Respiratory physiology Flashcards
What are the functions of the respiratory system ?
- Gas exchange
- Acid base balance
- Protection from infection
- Communication via speech
Which two mechanisms does gas exchange reply most heavily on ?
Inhalation and exhalation
What is meant by a ‘ steady state of volume ‘?
Volume of gas exchange at the lungs matches the volume of gas exchange at the tissues
Why is a steady state of volume important?
Ensures that supply equals demand and there isn’t a build up of gas in the circulation
What is Acid-base balance ?
The regulation of the ECF pH. It is controlled by the repiratory and renal systems working together.
Very broadly, what are the two ways in which the reparatory system can be classified ?
- External and internal respiration
- Pulmonary and systemic
Describe the external and internal respiration
The external - Getting oxygen in and carbon dioxide out and around the body.
The internal - Use of oxygen and production of Carbon dioxide in cellular reactions
Describe pulmonary and systemic circulation
Pulmonary - heart to lungs and back. Arteries have de-oxygenated blood while veins have oxygenated blood.
Systemic - Heart to tissues and back. Arties have oxygenated blood while veins have de-oxygenated blood.
Name the 8 terminologies used to describe breathing
Tidal volume Residual volume Expiratory reserve volume Inspiratory reserve volume Total lung capacity Inspiratory capacity Vital capacity Functional residual capacity
What is the tidal volume ?
500ml which is expired and then inspired in a normal breath at rest
What is residual volume?
1200ml of air which is always found within the lungs and you cant remove.
What is the function of the residual volume ?
- Prevents alveoli from collapsing which means that they require less energy to fill with air.
- Allows gas exchange to continue continually (i.e. even while not actively inspiring)
What is the expiratory reserve volume ?
The volume of air which you can voluntarily expire but don’t breath out in a normally expiration at rest
What is the inspiratory reserve volume ?
The volume of air which you can voluntarily inhale but don’t breath out in a normally inhale at rest
What is the total lung capacity ?
The total amount of air which a person can hold in there lungs. In an adult this is normally 6l
What is inspiratory capacity ?
The volume of air which you can voluntarily inhale including the volume you normally inhale at rest
What is vital capacity ?
The volume or air in our lungs that we have control over i.e. the total volume we can breath in from when out lungs feel empty or the total volume we can breath out when out lungs are full.
What is vital capacity used for?
The vital capacity is used to measure lung function
What is the functional residual capacity ?
The volume of air left in your lungs at the end of a normal exhalation at rest
When thinking about the terminology of breathing what is a capacity ?
Number of volumes added together
What is the normal number of breaths per minuite ?
12-18 at rest
40-45 in exercise
What are the recall points for ‘the respiratory system’
Functions
Classifications
Terminology of breathing
Draw diagram of the different terminologies of breathing
-
What part of the respiratory tract make up the upper respiratory tract ?
Nose
Pharynx
Epiglottis
Larynx
What is the role of the nose in the respiratory system ?
Allows air to enter the body.
Contains cilia and mucus which trap particles and warm and moisten the air.
Why doesn’t air just enter through the mouth ?
Less surface area and therefore it more uncomfortable
What is the role of the pharynx in the respiratory system ?
It is the throat and is shared with the digestive system
What is the role of the Epiglottis in the respiratory system ?
Where the pharynx becomes the larynx there is a small flat of tissue that folds over the trachea. Normally it is open to allow air into the lower respiratory tract but when we swallow it closed to prevent food from entering it (aspirating).
What parts of the respiratory system are considered to be part of the lower respiratory tract?
Trachea
Bronchi
Lungs
Describe the path of air though the airways
Trachea Primary bronchi Secondary bronchi Tertiary bronchi Bronchioles Alveoli
Describe the trachea
The largest airway is the trachea. It is a semi-rigid tube (patent) whose shape is maintained by C shaped rings of cartilage.
Describe the bronchi
The trachea splits into two primary bronchi one for each lung. The right primary bronchi is wider and more vertical than the left primary bronchi. Therefore aspirated foreign bodies are more likely to get stuck in the left bronchi.
The primary bronchi then split into secondary bronchi (one secondary bronchi for each lobe of the lung) and then split into tertiary bronchi (one for each bronchopulmonary segment of the lung). The amount of cartilage decreases the further into the lung you go until there is no cartilage at all. Then these airways are held open by physical forces in the thorax.
Tertiary bronchi then divide multiple times to from bronchioles which divide multiple times forming alveoli.
Where does gas exchange occur?
Gas exchange occurs in the alveoli and some bronchioles called respiratory bronchioles. Gas exchange is able to occur here due to a large thin surface.
Describe resistance in the airways
In the large airways there is a high level of resistance to air flow while in the small vessels there is a low level of air flow resistance. This is the case because the cumulative diameter of all the little vessels is higher than the diameter of the large vessels and so air flow more easily in the small vessels with larger diameter. Imagine a series of roads, sometimes the biggest are the once’s with most traffic and slowest moving cars. Contraction of the bronchial smooth muscle can also increase the airway resistance by decreasing the airway diameter.
Describe the basic structure of the right lung
The right lung has three lobes (Superior, middle and inferior) which are separated by a horizontal and then oblique fissure.
Describe the basic structure of the left lung
The left lung is slightly smaller because of the positioning of the heart. It has two lobes (superior and inferior) which is separated by an oblique fissure.
What volume of fluid is found in each pleural cavity ?
3ml
What is the process by which the fluid in the pleural cavity is produced?
Filtration
What cells can be found in the pleura ?
Macrophages, lymphocytes and mesothelial cells
What is the role of the fluid found in the pleural cavities
Acts like a glue keeping the two sides of the pleura together. It prevents the lungs from separating from the ribcage and diaphragm (the lungs will follow the movements of the ribcage and diaphragm, if the ribs expand so will the lungs and it prevents the recoil of the lungs when they are stretched). At the end of a normal expiration an equilibrium is reached between the lungs which want to recoil a bit and the chest wall that wants to expand a bit. Both are prevented from doing so by the cohesive force of the pleural fluid.
What components make up alveoli ? Give a brief statement about there function
Macrophages - Increase lung immune function
Type I pneumocyte - Allow for gas exchange
Type II pneumocyte - Secrete surfactant
Blood vessels - Always surrounded by type I pneumocytes
Elastic fibres - Surround type I pneumocytes allowing for lung expansion
What are the two types of pleuritic pleura
In fact just one pleura but two sides;
Visceral (next to the lung)
Parietal (next to the chest wall)
Recall points for ‘anatomy of the respiratory system’
Parts
Airways
Lungs
Alveoli
What are the names of the four laws which govern the mechanics of breathing?
Boyle’s law
Dalton’s law
Charles Law
Henry’s law
What does Boyle’s law state?
The pressure exerted by a gas is inversely proportional to its volume
What does Dalton’s law state?
The total pressure of a gas mixture is the sum of the pressures of the individual gases
What does Charles Law state?
The volume occupied by a gas is directly related to the absolute temperature.
What does Henry’s law state?
The amount of gas dissolved in a liquid is determined by the pressure of the gas and its solubility in the liquid.
Using your knowledge of the laws of pressure how does breathing work?
Inspiration - Check wall expands, lungs expand, volume increases and so pressure decreases, air moves down its pressure gradient into the lungs
Expiration - the opposite
Which muscles are involved in inspiration?
External intercostal muscles
Diaphragm
and occasionally the sternocleidomastoid and scaenas muscles
What movement is caused by the muscles of inspiration?
Upward and outward movement of the ribcage
What muscles are involved in expiration?
Normally passive but can involve the internal intercostal and abdominal muscles.
Describe what happens to the diaphragm through respiration
Diaphragm contacts and flattens to increase volume. It is innervated by the phrenic nerve which causes a contract when it fires.
Describe the resistance of the airways during the breathing cycle?
Airways are forced open during inspiration by physical forces.
Airways are compressed by physical forces on expiration.
Therefore resistance is greatest on expiration. This isn’t noticed by most people but can aggravate asthma.
What are the three different pressure associated with the lungs ?
Intro-thoracic pressure
Intro-pleural pressure
Transpulmonary pressure
What is intro-thoracic pressure?
Pressure of the thoracic cavity. If the pressure is greater than atmospheric pressure when it is positive. This is what gives rise to inspiration and expiration and will vary throughout the breathing cycle.
What is intro-pleural pressure?
Pressure within the inside of the pleural cavity. In healthy lungs this is always negative. Due to the tension of the chest wall and lungs there is an increase in volume and decrease in pressure the less air that is found in the lungs.
What is transpulmonary pressure?
Alveolar pressure - Intra-pleural pressure
Almost always positive
What is surfactant?
It is a detergent like fluid which is produced by type II pneumocytes.
What are the functions of surfactant?
- Reduces surface tension
- Helps to prevent alveoli from collapsing
- increases lung compliance
- Reduces the lungs tendency to recoil
How does surfactant prevent alveolar collapse?
Water forms a film on the surface of the alveoli. This creates an air water interface. The water molecules are attracted to each other creating an inward directed force which would result in the collapse of the alveoli.
Surfactant sits in between the water molecules and prevents this attraction from forming.
Which law does surfactant follow?
The law of LaPlace where P = 2 T/r
Is surfactant more effective in large or small alveoli?
Small because of the higher concentration
What is IRDS?
Infant respiratory distress syndrome.
Surfactant is complete at week 36. Babies born before that can have IRDS where there alveoli keep collapsing and so breathing requires much more energy.
Breathing air is already harder than amniotic fluid never mind having to inflate collapsed alveoli.
What is compliance?
Change in volume relative to the change in pressure. It does not tell anything about the stretch ability of the lungs (I.e. its recoil)
What does a highly compliant lung mean ?
A small increase in oxygen causes a large increase in volume
What happens to compliance as the pressure and volume increase
it increase
Why doesn’t the inspiration and expiration graph (of pressure against volume) interpose themselves ?
Because a higher pressure change is require to increase volume at low pressures and a greater decrease in pressure occurs per volume measure at the start of the expiration.
