The respiratory system

• •Cellular respiration – intracellular reaction•External respiration – movement of gases between the environment and the body’s cells
• •The respiratory tract is divided into upper and lower regions•The lower tract is also called the thoracic portion – because it is enclosed in the thorax•Conducting system, or airways consist of:

        Upper respiratory tract (Mouth basal      cavity, pharynx, larynx)

        Lower respiratory tract (Trachea, 2 primary bronchi, their branches, lungs)
• •Alveoli (singular alveolus) - site of gas exchange•Thoracic cage: bones and muscle of thorax and abdomen•Pleural fluid – between pleural membranes•Lowers friction between membranes•Holds lungs tight against the thoracic wall
• Pleurisy is inflammation of the pleura: makes breathing laboured. Usually caused by another condition, such as an infection.

  Pleural effusion is when pleural fluid accumulates e.g. in TB, also when body fluid volumes are disturbed.
• •Type I alveolar cells – gas exchange•Type II alveolar cells – produce surfactant•Connective tissue – elastin and collagen•Close association with capillaries•Failure of CFTR in cystic fibrosis leads to thick, sticky mucus
• 1. When we breathe we are performing inspiration (inhalation) and expiration (exhalation) :Quiet (or passive) breathing: normal breathing requires very little muscle contraction. The diaphragm is the dominant muscle involved in quiet respiration.2. Forced (or active) breathing: deeper breathing due to increased physical activity. Also deliberate breath control (e.g. singing or inflating a balloon). Several muscles are involved in forced inspiration and expiration.
• •Dalton’s law

    Total pressure equals sum of all partial pressures (Pgas)

  •Boyle’s law describes pressure-volume relationships•
• The Ideal Gas Equation: PV=nRT

  Where P is pressure, V is volume, n is the moles of gas, T is absolute temperature, and R is the universal gas constant, 8.3145 j/mol × K

  In the human body, assume that number of moles and temperature are constant. Leaves the following equation:

  V=1/P

  e.g. if the volume of gas increases, the pressure decreases, and vice versa

  Boyle’s law: P1V1=P2V2

   Also expresses this inverse relationship between pressure and volume.
• Dalton’s law

  The total pressure of a mixture of gases is the sum of the pressures of the individual gases

  •The pressure of an individual gas in a mixture is known as the partial pressure of the gas (Pgas)•The pressure exerted by an individual gas is determined only by its relative abundance in the mixture and is independent of the molecular size or mass of the gas.
• Inspiration occurs when alveolar pressure decreases

  Time 0

  When pressures are equal there is no air flow

  Time 0-2 sec: inspiration

  Expiration occurs when alveolar pressure increases

  Time 2-4 sec: expiration

  Time 4 sec

  Passive vs. active expiration
• Anatomical aspects

  •• The lungs (bronchi, bronchioles, alveoli)• Chest cavity (ribs/intercostal muscles) and the diaphragm muscle.•Pleural membranes (pleural fluids and pleural pressure).•

  Functional aspects

  •• Passive (shallow) breathing - lung elasticity (recoil), pressure gradients• Active (deep) breathing – different muscles involved larger tidal volumes up to vital capacity (maximum).
• •Total pulmonary ventilation is greater than alveolar ventilation because of dead space.•Alveolar ventilation is a better indication of how much fresh air reaches the alveoli. Fresh air remaining in the dead space does not get to the alveoli.
• Tidal volume  (TV) - the amount of air moved in or out of the lungs at rest (i.e. quiet/passive/shallow breathing) = ~500ml/0.5L

  Expiratory reserve volume (ERV) - the extra volume of air that can be forcibly blown out of the lungs, additional to that exhaled in the TV (tidal volume).

  Inspiratory reserve volume (IRV) - the extra volume of air that can be forcibly sucked into the lungs, additional to that normally inhaled in TV (tidal volume).

  Vital Capacity (VC) - the total volume of air that can be breathed in or out of the lungs = TV + ERV + IRV.
• •Two important measures used to monitor lung function are :•Forced vital capacity (FVC). The total amount of air that you blow out in one DEEP breath.

        and

  •Forced expiratory volume in 1 sec (FEV1) is the amount of air you can blow out within one second.•FVC varies with age, weight, sex etc., but most significantly can be reduced in disease.
• The body needs oxygen and removes carbon dioxide

  •Hypoxia – too little oxygen•Hypercapnia – increased concentrations of carbon dioxide

  To avoid hypoxia and hypercapnia, the body responds to three regulated variables

  •Oxygen•Carbon dioxide•pH
• •Breathing is bulk flow of air into and out of lungs•Individual gases diffuse along partial pressure gradients until equilibrium•Total pressure of mixed gas = sum of partial pressures of individual gases•
• •Gas exchange between blood and tissues

  
• • Gas exchange between alveoli and blood

  
• Unlike most solid soluble substances (such as salt), gases such as oxygen are MORE soluble in cold water than hot water
• At equilibrium, PO2 in air and water is equal. Low O2 solubility means concentrations are not equal
• When CO2 is at equilibrium, at the same partial pressure, more CO2 dissolves
• •Occurs by diffusion, over short distances, and with net movement down the concentration gradient  (note also, diffusion is as dissolved gas)
• •O2 entering alveoli ≈ O2 entering the blood•Fresh air into lungs ≈ 10% total lung volume at the end of inspiration•Ventilation and alveolar blood flow are matched:•Ensures efficiency of gas exchange between alveoli and capillaries
• •Gas entering the capillaries first dissolves in the plasma•Dissolved gas accounts for <2% of O2 in blood•Haemoglobin binds to oxygen

                 Hb + O2         HbO2 (oxyhaemoglobin)

  •4 hemes, so 4 O2 binding-sites•Haemoglobin transports most oxygen to the tissues
• •The four polypeptides in Hb allow it to display cooperative binding of oxygen, so the curve is ‘S-shaped’ (sigmoidal).•The shape of this binding curve illustrates the ideally adapted properties of human Hb as an oxygen transporter under physiological conditions.•Compared with other ways for this protein to work the cooperativity allows release of more oxygen at tissues and good binding in the lungs
• Diphosphoglycerate (also called BPG = bis phosphoglycerate)  is formed during glycolysis

  Its amount increases in blood when at high altitudes (low oxygen)
• Which lung volume cannot be directly measured? residual volume
• If the volume of a gas mixture doubles, the pressure: decreases by 50%.
• If plasma pH increases from 7.40 to 7.48, hemoglobin’s affinity for oxygen will increase so less oxygen will be released to the tissue.
• The oxygen-haemoglobin dissociation curve shifts to the right in response to increased H+ concentration.
• The upper respiratory tract includes all EXCEPT which of the following? Lungs
• The lungs are surrounded by pleural membranes.
• Boyle's law states that gas volume is inversely proportional to pressure.
• Which characteristic makes haemoglobin's structure such a good match for its function as an oxygen carrier? Each haemoglobin molecule can bind four oxygen molecules
• Most of the carbon dioxide in the blood is transported as: bicarbonate ions