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Physiology 1 > An introduction to kidneys & body fluid > Flashcards

An introduction to kidneys & body fluid Flashcards

1
Q

Give an overview of the water content of the body: the total body water, intracellular water and extracellular water

A
  • Total body water: 60% body weight
  • Intracellular water: 40% body weight (ICF compartment)
  • Extracellular water: 20% body weight (ECF compartment)
  • 60 40 20 rule
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2
Q

What does osmosis determine?

A

Osmosis determines movement of water between ICF and ECF

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3
Q

What is the extracellular fluid volume divided into?

A
  1. Plasma (3L)

2. Interstitial fluid (11L)

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4
Q

What is osmolarity?

A

Osmolarity is the total concentration of osmotically active solutes

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5
Q

Why must osmolarity be kept constant?

A

Osmolarity must be kept the same to avoid excessive shifts of water between ECF and ICF

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6
Q

What is the principle electrolyte of the ECF?

A

Sodium is the principal electrolyte of the ECF, therefore sodium (with associated anions) is the major determinant of ECF osmolarity

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7
Q

Why is the control of body fluids important?

A

• Cell structure and function
Large shifts between ECFV and ICFV will disrupt tissue structure and function

• Tissue perfusion
Depends on balance between circulating volume (plasma) and interstitial volume

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8
Q

What does salt and water balance depend on (2 key processes)?

A
  • Osmoregulation: maintain osmotic equilibrium between ICFV and ECFV
  • Volume regulation: maintain adequate ECFV to support plasma volume
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9
Q

How can plasma osmolarity be estimated?

A

2[Na] + 2[K] + [glucose] + [urea] (all in mmol L-1)

Typical:
2(135) + 2(4) + (5) + (5) = 288 mOsm L-1

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10
Q

How can we change the osmolarity of a solution?

A

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

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11
Q

What happens when plasma osmolarity rises?

A

1) Plasma osmolarity rises – more water needed

• Kidneys respond by producing small volume of concentrated urine (water retention)

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12
Q

What happens when plasma osmolarity falls?

A

2) Plasma osmolarity falls – too much water

• Kidneys respond by producing large volume of dilute urine (water excretion)

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13
Q

What is Volume regulation?

What are changes detected by?

A
  • Refers specifically to the control of the circulating (plasma) volume
  • Changes detected by stretch and pressure receptors in the cardiovascular system
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14
Q

What happens when there is a fall in blood volume?

What happens to sodium and water?

A

A fall in blood volume is opposed by sodium retention; water follows osmotically, restoring volume

Note: although the total amount of body sodium may be increased, concentration (and hence osmolarity) is little changed because the retained sodium brings water with it

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15
Q

What do the kidneys produce and what does the urinary tract do?

A
  • The production of urine is a by-product of kidney function.
  • The urinary tract is important for temporary storage and then to remove the urine from the body
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16
Q

What is the function of the kidney?

A
  • Osmoregulation
  • Volume regulation
  • Acid-base balance
  • Regulation of electrolytes balance (eg potassium, calcium, phosphate)
  • Removal of metabolic waste products from blood
  • Removal of foreign chemicals in the blood (e.g. drugs)
  • Regulation of red blood cell production (erythropoietin)
17
Q

Give an intro to the nephron

A
  • The nephron consists of special blood vessels and elaborate tubules (tiny tubes)
  • Microscopic, structures
  • 1.25 million per kidney
  • Where urine production begins
18
Q

Describe the structure of the nephron

A

Each nephron consists of several major structures:

  • Blood vessels
  • The glomerulus
  • Bowman capsule
  • The renal tubule
19
Q

Describe the arrangement of blood vessels and blood flow through the kidney and connect with nephrons

A

On image

20
Q

Describe the structural organisation of the renal nephron

A

On image

21
Q

What are the 4 basic processes of urine formation?

A
  1. Glomerular Filtration
  2. Tubular Reabsorption
  3. Tubular Secretion
  4. Excretion of water and solutes in the urine
22
Q

Describe the process of glomerular filtration

What is it?

How much does it produce

When does it stop (disease)?

What can be an index for GFR?

A
  • Is the amount of filtrate kidneys produce each minute
  • Averages 125 ml/min (approx 20% of renal plasma flow)
  • Is reduced in renal failure
  • Plasma creatinine can be used as an index of GFR
  • Hydrostatic pressure forces fluids and solutes through the glomerular capillary membrane
  • Small molecules pass readily- large ones (proteins) and cells cannot pass
  • This leads to a plasma ultra filtrate in the Bowman’s capsule
23
Q

Describe the process of reabsorption

A

Many substances are filtered and then reabsorbed from the tubular lumen into the peritubular capillaries

24
Q

Describe the process of tubular secretion

Why is it important?

A

Many substances are filtered and then reabsorbed from the tubular lumen into the peritubular capillaries

Tubular secretion is important for:
• Disposing of substances not already in the filtrate
• Eliminating undesirable substances such as urea and uric acid
• Ridding the body of excess potassium ions
• Controlling blood pH

25
Q

Describe the excretion of fluid and solutes in the urine?

A

On image

26
Q

Describe how the control of water balance (osmoregulation) is based on the control of the osmolality of the ECFV

A

On image

27
Q

What is the equation for the total water balance of the body?

A

Balance = input - output

28
Q

Describe what happens when we lose water, but there is no water available to drink

What does it result in?

A

Loss of water (sweat, breathing). Thirsty, but no water is available to drink
• Plasma osmolality rises
• Response is increased secretion of hormone, ADH (antidiuretic hormone, also known as vasopressin)

Results in:

  • Decreased urine volume
  • Increased urine osmolality
29
Q

Describe what happens when excess water is consumed?

What does this result in?

A

Increase in water absorption through GIT
• Plasma osmolality falls
• Response is reduced secretion of ADH

Results in:

  • Urine volume increases
  • Urine osmolality decreases
30
Q

Describe excessive and restricted water intake and its effect on renal output

A

On image

31
Q

How is plasma osmolarity maintained?

A
  1. It is maintained in the face of changes in water intake by retaining or by excreting water
  2. Done by ADH system, kidneys, and behavioural thirst response
32
Q

What is ECF volume determined by?

Where are these volume sensors located?

What is a fall in blood volume opposed by?

A
  • ECF volume is determined by the amount of sodium in this compartment
  • Sodium intake and excretion must be balanced to maintain constant ECF volume
  • Main volume sensors are in the cardiovascular system
  • A fall in blood volume is opposed by hormonal signals promoting sodium retention; water follows osmotically, restoring volume
33
Q

What is the total concentration of Na+ equal to?

What is the normal range?

How can we lose Na+

A

Intake - elimination

10 to > 400mmol/day

Sweat, diarrhoea and vomit

34
Q

Why is control of sodium balance important?

What can changes in sodium balance lead to?

A

Sodium is the major electrolyte if the ECFV

Changes in sodium balance lead to changes in ECFV which lead to blood volume and interstitial volume

35
Q

Describe how MAJOR HORMONE SYSTEMS ARE OF IMPORTANCE IN THE CONTROL OF SODIUM BALANCE

A
  1. Sodium retaining systems - The renin-angiotensin-aldosterone system (RAAS)
  2. Sodium eliminating pathways - Cardiac natriuretic peptides (ANP)

“ECF volume is determined by the amount of Na+ in this compartment. To maintain constant ECF volume (i.e., euvolemia), Na+ excretion must match Na+ intake. The kidneys are the major route for regulating excretion of Na+ from the body. Volume sensors located primarily in the vascular system monitor volume and pressure. When ECF volume expansion occurs, neural and hormonal signals are sent to the kidneys to increase the excretion of NaCl and water and thereby restore euvolemia. When ECF volume contraction occurs, neural and hormonal signals are sent to the kidneys to decrease NaCl and water excretion and thereby restore euvolemia. The sympathetic nervous system, the renin-angiotensin-aldosterone system, and natriuretic peptides are important components of the system needed to maintain steady-state Na+ balance.”

Physiology 1 (72 decks)

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