12 - GAS EXCHANGE 2: INTERNAL RESPIRATION Flashcards
EXTERNAL RESPIRATION
Oxygen diffuses from alveoli into pulmonary capillaries.
Carbon dioxide moves in the opposite direction
INTERNAL RESPIRATION
Oxygen diffuses from the systemic capillaries into the tissues, and carbon dioxide in the opposite direction
INTERNAL ENVIRONMENT
Internal environment is the environment required for life and metabolism.
Includes temperature, pH, glucose, gas levels.
It is the blood plasma and interstitial fluid.
CARRYING GAS: BLOOD
- Gases are carried by red blood cells (RBCs)
- Haemoglobin is the protein found in RBCs responsible for gas exchange 1g Hb can carry 1.34mls O2
- Different forms of haemoglobin include:
- Fetal
- Adult A
- Adult A2
- Some forms are responsible for sickle cell anaemia
- Men often have more haemoglobin (linked to menstruation and iron levels)
HAEMAGLOBIN
- Haemoglobin consists of a tetramer (4) globin polypeptide chains: a pair of (alpha) α-like chains and a pair of (beta) β-like chains.
- Adult haemoglobin, HbA, has the structure α2β2; (Alpha2beta2)
- Haemoglobin can bind 4 O2 molecules.
- When oxygen is bound to haemoglobin it is called ‘oxyhaemoglobin’
- Saturation of Hb with oxygen (SaO2) relates to the number of oxygen molecules bound e.g. if 2 molecules of oxygen are bound to one Hbmolecule, it is 50% saturated
HAEMOGLOBIN AND PARTIAL PRESSURE
The relationship between percentage saturation of Hb with oxygen, and partial pressure of oxygen is a sigmoid curve.
• In alveoli, PO2 is about 104mmHg, which means that Hb is almost 100% saturated - It has a high AFFINITY for oxygen
• In systemic veins, the partial pressure of oxygen is about 40mmHg, and Hb is around 77% saturated - It has a low affinity for oxygen
HAEMOGLOBIN AND CARBON DIOXIDE
Blood also carries Carbon dioxide
• When blood PCO2 is high, the affinity of Hb for oxygen falls
• The curve shifts to the right, and more oxygen is released
HAEMOGLOBIN AND PH
- When there is an increase in H+ ions, blood acidity increases (pH falls)
- Blood acidity has consequences for health and can result in cardiovascular problems, cellular problems and death
- Acidity increases with diet (ketone)
- Acidity increases with CO2
GAS TRANSFER: BLOOD TO MUSCLE
- In lungs oxygen moves along the gradient into the bloodstream and is bound by haemoglobin
- In the tissues, myoglobin has a higher affinity for oxygen so oxygen moves from the blood into the tissues
- O2 is then released to the cells
HOW IS CARBON DIOXIDE CARRIED?
- Carbon dioxide is a waste product of metabolism
- Carried to the lungs to be removed
- Some Carbon dioxide is dissolved in blood plasma (8%)
- 20% binds to Hb to form carbaminohaemoglobin
- Rest (72%) reacts with water in the cytoplasm of the RBC
ACID–BASE BALANCE
- The pH of arterial blood ranges from 7.35 to 7.45. The range is maintained by:
- Buffers
- H + loss in urine by the kidney
- Breathing out CO2
Why do we need a narrow range of pH?
- pH can change structures like DNA
- pH changes can damage enzymes involved in metabolism
- pH changes the amount of oxygen carried by blood.
ACID BASE BUFFER SYSTEM
Reversible chemical reaction that can absorb or release hydrogen ions (H+) in response to changes in the system.
If hydrogen ion concentration is kept constant, pH is kept constant
What happens if pH decreases?
(hydrogen ion level rises), it combines with bicarbonate to form carbonic acid
H+ + HCO3- => H2CO3
what happens if pH increases?
(hydrogen ion level falls) then carbonic acid dissociates to release more hydrogen ion
H2CO3 => H+ + HCO3-
WHAT DOES ACID BASE HAVE TO DO WITH THE RESPIRATORY SYSTEM?
CO2 mixes with water in the blood to form carbonic acid (H2CO3).
• Increased metabolism means more carbonic acid
• More carbonic acid means more breakdown into Hydrogen and Bicarbonate
(decrease in pH)
• Decrease in pH is detected by the chemoreceptors
• Stimulation of ventilation to get rid of excess CO2
T/F: Amount of Ventilation is directly related to blood CO2 level?
True
CONTROL OF BREATHING: CHEMICAL
• Dissolved CO2 (PCO2)
• pH ie bicarbonate ions
Peripheral chemoreceptors: carotid and aortic bodies
CHEMICAL CONTROL OF BREATHING: SUMMARY
Increased H + or decreased H+ Chemoreceptors (carotid body) Respiratory control centre (medulla) Respiratory muscles Increased frequency and depth of breathing stimulus reduced
OTHER INFLUENCES ON CONTROL OF BREATHING
Voluntary control - Useful for communication e.g. speaking, but limited in extent
Other CNS areas e.g. for emotion - Ventilation can be increased or reduced due to emotion; also transient effects such as gasping, sobbing.
Initiation reflex
- SURFACE AREA: THE HERING-BREUER INFLATION REFLEX
Healthy lungs are compliant (stretchy) to allow an increase in surface area
• What stops over-inflation?
• Hering-Bruer Inflation Reflex
• Normal breathing in infants
• Only during extreme exercise in adult
When activated by lung stretch, slowly adapting stretch receptors fire with increasing frequency.
High receptor activity inhibits further inflation, and expiration begins.
Also called the inspiratory off-switch
SUMMARY OF RESPIRATORY CONTROL
- Proprioceptors in muscles sense movement (exercise)
- Irritant receptors are located throughout airways and lungs (can stimulate coughing and sneezing)
- Stretch receptors in lungs prevent over-inflation
- Voluntary control- to control speech or anxiety
- Pain and emotional stimuli
- Chemoreceptors detect changes in pH (H+)
METABOLIC AND RESPIRATORY DISORDERS
Metabolic and respiratory disorders are interlinked. This means that there is a
degree of compensation which might hide an underlying condition.
Metabolic disorders:
Result in a change in pH (H +).
This can stimulate a change in breathing that will alter CO2 levels
Respiratory disorders:
Slower process as it involves a change in kidney function.
Change in pH stimulates an increase in bicarbonate resorption and synthesis
