7.1-7.3 Exchange surfaces and breathing

why do single-celled organisms not need specialised exchange surfaces

1) low metabolic activity = low O₂ and CO₂ demands

2) large SA:V

4 characteristics of an efficient exchange surface

increased surface area

thin layers

good blood supply

ventilation

increased surface area as a feature of an efficient exchange surface

provides area needed for exchange and overcomes the limitation of a small SA:V

thin layers as a feature of a specialised exchange surface

short diffusion distances = fast and efficient

good blood supply as a feature of a specialised exchange surface

maintains a steep concentration gradient = faster diffusion

ventilation as a feature of a specialised exchange surface

maintains concentration gradient = faster diffusion

diagram of the structure of the human gaseous exchange system

3 features of the nasal cavity

1) a large surface area with a good blood supply = warms the air to body temperature

2) a hairy lining = secretes mucus to trap dust and bacteria = protects lung tissue from irritation and infection

3) moist surfaces = increase humidity of incoming air = reducing evaporation from the exchange surfaces

why are the cartilage rings supporting the trachea incomplete

allows food to move easily down the oesophagus behind the trachea

goblet cells

secrete mucus onto the lining of the trachea to trap dust and microorganisms that have escaped the nose lining

cilia

beat and move mucus, trapped dirt, and microorganisms away from the lungs

inspiration

diaphragm contracts and lowers

external intercoastal muscle contract moving ribs upwards and outwards

vol of thorax increases so pressure decreases

expiration

diaphragm relaxes and moves up

external intercoastal muscles relax moving ribs down and inwards

vol of thorax decreases

forceful expiration

internal intercoastal muscles contract which pulls the ribs down hard and fast

abdominal muscles contract forcing diaphragm up

pressure in lungs increases

peak flow meter

device that measures the rate at which air can be expelled from the lungs

vitalograph

version of the peak flow meter

patient breathes out as quickly as they can through a mouthpiece and a graph of the forced expiratory volume in one second is produced

spirometer

used to measure different aspects of lung volume

tidal volume

the vol of air that moves into and out of the lungs with each resting breath

vital capacity

the vol of air that can be breathed in when the strongest possible exhalation is followed by the deepest possible intake of breath

inspiratory reserve volume

the max vol of air that can be breathed in over and above a normal inhalation

expiratory reserve volume

the extra amount of air that can be forced out of the lungs over and above the normal tidal vol of air that is breathed out

residual volume

the vol of air that is left in the lungs after exhaling as hard as possible

total lung capacity

the sum of the vital capacity and the residual volume

breathing rate

the number of breaths taken per minute

ventilation rate

the total vol of air inhaled in one minute

tidal volume x breathing rate

trachea

the main airway carrying clean, warm, moist air from the nose down to the chest

wide tube supported by incomplete rings of strong, flexible cartilage = stop trachea from collapsing

lined with a ciliated epithelium with goblet cells

walls contain smooth muscle and elastic fibres

describe the structure of the bronchi

goblet cells and ciliated cells to filter out dust and pathogens

incomplete rings of cartilage

smaller than trachea

divide into smaller bronchioles

walls contain smooth muscle and elastic fibres

describe the structure of the bronchioles

walls contain smooth muscle = contraction and relaxation = control amount of air reaching the lungs

lined with ciliated epithelium, but contain no goblet cells

walls contain elastic fibres

walls contain smooth muscle (not in smallest bronchioles)

describe the structure of alveoli

tiny air sacs

squamous epithelium lining = very thin, permeable for easy diffusion of gases

walls contain elastic fibres = elastic recoil

describe adaptations of the alveoli for effective gas exchange

1) large surface area = increases SA:V

2) thin layers = only single epithelial cell thick = very shot diffusion distance

3) good blood supply = alveoli are supplied with an extensive network of capillaries = maintain steep concentration gradient

4) good ventilation = breathing air moves in and out of alveoli = maintains steep concentration gradients

5) inner surface of alveoli is covered in a thin layer of lung surfactant = keeps alveoli inflated