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Systems Physiology > Renal Physiology I > Flashcards

Renal Physiology I Flashcards

1
Q

What is the function of Kidney?

A

Kidney functions

  • maintain constant body fluid volume
  • maintain constant fluid composition
  • Endocrine organ
  • Acid-base balance
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2
Q

What is Osmosis? What is Osmotic pressure difference? What is the formula for Osmolarity?

A

Osmosis- movement of water across cell membranes
The osmotic pressure difference across cell membrane is the driving force for movement of water.
Osmotic pressure- determined by number of solute particles in solution
Osmolarity= Concentration X number of dissociable particles (mOsm/L= mmol/L X number of dissociable particles)

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3
Q

Define oncotic pressure and explain why it is important

A

Oncotic pressure- osmotic pressure generated by LARGE molecules (such as proteins).
symbol: (pi)
oncotic pressure is an important force in KIDNEYS which regulates fluid movement across the glomerulus and peritubular capillaries.

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4
Q

Describe the body fluid compartments. how much makes up extracellular and intracellular parts? How is extracellular part further divided?

A

Body fluid is divided into extracellular and intracellular compartments.
Intracellular: 2/3 of total body fluid
Extracellular: 1/3 of total body fluid
The extracellular part is further divided into 1/4 PLASMA (1/4) and (3/4) INTERSTITIAL compartments
in the plasma- Sodium and water are present, which is regulated.
Kidney maintains extracellular body fluid (changes plasma fluid)

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5
Q

Define the terms filtration, reabsorption and secretion. How does excretion occur?

A

Filtered load- mass of material filtered through glomeruli (move fluid from glomerulus capillaries into Bowman’s capsule).
Reabsorption- process where material is transported from lumen or nephron tubule to peritubular capillaries
Secretion- process where material is transported from capillaries to lumen (tubule)
Excretion- where material moves through length of nephron and is a combination of reabsorption and secretion minus filtration
Excretion: filtration- reabsorption + secretion

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6
Q

What is GFR? What are its determinants? What is the equation for GFR?

A

Direct Determinants of GFR:
1. Kf- increased glomerular surface area (relax mesangial cells) and INCREASE in GFR
2. PGc- increase renal arterial pressure (hydrostatic), causes DECREASE Afferent arteriole resistance (arteriolar dilation) and INCREASE Efferent arteriole resistance (Efferent constriction) leading to DECREASED GFR
3. PBc (hydrostatic pressure of Bowman’s capsule) Increased intratubular pressure (obstruction of tubule or extrarenal urinary system) leads to DECREASED GFR.\
4. pi Gc: Increased systemic oncotic pressure (of glomerular capillary) leads to DECREASED renal Plasma flow and DECREASED GFR.
GFR= Kf x NFP (PGc- PBc- pi Gc)

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7
Q

Which factors affect arteriole calibers?

A

Factors that affect arteriole caliber:

  1. Renal sympathetic nerves
  2. Renin Angiotensin system
  3. Autoregulation
  4. Prostaglandins
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8
Q

Why is the regulation of GFR important?

A

Regulation of GFR, regulates the amount of fluid going into nephron tubules, which help regulate:
-amount of fluid being excreted/reabsorbed
-clearance of specific molecules (toxins, drugs, certain metabolites)
These function to help control fluid volume and composition

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9
Q

What is the impact of Glomerular oncotic pressure?

A

a

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10
Q

What are the factors that affect Kf?

A

kf is a filtration coefficient used to describe the product of permeability and Surface area.
Permeability- determined by size/space of fenestra between endothelial cells and Size of pores between podocytes of Bowman’s capsule
Surface area- determined by mesangial cell status and number of viable nephrons.

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11
Q

What happens to nephrons as you age?

A

As you age, you lose nephrons.

also people with diabetes and high blood pressure lose nephrons

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12
Q

What two factors influence Autoregulation?

A

Factors that influence Autoregulation:

  1. Myogenic response- intrinsic property of vascular smooth muscle.
  2. Tubuloglomerular feedback
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13
Q

Explain how sympathetic activation of nerves affect GFR?

A

increased activity of sympathetic nerves will release Norepinephrine, and circulating epinephrine that will increase renal vasoconstriction
Increased in renal vasoconstriction of afferent and efferent arterioles causes LARGE DECREASE in RBF and small INITIAL increase in PGC (hydrostatic pressure of glomerular capillary)
This leads to NET DECREASE in net filtration pressure, and small decrease in GFR
With time, if filtration continues with constricted arterioles, PGc decreases and there is a significant decrease in GFR.

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14
Q

How does Angiontensin II affect GFR in normal conditions?

A

Angiotensin II- powerful VASOCONSTRICTOR that decreases RBF.
Ang II constricts both efferent and afferent arterioles (> effect on efferent), that increases PGc (hydrostatic pressure of glomerular capillary). But reduction of RBF, causes decrease in PGc.
Decrease in RBF causes increase in pi Gc (oncotic pressure of capillary, similar to affect of symp nerves) . Ang II Decreases Kf by acting on mesangial cells.
Ang II Decreases GFR in normal conditions.

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15
Q

How is Angiotensin II formed?

A

Renin converts Angiotensinogen to Ang I.
ACE (Angiotensin converting enzyme) then converts Ang I into Ang II
For kidney, any situation that increases renin secretion will increase Ang II production.

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16
Q

How is Renin produced? Which factors control Renin secretion and thus Ang II production and how do they do that?

A 
Renin- produced by GRANULAR cells in afferent arteriole of the JG appartus. 
Renin is controlled by: 
1. Intrarenal baroreceptors
2. Macula densa
3. Renal sympathetic nerves 
4. Ang II
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17
Q

Explain the Tubuloglomerular feedback mechanism of autoregulation? What kind of mechanism is it? What is it’s influence?

A

Tubuloglomerular feedback- used to maintain a relatively constant GFR, if there are changes in mean arterial pressure.
Mechanism:
increases in arterial pressure, causes increases in GFR.
Increase in GFR, raises flow through tubules. increased flow , increases delivery of fluid to macula densa. This increase will then be detected and a Vasoconstrictor (Adenosine) will be generated by JGA (juxtaglomerular apparatus)
The vasoconstrictor will constrict the afferent arteriole and result in INCREASE in resistance, decreased PgC (hydrostatic pressure of glomerular capillary) and decrease GFR.

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18
Q

What are the local metabolites present in Renal system? how do they affect GFR, RBF?

A

local metabolites- Prostaglandin, Nitric Oxide, Dopamine which are all vasodilators that increase blood flow, and increase GFR?

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19
Q

how much of a person’s body weight does body water take up? How much intracellularly vs extracellular fluid?

A

Total body water- makes up 60% body weight
extracellular fluid- 20% of body weight
intracellular fluid- 40% of body weight

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20
Q

Explain the use of prostaglandin and how it affects GFR? How is it formed? What are the two major Prostaglandins of renal arterioles?

A

prostaglandin- local metabolites of arachidonic acid, produced by both Renal sympathetic stimulation and Ang II.
2 major prostaglandins produced in endothelial cells of renal arterioles are PGI2 (prostacyclin) and PGE2. Both are VASODILATORY agents that prevent excessive vasoconstriction during CV (cardiovascular) stress
prostaglandins increase RBF and increase GFR?

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21
Q

What role does NO (Nitric Oxide) play in regulating GFR?

what increases the production of NO?

A

Nitric Oxide (NO)- important VASODILATOR in control of renal blood flow.
it counteracts Ang II and catecholamines
When blood flow increases, a greater SHEAR FORCE acts on endothelial cells and increase NO production.
INCREASES RBF, and INCREASES GFR?

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22
Q

What is the role of dopamine in GFR regulation?

A

Dopamine- vasodilator produced by proximal tubule

serves to INCREASE RBF (renal blood flow) and INHBIT renin secretion

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23
Q

What kind of mechanism is the Tubuloglomerular feedback?

A

This mechanism is intrinsic (does not rely on extrinsic nerves or hormones) The mechanism will work if blood pressure is within autoregulatory range (80 to 160 mm Hg)

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24
Q

Explain how the 4 major inputs control renin secretion?

A

A hemorrhage (ruptured blood vessel) can lead to a decrease in arterial pressure.

  1. Decrease in arterial pressure can lead to DECREASE in stretch of granular cells (intrarenal baroreceptors), which lead to increase in Renin secretion
  2. Decrease in arterial pressure also leads to decreased rate of fluid delivery to macula densa which increases renin secretion
  3. Decrease in arterial pressure leads to INCREASE in activity of renal sympathetic nerves, which causes a direct stimulation of granular cells (B-adrenergic receptors) and Increase in Renin secretion
  4. Angiontensin II controls Renin secretion through negative feedback mechanism.
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25
Q

What factors influence the afferent and and efferent arteriole caliber?

A
  1. Renal sympathetic nerves
  2. Angiotensin II
  3. Autoregulation of Renal blood flow and GFR
  4. Local Metabolites
26
Q

How does Ang II affect GFR in pathological conditions?

A

in pathological conditions, like Renal Artery Stenosis (narrowing of renal arteries), the effects of Ang II on efferent arteriole are significant.
Ang II serves to Maintain GFR, and ensure that reduction is NOT that severe; here it is important that Ang II ALWAYS has GREATER effect on RBF than GFR.

27
Q

What are the functions of renal blood flow?

A

Renal blood flow functions:

  1. indirectly determines GFR
  2. modifies the rate of solute and water reabsorption by proximal tubule
  3. participates in the concentration (dilution) of urine
  4. Delivers O2, nutrients and hormones to nephron cells returns CO2, and reabsorbed fluid and solutes to circulation
  5. Delivers substrates for excretion in urine.
28
Q

What factors determine RBF?

A

RBF determined by:
1. Mean arterial pressure
2. The contractile state of renal arterioles
a change in arteriolar resistance will produce the SAME
3. Flow= Arterial pressure- renal venous pressure/R (resistance) effect on RBF regardless of it occurs in afferent or efferent arteriole..

29
Q

What happens to RBF if there is a change in arteriolar resistance? What about how arteriolar caliber affects GFR?

A

Changes in arteriolar caliber will affect RBF INDEPENDENT of whether afferent or efferent arteriole caliber is altered.
Arteriolar caliber affects GFR in way, depending on whether afferent or efferent caliber is altered.

30
Q

Describe Renal Blood Flow (RBF). What is the equation and what percent of Cardiac output does it make up? Describe the flow process.

A

Renal Blood flow: typically 1.1 L/min in adult
-20-25% of total CO (cardiac output)
RBF- flow from renal artery, interlobular artery, through afferent and efferent arterioles, peritubular capillaries, veins and renal vein.
RBF= aortic pressure- renal venous pressure/renal vascular resistance.

31
Q

What are the direct determinants of GFR?

A

Rate of filtration= permeability x surface area x Net filtration pressure.
Kf=Permeability x surface area
hence GFR= Kf (permeability x SA) x NET filtration pressure (NFP)

32
Q

Define what GFR is? What is the normal GFR?

A

GFR- Glomerular filtration rate
GFR is the volume of filtrate formed per unit time.
Normal GFR is approx. 180 L/day.

33
Q

What are the different aspects of glomerulus filtrate or cell barrier that regulates filtration?

A

Aspects of filtrate that regulate filtration:

  1. substance size (any substance > 70,000 Daltons is NOT filtered)
  2. Electrical charge- negatively charged particles LESS filtered. This is because surface of filtration barrier are coated with polyanions which repel negative charges.
34
Q

Describe the anatomy of the kidney? What are the major structures.

A

Kidney- paired organ that had a deep fissure called Hilum, that passes through renal vessels and nerves in which lies Renal pelvis.
Renal pelvis divides into major calyxes. The calyx is cupped and around renal pyramid.
Kidney is bisected, it is divided into renal medulla (inner region) and outer renal cortex.
renal medulla made up of renal pyramids. Apex of pyramid project into minor calyx. Each apical tip is called papillae.

35
Q

Describe the flow of urine through different structures in the kidney.
what is the functional unit of a kidney? how many does each person have in each kidney?

A

Urine flows from renal pyramids, through papillae, to calyxes. The calyxes then empty into renal pelvis and from there to ureter and bladder.
Functional unit of human kidneys: NEPHRON
there are 1 million nephrons per kidney.

36
Q

How are Afferent and efferent arterioles constricted?

A

Afferent and efferent arterioles are richly supplied with sympathetic noradrenergic neurons. This neurotransmitter will act on both of the arterioles via alpha-adrenergic receptors an d cause constriction of arterioles.

37
Q

Explain the path of blood supply to the nephrons.

A

Blood enters each kidney via renal artery. renal artery then subdivides into smaller branches till you reach afferent arterioles which lead to glomeruli.
The afferent arterioles then go through glomeruli capillaries and recombine to form efferent arterioles. Efferent arterioles will then subdivide into peritubular capillaries which distribute throughout the length of the nephron.

38
Q

What is an example of a peritubular capillary?

A

Vasa recta- type of peritubular capillaries which are long and straight and drape (like Hair-pin loops) along loop of Henle

39
Q

Describe the Juxtaglomerular (JG) apparatus and where it is located. Which cell types are part of this apparatus?

A

Juxtaglomerular (JG) Apparatus- portion of tubule where the late thick ascending limb of Henle’s loop courses between the arterioles.
JG apparatus made up of 2 cells:
1. Granular cells (or juxtaglomerular cells)- differentiated smooth muscle cells in the walls of arterioles.
2. Macula densa cells

40
Q

What is the main function of granular cells?

A

Granular cells- SECRETE the hormone RENIN

41
Q

What is the function of macula densa?

A

Macula Densa- contributes to the Control of GLOMERULAR FILTRATION rate and to the SECRETION of RENIN.

42
Q

What does a nephron in a kidney consist of?

A

Nephron- consists of RENAL CORPUSCLE and TUBULE.

43
Q

What structures are part of renal corpuscle? where is the glomerulus found?

A

Renal corpuscle consists of glomerulus (glomerular capillaries), Bowman’s space and Bowman’s capsule.
The glomerulus of all nephrons is found in Renal Cortex

44
Q

What are the different tubular segments that the nephron is divided into?

A

Tubule segments:

  1. Proximal convoluted tubule
  2. Descending thin limb of Henle’s loop
  3. Ascending thin limb of Henle’s loop
  4. Thick ascending limb of Henle’s loop
  5. Distal convoluted tubule
  6. Cortical collecting duct
  7. Medullary collecting duct
45
Q

Describe the path of medullary collecting ducts all the way to bladder.

A

The inner medullary collecting ducts merge to form hundreds of large ducts that each empty into a calyx of renal pelvis.
Each renal pelvis is continuous with the ureter, which empties into the bladder.
hence nephrons elaborate the fluid within them to produce different amount and composition of urine depending on individual’s status.

46
Q

%Describe the different changes in osmolarity that occur between Extracellular fluid and Intracellular fluid.

A

A) Addition of pure water- if there is an increase in pure water in ECF, the osmolarity of ECF will be REDUCED, and water will move from ECF to ICF (hypoosmotic volume expansion)
B) Addition of hypertonic saline- If the ECF becomes hyperosmotic (increased Na), then water moves from the ICF into ECF. There will be a contraction of the ICF and an enlargement of ECF (hyperosmotic volume expansion)
C) Loss of pure water- if there is a loss of pure water, or more water than salt (Sweating), then BOTH ECF and ICF contract and osmolarity INCREASES (hyperosmotic volume contraction)
D) Addition of hypotonic saline- injection of hypotonic saline will cause DECREASE Osmolarity in ECF first, which will equilibrate with ICF. Volume will increase (hypoosmotic volume expansion)

47
Q

What are other changes in fluid composition/volume do kidneys control?

A

Kidneys also control:
Diarrhea/hemorrhage- isosmotic volume contraction
Drinking Gatorade- isoosmotic volume expansion

48
Q

What is the function of the Filtration slit diaphragm? Where is it located it and what is it’s function?

A

Filtration slit diaphragm- functions as a SIZE-SELECTIVE FILTER
IT is located between the podocyte processes.
It is composed of several proteins including Nephrin, NEPH and Podocin, along with intracellular proteins CD2-AP and Alpha- actinin.

49
Q

Differentiate between GFR and glomerular filtration.

A

GFR (Glomerular Filtration Rate)- rate at which material/substances are filtered through the glomerular capillaries. It is an index of kidney function
Glomerular filtration- bulk flow of fluid from glomerular capillaries into Bowman’s capsule.

50
Q

What is contained in the glomerulus filtrate? What is the order of filtered substances?

A

Glomerulus filtrate- fluid within bowman’s capsule normally does NOT contain any cells, are essentially protein-free and contains most inorganic ions and LOW molecular weight organic solutes.
Filtered substances go through:
1. Fenestrate in glomerular-capillary endothelial layer
2. Basement membrane
3. Slit diaphragms between podocyte processes.

51
Q

What would happen to volume of ECF if you drank gatorade?

A

Drink Gatorade (contain electrolytes, ions):
You would have an INCREASE in EC volume, and Osmolarity stays the SAME .
any added ions, volume, have not changed osmolarity.
gatorade (isoosmotic fluid)

52
Q

What are the major structures of kidney? How is fluid drawn from these parts?

A 
Kidney contains:
outer cortex
medulla (pyramid)
-minor calyx
-major calyx
Fluid is drawn from outer cortex to medulla, which goes to calyx and into renal pelvis and then ureter, to bladder.
53
Q

What is the functional unit of a kidney? How many are there?

A

NEPHRON- functional unit of kidney
1 million nephrons per kidney
nephron segments:
outer cortex, inner medulla

54
Q

Describe the flow of fluid starting from the nephron .

A

starting from Nephron, fluid flows through afferent arterioles towards the glomerulus (capillaries). Fluid then flows out of glomerulus into Bowman’s capsule and into proximal tubule.
The fluid will move into descending loop of Henle and then into thin ascending loop, then to thick ascending loop of Henle.

55
Q

Where is the macula densa located?

A

Macula densa- located between the thick ascending and thin descending loop of Henle.

56
Q

Distinguish between where peritubular capillaries and vasa vacta are located.

A

Peritubular capillaries- wrap around arterioles (efferent)

Vasa Vacta- wrapped around loop of Henle

57
Q

What is a podocyte slit diaphragm made of?

A

Podocyte slit diaphragm:

made of all the proteins that control the gap between the podocytes.

58
Q

What are the different aspects of the glomerulus endothelial cell barrier that regulate filtration of substances?

A

Aspects of glomerulus-endothelial cell barrier that regulates filtration-
Permeability
1. size of space/fenestra between endothelial cells
2. size of spaces between epithelial podocytes of Bowman’s capsule.

59
Q

Where a mesangial cells located? What occurs when these cells relax vs contract?

A

Mesangial cells- are located in the Middle of Bowman’s capsule
If mesangial cells RELAX, Surface Area increases and Kf INCREASES
if mesangial cells CONTRACT, SA decreases, Kf decreases and Glomerular filtration rate (GFR) will Decrease

60
Q

What is the equation for Net filtration pressure? What is the overall equation for GFR and why?

A

Net Filtration Pressure (NFP):
NFP= (PGC + Pi BC) - (PBC+ pi GC)
since no protein in bowman capsule, oncotic pressure (pi BC) = 0
overall equation for GFR: GFR= Kf x NFP (PGc- PBc- pi GC)

61
Q

What are the pressure values for hydrostatic pressure in Bowman’s capsule and glomerulus? Why does Glomerular capillary oncotic pressure change?

A

Hydrostatic pressure for Bowman’s capsule (constant)- 15 mmHg
Hydrostatic for Glomerular capillary (constant)- 60 mmHg
There are changes along Glomerular capillary oncotic pressure due to Reabsorption of fluid

Systems Physiology (19 decks)

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