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39 Cards in this Set

  • Front
  • Back

What is the role of the thoracic cavity?

The walls provide mechanical source of ventilation (through changes in volume--> air flows in when thoracic cavity expands and out when it becomes smaller again)

What lines the cavity?

Lined with pleura

What binds the cavity?

Ribcage and intercostal muscles
Sternum
Thoracic vertebrae
diaphragm
Thoracic inlet (opening bound by the 1st ribs, 1st sternebra, and 1st thoracic vertera).
It is flattened laterally (deeper then it is wide).
Variation in shape between and even in species

What is the pleura

Serous membranes covering all surfaces within the thoracic cavity.
Forms the mediastinum between pleural cavities.


Pulmonary or visceral pleura cover the surfaces of the organs and vessels in the thorax, parietal pleura lines the inner walls of the thoracic cavity.
Loose connective tissue attaches pleura to underlying tissue

What are the three types of parietal pleura?

Costal, diaphragmatic, mediastinal.
Continuous with the pulmonary pleura.

What is the sternopericardial ligament?

Folds of pleura attaching the heart to the sternum.

What is the plicavenae cavae?

Fold of pleura suspending caudal vena cava

What are the pleural cavities?

Continuous with each other, two complete sacs. Airtight cavities containing small amount of fluid. And the mediastinum

What is the mediastinum?

Encloses the heart, thymus, trachea, oesophagus, major thoracic vessels and nerves, and tracheal bifurcation NOT the lungs.
Completeness and consistency vary between species (thick in ruminants, thin and incomplete in the horse and dog. So if you get air in one pleural cavity, you're more likely to get air in the other)

What are the divisions of the mediastinum?

Cranial (cranial to the heart)
Middle (containing the heart)
Cadual (caudal to the heart)

What are the muscles involved with relaxed inspiration?

Requires active muscular contraction.
Diaphragm is the principle muscle of inspiration.



What is the diaphragm?

Thin sheet of muscle and tendon, separating thoracic from abdominal cavity.

What are the attachments of the diaphragm?

Transverse process of the first 2-3 lumbar vertebrae.
Internal aspect of the ribs near the costal arch
caudal end of the sternum

What are the muscles used during forced inspiration?

External intercostal and scalenus muscles. Draw the ribs cranially and laterally--> expansion of the thorax

What are the external intercostal muscles

Run caudoventrally between adjacent ribs

What is the scalenus

originates on transverse processes of the cervical vertebrae and inserts on the first few ribs

How does expiration occur?

Passive, utilizes elastic recoil of the lungs. Expulsion of air continues until contraction of the thorax reaches point of equilibrium between elastic recoil of lung tissue and resistance to stretching of inspiratory muscles.
The vacuum around the pleural cavity ends up pulling against the diaphragm and intercostal muscles which are resisting the stretch. The elastic recoil of the lungs and the intercostal muscles oppose each other

Why does active expiration occur?

It occurs when the requirement for ventilation is elevated (need to increase the volume of the thorax, get more on inspiration but also decrease the volume of the thorax more on expiration--> doable with accessory muscles of the thorax. The intercostal muscles pull the ribs together compressing the volume of the thorax. The abdominal muscles also play a role).

How does the active expiration occur?

Contraction of expiratory muscles (internal intercostal and abdominal muscles) reduces volume of the the thorax, below equilibrium.

What are the internal intercostal muscles?

They run caudodorsally between adjacent ribs and collapse thoracic cavity

How do the abdominal muscles play a role in forceful expiration?

Move the viscera cranially, putting pressure on the diaphragm. Diaphragm pushes into thorax allowing for further ventilation

How is the diaphragm innervated?

phrenic nerve, originates from spinal cord in 5-7th cervical nerves

How are the other respiratory muscles innervated?

intercostal nerves leave the nerve at the relevent spinal segment

What are the structures that provide mechanical support in ventilation of birds?

Birds have no diaphragm (one large coelom). On inspiration, ribs are drawn forward and outwards and the sternum is lowered via the muscles in their body wall

What is the ventilation process?

The change in vol in the thorax results in changes of air pressures in the lungs, creating pressure gradients from external environment and the alveoli air. Gas flows from an area of high pressure to an area of low pressure (movement of air dependent on pressure gradients).

How does air pressure affect the flow of air?

The atmospheric pressure is normally 760mmHg, the alveolar pressure is also normally 760mmHg. These pressure are decreased during inspiration and increased during expiration (when the muscles compress the thorax against the closed glottis).
The intrapleural pressure is slightly lower (~756mmHg) allowing for the air to move through into the capillaries.

What is the transmural pressure gradient?

Difference between alveolar and intrapleural pressure

The mechanics of inspiration

Contraction of diaphragm-->expansion of the thorax (drop in the pressure of the pleural cavity)--> expansion of the lungs (drop in the intra-alveolar pressure)--> air flows down the pressure gradient into the lungs until the pressure is equal to the atmospheric.

Mechanisms of expiration

relaxation of the inspiratory muscles-->decreased vol in the thorax (increased pressure in the pleural cavity)-->decreased volume in the lungs (increased pressure in the intra-alveolar pressure)--> air flows down the pressure graident and out of the lungs.

The mechanics of forced inspiration

Contraction of the diaphragm and the accessory muscles-->increase thoracic volume above resting inspiratory volume (decreased pressure in the pleural cavity beyond resting inspiratory pressure)--> increased lung volume above resting inspiratory volume (decreased intra-alveolar pressure beyond resting inspiratory pressure)--> creating a larger pressure gradient and greater inflow of oxygen.

The mechanics of forced expiration

Contraction of the muscles of expiration and relaxation of the diaphragm--> reduction in thoracic volume beyond resting volume (increasing the intra-plural pressure beyond resting pressure)-->reduction in lung volume beyond resting volume (increasing intra-alveolar pressure beyond resting pressure)--> greater pressure gradient and a faster more complete emptying of the lung

What is a pneumothorax?

Entry of air into the pleural space due to trauma to lung or thoracic wall. The air flows into the thorax resulting in loss of partial vacuum and lung collapse (due to the external pressure). It's important that the mediastinum remains intact so the second lung doesn't collapse.

What are the two different ways a pneumothorax can develop?

Either by a hole in the thoracic wall or a hole in the lung. When you lose the air tight seal, you'll equilibriate between the alveoli and the atmosphere which will cause the lung to collapse. Since there's no longer a vacuum, the lung is no longer able to expand.

What is anatomical dead space?

The volume of airways that does not participate in gas exchange (everything from the nose to the terminal bronchioles)

What is physiological dead space?

The total volume of airways not participating in gas exchange. This will include the anatomical dead space plus the vol of any alveoli with inadequate circulation

What is alveolar ventilation?

Due to the existence of dead space, not all air breathed in is available for gas exchange. It tells us how much air enters (or leaves) the alveoli in one minute (more useful compared to pulmonary minute ventilation).

What is pulmonary minute ventilation?

Measured in ml/minute
Tidal volume (ml/breath) x RR (breathes/minute)

How do we measure alveolar ventilation?

(tidal volume-dead space vol) X respiratory rate.

How do we increase pulmonary ventilation?

It is more beneficial to increase tidal volume compared to increasing respiratory rate (because all additional air taken in is available for gas exchange. By doubling your resp rate and NOT increasing the tidal vol, you will decreased the alveolar ventilation.

Ex. Panting dog increases resp rate to cool down, but doesnt increase O2. Maximizes vol of air moving through dead space.