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3.1 Exchange Surfaces and Breathing (Components of mammalian gas exchange…
3.1 Exchange Surfaces and Breathing
Why do we need an exchange surface
SA:V
larger SA:V means SA is large enough to supply all cells with sufficient oxygen
bigger organisms have smaller SA:V so need a specialised gas exchange surface
Metabolic activity
more metabolic activity = greater need for oxygen
mammals need to keep themselves warm, so need more energy
Single celled organisms
cytoplasm is close to environment of cell; diffusion is enough to keep organism alive - no need for exchange surface
Multi celled organisms
have many layers of cells, so diffusion pathway is greater; diffusion is not enough o supply innermost cells
Features
increased surface area
can be achieved by folding walls of exchange surface e.g. root hairs, villi
to provide more space for molecules to pass through
thin layer permeable to substances passing through
reduce diffusion distance e.g. alveoli in lungs
ventilation
maintain steep concentration gradient for diffusion; either bring supplies to supply side, or remove products from demand side e.g. gills in fish
Components of mammalian gas exchange system
cartilage
a form of connective tissue
ciliated epithelium cells
a layer of cells that have many hair like extensions called cilia to waft away mucus and dust from the lungs to the back of the throat where they can be swallowed
goblet cells
cells that secrete mucus to trap pathogens
smooth muscle
involuntary muscle that contracts without the need for conscious thought
elastic fibres
protein fibres that can deform then recoil to their original size
trachea
the main airway leading from the back of the mouth to the lungs
bronchi and bronchioles
smaller airways leading into the lungs; supported by C shaped rings of cartilage to prevent collapse during inhalation
alveoli
tiny folds of the lung epithelium to increase surface area, lined by thin layer of moisture (surfactant) to prevent alveoli from collapsing; comprised of squamous epithelial; supported by C shaped rings of cartilage to prevent collapse during inhalation
diaphragm
a layer of muscle beneath the lungs
intercostal muscles
muscles beneath the ribs
lungs
pair of inflatable sacs in the chest cavity where gas exchange happens
ventilation
the refreshing of air into the lungs so there is a higher O2 concentration in the blood and a lower CO2 concentration
blood capillary
consists of squamous epithelial cells, so are flattened and only one cell thick, reducing diffusion distance
Mechanism of ventilation: mammals
Inhalation
diaphragm contracts, becomes flatter, and moves down
external intercostal muscles contracts to raise the ribs
volume of chest cavity increases
pressure in chest cavity drops below atmospheric pressure
air moved into lungs
elastic fibres of alveoli stretch
Exhalation
diaphragm relaxes and is pushed up
volume of chest cavity decreases
external intercostal muscles relax and ribs fall
pressure in chest cavity rises atmospheric pressure
air moved out of lungs
elastic fibres of alveoli recoil
Mechanism of ventilation: bony fish
change in volume of buccal cavity (mouth) keeps water flowing over the gills, and coordinated with movement of operculum
operculum
a bony flap that covers and protects the gills; as water is pushed from the buccal cavity, operculum moves outwards, and water flows through the gills
gill made up of gill filaments and gill lamellae (plates)
filaments
slender branches of tissue that make up the gills
lamellae
folds of the filaments to increase surface area
Countercurrent flow
blood flows over the gill arch and water flows ion the opposite direction over the gills; maintain steep concentration gradient and absorb maximum amount of oxygen from lungs
Mechanism of ventilation: insects
spiracles
an external opening or pore that allows air in or out of the trachea
trachea/ tracheoles
air filled tubes in insects
tracheal fluid
fluid found at the end of tracheoles, where gas exchange happens between fluid and tracheoles; active tissue withdraws fluid to increase surface area of tracheole wall exposed to air ; more oxygen absorbed when insect is active
open circulatory system
body fluid acts as both blood and tissue fluid
Ventilation
movement of wings alter volume of thorax; thorax volume decreases, air in tracheal system put under pressure and air pushed out of system; thorax volume increases, air in tracheal system drops in pressure, air pushed into system
open and close valves of spiracles to alter volume of abdomen; abdomen expands, spiracles at front open and air enters tracheal system; abdomen reduces, spiracles at rear open and air leaves tracheal system
Sammer Sheikh