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Flashcards in Respiratory Deck (42)
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Which parts of the upper respiratory system are characterised by C-shaped cartilagenous rings? 

Trachea & principle bronchi (main bronchi). 


What is the name of the muscle that spans the "gap" in the C-shaped cartilaginous rings of the trachea?

Trachealis muscle.

Weakness in this muscle can lead to tracheal collapse, as is seen more often in certain dog breeds such as the Yorkshire Terrier.


What types of cells are located in the epithelium of the trachea and principle bronchi?

Ciliated epithelial cells

Goblet cells

Basal cells


What types of cells are located in the bronchioles? Which cells do not exist in the bronchioles?

Clara cells

Ciliated epithelial cells

Basal cells

There are no goblet cells in the bronchioles or further down in the respiratory tract. 


How do lobar bronchi change their calibre?

Even though lobar bronchi have irregular plates of cartilage around them, they change their calibre by contraction or relaxation of smooth-muscle bands arranged in a spiral. 


Since lobar bronchi don't have C-ringed cartilage but rather irregular plates of cartilage and a spiral band of smooth muscle, how do they manage not to collapse? 

They are encased in a vascular sheath that keeps them open. 


Do bronchioles have cartilage, vascular sheath or smooth muscle cells?

Bronchiole walls are lined with smooth-muscle cells. They do not have cartilage or a vascular sheath.


What are clara cells? Where are they located and what is their purpose?

Clara cells are located in the bronchioles, in the conducting, terminal & respiratory bronchioles. They can be both ciliated with microvilli & non-ciliated. They secrete anti-adhesive agents that prevent adhesion to the bronchiolar walls that could cause collapse.

One major function is the synthesis and secretion of the material lining the bronchiolar lumen. This material includes glycosaminoglycans, lysozymes, and conjugation of the secretory portion of IgA antibodies. These play an important defensive role, and they also contribute to the degradation of the mucus produced by the upper airways.

Clara cells also act as a stem cell and multiply and differentiate into ciliated cells to regenerate the bronchiolar epithelium.


What is the correct order of the tubes through which air enters the respiratory tract?

A. Principle bronchi, lobar bronchi, conducting brochioles, respiratory bronchioles, terminal bronchioles, alveoli

B. Principle bronchi, lobar bronchi, conducting brochioles, terminal bronchioles, respiratory bronchioles, alveoli

C. Principle bronchi, lobar bronchi, respiratory bronchi, terminal bronchioles, alveoli

B. Principle bronchi, lobar bronchi, conducting brochioles, terminal bronchioles, respiratory bronchioles, alveoli


What type of cells make up the thin epithelium of the alveolar sacs/alveoli?

Type I & Type II alveolar cells, aka pneumocytes.



Histologically, what is the difference between Type I & Type II pneumocytes (aka alveolar cells), and what in particular is important about Type II pneumocytes?

Type II are granular and roughly cuboidal. Type I cells do not appear granular and they are bigger than Type II.

Type II are secrete surfactant for maintaining alveolar spaces and preventing collapse.  Surfactant phospholipids are stored in Type II pneumocytes in lamellar bodies, which are specialized vesicles. Release of surfactant in lamellar bodies occurs from an infant's first breath onwards.

Type II pneumocytes can replicate in the alveoli and will replicate to replace damaged Type I pneumocytes.

Type II pneumocytes are typically found at the alveolar-septal junction. Although they comprise 60% of the alveolar lining cells, because of their shape they cover a much smaller surface area than type I cells


What makes up the alveolar septum? Why is it important?

The thick alveolar septum is comprised of collagen & elastic fibres, allowing inflation & deflation of the lung.

In some diseases, there is a buildup of collagen that inhibits inflation or a loss of elastic fibres, which results in not enough recoil.

Eg., Emphysema - a breakdown of the alveolar wall, thus losing gas-exchange surface & elastic-recoil potential as elastic fibres are degraded due to macrophages secreting elastase & collagenase.

Lung Fibrosis: aka “scarring of the lung” - excess fibrous tissue builds up in lungs


What muscles are involved in inspiration? 

Muscles of diaphragm - contract, move diaphragm caudally to expand thorax

External intercostal muscles - expand ribcage; when they contract, they pull ribs cranially & ventrally to enlarge thoracic cavity

(Accessory) Scalene Muscles - lift first rib & expand chest cavity in some species, pulling sternum cranially



Which muscles are engaged in expiration of air in the lungs?

Usually, expiration is a passive event, except in horses, which breath biphasically with passive followed by active phases

Abdominal musclesrectus abdominis, internal & external obliques & transverse abdominis:

- Pull in/decrease thoracic cavity during exercise & activity; otherwise expiration is passive

- When these contract, pressure inside the abdomen is raised & diaphragm is pushed cranially (ie., it relaxes)

- Contract forcefully during coughing, vomiting & defecation.

Internal intercostal muscles:

- Pull ribs caudally & inward during active expiration, the OPPOSITE of external intercostal muscles, decreasing thoracic volume.
- Stiffen the intercostal spaces to prevent them from bulging outward during straining.


What is the importance of surfactant produced by Type II pneumocytes in terms of alveoli?

This ability of alveoli to resist collapse (alveolar collapse = atelectasis) is due to the production of pulmonary surfactant.

The surfactant, a polar phospholipid containing DPPC (dipalmitoyl phosphatidylcholine) holds the alveoli open as the DPPC’s polar heads repel each other. Also, the mix of proteins and lipids are able to form and re-form, avoiding pooling across the alveolar surface.

Thus, surfactant:

1/ increases compliance of the lung & reduces the work of expanding it with each breath

2/ promotes stability of each alveolus

3/ keeps alveoli dry, ie., preventing oedema (fluid/plasma from blood leaking into lung tissue). 



How does Infant Respiratory Distress Syndrome illustrate the importance of surfactant in the lungs? 

Babies, whose lungs don’t produce surfactant, suffer from:

1. atelectasis - alveolar collapse 

2. stiff lungs with low compliance

3. alveoli filled with transudate

They can be treated with synthetic surfactant.


What is the bronchial circulation

Bronchial circulation refers to arterial blood that supplies the metabolic needs of tissue of the bronchial tree. Inside the lung, it anastomoses with capillaries of the pulmonary circulation.



How does the pulmonary circulation differ from the bronchial circulation?

The pulmonary circulation oxygenates blood in the lungs, then returns that blood via the pulmonary veins into the left atrium, then left ventricle to be pumped out via the aorta into the systemic circulation. 

The bronchial circulation starts with fully oxygenated blood directly from the aorta. The blood enters arteries of the bronchial tree, then forms anastomoses with the capillary system of the pulmonary circulation, where it gives up oxygen to the lung tissue. 

It returns, partly deoxygenated, via the pulmonary vein to the left atrium. While in the pulmoary vein, it mixes with oxygenated blood.

It also returns, mixed (oxygenated & deoxygenated) via bronchial veins (different from pulmonary veins) & the azygous venous system to the RIGHT ATRIUM


In speaking of the bronchial circulation, what is the common capillary network & "shunt"?

The common capillary network refers to the capillary beds of respiratory bronchioles that are shared by arteries of both the pulmonary & bronchial systems.

The “shunt” refers to blood that enters the arterial system without going through ventilated areas of the lung. The partly deoxygenated blood, after perfusing the lung tissue, returns back to the left side of the heart via the pulmonary veins, without having to go through the alveolar system, then pumped out again through the aorta. This blood is mixed with the oxygenated blood of the pulmonary veins before it enters the heart.

Shunt is helpful, for example, if there is an obstruction in the pulmonary artery that conveys venous blood to the lungs. Some of the oxygenated blood from the bronchial circulation (oxygenated via anastomoses with pulmonary capillaries) can be returned to the left atrium.


What is the typical PO2 of inspired air (atmospheric air)?

150 mmHg


Typically, the PCO2 of inspired air (atmospheric air) 

0 mmHg


What is the PO2 & PCO2 of deoxygenated blood pumped through the pulmonary arteries down to the lungs and alveoli?

PO2 = 40 mm Hg 

PCO2 = 45 mm Hg


What are the PO2 & PCO2 of oxygenated blood returning to the heart to be pumped out of the aorta? 

 PO2 = 100 mm Hg

 PCO2 = 40 mm Hg 


Which group of respiratory neurons in the brain's medulla are responsible for controlling inspiration? 

DRG - dorsal respiratory group

- cause contraction of the diaphragm, opening of the chest cavity & allowing air to come in, thorax becomes subatmospheric.
- driven by apneustic centre & causes inspiration
- DRG will continue to fire if there are no negative signals stopping it 


The DRG (dorsal respiratory group) will continue to fire, causing more inspiration, unless it receives a "stop" signal. Where does that signal come from?

Pneumotaxic Centre 


Pontine Respiratory Group (PRG)



What is the role in breathing of the Apneustic Centre in the lower pons?

- sends signals to DRG to delay the 'switch off' signal of the inspiratory ramp provided by the pneumotaxic center

- effect is to ⬆breathing (ie., delays negative feedback to dial down DRG inspiration)

- controls the intensity of breathing

- inhibited by pulmonary stretch receptors. However, it gives positive impulses to the inspiratory (I) neurons.


What is the role in breathing of the Pneumotaxic Centre aka Pontine Respiratory Group (PRG)?

Located in the in the rostral-dorsal-lateral pons, the PRG:

- cyclically ⬇ inspiration

- antagonises the apneustic centre

- switches off DRG “inspiratory ramp”, causing deflation of lung & letting air to move out

- alters the bursting pattern of the dorsal respiratory group.

When we find ourselves needing to breath faster, the pneumotaxic area tells the dorsal respiratory group to speed it up. And when we need to take longer breaths, the pneumotaxic area tells the dorsal respiratory group to prolong its bursts. All the information from the body that needs to feed into the control of our breathing converges in the pneumotaxic area, so that it can properly adjust our breathing.
- receives signals from chemoreceptors


What is the role in breathing of the Ventral Respiratory Group (VRG)? 

VRG kicks in during exercise and heavier breathing, mainly involved in expiration, some inspiration. 


The VRG is an expiratory centre, while the DRG is an inspiratory centre.


What are the two main groups of chemoreceptors in the body that detect oxygen & carbon-dioxide levels in the blood, thus affecting the respiratory centres to induce greater or lesser gas exchange?

Central chemoreceptors:

- ventral surface of medulla near exit of CN 9 & CN 10

- detect changes in CO2 in blood in brain indirectly by detecting H+

- since there is no Hb in the blood in the brain to take up (buffer) H+, then H+ & bicarbonate ions will be present due to the dissociation of carbonic acid formed initially by CO2 & H2O

- very sensitive to changes in CO2 that diffuses across BBB

- stimulates ventilation

- ⬇ & ⬆ breathing

Peripheral chemoreptors:

- aortic & carotid bodies (in & off the aortic arch)

- detect O2 levels directly in arterial blood but ONLY LARGE DECREASES of O2

- aortic bodies: contained in the walls of the aorta - induce reflex ⬆ breathing

- carotid bodies: contained in the carotid sinus, a small swelling of nerve fibres where the carotid artery branches into the internal & external carotid arteries

- not as important as central chemoreceptors


What are the FOUR TYPES of respiratory neurons IN THE LUNGS that send signals to the brain's respiratory centre?

1. Pulmonary Stretch Receptors

2. Irritant Receptors

3.   J-Receptors (“juxtacapillary receptors”)

4. Bronchial C-fibres

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