Gas Exchange And Transport

Question 1

Hypoxia

Answer 1

Low levels of oxygen in the body

Question 2

Hypercapnia

Answer 2

High levels of carbon dioxide in the body. Symptoms include decline in CNS function, confusion, coma, or death

Question 3

Acidosis

Answer 3

When CO2 levels increase pH drops leading to acidosis

Question 4

Gases require a

Answer 4

Pressure gradient in order to diffuse from one area to another. When the gradient reaches equilibrium diffusion stops.

Question 5

When talking about gases we mean they’re partial pressure

Answer 5

Not the concentration.

*Example partial pressure of alveolar air is 100 mg of mercury, partial pressure of venous blood is 40 mg of mercury period is so oxygen diffuses from air into blood until the P02 of blood reaches 100 MMHG equilibrium

Question 6

Some potential problems with this system (gas exchange) involve 

Answer 6

1.  Low partial pressure of oxygen in the alveoli: mostly associated with high altitudes
2. Inadequate ventilation: relates to lung compliance, increased resistance, or just cessation of breathing
3. Other considerations are the rate of diffusion and solubility of the gases

Question 7

As atmospheric pressure decreases

Answer 7

 partial pressure of oxygen decreases, so change in pressure decreases, meaning less oxygen is available to be moved into blood.

Question 8

Diffusion rate will affect

Answer 8

How much gas is able to move into blood

*example if partial pressure of oxygen is normal, if it has trouble diffusing into plasma then it’s a problem

Question 9

Ficks law of diffusion rate

Answer 9

Diffusion rate =
(surface area x pressure gradient x permeability) / distance2

Normally all of these are constant except pressure gradient

Question 10

However in some pathologies diffusion rate may be influenced by

Answer 10

1. Surface area may decrease
   example emphysema destroys alveolar cells decreasing surface area
2. Permeability may decrease example fibrotic diseases thicken the membrane decreasing Permeability
3. Diffusion distance may increase example: excess alveolar fluid such as pulmonary Edema caused by a decrease in left ventricular function or mitral valve disorders affect normal capillary pulmonary filtration/absorption rates that increase interstitial fluid and increase diffusion distance

Question 11

Solubility of gases will influence (ability to dissolve into a fluid namely plasma here)

Answer 11

How much moves from air into plasma. The amount varies with pressure gradient, the gases solubility which is constant and temperature which in mammals is also relatively constant

Question 12

Oxygen is not very soluble into

Answer 12

Fluids
🤔example at equilibrium partial pressure of oxygen is 100 mg of mercury, air contains 5.2 mm of oxygen per liter, but water contains only 0.15 mmol of oxygen per liter.

Question 13

Because oxygen is hard to dissolve it necessitates

Answer 13

A helper to get into the blood in order to be transported a.k.a. hemoglobin

Question 14

CO2 is 20 times more soluble then

Answer 14

Oxygen, for comparison equalliberated partial pressure of CO2 100 mg of mercury call my air contains 5.2 million moles of carbon dioxide per liter but water contains 3.0 mill the moles per liter of CO2. So CO2 dissolves much easier into plasma therefore no need for a transport molecule.

Question 15

Mass delivery of oxygen depends on

Answer 15

Concentration of oxygen in blood and the flow rate (Q) of blood

Question 16

So if blood contains 200 mL of oxygen per liter and flow rate is 5 L per minute

Answer 16

1000 mL of oxygen is available for use by tissues every minute

Question 17

Using the concept of mass balance one in, one out we can calculate the amount of oxygen that is used by the tissue simply by

Answer 17

Subtracting the venous oxygen concentration from the arterial oxygen concentration
(O2 consumption = [O2]arterial - [O2]venous)

Question 18

Ficks equation

Answer 18

If arterial and venous oxygen concentration is known, can be used to estimate cardiac output or oxygen consumption rate QO2 that is used all the time and physiological experience and medical diagnosis: QO2 = CO x ([O2]arterial - [O2]Venus)

Question 19

Because if it low solubility only

Answer 19

2% of oxygen is transported as being dissolved in the plasma. 98% of it is transported by being loosely and reversed of bully bound to hemoglobin. The binding is strong enough to coax oxygen into the blood but loose enough to let it go at the tissues (compared to carbon monoxide which is very tightly founded to hemoglobin and does not let go which is why it’s so deadly)

Question 20

Oxyhemoglobin

Answer 20

Hb+O2 HbO2

Question 21

Each hemoglobin molecule contains

Answer 21

Four Heme groups that can bind up to four oxygen molecules

Question 22

The binding and disassociation follows the law of mass action

Answer 22

increase oxygen causes increase oxyhemoglobin
And vice versa
This is convenient because when oxygen is high in the lungs it forms a lot of oxyhemoglobin for transport and where oxygen is low in the tissues where we need oxygen to be delivered it disassociate and lets the oxygen unbind

Question 23

The total amount of oxygen in the body as oxyhemoglobin

Answer 23

Is actually higher than what is needed at the tissues allowing for a reserve for increased activity

Question 24

Partial pressure of oxygen determines the

Answer 24

Percentage of hemoglobin that is bound to oxygen. termed the percent saturation of hemoglobin.

Question 25

Percent saturation of hemoglobin mathematically

Answer 25

(Amount of bound oxygen/amount of potential binding sites) x100

Question 26

So if all of the binding sites have oxygen down to them

Answer 26

The hemoglobin saturation is 100%

Question 27

OXY hemoglobin saturation curve a.k.a. disassociation curves

Answer 27

Plot the percent saturation against partial pressure of oxygen to show the characteristics of how oxygen binds and unbinds at varying levels of oxygen, physiology relevant because partial pressure of oxygen changes and thus oxygen is picked up/delivered between the lungs and tissue

Question 28

Saturation curves are created in a lab

Answer 28

By exposing a blood sample to a particular partial pressure of oxygen of air in a close test tube allowing it to equilibrium than measuring how much of the oxygen binds to the hemoglobin. The curve typically follows an S shape sigmoidal curve and reveals some interesting stuff

Question 29

What are three things that the oxyhemoglobin saturation curve reveal

Answer 29

1. Alveolar partial pressure oxygen usually around 100 mg of mercury so the hemoglobin saturation is nearly 100%
2. High partial pressure of oxygen, though the saturation does not change much so not much oxygen can be delivered at this range so most stay bound to hemoglobin
3. The largest change in saturation a.k.a. delivery of oxygen occurs at the partial pressure between 20 and 40 mg of mercury conveniently this is the range that cells in the tissue are usually at so a lot of oxygen is picked up in the alveoli and then is able to be released at the tissue

Question 30

The saturation curves change with

Answer 30

Temperature, pH, and CO2 levels (the binding properties of hemoglobin change and lowers the ability of it to carry oxygen)

Question 31

The curve shifts to the right as

Answer 31

Temperature and carbon dioxide increase, or pH decreases

Question 32

The largest affect is on the saturation curve is

Answer 32

 steep part of the curve, so as these physiologically important factors change the amount of oxygen being delivered also changes to help undo any adverse effects (example of low pH or high CO2)

Question 33

As the Cell runs out of oxygen they switch to

Answer 33

Glycolysis anaerobic metabolism, which increases hydrogen and decreases pH. This causes a shift to the right in the saturation curve more oxygen is released at the tissues the cells are able to switch back to aerobic metabolism. This particular shift is due to pH termed the Bohr effect

Question 34

Saturation curves change Increasing temperature and carbon dioxide both which are influenced by activity/exercise

Answer 34

Increase exercise > increase in carbon dioxide > a decrease in Oxyhemoglobin saturation > an increase in oxygen delivery

Question 35

Another influence on saturation (curve) is

Answer 35

With the release of 2,3 - BPG (bisphosphoglycerate) which is a byproduct of glycolysis, but also is released in response to anemia or high altitude. 2,3 -BPG shifts the saturation curve to the right lowering the infinity hemoglobin to oxygen

Question 36

Fetal hemoglobin shows a higher affinity for

Answer 36

Oxygen which shifts the curve to the left. Which is adaptive considering placental blood has a lower oxygen concentration. This is due to the hemoglobin beta subunits being replaced by gamma subunits which does not interact well with 2,3-BPG. At birth the newborn begins making blood with the beta subunits 

Question 37

What are the three ways that the transport of carbon dioxide occurs

Answer 37

1. Conversion of HC03 bicarbonate 75%
2. Bound to hemoglobin ~23%
3. Dissolve in plasma ~2%
   Note that the first to take place in the red blood cells

Question 38

Conversion of carbon dioxide to bicarbonate is a reaction that occurs through

Answer 38

Mass action increasing levels of the reaction or products were driving reaction in the opposite direction. Their reaction takes place in the erythrocytes and uses the enzyme carbonic anhydrase.
CO2+H2O HCO3- + H+

Question 39

As carbon dioxide dissolves into blood enters the

Answer 39

Erythrocyte driving the formation of bicarbonate but in order for the reactions to keep going bicarbonate must leave the cell. This occurs the action of an anti-porter which transports chloride in and simultaneously transfers bicarbonate out into the plasma termed the chloride shift

Question 40

In the plasma bicarbonate acts as a 

Answer 40

Very important buffer preventing changes in blood pH (recall blood pH must be maintained within a very narrow limit 7.35 to 7.45 in order to function properly) 

Question 41

Meanwhile the hydrogen formed in the reaction

Answer 41

Binds to the hemoglobin to form HbH, preventing lowering pH in the cell, if CO2 levels exceed the ability to bind all the hydrogen it can lead to respiratory acidosis

Question 42

Some CO2 diffuses into the erythrocytes and binds to Amino groups on hemoglobin for me

Answer 42

Carbaminohemoglobin a reversible process since this binding takes place away from the heme groups it does not affect the ability of hemoglobin to bind it with oxygen at the same time

Question 43

Even though carbon dioxide has a higher affinity then oxygen the amount that is able to dissolve into the plasma

Answer 43

Isn’t high enough to transport enough away requiring other mechanisms. Once blood reaches the alveoli the processes simply reverse as pressure of CO2 is lower and mass action drives its removal: bicarbonate is transported back into the cell through chloride shift and converted back to CO2 by carbonic anhydrase, carbaminohemoglobin disassociate; CO2 diffuses in to alveolar air down its pressure gradient

Question 44

Regulation of ventilation is complex that relies on stimulation of respiratory skeleton muscles which is considered normally voluntary so it is believed that breathing patterns are controlled by

Answer 44

The CNS through a central pattern generator model. In this model, pacemaker neurons in a medulla oblongata and ponds set the basic rhythm with input from chemo receptors and higher brain centers. This info comes from patience with brain damage love animals and beheadings

Question 45

Historically regions of the medulla/pons were considered different respiratory groups but

Answer 45

It appears that they control is more of a network than a distinct group with unique functions

Question 46

The current Respiratory model

Answer 46

1. Respiratory neurons in the medulla control muscles involved with inspiration and expiration
2. pontine neurons integrate sensory information to modulate medullary controls.
3. Rhythmic patterns originate from a network of spontaneously firing neurons in the brain stem
4. Breathing is modulated by input from chemo receptors and Mechanoreceptor reflexes and higher brain centers

Question 47

Important regions in the brain

Answer 47

1. Respiratory Neurons formally known as centers in the medulla located in the dorsal respiratory group DRG control inspiration through glossopharyngeal(cnix), Vagus (cnx), and phrenic nerves.
2. Pontine respiratory groups coordinate smooth initiation and termination of breathing
3. Ventral respiratory groups VRG in the mid to that has different functions including pacemaker patterns of breathing, active expiration and inspiration example controlling larger breaths during exercise. Control the pharynx, larynx, and the tongue the latter being partly responsible for sleep apnea. 

Question 48

The chemical composition of plasma and CSF

Answer 48

CO2, O2, ph influence respiratory rates in order to maintain homeostasis. Of these CO2 has the largest influenced

Question 49

Chemo receptors are located peripherally and centrally

Answer 49

1. Peripheral chemo receptors: are located in the carotid bones near the barrow receptors that help monitor blood pressure. Their glomus cells monitor plasma for low O2 and pH and high CO2 levels.

Question 50

Peripheral chemo receptors have to have oxygen levels that are really low

Answer 50

Before the cells are stimulated less than 60 mmHg (which is the equivalent of being at 3000 m above sea level, Lake Tahoe is 1900 m, mount Everest is about 9000 m.)

*High CO2 levels and low pH in the plasma are the main triggers that will increase ventilation rate. The mechanism isn’t well understood it may involve the polarizing cells that alter sensitivity and increase the release of neurotransmitters to stimulate ventilation

Question 51

Central chemo receptors

Answer 51

Are located in the medulla, adjacent to respiratory Control and Neurons centers. They mainly Cue on increased CO2 in CSF, but in an indirect way: increased CO2 causes increased formation of bicarbonate and hydrogen which causes increase in hydrogen that stimulates ventilation. however, hydrogen does not cross the blood brain barrier where CO2 can, so it’s the hydrogen formed by the CO2 that seems to initiate the response

Question 52

Central chemoreceptor response

Answer 52

The response is strong at first but will adapt to increase CO2 by producing more bicarbonate buffer to handle the increase hydrogen.

Because of this oxygen which normally plays a small role in signaling an increase in breathing can start to play a larger role in the signal process.

*People with COPD may adapt to increase CO2 relying on decrease in oxygen is the primary signal to start breathing faster. If they are administered too much oxygen the signal is satisfied and they just stopped breathing

Question 53

Because CO2 is the primary signal that initiates the urge to breathe

Answer 53

You can trick your body by hyper ventilating to blow off CO2 which allows holding your breath longer. Skin divers often do this and stay underwater longer however it’s dangerous his oxygen levels can drop to very low level before the urge to breathe kicks in online you just pass out and start breathing again underwater a pass out and die