Topic 7 Flashcards
What is meant by the term “external respiration”?
The exchange of gases between the blood and the external environment
The average adult takes how many breaths per minute and exchanges more than how many litres of air per day?
- 12 - 18
* 8000
Which structures form the upper respiratory tract?
- The nasal cavities
- The pharynx
- The larynx
The walls of the bronchi contain what?
Why?
- Cartilage
* To prevent their collapse
What is the smallest division of the bronchi?
Terminal bronchioles
What are the pleura?
Thin membranes which line fluid-fillid cavities between the lungs and the inside of the thoracic (chest) wall
What structure does the base of each lung rest on?
The diaphragm
What are cardiac impressions?
The grooves on each lung which the heart sits within
What are the structures of the conduction zone of the respiratory system?
- The nasal passages
- The pharynx
- The larynx
- The bronchi
- The bronchioles
How many times do the terminal bronchioles further divide, and into what?
- Seven
* Respiratory bronchioles, alveolar ducts, alveolar sacs
What are the holes in the walls of the alveolar sacs called?
Alveolar pores
In an adult human, roughly how large is the respiratory surface?
140 sq m / the size of a tennis court
Why is the respiratory surface so large?
To increase capacity to exchange CO2 and O2
In which structures within the lungs does CO2/O2 exchange occur?
- The respiratory bronchioles
- Alveolar ducts
- Alveoli
What is haemoglobin?
A globular, iron-containing protein present in red blood cells which binds oxygen and transports it to tissues
What are the steps of the flow of air from the conduction zone through to the respiratory zone?
- Air is taken in through the nasal cavities
- Air passes down the pharynx, past the epiglottis and into the larynx
- From the larynx, air travels into the trachea and into the bronchi
- Air moves through the terminal bronchioles into the respiratory bronchioles
- Air passes into the alveolar ducts and into the alveolar sacs
What are the muscles of respiration?
- Diaphragm
* Intercostal muscles
Which nerve innervates the diaphragm?
Where in the brain does that nerve originate?
- The phrenic nerve
* The medulla
Where do the intercostal nerves receive their neuronal inputs from?
The thoracic nerves of the spinal cord
What type of muscle surrounds the bronchi and bronchioles?
Smooth muscle
During which part of respiration are the external intercostal muscles most active?
Inhalation
During which part of respiration are the internal intercostal muscles most active?
Forced respiration
A _______________ is the reason that air is drawn into and forced out of the lungs?
Pressure gradients
Is expiration a passive or active process?
Passive
What is the mechanism by which the ribcage, diaphragm and lung tissues return to their pre-inspiratory positions?
Elastic recoil
Put in broad terms, what are the factors which can regulate pulmonary ventilation?
- Pressure gradients
- Surface tension
- Airway resistance
- Lung compliance
What is meant by the term “compliance” in reference to lungs?
The ease with which the lungs and pleura expand and contract based on changes in pressure
What is airway resistance?
The friction that is generated when the air passes along the structures in the conduction and respiratory zones
What does Boyle’s law state?
That at a constant temperature, an increase in pressure causes a proportional decrease in volume
PV = k
In physiology, how is a unit of pressure conventionally measured?
Millimetres (mm) of mercury (Hg) - mmHhg
What does mmHg refer to?
The height of a column of mercury attached to an instrument which detects pressure
How many Pa is 1 mmHg equivalent to?
133 Pa
At sea level, the atmospheric pressure on Earth is about what?
760 mmHg
Describe the process of inhalation and exhalation in regards to pressure
- During inhalation, the volume of the lungs increases and the pressure inside the lungs decreases below that of atmospheric pressure
- This creates a pressure gradient which draws air into the lungs
- During exhalation, the lungs return to their original size and pressure in the lungs rises compared with atmospheric pressure and air moves out
What is meant by the term “partial pressure”?
The pressure that one component of a mixture of gases would exert if it were alone in a container
How is partial pressure calculated?
By multiplying the percentage of the particular gas in the atmosphere by the total atmospheric pressure
What is the notation used to represent partial pressure?
An italicised ‘P’
What is meant by the term “surface tension”?
Chemical forces that hold liquids in their smallest surface area possible
What shape are the alveoli?
Round
In which direction does surface tension put pressure on the inside of the alveolus?
Inwards
How does the lung combat the surface tension of water to ensure that the alveoli can expand with each breath?
Cells within the alveoli secrete surfactant
What is a surfactant?
A phospholipid substance which breaks the surface tension of water by attaching to the water molecules and preventing them from interacting with each other
What is the surface tension in the alveolus reduced to thanks to the surfactant?
Near-zero levels
What kind of effect can insufficient surfactant production cause?
Breathing difficulties
What is compliance (with regard to lungs)?
The ease with which the lungs and pleura expand and contract based on changes in pressure
What is the effect of low lung compliance on the pressure gradient needed to get lungs to expand and contract?
It means that a higher than normal pressure is needed
What is the outcome of high lung compliance?
The lungs move in response to small changes in pressure which makes exhalation difficult because the elastic recoil is decreased
High lung compliance is a characteristic of which disease?
COPD - chronic obstructive pulmonary disease
Is the airflow resistance in a bronchiole higher or lower than in a bronchus?
Higher - the radius of a bronchiole is smaller than that of a bronchus. A smaller radius equals higher resistance
How is lung capacity calculated?
From the volume of air that is exchanged during normal and forceful breathing
With regards to breathing, what does resting tidal volume refer to?
The amount of air entering or leaving the lungs in a single normal breath
What is the resting tidal volume of an average adult?
About half a litre
What is inspiratory reserve volume?
The air you take when you take an extra deep breath
What is expiratory reserve volume?
The extra volume you breathe out when you breathe out for as long as you can after a normal intake of breath
What is the average inspiratory volume for an adult?
About 2 to 3 litres
What is the average expiratory reserve volum for an adult?
About 1 litre
What is “vital capacity”?
The sum of the tidal, inspiratory and expiratory volumes
What is “total lung capacity”?
The sum of all the volumes, including the residual volume
What does total lung capacity represent?
The maximum amount of air that the lungs can hold
What is “residual volume”?
The amount of air left in the lungs in addition to the expiratory reserve volume
What is “tidal volume”?
The amount of air entering or leaving the lungs in a single resting breath
What is spirometry?
The test used to measure lung function
What is “forced vital capacity” (FVC)?
The total volume of air that can be forcefully blown out
What is “peak expiratory flow” (PEF)?
The maximum rate at which air is forcefully expired (litres per second)
What is “forced expiratory volume” (FEV1)?
The amount of air that is forcibly blown out within the first second of a spirometry test
What values are used to evaluate lung function?
The FEV1 (forced expiratory volume) and FVC (forced vital capacity) ratio
What is the average FEV1/FVC (forced expiratory volume/forced vital capacity) ratio in healthy individuals?
0.8 - meaning that 80% of total volume of air is blown out within the first second (of a spirometry test)
What biological/physiological factors can affect normal lung function?
- Age
- Height
- Ethnicity
- General fitness
What happens to lung function with age in both men and women?
It decreases
How is most O2 carried in the blood?
By erythrocytes which contain haemoglobin (Hb)
What is haemoglobin formed of?
It is a protein which is formed of four polypeptide chains called globins
What are the names of the two types of polypeptide chains which form haemoglobin?
- Alpha
* Beta
What is a haem group?
A small non-protein structure
What are the molecules in the centre of a haem group?
An iron ion (FE2+), which binds to one O2 molecule
How many O2 molecules can one Hb molecule carry
Four
What is oxyhaemoglobin?
Haemoglobin which is bound to oxygen molecules
What does oxyhaemoglobin do?
It transports oxygen from blood vessels in the lungs to the cells in the rest of the body
Where in the lungs does oxygenation of haemoglobin occur?
In the capillaries surrounding the alveoli of the lungs
What is the type of relationship which governs the binding of O2 to Hb?
Positive cooperativity
What is positive cooperativity?
When the change in shape of the first subunit makes easier the binding of substrate to the second unit
What form of Hb is predominant in the blood carried by the pulmonary arteries?
Deoxyhaemoglobin - pulmonary arteries carry CO2-rich blood, therefore deoxyhaemoglobin will be the predominant form of Hb in these vessels
What is the binding and dissociation of O2 to and from haemoglobin dependent on?
The PO2 (partial O2 pressure)
What does the term “affinity” refer to?
The strength of binding between two particles or proteins. Low affinity means the particles can be easily separated; high affinity means the binding is strong
Does the binding of O2 to Hb have high or low affinity?
Low - this is why O2 is easily transferred to tissues
During exercise, what happens to muscle cells?
They become more active and produce more CO2 and heat, which increases the acidity and content of the haemoglobin protein 2,3-diphosphoglyceric acid (DPG)
With regards to oxygen saturation, what is P50?
A representation of haemoglobin-oxygen affinity
What is the normal P50?
26.7 mmHg
When CO2 levels are low, does the affinity of haemoglobin for oxygen increase or decrease?
Increase
What are the biological factors which affect the affinity of Hb binding of O2?
- CO2
- Acidity
- 2,3-DPG
- Exercise
- Temperature
What is the Bohr effect?
The decrease in the oxygen affinity of haemoglobin in the presence of high pH or high CO2. It manifests as a right-shift in the Oxygen-Haemoglobin Dissociation Curve
The chemical reaction between water and CO2 generates what?
- Bicarbonate
* Hydrogen protons
Do hydrogen ions increase or decrease the pH of a solution?
Decrease
What is the acid which is formed when carbon dioxide combines with water in the erythrocytes?
Carbonic acid
The reaction between carbon dioxide and water is facilitated by which enzyme?
Carbonic anhydrase
What does carbonic acid dissociate into?
- A bicarbonate ion
* A proton
What is the chloride shift?
The process where chloride ions move into erythrocytes from the blood in order to balance its charge
What is carbaminohaemoglobin?
Haemoglobin which is bound to carbon dioxide
In the alveoli, binding of O2 to HbH+ (protonated haemoglobin) results in what?
The release of free H+ ions
What is the Haldane effect
The influence of oxygen on haemoglobin transport of carbon dioxide
Which gas greatly reduces the capacity of blood to carry O2?
Carbon monoxide - because the affinity for Hb is higher than the affinity oxygen
The replacement of which amino acid disrupts the structure of haemoglobin and causes sickle cell anaemia?
What amino acid replaces it?
- Glutamic acid
* Valine
How is sickle cell denoted?
HbS
Why do the erythrocytes change shape in sickle cell anaemia?
Because glutamic acid normally helps Hb retain its shape
How long do sickled cells live in comparison to normal erythrocytes?
20 days instead of 120 days
If you were heterozygous for the HbS (sickle cell) allele, will you develop sickle cell anaemia?
No - you would have one mutated allele, and one normal allele. Sickle cell is recessive, therefore two mutated alleles must be present
What are thalassaemias?
A group of recessive disorders which cause anaemia due to the decreased/absent synthesis of a globin chain of haemoglobin
How many alleles is disease susceptibility to thalassaemias dependent on?
Four
