-75% in infants


What is intracellular fluid (ICF)?

Fluid found in the cell. Accounts for 2/3 body fluids


What is extracellular fluid (ECF)?

All fluid outside the cell, accounting for 1/3 of body fluid.


What is ECF made up of?

20% plasma, 80% interstitial fluid


Where do we gain water from (mL per day)?

1600mL drinking (adjustible)
700mL food
200mL metabolism


Where do we lose water from (mL per day)?

100 mL feces
300 mL respiration
600 mL skin
1500mL kidneys (adjustible)


What are the body's main electrolytes?

Na+, Cl-, K+, Mg2+, Ca2+, HPO42-, HCO3-


What is the difference in concentrations of electrolytes in ECF vs ICF? Why are these important?

Na+, Cl- almost all in extracellular fluid
Na: 287 vs 10 mEq/L Cl: 217 vs 3 mEq/L
K+ much higher in intracellular fluid
K: 140 vs 8 mEq/L
This is important for setting membrane potentials, generating nerve activity, uptake of nutrients and expulsion of waste


What are the 3 processes in the formation of urine?

- Filtration
- Reabsorption
- Secretion


What is the equation for the amount of substance X in urine?

[X] excreted = [X] filtered - [X] reabsorbed + [X] secreted


Where do the 3 processes in urine formation occur?

Filtration occurs in the renal corpuscle, from blood plasma into the nephron
Tubular reabsorption occurs in the renal tubule and collecting duct, from the fluid to the blood
Tubular secretion (less important) also occurs in the renal tubule and collecting duct, from the blood to the fluid


What are the volumes of blood the kidney filters daily?

180L into the renal tubules daily, 178.6L reabsorbed- 1.4L is urine
Entire ECF is filtered about 12x per day


What is the rate of glomerular filtration?

125mL per minute


What are the differences between blood and filtrate?

They have similar solute concentrations, but filtrate has no large compounds, proteins or red blood cells


What is NFP?

Net filtration pressure: determines how much water and small dissolved solutes leave the blood


What does NFP normally sit at?



How do we calculate NFP?



What is GBHP?

The pressure gradient between afferent and efferent arterioles, forming the pressure within the glomerulus. This is the main driving force behind the movement of filtrate from the capillaries to the capsular space (50mmHg).
This allows the regulation of the pressure gradient to maintain flow and filtration, forming a buffer to changes in increases and decreases in BP


What is CHP?

Capsular hydrostatic pressure: the pressure exerted on the filtrate by the recoil of the glomerular capsule (usually 15mmHg). Pushes filtrate towards capillaries. This means the pressure can rise if there is a kidney stone etc.


What is BCOP? (kidney)

Blood colloid osmotic pressure: osmotic force of the proteins left in the plasma, exerting a pull on the water of the filtrate (25mmHg)


What happens if the afferent arteriole constricts?

There is less flow to the glomerulus and pressure drops, resulting in less urine production


What happens if the efferent arteriole constricts?

There is more backlog and pressure in the glomerulus, causing a greater output of urine.


What effect does renal arterial pressure have?

It is positively correlated with urine output, while filtration rate and flow seem to have little relationship with it.


What are the methods of maintaining glomerular filtration rate?

Autoregulation- change in diameter of smooth muscle in afferent or efferent arterioles due to blood pressure
Neural regulation- sympathetic nerve activity using NE can cause constriction of afferent arterioles via alpha receptors, increased renin. Leads to less GBHP
Hormone regulation: Using angiotensin II to constrict afferent and efferent arterioles reduces flow in general, while ANP relaxes the mesangial cells for an increased surface area for filtration.


What occurs in the proximal tubule?

70% of the glomerular filtrate is reabsorbed: 60% of NaCl and H20, 100% of glucose, as well as amino acids, nutrients and some HCO3.


How is Na+ reabsorbed in the proximal tubule?

- Na+ pumped into interstitial fluid by Na+/K+ ATPase, creating concentration gradients driving:
- Na+ entry into luminal membrane down its concentration gradient
- Some nutrients and ions enter via symporters (glucose/Na+) and some exit via antiporters (Na+/H+)
- H20 is reabsorbed by osmosis, as it follows the ions into the interstitial fluids. This also allows solutes remaining to be more concentrated, and move out of the tubule down their concentration gradients later on.
- Lipid soluble substance diffuse transcellularly
- Anions, K+ and urea diffuse paracellularly.


At the top of the thick descending loop of henle, what is the relative osolarity of the filtrate compared to blood?

The same, due to even movement of impermeable substances and water.


What occurs in the descending loop of henle?

Water is reabsorbed by osmosis as the interstitial fluid in the medulla is 2-4x more concentrated than the filtrate, and the walls are very water permeable
At its peak, the conc. is about 1200mOsm/L.


Why is the renal medulla so concentrated as it deepens?

The descending vasa recta absorbs much more NaCl than H20, making the blood very, very concentrated as it drops. The ascendign vasa recta absorbs much of the H2O lost by the descending loop of henle as it tried to decrease the osmolarity, returning it to its original osmolarity.


What occurs in the ascending loop of henle?

There are many Na-K-2Cl channels, especially in the thick zone, actively absorbing Na+ and Cl-, excreting K+. This section is practically impermeable to water, so the tubular content becomes more dilute, about 100mol/L entering the distal convoluted tubule.
As more Na and Cl are absorbed, urea accounts for a higher proportion of urine


What occurs in the distal tube and collecting duct?

More reabsorption of NaCl. Without ADH, this section doesn't reabsorb water, but with it, it does.


Which nephron produces dilute vs. conc. urine, and why is this?

The cortical nephrons produce dilute urine, while the juxtamedullary nephrons produce concentrated urine. This is because the juxtamedullary nephrons are the only ones that extend into the medulla, where IF concentration is higher, encouraging osmosis.


How does ADH act in the collecting duct?

It binds to the cell membranes, inserting vesicles into them to collect H2O (called aquaporin-2) via a second messenger
H2O leaves due to osmosis as the medullary conc. is high. The more ADH (and therefore vesicles), the more concentrated the urine


How does alcohol lead to dehydration?

It inhibits ADH, preventing reabsorption and resulting in a large amount of dilute urine, potentially resulting in dehydration as you urinate more than you are drinking.


What happens when you eat salt or drink isosmotic things or water, and what does this mean for exercise?

When you drink water, you get a rapid equilibrium in intra and extracellular fluid. The osmolarity of the extracellular fluid decreases and you get cell swelling
When you eat salt, it remains in the extracellular fluid, as it can't cross the cell membrane. This results in a large outflow of water from the cell to the fluid, and the cell shrinks
Isosmotic fluid remains in the ecf, and as it has the same osmolarity as cells there is no change in cell size.
- During exercise, you need H2O to prevent cell shrinkage due to water loss via sweat. You only need isotonic drinks if you need glucose, salt etc. It expands the plasma volume as it stays in the extracellular fluid


What is ADH and how is it synthesized/released?

ADH stimulates the insertion of aquaporin-2 vesicles in the luminal membrane of cells in the collecting duct. As the basolateral membrane is permeable to water, it is ultimately reabsorbed into the blood, resulting in concentrated urine
It is synthesized in the hypothalamus and stored in vesicles of the posterior pituitary gland. Osmoreceptors and baroreceptors stimulate the nerves cells of the hypothalamus to release ADH into the blood.


What role do osmoreceptors play in the ADH pathway?

When osmolality increases (ie. dehydration), or there is a high Na+ content of the plasma, the osmoreceptor cells shrink. They have stretch-inhibited cation channels, so the stretching causes the channel to open as they have processes anchoring them, forcing the channels open. This causes Na+ to enter, and causes an action potential to the posterior pituitary, releasing ADH


What are the interneurons running between the baroreceptors and the hypothalamus?

Supraoptic- closer to anterior pituitary, and paraventricular- closer to the posterior pituitary. They run down the infundibulum to the posterior pituitary.


What is the relationship between plasma osmolarity and ADH?

Higher plasma osmolarity = high ADH
At less that 280mOsm, no ADH, but we get thirst at 290mOsm- this mechanism is more sensitive than thirst.


What is the main trigger for ADH?

Increased osmolarity or Na+ in plasma


What is the osmolarity-driven pathway for ADH release?

Increased osmolarity
Detected by osmoreceptors in the hypothalamus
Travels to the posterior pituitary via nerves
Releases ADH
Targets collecting ducts in the kidneys- the principal cells become more permeable to H2O
This increases water reabsorption and results in scant urine, increased plasma volume and decreased plasma osmolarity
This then inhibits production of further ADH via negative feedback.


What is the pathway to ADH production via plasma volume or BP?

Decreased plasma volume or BP (10-15% lower)
This inhbits baroreceptors in the atria and large vessels
Nerve cells in the hypothalamus are stimulated, encouraging the released of more ADH
Targets collecting ducts in the kidneys- the principal cells become more permeable to H2O
This increases water reabsorption and results in scant urine, increased plasma volume and decreased plasma osmolarity
This then inhibits production of further ADH via negative feedback.


What are triggers for release of Renin?

Low NaCl concentration in the distal convoluted tubule
Decreased perfusion pressure
Increased sympathetic nerve activity (via baroreflex)
- So basically, low BP, blood volume or Na+


What are the most important hormones in the regulation of sodium reabsorption?

Angiotensin and aldosterone


How is renin formed?

It is an enzyme released by the juxtaglomerular cells of the kidney in response to decreased renal perfusion (blood flow)


How does angiotensin II affect renal physiology?

- It vasoconstricts, decreasing glomerular filtration by vasoconstricting the afferent arterioles, putting the blood in the capillaries at lower pressure
- It has a small affect on reabsorption in the proximal convoluted tubule
- Stimulates the release of aldosterone from adrenal cortex, which promotes more Na/K+ channels in the collecting duct, promoting greater Na+, Cl- and H2O reabsorption
It can also mimic thirst/salt intake, causing ADH to be released.


How is angiotensin II made?

Dehydration, Na+ deficiency, hemorrhage (in cells)
Decreased blood volume
Decreased BP
Juxtaglomerular cells produce increased renin
Combines with angiotensinogen from liver to form angiotesin I
Coverted to angiotensin II in the lungs via ACE
Travels to the adrenal cortex
Increased aldosterone
Works at kidney tubules to conserve Na+ and H2O, and secrete K+ and H+
Increased blood volume and vasoconstriction
Increased BP


What happens if excess salt is taken in?

NaCl is impermeable, so osmosis means water leaves cells into the plasma, increasing blood volume and BP
Decreased renin release and decreased angiotensin II
Decreased aldosterone and increased glomerular filtration rate
Reduced reabsorption of NaCl
Increaed loss of water and NaCl isosmotically in urine via natriuresis
Decreased blood volume

Low BP
increased stretching of atria and heart
Increased ANP
Reduced reabsorption of NaCl
Increaed loss of water and NaCl isosmotically in urine via natriuresis
Decreased blood volume


What is the primary regulator of NaCl?

RAA pathway


How do aldosterone and ANP work?

They do opposites:
Aldosterone promotes retention of NaCl, increasing water conservation
ANP promotes loss of NaCl (natriuresis), expelling more water


What does aldosterone do?

Acts on the distal tubule and collecting ducts to increase the trascription of the Na+/K+ ATPase for Na+ conservation and K+ excretion
- H2O conservation increases as it follows the movement of NaCl


Why is it important that ADH is concerned with water balance, and RAA is concerned with salt balance?

The two processes operate inependently


What do ACE inhibitors do?

They reduce the angiotensin II production, to help lose more H2O and reduce BP


What are the steps in restoring homeostasis?

1. BP restoration (takes seconds, vasoconstriction)
2. Restore osmolarity (except hemorrhage situations)
3. Restore blood volume- occurs over hour-to-hour basis and controlled by the kidneys.
4. Replenish blood cells if needed