Blood and Circulation Flashcards
What makes up total body water?
Intracellular fluid (ICF) + Extracellular fluid (ECF)
What does extracellular fluid consist of?
Plasma, interstitial fluid, transcellular fluid (cerebrospinal, synovial, intraocular fluids).
What is the average TBW for a man and a woman?
In a typical man TBW = 60%
In a typical woman TBW = 52% (because fat contains a low amount of water)
What are the 2 differences between the concentration of solutes in interstitial fluid and plasma?
1) The protein concentration in interstitial fluid is very low compared to the plasma.
2) Half the calcium in plasma is protein bound, which means that the total calcium concentration in the interstitial fluid reduces correspondingly as there is already low protein concentration in the interstitial fluid.
Explain what the dilution principle is
Add a known amount of solute to an unknown volume of a liquid.
Can then find the concentration of the solution.
Volume = amount ÷ concentration
(m/c x v)
How can the dilution principle be used to find the volume of different body fluid compartments?
Add a specific solute into the body, and find the concentration of that body compartment.
From this the volume of the body compartment can be calculated.
However because different body compartments have different properties, solutes that look different in different body compartments are used.
What solute is used to find total body water volume?
Tritiated water
3H2O
What solute is used to find extracellular fluid volume?
Inulin
What solute is used to find plasma volume?
Evans blue, 125 I albumin, must stay in vascular system.
Plasma proteins are labelled isotopically.
How can the intracellular volume be calculated?
Calculated by finding the difference between the total body water and the extracellular fluid.
How can the interstitial fluid volume be calculated?
Calculated by finding the difference between the extracellular fluid and plasma.
What factors have to be considered when finding the volume of body compartments in vivo?
1) Have to consider the equilibrium time for a given substance.
3H2O and inulin need time to distribute between the compartments.
2) 3H2O can be lost in urine and sweat.
3) Inulin is filtered by the kidney so will also be lost in urine.
4) Evans blue has a short half life of 10-30 mins so any measurements need to be taken quickly.
Why is transcellular fluid volume usually discounted?
It is relatively small
Define osmotic pressure
Pressure sufficient enough to prevent movement of water into a solution across a partially permeable membrane.
Has a low water potential so will attract water towards it.
It opposes hydrostatic pressure.
Define osmolarity
Number of moles of a solute per litre of water.
Define osmolality
Number of moles of a solute per kilogram of water. In a solution it would be the number of osmoles of solute per kilogram of solvent.
Units are the osmole.
How do you calculate the osmolality of solutions that dissociate in water?
Solutions that dissociate have 2 ions in the solution so the osmolality will double.
Outline the changes in osmolality when glucose is moved into the intracellular fluid?
When glucose moves into the intracellular fluid there will be more solute in this fluid. This therefore means the osmolality of the intracellular fluid will increase. Water moves from a low to high osmolality, so water will move into the intracellular fluid by osmosis.
What is the definition of total osmolality and and example of this?
Total osmolality = sum of osmolality due to each of the constituents of the solution.
An example of this is the plasma. Its osmolality is around 295 mOsmolkg-1.
How much do ions contribute to the osmolality of plasma?
Na+, Cl-, HCO3- contribute ot most of this.
Glucose and other small molecules contribute less than 10 mOsmolkg-1.
Plasma proteins contribute only 1 mOsmolkg-1.
What will happen if the osmolality of the plasma is increased?
Water moves from a low to high osmolality, so water will move into the plasma from other parts of the body.
What is the osmotic gradient if an RBC is placed in a hypotonic solution?
A hypotonic solution will have a low osmolality (less solute).
Water moves from a low to high osmolality. This means that water will move from the solution and into the RBC.
This will cause the RBC to burst by haemolysis.
What is the osmotic gradient if an RBC is placed in a hypertonic solution?
A hypertonic solution has a high osmolality (more solute). Water moves from a low to high osmolality. This means water will move from the RBC and into the solution. This will cause the RBC to undergo crenation.
Define tonicity
Tonicity is the influence of the osmolality of a solution on the volume of cells.
Define iso-osmotic
Two solutions with the same osmolality as each other.
Define isotonic
Two solutions with the same concentration of solute as each other, so there is no concentration gradient.
This can only occur if the solutes cannot cross the cell membrane.
What is a rule about isotonic and iso-osmotic solutions?
All fluids that are isotonic are also iso-osmotic (if they are the same concentration they have to be iso-osmotic).
BUT not all iso-osmotic solutions are isotonic with cells -> May have the same concentration of solute however in cells movement of water depends on the salt concentration of the blood, which may not be iso-osmotic with the solution even if it is isotonic.
What is an effective osmole?
When a solution is isotonic with the surrounding solution, and the solute cannot pass across the cell membrane. Means there is no net water movement.
What is an ineffective osmole?
When a solute is permeating and can pass across the cell membrane, so the solution cannot be isotonic with the surrounding solution.
Means there will be movement of water either in or out of the cell.
How is the rapid ingestion of 1L of water distributed in different body compartments?
ECF = 1/3 of TBW
ICF = 2/3 of TBW
Plasma = 20% of ECF
According to this each body compartment will increase by that specific volume.
How is the rapid ingestion of 1L of 0.9% saline solution distributed in different body compartments?
0.9% saline solution is around 300 mOsmoles, which is iso-osmotic to plasma. Means solutes pass cross the membrane.
However there are no ATPase pumps on cell membranes so Na+ ions cannot pass into the intracellular fluid. It is an effective osmole.
Means the saline solution is distributed only within the extracellular fluid.
The saline solution is iso-osmotic with the plasma and isotonic with ICF.
How is the rapid ingestion of 1L of 5% albumin distributed in different body compartments?
Albumin is a blood protein, so cannot pass across the cell membrane of blood vessels by diffusion. It is an effective osmole.
This means the albumin stays within the plasma only.
What are the 4 different pressures (Starling’s forces) that control the movement of fluid across capillary membranes?
Hydrostastic pressure from arteriole end of capillary = Pressure from the heart that forces fluid out of the capillary. It is highest in arteriole end and lower in the venue end due to loss of fluid.
Interstitial fluid hydrostatic pressure = Pressure from the fluid outside the capillary that forces fluid into the capillary.
Plasma colloid oncotic pressure = Osmotic pressure from the colloids in the capillary that pulls water into the capillary. The colloids cannot pass across the membrane.
Interstitial fluid colloid osmotic pressure = Osmotic pressure from the colloid in the interstitial fluid that pulls water out of the capillary. Lower than plasma oncotic pressure are there are less proteins here.
What is unique about the oncotic pressure gradient?
It remains the same as the protein concentration is always constant.
What is the process that occurs when the outwards forces from capillary exceed the inward forces?
Filtration
What is the process that occurs when the inward forces from the capillary exceed outward forces?
Reabsorption
Describe the tissue pressure balance in the normal capillary
In the arteriole side filtration takes place as hydrostatic > oncotic pressure.
In the venous side reabsorption takes places as oncotic > hydrostatic pressure.
The level of filtration and reabsorption is almost identical.
Describe the tissue pressure balance in the kidney glomerulus
Only filtration takes place.
The capillary pressure in the glomerulus is very high due to the need to filter lots of plasma.
Means the hydrostatic pressure is always greater than the oncotic pressure.
Describe the tissue pressure balance in the pulmonary capillaries
Only reabsorption takes place.
The pulmonary capillary pressure is very low as right side of heart has a weaker contraction.
Means the hydrostatic pressure is always lower than the oncotic pressure.
What is oedema and why does it occur?
Oedema is an imbalance of tissue fluid.
Occurs when filtration is greater than reabsorption and lymph drainage.
How does increased venous pressure cause pitting oedema?
What are its causes?
Hydrostatic pressure in the venous end increases. This means the hydrostatic pressure gradient doesn’t decrease below the oncotic pressure enough for reabsorption.
Can occur due to cardiac insufficiency, heart cannot produce enough pressure to pump blood around the body.
Can occur as a result of thrombotic blockage.
How does inflammation cause oedema?
Insect bites and sepsis can lead to release of mediators (bradikynin, thrombin, histamine).
These cause vasodilation in the arteriole part of the capillary so more blood arrives, increasing the pressure.
The tight junctions in the endothelial cells increase the permeability of the capillary.
Both of these actions increase the filtration in the arteriole side of the capillary, resulting in oedema.
How does reduced plasma protein levels cause oedema?
Reduced protein concentration in the capillary means that the hydrostatic pressure will be higher than the oncotic pressure for a greater length of the capillary, meaning there will be more filtration and less reabsorption.
Can occur in liver failure to produce albumin, malnutrition or nephrotic syndrome.
How does reduced lymph drainage cause oedema?
No drainage of lymphatic vessels means that the 3L of lymph produced per day will accumulate in the interstitial fluid.
This can lead to fibrotic scan tissue around the oedema area.
Can occur due to bancroftian filariasis, lymph node destruction.
How does a haemorrhage cause increased blood volume?
The haemorrhage causes a great reduction in blood volume, so the hydrostatic pressure in the capillary decreases.
Means the hydrostatic pressure will not be greater than the oncotic pressure for enough length of the capillary.
Results in more reabsorption than filtration, in order to try and increase the lost blood volume.
How is hypertension defined in mmHg?
When systolic pressure is over 140mmHg and diastolic pressure is over 90mmHg.
How is atherosclerosis affected by hypertension?
Increased pressure increases chances of things dislodging from the wall of the vessel and entering the circulation.
What happens to systolic blood pressure as you age?
It increases
What are the protective properties of oestrogen?
Oestrogen is protective to vasculature as it inhibits smooth muscle proliferation and promotes growth of endothelial cells.
List 4 consequences of hypertension
1) Increased cardiac work (due to more after load)
2) Ventricular hypertrophy
3) Increased distension of vasculature
4) Increased peripheral resistance
How does a higher blood pressure affect after load?
It increases the after load
How does an increase in after load affect the heart? (full explanation)
1) The pressure that ventricles have to exceed to force blood out is higher, so the end diastolic pressure is higher.
2) Means the ventricle has to stay in the isovolumetric contraction phase for longer to generate more pressure to exceed the end diastolic pressure.
3) The point at which the ventricular pressure falls below the aortic pressure is now higher, therefore less blood is ejected in each stroke.
How does an increase in after load affect the heart? (short answer)
Heart has to do more work to eject a smaller volume of blood, resulting in reduced cardiac output.
What factor determines the stroke volume?
The venous return to the heart
Define secondary hypertension
There is an identifiable cause of the decrease in cardiac output.
What is pheochromocytoma?
A tumour of chromaffin tissue which secretes adrenaline and noradrenaline, resulting in vasoconstriction therefore increased blood pressure.
How is pheochromocytoma treated?
Surgery or adrenoreceptor antagonists
How can a tumour of the anterior pituitary secrete that secretes excess adrenocorticotropic hormone cause secondary hypertension?
It stimulates the adrenal cortex to release more cortisol, resulting in the Cushing’s reflex so hypertension.
What is another hormone the adrenal cortex secretes other than cortisol that can increase blood pressure?
Aldosterone
How can balloon angioplasty reduce hypertension?
It widens the narrowing of the aorta to allow more blood flow.
Define primary hypertension
No identifiable cause. Can just start as increased tissue perfusion, but then it will affect cardiac output.
What is the main method of treating primary hypertension?
Lifestyle changes of exercise, reduced salt intake, reducing weight.
Outline the theory behind hypertension
1) The cerebral vascular resistance increases.
2) This decreases the cerebral perfusion, brain doesn’t not have enough oxygen.
3) This increases the sympathetic activity to increase blood pressure through vasoconstriction to increase the perfusion.
4) This increases the cerebral vascular resistance, which can then promote oxidative stress and inflammation, which causes the cycle to repeat again.
List other environmental factors other than deccreased cerebral perfusion that causes increased vascular resistance
1) Inulin resistance/diabetes
2) Obesity
3) Renal perfusion - or lack of