Chapter 20 "Internal and external respiration & gas transport"
Haldane effect
States that the amount of CO2 transported is affected by the PO2 The lower the PO2 and hemoglobin saturation with O2, the more CO2 can be carried in the blood & v.v.
What must happen for PO2 to have an effect on ventilation rate?
Substantial drop (60 mmHg) in arterial PO2 in order to stimulate increased ventilation
What system can directly change ventilation? What is an example?
The cerebral cortex Example: blowing up a balloon
What happens to CO2 concentration in blood is hemoglobin saturation with O2 and PO2 values are lowered?
The more CO2 can be carried in the blood
Reverse chloride effect
The opposite of the chloride effect that takes place in the capillaries, where CO2 leaves the cell (created by the joining of HCO3- and H+, which entered the cell) along with the chloride ion
What is the saturation of PO2 in systematic arterial blood?
100 mmHg with hemoglobin saturation of 98 %
What happens to HB affinity when O2 is released?
Affinity decreases
What happens to HB (hemoglobin) affinity when O2 binds?
Affinity increases
Ventilation
Amount of gas reaching the alveoli
Perfusion
Blood flow reaching the alveoli
What do these centers do?
Both centers control depth and rate of breathing depending on the body's demands
What happens to CO2 concentration when PO2 levels are raised along with hemoglobin saturation of O2?
Less CO2 can be carried in the blood
Carbonic acid- bicarbonate buffer system
Maintains homeostasis by controlling H+ levels in blood by either dissociating H2CO3 to release H+ when levels are down, and binding to combine HCO3 when levels are too high
What happens if PO2 levels in the tissues drop?
More oxygen dissociated from hemoglobin and is used in cells Respiratory rate or cardiac output don't need to increase
What is the most powerful respiratory stimulant?
Rising CO2 levels
Gas transport is a part of what system?
The cardiovascular system
What is external respiration?
The exchange of O2 and CO2 across the respiratory membrane
Chloride shift
The inflow of chloride ions into the erythrocytes to balance the quick diffusion of bicarbonate out of the cell via diffusion
What is different about the capillaries and the chloride shift?
The mechanism goes opposite directions in the capillaries; HCO3- moves into the erythrocytes and binds with H+ to form H2CO3 which is split into water and CO2. Then the CO2 diffuses out of the cell along with chloride ions (reverse chloride effect)
What respiration center has a dorsal and ventral group?
The medullary respiratory center
What are the effects of deeper breathing, increase in the PO2?
There is a minimal increase in O2 binding
How does the metabolically active tissues affect hemoglobin?
They modify the structure of hemoglobin and decrease it's affinity for O2
What happens if O2 levels in active tissue drop below the average of 40 mmHg?
This causes more oxygen to dissociate from hemoglobin and diffuse into the tissue
What is are the influences of PO2 on hemoglobin saturation?
1. Hemoglobin is almost saturated at a PO2 of 70 mmHg 2. further increases in PO2 produce only small increases in O2 binding 3. O2 loading & unloading is adequate when PO2 is below normal levels
What does a rise in body temperature do to respiratory rate?
A rise in body temp increases respiratory rate
What will happen to pulmonary ventilation when pH increases?
A rise in pH will decrease pulmonary ventilation
What are other high brain centers that influence breathing depth and rate? What are some examples?
Brain centers such as the hypothalamus and the limbic system, & cerebral cortex Examples: When we are cold or frightened
What has the most influence on respiratory centers?
Chemical factors
What is the structure of hemoglobin?
Made up of 4 chains: 2 alpha and 2 beta--- make up the protein part of the molecule (globin) Pigment contains one atom of iron at its core (heme)
How many molecules of O2 does a saturated hemoglobin carry?
4 molecules O2
Hypocapnia
A drop in PCO2 levels
How does CO2 diffuse compared to O2?
CO2 dissolves in equal amounts with O2 And CO2 is 20 times more soluble in plasma than O2
How is rate of breathing determined?
Determined by how long the inspiratory center is active
Hering-Breuer Reflex: what moderates it?
Protective response to prevent over inflation of the lungs Controlled by stretch receptors in the pleura that send signals to the medullary respiratory center to end inhalation and allow expiration to occur Act as a protective response
Deoxygenation: what is it and what does it form?
Unloading of oxygen from hemoglobin Produces dark red reduced hemoglobin, or deoxyhemoglobin
What happens if the respiratory membrane thickens?
It will impair gas exchange
Bohr Effect
The weakening of HB- oxygen bond due to a decline in pH
Eupnea
Normal, good, unlabored breathing (12-15 breathes/minute)
What type of bond holds together the oxygen and the iron? What does this allow?
Not a chemical bond, but a loose bond based on the weak attraction forces-- this allows oxygen to be released from it easily
What happens to the blood pH when H+ concentration goes up? What about down?
Rise in H+ = decrease in pH Drop in H+ = increase in pH
How many molecules of O2 does an unsaturated hemoglobin carry?
1-3 molecules O2
What are other factors that affect hemoglobin saturation and how do they do it?
1. An increase in temperature 2. Metabolization of glucose
Why do alveoli have a different composition than atmospheric air?
1. Gas exchange in the lungs 2. Humidification of air 3. Mixing of alveolar gas that occurs with each breath
What is the rate of unloading and loading of O2 regulated by?
1. PO2 2. Temperature 3. Blood pH 4. PCO2
What is external respiration affected by?
1. Partial pressure gradients and solubilities 2. Ventilation perfusion coupling 3. Structural characteristics of the respiratory membrane
What will happen to pulmonary ventilation when pH decreases?
A drop in pH will increase pulmonary ventilation
Why does myoglobin have a different dissociation curve?
Because it is a tertiary protein and is not susceptible to shape changes as the quaternary hemoglobin
What is the thickness and surface area of the respiratory membrane? Why is it like this?
About 0.5-1 um thick Has a large total surface area: 4o times that of one's skin The membrane has to be super thin in order for gases to move across via diffusion only
What causes a right shift of the hemoglobin dissociated curve?
Al changes that decrease the affinity of hemoglobin for O2 and lead to an increased O2 release
What is the composition of alveolar gas?
Alveoli contain more CO2 and water vapor than atmospheric air
How does the hemoglobin concentration affect the affinity for CO2 in blood?
As more O2 dissociates from the hemoglobin in tissue (because of a lower pH - Bohr effect), it frees up HB to combine with CO2 to form carbaminohemoglobin
How is depth of breathing determined?
By how actively the respiratory center stimulates the respiratory muscles
What is the best way to measure concentrations of gases in mixtures?
By measuring their partial pressure
Where is carbonic anhydrase located? What does it do here?
Carbonic anhydrase is located in the erythrocytes- where it catalyzes production of most of the bicarbonate found in venous blood
_____________ is a _________ acid which has a tendency to __________ into ______ ions and ________ ions.
Carbonic, weak, dissociate, H+, Bicarbonate (HCO3-)
What other factors can affect blood pH levels? Example?
Changes in breathing rate can also affect blood pH Example: slow, shallow breathing allow CO2 to accumulate in blood, which leads to a drop in pH Changes in ventilation (amount of gas reaching the alveoli) can also cause a change in pH
When alveolar PO2 is high, arterioles _____ When alveolar PO2 is low, arterioles ____
Dilate Constrict
When alveolar PCO2 is high, bronchioles ____ When alveolar PCO2 is low, bronchioles ____
Dilate (in order to ventilate alveolus) Constrict (alveolus doesn't need any O2 at the time)
Cortical controls: example?
Direct signals from the cerebral motor cortex that bypass medullary controls Example: Voluntary breath holding
Why does hematocrit increase during acclimatization?
Due to increased erythrocyte production caused by erythropoietin (EPO) from the kidneys= increase in body's hematocrit levels
Carbonic anhydrase
Enzyme that speeds up formation bicarbonate acid through CO2 to make it fast enough to work for our body
Internal respiration
Gas exchange between capillaries and tissues
Internal respiration
Gas exchange between the blood and tissues
External respiration
Gas exchange between the lungs and blood
Hypoxia & what is can be caused by?
Homeostatic imbalance where there is inadequate O2 delivery to the tissues Can be caused by: Too few RBCs Abnormal or too little HB Blocked circulation Metabolic poisons Pulmonary disease Carbon monoxide
Henry's Law
If a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid proportional to its partial pressure Meaning: The greater the partial pressure, more gaseous molecules will dissolve in the solution
Where are the two respiration centers?
In the CNS: 1. In the pons (pontine respiratory center) 2. Medulla (medullary respiratory center)- have a dorsal and ventral group
Where is molecular oxygen carried? Where do they go from here (binding)?
In the blood 1.5 % dissolved in plasma 98.5 % bound to the iron in hemoglobin 4 molecules of oxygen per hemoglobin
What causes a left shift of the hemoglobin dissociation curve?
Increase the affinity of hemoglobin for O2, and cause a decreased O2 release
Hyperventilation
Increased depth and rate of breathing that exceeds the body's need to remove CO2 Causes CO2 levels to decline (hypocapnia) May cause cerebral vasoconstriction and cerebral ischemia
Pontine respiratory center: what does it do?
Influences and modifies the activity of the VRG (ventral respiratory group) Smooth out transition between inspiration and expiration and vice versa
What causes us to cough/sneeze?
Irritation of the pulmonary irritant receptors in the larger airways of our body
How does emphysema affect surface area?
It breaks down the alveolar walls, which reduces surface area and impairs gas exchange
What happens to our minute ventilation when we exercise? Why does this happen?
It has to increase 10-20 fold Because it increases oxygen us and production of CO2
Ventral respiratory group (VRG): What does it do? What nerves play a role in its function?
It is a rhythm-generating and integrative center Sets eupnea (12-15 breathes/minute) Inspiratory neurons excite the inspiratory muscles via the phrenic and intercostal nerves Expiratory neurons inhibit the inspiratory neurons
What happens to the oxygen-hemoglobin curve if you increase the temperature?
It modifies the hemoglobin structure and decreases it's affinity for oxygen-- which enhances the unloading of O2 (shift the Oxygen- hemoglobin dissociation curve to the right)
What happens if surface area of the respiratory membrane declines?
It will impair gas exchange, because the larger the surface area, the more gas can be exchanged
How is oxygen loaded and unloaded? What does this affect?
Loading & unloading are facilitated by a change in 3-D shape of hemoglobin that affects the affinity of hemoglobin for O2
Oxygenation: what is it and what does it form?
Loading of hemoglobin with oxygen Leads to the formation of bright red oxygenated hemoglobin, or oxyhemoglobin
Dorsal respiratory group (DRG): where is it located and what does it do?
Located near the root of cranial nerve IX It integrates input from the peripheral stretch and chemoreceptors
Acclimation: what are some factors influenced?
Long-term adjustments made to cope with less atmospheric pressure Increase in the minute ventilation, and increase in hematocrit of blood (long term)
Partial pressure of PCO2 in internal respiration, what direction will it move?
PCO2 in tissues: 45 mmHg PCO2 in blood: 40 mmHg The gradient will cause the CO2 to move from the tissues into the blood
What is the saturation of PO2 in venous blood?
PO2 drops to 40 mmHg with saturation of 75%
What happens when the PO2 drops when tissues are resting or only moderately active?
PO2 drops to 40 mmHg with saturation of 75% Only 20-25% of oxygen is unloaded and the blood still contains enough to satisfy the needs of the tissues without an increased blood flow
Partial pressure of PO2 in internal respiration, what direction will it move?
PO2 in tissues: 40 mmHg PO2 in blood: 100 mmHg The gradient of 60 mmHg will lead to blood flowing out of the blood and into tissues
What is different when comparing internal and external respiration?
Partial pressures and diffusion gradients are flipped from each other
Apnea
Periods of breathing cessation that occurs when PCO2 is abnormally low
What is the partial pressure gradient for CO2 in external respiration? What is the diffusion rate like?
Pressure gradient for CO2 is much lower (5 mmHg) Venous blood PCO2: 45 mmHg Alveolar CO2: 40 mmHg Although the pressure gradient is low, it is still sufficient to cause a diffusion of CO2 to the blood to the alveolus
Oxygen-hemoglobin saturation curve
S shaped curve that shows that hemoglobin's affinity for oxygen increases as successive molecules of oxygen bind to the hemoglobin
What is the partial pressure gradient for oxygen (O2) in external respiration (totals), and what direction does the O2 flow because of this?
Pressure gradient for O2 is steep (64 mmHg) Venous blood PO2 is: 40 mmHg Alveolar PO2 is: 104 mmHG This pressure gradient causes the flow of O2 to move from the alveoli into the blood
Acute mountain sickness (AMS)
Quick travel to altitudes above 8000 feet, may produce symptoms such as: headaches, shortness of breath, nausea, and dizziness. In sever cases pulmonary edema may develop
Pulmonary irritant reflexes: where are they and what do they do?
Receptors in the bronchioles that respond to irritants They promote reflexive constriction of air passages Receptors in the larger airways mediate the cough or sneeze reflexes
What happens when CO2 levels increase and grow in the brain?
Respiratory centers increase the rate and depth of breathing
What happens when CO2 levels are decreased and levels drop in the brain?
Respiratory levels decrease the rate and depth of breathing
What also affects how the gas dissolves? What is an example?
The solubility of the gas Example: CO2 is 20 times more soluble in water than O2
Dalton's law of partial pressure
Total pressure exerted by a mixture of gases is the sum of the pressures exerted by each gas Meaning: The partial pressure of a gas is directly proportional to its percentage in the mixture
Where is carbon dioxide transported and how?
Transported in the blood via: 7-10% Dissolved in plasma 20% Bound to hemoglobin as carbaminohemoglobin 70% As bicarbonate ions in plasma
What is required for efficient gas exchange?
Ventilation and perfusion must be matched (coupled)
Edema
Watery buildup in the body's tissue or cavities
What happens when H+ levels are too high in the blood? What is this modification called?
When H+ levels are too high, pH goes down, and excess H+ is removed by combining with HCO3- Called the carbonic acid-bicarbonate buffer system
What happens when H+ levels are too high in the blood? What is this called again?
When H+ levels drop, and pH goes up, H2CO3 dissociates and releases H+ Carbonic acid-bicarbonate buffer system
Hypercapnia
When PCO2 levels rise in the blood
How is carbonic acid formed?
When carbon dioxide combines with water
What happens when cells metabolize glucose?
by metabolizing glucose, the cells use oxygen, causing the PO2 in the tissue to decrease. Oxidation of the glucose produces CO2, leading to increased PCO2 in the tissues, and increased heat. Addition of CO2 causes the formation of carbonic acid which lowers the pH