Respiratory System

Respiratory system The primary function of respiratory system is to obtain O2 for use by the body’s cell and to eliminate CO2 the cells produced

Respiratory system

Respiratory system Non-Respiratory Functions of Respiratory system: Route for heat and water loss from the body Enhancement of venous return to the heart Participates in acid base balance (through excreting CO2 which reduce acidity) The nose acts as organ of smell A major role in the process of vocalization

Major Part of Respiratory System

Respiratory system Alveoli : place where gas exchange occurs 300 million alveoli in both lungs Total surface area ~ 75m² Are surrounded by dense network of capillaries contain two types of cells a) alveolar cell type I b)alveolar cell type II secrete surfactant

Respiratory System Functionally the respiratory system consist of 2 portions: Conducting portion:[ nose, Pharynx, Larynx, Trachea, Bronchi, bronchioles and terminal bronchioles] filter, warm and moisten air and conduct it into the lungs Respiratory portion: where gas exchange occurs [ alveoli]  {functional unit of respiratory system}

Respiratory system Pleural Cavity

Mechanics of Respiration Respiratory movements (Inspiration & Expiration) are achieved by making pressure gradient between atmosphere and alveolar sacs Air always moves from a high pressure area to a low pressure area During inspiration air moves from atmosphere into the lungs During expiration air moves of the lungs to atmosphere

Mechanics of Respiration Three important pressure are considered in respiration :

Mechanics of Respiration Intra-alveolar pressure can be changed by altering the volume of the lungs

Mechanics of Respiration

Mechanics of Respiration During quite inspiration: Inspiratory muscle contract →increasing thoracic volume →decreasing intra-pleural pressure →decreasing intra-alveolar pressure (become less than atmospheric pressure (-1 mmHg)→ forcing air to move into the lungs (inspiration) Quite inspiration is an active process (need muscle contraction

Mechanics of Respiration

Mechanics of Respiration During quite expiration: Inspiratory muscle relax→ decreasing thoracic volume → increasing intra-pleural pressure → increasing intra-alveolar pressure (become more than atmospheric pressure (+1 mmHg)→ forcing air to move out the lungs (expiration) Quite expiration is passive process ( doesn't need muscle contraction) Forceful expiration is an active process

Respiratory Muscles Respiratory muscles two sets of muscles: Inspiratory muscles Expiratory muscles

Respiratory Muscles Inspiratory muscles: The diaphragm The external intercostals muscles

Respiratory Muscles The diaphragm: Main inspiratory muscle Seperates thoracic cavity from abdominal cavity Skeletal muscle, supplied by phrenic nerve During inspiration: It contracts and descends downward increasing the vertical dimension of the thorax, also it increases the anterposterior diameter of the thorax During expiration, it relaxes and moves upward decreasing thoracic volume

Respiratory Muscles The External intercostals Muscles: composed of fibers that run downward & forward between adjacent ribs Their contraction elevates the sternum increasing the anteroposterior and lateral dimensions of the thorax (the thoracic volume is increased) This enlarges the thoracic cavity in two dimensions: the lateral & the antero-posterior dimensions

Respiratory Muscles Accessory inspiratory muscles: Sternocleidomastoid scalenus Deeper inspiration can be accomplished by: Forceful contraction of both diaphragm & external intercostals Assistance by the accessory inspiratory muscles, which lie in the neck Contraction of accessory muscles raises the sternum & elevates the first two ribs, thus enlarging the upper portion of the thoracic cavity This extra enlargement will be followed by a greater expansion of the lungs, & a further dropping in intra-alveolar pressure accordingly

Respiratory Muscles Expiratory muscles: Abdominal muscles Internal intercostal muscles They contract during active forced expiration They don`t contract during quite expiration

Elastic behavior of the lung Elastic recoil of the lung refer to the ability of the lung to return to its pre-inspiratory volume at the end of inspiration Compliance of the lung refer to how much effort is required to stretch or distend the lung

Elastic behavior of the lung Lung elasticity (elastic behavior) depends on two important factors: Elastic fibers of lung tissues Surface tension of the fluid lining the alveoli ( is a force tends to reduce the size of alveoli and to resist the expansion)

Surfactant Is a phospholipoprotien complex Is produced by alveolar cell type II Lowers the alveolar surface tension Increases the lung compliance (facilitates lung expansion) Reduce the work needed to inflate the lung

Spirometry Measurement of the pattern of air movement into and out of the lungs during controlled ventilatory maneuvers.

Lung Volumes 4 Volumes 4 Capacities Sum of 2 or more lung volumes IRV IC VC TLC TV ERV FRC RV RV

Spirometry Measurement of the pattern of air movement into and out of the lungs during controlled ventilatory maneuvers.

Alveolar ventilation= (TV- dead space volume) X respiratory rate Pulmonary ventilation: is the amount of air which breathed in or out in one minute Pulmonary ventilation (minute ventilation)= tidal volume X respiratory rate = 500 ml X 12 = 6000 ml/minute Alveolar ventilation: is the amount of fresh air reached the alveoli in one minute Alveolar ventilation= (TV- dead space volume) X respiratory rate (500-150) x12 =4200 ml/min

Partial pressure of gases in atmospheric air Composition of atmospheric air: N2→78% O2 →21% CO2 →0.04% Other gases → 1% All of these gases participate to produce 760mmHg (atmospheric pressure) Each gas exerted pressure proportional to its % this is called partial pressure (p) N2 → pN2=78/100X760=600 mmHg O2 → pO2=21/100X760=160 mmHg CO2 → pCO2=.04/100X760=.3 mmHg

Partial pressure of O2 and CO2 in alveolar air PO2 =100 mmHg PCO2 =40mmHg Partial pressure of O2 and CO2 in pulmonary capillary

O2 and CO2 exchange across pulmonary and systemic capillaries caused by partial pressure gradients