MCQ محاضره فيزياء

• Lungs

  Supplier of O2 and disposer of CO2
• Functions of the lungs

  • Exchanging of O2 and CO2
  • Keeping the PH (acidity) of the blood constant
  • Heat exchange
  • Keeping the fluid of the body balance by warming and moisturizing the air we breathe
  • Controlled the flow of air for talking, coughing, sneezing, sighing, laughing, and sniffing
  • Voice production
• Breathing


  We breathe about 6 liters of air per minute
• Men breathe about 12 times per minute at rest, Women breathe about 20 times per minute, Infants breathe about 60 times per minute
• The air we inspire is about 80% N2 and 20% O2. Expired air is about 80% N2, 16% O2 and 4% CO2
• We breathe about 10 Kg of air each day. Of this the lungs absorbs 400 liters of O2 (0.5 Kg) and release a slightly smaller amount of CO2
• Each time we breathe, about 10^22 molecules of air enter our lungs. Each liters of air contain about 6 x 10^23 molecules (Avogadro's number)
• Air ways


  1. Air enters through the nose

  2. Warmed, filtered and moisturized

  3. Passes through trachea

  4. Trachea divides into two bronchi

  5. Bronchi divide and re-divide about 15 times into terminal bronchioles

  6. Terminal bronchioles supply air to millions of alveoli

  
• Alveoli


  • Small interconnected bubbles about 0.2 mm in diameter with walls only 0.4 μm thick
  • Expand and contract during breathing
  • Site of O2 and CO2 exchange
• Diffusion


  Transfer of O2 and CO2 into and out of the blood is controlled by the physical law of diffusion
• Molecules in a gas at room temperature move at about the speed of sound and collide about 10^10 times each second with neighboring molecules
• Mean free path (λ)

  • The average distance between collisions
  • In air λ = 10^-7 m, in tissue λ = 10^-11 m
• Breathing process


  1. Moving air in and out of lungs (ventilation)

  2. Oxygen-carbon dioxide exchange (diffusion)

  3. Pumping blood through lungs (perfusion)
• Alveoli


  • Pick up incoming oxygen and release outgoing carbon dioxide
  • Blood in capillaries in alveoli walls takes oxygen from alveoli and gives off carbon dioxide

  
• Breathing mechanics


  • Diaphragm and other muscles create pressure changes to push air in and out
  • Breathing in - muscles create pressure less than atmospheric to suck air in
  • Breathing out - lungs recoil and return to normal size
• Emphysema


  • Air sacs (alveoli) are damaged, inner walls weaken and rupture
  • Reduces surface area of lungs and oxygen reaching bloodstream

  
• Emphysema effects


  • Lungs become flabby and expand
  • Tissues do not pull hard on airways, allowing airways to collapse easily during expiration

  
• Asthma


  • Swelling (inflammation) of breathing tubes, increasing airway resistance

  
• Fibrosis


  • Membranes between alveoli thicken
  • Compliance of lungs decreases
  • Diffusion of O2 into capillaries decreases

  
• Cardiovascular system


  Delivers fuel, oxygen and removes waste products for body's cells
• Major components of cardiovascular system

  • Blood
  • Blood vessels
  • Heart

  
• Heart


  • Double pump that circulates blood through pulmonary and systemic circulations
  • Has valves to ensure one-way flow of blood
• Blood volume is not uniformly divided between pulmonary and systemic circulations

  
• Blood


  • Consists of red blood cells, plasma, white blood cells, and platelets
  • Has different flow properties than water due to components
• Fluid movement across capillary wall

  Driven by hydrostatic pressure forcing fluid out and osmotic pressure bringing fluid in
• Work done by heart

  • Pressure x Volume pumped
  • Left ventricle generates much higher pressure than right ventricle due to thicker muscle and circular shape
• Heart muscle action


  Contraction (systole) takes less than 1/3 of cardiac cycle, rest is relaxation (diastole)
• Transmural pressure


  • Pressure difference across blood vessel wall
  • Capillaries have very thin walls that can withstand low pressure due to Laplace's law
• Bernoulli's principle


  • Rapid fluid flow causes pressure reduction at edge of flow
  • Kinetic energy increases at expense of pressure (potential energy)
• The tension in a capillary wall is only about 24 dynes/cm, while a single layer of toilet tissue can withstand a tension of about 50,000 dynes/cm, which is about 3000 times greater than that the capillary has to withstand
• Bernoulli's principle


  Whenever there is a rapid flow of a fluid such as water, the pressure is reduced at the edge of the rapidly moving fluid
• Bernoulli's principle


  It is based on the law of conservation of energy, where pressure in a fluid is a form of potential energy (PE) and kinetic energy (KE) is due to the motion
• Bernoulli's principle applied to a frictionless tube

  1. Velocity increases in the narrow section, reducing potential energy (PE) of the pressure

  2. Velocity reduces on the far side of the restriction, converting kinetic energy (KE) back into potential energy (PE) and increasing the pressure
• Blood velocity


  Inversely related to the total cross-sectional area of the vessels carrying the blood, calculated as flow rate divided by cross-sectional area

  
• Average velocity in the aorta is about 30 cm/sec, while in a capillary it is only about 1 mm/sec, allowing time for diffusion of gases
• Viscosity (η)


  A characteristic of liquids, the viscosity of water is about 10-3 Pa s at 20°C, while the viscosity of blood is typically 3x10-3 to 4x10-3 Pa s
• Poiseuille's law


  The flow through a tube depends on the pressure difference, length of the tube, radius of the tube, and viscosity of the fluid
• Heart sounds are caused by vibrations originating in the heart and major vessels, often due to turbulent flow at the opening and closing of heart valves
• Work done by the heart

  Roughly the tension of the heart muscle and how long it acts, anything that increases muscle tension or contraction time will increase the work load
• Heart diseases


  Often have a physical component, such as increased work load or reduced ability to work at a normal rate