Introduction to the respiratory system Flashcards
What is the main function of the respiratory system?
- Delivery of 02 to the lungs for gas exchange and removal of CO2 produced by tissues out of the lungs
- I.e. external respiration
What is external respiration?
- exchange of gases between atmospheric air and blood
The respiratory system also has other important functions what are these?
- Acid-base balance (lungs and kidneys work together
- Immunity
- Thermoregulation (dog panting)
- site of metabolism/activation
- vocalisation/communication
What does the upper respiratory tract (URT) consist of?
- nasal cavity (plus paranasal sinuses)
- pharynx
- larynx
- Trachea
What does the lower respiratory tract (LRT) consist of?
- trachea
- bronchi and bronchioles
- alveolar ducts and alveoli
In the URT where does the air enter?
- air enters via nose (and sometimes the mouth in some species)
What determines whether mouth breathing is possible?
- anatomy of soft palate and larynx
In the URT what are the left and right nasal cavities divided by?
- nasal septum
What is found in the nasal cavities and what is it lined by?
- conchae AKA turbinates (scrolls of bone lined by mucosa)
- meatuses (openings/canals)
What are the nasal cavities mostly lined by?
- respiratory epithelium = pseudostratified columnar epithelium
Where is the pharynx found?
- at the region of cross-over between respiratory and alimentary tracts
In the URT what is the purpose of the epiglottis?
- protects airway during swallowing
- flaps shut and prevents food going down the trachea
What is the role of the conchae?
- filters air such as particulates
- ensures air comes into contact with olfactory surfaces
- humidifies air coming in
- degree of scrolls in species variable
You can find paranasal sinuses within the skull - what are they?
- Diverticular of nasal cavity = blind ending spaces
What animals have well developed paranasal sinuses?
- ox
- horse
What are the function of the paranasal sinuses?
- thermal and mechanical protection (can warm up air as it enters or cool it down and prevents mechanical forces being transmitted directly to the brains)
- lightens head
Why can paranasal sinuses cause clinical issues?
- narrow openings (blockage/access)
- lined by thin poorly vascularised respiratory epithelium (slow healing)
- roots of teeth (dental complications)
- frontal sinus extends into horns (in cattle)
What are the roles of the pharynx in respiration?
- the common cavity through which air and ingesta pass
- connects oral cavity to oesophagus and nasal cavity to larynx
- pathway through pharynx depends on epiglottis and soft palate
What is the dorsal border to the phalangeal area?
- base of the skull and C1-C2
What is the ventral border of the phalangeal region?
- larynx and mandible
What is the lateral border of the phalangeal region?
- pterygoid muscles and suspensory part of hyoid apparatus
What is the rostral border of the phalangeal region?
- soft palate separates rostral pharynx into dorsal and ventral (nasopharynx and oropharynx)
What does cuffing or folds of soft tissue around the pharynx cause?
- nose breathers
What connects the pharynx to trachea?
- musculocartilagenous organs
What type of epithelium is found near the pharynx (which is different to the respiratory epithelium elsewhere)?
- stratified squamous keratinised epithelium
What does the larynx function to do?
- protect trachea (aspiration of material into lower airway)
- vocalisation (vocal folds)
- pressure build up (glottis closure) e.g., coughing and defaecation
There are bilaterally symmetrical cartilages that form walls of larynx - Describe the rest of the structure?
- cartilages connect hyoid apparatus rostrally and trachea caudally
- synovial joints between cartilages (except epiglottis - elastic connections to flap)
- connected by muscles and ligaments - moveable
The larynx is innervated by branches of the Vagus - what are these?
- cranial laryngeal nerve - branches off near larynx
- caudal (recurrent) laryngeal nerve - goes down to base of heart and back up to larynx
What does the recurrent laryngeal supply?
- supplies all intrinsic muscles except circithyroideus
What causes paralysis in horses (roarers) of the RL nerve?
- usually left
- inability to abduct arytenoid cartilage
- vibrates (roars) and obstructs airflow
Where does the trachea extend from and to?
- Extends from larynx to bifurcation (into bronchi) at base of heart
There are C-shaped hyaline cartilages in the trachea described these:
- connect longitudinally by fibroelastic tissue to from a tube
- dorsally incomplete, bridged by tracheal muscle
Why are the C-shaped cartilages of the trachea dorsally incomplete?
- to allow food boluses to come down
The mucosal surface of the trachea is lined with what types of respiratory epithelium? and what does it also contain?
- lined by ciliated pseudostratified columnar
- interspersed with goblet cells (mucus)
What does the trachea divide into and then what does it do?
- the left and right mainstem bronchi
- enters the lungs
- (tracheal bronchus in ruminants and pigs)
The bronchi are histologically similar to trachea - what do are they lined with and interspersed with?
- lined by ciliated pseudostratified columnar epithelium
- interspersed with goblet cells
What ae the walls of the bronchi supported by and what can this do?
- supported by cartilage and smooth muscle
- this can change diameter (bronchodilation/constriction)
What do bronchi give way to?
- smaller conducting airways, bronchioles
Bronchioles are histologically distinct from bronchi - what are there features?
- lined by variably ciliated or non ciliated columnar epithelium
- walls are composed of smooth muscle
- lack cartilage and glands
- smaller size
- club cells
All airways up until bronchioles are conducting airways - what are these?
- no gas exchange happens here
- anatomic dead space
What are the respiratory airways?
- bronchioles to alveoli
- gas exchange happens here
What is the acinus?
- is the functional unit
- terminal bronchial and its distal structures
What can happen to acinus during surgery?
- they can get squashed when the animal is lead on its side
What do respiratory bronchioles look like?
- cuboidal epithelium (club cells) which produce secretions and source of new cells
- discontinuous wall opening into alveoli
Alveoli have 2 types of cells - what are these and what do they do?
- flattened squamous epithelium (type 1 pneumocytes) for gas exchange
- cuboidal cells (type 2 pneumocytes) secrete fluid (surfactant) which prevents alveolar collapse (atelectasis)
What do alveoli have that helps prevent collapse and what aids in efficient movement of air?
- share adjacent walls which helps prevent collapse
- gaps in septum (pores of kohn) connect alveoli for efficient movement of air
What are the components of the blood-gas interface?
- close contact, single cell layers
- surfactant
- alveolar epithelial cell (pneumocyte)
- epithelial basement membrane
- connective tissue around alveolus (don’t want too much)
- capillary basement membrane
- capillary endothelial cell
- blood plasma
- red blood cell
What do the lungs consist of?
- parenchyma (functional tissue)
- interstitium
What does the parenchyma (functional tissue) in the lungs consist of?
- bronchioles
- alveolar ducts
- sacs
What does the interstitium of the lungs consist of?
- elastic and collagenous soft tissue
- nerves
- glands
- blood
- lymph vessels
What are the lungs covered by?
- covered by pleura
What is pleura?
- serous membranes enclosing potential space and small amount of fluid
What are the two types of pleura and what do they line?
- parietal pleura lines thoracic walls
- visceral pleura covers lungs
What is the hilus medially?
- site of entry for all structures entering the lungs
- not covered by pleura
- blood vessels, airways, nerves entering lung
What are lung lobes?
- divisions based on infolding of pleura and primary branches of the left and right principal bronchi
The left lung has two lobes what are these?
- cranial (sometimes subdivided)
- caudal
The right lung has up to four lobes - what are these?
- cranial (subdivided in ruminants)
- middle (except horses)
- caudal
- accessory
What left and right lobes do dogs, cats and pigs have in their lungs?
- left = cranial (cr, cau)
- right = cranial, middle, caudal, accessory
What left and right lobes do cows, sheep and goats have in their lungs?
- left = cranial and caudal
- right = cranial (cr, cau), middle, caudal, accessory
What left and right lobes do horses have in their lungs?
- left = cranial and caudal
- right = cranial, caudal and accessory
Where is visceral pleura attached to and what does it contain?
- visceral pleura is attached to surface of lung including fissures and contains abundant elastic fibres
Parietal pleura lines the wall of the thoracic cavity and can be divided into 3 parts - what are these?
- Costal pleura lines inside of thoracic wall (rib cage)
- diaphragmatic pleura lines the cranial surface of the diaphragm
- mediastinal pleura lines the mediastinum
What is the diaphragm?
- musculotendinous sheet separating thoracic and abdominal cavity in mammals
Describe the structure of the diaphragm:
- central tendon portion
- openings for passage of structures e.g., aorta, oesophagus, vena cava
What does the diaphragm do?
- derives volume change of thorax and therefore negative pressure for breathing
The parietal pleura continue from thoracic walls over what? - and what does the pleura do here?
- over thoracic surface of diaphragm
- pleura reflects back on itself due to convex shape of diaphragm
What can the mediastinum be affected by?
- diseases such as tumours
What is the mediastinum?
- compartment between left and right pleural sacs
The mediastinum contains most (non-lung) thoracic structures what are these?
- heart in pericardiac sac
- trachea and oesophagus that are within thorax
- thymus
- mediastinal LNs
- great vessels (crania vena cava, aorta etc.)
- nerves including vagosympathetic trunk
What does the mediastinum not contain?
- lungs
- caudal vena cava (contained in its own fold, plica venae cavae)
- right phrenic nerve
What is the tidal volume?
- breathing volume at rest
What is the inspiratory reserve volume?
- extra air you can take in
What is expiratory reserve volume?
- extra air you can breathe out
What is residual volume?
- air that is constantly in the lungs as it keeps lung tissue slightly inflated
What is vital capacity?
- the maximum volume that can be breathed in and out
What is pulmonary circulation in the lungs?
- non-oxygenated blood from RV to lungs to LA
- gas exchange
- large volume, low pressure
- pulmonary arteries follow bronchi, veins do not always
What is bronchial circulation?
- From aorta to supply bronchial tree and its tissues
- low volume, high pressure
- oxygenated blood from LV to lungs to RV (via azygous)
What can also happen between bronchial and pulmonary circulation in the lungs?
- oxygenated blood to LA via anastomoses between bronchial and pulmonary circulation
- small right-to-left shunt
What does anastomoses between bronchial and pulmonary circulation help with?
- helps preserve lung tissue if the pulmonary supply becomes compromised
Describe the process of anastomoses:
- vasodilation of bronchial arteries increases flow
- increased blood flow is able to by-pass the obstructed pulmonary artery
- angiogenesis = new bronchopulmonary arterial anastomoses
Where does hypoxic vasoconstriction occur?
- in the lung pulmonary circulation
What does hypoxic vasoconstriction do?
- reflex vascular smooth muscle contraction
- areas that receive little alveolar oxygen also get reduced flow from the pulmonary artery
What does matching of ventilation and perfusion do?
- maximises oxygen exchange
