Lecture 2 - Structure of the alveoli, gas exchange, haemoglobin Flashcards
What are alveoli?
Are air filled pockets within the lungs where all gas exchange occurs
Outline the structure of the alveolar epithelium?
Type 1 pneumocytes - simple squamous - thin and flat
Type 2 pneumocytes - secrete surfactant
Alveolar macrophages - digest anything that shouldn’t be there (dust cells)
How are the alveoli organised?
Coated in the capillary bed, entangled between capillaries
Elastic fibres - enable passive elasticity
What is Henry’s Law?
When gas under pressure comes into contact with a liquid it dissolves until equilibrium is reached
At a given temp- amount of gas in solution is proportional to pp of that gas
What are 5 reasons for efficiency of gas exchange?
- Substantial differences in pp across the respiratory membrane
- Distance is short
- 02 and CO2 are lipid soluble
- Large sa
- Blood flow and airflow are coordinated
What is the difference between the pulmonary circuit and systemic circuit?
Pulmonary are the blood vessels that serve the lungs but systemic are the rest of the system
How does gas exchange occur at the lungs?
Blood arriving in the pulmonary arteries has a low PO2 and high PCO2
The lungs is the opposite
Forms a concn gradient and O2 enters and CO2 leaves
How does gas exchange occur in the systemic circuit?
Oxygenated blood mixes with deoxygenate blood lowering the Po2 of blood entering systemic circuit
Interstitial fluid - fills space between tissues - concn gradient in peripheral capillaries is opposite of the lungs O2 into the tissue
How are gases picked up and delivered?
In the blood plasma but can’t transport enough so need red blood cells
Outline red blood cells
- Transport O2 to and CO2 from peripheral tissue
-Removes O2 and CO2 from plasma allowing gases to diffuse in - Anucleate- large O2 carrying capacity
- O2 molecules bind to haemoglobin
What are the forms of haemoglobin?
Oxyhaemoglobin
Deoxyhaemoglobin
Carbaminohaemoglobin
Has 2 alpha and 2 beta chains with haem groups Fe2+ ions
What is the oxy-haemoglobin saturation curve?
Higher Po2 results in greater haemoglobin saturation
S shaped curve
As haemoglobin changes shape every time O2 binds - Making binding sites more available
Levels out as all sites are filled
Standardised - for pH 7.4 and 37 degrees
What are the effects of temperature on the oxy-haemoglobin saturation curve?
As temp increases - haemoglobin releases more O2
These effects are only significant in active tissues e.g. skeletal muscle
What are the effects of pH on the oxy-haemoglobin saturation curve?
Bohr effect
Co2 diffuses into rbc
Carbonic anhydrase catalyses formation of carbonic acid forming hydrogen ion and bicarbonate hydrogen ions diffuse out and lower the pH
Reduces haemoglobins affinity
Outline the metabolic activity within RBCs?
RBCs generate ATP by glycolysis forming lactic acid and BPG
BPG causes more O2 to be released by Hb
BPG levels rise when pH, stimulated by hormones yet if these levels are too low then O2 won’t be released
What are the 3 reversible pathways of CO2 transport?
Dissolve in the plasma (7%)
Bind to haemoglobin (23%)
Converted to carbonic acid (70%)
What is the chloride shift?
HCO3- moves out of the rbc in exchange for Cl-
How is CO2 delivered to the alveoli?
HCO3- enters as Cl- ions leave
It combines with H+
to form H2CO3
water is removed to form CO2
