Osmosis Video Stuff

Question 1

Cations vs anions

Answer 1

Anions = negative charged molecules

• intracellular = proteins and organic phosphates
• extracellular (both interstitial and plasma) = chloride and bicarbonate

Cations = positive charged molecules

• intracellular = potassium and magnesium
• extracellular (both interstitial and plasma) = sodium

Question 2

Gibbs-donnan effect

Answer 2

Large negatives charged proteins in the plasma repeal small anions into the interstitial fluid which conversely causes small cations to come into the plasma
- large proteins cant cross but this effect causes the plasma to remain relatively neutral charged

Question 3

How much of the cardiac output is renal blood flow?

Answer 3

25%

Question 4

What cells in the nephron secrete renin?

Answer 4

Juxtaglomerular cells in response to low blood pressure

Question 5

3 layers of glomerular filtration barrier

Answer 5

Separate blood vessels from bowman space

1) endothelium w/ fenestrations
- filters by size
- blocks RBC, solutes and proteins

2) basement membrane
- filters by size and charge
- blocks plasma proteins (albumin)

3) epithelium w/ podocytes and filtration slits
- filters by size and charge
- blocks plasma proteins

Question 6

What are the three forces that determine the glomerulus pressure?

Answer 6

1) Hydro static pressure of capillary blood (P(gc))
2) hydrostatic pressure of the bowmans space w/ filtrate (P(bs))
3) oncotic pressure of the glomerulus (pi(gc))

Net filtration pressure = P(gc)) - (p(bs)) + (pi(gc))

Question 7

Why does blood entering the efferent arteriole experience no filtration?

Answer 7

The oncotic pressure in the efferent arteriole reaches zero, which lowers the net filtration pressure

Question 8

How does changes in the oncotic pressure affect GFR?

Answer 8

High levels = lowers GFR
- increased amount of plasma/blood proteins

Low levels = increases GFR
- decreases amount of plasma/blood proteins

Question 9

How does changes in the hydrostatic pressure change GFR?

Answer 9

Increases in hydrostatic pressure within bowman space = lowers GFR
- urinary stone blockage

Decreases in hydrostatic pressure within bowman space = increases GFR
- idiopathic

Question 10

How does systemic blood pressure affect RBF?

Answer 10

Increases pressures in renal artery

Decreases resistance in renal arterioles

Both of these two increase GFR and RBF

Question 11

Two hormones that decrease renal blood flow

Answer 11

Adrenaline/ NE

• vasoconstriction afferent and efferent arterioles
• decreases GFR and RBF

Angiotensin-2

• released via RAAS system and renin
• vasoconstriction of efferent > afferent
• • this keeps GFR constant, while also lowering RBF

Question 12

Hormones that increases the RBF and GFR

Answer 12

1) Atrial naturetic peptide (ANP)
- released from atria of heart in response to increased stretching/ high blood pressure
- causes dilation of afferent and constriction of efferent arterioles
- mild increase in RBF, large increase in GFR

2) PGE
- released in sympathetic stimulation often in response to trauma
- dilates both the afferent and efferent arterioles dilate
- increases RBF and GFR

3) dopamine
- vasodilator afferent and efferent arterioles
- increases RBF/ GFR

Question 13

What is the BP range for auto regulation of renal blood flow?

Answer 13

80-200 mmHg

- within this range, myogenic stretch and tubuloglomerular reflex can auto regulate

Question 14

Why is PAH used to measure true renal plasma flow?

Answer 14

It gets filtered 100%

So plasma PAH = urine PAH+ Venous PAH

Question 15

Why does excreted PAH increase exponentially initially, but then tapers off into a linear pattern?

Answer 15

Excretion = filtered + secretion

• there is a select number of transport proteins able to take up PAH, whereas filtered is a constant number.*
• so initially both secretion and filtered increase Linearly, which causes excretion to be exponential or steeper increases. However once carrier proteins are fully saturated (Tmax), the secretion tapers off whereas the filtered number is still linear.
• therefore the excretion rate becomes equal to the filtered linear rate.

Question 16

How does glucose get reabsorbed?

Answer 16

SGLT and GLUT 1/2 receptors in PCT and Thick descending limb

SGLT = apical -> brush border
- uses secondary active transport via energy generated from cotransporter with sodium

GLUT1/2 = brush border to blood
- uses facilitated diffusion

Question 17

What is the normal blood plasma osmolality?

Answer 17

290-300

Question 18

What happens when osmolarity increases past 300 (usually only occurs in low blood volume)?

Answer 18

1) supraoptic neurons sense this decrease in osmolarity via aquaporin-4 channels and fires signals to the posterior pituitary to release ADH
2) baroreceptors sense decreased blood volume and constrict smooth muscles in vessels to increase blood pressure
3) ADH goes to collecting ducts binds to V2 receptors and upregulated aquaporins to be put into the lumen surface. This causes mass reabsorption of water. In addition, it causes blood vessel lumens to constrict as well
4) hypothalamus stops releasing ADH in decreasing plasma osmolarity (back to normal or even lower)

Question 19

What is the purpose of the corticopapillary gradient?

Answer 19

To ensure no unnecessary water loss

Is is essentially a osmolarity graident that increases as you get closer to the medulla and is directly tied to the loop of Henle

Question 20

Where does ADH bind to collecting duct

Answer 20

AVPR2 proteins
- converters ATP -> cAMP

Results in 2 actions:

1) increases aquaporins-2 protein production
2) allows for protein vesicles to fuse to cell membrane

Question 21

What is the function of angiotensin 2

Answer 21

1) causes posterior pituitary to increase production of ADH

2) ADH causes arteries in the body to constrict increasing blood pressure and up regulating aquaporin-2 proteins

Question 22

How is calcium reabsoprtion in the kidney?

Answer 22

Directly tied to sodium ion reabsoption

• 67% occurs in PCT
• 25% occurs in the TAL
• remaining is late DCT