1 ) A gas exchanging organ: Lungs. 2) A pump that ventilates the lungs which is the thoracic wall, that contains respiratory muscles which increase or decrease the size of thoracic cavity, N.B.: Centers that control respiratory muscles are present in the brain

I)Upper respiratory passages -Include: nose, nasal cavity, sinuses and pharynx. -They warm and humidify air :II)Lower respiratory passages A)Conductive portion: -Include: larynx, trachea, bronchi, bronchioles. -Conduct air to respiratory surfaces B)Respiratory portion: -Include respiratory lobules -Undergo gas exchange between air and blood

I)Upper respiratory passages: 1- Nose: Consists of : 1-External nares. 2-Vestibule: space in flexible part lined with hairs to filter particles. 3-Leads to nasal cavity.

Nose and nasal cavity

I)Upper respiratory passages: 2- Nasal cavity: -Is divided into right and left by nasal septum. -superior portion contains olfactory membrane for olfaction. -Nasal conchae (superior, middle and inferior) project into nasal cavity on both sides to swirl air → A-Elimination of foreign particles B-Potentiates smell sensation. C-Warming and humidifying air. -Hard and soft palate form the floor

I)Upper respiratory passages: 3-Pharynx: -Is a chamber between internal nares and larynx and esophagus. -Consists of 3 parts: A-Nasopharynx: behind the nasal cavity B-Oropharynx: behind oral cavity C-Laryngopharynx: is the lower part of pharynx

1-Larynx -The larynx is an enlargement in the airway between the pharynx and trachea. -Consists of :cartilage,vocal cords and glottis. -Functions: i-Provides continuous airway. ii-Acts as a switch to root food and air properly iii-Voice production: air passing through glottis vibrates vocal cords producing sounds.

Opening and closing of the vocal folds occurs during breathing and spee ch

2-The trachea: - Is a flexible cylindrical tube - Lies anterior to esophagus -Contains C-shaped rings of cartilage to be opened. -Splits into right & left primary bronchi

3-Primary bronchi: -Right and left. -Inside the lungs they branch get smaller in diameter about 23 times creating the bronchial tree. 4-Terminal bronchioles: -The last portion of conducting zone. -Contains no cartilage. -Each terminal bronchiole delivers air to respiratory bronchioles

The trachea: Right bronchus left bronch us

Respiratory lobule: -Each respiratory bronchiole and its generations is called the respiratory lobule. -Each respiratory bronchiole → alveolar ducts → alveolar sacs → alveoli. -Is the functional unit of the lung. -It undergoes gas exchange between air in respiratory passages and blood.

Respiratory lobule

 Lies inside the thoracic cavity.  The right and left lungs are soft, spongy, cone-shaped organs in the thoracic cavity.  The right lung has three lobes and the left lung two lobes

The Lungs right lung has three lobes the left lung has two lobes

1) Gas Exchange 2) Regulation of the pH of the blood 3) Body temperature regulation 4) Voice production (Vocalization) 5) Smell and Taste

6) Secretion of: 1 - Surfactant that act locally in the lung to keep it inflated 2- The fibrinolytic agents of the fibrinolytic system that lyse the minute clots in the pulmonary blood, 3- Angiotensm converting enzyme (ACE) that activates activates angiotensin I to angiotensin II. 7) Defensive Functions :Removal of foreign particles is achieved by : 1- Hairs in the nose 2-Sneezing reflex. 3- Cough Reflex 4-Secretion of immunoglobulins.

Gas Exchange in respiratory system

1) External Respiration: Which consists of: a- Pulmonary Ventilation: means the exchange of air between the lungs and atmosphere. b- Pulmonary Perfusion: means the flow of blood through the pulmonary capillaries. c- The Pulmonary Respiration: means exchange of gases between alveolar air and blood 2) Transport of oxygen and carbon dioxide by the blood. 3) The internal respiration: means exchange of gases between tissues and blood

 Means exchange of air between lungs and atmosphere.  It is achieved by respiratory movements, which occurs in cycles.  Each respiratory cycle is formed of inspiration and expiration.  Normal adult person breathes times/min.

Respiratory movements

 Impulses from inspiratory center in the brain stem→ contraction of inspiratory muscles: A- Contraction of the diaphragm → increased vertical diameter of thoracic cavity. B- Contraction of external intercostal muscles → elevation and eversion of the ribs → increased horizontal diameter of thoracic cavity.  A&B → increased thoracic cavity in all dimensions → expantion of the lungs →decreased intrapulmonary pressure 1mmHg below the atmospheric pressure →rush of air into the lungs till equilibration of pressure occurs.

 Normal expiration is a passive process.  Caused by relaxation of inspiratory muscles and elastic recoil of the lungs and chest wall →increased intrapulmonary pressure 1mmHg above the atmospheric pressure → rush of air out of the lungs till equilibration of pressure occurs.  N.B.The volume of air inspired or expired in each respiratory cycle during rest = tidal volume = 500ml air.

 Gaseous exchange occurs across pulmonary membrane  Pulmonary membrane consists of: 1- Alveolar membrane. 2- Interstitial fluid. 3- Capillary wall.  Gas exchange occurs by simple diffusion.  Thickness is about 0.6 microns.  Surface Area is about 70 m 2..

1) Pressure Gradient of gases across pulmonary membrane: Alveolar air Venous blood PO mmHg > 40 mmHg PCO 2 40 mmHg < mmHg - So, oxygen passes from higher pressure (alveolar air) --> lower pressure (in venous blood), -while CO2 passes from the higher pressure (venous blood) to lower pressure (in alveolar air)

Pulmonary respiration

2) Surface Area Of The Pulmonary Membrane  The rate of diffusion of gases across pulmonary membrane is directly proportional to the surface area of pulmonary membrane.  The Surface Area of Pulmonary Membrane increases in muscular exercise and decreases by pulmonary diseases e.g., emphysema 3) Nature and Thickness of Pulmonary Membrane: Change in the nature and thickness of pulmonary membrane → decreased gas diffusion across pulmonary membrane, e.g lung fibrosis. 4) Ventilation-Perfusion Ratio:  Is the ratio between air and blood in the lung  Increase or decrease of this ratio → decreased gas diffusion across pulmonary membrane

Oxygen is carried in the blood in 2 forms: A) Physical oxygen:  Free O2 molecules dissolved in plasma.  Small amount: 0.3ml/dl arterial blood (PO2=100mmHg) 0.13ml/dl venous blood (PO2=40mmHg) B) Chemical oxygen:  Oxygen combines with iron of hemoglobin.  Oxygen content: is the volume of oxygen in chemical combination with hemoglobin in 100 ml blood Oxygen content of arterial blood = 19ml/100ml. Oxygen content of venous blood = 14ml/100ml.  Chemical oxygen is the main O2 supply to the tissues.

The Total CO 2 : - CO 2 content in arterial blood: 48 ml/dl - It is carried in 2 forms: 1)In Physical Solution: 3 ml/dl CO2 dissolved in the plasma. 2) In chemical combination: 45 ml/dl A) As Bicarbonates (sodium and potassium bicarbonates) = 42 ml/dl B) As Carbamino Compound = 3 ml/dL CO2 combines with the proteins of plasma or hemoglobin of RBCs. The Tidal CO 2 : Is the volume of CO 2 given by tissue to blood= 4 ml/dl.  CO 2 content of venous blood: 48 ml/dl +4ml/dl = 52 ml/dl

 Means exchange of gases between blood and tissues.  O2 passes from blood to the tissues, while  CO2 passes from the Tissues to the blood.

 Normal respiration is produced as a result of signals originate from the respiratory center in the brain stem.  Respiration should be regulated to meet the metabolic needs of the body, so: -During rest → normal resting breathing -During exercise → stimulation of breathing, i.e increased rate and depth of breathing.  Regulation Of Respiration Occurs by: I. Chemical regulation. II. Nervous regulation.

Respiratory center

 Respiration is stimulated by: 1-Increased PCO 2 in arterial blood 2-Increased H+ concentration in arterial blood. 3-Decreased PO 2 in arterial blood  Respiration is inhibited by: 1-Decreased PCO 2 in arterial blood 2-Decreased H+ concentration in arterial blood. 3-Increased PO 2 in arterial blood  These chemical factors exert their effect on respiration by acting on the central and peripheral chemoreceptors

 Are highly specialized neurons for measuring the changes in chemical composition of blood.  Chemoreceptors are either central or peripheral  Central chemoreceptors : -Present in the brain stem -Stimulated by increased PCO2 in arterial blood  Peripheral chemoreceptors: -Present in large systemic arteries (aorta and carotid) -Stimulated by: *Decreased PO2 in arterial blood *Increased PCO2 in arterial blood *Increased H+ concentration in arterial blood  Stimulation of chemoreceptors → stimulation of respiration

 The function of the respiratory center is regulated by afferent impulses from:  (1)The Lungs: 1-Overstretch of the lungs→ Inhibition of inspiration and start expiration (protective mechanism for the lungs). 2-Inhalation of irritant materials, e.g. ammonia and cigarette smoke → Shallow rapid breathing and bronchioconstriction (to decrease the amount of the irritant gas in the lungs) +periodic sighs to maintain lung inflation. 3-Pulmonary congestion, pulmonary edema → Shallow rapid breathing and feeling of dyspnea

(2)Air passages: 1-Irritation of nasal mucosa → sneezing reflex. 2-Irritation of mucosa of trachea and bronchi → cough reflex. Sneezing and cough reflexes help the respiratory system to get rid of the irritant materials. 3-Stimulation of pharyngeal mucosa by food → inhibition of respiration → prevention of food aspiration into respiratory system and suffocation. (3)Muscles and joints: Movements of joints during exercise → stimulation of respiration

(4) Visceral reflexes: During vomiting → inhibition of respiration → prevention of food aspiration into respiratory system and suffocation. (5)Cerebral cortex: -Represents voluntary control over breathing. -Voluntary apnea: cerebral cortex sends direct impulses to inhibit the respiratory center → stoppage of breathing. -Voluntary hyperventilation: cerebral cortex sends direct impulses to stimulate the respiratory center → increased rate and depth of breathing.

Include: I)Hypoxia: decreased O2 supply to the tissues II)Cyanosis : bluish coloration of skin and mucous membrane III)Dyspnea: difficult breathing IV)Orthopnea: dyspnea on lying down, releived or partially releived by sitting.