Lecture 11: Gas Exchange

BISC 101 with Dr. Williams

animals have to take in _____ for cell respiration, and expel _____ to stay alive

O₂, CO₂

____ and _____ provide very different constraints on the design of gas exchange systems

air, water

gas exchange by diffusion is maximized by what three factors?

large area, small diffusion distance, partial pressure (concentration) gradient

larger organisms have ___________ to replenish oxygen around gas exchange surfaces

ventilatory mechanisms

circulatory systems use the pressure generated by one or more specialized organs (hearts) for __________ of gases (and nutrients, etc.)

bulk transport

in large organisms, gases are transported in specialized tissue (______) using specialized oxygen-carrying proteins (____________)

blood, respiratory pigments

what order are the four steps of gas exchange?

ventilation → gas exchange → circulation → cellular respiration

ventilation

movement of air/water through or around gas exchange surfaces (skin, trachae, gill, lung)

gas exchange

occurs by diffusion as O₂ and CO₂ move between air/water and blood at respiratory surface

circulatory systems

transports gases throughout the body delivering them to cells/tissues

gas exchange occurs by diffusion at tissues between _______ and ________

blood, cells

O₂ is ______ at sea level, plentiful!

21%

air is less _____ and _____ compared to water

dense, viscous

ventilation is relatively ______

easy

air can utilize…

bi-directional flow

gas exchange in air is ______ efficiency since we only extract _____ of O₂ in the air

low; 25%

gas exchange in water contains ____ less O₂ than air

less

how much oxygen does water contain vs air on average?

7ml/L (water) vs. 210ml/L (air)

high density/viscosity = _______

hard to move

breathing in water is relatively ___________

energy demanding

respiratory systems for animals who do gas exchange in water are unidirectional, making it _____________

high efficiency

what do small animals rely on due to lacking specialized gas exchange organs?

diffusion across their body surface

how thin are the walls of organisms lacking specialized gas exchange organs?

1-2 cells thick

how are small organisms without specialized gas exchange organs shaped?

long, thin, or flattened body shape

why does having a thin body help organisms without specialized gas exchange organs?

short diffusion distances as they rely on diffusion

what minimizes the distance substances must diffuse to enter/leave the cell in small organisms?

circulatory systems

Fick’s Law for rate of diffusion

(diffusion constant) x (area for gas exchange) x (difference in partial pressure of gar on either side of barrier to diffusion) / (distance)

O₂ from air diffuses across how many cell layers at gas exchange surfaces?

2 cell layers

at tissues, O₂ diffuses a short distance from ______ to _______

blood, cells

aquatic animals use what for gas exchange?

gills

gills increase ________ for gas exchange

surface area

organisms use _________ to maintain O₂/CO₂ gradients

ventilation

operculum

gill cover

fish gills are a ____________ system

countercurrent exchange

in fish, water moves ____ through the mouth and _______ through the operculum

in, out

ventilation occurs in fish through what two methods?

buccal pumping (pumping of the mouth) or ram ventilation (simply swimming forward)

what type of ventilation do fish use?

positive pressure ventilation

gills consist of 4 _________

gill arches (bone)

what does each gill arch have?

2 rows of gill filaments

what does each row of gill filaments have?

hundreds/thousands of gill lamellae

water flows through lamellae in the _________ direction to blood flow, which is known as countercurrent exchange

opposite

___________ exchange is much more efficient than ___________ exchange

countercurrent, concurrent

countercurrent flow means that a ________________ exists along the whole length of the lamella

positive partial-pressure gradient

the countercurrent exchange ________ the amount of O₂ extracted from water

maximizes

how does the insect tracheal system work?

air-filled tubes (trachea) branch throughout body + air sacs

how does the tracheal system in insects interact with rest of the body?

smallest (tracheoles) reach individual cells and have fluid-filled tips

what does the insect tracheal system rely on?

diffusion (small insects) or pumping movements of body

openings of the trachea (spiracles) regulate _________ and __________

air flow, water loss

what is the order structures from beginning to end in the mammalian respiratory system?

trachea → bronchi → bronchioles → alveoli

no gas exchange occurs in which three structures of the mammalian respiratory system?

trachea, bronchi, and bronchioles

how many alveoli are there in humans?

150 million

alveoli are responsible for what function and why?

site of gas exchange; large surface area to accomodate

how does diffusion occur in the mammalian respiratory system?

diffusion across the alveolus wall

what is the distance and surface area of the alveolus wall?

distance is 0.2 μm (1/200 of a page); SA is 140 m2 (1/3 basketball court)

what drives negative-pressure ventilation in the mammalian respiratory system?

changes in the volume and pressure of the chest cavity

inhalation in mammalian respiratory system

intercostal (rib) muscles contract, pulling ribs up and out as diaphragm moves down

during inhalation, how does the volume, pressure, and air change?

volume increases, pressure decreases (more negative), air comes in

exhalation in mammalian respiratory system

mostly passive; diaphragm and muscles relax

during exhalation, how does the volume, pressure, and air change?

volume decreases, pressure increases (less negative), air out

what happens during active exhalation?

muscles pull ribs down and in

what do active muscle tissues use?

oxygen (pO₂ decreases)

what do active muscle tissues produce?

carbon dioxide (pCO₂ increases)

regulation of ventilation in mammals mainly relies on changes in ______ and _______

pCO₂ and pH

what are the inputs of the respiratory system?

pH [CO₂] of cerebrospinal fluid, pH sensors in major blood vessels (carotid bodies)

what happens after pH [CO₂] of the cerebrospinal fluid and carotid bodies are input?

medulla oblongata receives signal and sets basic rhythm for breathing

how many breaths per minute does the medulla oblongata set?

12/14 breaths/min

what are the outputs of mammalian respiration in active muscle tissue?

neural signals to diaphragm and muscles of rib cage

breathing is normally regulated by…

involuntary mechanisms

how are oxygen and carbon dioxide transported in the blood?

partial pressure gradients of O₂ and CO₂ drive diffusion of gases in different parts of the circulatory system

carbon dioxide has _____ solubility in blood than O₂

higher

what is the solubility of carbon dioxide in the blood?

200mL CO₂/L of blood

_____ solubility of oxygen in the blood and high metabolic demands require specific adaptations for _____ and ______ of O₂

low, binding, transport

what is the solubility of oxygen in blood?

(4.5 ml O₂/L of blood)

what do respiratory pigments for oxygen do?

help with binding and transport of oxygen

CO₂ produced by cell respiration enters the blood to react with ______

water

what does the combination of tissue-produce carbon dioxide and water form?

carbonic acid

what enzyme does carbonic acid require?

carbonic anhydrase

what does carbonic acid rapidly dissociate to form?

bicarbonate ions and protons

what is the formula of carbon dioxide + hydrogen → carbonic acid → bicarbonate ions and protons

CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃^-

what are the 3 forms CO₂ is transported?

bicarbonate ions in blood plasma, bound to AA side-chains of hemoglobin, dissolved in blood plasma

what percent of CO₂ are transported as bicarbonate ions (HCO₃^-) in blood plasma?

70%

what percent of CO₂ are transported to bind to AA side-chains of hemoglobin?

23%

what percent of CO₂ are transported to dissolve in solution in blood plasma?

7%

respiratory pigments for O₂ transport have distinct ________ due to O₂-binding metal ions

colours

what is hemoglobin?

4 polypeptide chains (tetramer) each with a non-protein heme group with one iron ion (Fe²⁺)

what does the Fe²⁺ in hemoglobin bind to?

oxygen

which organism has green blood?

marine worm

what does the oxygen-Hb equilibrium curve describe?

how much oxygen % binds to hemoglobin with variation in pO₂

the oxygen dissociation curve is…

sigmoidal (S-shaped)

in cooperative binding, there is a _____ increases in O₂ unloading

17%

in noncooperative binding, there is a _______ increase in O₂ unloading

7%

on the steep part of the oxygen-hemoglobin equilibrium curve, a _________ in pO₂ leads to a _________ in how much O₂ is unloaded

small change, large change

Hb is __________ to changes in pO₂

very sensitive

what does shifting the oxygen dissociation curve change?

“affinity” for oxygen

left shift in oxygen dissociation curve = Hb saturates at lower pO₂ = __________

high affinity (good at lungs)

right shift in oxygen dissociation curve = Hb unloads O₂ at even higher pO₂ =__________

lower affinity (good at cells)

local ____________ can influence how strongly O₂ binds to hemoglobin

biochemical environment

CO₂ production by active tissues affects pH in what way?

decreases pH due to proton (H⁺) production

lower pH ___________ of hemoglobin for O₂ (how strongly O₂ is bound)

decreases affinity

what is the term for the following process:
Hb releases more O₂ in more active tissues during exercise due to decreased affinity since pH is lowered

Bohr shift