Pressure and Light Biology Notes PDF

Pressure and Light The purpose of this session is to help you understand what pressure is, so you can work from assessing your patients needs to planning the correct care. So, what is pressure?  A trough of high pressure, out in the Tasman moving towards NZ, will bring fine wea...

Pressure and Light The purpose of this session is to help you understand what pressure is, so you can work from assessing your patients needs to planning the correct care. So, what is pressure?  A trough of high pressure, out in the Tasman moving towards NZ, will bring fine weather.  Pressure Pressure is force exerted per unit area Measured in pascals, psi, mm Hg, Newtons per sq. m. The smaller the surface area, the higher the pressure – high heels vs. flat heels – pressure sores How do pressure sores occur?  Blood Pressure Blood pressure is the force of blood acting on an area of the blood vessels walls Normal blood pressure is approximately 120mmHg (systolic) when the heart is contracting) and 80 mmHg (diastolic) when the heart is relaxed Blood pressure is created by heart contracting and pushing blood out into the blood vessels Blood Pressure Cont. Veins contain valves to ensure blood flows in forward direction Muscle pump forces valves open to direct venous return  Colloid Osmotic Pressure - Review Pressure that opposes hydrostatic pressure produced by non-diffusible solutes e.g. plasma proteins Colloids ‘pull’ water toward them, thus instigating osmosis If capillary colloid osmotic pressure is low, water will be lost and blood volume will drop Thus, blood pressure will also drop & vice versa Therefore, capillary colloid osmotic  Laws Relating to Pressure Poiseuille’s law refers to pressure in flowing liquids – The flow rate of a liquid will be determined by the pressure difference, and the friction (resistance) between the fluid and the walls of the tube e.g. blood flow in blood vessels The higher the resistance, the lower the flow rate will be E.g. cholesterol deposit on arteries narrows artery and increases resistance to blood flow, thus a lower volume of blood can flow at any given time Consider Blood vessels – veins, venules, the vena cava, arteries, arterioles and capillaries. In which blood vessel would the blood be travelling the fastest? In which blood vessels would the blood be moving the slowest? Explain. How and Why?  The barium enema is a valuable diagnostic tool that helps detect abnormalities in the large intestine (colon). The barium enema, along with colonoscopy, remain standards in the diagnosis of colon cancer, ulcerative colitis, and other diseases of the colon. Consider a patient getting an enema. Raising the height of the container to increase the flow rate, will increase the pressure. This increase in pressure may cause some discomfort for your patient, or even cramping. In some circumstances it might damage the tissue! What would be a better way to increase the flow rate, without increasing the pressure? Atmospheric Pressure The pressure we experience on the earth’s surface Relates to the amount of atmospheric air above us At sea level, atmospheric pressure is 760 mmHg Ventilation relies on pressure differences between atmospheric pressure & intrapulmonary pressure Laws Relating to Pressure Boyle’s law relates to the relationship between pressure and volume of a gas The pressure exerted by a gas is inversely related to its volume i.e. the higher the volume, the lower the pressure E.g. pressure changes during ventilation Inspiration: lungs expand thus lung volume increases - pressure decreases Expiration: lungs deflate thus lung volume decreases - pressure increases Pg. 848 Laws Relating to Pressure Dalton’s law relates to partial pressure – The partial pressure of a gas relates to how much each individual gas contributes to a mixture of gases – i.e. atmospheric air (760 mmHg) is made up of: Nitrogen (597 mmHg) Oxygen (159 mmHg) Water (3.7 mmHg) Carbon Dioxide (0.3 mmHg) – E.g. the partial pressure of Nitrogen is 597 mmHg, thus it contributes 597 mmHg of pressure to the overall atmospheric pressure  Partial Pressure & Gas Exchange Partial pressure drives gas exchange Air moves from an area of high pressure to an area of low pressure When the partial pressure of O2 (PO2)is higher in the alveoli than the capillary (after inspiration), O2 will diffuse down the pressure gradient into the capillaries Gas Exchange This will increase the PO2 in blood compared to cells, thus O2 will diffuse into cells as blood passes Because cells have produced CO2, the PCO2 is higher in cells than blood, thus CO2 diffuses When you patient is on a ventilator you need to be very careful. This is especially important if the ventilator doesn’t go through the mouth or nose. As air enters the nose it is warned and humidified. Thus the partial pressure of wet and dry air are different, as the water vapour will exert pressure. Laws Relating to Pressure Pascal’s principle relates to pressure in liquids in an enclosed container – Any change in pressure in a liquid in an enclosed container is transmitted equally and undiminished to every part of the liquid e.g. water bed brain tumour Glaucoma Foetal deformity Negative and Positive Pressure Negative pressure is a term that refers to any pressure that is less than atmospheric pressure (e.g. suction) Positive pressure is a term that refers to any pressure that is greater than atmospheric pressure Applications of Pressure pressure sores central venous pressure (CVP) blood pressure, blood flow, venous return syringes, intra-venous (IV) infusion breathing and gas exchange, pneumothorax chest drains, haemovacs, positive pressure ventilators