Fluid dynamics Flashcards
Give examples of what is included in fluid input and output
intake:
-food and drink
-carbon metabolism
output:
-insensible fluid loss
-breathing
-sweating
-urine
What is the role of ions in fluid balance?
-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
Explain the movement of water and ions
-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
Define osmolarity
-the number of miliosmoles of solutes per litre of solution
What is OSM/I?
-A measure of osmotic concentration
-simply the number of solutes per volume of fluids
Explain how water intoxication oedema and dehydration occurs
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
Define isotonic
-the same solute concentration both outside and inside the cell
Define euvolaemic
having a normal level of blood
What is hypovolaemic?
where the body loses fluid volume
What is hypervolaemic?
where the body has too much fluid volume
What is hypotonic?
low solute concentration in a fluid, therefore high water potential
What is hypertonic?
high solute concentration in a fluid, therefore low water potential
What are the triggers for antidiuretic hormone (ADH)?
-blood concentration mainly sodium chloride
-low blood volume
-low blood pressure
-angiotensin
How are the triggers for ADH detected?
-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
What is thirst?
-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
What are the 4 major stimuli to thirst?
- hypertonicity= cellular dehydration acts via an osmoreceptor mechanism in the hypothalamus
- hypovolaemia= low volume sensed via the low pressure baroreceptors in the great vein and right atrium
- hypotension= the high pressure baroreceptors in the carotid sinus and aorta provide the sensors for this input
- angiotensin ii= this is produced consequently to the release of renin by the kidney (e.g in response to renal hypotension)
What bodily processes occur as a result of water intoxication?
-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
What is aldosterone?
-a mineralocorticoid hormone produced in the zone glomerulosa of the adrenal cortex that influences water and salt regulation in the body
What are the primary functions of aldosterone?
-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
What are the other effects of aldosterone?
-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
What are the primary results of aldosterone hyper secretion?
-adrenal tumours
-renin secreting tumours
-batters syndrome
-malignant hypertension
What are the secondary results of aldosterone hyper secretion?
-shrinkage of ECF volume
-severe heart failure
-cirrhosis of liver
Explain how Addisons disease occurs as a result of aldosterone hypo secretion
-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
What is atrial natriuretic function?
-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
What is diabetes insipidus?
-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
What is syndrome of inappropriate ADH secretion (SIADH)?
-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
Give examples of pathological fluid movements
-movement of fluids from vascular compartment to tissue spaces
-oedema
-sepsis or anaphylaxis
-true third spacing
What is true third spacing?
movement to non-functional extracellular fluid
How does fluid imbalance affect capillary transport?
-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
