Flashcards in Mod 3 Chap 7: Exchange Surfaces and Breathing Deck (31)
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
- 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.
- 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.
How do larger insects with higher energy demands increase the level of gaseous exchange?
Mechanical ventilation of tracheal system:
- air pumped into system by muscular pumping movements of thorax / abdomen, these movements change volume of body, which changes pressure in trachae + tracheoles, so more air drawn in / forced out.
Collapsible enlarged trachae or air sacs:
- act as air reservoirs to increase amount of air moved through gas exchange system. Usually inflated / deflated by ventilating movements of abdomen / thorax.
How does gas exchange take place in bony fish?
- Bony fish e.g. Cod are big active animals so have higher oxygen demand
- their SA:V ratio means diffusion = not enough to supply inner cells w/ O2 they need, + scaled covering prevents gas exchange
- so bony fish have evolved ventilatory system to take O2 from water + get rid of CO2 into water through flow of water over gills.
- gills are their organs of gaseous exchange
- gills have large SA, good blood supply, + thin layers for successful gas exchange
- in bony fish, gills covered by protective operculum (a bony flap) which helps maintain flow of water over gills.
Describe ventilation in bony fish through the gills and a water constant flow.
- fish need continuous flow of water over gills always for efficient gas exchange, even when stationary
- when swimming, current of water kept flowing over gills by opening mouth + operculum
- when stationary, water flow stops, so have evolved system involving operculum, which allows them to move water over gills constantly.
- mouth opens
- buccal cavity floor lowers
- this increases volume + decreases pressure of buccal cavity compared to outside
- water rushes into mouth down pressure gradient
- opercular cavity expands
- buccal cavity floor raises
- pressure inside buccal cavity now higher than opercular cavity
- water moves from buccal cavity over gills into opercular cavity
- mouth now closed + operculum opens
- sides of opercular cavity move inwards, increasing pressure
- water rushes out through operculum.
What extra adaptations to gills have other than a good supply and thin layers to help ensure the most effective possible gas exchange occurs in the water?
- tips of adjacent gill filaments overlap: increases resistance to flow of water over gill surfaces + slows water, = more time for gas exchange.
- water moving over gills + blood in gill filaments flow in opposite directions: sets up countercurrent exchange system to ensure steeper conc gradient maintained, so more gas exchange occurs
Describe the details required when drawing gas exchange systems in bony fish.
Operculum: flap covering gills
Bony gill arch: supports structure of gills
Efferent blood vessel: carries blood leaving gills in opposite direction to incoming water, maintaining steep conc gradient
Afferent blood vessel: brings blood into system
Water w/ high oxygen current passes over gills
Gill lamellae: main site of gas exchange in fish, have rich blood supply + large SA
Gill filaments: occur in large stacks (gill plates) + need flow of water to keep separate, exposing large SA required for gas exchange