Pulmonary anatomy/physiology and pathology

Question 1

Functions of the Respiratory System

Answer 1

Provides for gas exchange—intake of O2 for delivery to body cells and removal of CO2 produced by body cells.
* Helps regulate blood pH.
* Contains receptors for the sense of smell, filters inspired air, produces sounds, and excretes small amounts of water and heat.

Question 2

Pharynx

Answer 2

Two parts
* Nasopharynx-epithelial lining like the nose and trachea; ciliated columnar epithelium
* Oropharynx-epithelium like the oesophagus- stratified squamous
* The submucosa is rich in mucosa-associated lymphoid tissue (MALT)-
involved in sensing infections
* Pharyngeal wall has smooth muscle lining to keep lumen open.

Question 3

Problems with the larynx

Answer 3

Laryngitis is inflammation of larynx usually caused by a respiratory infection/ cigarette smoke.
* Inflammation of vocal folds causes hoarseness by causing swelling that affects vibration.
* Cancer of larynx is found in individuals who smoke. Additional risk factors alcohol, acid reflux, possible HPV infection (uncertain)

Question 4

Functions of trachea

Answer 4

Support and patency
* Muco-ciliary escalator
* Cough reflex
* Warming, humidifying, filtering

Question 5

Alveoli

Answer 5

Bronchioles: Cartlidge replaced by smooth muscle cells, non-ciliated epithelium & no goblet cells
Alveoli:
Septal cells produce surfactant, a phospholipid fluid that reduces surface tension-premature babies deficient in surfactant
Macrophages are immune defence cells

Question 6

Additional components

Answer 6

Lymph vessels
alveolar sac (collection of alveoli) Visceral pleura

Question 7

3 Physiological variables affecting breathing

Answer 7

Elasticity: ability of lung to return to normal shape after each breath. If elasticity reduced lungs remain overinflated and energy is needed to squeeze air out (emphysema)
* Compliance: Means stretchability. Usually, little effort needed to enlarge lung volume. Compliance and elasticity are opposite forces.
* Airway resistance: more effort required to move air into the alveoli (like raised blood pressure). Problem in asthma attacks

Question 8

Lung volume and capacity

Answer 8

Tidal volume= 500 ml/breath Total lung volume 6 L
Vital capacity 4.8 L

Question 9

Peak flow test

Answer 9

Peak flow measurement is a quick test to measure air flowing out of lungs.
* Also called peak expiratory flow rate (PEFR) or peak expiratory flow (PEF).
* Peak flow measurement mostly done by people who have asthma.
* Normal about 400-500 L/min

Question 10

External and internal respiration

Answer 10

Changes in partial pressures of O2 and CO2 in mmHg during external and internal respiration
Deoxygenated blood still has a lot of oxygen in it.
CO2 content of oxygenated and deoxygenated blood is not hugely different

Question 11

Rate of diffusion of molecules

Answer 11

Remember:
Co2 is > soluble than O2
Diffusion easier if small molecule, water soluble, a big difference in concentration exists and distance need to diffuse is small
J is rate of diffusion
*S is solubility
*wtmol is molecular weight *A is surface area
*ΔC is concentration difference *t is membrane thickness.

Question 12

oxygen

Answer 12

Carried as oxyhaemoglobin in red cells (98.5%)
The haem part of haemoglobin contains four ions of iron, each capable of binding to a molecule of O2
Oxygen and deoxyhaemoglobin (Hb) bind in an easily reversible reaction to form oxyhaemoglobin (Hb–O2)
Remainder dissolved in plasma (1.5%)

Question 13

Carbon dioxide

Answer 13

Waste product of metabolism
* Carried a HCO3 in plasma (70%)
* Combined with haemoglobin in red cells as carbamino-haemoglobins (23%)
* Dissolved in plasma (7%)

Question 14

Oxyhaemoglobin dissociation curve

Answer 14

Normal arterial saturation is 95-100%.
As PaO2 falls, SaO2 decreases in an S‐shaped curve. If PaO2 falls as low as 8 kPa (60 mmHg), SaO2 will remain around 90%.
Therefore, normal fluctuations in oxygenation, such as occur when singing, laughing and talking, do not cause major reductions in oxygen saturations.
If pH falls or CO2 rises, the curve shifts to release more oxygen

Question 15

Transport of CO2 and acid base balance

Answer 15

Most CO2 is transported as bicarbonate ions (HCO3 –).
* As CO2 enters red blood cell it combines with water to form carbonic
acid (H2CO3).
* H2CO3 then quickly dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-).
* Formation of H2CO3 is very slow in plasma; in red blood cells reaction speeded up by presence of the enzyme carbonic anhydrase.
* H+ combines with haemoglobin, but the HCO3– leaves red blood cell and enters blood plasma.

Question 16

Transport of CO2 and acid base balance pt2

Answer 16

Arrows show its in equilibrium and can go both ways. In tissues, where CO2 is higher, equation moves to the right. In lungs where CO2 is lower, it moves to the left.
* Arterial blood pH is mainly influenced by levels of H+. Normal pH is 7.35–7.45.
* Respiratory system helps maintain acid–base balance by controlling expulsion and
retention of CO2
* When pH falls (acidosis), respiratory rate increases, and more carbon dioxide is expelled. This results in greater amounts of hydrogen ions H+ and HCO3- combining to form carbonic acid (H2CO3). In other words, the equation moves from right to left. H+ levels are reduced, and as a result pH increases.
* H2CO3 is a weak acid and has a minimal effect on blood pH.
* If blood pH rises, respiratory rate and depth may fall, resulting in the retention of carbon dioxide. The above equation now moves from left to right and more H+ will be created.

Question 17

Terms used in respiration

Answer 17

Oxygen capacity
* The potential space for oxygen transported by haemoglobin (Hb) per 100 mL of blood (Hb × 1.39 = oxygen capacity per 100 mL of blood). Anaemia therefore affects oxygen delivery to tissues
Oxygen saturation (SaO2)
* The percentage of arterial haemoglobin carrying oxygen molecules SaO2 measured by a pulse‐oximeter usually >95%
Oxygen consumption (VO2)/oxygen extraction ratio
* The amount of oxygen utilised by body tissues each minute
Hypoxia
* Reduced oxygen in blood
Hyperbaric oxygen
* Increased % of oxygen administered, usually to improve poor respiration
Hypercapnia
* Increased CO2 present in blood

Question 18

Control of respiration

Answer 18

Control of respiration usually involuntary -Can be overridden by higher centres of brain
Main controllers
1. Respiratory centre in brain stem. Four groups of neurones
-An inspiratory group (breath-in) - Regular automatic firing of inspiratory group control the basic rhythm of breathing
-An expiratory group (breath out)
-A pneumotaxic group (controls rate and depth of breathing). -An apneustic group (controls rate and depth of breathing).
2. Chemoreceptors
-Central group of neurones in brain stem, bathed in cerebrospinal fluid. If CO2 rises or O2 falls central receptors stimulate faster breathing
-Peripheral chemoreceptors in carotid bodies-monitor pH, CO2 and O2 changes

Question 19

Asthma

Answer 19

Inflammation of airways. Allergic response. Increased eosinophils, bronchial constriction, thickened muscle layer, increased mucus
Treatment bronchodilators: sympathetic nerve stimulants & immune reducers (corticosteroids)

Question 20

Pneumonia

Answer 20

Pneumonia is infection or inflammation of alveoli. Commonest cause
bacterium Streptococcus pneumoniae . Often preceded by viral upper respiratory infection. Individuals then develop fever, chills, productive or dry cough. Treatment with antibiotics, bronchodilators, oxygen therapy.
* Tuberculosis: Caused by bacterium Mycobacterium tuberculosis usually affects lungs. People commonly exposed to it but immune response stops it spreading. Impaired immunity allows it to start to re-grow. Treatment is many months of special antibiotics.
* Coryza: Hundreds of viruses cause the common cold, most common are rhinoviruses . Symptoms include sneezing, excessive nasal secretion, dry cough, and congestion.
* Seasonal Influenza: (flu) caused by influenza virus. Its symptoms include chills, fever, headache, and muscular aches.
* Covid: Caused by a coronavirus. It is an RNA virus that can mutate. It binds to the ACE2 receptor (remember from cardiovascular lectures!) in the lungs. Usually relatively mild but can result in severe inflammatory response in some subjects, requiring ventilation.

Question 21

Chronic Obstructive Pulmonary Disease

Answer 21

Chronic obstructive pulmonary disease (COPD) is a respiratory disorder characterized by chronic obstruction of airflow. The principal types of COPD are emphysema and chronic bronchitis.
* Commonest cause smoking and pollution.
* Emphysema is when lung tissue destroyed leaving large gaps/air spaces that remain filled with air during exhalation. Surface area reduced therefore gas exchange falls. Subject becomes breathless, especially on exercise. Lung elasticity reduced causing air trapping. Chest becomes overexpanded.
* Chronic bronchitis characterized by excess secretion of bronchial mucus accompanied by a cough. Inhaled irritants cause inflammation, increased mucous production which is too thick, blocks airways and cilia stop working. More likely to get chest infections. Besides a cough, symptoms of chronic bronchitis are shortness of breath, wheezing, cyanosis (increased CO2), and pulmonary hypertension.

Question 22

Cancer of respiratory system

Answer 22

Lung cancer
* Most cases due to smoking but rarer forms are not related to smoking.
* Symptoms may include chronic cough with blood, weight loss and jaundice. Mesothelioma
* Rare form of cancer affecting pleurae of lungs (pleural mesothelioma). Virtually always caused by asbestos exposure.
* Signs and symptoms include chest pain, shortness of breath, pleural effusion, and unexplained weight loss.

Question 23

Cystic fibrosis

Answer 23

Genetic change of chloride channel
* Causes mucus to be excessively think * Blocks bronchioles, pancreatic ducts
* Treatment is with physiotherapy and new treatments to overcome chloride channel problem

Question 24

Carbon Monoxide Poisoning

Answer 24

Carbon monoxide (CO) is colourless, odourless gas found in tobacco smoke and in exhaust fumes from automobiles, gas furnaces, and space heaters.
* CO binds to the haem group of haemoglobin, 200 times more strongly than oxygen. At a concentration of 0.1%, CO combines with half the available haemoglobin molecules and reduces oxygen‐carrying capacity of blood by 50%.
* Elevated blood levels of CO cause carbon monoxide poisoning, which can cause lips and oral mucosa to appear bright, cherry‐red (colour of haemoglobin with carbon monoxide bound to it).

Question 25

High Altitude Sickness

Answer 25

As a person ascends in altitude, total atmospheric pressure decreases, with parallel decrease in the partial pressure of oxygen.
* PO2 decreases from 159 mm Hg at sea level to 73 mm Hg at 6000 meters (about 20,000 ft). Alveolar pO2 decreases correspondingly, and less oxygen diffuses into blood.
* Symptoms —shortness of breath, nausea, and dizziness—due to lower levels of oxygen in blood and alteration in pH from increased breath rate.
* Acclimatisation allows body to partially adapt to low oxygen levels

Question 26

Pneumothorax

Answer 26

Where air gets into the (potential) pleural cavity
* Can be spontaneous (mainly young people) or trauma
* Lung collapses
* Shortness of breath