Respiratory system Flashcards
Function of the respiratory system
Major function - supply oxygen to body and remove CO2
Phonation (voice production)
Assist with body temperature control
Regulation of acid-base balance
Sense of smell (olfactory sense)
Respiration occurs on three levels in the body
External
Internal
Cellular respiration
External respiration
The physical act of getting oxygen in and carbon dioxide out of the body
Internal respiration
The exchange of oxygen and carbon dioxide between the blood and the cell
Cellular respiration
Which involves the production of ATP by the cell
Upper respiratory tract contains
Nose, nasal cavity, nasal sinuses, pharynx, larynx and trachea
The external structure of the nose contain
External Nares or Nostrils.
Supported by nasal cartilages
Opened by muscles
Dilated nostrils are a sign of
are a sign that the animal is having trouble getting enough oxygen for its metabolic needs
The nose is lined with
hair to filter larger air-borne particles
The skin surrounding the nostril
is continuous with, and forms part of, the muzzle
Covered with hair and contains sebaceous and sweat glands.
More rigid in rooting animals
Function of the nose
Functions to warm, humidify, and filter air before it reaches the lungs
Highly vascular, so any trauma causes significant hemorrhage
Sneezing and coughing results when inflammation and debris irritate the sensitive mucosa
Expels harmful substances
Nasal cavity is
Separated from the mouth by the hard and soft palates
Nasal Conchae or Turbinates - bony scrolls lined with mucous membranes
Nasal conchae or Turbinates
Protect against noxious gasses and trap particles.
Numerous blood vessels below mucous membrane help warm the inspired air.
Layer of mucus
Naso lacrimal ductus
Drain excess tears from the eyes into the nasal cavity
Median Nasal Septum
Separates the nasal cavity into right and left halves
Nasal meatus
pathways between the conchae or turbinates
Ventral Nasal Meatus runs just dorsal to the hard palate.
Route for passing a stomach tube
Route for passing a stomach tube
Tube is directed medially
and ventrally through the ventral nasal meatus to the nasopharynx
Very vascular area: if the
tube is not manipulated gently, bleeding will occur
paranasal Sinuses
All domestic species have maxillary, frontal, sphenoid, and palatine sinuses
Sinuses are bilaterally symmetrical, mucous membrane lined and air-filled
Reduce weight of skull
Clinically, they are infection prone
Important in dentistry of the horse, dog and cat and in dehorning in cattle
Pharynx
The common passageway that connects the:
Oral cavity with the esophagus =
OROPHARYNX
Nasal cavity with the larynx = NASOPHARYNX
A common passageway for both food and air
Openings into the pharynx are - the mouth, 2 caudal nares, 2 eustachian (auditory) tubes, esophagus, and larynx
Nasopharynx
Floor is formed by the soft palate
Openings of auditory tubes:
Connect middle ear to nasopharynx
Equalize pressure on both sides of ear drum
Laryngopharynx
Common to both digestive and respiratory passages
Inspired air passes through the nasal cavity and enters the caudal nares
Passes through the pharynx to enter the larynx (voice box)
Food enters from the mouth, passes through the pharynx, and is forced into the esophagus by contractions of the pharyngeal muscles
Larynx is closed by the epiglottis.
Swallowing involves a complex series of actions
Stopping breathing
Covering the opening into the larynx (the glottis)
Moving the material to the rear of the pharynx
Opening the esophagus
Moving the material DORSALLY into the esophagus
Larynx are joined to the pharynx by
The voice box
Mucosa-lined, cartilaginous tube
joining the pharynx to the trachea
Larynx functions
Directs air to the trachea
Prevents the aspiration of ingesta
Houses the vocal organs
Made of segments of cartilage connected to each other and surrounded by muscles
Larynx is
Larynx is supported by the hyoid apparatus
Very delicate structure – need to be gentle when intubating and extubating animals
** Cats are very prone to laryngospasm
The pattern and number of laryngeal cartilages varies among species
Major cartilages of the larynx
Epiglottis
Arytenoid cartilages (paired)
Thyroid cartilage (adam’s apple)
Cricoid cartilage
The epiglottis
The epiglottis is leaf-shaped and is located rostrally
Projects forward from the ventral portion of the larynx
Tip is usually tucked up dorsal to the caudal rim of the soft palate while the animal is breathing
What is the function of the larynx while swallowing
Epiglottis is pulled back to cover the opening of the larynx (the glottis),
Prevents the swallowed material from entering the larynx
Arytenoid cartilages attach
The vocal folds
The thyroid cartilage in the larynx
Articulates with the hyoid apparatus
Attaches muscles associated with swallowing and phonation
Cricoid Cartilage in the larynx
Connects the thyroid cartilage to the trachea
Maintains the shape of the larynx so air may pass through
Vocal folds
The laryngeal cavity - contains the vocal folds which run from the arytenoid cartilages to the interior floor of the thyroid cartilage
What forms the glottis
Arytenoid cartilage and the vocal cords form the boundaries of the glottis (opening into the larynx)
The three main functions of the larynx
Voice production
Prevention of aspiration of foreign bodies
Control of airflow to and from the lungs
Voice production of the larynx
Causes phonation by relaxing and tightening the vocal cords as air pass over them causing them to vibrate
The pitch can be changed from a low pitch (relaxed vocal cords – open glottis) to a high pitch (tightened vocal cords – closed glottis)
Prevention if aspiration of foreign bodies larynx
Mainly through the trapdoor effect of epiglottis and muscle contractions which pull entire larynx forward and fold the epiglottis back over its opening
Backed up by vocal folds
Can meet in the midline to close the glottis
Control of airflow to and from the lungs larynx
By adjusting the size of the glottis with the vocal folds and by closing the glottis with the epiglottis
Trachea divides into two main bronchi at the
Tracheal Bifurcation or Carina
Occurs at about the level of the heart
Trachea is composed of
Trachea is composed of C-shaped hyaline cartilage with the opening of the “C” dorsal
Prevents the trachea from collapsing on inspiration
Allows the trachea to change in size
Trachea is lined with
Trachea is lined with pseudostratified ciliated mucosa, like the nasal passages
Works to trap foreign bodies
Trapped material is moved cranially towards the pharynx where it is swallowed
Trachea and mucous
Mucous helps trap foreign bodies
If there is large amount of dust in the air then an increased amount of mucus is produced
Accumulates and irritates the lining of the trachea
Stimulates coughing which clears the passageway
Lower resp tract
Starts with the bronchi and ends with the alveoli
Includes all the air passages in between
All the structures of the lower portion of the respiratory tract are located in the lungs
Bronchial tree
Air passages from bronchi to alveoli are collectively called the bronchial tree because the divide into smaller and smaller branches, just like a tree
Bronchioles
Bronchi divide into smaller bronchi until they are tiny bronchioles
These branch smaller. The smallest branches called alveolar ducts which terminate in alveolar sacs
Alveolar sacs look like a bunch of grapes
Smooth muscles in the bronchial tree allows for
bronchodilation (with relaxation of the smooth muscle) during increased oxygen demand and bronchoconstriction during rest
Bronchoconstriction
Can also get bronchoconstriction with irritants in the lungs – can lead to breathing difficulty. Examples are:
Feline asthma (allergic bronchitis)
Horses get ‘heaves’, a chronic allergic condition, usually to dust and fungal spores in hay
Alveoli
Numerous alveoli make up each alveolar sac
Sites for gas exchange
Alveoli are tiny, thin walled sacs
Surrounded by a network of capillaries
Alveoli contain
surfactant that reduces the
‘stickiness’ (surface tension) of the alveolar walls: assists in expansion during breathing and helps prevent complete lung collapse
Very important with premature babies
Surfactant often not properly formed
Contributor to non-viability of premature animals
Function of the lung
to exchange oxygen for carbon dioxide in the blood
Shape of lung
Each lung is a cone-shaped structure with its base at the diaphragm and apex close to the thoracic inlet
Lateral side of each lung is in contact with the thoracic wall
Except at the cardiac notch where it is in contact with the heart
Structure of the lung animal specific
Left cranial and caudal lobe
Left cranial lobe is partially subdivided and some call the caudal part the left middle lobe
Right cranial, middle and caudal lobe and an accessory lobe.
Horse: left and right lobes and an accessory lobe
Hilus
Each lung has a small, well defined area on its medial side called the hilus where air, blood, lymph and nerves enter and leave the lung
The only area of the lung that is “fastened in place”
Standard necropsy test on lungs to see if animal was born dead or alive
Cut a piece of lung and place it in some
water:
If lung sinks - no air ever entered
the lungs and the animal was born
dead
If lung floats - air has entered the
lungs so newborn was born alive
Blood supply to and from the lungs is
pulmonary circulation
The blood vessels get smaller and smaller as they branch their way down to the alveoli
Capillaries are and functions as
Capillaries network around each alveolus of the alveolar sac
The capillaries are so small that only one blood cell can move through the
vessel at a time
Ideal for CO2 to diffuse from the blood cell into the alveolus and O2 from the alveolus into the blood cell
Boundaries of the thoracic cavity
Dorsally: the thoracic vertebrae
Laterally: the ribs
Ventrally: the sternum
Caudally: the diaphragm
Cranially: 1st pair of ribs, 1st thoracic
vertebrae and cranial part of sternum
(manubrium)- this area is known as the
thoracic inlet
Thoracic cavity
Main contents are the lungs, heart, large blood vessels, nerves, trachea, esophagus, lymphatic vessels and lymph nodes
Note: the diaphragm is a thin sheet of skeletal muscle and the primary muscle used in respiration
Pleura
A thin membrane which covers the organs and structures in the thorax and lines the inside of the thoracic cavity.
Parietal pleura – lines the thoracic cavity
Visceral pleura – covers the thoracic organs
Between the pleura
Between the two pleura is a space containing a small amount of lubricating fluid
Ensures that no friction occurs during movement (especially breathing)
Mediastinum
Mediastinum – the junction of these 2 serosas near the thoracic midline
The portion of the thorax between the lungs that contains the heart and all the other thoracic structures
Except the lungs
Respiration
Air is drawn into the lungs
Oxygen is transferred from the alveoli into the blood.
CO2 in the blood is moved into the lungs
The waste CO2 is expelled into the environment
Inspiration
Process of drawing air into the lungs – inhalation
Power is provided by the diaphragm and the external intercostal muscles
Diaphragm is normally dome-shaped – it contracts and flattens on inspiration
Normal resting (abdominal) respiration
External intercostals are found between the ribs
Pull the ribs up and forward to expand the thoracic cavity
May be assisted by the shoulder, neck, and chest muscles
Stretching limb forwards during running helps expand the chest, landing compresses the chest
Forced expiration
Forced expiration is powered by the internal intercostal and abdominal muscles
Internal intercostals are found between the ribs deep to the externals
Pull caudally and rotate the ribs to
decrease thoracic volume
Abdominal muscles contract and push abdominal organs against the diaphragm to restore the dome shape and decrease thoracic volume
Dyspnea
Increased respiratory activity and effort- difficulty breathing
Apnea
Absence or cessation of breathing
Hypernea/hyperventilation
Increase in both rate or depth of breathing or both
Tachypnea/polypnea
Shallow rapid breath
Normal resp rate of bovine
18-20brpm
Normal resp rat of porcine and equine
8 to 16 brpm
Tidal volume
volume of air exchanged during ONE BREATH
Varies depending on the needs of the animal – exercising vs rest
Minute volume
volume of air exchanged
during ONE MINUTE of breathing
Equals the tidal volume X number of breaths
per minute
Residual volume
volume of air remaining
in the lungs after maximum expiration
Vital capacity
maximum amount of air
that can be expired after a maximal
inspiration
Total lung capacity
Vital capacity + residual volume
Exchange of gases in alveoli
Room Air contains about 20% oxygen and about 0.03% carbon dioxide
Blood entering lung capillaries has a much higher concentration of carbon dioxide and a lower concentration of oxygen
Oxygen and carbon dioxide diffuse through the capillary and alveolar walls down their concentration gradients
Results in a movement of carbon dioxide from the blood into the alveoli and oxygen from the air in the alveoli to the blood
Exchange rate is affected by what in alveoli
Exchange rate is affected if the distance the gas must cover increases – e.g. interstitial fluid (edema) in the lung
Can severely impact the amount of O2 absorbed!
Laryngeal edema
from inhalation of irritants, trauma from endotracheal intubation, or excessive panting in brachycephalic and obese dogs
If part of the lung collapses
If part of the lung collapses or has airway obstruction, oxygen levels in the alveoli decrease and the body responds with a local hypoxic vasoconstriction
This decreases the blood circulating through parts of the lung that aren’t allowing good gas exchange
Problem in generalized hypoxia
such as high altitude, it creates overall vasoconstriction in the lungs
Leads to increase in vascular resistance
Results in pulmonary hypertension
Causes right heart to work harder to pump against the resistance
May lead to right heart failure and peripheral edema
High mountain disease in cattle
Partial pressure of gasses
Total pressure of a mixture of gases is the
sum of pressures of each individual gas
Therefore each individual gas has its own pressure that is part of the total atmospheric pressure – i.e. it has a partial pressure
Gases can also have a partial pressure dissolved in a solution
Control of breathing
Muscles involved in breathing are under
voluntary control
The process of breathing is normally under
involuntary control
Control of breathing By the respiratory center in the brainstem
Has different control centers for inspiration,
expiration, and breath holding
All are subconscious
Can be overridden by conscious control
Medullary rhythmicity area
responsible for setting the rate
Primarily works through the inspiratory area (expiration is the passive result of inspiratory effort ending)
Has an automatic rhythmic signal for inspiration
Control of breathing is signaled by
Signal travels down the phrenic nerve to the diaphragm and through the intercostals nerves to the external intercostals muscles
Expiratory area is usually only activated during forced expiration
two main systems to control breathing
Mechanical control
and Chemical control
Mechanical control of breathing
Sets limits on normal inspiration and expiration
Works through stretch receptor in the lung
Receptors feed back to the respiratory center, which signals the muscles of inspiration and expiration
Chemical control of breathing
Chemoreceptors monitor CO2, pH, and O2 contents in the blood
Located in the brain, carotid artery and aorta.
Signals the respiratory center if any of these are out of balance
Concentration of O2 and CO2 effect breathing
Rising concentration of CO2 is more important than decreasing concentration of O2 in terms of stimulating breathing
CO2 and pH are linked if CO2 is high, this drives pH down and blood becomes acidic
By increasing respiratory rate, the body can ‘blow off’ the excess CO2 and bring the pH back to normal
If artificial ventilation is provided at too high of a rate during surgery
May blow off too much CO2
Animal may compensate by a period of breath-holding (apnea) until the CO2 levels rise enough to stimulate breathing again
Oxygen sensors
Signal to increase rate with mild hypoxia
With severe hypoxia the neurons may become too depressed to signal
may
lead to respiratory failure
Cough
protective reflex stimulated by irritation in the trachea or bronchi
Requires pressure against a closed glottis, then sudden release
Can be productive or non-productive – treated very differently
Sneeze
protective reflex stimulated by irritation in the
nasal passages
Yawn
slow deep breath stimulated by decrease in O2
levels in blood, by boredom, drowsiness, fatigue, or
anxiety
Sigh
deeper than normal breath that may be stimulated by decrease in O2 levels in the blood
Can be beneficial to give an occasional ‘sigh’ breath to anesthetized animals
Hiccups
spasmodic contraction of the diaphragm with a sudden closure of the glottis – usually temporary and harmless
Panting
mechanism to dissipate heat –increased
respiratory rate with decreased tidal volume
Primarily moves air through the upper airways to exchange heat
Physiological dead space
The part of the respiratory system where there is no
gas exchange.
Important during anesthesia. If a long endotracheal tube is placed with a long piece protruding, physiological dead space increases and reduces gas exchange.
Emphysema
destruction of alveolar
membranes leads to larger lung chambers and decreased surface area available for gas exchange
Atelectasis
is collapse of the alveoli – often results from airway obstruction or lack of surfactan
Stridor
High pitched, upper resp problem
Stertor
Low pitch, flaccid tissue vibrating in the airway
Sinusitis
Inflammation and congestion of the paranasal sinuses
Can become so severe it obstructs drainage – very painful
May require surgical intervention – trephinate to drain
Dorsal displacement if the soft palate
with vigorous exercise the soft palate rises and the epiglottis falls below it, reducing the diameter of the nasopharynx
Laryngeal hemiplegia
Afflicted horses are known as “Roarers”.
Paralysis of the recurrent laryngeal nerve (usually the left)
May be due to injury or genetics
The vocal cords hang slack in the tracheal lumen and cause “roaring” sound when expired air passes over them during exercise, hence the name
Obstructs air flow
Can be surgically fixed – laryngeal tie-back or laryngeal ventriculectomy (removal of the ventricle on the affected side so the scar tissue holds the vocal fold out of the way of the air flow)
Laryngeal paralysis
Like laryngeal hemiplegia but in dogs
Older dogs with noisy respiration
Heaves
(RAO – Recurrent Airway Obstruction) similar to chronic obstructive pulmonary disease – COPD in humans
Chronic allergic disease of the horse characterized by constricted airways, laboured respiration, chronic cough, and lack of stamina. The horse is alert and does not have a fever.
The disease is most common in stabled horses
Average age of onset is 9-12 years
Course of disease is progressive
Pneumothorax
Free air in the chest
Can result from a hole in the chest wall and/or from a punctured lung
The problem may be self-limiting and the air absorbed
If large volumes of air enter the pleural cavity, the lung will collapse
Pleural effusion
An abnormal accumulation of fluid in the pleural space.
Reduce ability of the lung to inflate. Lung lobes “float” in pleural fluid.
Several causes: fluid can accumulate from heart failure, hemorrhage, lymph vessel leakage, pus, cancer
Pulmonary edema
An abnormal accumulation of fluid in the airways and alveoli.
Associated with circulatory disorders such as left ventricular failure, anaphylactic shock or severe allergies
Auscultation of the chest may reveal fluid sounds
Pneumonia
Inflammation of the lung.
Usually reserved for infectious causes
Pneumonitis for non infectious
More serious and potentially life-threatening than bronchitis
Mucus and fluids can accumulate and plug sections of the lungs, decreasing body’s ability to exchange gasses
Note: aspiration pneumonia can occur if an anesthetized animal is not intubated or is extubated too early. Also with administration of mineral oil, etc.
Diaphragmatic hernia
is usually the result of trauma (H.B.C.’s in particular) but can also be congenital
Depending on the size of the opening and whether abdominal contents have entered the chest, the animal may or may not show symptoms
Can be life-threatening, particularly if the abdomen is opened and the hernia has not been diagnosed
A considerable volume of abdominal viscera may gradually pass through a relatively small tear because of the negative pressure in the thorax.
