6.4 gas exchange Flashcards
what is ventilation?
process where air is cycled in and out of the lungs
- can be monitored by data logging w spirometer / chest belt and pressure meter
what occurs during gaseous exchange and where does it occur?
takes place in the lungs where carbon dioxide diffuses out of bloodstream into air in lungs, and oxygen in air in lungs diffuses into bloodstream
what is cellular respiration?
biochemical processes that releases energy from glucose with use of oxygen and other substances
why is there a need for concentration gradient of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries to be maintained and how is it maintained?
- ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries
- gases not pumped or undergo active transport to enter or leave blood stream
- gases transported via diffusion, hence rate is dependent on concentration gradient of gases between bloodstream and air in lungs
- blood entering lungs low in oxygen concentration and high in carbon dioxide concentration
- if ventilation does not take place at high enough rate, carbon dioxide will build up in lungs while oxygen concentration will drop
- hence, ventilation cycles fresh atmospheric air into lungs to maintain concentration gradient of gases
how does air progress for gaseous exchange?
- air enters via nostrils, where air is filtered by nose hair and warmed by capillaries near inner surface of nose
- passes through pharynx, then to larynx and vocal cords
- enters trachea held together by cartilage rings
- air is then split and moves into pair of bronchus tubes (bronchi)
- bronchi then branch into bronchioles
- air finally enters into alveoli where gaseous exchange take place
elaborate a little on the structure of trachea (the key structure of trachea)
strengthened by presence of cartilaginous rings that hold tube open despite changes in pressure within due to ventilation
elaborate a little on structure of bronchi (how do left and right differ?)
- 2 bronchi in human body, supplying 2 lungs
- left bronchus tube branches at greater angle than right bronchus, as heart is situated to left of the median line (closer to the left lung)
- left lung is smaller than right lung due to position of heart
what are the adaptations of alveoli that help carry out their purpose?
- main function of alveoli is to facilitate gaseous exchange
adaptations:
- thin alveolar walls (one-cell thick)
- richly supplied with capillaries
- presence of thin film of moisture (with surfactants)
- spherical in shape to increase surface area available for gaseous exchange
what are type I pneumocytes and their purpose?
- extremely thin alveolar cells adapted to carry out gas exchange
- pneumocytes aka alveolar cells, make up alveoli in lungs
- type I pneumocytes: squamous (thin and flat) cells that cover about 90% of surfaces within alveoli
- pneumocytes extremely thin to reduce distance that gases have to diffuse to travel between air in lungs and bloodstream
- cells also capable of taking in small particulates via pinocytosis to remove them from alveolar surface
- specialised cells also incapable of mitosis, hence susceptible to damage as not easily replaceable
what are type II pneumocytes and their purpose?
- secrete a solution containing surfactant that creates moist surface inside alveoli to prevent sides of alveolus adhering to each other by reducing surface tension
- pneumocytes aka alveolar cells, make up alveoli in lungs
- type II pneumocytes secrete solution known as pulmonary surfactant, contains phospholipids that help lower surface tension of fluid
- layer of moisture required for efficient solution of gases (like oxygen) to facilitate diffusion of gases from air into bloodstream
- reduction of surface tension reduces forces of attraction of water molecules at surface of solution, hence prevents thin alveolar walls from sticking to each other
- if alveolar walls stick to each other, reduces surface available for diffusion of gases
how do pressure changes inside thorax occur?
- muscle contractions cause pressure changes inside thorax that force air in and out of lungs to ventilate them
- muscles primarily involved in ventilation are diaphragm, and internal and external intercostal muscles
- to force air into lungs, lungs operate on negative pressure system, where pressure within lungs forcefully lowered to below (hence negative) atmospheric pressure
- to generate negative pressure, volume of lungs must increase
- pressure is inversely proportional to volume of lungs (Boyle’s Law) (PV = nRT)
what occurs during inhalation?
- to increase volume of lungs, diaphragm will contract and pull downwards, increasing volume of chest cavity
- ribcage will also expand with contraction of external intercostal muscles
- lowers pressure of chest cavity, hence lung expands
- with expansion of lungs, pressure drops below atmospheric pressure and air rushes into lungs
- important to note lungs themselves do not contain any muscles
- why?
muscles can only contract but what you want in lungs is for air to enter and lungs must forcefully expand -> vol increases, pressure drops bc PV=nrt where nrt is a constant
need muscles that can only shorten to cause expansion: how?
why are different muscles used for inhalation and expiration and what muscle is now used for expiration?
- different muscles required for inspiration and expiration because muscles only do work when they contract
- muscles capable of contraction, but not capable of forced expansion
- hence for exhalation, when lung and chest cavity must decrease in volume, same set of muscles cannot forcefully expand
- separate set of muscles hence needed to lower volume of chest cavity: internal intercostal muscles
- elasticity of diaphragm and other elastic tissues in chest generally sufficient for normal exhalation
- internal intercostal muscles more involved in forced exhalation (sighing), talking or shouting or singing
what are antagonistic muscles?
pair of 2 sets of muscles where contraction of 1 set opposes action of contraction of other set of muscles
how are intercostal muscles an example of antagonistic muscles?
external intercostal muscles when contracted causes ribcage to expand and rise, while internal intercostal muscles when contracted pulls ribs closer together
