Exchange surfaces

What is gas exchange

• the process which respiratory gases are exchanged between the cells of an organism and the environment

Why do organisms require gas exchange

• they need to let oxygen and nutrients in

• they need to remove waste products (CO2)

What is a gas exchange surface

• A specialised surface where oxygen and carbon dioxide sre exchanged between an organism and an environment

Why are gas exchange surfaces needed

• because organisms may have a far diffusion distance

• this means diffusion alone is not sufficient

• so exchange system is needed to meet demands

What 3 factors determine if an organism needs an exchange system

• Size

• Surface Area: Volume ratio

• Level of activity

What is the effect of size on the need for a gas exchange system

• the larger an organism, the more cells it has

• so there is a greater metabolic demand

• sa:vol decreases

• so diffusion alone is insufficient

• exchange system is needed

What is the effect of SA:Vol on the need for a gas exchange system

• the smaller the organism, the larger the SA:Vol ratio

• diffusion distance is short enough

• diffusion alone is efficient

• exchange system is not needed

What is the effect of level of activity on the need for a gas exchange system

• the more active an organism is, the more energy (ATP) needed

• so more oxygen and nutrients are required for respiration

• so more efficient gas exchange is needed

• gas exchange system is needed

What are the features of a good exchange system

• large surface area

• thin barrier / one cell thick

• rich blood supply

• moisture

What is the effect of a large surface area

• there is more space for gas exchange to take place

• this increases the rate of diffusion

• achieved by folding

• eg. root hair cell has many hairs to increase the rate of absorption of water and mineral ions

What is the effect of a thin barrier

• decreases the diffusion distance that substances need to travel over

• eg. alveoli are one cell thick which decreases the distance where O2 and CO2 are exchanged, increasing the rate of diffusion

What is the effect of a good blood supply

• the blood can constantly take oxygen away and bring more CO2

• this maintains the concentration gradient

• eg. Alveoli are enveloped in capillaries, creating a rich blood supply

What is Fick’s law

Rate of diffusion ∝ SA X Concentration difference / diffusion distance

What is the effect of an increased surface area using ficks law

• if SA increases, rate of diffusion increases

• so more oxygen diffuses efficiently

What is the effect of a thin membrane using Fick’s law

• if thickness of membrane decreases, rate of diffusion increases

• so oxygen diffuses efficiently

What is the effect of having a good blood supply using Fick’s law

• an increase in efficient blood supply means rate of diffusion will increase

• so oxygen diffuses more efficiently

How does gas exchange occur in single-celled organisms

• gas exchange takes place by diffusion

• oxygen can directly enter the cell through the plasma membrane which is very thin and CO2 can leave

• they have a large SA:Vol ratio, meaning rate of diffusion is fast and distance is short, making diffusion alone efficient

How does gas exchange occur in multicellular organisms

• gas exchange takes place by diffusion

• the cells are deep within the body, so this increases the diffusion distance

• they have a large size, so a smaller SA:Vol ratio

• they have a higher metabolic rate then single-celled organisms, so they use up oxygen and nutrients faster

• diffusion alone is insufficient so they require exchange surfaces

How are the lungs of a mammal adapted for gas exchange

• millions of alveoli which are very small provide a large surface area for gas exchange to take place

• alveoli are lined by a surfactant (moisture) which reduces surface tension, allowing gases to dissolve

• alveolar wall made of squamous epithelial tissue is 1 cell thick and capillary endothelium is 1 cell thick, shortening diffusion distance

• alveoli surrounded by network of capillaries, good blood supply which maintains concentration gradient of gases

What is ventilation

• The process of moving air in and out of the lungs to maintain a steep concentration gradient for gas exchange

• Involves inhalation and exhalation

Describe the process of inhalation / inspiration

• diaphragm contracts and flattens

• external intercostal muscles contract, internal muscles relax

• ribs move outwards and upwards

• increased volume in thoracic cavity

• decreased pressure in thoracic cavity

• allows air into the lungs

Describe the process of exhalation / expiration

• diaphragm relaxes into domed shape

• internal intercostal muscles contract and external muscles relax

• ribs move downward and inwards

• volume of thoracic cavity decreases

• pressure in thoracic cavity increases

• air is forced out of lungs

How is simple squamous epithelium adapted for its function (alveoli eg)

• thin flat cells, shortening diffusion distance

• thin basement membrane

• surrounded by capillaries to support the flow of O2 and CO2

• alveolus wall contains elastic fibres, allowing them to stretch during inhalation and recoil during exhalation

What is the bronchial tree and what are the features of these airways

• trachea, bronchi, bronchioles

• large to support flow

• supported by cartilage to prevent collapsing

• flexible to allow movement without restricting air flow

How is ciliated epithelium adapted for its function

• tall column shaped cells

• lines airways

• consists of cilia on surface which moves in synchronised pattern to waft mucus to back of throat

• mucus secreted by goblet cells in order to trap pathogens

What are the features of the bronchus

• cartilage

• ciliated epithelium, with goblet cells

• mucus glands

• smooth muscle

• elastic fibres

What are the features of the bronchioles

• non ciliated epithelium

• elastic fibres

• smooth muscle

• SOMETIMES cartilage

What are the features of the trachea

• cartilage (C shaped rings)

• ciliated epithelium with goblet cells

• mucus glands

• smooth muscle

• elastic fibres

What are the features of the alveoli

• squamous epithelial tissue

• elastic fibres

What is a spirometers function

• a device used to measure lung function by recording the volume of air inhaled and exhaled during breathing

• it produces a spirometer trace, which shows changes in lung volume over time

• also measures oxygen uptake, indicating rate of respiration

How does a spirometer work

• calibrate the spirometer - to calculate accurate volumes

• fill the drum with fresh medical grade oxygen - to ensure the normal levels are breathed in

• ensure subject is in good health - to avoid medical issues arising/inaccurate results

• subject wears nose clip - to prevent air passing through nose

• subject breathes normally into machine through mouthpiece - to see normal breathing rate (TV)

• subjects exhaled air passes through soda lime - which absorbs CO2

• turn on kymograph - records spirometer trace

• subject breathes normally for at least 3 breaths - to calculate average TV

• the drum will move up and down - up: exhale, down: inhale

What are the safety precautions when using a spirometer

• subject must be in good health: no respiratory conditions

• medical grade O2

• fresh soda lime

• sterile mouthpiece

• water chamber not overfilled

• no leaks: petroleum jelly

What is the tidal volume

• the amount of air inhaled or exhaled during normal breathing

• usually 0.5dm in adults

• average calculated with 3 waves

What is vital capacity

• the maximum volume of air that can be exhaled after a deep inhalation

• usually 2.5-5.0dm in adults

What is the residual volume

• air remaining in the lungs after maximum exhalation

• usually 1.5dm in adults

What is total lung capacity

• vital capacity + residual volume

What is inspiration and expiratory reserve volume

• IRV: extra air that can be inhaled after a normal breath

• ERV: extra air that can be exhaled after a normal breath

What factors affect vital capacity

• age: less recoil/elasticity of alveoli, less SA, more surface tension, less volume

• gender: males are typically larger, bigger lungs, bigger volume

• fitness: increased lung capacity

• respiratory conditions (health): unable to force air out of lungs properly, decreased lung capacity