Physiology Flashcards
What is internal respiration?
The intracellular mechanisms which consume oxygen and produce carbon dioxide
What is external respiration?
The sequence of events that lead to the exchange of oxygen and carbon dioxide between the external environment and the cells of the body
What are the four steps of external respiration?
Ventilation, gas exchange between alveolar air and blood, transport of gases between lungs and tissues, gas exchange between blood and tissues
What are the three body systems involved in external respiration?
Resp, CV, Haemotology
How does air move (in regards to pressure)?
Air moves from an area of high pressure to an area of low pressure
What muscles contract during inspiration?
Diaphragm and external IC muscles?
What are the accessory muscles of inspiration?
Scalene and sternocleidomastoid
Explain intrapleural fluid cohesiveness
Water molecules in the intrapleural fluid are attracted to eachother and resist being pulled apart - pleural membranes tend to stick together
Explain negative intrapleural pressure
sub-atmospheric intrapleural pressure creates a transmural pressure gradient across the lung wall and across the chest wall. So the lungs are forced to expand outwards while the chest is forced to squeeze inwards
How does diaphragmatic contraction cause inspiration?
Diaphragm contracts and flattens - increases vol of thorax - decreases pressure in lungs ( controlled by phrenic nerve from C3,4 & 5
How does external IC contraction cause inspiration?
external IC contraction lifts the ribs and moves out the sternum - increases thoracic vol - decreases pressure in lungs
What is passive expiration caused by?
Elastic recoil of the lungs
How does a pneumothorax affect pressure in lungs?
Abolishes transmural pressure gradient
What causes the lungs to recoil during expiration?
Elastic connective tissue in the lungs and alveolar surface tension (more important)
What is alveolar surface tension?
Attraction between water molecules at liquid air interface. In the alveoli this produces a force which resists the stretching of the lungs. If the alveoli were lined with water alone, the surface tension would be too strong - the alveoli would collapse
According to the law of Laplace:
the smaller alveoli have a higher tendency to collapse
What is pulmonary surfactant and what does it do?
PS is a complex mixture of lipids and proteins secreted by type II alveoli. It lowers alveolar surface tension by interspersing between the water molecules lining the alveoli. Prevents smaller alveoli from collapsing and emptying their contents into the larger alveoli
What is respiratory distress syndrome of a new born?
Developing fetal lungs are unable to synthesise surfactant until late in pregnancy (means prem babies don’t have enough pulmonary surfactant) - causes resp distress syndrome of the newborn. Baby makes v. strenuous inspiratory efforts in an attempt to overcome the high surface tension and inflate the lungs
What is alveolar interdependence?
If an alveolus starts to collapse then the surrounding alveoli are stretched. They then recoil - exerting expanding forces in the collapsing alveolus to open it.
What are the forces keeping the alveoli open?
Transmural pressure gradient, pulmonary surfactant and alveolar interdependence
What are the forces promoting alveolar collapse?
Elasticity of stretched pulmonary connective tissue fibres and alveolar surface tension.
What are the four factors which influence gas transfer across membranes?
partial pressure gradient, diffusion coefficient, SA, membrane thickness
What is the following description describing?
The processes that exchange oxygen and carbon dioxide between the external environment and the cells of the body
External respiration
What is the following description describing?
Comprises ventilation, gas exchange between the alveoli and blood, gas transport and gas exchange at the tissues
External respiration
Which receptors influence the pons?
Peripheral chemoreceptors
What changes does the pons respond to?
Decreased pH
Increased H+
Increased PCO2
Decreased PO2
What effect does the pons cause on the resp rate?
It increases
Does smoking affect idiopathic fibrosis?
It increases the risk two-fold
What’s the cure for IPF?
There isn’t one
