Bio B3 and B4 Review Flashcards
Define Gas exchange
the exchange (diffusion) of oxygen and carbon dioxide to and from the blood at the alveoli and the respiring tissues.
Define ventilation
the movement of air into and out of the lungs in two stages: inspiration and expiration. This is controlled by the movement of the diaphragm and ribcage.
State the location of gas exchange in humans
internally, which allows for gas exchange with the blood
Outline the mechanism of gas exchange in humans.
gas exchange occurs in small air sacs called alveoli inside the lungs
Describe how the structure of the alveoli increases surface area for gas exchange.
millions in number each with own netowkr of capillaries, membranes of alveoli and capillaries are very thin so diffusion path is short, surfaces are wet so gasses are dissolved.
Properties of gas-exchange surfaces
Permeable → oxygen and carbon dioxide can diffuse across freely
Large → the total SA is large in relation to the volume of the organism
Moist → the surface is covered by a film of moisture in terrestrial organisms so gasses can dissolve
Thin → the gasses must diffuse only a short distance, in most cases through a single layer of cells
maintenance of concentration gradients
Diffusion evens out concentration gradients, which could slow –>
In small aerobically respiring organisms, it is cell respiration that maintains concentration gradients
rate of ventilation
adjusted according to the carbon dioxide concentration of the blood
Fish:
Take in fresh water through their mouth and pump it over their gills then out through the gill slits
Outline the flow of air into the lungs.
the lungs in the trachea and bronchi and then to the alveoli in bronchioles
State the role of smooth muscle fibres in the bronchioles.
allows the width of airways to vary
bronchus and bronchioles
the bronchus branches repeatedly to form bronchioles
alveoli from bronchioles
Alveolar ducts branch off from the bronchioles, each leading to a group of five or six alveoli (air-sacs)
alveoli
surrounded by a dense capillary network, capillary wall is extremely thin –> air and blood are short distance
monolayer on the surface of the moisture lining the alveoli
Molecules form a monolayer on the surface of the moisture lining the alveoli, with the hydrophilic heads facing the water and the hydrophobic tails facing the air
This reduces the surface tension and prevents the water from causing the sides of the alveoli to adhere when air is exhaled from lungs
Prevents collapse of the lung
cartilage
Trachea and bronchi have cartilage in their walls to ensure they remain open when low air pressure
Mechanics of ventilation:
Inspiration
External intercostal muscles contract
Diaphragm contracts
Abdominal muscles relax
Chest volume increases
Pressure in lungs decrease
expiration
Internal intercostal muscles contract
Diaphragm relaxes
Abdominal muscles contract
Chest volume decreases
Pressure in lungs increases
Capillaries
narrowest blood vessels
Branch and rejoin repeatedly to form a capillary network
Transport blood through almost all tissues in the body
Exceptions: lens and cornea
(Capillary network in any tissue increases scope for diffusion between the blood and tissue cells bc narrow capillaries have a total SA that is greater than fewer wider blood vessels)
Capillary wall
consists of one layer of endothelium cells (coating of extracellular fibrous proteins which are crosslinked to form a gel - basement membrane)
basement membrane
acts as a filter that allows small particles to pass
Fluid that leaks out: tissue fluid
tissue fluid
Contains oxygen, glucose, and all other substances in blood plasma to pass through basement membrane
The fluid flows between the cells in a tissue, allowing them to absorb useful substances and excrete waste products
Then re enters the capillary network
Structure of arteries and veins
Arteries: carry pulses of high-pressure blood away from the heart to the organs of the body
Veins: carry a stream of low-pressured blood from the organs to the heart
arteries vs veins
Arteries
Thicker wall
Narrower lumen
Circular in section
Inner surface corrugated
Fibers visible in the wall
Veins
Thinner wall
Wider lumen
Circular or flattened in section
No inner surface corrugation
Few or no fibers visible in the wall
Wall of artery:
Tunica externa → a tough outer layer of connective tissue with collagen fibers
Tunica media → a thick layer containing smooth muscle and elastic fibers made of the protein elastin
Tunica intima → a smooth endothelium forming the lining of the artery; in some arteries the tunica intima also includes a layer of elastic fibers
Lumen → space inside artery through which blood flows
Arteries have narrow lumens , which helps them to maintain high blood pressures and high velocities of blood flow
Artery walls are relatively thick and contain elastic fibers and tough collagen fibers
fibers
Elastic fibers are proteins that can stretch and then recoil (make up as much as 50% of the dry mass of artery walls)
Collagen fibers are tough rope-like proteins with high tensile strength
These features make arteries strong enough to withstand high and variable blood pressures without bulging outwards
systolic pressure
peak pressure in an artery causes the wall of an artery to be pushed outwards, widening the lumen and stretching the wall
When stretched, elastic fibers store potential energy & at the end of each heartbeat the pressure in arteries falls and the stretched elastic fibers return the energy by recoiling and squeezing the blood in the lumen
vasoconstriction vs vasolidation
when smooth muscles cells of artery wall contract and diameter of lumen is narrowed vs when smooth muscle cells relax, lumen widens, and blood flow is increases
vein walls
Wall of a vein contains less elastic fibers than wall of an artery
Fewer smooth muscles because veins are not used to adjust blood flows
Blood in veins is lower pressure than in arteries → wall does not need to be thick
Potential problem from low blood pressure in a vein → backflow towards the capillaries and insufficient return of blood to the heart
^to maintain circulation: veins contain pocket valves
pocket valves
Consists of three cup-shaped flaps of tissue projecting into the vein
If blood starts to flow backwards, it gets caught in the flaps of the pocket valve, which fill with blood and close the valve → blocks lumen of the vein
When blood flows towards the heart, flap gets pushed to side → pocket valve opens and blood can flow freely
