Respiration Flashcards
Describe the great oxygenation event
- Little free O2 in the atmosphere, until the “Great Oxygenation Event”
- Cyanobacteria living in the oceans started producing oxygen through photosynthesis
- As oxygen built up in the atmosphere anaerobic bacteria were killed leading to Earth’s first mass extinction
Why is oxygen used in respiration
O2 is well suited to serve as an electron acceptor in the oxidation of carbon-based fuels.
- O2 is stable and consequently accumulated in the Earth’s atmosphere
- The reduction of O2 provides one of the largest free energy release per electron transfer (just less than fluorine)
- Aerobic metabolism yields at least 4-fold more energy per molecules of glucose oxidized than the most efficient anaerobic pathways
- The ability of O2 to diffuse across biological membranes and to bind heme moieties* in proteins (e.g. hemoglobin and cytochromes) facilitates O2 delivery to systemic organs and mitochondrial electron transfer functions.
what are Heme moieties
*Heme moieties = prosthetic groups, specifically iron-containing porphyrin rings, found in proteins like hemoglobin and cytochromes, crucial for oxygen transport and electron transfer
what do animals require for gas exchange
Animals require large respiratory surfaces for exchange of gases between their cells and the respiratory medium (air or water)
how does gas exchange occur
- Gas exchange takes place by diffusion
- Gases diffuse down pressure (not concentration) gradients in lungs and other organs as result of differences in partial pressure
- Partial pressure is the pressure exerted by a particular gas in a mixture of gases (Dalton’s law)
- This also applies to gases dissolved in liquids (Henry’s law)
how can small animals exchange gases
Diffusion over whole body - capillaries near the surface
Used in small organisms
what are the two mediums animals can extract O2 from, and how do they compare
- Animals can extract O2 from air or water
- In a given volume (and pressure) there is less O2 available in water compared to air
- Water is ~800x denser and 50x more viscous than air, and therefore more difficult to move (”ventilation”)
- O2 solubility decreases with temperature and [solute]
- Obtaining O2 from water requires a much greater effort
what are the stats for O2 in water vs air
O2 partial pressure = 160 mm in air, 160 mm in water (ratio 1:1)
O2 concentration = 210 ml/L in air, 7 ml/L in watert (ratio 30:1)
Density of air = 0.0013 Kg/L and water = 1 Kg/L (ratio 1:770)
Viscosity of air = 0.02 cP, viscosity of water = 1 cP (ration 1:50)
what are gills
Gills are outfoldings of the body that create a large surface area for gas exchange
Gills can be external or internal
How do gills exchange gases
Fish gills use a countercurrent exchange system
Blood flows in the opposite direction to water passing over the gills
Blood is always less saturated with O2 than the water it meets
In fish gills, more than 80-90% of the O2 dissolved in the water is removed as water passes over the gills.
Describe the tracheal system
Consist of a network of branching tubes throughout the body
Supply O2 directly to every body cell
Spiracles are gated to minimize water loss
sacs for air storage
The respiratory and circulatory systems are separate
Larger insects must actively ventilate their tracheal system to meet O2 demands
How do amphibians like frogs breath
An amphibian such as a frog ventilates its lungs by positive pressure breathing, which forces air down the trachea
Frog:
- Air enters pocket of buccal cavity
- Glottis opens, Elastic recoil of lungs and compression of chest wall reduces lung volume, air is forced out of the lungs and out the mouth and nares
- Mouth and nares close, floor of buccal cavity rises, air is pushed into lungs
- Glottis closes, gas exchange occurs in lungs
How do birds breath
Birds have 8 or 9 air sacs that function as bellows that keep air flowing through the lungs
Air passes through the lungs in one direction only
Passage of air through the entire system of lungs and air sacs require two cycles of inhalation and exhalation
Ventilation in birds is highly efficient
Inhalation: Air sacs fill
Exhalation: Air sacs empty; lungs fill
how is the respiratory system kept clean
Cilia and mucus line the epithelium of the air ducts and move particles up to the pharynx
This “mucus escalator” cleans the respiratory system and allows particles to be swallowed into the esophagus
How do mammals breath
A system of branching ducts conveys air to the lungs
Air inhaled through the nostrils is filtered, warmed, humidified, and sampled for odours
The pharynx directs air to the lungs and food to the stomach
Swallowing moves the larynx upwards and tips the epiglottis over the glottis in the pharynx to prevent food from entering the trachea
Trachea splits into two bronchi which further divide into bronchioles
How do mammals make vocalizations
Exhaled air passes over the vocal cords in the larynx to create sounds
What can mutations in the CFTR gene do to the respiratory tract
Mutations in cystic fibrosis transmembrane conductance regulator (CFTR) gene results in Cl-/HCO3- imbalances. Low Cl results in the generating of a thick, sticky, mucous lining.
Where are gases exchanged in mammals
- O2/CO2 exchange takes place in alveoli, air sacs at the tops of bronchioles, which have a moist film of the epithelium
- Millions of alveoli: total surface area = 100 m^2 in humans
What are Alveoli like
- Alveoli lack cilia and are susceptible to contamination
- Secrete surfactants (detergent) at the surface of alveoli to break surface tension (help keep shape)
- Preterm babies lack surfactant and artificial surfactants are needed
how do mammals breath
Mammals ventilate their lungs by negative pressure breathing, which pulls air into lungs
Lung volume increases as intercostal muscles and the diaphragm contract
what’s up with lung volume
The tidal volume is the volume of air inhaled with each breath
Maximum tidal volume is the vital capacity
After exhalation a residual volume of air remains in the lung
how do pressure differences affect diffusion in the alveoli vs tissue capillaries
Blood arriving in the lungs has a low partial pressure of O2 and high partial pressure of CO2 relative to air in the alveoli
In alveoli, O2 diffuses into the blood and CO2 diffuses into the air
In tissue capillaries, partial pressure gradient favour diffusion of O2 into the interstitial fluids and CO2 into the blood
how do O2 and CO2 move in the circulatory system
- O2 diffuses down the PO2 gradient
- from alveolar spaces into lung capillaries
- from systemic capillaries to tissues
- CO2 diffuses down the PCO2 gradient
- from tissues to systemic capillaries
- from lung capillaries to alveolar spaces
What are respiratory pigments
Respiratory pigments, proteins that transport Oxygen, greatly increase the amount of oxygen that blood can carry
what Respiratory pigments do arthropods use
Arthropods and many molluscs have hemocyanin with copper as the oxygen binding component
what respiratory pigment do most vertebrates use
Most vertebrates and some invertebrates use hemoglobin
Single hemoglobin molecules are dimers (alpha/beta subunits) which harbour 4 iron-containing heme group
Each Hb can carry up to four O2 molecules
What is binding affinity
Binding = receptor + ligand
Binding affinity defines how high a concentration of ligand is needed to have have a certain % binding. A high affinity ligand will approach maximum binding % at a lower concentration.
How does the absorbance of HbO2 compare to Hb
Hemoglobin bound to O2 (HbO2) has a different absorbance spectra compared to unbound Hb
At around a 630 nm wavelength, HbO2 and Hb have the biggest difference between their absorbance. Using the absorbance, you can determine a ratio of the two forms.
what does the saturation curve of hemoglobin tell us
Hemoglobin has an S shaped structure on a saturation vs pO2 curve.
Hemoglobin has 4 subunits which “talk” to each other causing this curve.
Hemoglobin has two states, a tense state and a relaxed state.
How do the two states of Hb work
The amount of time spent in each state is determined by O2
T-state is highly favoured when their is little oxygen (low affinity)
R-state is highly favoured with lots of oxygen
The more oxygen you add, the more likely it is the hemoglobin will change to the relaxed state.
Why does Hb have two states
This system allows hemoglobin to take in oxygen in the pulmonary capillaries and let it go in the systemic capillaries
what is protoporphyrin
O2 binds to protoporphyrin (Fe2+), it makes a coordinate covalent bond where both electrons come from the oxygen, allows easier release than a normal covalent bond
describe the tense state of Hb
Tense (T) state:
- Low affinity for oxygen
- Deoxygenated form
- Compact structure, harder for oxygen to bind
- Low cooperativity (one oxygen binding does not help other to bind)
describe the relaxed state of Hb
relaxed (R) state:
- High affinity for oxygen
- Oxygenated form
- Ope structure, easier for oxygen to bind
- High cooperativity (one oxygen binding makes it easier for others to bind)
what is P50
P50 is the partial pressure at which half the Hb molecules are occupied with O2 (about 30 mm Hg)
what is saturation and partial pressure of O2 in lungs, and tissues during exercise and rest
100 mm Hg in lungs (100% o2 saturation)
tissue during exercise is about 16 mm Hg and 18% saturation
Tissues at rest is 40 mm HG with 70 % saturation
what percent is the unloading of O2 to tissues at rest vs exercise
O2 unloading to tissues at rest is about 30%
O2 unloading to tissues during exercise is about 82%
what is Bohr shift
CO2 produced during cellular respiration lowers blood pH and decreases the affinity of hemoglobin for O2 (increases in P50) thereby aiding in O2 delivery
Hemoglobin retains less O2 at lower pH (higher CO2 concentration)
Low pH increases P50 decreases affinity
This is called the Bohr shift, and helps hemoglobin release more O2 in areas with high CO2 (near tissues)
What is BGP
Bis-Phosphoglycerate, also called DPG (di-phosphoglycerate)
BGP binding site
A single molecule of 2,3-BPG binds to a positively charged cavity formed by the beta-chains of deoxyhemoglobin
Deoxy-Hb - 1BPG
Oxy Hb - no central cavity
Normal blood = 5 mmol/L
Blood from individual adapted to high altitudes = 8 mmol/L
BPG shifts curve to the right, helps keep steepest part at the right point to allow unloading of O2 when at activity.
what is Myoglobin
Myoglobin is found in muscles
Monomeric (1 alpha + 1 beta subunit)
No cooperativity
High affinity for O2 (higher than hemoglobin)
Serve as an emergency store of O2
describe blood type ABO incompatibility and fetus dissociation curves
Blood type (ABO) incompatibility reactions give rise to jaundice in newly born babies, due to attack and breakdown of RBCs
Fetus hemoglobin has higher affinity than mother
How is CO2 transported
Hemoglobin also helps transport CO2 and assists in buffering blood
~7% of CO2 from respiring cells diffuses into the blood and is transported in blood plasma
~23% binds to amino groups on hemoglobin (Carbaminohemoglobin)
~70% transported as bicarbonate ions (HCO3-)
- in the lungs, the relative partial pressures of CO2 favours the net diffusion of CO2 out of the blood
how does CO poisoning happen
CO binds to the heme group in hemoglobin about 200-250 times more strongly than oxygen
Forms Carboxyhemoglobin (HbCO)
what sensors control breathing
Sensors in the aorta and carotid arteries monitor O2 and CO2 concentrations in the blood
These sensors signal the breathing control centres, which respond as needed
what parts of the brain control breathing
Additional modulation occurs in the pons, which is located next to the medulla in the brain
The main breathing control centre is located in the medulla oblongata of the brain
what can seals do
Diving mammals have evolutionary adaptations that allow them to perform extraordinary feats
- Weddell seals in antarctica can remain underwater for 20-60 minutes
- Elephant seals can dive to 1,500m and remain underwater for 2 hours
How can diving animals stay underwater for a long time
Such animals have a high blood to body volume ratio
Deep-diving air breathers stockpile O2 and deplete it slowly
Diving mammals can store oxygen in their muscles in myoglobin proteins
Diving mammals also conserve oxygen by
- Changing their buoyancy to glide passively
- Deceasing blood supply to muscles
- Deriving ATP in muscles from fermentation once oxygen is depleted (i.e. anaerobic respiration)
Ice fish
Ice fish exhibit a unique physiology that allows them to survive in extreme cold conditions. They lack hemoglobin, the molecule that carries oxygen in the blood, which is unusual for vertebrates. Instead, they have a high concentration of body fluids to prevent ice formation in their bodies. This adaptations helps them thrive in frigid waters.
