The Respiratory System

The Respiratory System Intro

• The respiratory system is essential breathing equipment
• Inhaled and exhaled gases circulate through body tissues and cells
• The system excretes excess and waste
• Oxygen functions as a food source, while carbon dioxide is considered waste

Respiration Definition

• Respiration involves exchanging oxygen and carbon dioxide between the atmosphere and body cells
• Inspiration and expiration are key processes
• Diffusion transports oxygen from pulmonary alveoli to blood and carbon dioxide from blood to alveoli
• The system facilitates oxygen and carbon dioxide transport throughout the body

Structure of the Respiratory System

• The upper respiratory structures include the nasal cavity, pharynx, larynx, and trachea
• The lower components include the bronchi/bronchioles, lungs, pleura, diaphragm, ribs, and intercostal muscles

The Nose and Nasal Cavity

• The nose is the only externally visible part of the respiratory system
• It serves as the entry point for air
• Air enters through the nostrils and passes into the nasal cavity
• The nasal cavity is divided into two sections by the nasal septum that contains hyaline cartilage
• The nasal cavity is separated from the oral cavity by the palate

Function of the Nose and Nasal Hairs

• Warming effect is due to dense blood vessels
• Nosebleeds can result in significant blood loss
• Particles are trapped and adhere to mucus, which prevents drying
• Air travels over the moist mucosa
• Air becomes saturated with water through humidification

Additional Details about the Nose

• The nose is supported by a rich blood supply
• The olfactory nerve in the nasal cavity enables the sense of smell
• Air passing through the nasal cavity is temperature-regulated to within 1 degree
• The nasal fossae mucosa is lined with mucus, secreted by ciliated columnar epithelium with goblet cells
• It contributes significantly to taste through posterior communication with the mouth

The Palates

• The hard palate forms the floor of the nasal cavity
• Separates nasal and oral cavities
• The soft palate extends posterior to the hard palate
• Divides the superior nasopharynx from the lower pharynx

The Pharynx

• The pharynx is essential throat structure behind the nasal cavity
• Found behind the mouth and above the oesophagus and larynx
• The human pharynx is divided into the nasopharynx, oropharynx, and laryngopharynx
• The pharynx is also crucial for vocalization
• Transports food from the mouth to the oesophagus while warming, moistening, and filtering air before it enters the trachea
• The pharynx functions as part of the digestive and respiratory systems

Nasopharynx

• It measures 2 to 3 cm wide and 3 to 4 cm long
• The space is located above the soft palate at the back of the nose
• Connects the nose to the mouth, allowing breathing through the nose
• The soft palate separates it from the oropharynx
• Adenoid tissue fights infections, as well as openings to the Eustachian tubes connect to the ears
• It serves as the main drainage route for lymphatic fluids, usually draining into the throat, nose, or ears

Oropharynx

• Accepts air from the nasopharynx and passes it to the laryngeal pharynx
• Accepts food from the mouth for passage to the oesophagus
• The oropharynx and related structures stop food/liquids from entering the lungs
• Choking can occur if this happens, could have life threatening outcomes

Laryngopharynx

• Lined by stratified squamous epithelium
• Functions to pass both food and air
• Air entry is temporarily paused during swallowing to allow food to pass safely to the oesophagus
• Functions to stop food from entering the respiratory tract or choking the trachea

Larynx

• It allows air passage while preventing food and drink from blocking the airway
• Known as the "voice box," it contains vocal folds for speech/singing
• Composed of thyroid cartilage (Adam's apple, hyaline cartilage), cricoid cartilage (hyaline cartilage), and epiglottis (elastic cartilage)

Lower Respiratory Tract

• The bronchi conduct air into the lungs
• The right and left bronchus branch into secondary and tertiary branches
• Then branch into smaller tubes (bronchioles)
• No gas exchange occurs in the bronchi
• Contains progressively less cartilage and more smooth muscle

Bronchioles

• Smooth muscle dominates with no cartilage
• Decreasing muscle and connective tissue allows for a single layer of epithelial cells remaining
• The function of the bronchioles is to deliver air to the network of millions of alveoli
• There are three types: lobular, terminal, or respiratory

Cilia

• Lobular and terminal branches referred to as the dead space since no air exchange occurs here
• Bronchioles are tiny, only 0.3 – 1mm in diameter
• Bronchiole walls are lined with cilia
• Cilial are finger like projections
• The cilia's function is to remove debris and microbes

The Alveoli

• There are millions of alveoli
• If stretched end to end they would cover a tennis court
• Air exchange occurs here
• Once O₂ reaches the alveoli, it diffuses through a single cell in an alveolus and a single cell in a capillary to enter the bloodstream
• Simultaneously, CO₂ is released from the capillary to the alveoli and then is exhaled

Gas Exchange

• External respiration involves air flow into & out of the lungs
• Internal respiration involves capillary gas exchange in body tissues
• Air flow from the external environment happens due to pressure changes in the lungs
• The alveolar gas exchange has three matching factors: Surface area, partial pressure gradients of gases & ventilation and perfusion

Pleural Cavities and Membranes

• The pleural cavity is a fluid-filled space between the 2 pulmonary pleurae
• The outer pleura (parietal) attaches to the chest wall
• The inner pleura (visceral) covers the lungs and adjoining structures
• The Pleural Cavity is considered a potential space
• The 2 pleurae adhere to each other through a serous thin film in normal conditions

Anatomy of the Lungs

• Lobes are separated by fissures
• The right lung has three lobes: superior, middle, and inferior
• The left lung only has two: superior and inferior
• The bronchopulmonary segment is a division of a lobe
• Each lobe houses bronchopulmonary segments
• Each segment receives air from its own tertiary bronchus and is supplied with blood by its own artery.
• A pulmonary lobule is a subdivision formed as the bronchi branch into bronchioles
• Each lobule receives its own bronchiole that has multiple branches
• An interlobular septum is a wall composed of connective tissue, separating the lobules from each other

The Cardiac Notch

• The cardiac notch: the indentation seen on the left lung allows space for the heart

Blood Supply to the Lungs

• The blood supply plays a key part in gas exchange
• Functions as a transport system for gases throughout the body
• Additionally, parasympathetic/sympathetic nervous system innervation provides a level of control via dilation and constriction of the airway
• Major function: performs gaseous exchange
• Blood from the pulmonary circulation is required
• Deoxygenated blood travels and erythrocytes pick up the O₂
• Erythrocytes transport to body tissues
• The pulmonary artery carries deoxygenated blood to the alveoli
• This artery branches and becomes smaller in diameter
• One arteriole and one venule supply and drain one pulmonary lobule
• Pulmonary arteries become the pulmonary capillary network near the alveoli
• The capillary network consists of tiny vessels with very thin walls
• The pulmonary capillary network branches and follows the bronchioles and the structure of the alveoli
• At this point, the capillary wall meets the alveolar wall
• This creates the respiratory membrane
• Oxygenated blood drains from the alveoli via multiple pulmonary veins
• These veins exit the lungs through the hilum

The Hilum

• Is a wedge-shaped area on the central portion of each lung
• Hilum has the bronchi, arteries, veins, and nerves entering and exiting lungs
• Left hilum normally slightly higher in the chest than the right
• Visualizing on chest X-rays can be difficult since there is no clear view
• Further scans required to determine if issue present

The Intercostal Muscles

• Muscles located in the ribs
• There are three layers that aid with breathing
  • External muscles sit outside the ribs
  • Internal muscles sit between the ribs
  • Innermost muscles sit inside the ribs
• They are innervated by the intercostal nerves
• Blood supply is from the intercostal artery and vein

Thoracic (Rib) Cage

• The thoracic rib cage surrounds and protects the heart and lungs
• There are 12 thoracic vertebrae, 24 ribs plus the sternum
• The first seven ribs connect to the sternum via costal cartilage
• Three of the remaining five have costal cartilage connected to the cartilage above
• The last two floating ribs are connected by cartilage to muscle in the abdominal wall

During Inhalation

• The diaphragm relaxes and the lungs expand
• The innermost intercostal muscles relax
• The external intercostal muscles contract to expand the chest cavity
• This expansion enables the lungs to fill with air
• Due to extra space negative pressure created
• Following air filling lungs, gases exchange as exhalation begins

During Exhalation

• Air is forced out
• The chest cavity must become smaller
• The diaphragm and the external intercostal muscles contract
• This applies force to the base and sides of the lungs
• The innermost intercostal muscles contract while the external intercostal muscles relax
• The cavity contracts and air is forced out

Accessory Muscles of Respiration

• Do not play an active role in breathing
• Considered accessory muscles because they assist in elevating the rib cage
• The sternocleidomastoid and the scalene muscles are also part of this process
• Some other neck muscles considered to be accessory muscles of respiration