ch 18 O2 transport and regulation

4 processes of respiration

1. ventilation

2. pulmonary gas exchange

3. gas transport

4. cellular respiration

ventilation (step of respiration)

step 1 of respiration; Movement of air in and out of lungs (atmosphere O2 → lungs)

pulmonary gas exchange (step of respiration)

step 2 of respiration;

(O2 in lungs to blood)

O2 enters blood at alveolar-capillary interface, CO2 leaves.

oxygen moves from the lungs to blood, while CO2 moves from the blood to the lungs

Gas Transport (step of respiration)

step 3 of respiration; (blood), blood carries oxygen from the lungs to cells and CO2 from cells to the lungs

Cellular respiration (step of respiration)

step 4 of respiration;

(blood → cells)

oxygen is released to cells and CO2 is picked up from them!

in which direction do gases diffuse?

from areas of higher partial pressure to lower partial pressure

average of PCO₂

40 - 46 mmHG

average of PO₂

40 - 160 mmHg

diabetes pateints take a super long time to reocver becasue…

bad perfusion damages peripheral nerves; don’t feel the pain

cells form a ________ ______ between lung and blood

diffusion barrier

made of

• alveolar air space (with surfactant)

• Alveolar epithelium

• Fused basement membranes

• Endothelial cell nucleus

• Plasma

• Red Blood Cell (RBC)

hypoxia

dangerous condition where tissues or organs in the body do not receive enough oxygen to function properly.

pathologies causing hypoxia

• emphysema

• fibrotic lung disease

• pulmonary edema

• asthma

normal PO2

100 mmHg

emphysema

Destruction of alveoli → less surface area for gas exchange   → low PO2

• due to smoking

• damages elastic fiber

• damaged, inelastic air sacs (alveoli) that trap air, making it hard to breathe

fibrotic lung disease

Thickened alveolar membrane slows gas exchange; loss of lung compliance may decrease alveolar ventilation → low PO2

• due to dirty air (ex. working in a minefiled)

• lung grows thicker, increasing diffusion distance —- supposed to be simple squamous epithelium

Lung compliance

a measure of the lung's ability to stretch and expand (distensibility) during breathing

pulmonary edema

Fluid in interstitial space increases diffusion distance → low PO2.

arterial PCO2 may be normal due to higher CO2 solubility in water

• rate of diffusion decreases

• very similar to fibrotic lung disease — both increase diffusion distance

asthma

Increased airway resistance decreases alveolar ventilation → PO2

constricted bronchioles!!

Sequence of Oxygen Movement

Atmospheric O2 → Alveolar O2 → Plasma O2 → HbO2 (hemoglobin O2)

atmospheric O2 affects

all other O2 (alveolar, plasma, and hemoglobin)

Atmospheric O2 is affected by..

altitude, humidity

• o2 is low in high altitudes

Alveolar O2 is affected by…

lung compliance (lung’s ability to stretch), airway resistance, rate and depth of breathing

Plasma O2 is affected by…

factors affecting diffusion (distance, surface area, barrier permeability)

alveolar gas exchange is influenced by

O2 reaching the alveoli

gas diffusion between alveoli and blood

adequate perfusion of alveoli

oxygen reaching the alveoli is influenced by

• Composition of inspired air (e.g., altitude, humidity).

• Alveolar ventilation: Affected by rate and depth of breathing, airway resistance, lung compliance.

alveolar ventiliation is affected by:

• rate and depth of breathing

• airway reistance

• lung compliance

Gas diffusion between alveoli and blood is influenced by:

barrier thickness, amount of fluid, surface area, diffusion distance

when temperature remains constant, the amount of gas that disccolves in a liquid depends on…

the solubility of the gas in the liquid and partial pressure of the gas

oxygen solubility is

LOW;

CO2 solubility is

HIGHER (than O2)

CO2 dissolves in water (plasma) much easier than O2

anemia

not enough red blood cells or dont have healthy RBCS

• we need RBCs to carry O2

causes: accelerated RBC loss. hemolytic anemias, decreased RBC production, etc

sickle cell anemia

hereditary disease where they have unhealthy misshapen RBCs — so O2 has difficulty reaching the body

O2 movement is driven by

concentration (pressure)

hematocrit

a test to see if someone has anemia: measures the percentage of your total blood volume that consists of red blood cells (RBCs)

total blood O2 =

O2 dissolved in plasma (PO2) + O2 bound to hemoglobin (HbO2).

hemoglobin’s role in blood

More than 98% of oxygen in blood is bound to hemoglobin in red blood cells; less than 2% is dissolved in plasma!!!

• Without hemoglobin, O2 carrying capacity is very low

• also carries CO2 and CO (carbon monoxide)

Is most blood dissolved in plasma or bound to hemoglobin?

More than 98% of oxygen in blood is bound to hemoglobin in red blood cells; less than 2% is dissolved in plasma.

how CO2 transports in blood (3)

• dissolved CO2: 7%

• HbCO2: 23% — CO2 binds to hemoglobin

• HCO3- (bicarbonate): 70%

HCO3- (bicarbonate)

stores CO2 in a non-acidic form (buffer) to maintain pH

• main buffur

hemoglobin’s role in CO2 transport

it grabs H+ so the blood doesnt get too acidic (backup buffer)

the whole story of CO2 and pH

1. Cells make CO₂ (waste)

2. CO₂ enters red blood cells

3. It turns into carbonic acid (H₂CO₃)

4. Then breaks into:

• H⁺ (acid)

• HCO₃⁻ (bicarbonate)

5. The H⁺ could make blood acidic BUT hemoglobin grabs it → prevents pH from dropping

when CO2 is too high, the pH…

becomes acidic

chloride shift

when bicarbonate leaves the RBC, it loses a negative charge, so chloride must come in to balance the negative charge

the amount of oxygen bound to hemoglobin depends on

plasma O2 and the amount of hemoglobin

hemoglobin increases

oxygen transport

what determins the % saturation of hemoglobin?

plasma O2

what determines the total number of Hb binding sites (calculated from Hb content and number of RBCs?

the amount of hemoglobin

if # of RBCs increase, more _________ is carried to your tissues

oxygen

hemoglobin consists of ___________, centered around a _____ group

4 polypeptides, heme group

hemoglobin can carry up to

4 oxygen molecules

4 polypeptides of hemoglobin

2 alpha and 2 beta

gas exchange: oxygen diffusion

alveoli (lungs) → blood → peripheral tissue

moves from high PO2 in ungs to low PO2 in blood and in peripheral tissue

gas exchange: carbon dioxide diffusion

peripheral tissue → blood → alveoli (lungs)

normal HbO2% saturation curve

shows how full your hemoglobin “taxis” are depending on how much O2 is avaliable

in a resting cell (40 mmHg), 75%

in alveoli (100mmHg), 99%

higher pressure on the curve means

hemoglobin is loading up on O2

lower pressure on the curve means

hemoglobin is unloading up O2

left shift in Hb curve

Hemoglobin has a higher affinty for O2

grabs O2 easier and is stingier

right shift in Hb curve

Hb has a lower affinity for O2

easier to release O2

results in lower saturation at a certain pressure compared to the normal curve bc of O2 release

factors that decrease affinity of Hb for O2 (right shift)

increased CO2

increased temperature

increased acidity (lower pH)

increased 2,3-DPG

factors that increase affinity of Hb for O2 (left shift)

less acidity (higher pH)

lower temperature

lower PCO2

lower 2,3-DPG

fetal hemoglobin causes a

fetal Hb has a higher affintiy for O2 than adult Hb, becasue it has to steal O2 from its mother’s blood

• left shift!!!

Carbon monoxide poisoning

CO binds to Hb on the exact same spot as O2 on Hb, but much mroe strongly, leaving less seats for O2 to bind

treatment for carbon monoxide poisoning

breathing in pure O2 to get ride of the CO

is CO poisoning a right or left shift?

it is am extreme right shift case

• decreases affinity for O2

How does the body respond to hypoxia/high altitudes?

increased erythropoitin, a hormone, that travels to the bone marrow and tells it to produce more RBCs

• with RBCs, there are more taxis to pick up whatever O2 is avaliable

hypoxia

low oxygen; can be due to higher altitudes

total arterial O2 content

• oxygen dissolved in plasma (PO2 of plasma) (2%)

  • influenced by rate and depth of breathing, airway resitance, and lung compliance, surface area, diffusion distance (membrane thickness)

• oxygen bound to Hb (98%)

  • influenced by % saturation of Hb, total number of binding sites — PCO2, pH, temperature, 2,3-DPG, Hb content per RBC, number of RBCs

neural control of breathing

• involuntary

  • controlled by medulla oblongata & pons

  • ex. pacemaker for breathing

• voluntary

  • controlled by higher brain centers (cerebral cortex), skeletal

  • ex. holding your breath or speak

• emotions

  • limbic system

  • ex. gasping when scared

respiratory control centers

• medulla oblongata

• pons

• dorsal respiratory group (DRG)

• ventral respiratory group (VRG)

medulla oblongata

initiates respiration; one of the pacemakers

pons

modulates respiration; acts as the bridge and smooths the transition between inhaling and exhaling; talks between DRG & VRG!

dorsal respiratory group (DRG)

in the medulla; quiet breathing (inspiration)

• triggers diaphragm to inhale

ventral respiratory group (VRG)

in medulla: forced breathing (expiration)

ex. when you exercising and need to more air out of your lungs quickly

chemoreceptor response

thermostat for breathing

central (medullary) chemoreceptors

CO2 can cross the BBB but H+ (acid) cannot

when CO2 gets into the cerebrospinal fluid, it turns into H+

brain senses the acid and screams breathe (increased ventilation) to get rid of the CO2

receptors that ONLY detect CO2 levels via H+

when CO2 gets into the cerebrospinal fluid, it turns into

H+

Which can cross the BBB: CO2 or H+?

CO2

it crosses and then turns into H+

peripheral chemoreceptors (neck/heart)

detects CO2, pH, and ocygen

• only detects when O2 is at a dangerously LOW levels (below 60mmHg)

what is primary driver for breathing?

CO2 levels detected as H+ in the brain

pre-botzinger complex

pacemaker for cells

fetal hemoglobin

left shift