RESPIRATORY SYSTEM LECTURE 1 + 2

THE LUNG

Conducting zone

Nose, nasal cavity, nasopharynx, oropharynx, laryngopharynx, larynx, trachea, bronchi, bronchioles, and terminal/conducting bronchioles

Treatment for asthma

An inhaler that contains a volatile spray of ß-agonist (stimulant) which relaxes smooth muscles ie salbutamol (ß2-adernoceptor agonist)

Surfactant insufficiency

Premature babies do not have enough surfactant prior to 24 weeks due to to no type II cells

Function of conducting zone

To filter, warm, humidify, and conduct air

Respiratory zone

Respiratory bronchioles, alveolar sacs, and alveoli

Function of respiratory zone

Main sites of gas exchange between blood and air

Functions of respiratory system

Gas exchange, regulate blood pH, receptors for smell, filters air, produces vocal sounds, and excretes small amounts of water and heat

Nasal septum

Divides the nasal cavity into right and left sides

Internal nares/choanae

Two openings in the nasal cavity that allows communication with the pharynx

Paranasal sinuses

Four paired, air-filled cavities within the skull, named after the bones they're in: the frontal, sphenoid, ethmoid, and maxillary sinuses. They produce mucus to moisten and protect the nasal passages, lightens the skull, helps to warm and humidify inhaled air, and adds resonance to speech

Respiratory epithelium

Pseudostratified ciliated columnar epithelium with numerous goblet cells that line the respiratory region

Nostril hairs

Filter the air of large dust particles

Nasal meatuses

A superior, middle, and inferior portion of the nasal cavity divided by projections of the superior, middle, and inferior nasal conchae/turbinates. It is lined with a mucous membrane

Function of nasal meatuses

It increases surface area and prevents dehydration by trapping water droplets during exhalation. It also warms air by the extensive blood capillary network and traps dust particles and moistens the air by the mucous

Olfactory epithelium

Near the superior nasal conchae and adjacent septum, it contains cilia but no goblet cells

Function of pharynx

Passageway for air and food, a resonating chamber for speech sounds, and houses the tonsils. Divided into the nasopharynx, oropharynx, and laryngopharynx

Soft palate

Forms the posterior portion of the roof of the mouth and is a partition between the nasopharynx and oropharynx lined by mucous membranes. It opens into two internal nares, two Eustachian tubes, and the oropharynx

Nasopharynx

Lined with respiratory epithelium, the cilia move the dust-laden mucous towards the laryngopharynx. It also exchanges small amounts of air with the Eustachian tubes to equalise air pressure between the middle ear and the atmosphere

Oropharynx

Both respiratory and digestive functions therefore lined with nonkeratinised stratified squamous epithelium. It houses the palatine and lingual tonsils

Laryngopharynx

Both respiratory and digestive functions therefore lined with nonkeratinised stratified squamous epithelium. It opens into the oesophagus posteriorly and larynx anteriorly

Larynx

Walls of larynx are composed of thyroid cartilage, epiglottis, and cricoid cartilage, as well as pairs of arytenoid, cuneiform, and corniculate cartilages.

Cavity of the larynx

A space that extends from the entrance of the larynx down to the inferior border of the cricoid cartilage

Laryngeal vestibule

Portion of the cavity of the larynx above the vestibular folds (false vocal cords)

Infraglottic cavity

Portion of the cavity of the larynx below the vocal folds

Thyroid cartilage

Two fused plates of hyaline cartilage that form the anterior wall of the larynx and give it a triangular shape (Adam’s apple)

Epiglottis

‘Stem’ of the epiglottis attached to the thyroid cartilage while the ‘leaf’ of the epiglottis is unattached and free to move up and down. Covers the glottis during swallowing

Glottis

A pair of folds of mucous membrane (vocal folds/true vocal cords) in the larynx and the space between them (rima glottidis)

Arytenoid cartilages

Triangular pieces of mostly hyaline cartilage that form synovial joints with the cricoid cartilage and have a wide range of mobility. It influences changes in position and tension of the vocal folds

Trachea

Divides into right and left primary bronchi and lined with respiratory epithelium. It has 16 - 20 incomplete horizontal rings of hyaline cartilage resembling the letter C so the tracheal wall does not collapse inwards

Trachealis muscle

Transverse smooth muscle fibres and elastic connective tissue within a fibromuscular membrane that spans the open part of each C. Allows the diameter of the trachea to change subtly during inhalation and exhalation to maintain efficient airflow

Right primary bronchus

Goes into the right lung and is more vertical, shorter, and wider therefore objects are more likely to enter the right than the left. It gives rise to the superior, middle, and inferior lobar bronchi

Left primary bronchus

Goes into the left lung and gives rise to the superior and inferior lobar bronchi

Primary bronchi

Contains incomplete rings of cartilage and lined with respiratory epithelium then further divides into lobar bronchi when entering the lung

Carina

An internal ridge where the trachea divides into right and left primary bronchi. The mucous membrane of the carina is one of the most sensitive areas of the entire larynx and trachea and responsible for triggering a cough reflex. Widening and distortion is a serious sign of carcinoma of the lymph nodes

Lobar bronchi

Smaller bronchi that conducts air to each lobe of the lung, right has 3 and left has 2. It continues to branch forming segmental bronchi

Segmental bronchi

There are 10 in the right lung and 8 on the left lung and these are responsible for supplying the specific bronchopulmonary segments. It then divides further into bronchioles

Bronchioles

Undergoes extensive branching, with the smallest being called terminal bronchioles

Terminal bronchioles

Contain Clara cells, columnar, nonciliated cells interspersed among the epithelial cells and are the end of the conducting zone. It contains macrophages to remove inhaled particles

Club cells

Protect gains harmful effects of inhaled toxins and carcinogens, produce surfactant, and functions as stem cells (give rise to various cells of the epithelium)

Bronchial tree

The extensive branching from the trachea through the terminal bronchioles. Three major structural changes occur as you go down

First major change

Mucous membrane goes from respiratory epithelium to ciliated simple columnar with some goblet cells in larger bronchioles to most ciliated cuboidal with no goblet cells in smaller bronchioles to mostly nonciliated simple cuboidal in terminal bronchioles.

Second major change

Plates of cartilage gradually replace the incomplete rings of C in main bronchi and finally disappear in distal bronchioles

Third major change

As amount of cartilage decreases, the amount of smooth muscle increases however no cartilage can result in muscle spasms blocking off the airways (asthma)

Pleural membrane

Each lung is enclosed in a double layer. The parietal pleura lines the wall of the thoracic cavity and the visceral pleura lines the lungs. This creates a space in between called the pleural cavity which contains serous fluid to reduce friction. This fluid also causes the two membranes to stick together due to surface tension

Pleurisy (pleuritis)

Inflammation of the pleural membrane, early symptoms can be pain due to friction between the two layers. If the inflammation persists, serous fluid builds up causing pleural effusion

Base of each lung

Broad inferior portion of the lung which is concave and fits over the convex area of the diaphragm

Apex of each lung

Narrow superior portion of the lung

Costal surface of each lung

The surface lying against and matches the rounded curvature of the ribs

Hilum/root of each lung

In the mediastinal surface of each lung, though which bronchi, pulmonary, blood vessels, lymphatic vessels, and nerves enter and exit

Thoracentesis

Removal of excessive fluid in the pleural cavity can be accomplished without injuring lung tissue by inserting a needle anteriorly through the seventh intercostal space along the superior border of the lower rib to avoid damage to intercostal nerves and blood vessels

Oblique fissure

In the left lung, it separates the superior and inferior lobe

In the right lung, the superior part of the fissure separates the superior lobe from the inferior lobe. The inferior part of the fissure separates the inferior lobe from the middle lobe, bordering superiorly by the horizontal fissure

Bronchopulmonary segment

Each of these have many small compartments called lobules

Lobules

Wrapped in elastic connective tissue and contains a lymphatic vessel, a venule, and a branch from a terminal bronchiole

Respiratory bronchioles

Microscopic branches that divided from terminal bronchioles that contain alveoli on their walls and are the start of the respiratory zone. These then divide further into several (2-11) alveolar ducts

Alveolar ducts

Consist of simple squamous epithelium and around its circumference are numerous alveoli and alveolar sacs

Alveolus

A cup-shaped out pouching lined by simple squamous epithelium and supported by a thin elastic basement membrane

Alveolar sac

Consists of consists of two or more alveoli that share a common opening

Type 1 alveolar (squamous pulmonary epithelial) cells

Thin simple squamous epithelium that form a nearly continuous lining of alveolar wall and are the main sites of gas exchange

Type 2 alveolar (septal) cells

Fewer in number and are found between type 1 alveolar cells. Round or cuboidal epithelium with free surfaces containing microvilli, secrete alveolar fluid, keeping the surface between air and cells moist

Surfactant

A component of alveolar fluid, it is a complex mixture of phospholipids and lipoproteins. It lowers the surface tension of alveolar fluid which reduces the tendency of alveoli to collapse

Alveolar macrophages

‘Dust cells’ are phagocytes that remove fine dust particles and other debris from the alveolar spaces

Respiratory membrane

It has four layers, a layer of type 1 and 2 alveolar cells and associated alveolar macrophages (alveolar wall), then an epithelial MB, then a capillary BM often fused to the epithelial BM, then the capillary endothelium. It is thin (0.5 µm) allowing for rapid diffusion

Bronchial arteries

Branching from the aorta and deliver oxygenated blood to the lungs by flowing through the muscular walls of the bronchi and bronchioles

Pulmonary inhalation

Inflow and outflow of air and involves the exchange of air between the atmosphere and the alveoli of the lungs due to pressure gradients

External (pulmonary) respiration

Exchange of gases between the alveoli of lungs and the blood in pulmonary capillaries across the respiratory membrane. Blood gains O₂ and loses CO₂

Internal respiration

Exchange of gases between blood in systemic capillaries and tissue cells. Cellular respiration occurs and blood loses O₂ and gains CO₂

Inhalation

Air pressure inside the lungs is equal to the air pressure of the atmosphere (1 atm/760 mmHg). An active process that lowers air pressure inside by increasing the size of the lungs via contraction of the diaphragm with resistance from external intercostals

Boyles law

P₁V₁ = P₂V₂ The inverse relationship between volume and pressure, if one increases then the other must decrease

Diaphragm

Contraction causes it to flatten increasing the vertical diameter of the thoracic cavity. It is responsible for 75% of air that enters the lungs during quiet breathing. Relaxation causes it to rise superiorly decreasing the vertical diameter of the thoracic cavity

External intercostals

Contraction causes the ribs to elevate increasing in the anteroposterior and lateral diameters of the chest cavity. It is responsible for 25% of air that enters the lungs during quiet breathing. Relaxation causes the ribs to depress decreasing the anteroposterior and lateral diameters of the chest cavity

Intrapleural pressure

It is always subatmospheric (756 mmHg), inhaling causes the volume to increase and the pressure to be about 754 mmHg. This is because the parietal pleura is pulled outwards in all directions and the visceral pleura are pulled along with it.

Alveolar (intrapulmonic) pressure

Initially equal to atmospheric pressure, it drops to 758 mmHg, creating a pressure gradient inwards to the lungs

Accessory muscles of inhalation

Sternocleidomastoid muscles, scalene muscles, and the pectoralis minor muscles. These muscles contract during deep and forceful inhalations to increase the volume of the thoracic cavity even more

Exhalation

A passive process that makes the pressure in the lungs greater than the atmosphere as no muscular contractions occur. Instead, it is due to the elastic recoil of the chest wall and lungs and the inward pull of surface tension due to the film of alveolar fluid. It is only active during forceful breathing as muscles of exhalation are recruited and contracted, which may cause intrapleural pressure to briefly exceed atmospheric pressure

Muscles of exhalation

Abdominal and internal intercostals

Abdominal muscles

Contraction moves the inferior ribs downward and compresses the abdominal viscera, forcing the diaphragm superiorly

Internal intercostals

Contraction pulls the ribs inferiorly, decreasing the volume of the thoracic cavity