Respiratory pump Flashcards
What is the respiratory pump?
The negative pressure created in the thoracic cavity aids venous return to the heart
inspiration = leads to expansion of the lungs, cardiac chambers (right atrium [RA] and right ventricle [RV]), and the thoracic superior and inferior vena cava (SVC and IVC, respectively).
This expansion causes the intravascular and intracardiac pressures (e.g., right atrial pressure) to fall. Because the pressure inside the cardiac chambers falls less than the Ppl, the transmural pressure (pressure inside the heart chamber minus the Ppl) increases, which leads to cardiac chamber expansion and an increase in cardiac preload and stroke volume through the Frank-Starling mechanism.
Furthermore, as right atrial pressure falls during inspiration, the pressure gradient for venous return to the right ventricle increases.
What are the muscles involved in the respiratory pump and what nerves supply them?
Diaphragm - Phrenic nerve (C3, C4, C5)
External intercostals - thoraco-lumbar nerve roots
What are the other nerves (non-motor) involved in the respiratory pump?
Sensory receptors, C fibres, afferent nerve supply via the vagus nerve
Sympathetic-parasympathetic balance
Describe inspiration
- Diaphragm and inspiratory intercostals contract (phrenic nerves innervate diaphragm causing it to contract, dome moves downwards into abdomen, enlarging thorax)
(simultaneously intercostal nerves cause intercostal muscles to contract, leading to upwards and outwards movement of the ribs and further increase in thorax size)
- Thorax expands
- P ip becomes more subatmospheric
(pressure of intrapleural fluid surrounding lungs)
(as thorax increases in size, the thorax wall moves further away from the lung surface, volume increases so that the intrapleural fluid decreases)
- Increase in transpulmonary pressure (this is greater than lung recoil so lungs expand further)
- Lungs expand
- P alv becomes subatmospheric (alveloi increase in size when lungs expand, so pressure decreases)
- Air flows into alveloi via bulk flow
Describe exhalation
- Diaphragm and inspiratory intercostals stop contracting (motor neurons decrease firing so muscles relax)
- Chest wall recoils inward
- Pip moves back towards preinspiration value
- Transpulmonary pressure moves back towards preinspiration value
- Lungs recoil to preinspiration size
- Air in alveoli becomes compressed due to smaller lung size
- Palv becomes greater than Patmospheric
- So air flows from alveolar into airways and out into the atmosphere
What is inspiration
The movement of air from the external environment through the airways into the alveoli during breathing
What is exhalation
The movement of air from the alveoli through the airways to the external environment during breathing
Describe the structure of the airways
- mouth or nose
- pharynx
- larynx (causes sounds of breathing due to vocal cords)
- trachea (1)
- bronchi (2) contain cartilage
- bronchioles (16) (smooth muscle, no acrtilage)
- terminal bronchioles (32-60000)
- respiratory bronchioles (alveoli attach to walls)
- alveolar ducts
- alveoli sacs (entirely alveoli)
What is in the conducting zone?
No alveoli, and no gas exchange
- mouth or nose
- pharynx
- larynx (causes sounds of breathing due to vocal cords)
- trachea (1)
- bronchi (2) contain cartilage
- bronchioles (16) (smooth muscle, no acrtilage)
- terminal bronchioles (32-60000)
What is in the respiratory zone?
Area of gas exchange
- respiratory bronchioles (alveoli attach to walls)
- alveolar ducts
- alveolar sacs (entirely alveoli)
How do the nasal and oral cavities protect the body
- They contain cilia and mucus and macrophages
- Macrophages can phagocitize inhaled pathogens
- The cilia constantly beat upwards towards the pharynx
- Mucus trap air borne particles, this is continuously and slowed moved by the cilia to the pharynx and then swallowed (mucous escalator)
What can decrease the number and activity of cilia
Smoke from chronic smoking (this is why smokers often cough up mucus that cilia would normally clear)
-smoking also damages macrophages that engulf bacteria
What fluid is impaired in cystic fibrosis? What does this impair?
normally the airway epithelium secretes a watery fluid that the mucus can freely ride on
- in CF the fluid becomes thick and dehydrated, this means it can obstruct the airway
- mutation in CFTR protein = problems in water and salt movement
How is CF usually treated?
- Therapy to improve clearance of mucus from the lung
- Aggressive use of antibiotics to prevent pneumonia
- Lung transplantation? -often other parts of GI tract, eg. pancreas
What cells are alveolar sacs lined with
- Type I alveolar cells, one cell thick, numerous
- Type II alveolar cells, thicker, produce surfactant
- in many places there is no interstitial space and the basements membranes of the alveolar-surface epithelium and capillary wall endothelium fuse. air is separately by 0.2micrometres
- contain capillaries, and very small interstitial space (interstitial fluid and loose connective tissue meshwork)
What features increase diffusion?
- Large SA
- Thin diffusion distance due to thin barrier
How are larger expiration volumes achieved during exercise? -forced expiration
- Larger volumes are achieved by contraction of a different set of abdominal muscles and intercostal muscles which actively decreased thoracic dimensions
- The internal intercostal muscles insert on the ribs so that their contraction pulls the chest wall downward and inwards, decreasing thoracic volume.
- This smaller size, increases pressure of alv, and so more air is forced out
- Contraction of the abdominal muscles increase intra-abdominal pressure and forces the relaxed diaphragm up into the thorax
What is lung compliance
The magnitude of change in lung volume produced by a given change in transpulmonary pressure
C L = ∆V l / ∆P tp
(lung compliance) = (change in lung volume) divided by (given change in transpulmonary pressure )
The greater the lung compliance the easier it is to expand the lungs at any given change in transpulmonary pressure. compliance can be considered the inverse of stiffness.
- A low lung compliance (increased stiffness) means that a greater change in transpulmonary pressure must occur before lung expansion occurs. This requires more vigorous contractions of the diaphragm and inspiratory intercostal muscles.
- People with low lung compliance due to disease tend to breathe shallowly and at a high frequency to inspire an adequate volume of air
What two things affect lung compliance
- Stretchability of lung tissues (therefore thickness)
2. Surface tension (surfactant)
What increases surfactant levels
A deep breath stretches the type II cells, this stimulates secretion of surfactant
