Respiratory system Flashcards
What are the two kinds of respiration?
Internal- within the cell, CO2 produced from glycolysis and krebs cycle, O2 produced by oxidative phosphorylation
External- ventilation, exchange and transport of gases around the body
What are the two sections of the respiratory system?
Conducting zone- provide pathways to get air to and from the respiratory zone
Respiratory zone- where gas exchange takes places
What structures are in the conducting zone? What is their function?
Nose, nasopharynx, osopharynx, pharynx, larynx, trachea and bronchial tree
Conditions the incoming air by filtering, warming and humidifying
Structure of the bronchial wall
Reinforced with cartilage
Smooth muscle
Mucous glands
Elastic tissue
Structure of respiratory epithelium
Ciliated epithelia
Goblet cells
Sensory nerve endings
Structure of bronchioles
Lack of cartilage support
Lined by respiratory epithelium
Proportionately more smooth muscle
Structure of alveoli
Large surface area
Fed from terminal bronchiole
Thin walled
What is the air blood barrier?
Sandwich created by flattened cytoplasm of type I pneumocytes and the capillary wall
Large surface area for gas exchange to take place
How do pressure gradients aid inspiration and expiration?
Inspiration- atmospheric pressure > pressure in alveoli so air moves into the lungs
Expiration- atmospheric pressure < pressure in alveoli so air moves out of the lungs
Quiet inspiration
Uses primary muscles of inspiration- diaphragm and external intercostal muscles
Increases thoracic and lung volume
Air movement follows principles of Boyle’s law- increase in volume leads to decrease in pressure so air moves down pressure gradient
Forced inspiration
Primary muscles as well as accessory or secondary muscles used- scalenes, sternocleidomastoids, neck and back muscles, upper respiratory tract muscles
Quiet expiration
Passive process using elastic recoil, there are no primary muscles of expiration
Relaxation of external intercostal muscles and diaphragm
Elastic forces return the lungs to their usual size
Forced expiration
Uses accessory muscles- internal intercostal muscles, abdominal muscles, neck and back muscles
What is the pleura and it’s function?
Pleural cavity filled with secretions
Prevents lungs from sticking to the chest wall and enables free expansion and collapse of the lungs
What is lung compliance?
Measure of elasticity- the ease with which the lungs and thorax expand during pressure changes
Low compliance means more work is required to inspire and high compliance means more work is required to expire
How do disease states effect lung compliance?
Emphysema- high lung compliance
Fibrosis- low lung compliance
What are the two major components of the elastic recoil of the lungs?
Anatomical- elastic nature of cells and the extracellular matrix
Surface tension generated at the air-fluid interface
How does surface tension at the air-fluid interface impact the volume of alveoli?
There are many air sacs of different volumes and because of Laplace’s equation, the pressure in larger sacs is lower than smaller ones
This means air will flow from smaller alveoli to larger ones which means they will collapse
How is the problem of smaller alveoli collapsing solved?
Lung surfactant which is produced by type II pneumocytes
Reduces surface tension
Composed of a number of lipids and proteins
What is the only lung volume that cannot be measured with a spirometer?
Residual volume
What is anatomical dead space?
Volume of conducting airways, at rest 30% of inspired air volume
What is physiological dead space?
Volume of the lungs that isn’t participating in gas exchange- conducting zone and non-functional parts of the respiratory zone
What is Poiseuille’s law?
Airway resistance is proportional to gas viscosity and the length of the tube but is inversely proportional to the fourth power of the radius
What is the relationship between air flow in the lungs and the pressure gradient?
The flow of air into or out of the lungs is proportional to the pressure gradient and inversely proportional to the resistance
Airway resistance in different parts of the respiratory system
Pharynx + larynx- 40%
Airways less than 2mm in diameter- 40%
Airways more than 2mm in diameter- 20%
What factors influence airway resistance?
Airway diameter
Increased mucous secretion will reduce airway diameter and therefore increase resistance
Oedema- increased fluid retention in lung tissue will cause swelling and narrowing of airways and will therefore increase resistance
Airway collapse- also narrows airway
Parasympathetic control of smooth muscle in the bronchioles
ACh is released from the vagus nerve and acts on muscarinic receptors
Leads to constriction
Sympathetic control of smooth muscle in the bronchioles
Norepinephrine is released from nerves
Leads to dilation
What humoral factors influence the control of brionchiole smooth muscles?
Epinephrine circulating in the blood leads to dilation
Histamine is released during inflammatory processes and this leads to constriction
What is Dalton’s law?
The total pressure of a mixture of gases is the sum of their individual partial pressures
What is Henry’s law?
Used to determine the concentration of a gas dissolved in a solution
[Gas] = s x P
s = solubility coefficient and P = partial pressure of gas
Structure of haemoglobin
Tetrameric structure with four subunits, each containing a haem unit and a globin chain
2 alpha chains and 2 beta chains
What are the two states a haem group can be in?
Tense- low affinity for oxygen
Relaxed- high affinity for oxygen
What enzyme is responsible for the conversion of Fe3+ back to Fe2+ in haem?
Why is this important?
Methaemoglobin reductase
Haem is only able to bind to oxygen when iron is in it’s Fe2+ state
How is fetal haemoglobin different?
The beta globin chains are replaced with gamma chains
Leftwards shift in Hb-O2 curve as it has a higher affinity for oxygen
In what states is CO2 carried by the blood?
What are these called as a collective?
Dissolved CO2, carbonic acid, bicarbonate, carbonate, carbamino compounds
Total CO2
What are the two kinds of diseases effecting the lungs?
Obstructive- reduction of flow through airways
Restrictive- reduction in lung expansion
What are obstructive lung diseases caused by?
Narrowing of airways which could be due to excess secretions, bronchoconstriction, or inflammation
What lung volume do obstructive lung diseases reduce?
Forced expiratory volume (FEV1)
Sharp fall in flow-rate which gives a concave shape to the flow-volume loop
What lung diseases are classed as obstructive?
Chronic bronchitis- persistant cough and excessive mucus secretion
Asthma- inflammatory disease, hyperactive airways
Chronic obstructive pulmonary disease (COPD)- structural diseases
Emphysema- loss of elastin
What are the two types of asthma?
Atopic/extrinsic- allergies and contact with inhaled allergens
Non-atopic/intrinsic- respiratory infections, cold air, stress, exercise, inhaled irritants, drugs
What is the body’s response to the hyperactivity of airways seen in asthma?
Movement of inflammatory cells into airways
Release of inflammatory mediators such as histamine and subsequent bronchoconstriction
What are short term treatments for asthma?
Short acting B2-adrenoceptor agonists like salbutamol
Causes dilation of airways
What are long term treatments for asthma?
Inhaled steroids- glucocorticoids belclometasone act to reduce the inflammatory responses
Long acting B-adrenoceptor agonists
What are two types of causes of restrictive lung diseases?
Reduced chest expansion- chest wall abnormalities, muscle contraction deficiencies
Loss of compliance/fibrosis- normal aging process, increase in collagen, exposure to environmental factors
What lung volume is reduced by restrictive lung disease?
Decreased vital capacity and FVC
What is asbestosis?
Slow build up of fibrous tissue that leads to loss of compliance
How is breathing regulated centrally?
Centres in the medulla generate the basic respiratory rhythm
Involuntary mechanism but can be altered consciously
What medullary centres are in control of inspiration?
Dorsal respiratory group (DRG) sends signals to the inspiratory muscles
Ventral respiratory group (VRG) controls inspiration and expiration, inactive during quiet respiration, during activation helps forceful expiration and inspiration
What centres in the pons also control breathing?
Pneumotaxic centre- increases heart rate by shortening inspirations, inhibitory effect on inspiratory centre
Apneustic centre- increases depth and reduces rate by prolonging inspirations, stimulates inspiratory centre
What is the Hering-Breuer reflex?
Stretch receptors in the lung send signals back to the medulla to limit inspiration and prevent over-inspiration of the lungs
What is the function of central chemoreceptors in the regulation of breathing?
Monitor conditions in the cerebrospinal fluid by sensing CO2 and pH
When there is a rise in CO2 stimulation leads to an increase in ventilation
What is the function of peripheral chemoreceptors in the regulation of breathing?
Located in the carotid body and the aortic arch
Respond to increases in CO2, decreases in pH and O2, stimulation leads to increases in ventilation
