Fluid dynamics

Question 1

Give examples of what is included in fluid input and output

Answer 1

intake:
-food and drink
-carbon metabolism

output:
-insensible fluid loss
-breathing
-sweating
-urine

Question 2

What is the role of ions in fluid balance?

Answer 2

-ions are able to pass through the capillary membrane
-phospholipid layer stops large molecules and charged particles
-if sodium is ingested, usually as salt, it will go into the plasma
-increased concentration draws water from the cell to maintain balance
-this can dehydrate cells

Question 3

Explain the movement of water and ions

Answer 3

-water moves down a concentration gradient from high water potential to low water potential, via osmosis
-ions move across the phospholipid membrane via active transport, using energy from ATP

Question 4

Define osmolarity

Answer 4

-the number of miliosmoles of solutes per litre of solution

Question 5

What is OSM/I?

Answer 5

-A measure of osmotic concentration
-simply the number of solutes per volume of fluids

Question 6

Explain how water intoxication oedema and dehydration occurs

Answer 6

water intoxication oedema
-too much fluid gain, and not enough fluid loss, therefore input outweighs output= fluid gain

dehydration
-not enough fluid gain, and too much fluid loss, therefore output outweighs input= fluid loss

Question 7

Define isotonic

Answer 7

-the same solute concentration both outside and inside the cell

Question 8

Define euvolaemic

Answer 8

having a normal level of blood

Question 9

What is hypovolaemic?

Answer 9

where the body loses fluid volume

Question 10

What is hypervolaemic?

Answer 10

where the body has too much fluid volume

Question 11

What is hypotonic?

Answer 11

low solute concentration in a fluid, therefore high water potential

Question 12

What is hypertonic?

Answer 12

high solute concentration in a fluid, therefore low water potential

Question 13

What are the triggers for antidiuretic hormone (ADH)?

Answer 13

-blood concentration mainly sodium chloride
-low blood volume
-low blood pressure
-angiotensin

Question 14

How are the triggers for ADH detected?

Answer 14

-detected by osmoreceptors
-a group of specialised cells located in the anterior hypothalamus
-they carry out the function of detecting changes in plasma osmolality together with the synthesis of ADH

Question 15

What is thirst?

Answer 15

-most important factor controlling thirst is the osmolarity (concentration) of body fluids
-osmoreceptor cells are probably found in the hypothalamus in the subfornical organ and are cells which respond to dehydration by initiating an electrical signal
-a decrease in blood volume/ pressure may also induce drinking

Question 16

What are the 4 major stimuli to thirst?

Answer 16

1. hypertonicity= cellular dehydration acts via an osmoreceptor mechanism in the hypothalamus
2. hypovolaemia= low volume sensed via the low pressure baroreceptors in the great vein and right atrium
3. hypotension= the high pressure baroreceptors in the carotid sinus and aorta provide the sensors for this input
4. angiotensin ii= this is produced consequently to the release of renin by the kidney (e.g in response to renal hypotension)

Question 17

What bodily processes occur as a result of water intoxication?

Answer 17

-dilution of extracellular body fluids
-leads to swelling of cells, coma and death

This is associated with
-early renal disease
-heart failure
-excessive ADH production
-polydipsia
-gastrointestinal disease
-poorly controlled administration of fluids

Question 18

What is aldosterone?

Answer 18

-a mineralocorticoid hormone produced in the zone glomerulosa of the adrenal cortex that influences water and salt regulation in the body

Question 19

What are the primary functions of aldosterone?

Answer 19

-act on the distal convoluted tubule and collecting duct of kidney nephrons
-favouring sodium and water reabsorption and potassium excretion while also contributing to acid-base balance
-to execute these tasks it influences epithelial sodium channels, sodium-potassium pumps, hydrogen ion ATPases, and bicarbonate-chloride anti porters

Question 20

What are the other effects of aldosterone?

Answer 20

-affects blood pressure by regulating the sodium gradient in the nephron to either increase or decrease the water reabsorbed to contribute to extracellular fluid
-ADH is often released simultaneously with aldosterone in order to support water reabsorption to the ECF

-its a key player in the multi-factorial regulation of salt, potassium, blood pressure, and acid-base balance

Question 21

What are the primary results of aldosterone hyper secretion?

Answer 21

-adrenal tumours
-renin secreting tumours
-batters syndrome
-malignant hypertension

Question 22

What are the secondary results of aldosterone hyper secretion?

Answer 22

-shrinkage of ECF volume
-severe heart failure
-cirrhosis of liver

Question 23

Explain how Addisons disease occurs as a result of aldosterone hypo secretion

Answer 23

-autoimmune destruction of adrenal glands
-a deficiency of aldosterone causes the body to excrete large amounts of sodium and retain potassium, leading to low levels of sodium and high levels of potassium in the blood
-the kinds are unable to concentrate urine causing excessive urination and dehydration
-severe dehydration and a low sodium level reduce blood volume and can culminate in shock

Question 24

What is atrial natriuretic function?

Answer 24

-the monocytes of the atria produce a 28 amino acid cyclical peptide known as (alpha) ANP

-ANP is released in response to stretch of the monocytes associated with increased venous return. ANP release may also occur in response to increased plasma concentration, but no osmosis-receptor has been identified

-ANP acts on kidney to cause an increase in GFR.
-It may also directly inhibit tubular tubular sodium transport in the distal tubule and increase vasa recta blood flow leading to medullary wash out

-ANP also inhibits renin release and ADH release, and may inhibit thirst

Question 25

What is diabetes insipidus?

Answer 25

-a lack or decrease in the release or action of ADH in termed
-characterised by the production of large volumes of dilute urine (up to 40 litres per day)
-nocturia is a major feature

type 1 is central= results from an absolute or relative deficiency of osmoregulated ADH secretion

type 2 is nephrogenic= inability to concentrate urine in response ADH

Question 26

What is syndrome of inappropriate ADH secretion (SIADH)?

Answer 26

-common as a transient effect following surgery
-due to excessive ADH production/ action
-leads to fluid retention and hypotonicity
-much more difficult to deal with then fluid depletion
-often transient

Question 27

Give examples of pathological fluid movements

Answer 27

-movement of fluids from vascular compartment to tissue spaces
-oedema
-sepsis or anaphylaxis
-true third spacing

Question 28

What is true third spacing?

Answer 28

movement to non-functional extracellular fluid

Question 29

How does fluid imbalance affect capillary transport?

Answer 29

-increased blood pressure
-blockage of venous system
-increased back pressure in the venous system
-lymphatic blockage
-increased permeability of capillaries
-loss of protein, liver disease, burns, malnutrition, kidney disease