Lecture 11 - Microscopic structure of gas exchange Flashcards
what is the smallest unit in which gas exchange occurs?
alveoli
where are alveoli scattered?
within the walls of respiratory bronchi
where are alveoli continuous? what do they lead to?
in walls of alveolar ducts which lead to terminal alveolar
what are the two cell types of the alveoli epithelial cells
type 1 alveolar epithelial cells
type 2 alveolar epithelial cells
describe the shape and function of type 1 alveolar cells, can they divide?
- very flattened cells, sit on basement membrane
- terminally differentiated (cannot divide)
- allow gas diffusion across cytoplasm
describe the shape and function of type 2 alveolar cells
- cuboidal
- cytoplasmic granules contain surfactant (surface tension)
- divide to replace type I and II cells
other than type I and II epithelial cells, what else can be found within the alveoli?
macrophages
how are alveolar seperated? what do they contain
by inter alveolar septa: contain fibroblasts, mast cells and macrophages
what are alveolar pores?
holes in septa between adjacent alveoli, allow passage of air between alveoli
blood - air barrier
oxygen must diffuse across;
- alveolar fluid
- alveolar epithelium
- basement membrane of alveolar epithelium
- basement membrane of capillary cell
- capillary endothelial cell
how thick is the blood - air barrier
0.2 - 2 micron thick
what are pulmonary macrophages, where are they present?
present in 3 locations
1. intravascular: associated with endothelium
2. interstitial
3. alveolar: function to clear alveolar surface - removed via trachea
can proliferate locally
what does the interlobar septa contain?
collagen and elastic fibres
blood vessels
what is partial pressure?
pressure exerted by a given gas in a mixture of gases
alveolar air
water vapour added to air in inspiration --> changes in partial pressure o2 = 146 CO2 = 0.27 N2 = 556 H20 = 47
how much alveolar air is replaced with each normal breath?
around 15% total alveolar air replaced with each breathe, air enters alveolus, diluted by stale air remaining
how does partial pressures of gasses change in liquid?
determined by concentration of gas dissolved in fluid
O2 bound to Hb, does not contribute to PO2
CO2 dissolved in blood equilibrates to H+ and HCO3-
partial pressure gradients
gases diffuse from area of high partial pressure to area of low partial pressure, passive diffusion down
how is the rate of diffusion through tissues (DR) determined?
DR = PD x A x DC / T PD = partial pressure gradient A = surface area available DC = diffusion coefficient T = thickness of barrier
describe the diffusion co-efficient (DC)
each gas has co-efficient
CO2 more soluble than O2 in water, therefore it diffuses more quickly
factors limiting diffusion may result in hypoxia without hypercapnia because CO2 diffuses out so fast
how is surface area available increased or decreased?
increased during exercise
decreased in diseased state
how is barrier thickness increased?
increased in disease - pulm oedema, pulmonary fibrosis, pneumonia
what is a gill
water contains less O2 than air = makes use of gills
gills = delicate evagination of tissue protruding into surrounding water, consist of this epidermis highly perfused
how does a fish breath underwater?
- take water into mouth while operculum is closed,
mouth is then shut and operculum opened, forcing water over gills and out through operculum
is flowthrough in a fish uni- or bi- directional
uni-directional
