PBL Week 8 Flashcards
What is the anatomy of the respiratory system?
Split into 2 zones: Conducting zone brings air in and out of lungs (trachea, bronchi, bronchioles, nasal cavity, pharynx, larynx). Respiratory zone is where gas exchange happens (bronchioles, alveolar ducts, alveolar sacs).
The conducting airways are lined by cilia and goblet cells, which produce mucus, trapping any small particles and transporting them away. Walls contain smooth muscle innervated by sympathetic (relaxes and dilates airways) and parasympathetic (contracts and narrows the airways) nerve fibres.
Alveoli are outpouching of the walls of the bronchioles, alveolar ducts and alveolar sacs. They are the site of efficient gas exchange due to their thin walls, large surface area and good blood supply. Elastic fibres and epithelial cells (type 1 + 2 pneumocytes) in the walls of the alveoli create a surfactant that stops them from collapsing.
The diaphragm is the most important muscle for inspiration. When it contracts, it pushes the abdominal contents downwards and increases the volume of the thoracic cavity. Intercostal muscles also contract to lift the ribs upwards and outwards, allowing the lungs to breathe in more air. Expiration is usually passive, but is assisted by muscles during exercise.
What are the physiological function of the respiratory system?
The main function of the respiratory system is the exchange of O2 into the blood for CO2 from it. This process happens at the avleoli. An important rule for this is Dalton’s law of partial pressures, where in a mix of gases, partial pressure of a gas = the total pressure of the gas mixture x the fraction of the mixture the gas takes up.
The speed at which gas exchange happens is due to the pressure difference and surface area. Alveoli have very large surface areas due to their outside consisting of multiple, very thin layers. Fick’s law states that the volume of gas being transferred per minute = the diffusing capacity of the lung x partial pressure difference of the gas. For example, PpO2 in deoxygenated blood is 40mmHg while it’s 100mmHg in alveolar air, leading to diffusion into the blood.
In the blood, O2 is carried in 2 forms; dissolved or, in most cases, bound to Haemoglobin. The PpO2 infuences the binding of O2 to Hb; as PpO2 increases, the saturation of Hb increases in a sigmoidal relationship. CO can also bind to Hb. CO2 is either dissolved in plasma, carried by Hb or, in most cases, carried by bicarbonate.
What is the normal capacity for the lungs and how does this change with age, gender and ethnicity?
4 measures of lung capacity: the amount of air from normal, quiet breathing (tidal volume, TV), the amount of extra air above tidal volume from a forceful inhale (inspiratory reserve volume, IRV), the amount of extra air below tidal volume from a forceful exhale (expiratory reserve volume, ERV) and the air left over in the lungs after a forceful exhale (residual volume, RV).
Also 4 capacities: inspiratory capacity (TV + IRV), vital capacity (TV + IRV + ERV), functional residual capacity (ERV + RV) and total lung capacity (TV + IRV + ERV + RV). The normal total lung capacity is 6L, however this number can change depending on a variety of factors. For example, females often have a smaller lung capacity than males, due to having smaller lungs on average. Ethnicity also matters; studies have shown that those who are of a European descent have a larger lung capacity than those of an African or Asian descent. This is likely due to genetic differences. Finally, age leads to a decline in the function of the lungs; the ERV actually declines by 1-2% every year from the age of 25.
What are the different factors that impact lung function?
Compliance refers to the lung and chest walls’ ability to expand, while elasticity is the measure of their ability to recoil. Emphysema destroys alveolar walls, reducing elasticity and increasing compliance. Pulmonary fibrosis increases scar tissue in the lungs, making them hard to expand (increasing elasticity and reducing compliance). The thoracic cage also has elasctic characteristics, so diseases like kyphosis can reduce compliance. Lung diseases like pulmonary fibrosis will also lead to a reduced total lung capacity.
Diffusing capacity of gas exchange may be affected by thicker alveolar membranes (like in pulmonary fibrosis) or less surface area (emphysema, removal of part of lung).
Hypoxeamia is a decrease in arterial PpO2 and can result from reduced PpO2 in the atmosphere, such as at higher altitudes. Hypoventilation, as can happen with the weakness of respiratory muscles, can also impair oxygenation. This will mean more breaths will need to be taken to oxygenate the blood. When present, CO can also bind to Hb in blood, leading to reduced O2 in blood and eventually death.
Finally, age can have an effect on our lung function.
What are the different tests used to assess lung function?
Spirometer can be used to measure the different volumes and therefore the different capacities, too. By measuring forced vital capacity (FVC) and the forced expiratory volume in 1 second (FEV1), we can determine how much air a patient can exhale in the first second (FEV1/FVC, normally 0.8/80%). An airflow obstruction leads to a value of 70%, while lung diseases like pulmonary fibrosis leads to a reduced total lung capactiy and a value of 80-85%. Shortness of breath leads to a higher value of FEV1.
The diffusing capactiy of a patient can be assessed by letting the patient breath in a gas containing a small amount of CO, with the rate of disappearance of CO used to calculate whether the diffusing capacity is normal or not.
Lung volume tests are more precise versions of spirometers. They measure the total lung capacity and whether it’s too high (obstructive conditions like COPD, asthma, bronchitis) or too low (restrictive conditons like pulmonary fibrosis or sarcoidosis.
What are the types of cellular receptors and their signalling pathways in human cells?
Membrane receptors are proteins that allow cells to communicate with the rest of the body. A ligand is an ion or molecule (e.g hormone, neurotransmitter etc) that bind to these receptors and trigger changes within the cell. The ligand binds by induced fit, forming a ligan-receptor complex, changing the structure of the receptor and triggering an intracellular response. This is called signal transduction.
The membrane receptors come in 3 forms: ligand-gated ion channels (ligand binding opens an ion channel, letting ions into/out of the cell), G-protein coupled receptors (uses G-proteins to start a secondary messenger cascade, which modulates cellular function) and enzyme linked receptors (ligand binding results in enzymatic activity). Drugs can inhibit or assist these receptors, allowing drugs to control the reactions inside the cell.
What are the different hormones inside the body?
3 major types of hormone:
Proteins - form long or small chains, are charged (so water soluble) but cannot pass through membranes, so attach to receptors on cell surface, activating a cascade of secondary messengers inside the cell.
Steroids - made from lipids (mostly cholesterol) and are formed of carbon rings. Can easily pass membranes, so attach to receptors inside the cell (are primary messengers). They often affect protein transcription/translation.
Tyrosine derivatives - made from Tyrosine. Can act similarly to protein or steroid hormones.
What is pharmacology and the key pharmacological concepts?
Pharmacology is the science of drugs and their effect on living systems. Key pharmalogical terms to know are:
Agonist - a drug capable of binding to a receptor, mimicking a naturally occurring substance.
Antagonist - Blocks or reduces the effect of an agonist, stopping it from binding to a receptor.
Half Life - the time taken for a drug to half in concentration in the plasma. Is a measure of how quickly the drug breaks down.
Physiological agonist/antagonist - drugs that mediate the same effect as agonists/antagonists via alternative receptors or mechanisms.
Allosteric modulator - a drug that binds to a receptor distinct from the active site, which changes the structure of the receptor.
What is the impact of air quality on health in the 20th and 21st centuries?
Poor air quality can have many health consequences, leading to diseases such as respiratory infections, lung diseases and cancer. In the UK, the levels of air pollutants were incredibly high, peaking around 1900. However, the public health act of 1891 and the fact that more people were using gas instead of coal lead to a gradual decline. Nowadays, air pollution in London is just a fraction of what it once was.
However, rapidly developing countries (such as india and china) have terrible air pollution, leading to increased levels of respiratory diseases. This has become such a problem that people in China often have to wear masks to avoid inhaling in the smog, especially in the larger cities.
Discuss the impact chronic lung diseases have on the NHS.
Lung diseases cause around 20% of deaths in the UK, with lung cancer being one of the biggest killers, especially since they are often caused by something avoidable (smoking). This puts unnecessary strain on the NHS.
