Respiratory System

Year 1 - Semester 2

respiration

the exchange of gas at the alveoli

ventilation

the movement of air through the airways

Which structures are included in the respiratory zone?

alveoli

Which structures are included in the ventilatory zone?

all tubes that transport air from the atmosphere to the alveoli

Which structures form the boundaries of the thorax?

thoracic inlet, diaphragm, ribcage, thoracic spine

What is the diaphragm?

a dome shaped musculotendinous sheet which allows air movement in the thorax to occur

Where does the costal portion of the diaphragm attach?

xiphoid process of the sternum and costochondral junctions of ribs 8-12

Where does the crural portion of the diaphragm attach?

ventral surfaces of L1-L4

pleura

a double layer of simple sqamous epithelium lying on connective tissue which lines the thoracic cavity

what are the 2 layers of the pleura?

visceral and parietal

pleural sac

the potential space between the parietal and visceral pleura which contains a small amount of fluid to enable the lung lobes to move freely over one another and other structures, it has a negative pressure

Where is the visceral pleura found?

attached to the lungs

Where is the parietal pleura found?

attached to the body wall

What are the 3 sections of the parietal pleura?

mediastinal, costal, diaphragmatic

Where is the mediastinal pleura found?

surrounding the mediastinum

Where is the diaphragmatic pleura found?

lining the diaphragm

Where is the costal pleura found?

lining the inner surface of the ribs

Plica vena cava

a fold of pleura in which the caudal vena cava runs to the heart

What is the importance of the negative pressure in the pleural sac?

It holds the lung against the body wall

Pathway of air into the body

1. external nares/ nostrils

2. turbinates/ conchae in nasal cavity

3. nasopharynx

4. vestibule through the glottic cleft

5. larynx

6. trachea

turbinates/conchae

4 scrolls of bone lined with vascular mucosa which contains mucous glands, left/right dorsal/ventral

function of turbinates/conchae

To warm, humidify and filter air

meati

the 4 interconnected pathways through the nasal cavity created by the tubrinates/conchae

How does the epiglottis protect the trachea?

It diverts food material away from the airway toward the oesophagus to prevent aspiration of food

What happens when something contacts the vestibular mucosa?

An immediate reflex cough is stimulated

How do the vocal folds protect the trachea?

They close which blocks the glottic cleft during swallowing

structure of the trachea

incomplete rings of cartilage joined by tracheal muscle form a fibrocartilaginous framework held by elastic connective tissue, the interior is lined with ciliated mucosa and exterior has a connective tissue layer

How do the trachea in cats and dogs differ from other species?

the tracheal muscle sits outside cartilage rings while it sits inside in other species

tracheal bronchus

an extra bronchus above the true left and right primary bronchi on the right hand side which supplies the cranial lobe of the right lung

which species is a tracheal bronchus found in?

ruminants and pigs

lobes of the right lung

cranial, middle, caudal, accessory

lobes of the left lung

cranial and caudal

how many primary bronchi are there?

2

Where do the primary bronchi split into secondary/lobar bronchi?

At the lobes of each lung

Which lung lobe does a horse lack?

right middle

How does the appearance of dog and horse lungs differ?

horse lacks a right middle lobe, dog has very obvious external fissures between lobes and horse has little external division

bronchopulmonary segment/ primary lobule

portion of lung tissue supplied by a tertiary bronchus, separated from others by connective tissue

What causes the marbled appearance of some lungs?

connective tissue dividing bronchopulmonary segments connects with the visceral pleura

what type of epithelium lines the airways of the ventilation system?

pseudostratified ciliated columnar containing goblet cells and submucosal glnads

mucociliary escalator

the movement of cilia which pushes mucous in the opposite direction to air, allowing mucous to move up the trachea and out of the mouth via coughing to expel particles it has trapped

What happens to bronchi as they continue to divide?

they gradually lose cartilage rings and gain smooth muscle

terminal bronchioles

the last division of bronchioles before the respiratory zone

features of terminal bronchioles

no cilia, goblet cells or submucosal glands

features of respiratory bronchioles

alveolar outpouchings in walls enable gas exchange to occur, bronchioles feed into alveolar ducts and sacs

what type of epithelium are type 1 alveolocytes?

simple squamous

what type of epithelium are type 2 alveolocytes?

cuboidal

function of type 1 alveolocytes/pneumocytes

to allow alveoli to participate in gas exchange

function of type 2 alveolocytes/pneumocytes

to produce surfactant and alveolar macrophages

where are club/clara cells found?

in terminal bronchioles

function of club/clara cells

to detoxify pollutants, secrete proteins and produce some surfactant (replace cilia and goblet cells)

bronchovascular bundle

a bundle of connective tissue containing a bronchus, artery and vein which is found in bronchopulmonary segments

Which vessels supply the tissues of the lung with oxygen?

bronchial arteries

Which vessels drain the tissues of the lung?

bronchial veins which empty into the azygous vein

which nerve provides parasympathetic innervation to the lungs?

vagus nerve

which plexus provides innervation to the lungs?

pulmonary plexus

how can blood supply to the lungs be modified?

via sympathetic and parasympathetic nerve vessels

Which structures are the sympathetic nerve supply able to innervate in the lungs?

blood vessels only

How are airway smooth muscles controlled?

adrenaline and noradrenaline acting on B2 adrenoreceptors

eupnoea

normal breathing

resting respiratory rate

number of breaths taken in a minute at rest

tachnypnoea

increased respiratory rate

hyperpnoea

increased respiratory depth

dyspnoea

increased respiratory effort

apnoea

absence of breathing

bradypnoea

decreased respiratory rate

Which direction do external intercostal muscles run?

caudoventrally

What prevents the lungs from collapsing during expiration?

negative pressure within the pleural space

What happens during inspiration at rest?

the diaphragm contracts and flattens caudally and external intercostal muscles contract and lift the ribs out and cranially which increases the volume of the thoracic cavity, lungs expand due to negative pressure in the pleural space

What happens during expiration at rest?

elastic properties of the lungs and muscles cause recoil of the thorax which increases pressure inside the alveoli above atmospheric pressure which forces air out

What happens during active expiration?

abdominal muscles contract and push abdominal contents cranially which forces the relaxed diaphragm to dome up into the thorax and costal portions of the internal intercostal muscles pull the ribs caudally and inwards which reduced the volume of the thorax and increases pressure inside the alveoli

What usually follows active expiration?

passive inspiration

Which species has active and passive phases to both inspiration and expiration?

horse

which species has an active phase of expiration at rest?

dogs

compliance of lungs

the degree to which a decrease in transpulmonary pressure leads to an increase in volume of the lungs (ability of lungs to expand to take up air when pressure decreases)

which factors determine the compliance of the lungs?

elasticity of the lungs and thoracic cage and surface tension in the alveoli

how is surface tension created in the alveoli?

fluid which lines the alveoli to facilitate diffusion and dissolution of gases forms hydrogen bonds between water molecules

why is surface tension a problem in the lungs?

it reduces surface area of the alveoli and resists expansion of the lung by creating an inward force that promotes alveolar collapse and causes fluid to be drawn into air spaces

function of surfactant in alveoli

to reduce the formation of hydrogen bonds between water molecules to reduce surface tension in alveoli

how does the size of alveoli affect their internal pressure?

smaller alveoli have a higher internal pressure which would cause them to collapse if they didn’t have a higher concentration of surfactant to balance it out

why do premature neonates often struggle to breathe?

They are not yet producing enough surfactant so lungs cannot fully expand

How is the release of surfactant stimulated in adults?

by sighing

Why is resistance in the lower airways lower during inspiration?

they are distended during inspiration as bronchial connective tissue is attached to the visceral pleura so is pulled open when the lungs expand

Why is resistance in the upper airways higher during inspiration?

the negative pressure generated to pull air into the lungs tends to collapse the compliant, non-rigid airway walls and turbulence is greater as the speed of flow of air is the highest

which nervous system innervates the smooth muscle in airway walls?

autonomic

How does the sympathetic nervous system affect airways?

beta-2 adrenoreceptors are stimulated which causes the airways to dilate

How does the parasympathetic nervous system affect the airways?

causes constriction

tidal volume

the volume of air moved during a respiratory cycle

What is the average tidal volume in a normal resting dog?

10ml/kg

formula for minute ventilation

tidal volume x respiratory rate

residual volume

the volume of air that remains in the lungs after a full expiration

A

inspiratory reserve volume

B

vital capacity

C

total lung capacity

D

tidal volume (at rest)

E

expiratory reserve volume

F

residual volume

G

functional residual capacity

functional residual capacity

the total amount of air left in the lungs after a nromal expiration at rest

fraction of a gas

the proportion of a gase mixture that consists of the gas of interest

partial pressure of a gas

the pressure exerted by a specific gas within a gas mixture