Respiratory System Anatomy

• Respiratory system organs include the nose, pharynx, larynx, trachea, bronchi, and lungs with alveoli.
• Gas exchange between blood and the external environment occurs in the alveoli of the lungs.
• The upper respiratory tract consists of passageways from the nose to the larynx.
• The lower respiratory tract consists of passageways from the trachea to the alveoli.
• Passageways to the lungs purify, humidify, and warm the incoming air.

The Nose

• It is the only externally visible part of the respiratory system.
• Nostrils (nares) are the entry point for air.
• The nasal cavity is the interior of the nose.
• The nasal septum divides the nasal cavity.
• Olfactory receptors for the sense of smell are in the superior nasal cavity, beneath the ethmoid bone.
• Respiratory mucosa lines the nasal cavity.
• Respiratory mucosa moistens air.
• Respiratory mucosa traps incoming foreign particles.
• Respiratory mucosa destroys bacteria chemically through lysozyme enzymes.
• Respiratory mucosa moves contaminated mucus to the throat, where it is swallowed and digested.
• Superior, middle, and inferior conchae are projections from the lateral walls.
• Conchae increase the surface area of the mucous membrane to trap inhaled particles.
• Superior, middle, and inferior nasal meatuses are air passageways.
• The palate separates the nasal cavity from the oral cavity.
• The hard palate is anterior and supported by bone.
• The soft palate is posterior and unsupported.

Paranasal Sinuses

• They are cavities within the frontal, sphenoid, ethmoid, and maxillary bones, surrounding the nasal cavity.
• Functions of the sinuses are to: lighten the skull, act as resonance chambers for speech, and produce mucus.

The Pharynx

• The pharynx is commonly called the throat.
• It is a muscular passageway from the nasal cavity to the larynx.
• The three regions of the pharynx are:
• The nasopharynx is the superior region behind the nasal cavity.
• The oropharynx is the middle region behind the mouth.
• The laryngopharynx is the inferior region behind the larynx, connected to the esophagus.
• The oropharynx and laryngopharynx serve as a common passageway for air and food.
• The epiglottis directs food into the esophagus.
• Pharyngotympanic (Eustachian) tubes open into the nasopharynx.
• Pharyngotympanic tubes drain the middle ear and can transmit infections from the pharynx to the middle ear.
• The tonsils are clusters of lymphatic tissue that protect the body from infection.
• There are four types of tonsils in the pharynx.
• The pharyngeal tonsil (adenoid) is in the nasopharynx.
• The palatine tonsils (2) are located in the oropharynx at the end of the soft palate.
• The lingual tonsil is at the base of the tongue.
• Tubal tonsils protect the openings of the pharyngotympanic tubes.

The Larynx

• The larynx is commonly called the voice box.
• It is inferior to the pharynx.
• The larynx routes air and food into proper channels, and plays a role in speech.
• The larynx is made of eight rigid hyaline cartilages.
• Epiglottis, Thyroid, Arytenoid and Cricoid are the four main cartilages.
• The thyroid cartilage (Adam's apple) is the largest cartilage.
• The epiglottis is a spoon-shaped flap of cartilage that protects the superior opening of the larynx.
• The epiglottis routes food to the esophagus and air toward the trachea.
• During swallowing, the epiglottis rises and forms a lid over the opening of the larynx.
• Vocal folds (true vocal cords) are a pair of folds of mucous membrane.
• Vocal cords vibrate with expelled air, allowing speech.
• The glottis is the opening between the vocal cords

The Trachea

• The trachea is commonly called the windpipe.
• It is a 4-inch-long tube that connects to the larynx.
• The trachea's walls are reinforced with C-shaped rings of hyaline cartilage to maintain a patent airway.
• The trachealis muscle is part of the structure.
• The trachea is lined with ciliated mucosa.
• Cilia beat in a superior direction.
• Goblet cells produce mucus.

The Main Bronchi

• The main bronchi are formed by division of the trachea.
• Each bronchus (primary bronchus) enters the lung at the hilum (medial depression).
• The right bronchus is wider, shorter, and straighter than the left bronchus.
• Bronchi subdivide into smaller branches called the secondary and tertiary bronchi.

The Lungs

• They occupy the entire thoracic cavity except for the central mediastinum.
• The apex of each lung is near the clavicle (superior portion).
• The base rests on the diaphragm.
• Each lung is divided into lobes by fissures.
• The left lung has two lobes.
• The right lung has three lobes.
• Serosa covers the outer surface of the lungs.
• Pulmonary (visceral) pleura covers the lung surface.
• Parietal pleura lines the walls of the thoracic cavity.
• Pleural fluid fills the area between layers, to allows the lungs to glide over the thorax, and decreases friction during breathing.
• Pleural space (between the layers) is more of a potential space.
• The bronchial (respiratory) tree is a network of branching passageways and conduits to and from the respiratory zone.
• Main bronchi (primary)subdivide into smaller branches (secondary and Tertiary bronchi ) and eventually into bronchioles.
• All except the smallest passageways have reinforcing cartilage in the walls.

Respiratory Zone

• Terminal bronchioles lead into respiratory zone structures and terminate in alveoli.
• The respiratory zone is the only site of gas exchange, it includes: respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli (air sacs) are in millions and make up the bulk of the lungs
• Conducting zone structures include all other passageways
• Alveoli are largely composed of simple squamous epithelial cells.
• Alveolar pores connect neighboring air sacs.
• Pulmonary capillaries cover external surfaces of alveoli.
• Stroma of the lung is elastic connective tissue.
• The elasticity of the stroma allows the lungs to stretch and recoil
• The respiratory membrane (air-blood barrier) has air on one side and blood flowing past on the other.
• The respiratory membrane is formed by alveolar and capillary walls.
• Gas crosses the respiratory membrane by diffusion.
• Oxygen enters the blood.
• Carbon dioxide enters the alveoli.
• Alveolar macrophages ("dust cells") add protection by picking up bacteria, carbon particles, and debris.
• Surfactant-secreting cells secrete surfactant, a lipid molecule.
• Surfactant molecule coats gas-exposed alveolar surfaces.

Respiratory Physiology

• There are four events of respiration.
• Pulmonary ventilation is moving air into and out of the lungs (commonly called breathing).
• External respiration is gas exchange between pulmonary blood and alveoli: Oxygen is loaded into the blood, carbon dioxide is unloaded from the blood.
• Respiratory gas transport-transport of oxygen and carbon dioxide via the bloodstream.
• Internal respiration is gas exchange between blood and tissue cells in systemic capillaries.
• Gas moves from an area of higher concentration to an area of lower concentration.
• Pulmonary ventilation is a mechanical process that depends on volume changes in the thoracic cavity.
• Volume changes lead to pressure changes, which lead to the flow of gases to equalize pressure.
• Two phases of pulmonary ventilation are inspiration and expiration
• Inspiration is the flow of air into the lungs.
• Expiration is air leaving the lungs.
• During inspiration (inhalation), the diaphragm and external intercostal muscles contract, making the thoracic cavity bigger, and lungs expand.
• This causes intrapulmonary volume to increase and the gas pressure inside the lungs becomes less than the atmospheric pressure.
• Air flows into the lungs until intrapulmonary pressure equals atmospheric pressure.
• Expiration (exhalation) is a passive process that depends on natural lung elasticity.
• During expiration the Intrapulmonary volume decreases, gas pressure increases, and gases passively flow out to equalize the pressure
• Forced expiration involves contraction of internal intercostal muscles to depress the rib cage.
• Intrapleural pressure, within the pleural space, is always negative.
• Maintaining negative intrapleural pressure is a major factor preventing lung collapse.
• If intrapleural pressure equals atmospheric pressure, the lungs recoil and collapse.

Respiratory Volumes and Capacities

• Respiratory volumes and capacities are done to assess the respiratory system.
• Tidal volume (TV) is normal quiet breathing: 500 ml of air is moved in/out of lungs with each breath.
• Inspiratory reserve volume (IRV) is 3,100 ml, is the amount of air that can be forcibly taken in above the tidal volume.
• Expiratory reserve volume (ERV) is 1,200 ml, amount of air that can be forcibly exhaled beyond tidal volume.
• Residual volume (RV) is 1,200 ml. It is the air remaining in lung after expiration, and cannot be voluntarily exhaled
• Vital capacity is the total amount of exchangeable air.
• It can be calculated using this equation: Vital capacity = TV + IRV + ERV
• 4,800ml in men; 3,100ml in women
• Total Lung Capacity = TV+IRV+ERV+RV = 6000 ml.
• Respiratory capacities are measured with a spirometer.

External Respiration

• During external respiration, oxygen is loaded into the blood.
• Oxygen diffuses from the oxygen-rich air of the alveoli to the oxygen-poor blood of the pulmonary capillaries.
• Carbon dioxide is unloaded out of the blood.
• Carbon dioxide diffuses from the blood of the pulmonary capillaries to the alveoli.

Gas Transport in the Blood

• During oxygen transport in the blood, most oxygen travels attached to hemoglobin and forms oxyhemoglobin (HbO2).
• A small dissolved amount is carried in the plasma.
• During carbon dioxide transport in the blood, most carbon dioxide is transported in the plasma as bicarbonate ion (HCO3¯)
• A small amount is carried inside red blood cells on hemoglobin, at different sites than oxygen.
• For carbon dioxide to diffuse out of blood into the alveoli, it must be released from its bicarbonate form:
• Bicarbonate ions combine with hydrogen ions and form carbonic acid (H2CO3)
• Carbonic acid splits to form water + CO2.
• Carbon dioxide diffuses from blood into alveoli.

Internal Respiration

• Internal respiration is the exchange of gases between blood and tissue cells.
• Carbon dioxide diffuses out of tissue cells to blood (called loading).
• Oxygen diffuses from blood into tissue (called unloading).

Control of Respiration

• Neural centers that control rate and depth of breathing are located in the medulla and pons
• Normal respiratory rate (eupnea) is 12 to 15 respirations per minute
• Hyperpnea is increased respiratory rate, often due to extra oxygen needs.
• Hypopnea: Abnormally slow or shallow breathing.