1 Respiratory System

 Understand what is meant by the terms “internal respiration” and “external respiration”  Know the four steps of external respiration  Understand Ventilation - the first step of external respiration  Know the basic anatomy of the pulmonary airways and the pleural space.  Know the mechanics and pressure changes of inspiration and expiration, and understand the concepts of transmural pressure and compliance  Understand alveolar surface tension and pulmonary surfactants. Objectives

 Respiration is the process by which oxygen is taken in and carbon dioxide is given out.  Respiration is classified into two types:  external respiration  internal respiration Does the respiratory system accomplish all the steps of external respiration?

 Air moves from the region of high pressure to region of low pressure.  Air moves in and out of the lungs because the alveolar pressure is alternate less than or greater than atmospheric pressure.  Changes in alveolar pressure occur as a result of changes in lung volume (Boyle’s law).

 During inspiration, thoracic cage enlarges and lungs expand so that air enters the lungs easily.  During expiration, the thoracic cage and lungs decrease in size and attain the preinspiratory position so that air leaves the lungs easily.  During normal quiet breathing, inspiration is the active process and expiration is the passive process

Accessory muscles of inspiration Muscles of active expiration Major muscles of inspiration Sternocleidomastoid Scalenus Sternum Ribs External intercostal muscles Diaphragm Internal intercostal muscles Abdominal muscles Major muscles of inspiration

 Transmural pressure (transpulmonary pressure) is the pressure difference between alveolar pressure and pleural pressure.(P transpulmonary = P alveoli - P pleural space ) A positive transmural pressure work to expand the container(P inside>p outside). A negative transmural pressure works to collapse the container (P inside<p outside).

pleural pressure

At rest 1- All respiratory muscles are relaxed. 2-This is the neutral or equilibrium point of the respiratory system. No air is flowing through the open glottis, because alveolar pressure equilibrated by the atmospheric pressure, which is considered to be zero reference pressure. 3- Intrapleural pressure is negative (subatmospheric) because the inward elastic recoil of the lungs is opposed by the outward-recoil of the chest wall.

During Inspiration 1-Inspiration is induced by the contraction of the diaphragm and external intercostal muscles that expand the chest wall. The net result is to make intrapleural pressure more negative. 2. The more negative causes lung transmural pressure to increase, which in turn causes expansion of the lungs. 3. The rise in volume causes pressure to decrease, resulting in a negative (subatmospheric) alveolar pressure. 4. Because alveolar pressure is now less that atmospheric, air rushes into the lungs.

During expiration 1-Relaxation of the muscles of inspiration returns intra-pleural pressure back to its original level, resulting in a decreased transmural pressure. 2- The drop in transmural pressure reduces alveolar volume, which increases alveolar pressure. 3-The elevated alveolar pressure causes air to flow out of the lungs. 4-The outflowing air equilibriates alveolar pressure with atmospheric pressure, airflow stops.

 Ventilation occurs as a result of pressure differences induced by changes in lung volume.  Physical properties that affect lung function:  Compliance.  Lung recoil force.

 Compliance : the change in lung volume (tidal volume) divided by the change in surrounding pressure.

 lung recoil  Components of Lung Recoil the collagen and elastin fibers of the lung (i.e lung elasticity) The surface tension forces in the fluid lining the alveoli. Surface tension forces are the greatest component of lung recoil (2/3 of the total force).  The relationship between the surface tension and the pressure inside a bubble is given by the law of LaPlace.

Very compliant lungs (easy to inflate) have low recoil. Stiff lungs (difficult to inflate) have a large recoil force.

 Spirometer consist of an air filled drum floating in water.  As the person breath air in and out of the drum through a tube connecting the mouth to the air chamber, the drum rises and falls in the water chamber. This rise and fall can be recorded as spirogram, which is calibrated to volume changes.

Tidal volume : amount of air that enters or leaves the lung in a single respiratory cycle. Functional residual capacity (FRC): amount of gas in the lungs at the end of a passive expiration; it is a marker for lung compliance??? lnspiratory capacity (IC): maximal volume of gas that can be inspired from FRC lnspiratory reserve volume (IRV): additional amount of air that can be inhaled after a normal inspiration Expiratory reserve volume (ERV): additional volume that can be expired after a passive expiration Residual volume (RV): amount of air in the lung after a maximal expiration Vital capacity (VC): maximal volume that can be expired after a maximal inspiration Total lung capacity (TLC): amount of air in the lung after a maximum inspiration

Residual lung volume cannot be measured directly by spirometry  Respirometer is filled with air containing a known quantity of helium.  Initially, the person expires normally. At the end of this expiration, the remaining volume in the lungs is equal to the functional residual capacity.  Then, the subject breathes from respirometer. Helium from respirometer enters the lungs and starts mixing with air in lungs.  After few minutes of breathing, concentration of helium in the respirometer becomes equal to concentration of helium in the lungs of subject.  After equilibration of helium between respirometer and lungs, concentration of helium in respirometer is determined.  Functional residual capacity is calculated by the formula:

 Restrictive Disease:  Makes it more difficult to get air in to the lungs.  They “restrict” inspiration.  Decreased VC; Decreased TLC, RV, FRC  Includes: ▪ Fibrosis ▪ Muscular diseases

 Obstructive Disease  Make it more difficult to get air out of the lungs.  Decrease VC; Increased TLC, RV, and FRC  Includes: ▪ Emphysema ▪ Chronic bronchitis ▪ Asthma

 TYPES OF LUNG FUNCTION TESTS:  Static Lung Function Tests: based on volume of air that flows into or out of lungs.  Dynamic Lung Function Tests: based on the rate at which air flows into or out of lungs. ▪ These tests include forced vital capacity(FVC), forced expiratory volume in 1 sec (FEV1)…etc ▪ Dynamic lung function tests are useful in determining the severity of obstructive and restrictive lung diseases.

Forced vital capacity (FVC) and forced expiratory volume in 1 sec (FEV1)

 Ventilation is the rate at which air enters or leaves the lungs. Ventilation in respiratory physiology is of two types: 1. Pulmonary ventilation : ▪ Pulmonary ventilation is defined as the volume of air moving in and out of respiratory tract in a given unit of time during quiet breathing. It is also called minute ventilation or respiratory minute volume (RMV). ▪ It is calculated by the formula: ▪ Pulmonary ventilation = Tidal volume × Respiratory rate = 500 mL × 12/minute = 6,000 mL/minute.

 Alveolar ventilation:  is the total volume of new air entering the alveoli and adjacent gas exchange areas each minute.  It is calculated by the formula:  Alveolar ventilation = (Tidal volume – Dead space) x Respiratory rate = (500 – 150) mL × 12/minute = 4,200 mL (4.2 L)/minute.

 DEAD SPACE  is defined as the part of the respiratory tract, where gaseous exchange does not take place.  TYPES OF DEAD SPACE 1. Anatomical dead space 2. Physiological dead space.  Volume of normal dead space is 150 mL.  Under normal conditions, physiological dead space is equal to anatomical dead space.  Physiological dead space increases during respiratory diseases, which affect the pulmonary blood flow or the alveoli.

150 Airway dead-space volume (150 ml) After inspiration, before expiration Alveolar air Even though 500 ml of air move in and out between the atmosphere and the respiratory system, only 350 ml are actually exchanged between the atmosphere and the alveoli because of the anatomic dead space

150 During expiration 500 ml expired to atmosphere ml fresh air from dead space (left from preceding inspiration) 350 ml “old” alveolar air 500 ml “old” alveolar air Expired 350 ml expired to Atmosphere 150 ml remain in dead space

150 During inspiration 500 ml fresh air enter from atmosphere ml fresh air reach alveoli 150 ml fresh air remain in dead space 500 ml enter alveoli 150 ml “old” air from dead space (left from preceding expiration) 350 ml fresh air from atmosphere

 Pulmonary Circulation.  Low-pressure, high-flow circulation  Receives 100% of right ventricle blood flow.  Pulmonary artery supplies venous blood from all parts of the body to the alveolar capillaries where oxygen is added and carbon dioxide is removed.  Pulmonary veins then return the blood to the left atrium to be pumped by the left ventricle though the systemic circulation.  Bronchial Circulation.  High-pressure, low-flow circulation  Receive 1-2% of left ventricle blood flow.  supplies systemic arterial blood to the trachea, the bronchial tree including the terminal bronchioles, and the supporting tissues of the lung.  Bronchial artery empties into the pulmonary veins and enters the left atrium, rather than passing back to the right atrium.

 „ PULMONARY BLOOD VESSELS  „ Pulmonary Artery: ▪ Pulmonary artery has a thin wall (1/3 of thickness of the systemic aortic wall). ▪ Pulmonary blood vessels are highly elastic and more distensible. ▪ Smooth muscle coat is not well developed in the pulmonary blood vessels. ▪ Pulmonary capillaries are larger than systemic capillaries. Pulmonary capillaries are also dense and have multiple anastomosis (Physiological shunt is present).  pulmonary veins are thin & short  Lymphatics ▪ rich lymphatic drainage to the right thoracic duct to prevent edema

 PULMONARY BLOOD PRESSURE  Pulmonary blood vessels are more distensible than systemic blood vessels. So the blood pressure is less in pulmonary blood vessels. Thus, the entire pulmonary vascular system is a low pressure bed.  Pulmonary Arterial Pressure  Systolic pressure : 25 mm Hg  Diastolic pressure : 8 mm Hg  Mean arterial pressure : 15 mm Hg.  Pulmonary Capillary Pressure  Pulmonary capillary pressure is about 7 mm Hg. This pressure is sufficient for exchange of gases between alveoli and blood.  The mean pressure in the left atrium and the major pulmonary veins averages about 2 mm Hg (varying from as low as 1 mm Hg to as high as 5 mm Hg).

 Blood volume of the lungs:  450 ml ( 9% of total blood volume).  70 ml are found in the capillaries, the reminder is divided equally between the pulmonary arteries and veins.  The lungs serves as blood reservoir:  The quantity of blood in the lungs varies as little as ½ normal up to twice normal.  if the person is bleeding or blowing air out hardly the volume can reach 250 ml.  if the person has left heart failure or mitral valve stenosis or miteral valve regurgitation the volume can reach 900 ml