Physiology Exam 3 Lecture 10B [Respiratory gas exchange and transport: Harata]

Airflow is regulated by

smooth muscle of the bronchiole

Blood flow is regulated by

Pulmonary arteriole (Smooth muscle)

If there is large blood flow and small airflow

If there is large airflow and small blood flow

Pulmonary circulation makes

gas exchange efficient

Systemic circulation matches

blood supply to metabolic needs

Pulmonary arterioles: Decreased O2

Vasoconstriction

Pulmonary arterioles: Increased O2

Vasodilation

Systemic arterioles: Increased O2

Vasoconstriction

Systemic arterioles: Decreased O2

Vasodilation

Ventilation-perfusion ratio (V/Q ratio)

The efficiency of oxygenation

Ventilation (V) = rate of air flow to alveoli

Perfusion (Q) = rate of capillary blood flow to alveoli

Normal V/Q ratio

0.8 ~1.0

Change from the normal V/Q ratio is called

V/Q mismatch

Ventilation and perfusion flows are not the same across

the lungs

Differences at top and bottom of lungs

Flow rate either airflow or blood flow varies at different lung regions, because of gravity effects, creating a non-constant V/Q ratio

The variable V/Q ratio is considered physiological at the local level. at the level of individual alveoli

Pathological V/Q mismatch cannot be compensated by

local controls

Normal V/Q ratio allows

efficient oxygenation of blood

Decreased V/Q mismatch is often caused by

decreased airflow due to block of alveolar ventilation in pulmonary problems leading to shunting blood flow

- Chronic obstruction pulmonary disease (COPD)

- Pneumonia

Increase V/Q ratio is often caused by

Decrease blood flow due to block of alveolar blood perfusion in vascular problems, leading to functional dead space in airways

- Pulmonary embolism

- Heart failure

Good schematic image V/Q ratios

SUMMARY: Physiological changes in ventilation and perfusion can be regulated locally in lung areas, by

bronchiolar and arteriolar smooth muscles, respectively

SUMMARY: The efficiency of blood oxygenation can be expressed as the

ventilation-perfusion ratio (V/Q)

SUMMARY: In V/Q mismatch, the ratio of air flow is not similar to that of

blood flow

SUMMARY: Pathological, low V/Q ratio can be produced by

block of alveolar ventilation. this condition results in shunting of blood flow

SUMMARY: Pathological, high V/Q ratio can be produced by

blocking of alveolar blood perfusion. This condition results in functional dead space in airways. Dead space is the conducting respiratory passageway that does not contribute to gas exchange in the alveoli

Partial pressure

pressure exerted by each gas in a mixture

total pressure x fractional composition of the gas in mixture

Px = Partial pressure of gas x

Henry's law states that the

amount of dissolved gas is proportional to its partial pressure in the gas phase

Each gas within a mixture exerts its own

partial pressure essentially independently of other gases in the mixture

Henry's law: The higher the partial pressure

the higher the concentration of physically dissolved gas

Gas exchange involves simple passive diffusion of

O2 and CO2 down their own partial pressure gradients. From the high to low partial pressure compartments

No active transport mechanism exist for these gases (O2, CO2)

very very very true

Gotta know this figure

8 Steps of O2 and CO2 exchange caused by partial pressure gradients

1. Alveolar P(O2) remains relatively high and alveolar P(CO2) remains relatively low because a portion of the alveolar air is exchanged for fresh atmospheric air with each breath

2. In contrast the systemic venous blood entering the lungs is relatively low in O2 and O2 and high in CO2 having given up its O2 and picked up CO2 at the systemic capillary level

3. The partial pressure gradients established between alveolar air and pulmonary capillary blood induces passive diffusion of O2 into the blood and CO2 out of the blood until the blood and alveolar partial pressure becomes equal

4. The blood leaving the lungs is thus relatively high in O2 and low in CO2. it arrives at the tissue with the same blood-gas content as when it left the lungs

5. The partial pressure of O2 is relatively low and that of CO2 is relatively high in the O2 consuming, CO2 producing tissue cells

6. Consequently, partial pressure gradients for gas exchange at the tissue level favor the passive movement of O2 out of the blood into the cells to support their metabolic requirements and also favor the simultaneous transfer of CO2 into the blood

7. Having equilibrated with the tissue cells, the blood leaving the tissues is relatively low in O2 and high in CO2

8. The blood then returns to the lungs to once again fill up on O2 and dumb off CO2

Ficks law of gas diffusion

Fick's law: (P1 - P2) Partial pressure gradient

Rate of transfer increases as partial pressure gradient increases

Comment:

Major determinant of rate of transfer

Fick's law: Surface area of the alveolar capillary membrane (A)

Rate of transfer increases as surface area increases

Comment:

Surface area remains constant under resting conditions

Surface area increase during exercise

Surface area decrease with pathological conditions such as emphysema and lung collapse

Fick's law: Thickness of alveolar capillary membrane (T)

Rate of transfer decreases as thickness increases

Comment:

Thickness normally remains constant

thickness increases with pathological conditions such sa pulmonary edema, pulmonary fibrosis, and pneumonia

Fick's law: Diffusion constant (D)

Rate of transfer increases as diffusion constant increases

Comment:

Diffusion constant for CO2 is 20 times that of O2 offsetting smaller partial pressure gradient for CO2; therefore approximately equal amounts of CO2 and O2 are transferred across the membrane

Emphysema

Destruction of alveoli

- Decrease in Surface area

- Increase of thickness

= decrease gas exchange rate

SUMMARY: Exchange of O2 and CO2 between alveoli and capillaries is driven by

partial pressure gradients for each gas

SUMMARY: Dissolved gases flow down their

partial pressure gradients, just as ions flow down their concentration gradients

SUMMARY: The rate of gas transfer across alveolar membranes depends on

Fick's law of gas diffusion

SUMMARY: Fick's law involves four factors

1. Partial pressure gradient of the gas

2. Surface area available for transfer

3. Thickness

4. Diffusion constant of the gas

SUMMARY: The four factors of fick's law are affected upon

various disease conditions

O2 method of transport in the blood

Physically dissolved: contributes to P(O2)- 1.5 %

Bound to hemoglobin - 98.5 %

CO2 Method of transport in the blood

Physically dissolved: contributes to P(CO2) - 10%

Bound to hemoglobin- 30%

As bicarbonate - 60%

Hb is the protein contained in

Red blood cells

Hb is responsible for

delivery of O2 to the tissue

Hb contains _ heme molecules each of which contains an iron ion

4

Each iron can bind

one O2

Each Hb can bind ___ O2

4

When not combined with O2, Hb is referred to as

reduced hemoglobin of deoxyhemoglobin

P(O2) is a primary determinant of percent

hemoglobin saturation with O2

Hb affinity for O2 increases as more O2 molecules become bound this is known as

cooperatively

- Sigmoidal curve

The O2 bound to Hb does not

contribute to P(O2) of the blood

Binding O2 of Hb removes O2 from the

blood

O2 binding Hb reduced P(O2) and maintains

the partial pressure gradient that drives O2 from alveoli into the blood

Hb increases the total content of

O2 in the blood

Oxygen-Hemoglobin dissociation curve is

sigmoidal because the O2-Hb binding is cooperative

A rightward shift of the O2-Hb dissociation curve is due to

Increase P(CO2)

Increase Acid (H+)

Increase Temperature

Increase 2,3-Bisphosphoglycerate

With a rightward shift affinity for O2 is

reduced

O2 saturation decreases slightly at high

P(CO2)

O2 saturation decreases at a large extant at

Low P(O2)

More O2 is unloaded from Hb at a low

P(O2)

2,3-Bisphosphoglycerate production is increased in red blood cells when

Arterial HbO2 is chronically below normal

Ex/

- living at high altitudes

- suffering from disease such as anemia

A leftward shift in the O2-Hb saturation curve is due to

Increased Carbon Monoxide

A leftward shift =

increase Affinity of Hb to O2

Co has 240 times higher affinity for Hb than

O2

Co-hemoglobin is called

Carboxyhemoglobin

When Hb-CO: _________ oxygen is unloaded in the tissues, even when PO2 becomes low. This causes hypoxic tissue injury

Little

CO is _________ because it is odorless, colorless, tasteless, and nonirritating

not detectable

SUMMARY: 98.5% of O2 in blood is transported in a form

bound to hemoglobin

SUMMARY: hemoglobin is a tetrameric heme-containing protein that can bind

4 O2 molecules per hemoglobin complex

SUMMARY: binding of O2 to Hb removes it from the blood thus

reducing PO2. this helps maintaining the pressure gradient to drive O2 from alveoli into the blood

SUMMARY: Oxygen Hemoglobin dissociation curve describe how

O2 is bound to Hb at alveoli and how O2 is unloaded to tissue

SUMMARY: Hb affinity for O2 is reduced when

Increase PCO2

Increase Acid

Increase Temperature

Increase 2-3-BPG

Leads to a rightward shift of the curve and to efficient unloading of O2 at peripheral tissues

SUMMARY: The effect increase PCO2 and Increase H+ on the O2-Hb dissociation curve is known as the

Bohr effect

SUMMARY: CO induces a

left-ward shift of the O2-Hb saturation curve, and inability of Hb to unload O2 at tissues

Approximately 6-% of CO2 is carred in the blood as

bicarbonate ion

In RBC the enzyme _______ catalyzes the rapid conversion of CO2 and H+ and Bicarbonate

carbonic anhydrase

Spontaneous reaction in the blood of CO2 and H2O is

Catalyzed reaction in RBC of CO2 and H2O is

Slow

Fast

Law of mass action

If the concentration of one substance involved in a reversible reaction is increased the reaction is driven toward the opposite side

Conversely, if the concentration of one substance is decreased the reaction is driven toward that side

Three ways of transporting CO2 from tissues to lungs

Bohr effect: Increased O2 unloading by Increase CO2 and H+

Haldane effect: Hb binding with CO2 and H+ inducing O2 unloading

Hb passengers: O2 to tissue; CO2 and H+ to lungs

SUMMARY: CO2 is produced in the tissue, diffuses into the bloodstream and is transported to the lungs for excretion

yea true

SUMMARY: CO2 is transported in the blood primarily as

HCO3 (bicarbonate) or bound to Hb.

Only 10% is dissolved in plasma

SUMMARY: Since CO2 is quickly converted to bicarbonate by ________, this reaction allows for the continued uptake of CO2 into the blood, down its concentration gradient

Carbonic anhydrase

SUMMARY: Hb plays a key role: Hb carries O2 and CO2, and binds H+ that results from

bicarbonate production

SUMMARY: CO2 bound directly to Hb is called

Carbaminohemoglobin

SUMMARY: The Bohr effect

describes the role of increased CO2 and H+ in tissue, in inducing the unloading of O2 from Hb

SUMMARY: The Haldane effect

Describes the role of the unloading of O2 from Hb in freeing Hb to bind with CO2 and H+, allowing them to be carried to their common destination: lungs

Chronic Obstructive pulmonary disease (COPD) includes

emphysema and chronic bronchitis and they often occur together

COPD is a chronic inflammatory lung disease that causes

obstructed airflow from the lungs and breathing-related problems

COPD symptoms include

Breathing difficulty

Cough

Mucus production

Wheezing

COPD is typically caused by

long-term exposure to irritating gases or particulate matter, most often from cigarette smoke

Emphysema

a condition in which the alveoli are destroyed

Chronic bronchitis

inflammation of the lining of the bronchi and bronchioles. Characterized by daily cough and mucus (sputum) production