Mod 3 Chap 7: Exchange Surfaces and Breathing Flashcards
What is the need for specialized exchange surfaces?
diffusion alone is not enough to supply needs of single celled organisms as:
- metabolic activity usually low so oxygen demands + CO2 production of cell = relatively low
- SA : Vol ratio is large
Larger organisms = made up of more millions/billions of cells, tissues, organs + organ systems
More energy animal uses e.g. for movement means oxygen demands of muscle cells deep in body = high + will produce lots of CO2.
Distance between cells needing oxygen + supply of oxygen = too far for effective diffusion to happen
Also, bigger the organism, = smaller the SA:V ratio, so gases not exchanged fast enough in large amounts for organism to survive.
THEREFORE specialized exchange surfaces needed!
What are the features of an efficient exchange surface?
- INCREASED / LARGE SA: needed for exchange + overcomes limitation of SA:V ratio of larger organisms.
E.g. Villi of small intestine in mammals - THIN LAYERS: makes diffusion distances shorter, making process fast + efficient.
E.g. Alveoli in lungs - GOOD BLOOD SUPPLY: ensures substances constantly delivered to + from exchange surface, maintaining steep conc gradient for diffusion
E.g. Alveoli in lungs - VENTILATION TO MAINTAIN DIFFUSION GRADIENT: makes process more efficient for gases too by maintaining concentration gradients
E.g. Gills of a fish (ventilation = flow of water carrying dissolved gases)
What are the structures and components of the mammalian gaseous exchange system?
Gaseous exchange takes place in lungs.
Key structures and components in gas exchange:
- nasal cavity
- trachea
- bronchus
- bronchioles
- alveoli
- pleural cavity
Describe the function of the nasal cavity in gaseous exchange.
- large SA + good blood supply, so warms air to body temp
- hairy lining that secretes mucus to trap dust + bacteria, preventing irritation + infection of lung tissue
- moist surfaces: increases humidity of incoming air, reducing evaporation from exchange surfaces
Describe the function of the trachea in gaseous exchange.
- main airway carrying clean, warm, moist air from nose into chest
- wide tube supported by c-shaped cartilage rings, to stop trachea from collapsing, + are incomplete so food can move easily down oesophagus behind trachea
- lined w/ ciliated epithelium, w/ goblet cells between + below epithelial cells, that secrete mucus onto trachea lining to trap extra dust + micro organisms
- cilia beat + move mucus w/ any trapped dirt away from lungs
Describe the function of the bronchi in gaseous exchange.
- trachea divides to form left bronchus, leading to left lung, + right bronchus leading to right Lung.
- similar in structure to trachea, w/ same supportive rings of cartilage, but are smaller than trachea
Describe the function of the bronchioles in gaseous exchange.
- bronchi divide in lungs to form smaller bronchioles (1mm or less)
- have no cartilage rings
- walls contain smooth muscle, when it contracts, bronchioles constrict, but when smooth muscle relaxes, bronchioles dilate, this controls amount of air reaching lungs
- bronchioles lined w/ thin layer of flattened epithelium, making some gas exchange possible.
Describe the function of the alveoli in gaseous exchange.
- tiny air sacs, the main gas exchange surfaces of body
- unique to mammalian lungs
- diameter of 200-300 micrometres
- consist of thin layer of flattened epithelial cells w/ collagen + elastic fibres.
- elastic tissues allow alveoli to stretch as air drawn in, + help squeeze air out when return to resting size. (“Elastic recoil”)
What are the main adaptations of the alveoli for efficient gaseous exchange?
- Large SA
- thin layers: only one epithelial cell thick, so diffusion distance = short
- good blood supply: supplied by network of 280 million blood capillaries, maintaining steep conc gradient
- good ventilation: maintains steep diffusion gradients
What components are involved in ventilating the lungs?
- rib cage: provides semi rigid case, which pressure can be lowered in w/ respect to air outside
- diaphragm: broad, domed sheet of muscle, forms floor of thorax
- external intercostal muscles + internal intercostal muscles: found between ribs
- pleural membranes: line thorax + surround lungs
- pleural cavity: usually filled w/ thin layer of lubricating fluid so membranes slide easily over each other as you breathe.
Describe the process of inhalation / inspiration.
- diaphragm contracts, flattens + lowers to allow lungs to inflate
- external intercostal muscles contract to pull ribs up + out.
- volume of thorax increases, so pressure decreases, drawing air in
Describe the process of exhalation / expiration.
- diaphragm relaxes so moves up into dome shape
- external intercostal muscles relax so ribs move down + inwards by gravity
- thorax volume decreases, so pressure increases, forcing air out.
Forceful exhalation:
- occurs using energy
- internal intercostal muscles contract, pulling ribs down hard + fast
- abdominal muscles contract, forcing diaphragm up to increase pressure in lungs rapidly.
Define the tidal volume.
The volume of air that moves into + out of lungs during a normal resting breath.
Define the vital capacity.
The largest volume of air that can be moved into + out of lungs in one breath.
Define the inspiratory reserve volume.
The maximum volume of air that can be breathed in above normal tidal volume of air you breathe in.
Define the expiratory reserve volume.
The extra amount of air that can be forced out of lungs over normal tidal volume of air you breathe out.
Define the residual volume.
The volume of air that remains in lungs after biggest exhalation possible.
Define the total lung capacity.
The maximum volume of air that lungs can hold, so is sum of vital capacity + residual volume.
What is the breathing rate?
The number of breaths taken per minute.
What is the ventilation rate?
The tidal volume of air inhaled in one minute.
Ventilation rate = tidal volume x breathing rate
Describe the relationship between tidal volume, breathing rate and oxygen uptake.
When oxygen demands of body increase, e.g. During exercise, tidal volume of air can increase from 15% to 50% of vital capacity w/ each breath.
Breathing rate can also increase, in this way, ventilation of lungs + so oxygen uptake during gaseous exchange can be increased to meet demands of tissues.
How does gas exchange take place in insects?
- air enters + leaves through spiracles (small holes in thorax + abdomen), but water also lost.
- spiracles opened / closed by sphincters, but kept closed as much as poss to minimize water loss.
- spiracles closed when insects = inactive + O2 demands = low, but open when demand raised / CO2 levels build up.
- trachae lead away from spiracles, carrying air into body
- trachae lined by spirals of chitin to keep them open
- trachae branch into narrower tubes called tracheoles, which have no chitin lining so = permeable to gases (as chitin is impermeable)
- tracheoles spread through tissues + between individual cells, where most of gas exchange takes place
- air moves along trachae + tracheoles by diffusion to reach all tissues
- vast no. of tracheoles gives large SA for gas exchange
- O2 dissolves in moisture on walls of tracheoles + diffuses into surrounding cells
Describe the tracheal fluid in insects and its function.
- located at end of tracheoles
- limits penetration of air for diffusion
What happens when oxygen demands build up in insects?
e. g. When insect is flying
- lactic acid builds up in tissues
- results in water moving out of tracheoles by osmosis
- exposes more SA for gas exchange.
