Respiratory System I

Question 1

What is the role of the nasal passage?

Answer 1

High resistance flow of air, warms and moistens air to protect lungs.

Question 2

Describe the respiratory tree

Answer 2

First component is the trachea, branches in the upper chest to form two main bronchi (Right bronchus is larger) which split into two lobar bronchi on the left, three on the right (corresponding to lung lobes). Each lobar bronchus divides into two and this repeats for 23 total generations of airways, where the trachea is gen. 0. These are all conducting airways, moistening and warming with no exchange.

Question 3

What makes up the airways beyond the bronchi?

Answer 3

Generations 12-19 are called bronchioles, those in generation 16 which link the bronchioles to the respiratory surface are called terminal bronchioles. 16-19 is the respiratory bronchioles (transitional airways) where exchange takes place and beyond this is the alveolar ducts and sacs (respiratory airways).

Question 4

Describe the cartilage of the airways

Answer 4

The trachea and primary bronchi are held open with C-shaped rings of cartilage, in smaller bronchi this becomes overlapping plates. Bronchioles don’t have cartilage, allowing collapse during forced expiration.

Question 5

Describe the smooth muscle of the airways

Answer 5

present in all walls except the alveolar sacs (not ducts). It makes up most of the most of the thickness of the walls of the terminal bronchioles.

Question 6

Describe the epithelium of the airways

Answer 6

The nasal passages to the bronchi are lined with pseudostratified columnar ciliated epithelium, containing many mucus secreting goblet cells. Beneath the epithelium are submucosal glands secreting. In the bronchioles the epithelium transitions to simple ciliated cuboidal.

Question 7

What is the mucociliary escalator?

Answer 7

Cilia beat continuously in a coordinated, wave like metachronal rhythm. This wafts inhaled particles in the mucus secreted by the goblet cells up towards the mouth.

Question 8

Describe the structure of an alveolus.

Answer 8

about 300 mill alveoli with ~1000 pulmonary capillaries each - huge exchange SA. The thin alveolar septa consists of type I and II alveolar cells. I are squamous epithelial while II are thicker and produce fluid lining and secrete pulmonary surfactant. Linking alveoli together to form lung parenchyma. Alveoli connected by pores of Kohn.

Question 9

Describe the alveolar capillary unit

Answer 9

Pulmonary capillaries lie beneath alveolar epithelium. Cell membranes of the two have a shared basement membrane of very little intersitial space - usually Between the capillaries in the alveolar wall are elastin and collagen fibres of lung connective tissue, linking alveoli together to form lung parenchyma.

Question 12

Describe the pleura of the lungs

Answer 12

The chest wall is lined by the parietal pleura, separated from the visceral pleura lining the lungs by intrapleural fluid - lubricating liquid (about 10ml). The pleura are joined at the root of the lungs, and consist of two layers of collagenous and elastic connective tissue. Beneath the visceral pleura is the limiting membrane of the lungs - together limit expansion.

Question 13

What is the mediastinum?

Answer 13

The central part of the chest cavity occupied by the heart and large blood vessels - only part not occupied by lungs.

Question 14

Describe the innervation of the respiratory skeletal muscle

Answer 14

Rhythmical breathing depends on impulses from the phrenic (to diaphragm) and intercostal (to muscles) motor nerves. Rhythmical discharge is governed by specific groups of brainstem nerve cells.

Question 15

Describe the innervation of respiratory smooth muscle

Answer 15

The bronchi and bronchioles are supplied by parasympathetic cholinergic fibres reaching the lungs via the vagus nerves - activation causing bronchoconstriction. No sympathetic innervation - bronchodilation is a respone to circulating (nor)epinephrine acting on I2 adrenergic receptors.

Question 16

How is respiratory smooth muscle tone regulated?

Answer 16

Regulated by autonomic fibres that secrete nitric oxide

Question 17

What drugs cause airway constriction and relaxation?

Answer 17

Salbutamol binds I2 adrenergic receptors to relax smooth muscle and overcome asthma spasms. Substance P and neurokinin A cause constriction.

Question 18

What is a spirometer?

Answer 18

Water sealed air tight chamber, movement up and down can be used to measure changes in volume of air. Used to measure lung volumes.

Question 19

What is total lung capacity?

Answer 19

Absolute maximum amount of air a patient is able to breath in

Question 20

What is residual volume?

Answer 20

The volume of air remaining in the lungs following a maximal expiration.

Question 21

What is the vital capacity?

Answer 21

Equal to the volume of air expired during a maximal expiration following a maximal inspiration. Basically the biggest change in volume your lungs can undergo

Question 22

What is the tidal volume?

Answer 22

volume of air inhaled and exhaled with each breath. much smaller than vital capacity at rest. (0.5/5L)

Question 23

What is inspiratory reserve volume?

Answer 23

This is the difference between lung volume after a normal breath and vital capacity or total lung volume.

Question 24

What is expiratory reserve volume?

Answer 24

The volume of air that can be forced from the lungs following a normal expiration.

Question 25

What is the functional residual capacity?

Answer 25

The volume of air left in the lungs after a normal expiration, rather than forced (giving residual volume)

Question 26

What is the intrathoracic pressure

Answer 26

The pressure outside the lungs AKA intrapleural pressure. Measured relative to atmospheric pressure where - is less and + is greater than.

Question 27

Describe the pressure changes of the respiratory cycle

Answer 27

After a quiet expiration, intrapleural pressure is about -0.5kPa. During inspiration this becomes more negative ~-1kPa and then rises again during expiration. Alveolar pressure dips a little below atmospheric (-0.25kPa) during inspiration and above during expiration.

Question 28

What causes the negative intrapleural pressure

Answer 28

the elastic recoil of the lungs. If the chest wall is punctured, air rushes into the chest cavity (pneumo-thorax), where pressure equalises with atmosphere and the lungs collapse.

Question 29

What is lung compliance?

Answer 29

The change in intrathoracic volume for a given change in intrapleural pressure. Indicates ease of change in volume and the higher the better. Typically healthy young person has a compliance of about 1 litre per kPa

Question 30

What is the equation for lung compliance?

Answer 30

dV/dP

Question 31

What factors determine lung compliance?

Answer 31

The elasticity of the lung tissue and chest wall (opposing forces) and above all the surface tension forced in the alveoli, which is why its hardest to inflate the lungs in collapsed state (0.8-1kPa) and beyond this pressure dP is roughly proportional to dV.

Question 32

What is the importance of lung surfactant

Answer 32

Phospholipid surfactant secreted by type II alveolar cells reduces cohesive forces on the alveolar surface, increasing lung compliance, also minimises alveolar collapse. It has greater effect over a smaller area (greater concentration) and is used and then broken down. Hypoxia and trauma may increase breakdown and decrease levels. Not fully from 4th to 7th month gestation. Infant respiratory distress syndrome.

Question 33

How is forced vital capacity measured?

Answer 33

Following a maximal inspiration, the subject is asked to breathe out fully as fast as possible. The volume of air expired is measured as a function of time (with a pneumotachograph).

Question 34

What is the forced expiratory volume at 1s (FEV1)

Answer 34

This is the volume of air expired during the first second of forced vital capacity. In healthy young people its about 85% vital capacity. Declines with age to about 70% at 60. A low FEV1/FVC indicates obstructive disease.

Question 35

What is peak expiratory flow?

Answer 35

AKA maximal expiratory flow rate. Measured with a pneumotachograph during forced expiration following maximal inspiration. Max flow rate normally reached in 0.1s and healthy figure is 8-10 L/s, reduced by obstructive but not restrictive diseases.

Question 36

How are restrictive lung diseases diagnosed?

Answer 36

Restrictive diseases compromise the ability of the lungs to expand. As such FEV1/FVC and peak expiratory flow might look normal but vital capacity is abnormally low.

Question 37

What is the anatomical dead space?

Answer 37

The volume of air inspired which does not mix with air in the alveoli

Question 38

What is the physiological dead space?

Answer 38

The volume of air inspired which does not take part in gas exchange

Question 39

What is the alveolar ventilation:perfusion ratio?

Answer 39

Quantifies the relationship between availability of air and blood to alveoli. = Va/Q or alveolar ventilation rate over Pulmonary blood flow.

Question 40

How does Va/Q vary across the lung at rest?

Answer 40

Both ventilation and perfusion fall with hight above base of lungs - but perfusion falls faster. As a whole for the lungs the ratio is about 4.2L/min / 5L/min = 0.84. At base of the lungs this is about 0.6 and the ratio rises up the lungs. Perfect matching - ratio of 1, occurs ~2/3 way up, then rises steeply to about 3 at apex.

Question 41

Through what range can Va/Q theoretically vary?

Answer 41

From 0, where perfused lungs have no ventilation but are perfused, to infinity, where ventilated lungs have no blood supply.

Question 42

What happens when alveoli are poorly ventilated but well perfused?

Answer 42

partial pressures of O2 and CO2 will tend to equilibrate with those of the blood, so PO2 will be lower than normal but PCO2 will be similar to normal.

Question 42

What happens when well ventilated alveoli are poorly perfused with blood?

Answer 42

Blood leaving the alveoli will have a low PCO2 a conc. grad. favours loss of CO2 from blood, but a PO2 of blood won't increase much in the body as what little blood reaches the lungs will be quickly saturated

Question 43

What pressures determine blood flow to different parts of the lungs?

Answer 43

Varying hydrostatic pressure in different pulmonary arteries and veins, and the pressure of the air in the alveoli. At the apex of the lung, well above the origin of the pulmonary artery, hydrostatic pressure cancels the blood pressure so that blood only flows during systole.