Lung development, structure and gas movement Flashcards
What are the three tubular systems that are packed within the lungs called?
Airway
Pulmonary blood supply
Bronchial blood supply
Name the 5 stages during lung development
1) Embryonic
2) Pseudoglandular
3) Canalicular
4) Saccular
5) Alveolar
Describe the embryonic stage of lung development
- Formation of left and right lung lobes 26days-6weeks
- The primordial lung (lung anlage) develop as buds whihc extend outwards from the fetal foregut (oesophagus)
Describe the Pseudoglandular stage
- Formation of the gas conducting airway of the respiratory tree
- Fluid secretion into the airways creates a distending pressure that provides support for growth
What does Irregular dichotomous branching mean?
- Allows airways to fill spaces of varied dimensions which achieves even distribution of gas
- Allows distributuion of mechanical strain of breathing evenly
What gradient drives fluid movement into the airway lumen giving mechanical support for 3D growth?
Chloride gradient
Cl- is accumulated against its electrochemical gradient. Is there a higher number of Cl ions in the blood plasma or Airway lumen
Higher in blood plasma
Describe the canalicular stage?
Airways and blood vessels meet to form an interface. The blood-gas barrier
Describe the formation of the blood gas barrier
- Epithelial cells begin to differentiate
- Basement membrane forms
- Capillaries adhere beneath basement membrane
What type of cells are formed to make the barrier to capillary making the gas exchange surface?
Type I pneumocyte
Where does deoxygenated blood from the body return to?
The right atrium of the heart, contraction of the right atrium pushes blood tp the right ventricle, then sends blood through pulmonary artery to the lung
Why is the pulmonary artery called an artery?
Conducting blood from heart and sending to an organ
After the pulmonary artery brings the deoxygenated blood to the lung, what happens?
Lung oxygenates the blood and then returns to the left atrium along the pulmonary veins
Why is the pulmonary vein called a vein?
Conducting blood from an organ to the heart
What happens to the oxygenated blood in the left atrium?
Contraction of the left atrium pumps blood into the left ventricle which then contracts and circulates the blood around the body
The lining of the alveolar space is called what?
The pulmonary surfactant
What type of environment is the lung?
Sterile
Describe stage 4 (saccular)
- Formation of the first septal fold of the early alveolus
- Defines gas exchange zone of the lung: The respiratory acinus
The bifurcating airway terminus is formed in the 4th stage, what are the thin walled airways maintained by?
Patent by Cl- driven fluid secretion into the luminal space
What is stage 5 of the lung development and describe it
- Alveolar
- Increase in gas exchange surface area by pocketing on the wall of the sacular lung
- Asingle capillary network occupies the septal walls between each alveolus and the membranes thin to aroun 200nm
How is fluid cleared from the lung at birth?
Fluid absorption in the fetal lung is driven by the epithelial Na+ channel (ENaC)
What is ENaC?
A Na+ selective channel found in all secretory epithelia
Briefly describe what happens in clearing the lungs at birth
- Maternal cortisol increases in the last trimester and crosses into fetal circulation and induces ENaC subunit gene expression.(Epithelial sodium channel)
- During labour, a rise in maternal adrenaline crosses into fetal circulation and activates the channel
- Fluid is then rapidly cleared from the fetal lung in preparation for the first breath
Describe the fractal design of the airway and vasculature
A repeated geometric shape repeated at different magnitudes
Packs colossal proportions into a confined space
What is the average size of the gas exchnage surface area?
130m^2
What is the average distance travelled by gas from atmosphere to alveolus?
25cm
What is the tensile pressure required to rupture the blood gas barrier?
o.5MN.m-2
same to rupture ceiling tile
Why use partial pressure gradients in respiratory physiology?
Tells you the direction of movement of gas
Alveolar ASL (Airway surface liquid) has lower ....... concentration BUT higher ......... than venous blood? (fill in blanks)
O2
Partial pressure
Airway branching has two consequences for lung function. What are they?
Increases surface area fro gas exchange
Dissipates resistance to air flow as airway diameter narrows towards the respiratory zone
A resistance of total airway diameter at each branch generation reduces resistance at what fold?
16 fold
The bulk flow of gas into the conductive zone is driven by difference in …… caused by expansion and relaxation of the chest cavity
(fill in blank)
net pressure
Gas movement in the airway arises by what?
Convection not diffusion
In what circumstances does gas move into the alveoli?
- Alveolar pressure less than atmospheric
- Airways are open
Gas moves out of the alveoli if what?
- Alveoli pressure is greater than atmospheric
- Airways are open
Alveolar pressure is the sum of what?
- Elastic recoil pressure (always collapsing)
- Pleural pressure-variable by muscular effort
How do we create breathing (inspiration)?
External intercostal muscles inbetween rib cages pull structure of rib up and out and diaphragm contracts which lowers th epressure in the airways creating more space for gas to enter the airways
Name the main inspiratory muscle and describe it
- Diaphragm - dome shaped, sits above the liver
- Has phrenic nerves, C3-5
- Flattens on contraction
- Moves 1cm in quiet breathing, up to 10cm
- Major inspiratory muscle
Within the external intercostals where are the intercostal nerves located?
rib level
What are the accessory muscles and what do they cause?
Sternocleidomastoid
Scalenes
Chest expands, intrapleural pressure falls
Describe the process of expiration
Internal intercostal muscles depress the upper rib more than raising the lower rib
Why is expiration mainly passive during quiet breathing?
Elastic recoil pressure is sufficient
What is forced expiration?
Exercise, voluntary (cough, sneeze, defeaction)
What are the main muscles used in expiration?
Abdominal wall-push guts up against diaphragm
Internal intercostals
