6. Respiratory System

what is the main function of the lungs?

to oxygenate blood by bringing inspired air into close relation with deoxygenated blood in the pulmonary circulation

what are the two lungs separated by?

the mediastinum, containing the heart, great vessels and trachea

where are the lungs located?

within the thorax and extend from their apex, just above the first rib superiorly, level with T1, to the diaphragm inferiorly, level with T12 at their most inferior point in the posterior thorax on inspiration

how do the lungs attach to the heart and trachea?

by the structures that comprise the roots of the lungs

what structures form the root of the lung?

the bronchus, nerves, lymphatic vessels and the pulmonary vessels entering and emerging from the lung at its hilum

what does the visceral pleura do at the hilum?

reflects to become the parietal pleura and vice versa

what divides the lungs into lobes?

the horizontal and oblique fissures

how many lobes does the right lung have?

3

how many lobes does the left lung have?

2

what is the cardiac notch?

indents the anteroinferior aspect of the superior lobe of the left lung

what are the surfaces of the lung?

costal, mediastinal and diaphragmatic

what are the borders of the lung?

anterior, inferior and posterior

where does the apex of the lung extend to?

into the root of the neck, above the 1st rib

what is the visceral pleura?

covers the lungs and is adherent to all its surfaces, including the horizontal and oblique fissres, it cannot be separated from the lungs

what is the parietal pleura?

lines the pulmonary cavities, it is adherent to the thoracic wall, the mediastinum and the diaphragm

what are the subparts of the parietal pleura?

costal pleura; mediastinal pleura; diaphragmatic pleura; cervical pleura

what is the costal pleura?

covers the internal surfaces of the thoracic wall

what is the mediastinal pleura?

covers the lateral aspects of the mediastinum

what is the diaphragmatic pleura?

cover the superior aspect of the diaphragm on each side of the mediastinum

what is the cervical pleura?

extends through the superior thoracic aperture forming domed pleura over the apex of the lung

what is the pleural cavity?

potential space between the layers of pleura

what is the pleural cavity filled with?

serous pleural fluid which lubricates the pleural surfaces and allows the layers of the pleura to slide smoothly over each other during respiration

what does the pleural fluid do?

provides the surface tension that keeps the surface of the lung in contact with the thoracic wall; consequently the lung expands and fills with air when the chest expands and the diaphragm flattens

how does a lung collapse occur?

If a significant amount of air or fluid enters the pleural cavity, the surface tension adhering the visceral and parietal pleura is broken and the pleural cavity becomes a real space

what is a pneumothorax?

a common cause of lung collapse - a puncture wound to the thorax results in air rushing into pleural cavity

what is a hydrothorax?

accumulation of fluid in the pleural cavity may result from pleural effusion (escape of fluid into the pleural cavity)

what is a haemothorax?

blood entering pleural cavity more usually a result of injury to the major intercostal vessel (usually by a fractured rib) than laceration to the lung

how is a collapsed lung treated?

fluid needs to be drained from the pleural cavity using a chest drain

what does the upper respiratory system consist of?

nasal cavity, pharynx, larynx

what does the lower respiratory tract consist of?

trachea, bronchi, bronchioles, alveoli, lungs

what is the purpose of the upper respiratory system?

to condition inspired air before it reaches the lungs. before reaching the lungs air is: warmed to body temperature, humidified, filtered for particulates

what is the lower respiratory system concerned with?

gas exchange, conducting inspired air to the tissues involved in gas exchange and further trapping and removal of particulates

where is the rhythm of breathing controlled from?

the respiratory centres of the brainstem

where is the respiratory centre located?

in the lower part of the brainstem in the medulla oblongata

when are inspiratory neurons active?

during inspiration and inactive during expiration

when are expiratory neurons active?

during expiration but not inspiration

what can the rhythm of breathing be modified by?

the afferent information

where does afferent information come from?

chemoreceptors, the brain and receptors in the lungs

what happens if you sever the brainstem below the pons but above the medulla?

produces irregular breathing

what happens if you sever the spinal cord at the brain stem?

results in a cessation of breathing

what are the accessory muscles of inspiration?

stermocleidomastoid (elevates sternum); Scalenes group (elevate upper ribs); pectoralis minor

what are principal muscles of inspiration?

External intercostals; Interchondrial part of internal intercostals (elevates ribs); diaphragm (dome descends, thus increasing vertical dimension of thoracic cavity, also elevates lower ribs)

what are the muscles involed in quiet breathing?

expiration results from passive elastic recoil of the lungs rib cage and diaphragm

what are the muscles involved in active expiration?

internal intercostals except interchondrial part (pull ribs down); abdominals (pull ribs down, compress abdominal contents thus pushing diaphragm up); quadratus lumborum (pulls ribs down)

what is the diaphragm?

a thin, musculotendinous, dome-shaped sheet of muscle that separates the thorax from the abdomen

what is the diaphragm attached to?

the lower ribs and is innervated by the right and left phrenic nerves, which have their origins at the third to fifth cervical segments (C3-C5) of the spinal cord

what is the highest point of the diaphragm at rest?

is level with T9, inferiorly it is attached to the body wall level with T12

where does the blood supply of the diaphragm originate?

from the intercostal arteries and drains to the inferior vena cava

what happens to the diaphragm when it contracts?

it flattens

why does the diaphragm contract?

increases volume of thorax and aids inspiration. The concurrent reduction in abdominal volume is possible due to the malleable nature of many of the abdominal organs. rib margins are lifted and moved out, which increases the transverse diameter of the thorax

what does the diaphragm do in quiet breathing?

contracts and flattens, the apex moves inferiorly by 1-2cm

what does the diaphragm do in deep breathing?

can move inferiorly up to 10 cm

what happens if the diaphragm is paralysed?

it moves higher up the thoracic cavity during inspiration because of the fall in thoracic pressure

where are intercostal muscles located?

between the ribs

how many sets of intercostals are there?

11 of each exterior and interior

where does the blood supply for intercostals come from?

the intercostal arteries and drains to the intercostal veins

what are the intercostals innvervated by?

the intercostal nerves

where do external intercostals muscles extend from?

the tubercles of the superior ribs of the intercostal space dorsally, to the cartilages of the ribs ventrally on the inferior rib

where do external intercostal muscles end?

ventrally in thin membranes, the **anterior (external) intercostal membranes** which continue forward to the sternum

what do external intercostal muscles do?

pull the ribs upwards and forwards during inspiration causing and increase in both the lateral and anteroposterior diameters

where do internal intercostal muscles begin?

ventrally, at the sternum in the interspaces between the cartilages of the true ribs (ribs 1-7) and at the ventral extremities of the cartilages of the false ribs (8-12)

where do internal intercostal muscles extend?

downward as far as the angles of the ribs, where they continue to the vertebral column as thin membranes called the **posterior (internal) intercostal membranes**

what do internal intercostal muscles do?

pull the ribs down and inward during active respiration

what are innermost intercostal muscles?

incomplete and variable; pass from rib to rib deep to internal intercostals; fibres pass in same direction as internal intercostals; separated from internal intercotals by the bundle of intercostal blood vessel and nerves

how do the inspiratory muscles move during quiet breathing?

the diaphragm provides most of the inspiratory force, however the external intercostal muscles may be used.

how do the inspiratory muscles move during forced breathing?

accessory muscles are used in conjunction with the diaphragm and external intercostal muscles to bring large volumes of air into the lungs.

what are the accessory muscles?

the sternocleidomastoids and the scalenes

how do the expiratory muscles move during quiet breathing?

entirely passive, relying on the elastic recoil of the lungs and the weight of the rib cage to reduce the volume of the thorax and push air out of the lungs.

how do the expiratory muscles move during forced breathing?

becomes an active process involving the internal intercostals and abdominal muscles.

what are the tree like structures embedded in lung tissue?

the vascular tree and the airway tree

what is the vascular tree?

composed of the arteries, veins and capillaries which conduct poorly oxygenated blood to the lungs and returns highly oxygenated blood to the heart.

what is the airway tree?

consists of air-filled branching tubes, originating from the trachea, which conduct ‘new’ atmospheric air to the gas exchange surfaces and return ‘used’ air to the environment

what is a pulmonary oedema?

a build up of fluid in the interstitial space in the lungs. This increases the diffusion distance of gases between blood and the alveoli

how do pulmonary oedemas develop?

often secondary to another condition such as left heart failure, renal failure, pneumonia or cirrhosis of the liver

what are the early symptoms of a pulmonary oedema?

shortness of breath, cough and various disruptions to the rate and rhythm of breathing

what are the later symptoms of a pulmonary oedema?

cyanosis and a cough with a foaming red sputum

what is the treatment for a pulmonary oedema?

treat the hypoxia using 100% oxygen while later treatment goes on to address the underlying cause

what is the trachea?

single widest of the conducting airways, however it has the smallest total cross-sectional area and therefore is responsible for most of the airway resistance

what prevents trachea collapse on inspiration?

the surrounding and supporting rings of hyaline cartilage

what does the trachea bifurcate into?

two primary bronchi which enter the lung. These form the trunks of each of the lungs and go on to further divide (up to 11 times) into smaller and smaller bronchi. These conducting tubes are also supported by rings of cartilage

what do the first 17 generations of airway form?

the conducting zone of the lower respiratory system

when can bronchioles be found?

At about the 12th division of the bronchi

what are bronchioles?

small, collapsible passageways with smooth muscle walls

when do bronchioles become respiratory bronchioles?

after further branching up to 11 times

what are respiratory bronchioles?

the transition between the conducting airways and the gas exchanging tissues of the lung

where do respiratory bronchioles terminate?

at the alveolar ducts which lead to the alveoli

what forms the respiratory zone of the lower respiratory system?

structures from the respiratory bronchioles to the alveoli

what are alveoli?

the primary site of gas exchange. They are small outpockets which greatly increase the surface area for gas exchange

how are alveoli arranged?

in lung lobules which are a cluster of alveoli surrounded by elastic fibres and a network of capillaries

what are lung lobules?

a cluster of alveoli supplied by a single respiratory bronchiole, surrounded by the connective tissue of the lung

what is emphysema caused by?

largely associated with smoking. It is caused by gradual damage to the alveoli, usually by irritants or infection, which makes them loose their natural elasticity

what is emphysema?

the lungs are unable to expel all the air on expiration and leaves them feeling continually over inflated and the patient struggles to force air in and out of their lungs

what can emphysema lead to?

a state of chronic hypoxia causing fatigue and weight loss. It may only start off as breathlessness however it may lead to the patient being housebound and reliant on oxygen supplies

how can emphysema be complicated?

by combination with chronic bronchitis, where the lungs are unable to clear mucus (due to damage to the respiratory epithelium, often by smoking) which becomes infected.

This combination is called Chronic Obstructive Pulmonary Disease (COPD)

what is asthma?

a patient experiences difficulty breathing as the conducting airways become restricted as the diameter reduces

what is the current theory of asthma?

immunological disease caused by immune system over-reacting to an antigen that would normally be over looked

what is status asthmaticus?

an acute asthma attack, triggered by an irritant

what are the treatments for an acute asthma attack?

bronchodilators such as salbutamol (ventolin) are used. Prophylactic inhaled steroids such as beclomethasone dipropionate (BDP) helps reduce long-term airway damage

what are cavities lined with?

pseudostratified columnar epithelium

what do columnar cells have?

numerous cilia on their surface