1. Structure and function of the respiratory tract

Question 1

Give four functions of the respiratory system

Answer 1

1. Take up of oxygen and removal of CO2
2. Acid/base balance
3. Immune regulation
4. Metabolism of vasoactive compounds

Question 2

What is oxygen tension?

Answer 2

Same concept as the partial pressure

Question 3

What is tidal volume?

Answer 3

1/3 of lung volume that is breathed in and out

Question 4

What is inspiratory reserve volume?

Answer 4

Lungs are completely inflated

- 2/3 of lung capacity at rest

Question 5

What is inspiratory capacity?

Answer 5

Inspiratory reserve volume + tidal volume

Question 6

What is expiratory reserve volume?

Answer 6

Deep breath out

Question 7

What is residual volume?

Answer 7

Air that is left after the respiratory cycle is completed

Question 8

What is the functional residual capacity?

Answer 8

Amount of remaining air after normal tidal breathing

Question 9

How is vital capacity calculated?

Answer 9

Inspiratory capacity + expiratory reserve volume

Question 10

Why do structures in the thorax appear shiny?

Answer 10

Covered by epithelial membrane called the pleura

Question 11

Describe species variation in the left lung

Answer 11

All domestic species have two lobes (cranial and caudal)
- cranial clearly divided into two parts both supplied by the same bronchus
Horse = looks like one large lobe but anatomically there is two

Question 12

Describe species variation in the accessory lobe

Answer 12

Ventral midline between caudal lobes of left and right lung

Own pleura = mediastinal recess

Question 13

Describe species variation in the right lung

Answer 13

Four lobes - cranial, middle, caudal and accessory (sits underneath the heart in ventral midline between caudal lobes of left and right) - not horse
Ruminants = looks like five lobes but the two most cranial are supplied by the lobar bronchus
Ruminant and pig = cranial lobe supplied by tracheal bronchus

Question 14

What is the visceral (pulmonary) pleura?

Answer 14

Attached to the surface of lung including fissures

- contains abundant elastic fibres

Question 15

What is the parietal pleura?

Answer 15

Derived from somatic mesoderm
Lines the walls of the pleural cavity
Divided into three compartments:
1. Costal pleura lines inside of lateral wall of rib cage
2. Mediastinal pleura lines the mediastinum
3. Diaphragmatic pleura lines the cranial surface of the diaphragm

Question 16

What is the mediastinum?

Answer 16

Partition between left and right pleural sacs

Contained within own fold of parietal pleura - plica venae cavae

Question 17

How is the mediastinum formed?

Answer 17

Apposition of mediastinal pleura of right and left pleural sacs with connective tissue filling between

Question 18

What structures does the mediastinum contain?

Answer 18

Heart in pericardiac sac 
Thoracic trachea + oesophagus 
Thymus 
Mediastinal LN 
Great vessel 
Nerves

Question 19

What is the epiglottis and what is its function?

Answer 19

Cartilage that can move and fold over the opening of the trachea
- protects respiratory tract from inspiration of food or water

Question 20

What is the pharynx?

Answer 20

Common cavity through which air and ingested material pass

- connects oral cavity with oesophagus and nasal cavity with larynx

Question 21

Describe the location of the pharynx

Answer 21

Dorsally - bordered by the base of the skull and the two cranial cervical vertebrae
Ventrally - bordered by the larynx and the mandible
Laterally - bordered by the pterygoid muscles and suspensory part of the hyoid apparatus
Soft palate - separates the rostral part of the pharynx into dorsal and ventral portion into nasopharynx and oropharynx

Question 22

What is the larynx?

Answer 22

Bilaterally symmetrical tube-shaped musculocartilagenous organ
- connects pharynx to trachea

Question 23

What is the function of the larynx?

Answer 23

Protects the trachea preventing aspiration of foreign material during swallowing
Increases intra abdominal pressure
Vocalisation

Question 24

How is the larynx formed?

Answer 24

Walls are formed by the laryngeal cartilages and connecting muscles and ligaments
Join the larynx to hyoid apparatus rostrally and trachea caudally

Question 25

Describe the clinical importance of the caudal (recurrent) laryngeal nerve

Answer 25

Paralysis usually of the left recurrent laryngeal nerve results in stertorous sound produced at inspiration

• caused by air flow passively vibrating a lax adducted vocal fold
• paralysis of dorsal cricoarytenoid muscle which is an abductor of arytenoid cartilage and vocal fold

Question 26

What are theories surrounding the paralysis of the caudal laryngeal nerve?

Answer 26

Particularly prevalent in racehorses which could be due to high cardiac output
- changes in pressure of the aorta cause paralysis of the left recurrent laryngeal nerve

Some dogs in later stages of life

Question 27

How might a paralysed caudal laryngeal nerve be treated?

Answer 27

Tieback operation which keeps the vocal chords open

Question 28

What are the conducting airways?

Answer 28

Trachea to terminal bronchioles

• no gas exchange
• anatomic dead space

Question 29

What is the respiratory zone?

Answer 29

Respiratory bronchioles to alveoli

• gas exchange occurs
• functional unit distal to terminal bronchiole is called the acinus

Question 30

What are the cells lining the trachea?

Answer 30

Pseudostratified ciliated epithelial cells and goblet cells

Question 31

What are cells lining the bronchioles?

Answer 31

Cuboidal epithelium
Exocrine cells = clara cells
- secrete surface active agent which makes them less likely to collapse

Question 32

What is atelectasis and how is it prevented?

Answer 32

Adjacent alveoli share the alveolar septum/wall

- which helps prevent alveolar collapse

Question 33

Describe the function of the Pores of Kohn?

Answer 33

Gaps in alveolar septa to enable more efficient movement of inspired air between alveoli