CGIER 6 Flashcards
Density explain
Density refers to the amount of mass contained in a specific volume. It’s a measure of how much “stuff” (mass) is packed into a given space
Define ‘density’ and units
Density is defined as mass per unit volume, unit kg/m3
Density formula
(D= M/V )
Define pressure
Pressure is defined as force per unit area, unit is the pascal (Pa)
Pressure explain
Pressure refers to the force applied a surface of an object per unit area. how much force is distributed over a specific area.
Pressure formula
(Pressure = Force / Area)
Define Pascal’s Principle and discuss its role in a range of clinical situations.
Any change in pressure applied to a completely enclosed fluid is transmitted undiminished to all parts of the fluid and the enclosing walls.
Pascal’s Principles role in a range of clinical situations.
1) Onset of Glaucoma
2) Protection of the unborn baby in the womb
3) Screening for brain tumours
4) Decubitus Ulcers (bedsores)
Onset of Glaucoma explanation
In a normal eye, excess fluid can be released through the trabecular meshwork.
In glaucoma, the fluid cannot escape and causes a significant increase in the intra-ocular pressure (up to ~85 mm Hg).
This can result in permanent damage to the optic nerve and, if untreated, blindness.
Lasers can be used to create a number of exit channels for the excess fluid and therefore reduce pressure.
how much Aqueous humor is produced in the eye daily ?
Approximately 5 cm3 of aqueous humor is produced within the eye every day,
Protection of the unborn baby in the womb explanation
The unborn baby is surrounded by amniotic fluid within the womb.
This is excellent for diffusing or distributing the effect of any sudden force applied to the abdomen of a pregnant woman
Screening for brain tumours explanation
Cerebrospinal fluid (CSF) is an enclosed fluid (~150 cm3) which surrounds the brain and spinal cord.
A brain tumour will cause a reduction in the volume in which the CSF is contained, resulting in an increase in the fluid pressure of the CSF.
The pressure of the CSF can be determined by inserting a spinal tap (connected to a water manometer) between the 3rd and 4th lumbar vertebrae.
If the pressure is greater than normally accepted values, this may be indicative of a brain tu
Decubitus Ulcers (bedsores) explanations
These are pressure ulcers caused by patients spending prolonged periods in the same position.
They tend to occur around bony regions such as elbows, heels, hips, shoulder blades (i.e. those regions in ‘contact’ with mattress etc. where pressure is applied), and result from restricted blood flow in these regions.
Describe how pressure varies with volume in the bladder (Laplace law)
The larger the vessel radius is, the larger the wall tension required to withstand a given internal fluid pressure Laplace’s Law
Laplace law formula in spherical formula
T = Pr/ 2
Laplace law formula in cylindrical formula
T = Pr
Passive filling
Physical Dynamics of Bladder
Passive filling
Filling the bladder with a fluid will exert a pressure on the wall of the bladder and generate a stress within the wall.
What is Muscular contraction
Contraction of the muscle will generate a pressure on the fluid within the lumen.
The magnitude of the pressure change depends on the dimensions of the lumen, P=T/r
Application of Laplace’s law on Circularly System
Heart wall in the left ventricle is thicker and the radius is smaller than the right ventricle. The pressure in the left ventricle is larger than the right ventricle by several times.
Aneurysms: ballooning of the vessel increases its radius and increases the tension on already weakened wall.
Enlarged Heart (congestive heart failure)
As radius increases, must exert larger force in order to create sufficient blood pressure resulting in damage.
Explain how pressure varies with fluid depth (hydrostatic pressure = rgh)
A tank of height h and cross-sectional area A is filled with water of density
The volume of the tank V= Ah
mass= ρV= ρAh
Weight W= mg= ρgAh
Illustrate a number of clinical uses of hydrostatic pressure
Define ‘atmospheric pressure’
Caused by a blanket of air around the earth, and the pressure results from the ‘weight’ of the air.
Atmospheric pressure is given as H.
Explain the use of a manometer to measure fluid pressure.
manometer is a U-shaped tube filled with Hg and is used to measure atmospheric pressure
Pabsolute= Patm+ rgh
Pabsolute :is the total pressure
Patm: is atmospheric pressure.
rgh: is the gauge pressure
The excess pressure above Patm is called Gauge Pressure.
r: is the density,
h: is the height of mercury (Hg)
g: is acceleration due to gravity
