Nitrogen, Oxygen, Carbon Dioxide, Carbon Monoxide, Helium

The center of all lobe structures where all blood vessels emerge from and where the large principal bronchus emerges from. Not covered by pleura

1. Conducting airways
2. Respiratory airways

The lungs are highly compliant because only a slight change in thoracic pressure can cause a large change in volume (expansion of the lung)
- Compliance = change in volume/ change in pressure

Bronchial Circulation and Pulmonary Circulation

Functional Residual Capacity

Costal pleura, mediastinal pleura, and diaphragmatic pleura

Upper: pharynx, larynx, nasal cavity, nasopharynx, and trachea
Lower: area from end of the pharynx down into the smallest alveoli within the lung.

Phrenic Nerve

Bicarbonate

-Take up of O2
-Removal of CO2
-Acid-base balance mediated by CO2
-Immune regulation
-Site for metabolism of various vasoactive compounds
-Thermoregulation

Important muscle used for breathing because the movement of the diaphragm/contraction of the diaphragm causes the rib cage to expand and therefore, the pressure within the thorax, which is the internal space, is reduced.

Located in the conducting zone and it’s called this because there is ventilation taking place but no gas exchange. Gas exchange takes place in the respiratory zone.

- INTERNAL intercostals help in the reduction of thoracic volume so there may be muscular activity. These muscles are called accessory muscles.
- Accessory respiratory muscles include the external intercostals that help pull the ribs apart.

• CO is poisonous because it has a much higher affinity for hemoglobin (250x greater) than hemoglobin has for oxygen. CO binds in the same way O2 does, inhibiting O2 from binding.

1. Tidal Volume
2. Inspiratory Reserve Volume
3. Inspiratory Capacity
4. Expiratory Reserve Volume
5. Residual Volume
6. Vital Capacity
7. Functional Residual Capacity
8. Total Lunch Capacity

-Lines the mediastinum (central part of thorax)
-The mediastinum is the partition between the L and R pleural sacs
-Formed by apposition of mediastinal pleura of R and L pleural sacs with connective tissue filling between
-Contains most of the structures in the thoracic cavity
-Heart in pericardiac sac, Thoracic trachea, Thoracic esophagus (runs through mediastinum), Thymus (runs through heart), Mediastinal lymph nodes, Great vessels, Nerves
- Does NOT contain: Lungs, caudal vena cava, R phrenic nerve (The plica venae cavae: is parietal pleura that contains the R caudal vena cava and R phrenic nerve.)

Paralysis of the L recurrent laryngeal nerve results in "roaring" (a stertorous sound produced at inspiration because the air flow is vibrating a lax adducted vocal fold)
- horse tries to breathe in and can't because the dorsal cricoarytenoid muscle, which can't move. since this muscle can't move, we have paralysis of the L recurrent laryngeal nerve.

o Produced by cells within the alveolus called type 2 alveolar epithelial cells/ type 2 pneumocytes
♣ These cells are dotted about the surface of the alveoli and secrete surfactant, which is a polar phospholipid.
o Increases lung compliance, making it easier to expand with inspiration.
o Reduces the energy needed to inflate the lung by lining the alveoli.
o Little air always left in the airways of the lungs are within the alveoli themselves, meaning there is less energy required, less work, and less that needs to be done to reinflate the lung during inspiration.
o One of the roles of surfactant is to prevent lots of liquid from moving from the underlying pulmonary cavities into the alveoli.
♣ Infant respiratory distress syndrome:
• Effect of lack of surfactant that causes
o Stiff lungs with low compliance – lungs don’t expand easily
o Alveolar collapse
o Alveoli filled with transudate – oxygen isn’t very diffusible so having lots of transudate sitting within the alveoli is going to make gas exchange much less effective in infants.
• Treatment: treat with synthetic surfactant:
o Helps infant breathe more normally until the type 2 alveolar epithelial cells are sufficiently developed to produce surfactant on their own.

1. Atelectasis (alveolar collapse): We will no longer have adequate alveolar ventilation, which will affect gas exchange.
2. Tracheal/ bronchial collapse
- The collapse of the airways is going to create less air flow and that will affect gas exchange.
- If there’s no air moving within the bronchioles, we won’t have oxygen exchange at the trachea or large bronchi.
3. Bronchoconstriction
- Bronchioles have well developed bronchial smooth muscle layer
- If the muscles constrict in response to some kind of noxious stimulus or an allergic response, the ventilation will be compromised, effecting gas exchange.

o Horse – horse breathes much more slowly rest than cow. The horse has a much lower respiratory frequency and much higher tidal volume, which may be due to evolution. A horse is adapted as a flight animal so it has a large tidal volume and always has a large reserve of O2.
o Cow – a ruminant and has to take up more of its body space for the digestive apparatus and therefore, may not be able to have a large tidal volume but has a higher respiratory frequency to compensate for this.

Pig – 6 lobes total R – 4 (cranial, middle, caudal, accessory), L – 2 (bilobed middle, caudal)
Horse – L -2 (cranial, caudal. Cranial is NOT subdivided into cranial and caudal parts), R – 3 (cranial, caudal accessory. Middle is absent.)
Sheep – L – 2 lobes (cranial, caudal), R – 4 lobes (cranial, middle, accessory, caudal)
Cow/ ox – L – (cranial lobe –divided into 2 segments, caudal lobe), R – 4 lobes (cranial, medial, caudal, accessory

• The cells of the mucociliary escalator are ciliated epithelia and goblet cells that secrete mucus. These are found in the tranchea and bronchi. NOT FOUND IN BRONCHIOLES.
• Their purpose is to trap foreign material and waft it away from the respiratory tract.
• The continued movement of cilia that is involved in preventing microbes from adhering, binding, and colonizing. It serves as an important defense barrier because it facilitates continuous movement of microbes.

- Race horses are prone to exercise induced pulmonary hemorrhage (EIPH)
o Small blood vessels deep in the lung burst under high pressure, bleeding into the airway.
o May be related to training and to enormous cardiac output that these animals can deal with but their lung capacity (pulmonary vessels) may not be able to cope with the increase in CO under extended/extensive training.
(Visible epistaxis can be seen in a small proportion of EIPH cases).

• In exercise, we have more acidity, which can be caused by increase in CO2
o As muscle cells are working, they respire more and produce more waste CO2. This affects the blood by making it more acidic.
-This will shift the curve to the right (pH= 7.2 RED CURVE), meaning hemoglobin will have a lower affinity for oxygen, so it’s more efficient in removing the oxygen and delivering it to the working muscle.
o If we have an alkalotic experience (pH is slightly increased), we’ve got reduced CO2, so then hemoglobin will have a slightly higher affinity for oxygen and more oxygen will bind curve will shift to the left (ph = 7.6 BLUE CURVE)