Respiration Flashcards
Which lung lobe does a horse lack?
Right middle
What is the difference between respiration and ventilation?
Respiration=exchange of gases at the alveoli
Ventilation=movement of air through the airways
Which epithelium lines the airways?
What does this also contain?
Ciliated columnar epithelium
Goblet cells and submucosal glands
What is the name of the function which moves mucus up towards the pharynx to be swallowed?
Mucociliary escalator function
Particles how small may still reach the alveoli despite the mucociliary escalator function?
Less than 5um
The epithelial lining of the terminal bronchioles contain which cells? What do they produce?
What does the lining lack?
Clara cells
Produce surfactant
Lacks cilia and goblet cells
What is a bronchovascular bundle composed of?
A bronchus, artery and vein
Which arteries supply the lung itself? Where do they arise from?
Bronchial arteries which arise from aorta
How does venous drainage of the lung tissue occur?
Via bronchial veins which empty into the azygous vein, or sometimes directly into the left atrium.
Which nerve provides parasympathetic supply to the lungs?
Vagus
What is the structural difference between bronchi and bronchioles?
Bronchioles have no cartilage in their walls
What are the names of the 5 developmental stages of the lungs?
Embryonic, pseudoglandular, canalicular, terminal sac and alveolar
When do respiratory muscles start contracting in the foetus?
From the first trimester
What is the normal respiratory rate of a dog?
What about a horse?
20-30 brpm
10-12 brpm
Which word means normal breathing?
Eupnoea
Which word means increased resp rate?
Tachypnoea
Which word means increased respiratory depth?
Hyperpnoea
Which word means increased respiratory effort?
Dyspnoea
Which word means absence of breathing?
Apnoea
What is compliance?
What does it depend on?
The degree to which a change in transpulmonary pressure leads to a change in volume of the lung
Depends on elasticity of lungs and thoracic cage, and surface tension in the alveoli
What is meant by tidal volume?
What is the value in a normal dog?
Volume of air moved during a respiratory cycle
10-15ml/kg
How do you calculate minute ventilation?
Tidal volume x respiratory rate
What is the partial pressure of oxygen in normal room air?
160mmHg
What is meant by dead space?
Areas which are ventilated but don’t participate in gas exchange
In which part of the airways is the speed of air flow highest?
Trachea and large bronchi
How do you increase the minute ventilation, eg during exercise?
By increasing respiratory rate, tidal volume, or both
What is the residual volume (of the lungs)?
The volume of air that remains after a full expiration
One litre of plasma can carry how much O2 in solution?
3ml
When fully saturated, how much O2 can one gram of Hb carry?
1.36-1.39ml
What is the oxyhaemoglobin dissociation curve affected by?
Temperature, pH, PCO2, and concentration of 2,3-diphosphoglycerate in RBCs
Which animals’ Hb does not bind 2,3-DPG?
Ruminants and foetus’
In which 3 ways are CO2 transported in the blood?
- Dissolved in plasma (5%)
- As carbamino compounds (30%)
- As bicarbonate (HCO3-) ions (65%)
What are lobar bronchi?
Secondary bronchi
Why does a dog have very obvious external fissures between lung lobes yet a horse has barely any?
All to do with gait
Those species with a more bounding gait require greater freedom of movement, and hence more external separation
What is a the name given to the junction between cartilage and bone on ribs?
Costochondral junction
In which species is there obvious surface marbling of the lung?
Pig
Why is the lung a common site for spread of neoplasia and secondary infections?
There are no arteriovenous anastomoses in the lungs, meaning all blood must pass through a capillary bed. Therefore the lungs act as a sieve, filtering infectious agents, emboli and neoplastic cells from the blood.
In respiratory embryology, what is the difference between the positions of the left and right principal bronchi?
The right bronchus continues in a more midline position, while the left deviates laterally
Which bronchi supply the bronchopulmonary segments?
Segmental bronchi
Describe the 5 stages of development of the lungs
- Embryonic: from the formation of the laryngo-tracheal groove to the formation of segmental bronchi. Mucosal and submucosal glands develop in epithelium. Smooth muscle, cartilage and connective tissue form.
- Pseudoglandular: Lungs extend, conducting branches of the bronchial tree form and vascularisation begins.
- Canalicular: Airway lumens enlarge, respiratory bronchioles form
- Terminal sac: Respiratory bronchioles give off terminal sacs lined with cuboidal epithelium which organises into Type 1 and 2 alveolocytes. Surfactant production.
- Alveolar: Capillaries associate closely with alveolar lining. Surfactant production increases. Continues post-natally.
How does the early embryo achieve gaseous exchange?
Diffusion through uterine fluids
How does a foetus cope with its state of relative hypoxia? (2)
- Higher cardiac output ensures tissues receive more blood per minute
- Higher affinity of foetal haemoglobin for O2
What is meant by respiratory rate?
Number of breaths taken in one minute
What is the respiratory rate of a horse?
10-12 brpm
Movement of air occurs due to what?
Changes in the pressure inside the alveoli
What action does contraction of the external intercostal muscles have on the ribs?
Lifts them out and cranially
How are the lungs held against the thoracic wall?
By negative pressure within the pleural space
What action does contraction of the internal intercostal muscles have on the ribs?
Lifts the ribs caudally and inwards
How do you calculate compliance?
Increase in volume of lung
divided by
Increase in transpulmonary pressure
When may compliance be altered?
Some disease states, and in obese animals
Why do neonates often struggle to survive?
Inadequate production of surfactant which can lead to respiratory distress syndrome, which presents with severe dyspnoea (laboured breathing). Reduced surfactant means increased surface tension in the alveoli
Why, when a large alveolus adjoins a small alveolus, doesn’t the small alveolus collapse?
(Would expect collapse due to high surface tension)
The total amount of surfactant inside an alveolus is the same regardless of size; a small alveolus will have a higher concentration of surfactant, and hence a lower surface tension
How are horses able to reduce resistance to nasal airflow?
Have very distensible nares
Are able to reduce the size of blood vessels in their nasal passages
What make up the respiratory zone?
Respiratory bronchioles, alveolar ducts, alveolar sacs
Why is PAO2 (alveolar partial pressure) always lower in the alveoli than in the airways?
Because of the constant diffusion of O2 into the blood
What are the normal values for PAO2 and PACO2? (alveolar)
PAO2=100mmHg
PACO2=40mmHg
Why is hypoxia common in pulmonary disease?
Oxygen is not very soluble and is bound to haemoglobin, so over-ventilated alveoli can not transfer enough O2 to compensate for under-ventilated ones
What is meant by cooperative binding?
Binding of one O2 molecule to haemoglobin increases the affinity for other units of O2
What is meant by the chloride shift?
HCO3- (formed from CO2+H2O) diffuses out of RBCs in exchange for Cl- ions to maintain the electrochemical neutrality of the cell
What are the 2 kinds of vessels which supply the lung and what do they do?
Alveolar=capillaries which run in the alveolar septa and participate in gas exchange
Extra-alveolar=pulmonary arteries, arterioles, venules and veins which move blood to and from the lung
The blood supply of the lung is preferentially distributed where?
Why
To the dorsocaudal regions, due to the branching pattern of the arteries
How do you calculate pulmonary vascular resistance (PVR)?
(P pulmonary artery-P left atrium) / Q
P=pressure
Q=cardiac output
What is the net effect of sympathetic and parasympathetic innervation?
Sympathetic=vasoconstriction (a receptors; b receptors cause vasodilation)
Parasympathetic=vasodilation (action of nitric oxide on muscarinic receptors)
What stimulates the release of nitric oxide?
Parasympathetic nervous system
Mediators such as bradykinin
Released from endothelium in response to increased flow of blood in vessel, which causes shear stress to the endothelial cells
Which side of the heart does pulmonary circulation arise from?
Right
What are the inputs of the central pattern generator? (CPG)
Pulmonary stretch receptors, irritant receptors, muscle spindle stretch receptors and Golgi tendon organs, peripheral chemoreceptors, central chemoreceptors
What do the peripheral chemoreceptors monitor?
What about central chemoreceptors?
PaO2, PaCO2, arterial H+
PaCO2 only
What is the normal pH of blood in domestic animals?
7.4
Blood pH outwith what range is incompatible with life?
6.85-7.8
The greatest output of action potentials from peripheral chemoreceptors occurs when PO2 drops below what range?
60-70mmHg
Where is the respiratory centre of the brain?
Medulla oblongata
Which pH values are classed as acidosis and alkalosis?
Acidosis= 8.0
What are the 3 mechanisms that balance acidosis/ alkalosis?
Buffers-first line of defence, fast-acting
Lungs-second line of defence, fast-acting
Kidneys-take longer to act but have the highest capacity to effect change
What is the definition of a buffer?
A substance which can bind or donate H+ ions, thereby altering pH
What is the definition of a strong and weak acid?
Strong acid=one which dissociates completely in water, eg HCl. Makes a useless buffer
Weak acid=one which dissociates incompletely in water, eg H2CO3. Makes a good buffer
What role does myoglobin play in the respiratory system during exercise?
Oxygen stores are released at low cell pH
More CO2 -> more H+ -> low pH
Bronchodilation:
Which receptors are involved? What stimulates them? Sympathetic or parasympathetic?
B2 adrenoreceptors
Catecholamines
Sympathetic
Bronchoconstriction:
Which receptors are involved? What stimulates them? Sympathetic or parasympathetic?
Muscarinic receptors
Vagus nerve
Parasympathetic
Why would B blockers be contra-indicated in patients with asthma?
(Used to control cardiac tachyarrythmias)
Asthma causes bronchoconstriction
A side effect of B blockers is bronchoconstriction
What effect does increased cAMP have?
Bronchodilation
What are crystalloids?
Water-based solutions with small-molecular-weight particles, freely permeable to the capillary membrane
Buffered crystalloids contain what?
HCO3- or molecules (eg acetate, lactate) which are metabolised in the liver to form HCO3-
Balanced crystalloids contain what?
Electrolytes, in addition to Na+ and Cl-, making them similar to plasma
eg Lactated Ringers
What is a colloid?
A water-based solution with a molecular weight too large to freely pass across the capillary membrane.
Intravascular volume-replacing solution.
What is meant by respiratory rate?
Number of breaths taken in 1 minute
Between breaths (during the inspiratory and expiratory pauses), what is the pressure inside the alveoli?
Equal to atmospheric pressure: around 760mmHg at sea level
For inhalation to occur, alveolar pressure must be greater or less than atmospheric pressure?
What about exhalation?
Inhalation: less than
Exhalation: greater than
How is the size of the thoracic cavity increased during inspiration?
Diaphragm contracts, flattening caudally
External intercostals contract, lifting the ribs out and cranially
When might the pressure across the pleural space become positive?
Forced expirations eg coughing
What causes the lungs to expand in inspiration and prevents the lung from collapsing in expiration?
The change in pressure across the pleura
What follows an active expiration?
Passive inspiration
What do type II alveolar cells produce?
What does this contain?
Surfactant, which contains phospholipids, proteins and Ca2+
How does surfactant reduce surface tension?
Reduces the formation of hydrogen bonds between water molecules
Where is the speed of air flow greatest in the lungs?
Trachea and large bronchi
Why does inspired air consist of air and water by the time it reachews the lungs?
It is humidified in the airways
Which word means reduced PaCO2? (arterial PCO2)
Hypocapnia
What are the lobes of the right lung?
What about the left?
Right= cranial, middle, causal, accessory lobes Left= cranial (split into a cranial and caudal part), and caudal lobes
What is the function of the mucociliary escalator?
To remove foreign material and micro-organisms which managed to bypass the upper airway defences
What defines the division from bronchus to bronchioles?
Loss of cartilaginous rings which are replaced by smooth muscle
Loss of submucosal glands
What is the diameter of a bronchiole?
1mm
How is bronchiole structure maintained in the absence of cartilage?
Elastic tissue
Which cells are present in alveoli?
Type 1 alveolocytes (flattened epithelial cells)
Type 2 alveolocytes (produce surfactant)
Macrophages (phagocytose tiny foreign particles and infectious agents which reach the alveoli)
Why is the lung a common site for spread of neoplasia and secondary abscesses?
There are no arteriovenous anastomoses, which means all blood must pass through a capillary bed. It means the lungs acts as a sieve, filtering infectious agents, emboli and neoplastic cells from the blood.
Where does the lung receive its nerve supply from?
Pulmonary plexus. The vagus supplies the parasympathetic portion
What helps to stimulate expansion of the alveoli as the lungs develop?
Fluid in the foetal lungs, from secretion of alveolar cells and mucosal glands, plus some aspirated amniotic fluid
When do the carotid bodies develop their sensitivity to hypoxia?
First few weeks of life
Foetal haemoglobin has a higher affinity for O2 due to which 3 mechanisms depending on species?
In ruminants, foetal Hb is unresponsive to 2,3-DPG
In primates, foetal Hb has a reduced interaction with 2,3-DPG
Horses and pigs don’t have foetal Hb (only adult). The foetal erythrocytes contain a lower concentration of 2,3-DPG which means increased affinity for O2
(Increased 2,3-DPG causes a right shift-low O2 affinity)
Which part of the haemoglobin molecule does O2 bind to?
Haem unit (ferrous iron Fe2+)
Different types of Hb are defined by what?
The sequence of amino acids which make up the polypeptide chain of globin
In haemoglobin, what is globin?
A polypeptide which cradles the haem and prevents irreversible binding of the O2 to the ferrous iron (this would result in the oxidation of ferrous to ferric iron, and thus O2 would not be released at tissues)
How much oxygen can 1l of blood carry?
200ml
What is the average Hb concentration of mammalian blood?
150g/l
PO2 over which value yields only small increases in Hb saturation on a Hb saturation curve?
70mmHg
On a Hb saturation curve, Hb saturation drops rapidly when PO2 drops below which value?
60mmHg
What is the average tissue PO2?
40mmHg
CO2 is how many times as soluble as O2 in water?
1l of venous blood carries how much dissolved CO2?
20
29ml
The connective tissue sheath of the bronchovascular bundle is connected to what?
What is the clinical significance of this?
The visceral pleura
A drop in pleural pressure (eg on inspiration) causes a drop in pressure inside the bronchovascular bundle, leading to dilation of the vessels and the bronchus therein
In systemic circulation, what contributes the majority of resistance to bloodflow?
What about pulmonary circulation?
Arteriole
Capillaries
What is transmural pressure?
Pressure difference across the wall of the blood vessel
In which species is the smooth muscle layer in the small pulmonary arteries thin?
In which is it thick?
Thin= dogs, sheep, horses Thick= cattle and pigs, arteries are therefore very reactive
How does the CPG cause inspiration?
It rhythmically activates the neurones of the dorsal respiratory group, which stimulates the motor neurones innervating the external intercostal muscles and diaphragm
This causes contraction and hence inspiration
How does the CPG cause expiration?
The CPG activates expiratory neurones in the Bötzinger complex and ventral respiratory group of the caudal medulla oblongata
These send action potentials to the internal intercostal and abdominal wall muscles to force expiration
Explain the Hering-Breur reflex
Inspiration ceases in response to an ‘off switch’ in the pons which receives input from pulmonary stretch receptors. These prevent over-inflation of the lung.
Important in exercise and neonates
Where are irritant receptors located?
What are they stimulated by?
What kind of mechanisms do they initiate?
Epithelial lining of the airways
Stimulated by foreign material, deformation of the airways
Ones designed to protect the airways from further invasion eg coughing, bronchoconstriction, shallow breathing, increased mucous secretion
What is the function of golgi tendon organs and muscle spindle stretch receptors?
Located in respiratory muscles, particularly intercostals
Monitor the movements of the respiratory muscles to enable their strength of contraction to be modulated
Where are peripheral chemoreceptors located?
Carotid and aortic bodies
What do the carotid sinuses monitor?
Blood pressure
What are the carotid bodies innervated by?
Where are they located?
Glossopharyngeal nerve
Carotid bodies sit in the neck, close to the division of the common carotid artery into the internal and external carotid arteries
Where are the aortic bodies located?
What are they innervated by?
Around the aortic arch
Vagus nerve
What is the function of glomus cells?
Located in the carotid bodies, they depolarise when PO2 drops, sending action potentials to the brain via the carotid sinus nerve, to increase ventilation.
The greatest output of action potentials occurs when PO2 drops below 60-70mmHg
Where are central chemoreceptors located?
Brain
How is increased offloading of O2 in skeletal muscle achieved during exercise?
Increased temperature in working skeletal muscle during exercise. Affinity of Hb for O2 drops at higher temperatures, hence increased offloading.
ALSO
More CO2 during exercise, so increased carbaminoHb. Lower pH. Reduced affinity of Hb for O2, hence faster offloading at tissues.
Exercise causes increased O2 consumption by skeletal muscle. How does the respiratory system compensate for this?
Increased cardiac output
Increased RBCC
Increased respiratory rate and depth (tachypnoea and hyperpnoea)
Increased diffusion gradient for O2 at tissues
Myoglobin (oxygen stores released at low pH)
Lower affinity of Hb for O2 (hence faster offloading to skeletal muscle)
How is RBCC increased during exercise?
What is a problem with increased RBCC?
Short term= splenic contractions to release more RBCs
Longer term= increased erythropoietin production (hormone which produces RBCs)
Increased blood viscosity, increased cardiac workload
Bronchial diameter varies in response to what 3 things?
Autonomic nervous system
Non-adrenergic-non-cholinergic nerves, which cause release of bronchodilators such as nitric oxide
Bronchoconstriction response to irritant receptors in the airways
What is the net effect of the sympathetic nervous system on the bronchioles?
What about parasympathetic?
Bronchodilation, mediated by smooth muscle β2 adrenoreceptor stimulation by circulating catecholamines
Parasympathetic: bronchoconstriction via vagal stimulation of smooth muscle muscarinic receptors
What effects do the sympathetic and parasympathetic nervous systems have on mucus production in the airways?
Sympathetic: increases mucociliary clearance by causing the cilia lining the airways to beat faster, and reduces the release of inflammatory mediators from mast cells
Parasympathetic: increases mucus production
Name a drug which can be used to treat bronchoconstriction
B2 adrenoreceptor agonist, eg terbutaline, albuterol, clenbuterol, salbutamol
How do indirect cholinergics increase the activity of the parasympathetic nervous system?
What is a side effect?
Inhibiting the enzyme acetylcholinesterase to increase ACh at the synapse
Bronchoconstriction
What effect does cAMP have on bronchioles?
Causes bronchodilation
Give 2 examples of anti-tussives
Codeine and butorphanol
What are mucolytics used for?
To decrease the viscosity of bronchial secretions so they may be more readily moved by cilia and coughed up
What is the function of expectorants?
Increase fluidity of bronchial secretions to increase particle clearance
What is the function of decongestants?
Reduce nasal mucosa thickness to enable easier passage of air
What is the only respiratory stimulant used in veterinary practice?
How does it work?
Doxapram hydrochloride
It increases the sensitivity of the chemoreceptors to increase respiratory rate and tidal volume
When administering aerosols, what particle size is required to target the:
Trachea
Distal airways
Trachea= 2-20 microns
Distal airways= 0.5-5 microns
What kind of cartilage are the laryngeal cartilages made from?
Hyaline
Which is the only laryngeal muscle to open the glottis?
What is it innervated by?
Cricoarytenoideus dorsalis
Caudal laryngeal nerve (from recurrent laryngeal)
Name the muscles of the larynx
State their functions and innervations
Cricothyroid (tenses the vocal fold) (cranial laryngeal nerve) Cricoarytenoideus dorsalis (opens the glottis) (caudal laryngeal nerve) Cricoarytenoideus lateralis (closes the glottis) (caudal laryngeal nerve) Thyroarytenoideus (constricts the glottis) (caudal laryngeal nerve)
Which epithelium lines the alveoli?
Simple squamous
Which epithelium lines the bronchi?
What about bronchioles?
Pseudostratified columnar with a peribronchial sheath-a thick layer of connective tissue containing cartilage plates and serous glands
Cuboidal
Where are lymphocytes usually located in the airways? Why?
Located where the airways branch, because the branching causes slight turbulence in airflow, and pathogens/particles are thrown against the epithelium in these regions
What is the function of peribronchial and periarterial sheaths?
Holds all the nerves and ducts together in the tissue of the lamina propria
What does it mean if both pulmonary arteries and veins are associated in an airway?
They are nearing the hilus of the lung (where the airways, blood vessels, lymphatic vessels and nerves enter/leave the lung)
What epithelium is present in the trachea?
Pseudostratified columnar, cilia, goblet cells
Describe innervation to the lungs
Nerve supply to the lungs is via the pulmonary plexus within the mediastinum
The pulmonary plexus consists of sympathetic fibres largely from the Stellate ganglion, and parasympathetic fibres from the vagus nerve
