Respiratory System: Upper Tract Structure

• The respiratory system facilitates the exchange of oxygen and carbon dioxide between the blood, air, and tissues.
• Key organs include the nose, pharynx, larynx, trachea, bronchi, and lungs (specifically, alveoli).
• The respiratory tract serves as the pathway for air from the nose to the lungs.
• Air is cleansed by hairs, cilia, and mucus, warmed by blood vessels, and moistened.

Upper Respiratory Tract Structure

• Includes nasal cavities, pharynx, glottis, and larynx.

Nasal Cavity

• Hollow canals separated by a septum of bone and cartilage.
• Functions to filter, warm, and moisten the air.
• Paranasal sinuses are cavities within bones surrounding the nasal cavity that lighten the skull.
• Sinuses act as resonance chambers for speech.
• They produce mucus that drains into the nasal cavity.
• Mucous membrane lines the nasal cavity.
• Cilia moves mucus and trapped particles to the pharynx.
• Conchae are lateral projections that increase surface area and air turbulence.
• The nasal cavity is separated from the oral cavity by the anterior hard palate (bone) and posterior soft palate (muscle).

Pharynx

• A funnel-shaped passageway between the nasal cavity and larynx.
• Connects the nasal and oral cavities to the larynx.
• Has three regions: nasopharynx (air passageway), oropharynx (where oral cavity joins, for food and air), and laryngopharynx (opens to larynx).
• Tonsils, lymphatic tissue in the oropharynx, protect against inhaled pathogens.

Epiglottis

• A flap of tissue at the base of the tongue.
• Prevents food from entering the trachea, or windpipe, during swallowing.

Larynx

• The voice box; contains the vocal cords.
• Functions to produce sound.
• Vocal cords are elastic tissues that vibrate as air travels through, producing sound.
• The glottis is the opening or slit in the vocal cords.

Lower Respiratory Tract

• Includes the trachea, bronchi, bronchioles, lungs, and alveoli.

Trachea

• The windpipe, a flexible tube connecting the larynx to the bronchi.
• Directs air to the bronchi.
• Held open by C-shaped hyaline cartilage.
• Lined with pseudostratified ciliated columnar epithelial cells, where cilia sweep mucus loaded with dust away from the lungs.

Bronchi

• Left and right branched tubes of the trachea.
• Their function is to serve as passageways for air to the lungs.
• They subdivide into smaller and smaller branches called bronchioles.
• The right bronchus is wider, shorter, and straighter than the left bronchus.

Bronchioles

• The smallest branches of the bronchi, which lead to the alveoli.

Lungs

• Paired, cone-shaped organs that occupy the thoracic cavity.
• Contain alveoli, where gas exchange occurs.
• The apex (superior portion) is near the clavicle; the base (inferior portion) rests on the diaphragm.
• Each lung is divided into lobes by fissures: the left lung has two lobes, and the right lung has three lobes.
• The visceral pleura covers the lung, and the parietal pleura lines the walls of the thoracic cavity.
• Pleural fluid fills the area between pleura layers to allow gliding.

Alveoli

• Made of simple squamous epithelium surrounded by blood capillaries.
• Function in gas exchange.
• The respiratory membrane is extremely thin to aid in rapid gas exchange.
• Gas crosses the respiratory membrane by diffusion.
• Oxygen enters the blood, and carbon dioxide enters the alveoli.
• Macrophages add protection.
• Surfactant in alveoli prevents the lung from closing or collapsing.

Gas Exchange and Transport

• Respiration is the process of exchanging gases between the atmosphere and body cells.

External Respiration

• Exchange of gases between air and blood in the lungs.
• Blood entering the lungs is oxygen-poor and carbon dioxide-rich.
• The alveoli always have more oxygen than the blood.
• Oxygen moves by diffusion from an area of high concentration to an area of low concentration.
• Blood returning from tissues has higher concentrations of carbon dioxide than air in the alveoli.
• Pulmonary capillary blood gives up carbon dioxide.
• Blood leaving the lungs is oxygen-rich and carbon dioxide-poor.

Internal Respiration

• Exchange of gases between blood and body cells.
• Carbon dioxide diffuses out of tissue into blood, and oxygen diffuses from blood into tissue.

Gas Transport

• Oxygen transport in the blood occurs when oxygen binds inside red blood cells to hemoglobin (oxyhemoglobin); a small amount is dissolved in the plasma.
• Carbon dioxide is mostly transported in the plasma as a bicarbonate ion (HCO3-).
• A small amount is carried inside red blood cells on hemoglobin, but at different binding sites than those of oxygen

Mechanism of Breathing

• Ventilation is the manner in which air enters and exits the lungs.
• Has two phases: inspiration (air flowing into the lung) and expiration (air leaving the lung).

Inspiration

• An active phase of ventilation.
• The diaphragm and intercostal muscles contract.
• Size of the thoracic cavity increases.
• External air is pulled into the lungs due to an increase in intrapulmonary volume.

Expiration

• Mainly a passive process dependent on natural lung elasticity.
• The diaphragm and intercostal muscles relax.
• As muscles relax, air is pushed out of the lungs.
• Forced expiration can occur mostly by contracting internal intercostal muscles to depress the rib cage.

Nonrespiratory Air Movements

• Can be caused by reflexes or voluntary actions.
• Examples include cough, sneeze, laughing, crying, yawning, and hiccup.

Ventilation Control

• Normal breathing rate is 12-20 ventilations per minute.
• Controlled by the respiratory center in the medulla oblongata (brain).
• Nervous input: Intercostal and phrenic nerve stimulate muscles to contract for inspiration: lack of stimulation results in expiration
• Chemical Input: Level of carbon dioxide is the main regulatory chemical for respiration: increased carbon dioxide increases respiration

Respiratory Volumes

• Normal breathing moves about 500 ml of air with each breath (Tidal Volume [TV]).
• Respiratory capacities are measured with a spirometer.
• Many factors affect respiratory capacity including person's size, sex, age, and physical conditions.
• Inspiratory reserve volume (IRV) is the amount of air that can be taken in forcibly over the tidal volume, usually between 2100 and 3200 ml.
• Expiratory reserve volume (ERV) is the amount of air that can be forcibly exhaled, approximately 1200 ml.
• Residual volume is the remaining air in the lung after expiration, about 1200 ml.
• Vital Capacity is the total amount of exchangeable air calculated as TV + IRV + ERV.
• Dead space volume is the air that remains in the conducting zone and never reaches alveoli, about 150 ml
• Functional Volume is the air that actually reaches the respiratory zone, usually about 350 ml

Respiratory Disorders

• Tonsillitis occurs when tonsils become inflamed and enlarged, and can make breathing difficult: tonsils are the first line of defense against pathogens in the pharynx
• Laryngitis is an infection of the larynx that leads to an inability to talk audibly, disappears with treatment
• Chronic Obstructive Pulmonary Disease (COPD) describes progressive lung diseases and is the third leading cause of death in the U.S..
• Examples include chronic bronchitis, emphysema, and asthma.
• A chronic bronchitis airway becomes inflamed and fills with mucus, loss of cilia and normal cleansing action Caused by smoking cigars, cigarettes, and some pollutants.
• Emphysema is a chronic and incurable disorder where alveoli bursts and fuse into larger air spaces; reduces surface area for gas exchange; caused by prolong cigarette smoking