Respiratory system (Topic 6.4) Flashcards
What is Physiological respiration?
Physiological respiration involves the transport of oxygen to cells within the tissues, where energy production occurs
How is ventilation defined
The exchange of air between the atmosphere and the lungs – achieved by the physical act of breathing
What is gas exchange?
The exchange of oxygen and carbon dioxide between air in the alveoli and blood flowing in the adjacent capillaries via passive diffusion.
What is the purpose of ventilation?
The purpose of ventilation is to maintain concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries. This is because gas exchange is a passive process.
Why do the gases undergo passive diffusion?
Because there is a concentration gradient: the air in the alveolus has a higher concentration of oxygen and a lower concentration of carbon dioxide than the blood in the capillary.
How lungs function as a ventilation system
The lungs function as a ventilation system by continually cycling fresh air into the alveoli from the atmosphere
This means O2 levels stay high in alveoli (and diffuse into the blood) and CO2 levels stay low (and diffuse from the blood)
The lungs are also structured to have a very large surface area, so as to increase the overall rate of gas exchange
How is breathing defined?
Breathing is the active movement of respiratory muscles that enables the passage of air into and out of the lungs
What is the mechanism of breathing
The mechanism of breathing occurs according to the principle of Boyle’s Law (pressure is inversely proportional to volume)
- When the volume of the thoracic cavity increases, pressure in the thorax decreases
- When the volume of the thoracic cavity decreases, pressure in the thorax increases
What is inspiration?
Inspiration is when Muscles contractions causes an increase in the volume of the chest (thorax) which causes pressure in the lungs to become lessthan the atmospheric pressure, so air will moveintothe lungs from the atmosphere
What is expiration?
Muscles contractions causes a decrease in the volume of the chest (thorax) which causes pressure to become greaterthan the atmospheric pressure, so air will moveoutof the lungs to the atmosphere
Why are different muscles required for inspiration and expiration?
Because muscles only do work when they contract (generate a pulling force which is tension), and thus causes a movement in one direction, different groups of muscles are required to expand and contract chest volume
What does it mean by antagonistic pair of muscles? (Define and explain)
A pair of muscles which perform opposite movements at different times. One muscle will contract to cause a movement in one direction, and for this muscle to cause a movement in the opposite direction, another second muscle will contract to bring this muscle in the elongated state, doing work in the opposite direction.
If the alveoli were not ventilated, what would happen?
If the alveoli were not ventilated, equilibrium would be reached and no gas would be exchanged
Describe the ventilation system
Air enters the respiratory system through the nose or mouth and passes through the pharynx to the trachea
The air travels down the trachea until it divides into two bronchi (singular: bronchus) which connect to the lungs
The right lung is composed of three lobes, while the left lung is only comprised of two (smaller due to position of heart)
Inside each lung, the bronchi divide into many smaller airways called bronchioles, greatly increasing surface area
Each bronchiole terminates with a cluster of air sacs called alveoli, where gas exchange with the bloodstream occurs
Describe the structure of alveoli which makes it specialised for gas exchange
Alveoli function as the site of gas exchange, and hence have specialised structural features to help fulfil this role:
They have a very thin epithelial layer (one cell thick) to minimise diffusion distances for respiratory gases
They are surrounded by a rich capillary network to increase the capacity for gas exchange with the blood
They are roughly spherical in shape, in order to maximise the available surface area for gas exchange
Their internal surface is covered with a layer of fluid, as dissolved gases are better able to diffuse into the bloodstream
Define pneumocytes
Pneumocytes (or alveolar cells) are the cells that line the alveoli and comprise of the majority of the inner surface of the lungs
Outline type 1 pneumocytes
Type I pneumocytes
Type I pneumocytes are involved in the process of gas exchange between the alveoli and the capillaries
They are squamous (flattened) in shape and extremely thin (~ 0.15µm) – minimising diffusion distance for respiratory gases
Type I pneumocytes are connected by occluding junctions, which prevents the leakage of tissue fluid into the alveolar air space
Type I pneumocytes are amitotic and unable to replicate, however type II cells can differentiate into type I cells if required
Outline type 2 pneumocytes
Type II pneumocytes are responsible for the secretion of pulmonary surfactant, which reduces surface tension in the alveoli
They are cuboidal in shape and possess many granules (for storing surfactant components)
Type II pneumocytes only comprise a fraction of the alveolar surface (~5%) but are relatively numerous (~60% of total cells)
Why are type 2 pneumocytes important?
While this moist lining assists with gas exchange, it also creates a tendency for the alveoli to collapse inwards and resist inflation
This is because of the formation of hydrogen intermolecular bonds between liquid molecules which will cause the alveolus to collapse inwards. This is surface tension which minimises surface area and makes gas exchange impossible.
Type II pneumocytes secrete a liquid known as pulmonary surfactant which reduces the surface tension in alveoli (prevents or breaks hydrogen bonds between liquid molecules)
As an alveoli expands with gas intake, the surfactant becomes more spread out across the moist alveolar lining
This slows the rate of expansion, ensuring all alveoli inflate at roughly the same rate
Explain how inspiration occurs
The muscles responsible for inspiration are the diaphragm and external intercostals (plus some accessory muscles)
Diaphragm muscles contract, causing the diaphragm to flatten and increase the volume of the thoracic cavity
External intercostals contract, pulling ribs upwards and outwards (expanding chest)
abdominal muscles and internal intercostal muscles are relaxed
These movements increases volume of the thorax cavity and hence decreases pressure inside
Air flows into the lungs from outside
Explain how expiration occurs
The muscles responsible for expiration are the abdominal muscles and internal intercostals (plus some accessory muscles)
Diaphragm muscles relax, causing the diaphragm to curve upwards and reduce the volume of the thoracic cavity
Internal intercostal muscles contract, pulling ribs inwards and downwards (reducing breadth of chest)
Abdominal muscles contract and push the diaphragm upwards during forced exhalation
external intercostal muscles remain relaxed
Thorax cavity volume decreases and inside pressure increases
Air flows out of the lungs into the atmosphere
What is lung cancer, its impact and types
Lung cancer describes the uncontrolled proliferation of lung cells, leading to the abnormal growth of lung tissue (tumour)
The abnormal growth can impact on normal tissue function, leading to a variety of symptoms according to size and location
The tumours can remain in place (benign) or spread to other regions of the body (malignant)
Lung cancers are the most common cause of cancer-related death worldwide for two main reasons:
The lungs are vital to normal body function and thus the abrogation of their normal function is particularly detrimental to health
The lungs possess a very rich blood supply, increasing the likelihood of the cancer spreading (metastasis) to other body regions
The common symptoms of lung cancers include
The common symptoms of lung cancers include coughing up blood, wheezing, respiratory distress and weight loss
If the cancer mass compresses adjacent organs it can cause chest pain, difficulty swallowing and heart complications
