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Physiology > Renal Physiology 1 > Flashcards

Renal Physiology 1 Flashcards

1
Q

Give the basic functions of the kidney

A
  • Volume, osmolarity & electrolytes regulation
  • Control of arterial blood pressure
  • excretion of metabolic wastes and bio active substances such as hormones, toxins, antigens and drugs
  • Acid base balance
  • Erythropitein production
  • Activation of vitamin D for calcium balance
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2
Q

What is the functional unit of the kidney ?

A

Nephron

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3
Q

What is the flow through the kidney?

A

Renal —> segmental —> interlobar—> arcuate—> cortical radial (interlobular)—> afferent arterioles—> efferent arteriole —> peritubular capillaries

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4
Q

Contrast cortical and Juxtaglomerular nephrons

A

Cortical nephrons- 80-85% & short loops of Henle

Juxtaglomerular nephrons- 15-20% & having long loops of henle

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5
Q

Describe the juxtaglomerular apparatus

A

The structures present very close to the glomerulus make juxtaglomerular(JG) made up of three cell types:

  1. Granular cells(or juxtaglomerular cells) in afferent arteriole releases renin
  2. Extra Glomerular Mesangial cells(or lacis cells)
  3. Macula dense cells are modified epithelial cells of early DCT - sense NaCl load

JGA- auto regulates of the Glomerular filtration of the single nephron by tubuloglomerular feedback mechanism

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6
Q

What are the 3 basic functions of the nephron?

A
  1. Glomerular filtration- filtering of plasma in the Glomerular capillarie(1st step)
  2. Tubular Reabsorption- movement of substances from tubular fluid to blood
  3. Tubular secretion: movement of substances from the blood into the tubular fluid

What is remaining in the tubular fluid after three basic processes gets excreted in urine- renal excretion

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7
Q

How to calculate the amount of solute excreted?

A

Amount of solute excreted (E)= amount filtered(F)- amount reabsorbed(R)+ amount secreted (S)

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8
Q

What is renal blood flow?

A

1200 ml/min (RBF)

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9
Q

Describe Glomerular filtration & renal blood flow

A
  • GF is the 1st step in formation of urine
  • A portion of the blood as it flows through the Glomerular capillaries is filtered into Bowman’s space
  • The filtrate is called ultrafiltrate & has all components of plasma except for plasma proteins & blood cells
  • GFR( Glomerular filtrate rate) is expressed as mL per minute of liter per day
    - Approximately 120-125 mL/min or 180 L/day plasma is filtered in an adult

The entire plasma of 3 liters is filtered 60 times a day

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10
Q

What is the Effective Renal Plasma Flow(ERPF)?

A

700 ml/min

The amount of plasma flowing to the parts of the kidney that have a function in the production of constituents of urine)

GFR= 120 ml/min (both kidneys) (Glomerular filtration rate)

Filtration fraction(GFR/ERPF) 15-25%

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11
Q

Describe Glomerular filtration process & the barrier

A

Filtration occurs through filtration barrier which has three layers:

  • the endothelium of Glomerular capillary
  • the basement membrane (has negative charges)
  • epithelial cells(podocytes) surrounding the Glomerular capillary
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12
Q

What are the determinants of filter ability ?

A
  • Suze less than 10,000 kilodaltons are freely filterable
    - with larger molecules movement is restricted & ceases if more than 70,000 kilodaltons

-Charge
-If negatively charged & large filterability is restricted
- Positively charged molecules easily filtered
- Neutral charge is relatively easy to filter
Since serum proteins are negatively charged & large they cannot be filtered

-Shape affects the filtration

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13
Q

What is filterability?

A

Concentration ratio in ultra filtrate & plasma

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14
Q

How to calculate IF Filterability?

A

Means the concentration of solutes in plasma= concentration in Bowman’s space

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15
Q

What are the positive forces favoring filtration?

A

PGC= hydrostatic pressure in the glomerulus

piBS= is oncotic pressure in the Bowman’s capsule

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16
Q

What are the negative forces opposing filtration or forces favoring reaspbsorotion?

A

PBS= is the hydrostatic pressure

PiGC= Is the oncotic pressure in (Glomerular capillary )

17
Q

What is net filtration pressure(NFP)?

A

Is the difference of these forces

NFP= (PGC+ PIBS)- (PBC+ PIGC)

18
Q

Give an example of Glomerular filtration being determined

A

Forces favoring filtration (+)
PGC= 45 mm Hg(relatively constant )
PiBS= usuallly 0 mm Hg

Forces opposing filtration or forces favoring Reabsorption (-)
PBS- 10 mm Hg (relatively constant)

PiGC(on average)= 25 mm Hg (increases along capillary)

Net filtration pressure= the differences in these forces

NFP= (45-(10+ 25)= +10 mm Hg

19
Q

How do starling forces change in afferent and efferent arterioles ?

A

PGC decreases slightly from afferent to efferent due to along the length of the capillary; PiGC increases from afferent to efferent due to filtration of fluid

20
Q

How can GFR be determined by starling forces ?

A

GFR= Kf x (PGC-PBS- PiGC)

Where

Kf= filtration coefficient which is the product of:

 - Water permeability of the filtration barrier
 - Total surface area of the filtration barrier

Kf= 10- 15 ml/min mmHg (normally)

So if you alter any of the above factors GFR is affected

21
Q

What is the function of autoregulation ?

A

Autoregulation of blood flow in the kidneys maintains a nearly constant GFR when mean arterial blood pressure is between 80 and 180 mm Hg

22
Q

Summarize autoregulation of blood flow in the kidneys

A

Below 80 mm Hg- reduced blood pressure and increased 180 mm Hg-severe hypertension

Myogenic

Tubuloglomerular feedback

Without autoregulation increase in BP can lead to dramatic increase in GFR which could lead to serious losses of NaCl & water frommECF

23
Q

Summarize myogenic mechanism of autoregulation

A
  1. Increased blood pressure
  2. Increased Afferent arteriole stretch
  3. Non-specific cation channels open
  4. Depolarization
  5. Calcium channels open- increased intracellular calcium
  6. Afferent arteriole contracts
24
Q

Summarize tubuloglomerular feedback

A

-Increase in GFR, Increase in NaCl delivery

Releases ATP from macula densa cells.

- This splits into adenosine AMP & ADP
- Adenosine binds to its receptor in Afferent arteriole & vasoconstricts it

Construction of afferent:

  • decreased renal plasma flow (RPF)
  • Decreased GFR

This will maintain constant plasma flow. The mechanism fails with BP<80 or >180

Decreased delivery Na+ to macula densa dilates the arteriole & leads to increase in renal blood flow and GFR

25
Q

Explain the constriction of the tubuglomerular feedback

A

Vasoconstriction of the afferent arteriole increases resistance and decreases renal blood flow, capillary blood pressure (PH), and GFR

-Increased resistance of efferent arteriole decreases renal blood flow but increases PH and GFR

-

26
Q

Why should we measure GFR?

A

To assess renal function

27
Q

how can we measure renal function?

A

The volume of plasma rendered free of a s7bstance(Z) per unit time

Calculated as a ratio:

Cz = Amount of substance (Z) in urine X Urine flow rate/ concentration of (Z) arterial plasma

Cz= UzXV/Pz

Cz= clearance of Z
V= urine flow rate
Uz= urine con of Z
Pz= Arterial plasma con of Z
28
Q

Describe measurement of GFR

A

GFR could be estimated through clearance of a suitable substance:

  • freely filtered by glomerulus
  • Neither reabsorbed, nor secreted by the tubule
  • Not synthesized, stored or degraded by the kidney
  • Non-toxic and easy to measure in plasma & urine
  • That substance is inulin
  • Inulin is an exogenous product so it needs to infused so not used commonly
  • Clinically creatinine is used to measure GFR as it is produced endogenously
  • It is end product or pr9tein metabolism
  • It is not an accurate measure of GFR, as small quantities are secreted
  • However it is easy to measure

Cinulin=125 ml/min =GFR
Inulin clearance =GFR

29
Q

How to measure renal plasma and blood flow?

A

If the clearance o& a substance is greater than the GFR then net secretion occurred in the renal tubules

Glucose is an example of a substance that is completely reabsorbed, and the clearance of glucose is zero

If the clearance of a substance is less than the GFR net Reabsorption occurred

Para-aminohippuric acid (PAH) is freely filtered, is not reabsorbed and is secreted completely into the tubules. The clearance of PAH is equal to the renal plasma flow.

If the hematocrit is known this can be converted to the renal blood flow

30
Q

What is filtration fraction?

A

Filtration fraction= Glomerular filtration rate / renal plasma flow = GFR/RPF

normal FF= 0.15 to 0.2

This means that only 15 to 20% of plasma that enters the glomeruli is actually filtered

Renal blood flow= plasma+ blood cells & is calculated as RBF- RPF/1-Hct

(Hct is hematocrit or RBC volume)

Physiology (36 decks)

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