RESPIRATORY SYSTEM

Dr. A. R. JOSHIProfessor of Physiology

RESPIRATORY SYSTEM

• Respiration means exchange of gases

• Types :

– External respiration at lungs

– Internal respiration at tissues

BASIC FUNCTIONS OF LUNGS

• Ventilation of air

– Inspiration

– Expiration

• Diffusion of gases

• Perfusion of lungs by blood through pulmonary circulation

NORMAL BREATHING PATTERN

• Respiratory rate : 14 to 18 /minute

• Tidal volume: 350 to 500ml

• RMV : 6 to 8 litres/minute

• Inspiration (active) : 2.5 to 3 sec

• Expiration (passive): 2 to 2.5 sec

MUSCLES OF RESPIRATION

• Inspiratory Muscles

• Expiratory Muscles

• Accessary Muscles

INSPIRATORY MUSCLES

• Diaphragm:– Chief muscle– Big surface area– Changes vertical diameter of chest– Innervation by phrenic nerves– No fatigue– Works like involuntary muscle

INSPIRATORY MUSCLES

• External Intercostal Muscles:

• Bucket handle movement of ribs

(Lower part of chest)• Pump handle movement of sternum

(Upper part of chest)

OTHER MUSCLES

• Muscles of expiration• Work only while coughing or sneezing

• Accessary muscles of respiration• Work during exercise or disease

PREVENTION OF LUNG COLLAPSE

•Role of negative intra-pleural pressure

•Role of surfactant

REGULATION OF RESPIRATION

• Nervous regulation – Role of ponto-medullary respiratory centers:• Inspiratory Center (DRGN)• Expiratory Center (VRGN)• Apneustic Center• Pneumotaxic Center

• Chemical- Role of Carbon dioxide

Hydrogen ions

Lack of Oxygen

REGULATION OF RESPIRATION

• Nervous regulation– Role of reflexes:• Coughing reflex• Sneezing reflex• Hiccough • Deglutition reflex

Chemical Regulation

Role of carbon dioxide: powerful action

1.Central action (chemo sensitive area)

2.Peripheral action (carotid and aortic bodies)

Role of hydrogen ions

Role of lack of oxygen

DIFFUSION ACROSS RESPIRATORY MEMBRANE

• Structure• Factors affecting diffusion : ● thickness of membrane ● surface area of membrane ● pressure gradient of gas• Diseases : Pulmonary fibrosis & oedema

TRANSPORT OF GASES: OXYGEN

• Arterial O2 19 ml / 100ml of blood

• Venous O2 14 ml / 100 ml of blood

• Oxygen carried by Hb – 98%

dissolved form – 2%

• O2- Hb dissociation curve and its significance

OXYGEN CONCENTRATION IN VARIOUS TISSUES

• Alveolar PO2 : 104 mm of Hg

• Arterial PO2 : 95 mm of Hg

• Venous PO2 : 40 mm of Hg

O2dissociation curve…

O2 Dissociation Curve

TRANSPORT OF GASES : CARBON DIOXIDE

• Arterial CO2 level : 48 ml/100ml blood • Venous CO2 level : 52 ml/100ml blood• Transported as: ● bicarbonates : 70% ● carbamino compounds : 23% ● dissolved state : 7%

CARBON DIOXIDE CONCENTRATION IN VARIOUS TISSUES

• Alveolar PCO2 : 40 mm of Hg

• Arterial PCO2 : 40 mm of Hg

• Venous PCO2 : 45 mm of Hg

HYPOXIA (Lack of Oxygen at tissue level)

1. Hypoxic Hypoxia

• High Altitude

• Ventilatory defects like Asthma

• Diffusion defects like Pulmonary edema

• AV shunts like Fallots Tetrology

(PO2 of arterial blood is low)

HYPOXIA ( CONT..)

2. Anaemic Hypoxia e.g. Anaemia Carbon Monoxide poisoning3. Stagnant Hypoxia e.g. Congestive heart failure4. Histotoxic Hypoxia e.g. Cyanide poisoning (Note : Oxygen therapy is useful only in

cases of hypoxic hypoxia, when PO2 of Arterial Blood is low )

OXYGEN THERAPY

• Useful in hypoxic hypoxia (high altitude, hypoventilation, impaired diffusion )

• Limited value in other types of hypoxia

• Oxygen with small quantity of Carbon dioxide to maintain respiratory drive

HYPERBARIC OXYGEN THERAPY

• Increases dissolved Oxygen – at 2 atm.pressure - 4ml additional/dl

at 3 atm.pressure - 6ml additional/dl.• Useful in CO poisoning, dysbarism,

acute mountain sickness, locally in delayed wound healing & gas gangrene.

HAZARDS – OXYGEN THERAPY

• Irritation of airways

• Bronchopneumonia

• Retinopathy ( in premature babies )

• Derangement of cerebral activity

• Convulsions

ASPHYXIA(Lack of oxygen and excess of carbon dioxide)

• Causes:Foreign body obstruction in tracheaStrangulation Paralysis of respiratory muscles

Drowning Stages: Stage of Hyperpnea Stage of Central excitation Stage of Central failureTreatment: Tracheostomy & oxygen therapy

For assistance in Clinical Physiology

• Dr. A.R. Joshi

Professor of Physiology

(mobile : 9423523322)

email: aniruddharj@hotmail.com