L9 Mechanics of Ventilation

Question 1

describe the position of the Thoracic inlet

Answer 1

bounded by 1st ribs, 1st sterner and 1st thoracic vertebra

Question 2

the pleura forms how many cavities

Answer 2

2, mediastinal pleura meet at midline

Question 3

how does the pleura attache to the sternum

Answer 3

via the sternopericardial ligament

Question 4

how does the pleura enclose the vena cava

Answer 4

plica venae cavae (fold of pleura)

Question 5

which regions of the pleura enclose the heart

Answer 5

cranial and caudal and middle regions

Question 6

what is the pleura called on the lateral aspects of the thoracic cavity

Answer 6

costal pleura

Question 7

what is the pleura called most near to the lungs

Answer 7

visceral pleura

Question 8

what is the most caudal pleura called

Answer 8

diaphragmatic pleura

Question 9

during inspiration the diaphragm….

Answer 9

contracts (to form a larger space in the thoracic cavity)

Question 10

what is the diaphragm made from

Answer 10

tendinous sheet of collagen and muscle

Question 11

where does the diaphragm attach

Answer 11

transverse processes of first 2-3 lumbar vertebrae, lateral at costal arches and ventrally at the sternum

Question 12

which muscles are used for forced inspiration

Answer 12

external intercostal and scalenus muscles

Question 13

Describe the fibre position of the external intercostal and scalenus muscles

Answer 13

External intercostal runs caudoventrally between the ribs.

Scalenus originates on the transverse process of the cervical vertebrae and inserts on the first few ribs to draw cranial and laterally for expansion

Question 14

what does the diaphragm do during expiration

Answer 14

relaxes passively due to elastic recoil of lungs

Question 15

Air expulsion from the lungs continues until …

Answer 15

the thorax reaches a point of equilibration b/w the elastic recoil of the lungs and resistance to the stretching associated with inspiration

Question 16

Which muscles are used for forced expiration

Answer 16

internal intercostal and abdominal muscles contract to reduce the volume of the thorax below equilibration volume

Question 17

which nerve innervates the diaphragm

Answer 17

phrenic nerve

Question 18

what is atmospheric pressure?

Answer 18

760mm Hg

Question 19

what is intrapleural/ intrathoracic pressure?

Answer 19

~756mm Hg (lower than that inside a relaxed lung)

Question 20

What is alveolar pressure?

Answer 20

~760mm Hg as per atmospheric pressure. Changes during inspiration (decreases) and expiration (increases)

Question 21

what is the transmural pressure gradient?

Answer 21

difference b/w alveolar and intrapleural pressure

Question 22

describe what determines airflow during inspiration

Answer 22

diaphragm contracts > thorax expands > drop in pressure in pleural cavity > expansion of lungs > drop in intra-alveolar pressure > airflow down pressure gradient until pressure equal to atmospheric

Question 23

Describe what determines airflow during expiration

Answer 23

relaxation inspiratory muscles > decrease in thoracic and lung volumes > increase intra-alveolar pressure > airflow down pressure gradient out of lungs

Question 24

What is pneumothorax?

Answer 24

entry of air into the pleural space, leading to partial loss of vacuum and therefore lung collapse.
Either through hole in lung or thoracic wall

Question 25

If the mediastinum is broken, will both lungs collapse?

Answer 25

no, most species have two separate pleural cavities joined at the midline by mediastinum.

Question 26

What is respiratory dead space ?

Answer 26

the volume of gas in airways not involved in gas exchange. Both anatomical and physiological.

anatomical= areas not adapted for gas exchange e.g. nose to the terminal bronchioles

physiological= total vol gas not participating due to anatomy or alveoli without adequate circulation

Question 27

if the aim of an animal is to increase O2, it is more efficient for an animal to increase ____ rather than _____

Answer 27

better to increase tidal volume rather than respiratory rate. Because all additional air taken in will be available for gas exchange.

Question 28

What is the pulmonary minute equation

Answer 28

pulmonary minute ventilation (ml/ min) = Tidal volume (ml/ breath) x Respiratory rate (breaths/ min)

Question 29

Define tidal volume

Answer 29

volume air breathed in or out in a breath

Question 30

What is the equation to describe alveolar ventilation

Answer 30

= (tidal volume - dead space volume) x RR

therefore the volume of gas entering and leaving alveoli in one minute