3.1 Exchange Surfaces and Breathing

Why do we need an exchange surface

SA:V

Metabolic activity

Single celled organisms

Multi celled organisms

Features

increased surface area

thin layer permeable to substances passing through

ventilation

Components of mammalian gas exchange system

cartilage

ciliated epithelium cells

goblet cells

smooth muscle

elastic fibres

trachea

bronchi and bronchioles

alveoli

Mechanism of ventilation: mammals

Mechanism of ventilation: bony fish

Mechanism of ventilation: insects

change in volume of buccal cavity (mouth) keeps water flowing over the gills, and coordinated with movement of operculum

cytoplasm is close to environment of cell; diffusion is enough to keep organism alive - no need for exchange surface

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

more metabolic activity = greater need for oxygen

mammals need to keep themselves warm, so need more energy

have many layers of cells, so diffusion pathway is greater; diffusion is not enough o supply innermost cells

can be achieved by folding walls of exchange surface e.g. root hairs, villi

to provide more space for molecules to pass through

reduce diffusion distance e.g. alveoli in lungs

maintain steep concentration gradient for diffusion; either bring supplies to supply side, or remove products from demand side e.g. gills in fish

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

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

smaller airways leading into the lungs; supported by C shaped rings of cartilage to prevent collapse during inhalation

the main airway leading from the back of the mouth to the lungs

diaphragm

a layer of muscle beneath the lungs

intercostal muscles

muscles beneath the ribs

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

a form of connective tissue

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

protein fibres that can deform then recoil to their original size

cells that secrete mucus to trap pathogens

involuntary muscle that contracts without the need for conscious thought

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

elastic fibres of alveoli stretch

elastic fibres of alveoli recoil

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

spiracles

trachea/ tracheoles

tracheal fluid

an external opening or pore that allows air in or out of the trachea

air filled tubes in insects

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