3.1.1 - Exchange and Transport Flashcards
Factors affecting exchange system
Size
SA:V ratio
Metabolic activity
How does size affect the need for an exchange system
In single-celled organisms, the cytoplasm is very close to its environment. Diffusion will supply enough O2 and nutrients to keep the cells alive and active
In multicellular organisms have several layers of cells, so there’s a longer diffusion pathway. Diffusion is too slow to enable a sufficient supply to the innermost cells
How does SA:V affect the need for an exchange system
When organisms have a large SA:V their SA is large enough to supply all the cells with sufficient O2
V increases more quickly than SA so the SA:V is smaller in larger organisms so a specialised exchange surface is needed
How does metabolic activity affect the need for an exchange system
Metabolically active organisms need good supplies of O2 and nutrients to supply energy for movement and warmth so the exchange of substances need to be efficient
Features of a good exchange surface
Large surface area - achieved by folding walls and membranes
Thin, permeable barrier - shorter diffusion distance
Good blood supply - maintain steep concentration gradient (brings molecules to supply side and removes from demand side)
How are lungs adapted
Many alveoli - large SA:V
Thin barrier - short diffusion pathway
Good blood supply (capillaries) to carry dissolved gases to and from alveoli
Ventilation refreshes air in alveoli
Elastic tissue to stretch/ recoil to help expel air
Function of goblet cells
Produce mucus
Function of cartilage
Prevent collapse of airways
Why do the walls of alveoli contain elastic fibres
Expand (inhalation) to increase lung volume
Prevent alveoli bursting
Elastic fibres recoil
Inspiration
Diaphragm contracts to move down and become flat. Displaces digestive organs downwards
External intercostal muscles contract moving the ribs outward and upward
Volume of thorax increases
Pressure in thorax < atmospheric pressure
Air is drawn in through the nasal passages, trachea, bronchi and bronchioles into lungs
Thorax
Chest cavity
Lined with pleural membranes - space between these membranes is the pleural cavity - usually filled with lubricating fluid
Expiration
Diaphragm relaxes and is pushed up by displaced organs underneath
External intercostal muscles relax and ribs fall
Volume of thorax decreases
Pressure in thorax > atmospheric pressure
Air is moved out of the lungs
What does the alveoli consist of
Thin, flattened epithelial cells alone with some collagen and elastic fibres
Elastic recoil
When the elastic fibres in the alveoli return to their resting size, they help squeeze the air out
What is the inner surface of the alveoli covered in
A thin layer of solution of water, salts and lung surfactant
When O2 diffuses out of the alveoli, it first dissolves in the water before diffusing into the blood. Water can also evaporate into the air in the alveoli
Lung surfactant
Phospholipid that coats the surfaces of the lungs
Without it, watery lining of alveoli would have surface tension —> collapse
Collagen in alveoli
Ensures alveoli aren’t deformed as they stretch (support)
Distribution and function of capillaries
Over surface of alveoli
To provide a large surface area for exchange
Distribution and function of cartilage
In walls of bronchi and trachea
To hold the airways open and provide structural support
Distribution and function of goblet cells
In ciliated epithelium
To produce and release mucus
Distribution and function of smooth muscle
In walls of airways
Contracts to constrict or narrow the airways
Loose tissue
Contains elastic fibres, glands and blood vessels
Peak flow meter
Simple device that measures how much air can move out of (and therefore into) the lungs
Spirometer
Device that measures the movement of air in and out of the lungs as the person breathes
Also measures oxygen consumption as the chamber of soda lime absorbs carbon dioxide