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human anatomy and physiology > urine formation > Flashcards

urine formation Flashcards

1
Q

name the 3 Basic Processes of Urine Formation

A

Glomerular FILTRATION
Tubular REABSORPTION
Tubular SECRETION

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2
Q

explain glomerular filtration process of urine formation

A

Blood pressure forces water and most solutes in blood plasma across the walls of the glomerular capillaries

This produces the glomerular filtrate

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3
Q

Glomerular Filtration depends on what 3 main pressures

A

Net filtration pressure (NFP; total pressure promoting filtration) =

  1. Glomerular blood hydrostatic pressure (HP) (hydrostatic pressure = pressure exerted by a fluid)[promotes filtration], minus
  2. Capsular HP [opposes filtration], minus
  3. Blood colloidal osmotic pressure (BCOP; due to proteins in plasma) [opposes]

the first main pressure promotes filtration out whereas the other 2 oppose filtration

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4
Q

what is glomerular filtration rate

A

The pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity = hydrostatic pressure

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5
Q

explain how efferent arteriole diameter is greater than the efferent arteriole diameter

A

Efferent has higher resistance so increases BP upstream in glomerulus (55mmHg cf. 33 in capillaries elsewhere)

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6
Q

explain mesangial cells function and location

A

Mesangial cells (intraglomerular) contract to decrease surface area of capillaries, so glomerular filtration decreases

Positioned between capillaries

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7
Q

what is Glomerular Filtration Rate (GFR)

A

Amount of filtrate formed in all renal corpuscles of both kidneys each minute

adult 105-125ml/min (female-male)

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8
Q

what is the daily glomerular filtration rate in L/Day

A

150-180 L/day

but since 99% returned to blood, only 1-2 L excreted/day

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9
Q

what keeps the glomerular filtration rate constant and how

A

Homeostasis keeps GFR relatively constant by renal autoneural & hormonal regulation

  • angiotensin II increases BP
  • whereas ANP decreases BP

(BP = Blood Pressure. ANP = Atrial Natriuretic Peptide)

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10
Q

what can cause a decrease in glomerular filtration rate

A

Severe blood loss decreases GFR

But, high BP does not increase it much

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11
Q

what does Atrial Natriuretic Peptide (ANP) do?
and what happens when theres an increase/decrease in BP/volume

A

Opposes the Renin-Angiotensin system

An increase in BP/volume
ANP release
- Decrease renin, ADH & aldosterone

= Decrease in BP/volume

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12
Q

what happens If glomerular capillaries become damaged/permeable

A

Plasma proteins enter glomerular filtrate, leads to

Decreased BCOPressure, leads to

H2O drawn out of blood, leads to

Increased Net FP, leads to

Decreased blood volume & increased interstitial fluid volume, leads to

Oedema

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13
Q

what is oedema

A

build-up of fluid in body tissues, especially in feet and ankles

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14
Q

explain the tubular reabsorption basic process of urine formation

A

Filtered fluid flows along the renal tubule and through the collecting duct

Tubule and duct cells return ~99% of filtered water and useful solutes to the blood flowing through the peritubular capillaries.

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15
Q

tubular reabsorption is what kind of process

A

Selective process (to reclaim back into blood)

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16
Q

in tubular reabsorption transport across membranes may be ……

A

Active primary:
- Uses ATP
- e.g., Na+, bicarbonate ions (stabilises blood pH)

Active secondary:
- Uses ion’s electrochemical gradient
- e.g., glucose & amino acids

Passive
- e.g., urea, lipid soluble nonpolar components, H2O

17
Q

Transport maximum (Tm) reflects what

A

number of carriers available to transport substance (except for Na+)

18
Q

explain the tubular secretion basic process of urine formation

A

As fluid flows along the tubule and through the collecting duct, the tubule and duct cells remove substances from the blood in the peritubular capillaries and transports them into the fluid in the renal tubules e.g.,
- Wastes
- Drugs (e.g., penicillin, morphine)
- Excess ions

19
Q

how does tubular secretion act as a back up

A

to remove material that was not filtered out in the glomerulus

20
Q

what 2 tubular processes act as hormonal regulation

A

Hormonal regulation (angiotensin II & aldosterone) of both tubular reabsorption & secretion.

21
Q

Rate of urinary excretion of any solute =

A

rate of glomerular filtration
+ rate of secretion
minus rate of reabsorption

(tubular process 1+3-2= rate of urinary excretion)

22
Q

what is the filtered reabsorbed and excreted values of urea daily

A

54g filtered
24g reabsorbed
30g excreted

23
Q

what is the filtered reabsorbed and excreted values of glucose daily

A

162g filtered
162g reabsorbed
0g excreted

24
Q

what will happen if the tubule filtration reabsorption and secretion is disrupted

A

die in a few days as has immediate effects on composition of circulating blood

25
Q

show the Production of Dilute & Concentrated Urine

A

Dilute urine = 65mOsm/kg

Concentrated urine = 1200mOsm/kg

extracellular fluid = ~300mOsm/kg

26
Q

the production of dilute and concentrated urine is controlled by what

A

antidiuretic hormone

  • ADH, also called vasopressin
27
Q

what happens if antidiuretic hormone (ADH) is absent

A

urine contains high ratio of water to solutes (= dilute urine), as principal cells of collecting duct IMPERMEABLE to water

28
Q

what happens if antidiuretic hormone (ADH) is present

A

much water reabsorbed back into blood (= conc. urine) due to osmotic gradient maintained by:

  1. Differences in solute & water permeability & reabsorption in different sections of long loops of Henle & collecting duct
  2. Countercurrent flow in neighbouring desc & ascend limbs of loop
29
Q

what happens if there is too little water in the blood

A

its returned to normal by:
1. hypothalamus detects too little water in blood
2. pituitary gland releases ADH
3. kidneys maintain blood water level
4. so less water is lost in urine (urine more concentrated)
5. blood water levels return to normal

30
Q

what causes regulation of water reabsorption by ADH

A

negative feedback

31
Q

DIURESIS =

A

PRODUCTION of urine

32
Q

ANTIdiuresis =

A

reduced production of urine, hence ADH results in concentrated urine (less urine volume as water reabsorbed).

33
Q

what process happens is water conc is too high

A

some stimulus disrupts homeostasis by increasing blood water concentrations

this triggers osmoreceptors in hypothalamus this input sends nerve impulses to the control centre where the hypothalamus and posterior pituitary release ADH.

this output goes to effectors where cells in DCT and collecting duct become more permeable to water, which increases water reabsorption

this then causes an increase in blood water conc

this then returns to homeostasis when response brings plasma osmolarity ack to normal

34
Q

the release of ADH is stimulated or inhibited by what

A

Na in extracellular fluid

35
Q

explain the process of how Na in extracellular fluid stimulated or inhibits ADH release

A

high Na conc detected in bloodstream

then, pituitary gland(posterior lobe) stimulated to release ADH

then, ADH carried to kidney by the blood

then, increased reabsorption of water from kidney back into the blood stream
H2O then dilutes Na in the blood

this then lowers Na conc

36
Q

what happens in the collecting duct is ADH is present

A

If ADH present, water out of collecting duct (by diffusion), so concentrated urine produced

37
Q

explain the countercurrent multiplier system

A

The more salt actively pumped out of asc limb, the more conc will become the fluid passing through the desc limb into the asc limb

i.e., by pumping out solutes, the asc limb indirectly conc fluid being delivered to asc limb by the desc limb

As desc permeable to water but asc not & water move out by osmosis

human anatomy and physiology (52 decks)

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