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KBF- Kidney and Body Fluids > S1: An Introduction to Kidneys and Body Fluids > Flashcards

S1: An Introduction to Kidneys and Body Fluids Flashcards

1
Q

Name the two compartments the body water is distributed in

A

Intracellular fluid volume (ICFV) —- 40%

Extracellular fluid volume (ECFV)—20%

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2
Q

What happens if ICFV and ECFV aren’t in osmotic equilibrium?

A

There is fluid shifts between compartments

Water is generally free to move between them but it should move equally in both directions. Volume of ICF cannot change too much as cells cant change volume without major structural consequences

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3
Q

What is the extracellular compartment subdivided into?

A

Plasma space- the water in blood

Interstitial space- space outside the hut and outside the cells

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4
Q

Why must plasma volume be maintained?

A

It must be adequate to maintain perfusion pressure of the CVS

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5
Q

What barrier separates the intracellular and extracellular compartments?

A

Cell membrane

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6
Q

What barrier separates the interstitial space and plasma space?

A

Capillary wall

The capillary wall itself is made of cells and these will contribute to the intracellular volume as well as the blood cells themselves

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7
Q

Why is the control of body fluids important?

A

⭐️Cell Structure and Function = differences in osmotic pressure between ECF and ICF will lead to volume shifts which disrupts tissue structure and function

⭐️Tissue Perfusion= depends on balance between circulating volume (plasma) and interstitial volume. There has to be regulation of volumes so there is adequate pressure

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8
Q

What 2 factors are important in the movement of fluid between compartments?

A

Osmolarity (estimation of osmolar concentration of plasma and proportional to the number of particles per litre of solution)

Starlings principle of fluid exchange (balance between osmotic and hydrostatic forces)

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9
Q

What two processes are involved in the control of body fluids?

A
  • osmoregulation: control of the total solute concentrations of the ECFV
  • volume regulation: control of effective circulating volume (plasma volume) depends on balance between plasma and interstitial volume
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10
Q

Why does osmoregulation control body fluids?

A
  • Control of ECFV osmolarity in order to maintain osmotic equilibrium between ICFV and ECFV
  • Sodium (with its associated anions) is the principle electrolyte contributing to ECFV osmolarity
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11
Q

What is the ion that has the biggest impact on osmolarity than any other electrolyte or solute?

A

Na+

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12
Q

What is the mechanism of osmoregulation?

A

A rise in osmolality is a signal of dehydration and more water is needed.
• There are two ways to change the osmolarity of a solution:
1. Add/remove solute
2. Add/remove water

• The body accomplishes osmoregulation by adding or removing water not sodium

  • Plasmas osmolarity rises- more water needed (kidneys respond by producing small volume of concentrated urine, water retention)
    Plasma osmolarity falls- too much water (kidneys response by large volume of dilute urine, water excretion)
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13
Q

How do you change the osmolarity of a solution?

A
  1. Add/remove solute

2. Add/remove water

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14
Q

What is the mechanism of volume regulation?

A
  • Refers specifically to the control of the circulating (plasma) volume
  • Changes detected by stretch and pressure receptors in the cardiovascular system
  • A fall in blood volume is opposed by sodium retention

(sodium regulation is actually the mechanism of volume regulation - e.g. increase in sodium concentration means more water is needed so there will be an increase in ECFV)

The control of salt and water balance involves many organs

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15
Q

What organs are involved in the overall control of salt and water balance?

A 
Brain (pituitary, hypothalamus)
Heart (through cardiac output)
Kidneys 
Adrenal glands
And others
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16
Q

What causes dehydration?

A

Decreased water intake coupled with increased water loss (sweat, breathing)

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17
Q

Consequences of severe dehydration

A

Through dehydration, water volume is lost form the body as well as salt but the loss of water outweighs the loss of salt. As a result, there will be an increase in osmolality (especially in ECFV). Water moves out of the intracellular fluid into the extracellular fluid.

  • In the brain, this causes cell shrinkage
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18
Q

What is oedema?

A

Oedema is fluid imbalance between the plasma and interstitial space

  • It is due to an increase in water in the interstitial compartment which would occur if there was an increase in movement of water out of the plasma and into the interstitial space leading to tissue swelling.
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19
Q

Give some examples of what can cause oedema

A

Being on your feet all day which could make your ankle swell

Congestive heart failure (decrease in heart to sustain the cardiac output needed to maintain bp and adequate tissue perfusion). This drop in bp will lead to an build up in tissue fluid partially due to an imbalance in starlings forces.
The hydrostatic forces will be higher because there will be backing up of blood in the veins causing fluid to lead out.

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20
Q

What is Starlings forces?

A

Balance between osmotic forces and hydrostatic forces

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21
Q

List some functions of the kidney

A
  • The production of urine is the central process of kidney function (the urinary tract stores and then removes the urine)
  • Regulates homeostasis by regulating salt and water balance
  • Controls blood pressure (through salt and water balance as well as direct effects)
  • Regulation of electrolytes balance (potassium, calcium, phosphate)
  • Removal of metabolic waste/foreign chemicals products from the blood
  • Has its own endocrine function: releasing erthropoietin to regulate red blood cell production
22
Q

What is erythropoietin?

A

It is a glycoprotein that the kidney secretes into the blood (endocrine).

It regulates red blood cell production

23
Q

What is a nephron?

A

It is the functional unit of the kidney and consists of special blood vessels and elaborate epithelial tubes.
It is where urine production begins.

24
Q

What is the glomerulus?

A

It is a capillary network which sits inside the Bowman’s capsule.

25
Q

Were does urine (filtrate) travel from the glomerulus?

A

It travels from the Bowman’s capsule to the renal tube and then to the collecting duct where urine then drains into the ureter

26
Q

What is the network of capillaries that surrounds the rest of the tubules in a nephron called (glomerulus is at beginning)?

A

Peritubular capillaries supply renal tissue

27
Q

Explain the blood supply to the kidney

A

The renal artery enters the kidney and divides many times into smaller arteries (segmental, interlobar, arcuate, interlobular) and then into the afferent arterioles. These arterioles enter the glomerulus supplying each nephron. It then comes out as the efferent arteriole forming the peritubular capillaries around the rest of the tubule. They eventually coalesce into the renal vein through the vasa recta.

28
Q

Describe the structure of a nephron in relation to the medulla and cortex

A

The Bowman’s capsule, glomerulus and proximal convoluted tubule are the start of the nephron and sit in the cortex of the kidney. This then forms the descending loop of henle which goes through the outer medulla and into the inner medulla where it reaches its hair pin bend and then becomes the ascending loop of henle, this rises up through the inner medulla, through the outer medulla and forms the distal convoluted tubule in the cortex.
This then connects to the collecting duct and multiple collecting ducts come together to form the ureter.
The papilla is the bottom of the collecting duct.

29
Q

Name the 4 basic processes of urine formation

A
  1. Glomerular filtration (occurs in glomerulus and filtrate is forced out to be collected in Bowman’s capsule)
  2. Tubular Reabsorption (occurs in PCT, a lot of filtrate reabsorbed into peritubular capillaries)
  3. Tubular Secretion (occuring in DCT, with substances being secreted out of the blood back into the tubule)
  4. Excretion of Water and solutes in the urine
30
Q

Explain glomerular filtration (ultrafiltration)

A
  • Blood pressure (hydrostatic pressure) is the main force driving fluids and solutes through glomerular capillary network
  • Small molecules pass readily while larger ones such as plasma proteins and RBC cannot pass leading to a PLASMA ULTRA FILTRATE in the Bowman’s capsule
31
Q

What is glomerular filtration rate (GFR)?

A

It is the amount of filtrate the kidneys produce each minute.

This value is reduced in renal failure

32
Q

What test can be used for GFR?

A

Plasma creatinine

33
Q

Compare the afferent arteriole to the efferent arteriole

A

Afferent arteriole has a wider lumen and is closer to the heart so blood is at higher pressure

34
Q

Explain tubular reabsorption

A 
This occurs in the proximal convoluted tubule. 
Most substances (water, Na+, CL-, Glucose) are filtered an then almost all reabsorbed from the tubular lumen into the peritubular capillaries.
35
Q

Explain tubular secretion

A

It occurs in DCT, with substances being secreted out of the blood back into the tubule).
Also certain substances that were not initially filtered may be eliminate, e.g. potassium (high in EC), urea.
Control of K+ is generally though additional secretion as well as controlling H+.

36
Q

What is tubular secretion important for?

A
  • Disposing of substances not already in filtrate
  • Eliminated undesirable substances such as urea and uric acid
  • Ridding the body of excess potassium ions
  • Controlling blood PH
37
Q

What is the equation for urine secreted?

A

Amount filtered -Amount reabsorbed + Amount secreted = Urine Secreted

38
Q

What mechanism is osmoregulation and volume regulation based on?

A

Control of body water (osmoregulation)
Control of body sodium (volume regulation)

Both of these are based on negative feedback systems

39
Q

Describe the negative feedback system of osmoregulation

A
  • The control of water is based on the control of the osmolality of the ECFV.
    For example if there is less water coming in (fluid decrease) it will increase osmolality and excess fluid would dilute the fluid so decrease osmolality. And this is what is detected by the osmoreceptors in the hypothalamus. Any change is sensed and acted upon. Through controlling water excretion by the kidneys. This counteracts the rise/drop in water, which helps keep the osmolality at a similar value
40
Q

Balance = Input - Output

What happens if the balance value is not 0?

A

Input and output are not equal and so there is a change in osmolarity. This results in shifting of body fluids between ICFV and ECFV.

41
Q

Explain the physiological response to water restriction

A

Loss of water will cause a person to become thirsty but if there is no water available to drink, this will result in plasma osmolality rising.
It will continue to rise as body water is depleted but salts are not depleted at the same rate.
The rise in osmolality is detected in the brain and increased secretion of hormone ADH from pituitary gland.
ADH causes increased water reabsorption in the kidney meaning there is decreased urine volume and an increased urine concentration/osmolality.

42
Q

Explain the physiological response to water intake

A

Increase in water absorption through the gastrointestinal tract will cause plasma osmolality to fall due to decreased concentration of salts as it is more dilute.
This is sensed and the response is reduced secretion of ADH.
The effects of this is that urine volume is increased as there is less reabsorption in the kidney, hence the urine osmolality decreases as it is more dilute.

43
Q

How is plasma osmolality maintained?

A

It is maintained by retaining or excreting water by the ADH system, the kidneys and the behavioural thirst response

44
Q

What is the total body Na+ equation?

A

TOTAL BODY Na+ = INTAKE - ELIMINATION

45
Q

Why is control of sodium balance important?

A

It is the major electrolyte of the ECFV so changes in sodium concentration are going the lead to changes in the ECFV (blood volume and the interstitial volume).

Sodium balance is essentially volume balance

46
Q

What is the main sodium retaining system?

A

Renin-angiotensin-aldesterone system (RAAS)

47
Q

What is the main sodium eliminating pathway?

A

Cardiac natriuretic peptides (ANP)

48
Q

What are the 2 hormonal systems operating in sodium negative feedback?

A

sodium retaining system

sodium eliminating pathway

49
Q

Explain how the hormonal system balances increased sodium intake

A

Increase in sodium intake would cause an increase in the ECFV and the response to this would be to up-regulate the sodium excreting systems and down-regulating the sodium retaining systems. So more sodium is excreted and less is retained.

50
Q

Explain how the hormonal system balances decreased sodium intake

A

Decreased sodium intake would result in decrease in ECFV, and the excreting systems will be down regulated while the retaining systems will be up regulated so less sodium is excreted and more is retained.

KBF- Kidney and Body Fluids (14 decks)

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