Physiology Flashcards
What is meant by internal respiration?
The internal respiration refers to the intracellular mechanisms which consumes O2 and produces CO2
What is meant by external respiration?
The term external respiration refers to the sequence of events that lead to the exchange of O2 and CO2 between the external environment and the cells of the body
What are the four steps of external respiration?
- Ventilation
- Gas exchange between alveoli and blood
- Gas transport in the blood
- Gas exchange at the tissue level
How do the lungs recoil?
By the relaxation of inspiratory muscles because of their elastic properties(elastic connective tissue). The alveolar surface tension also contributes to the recoiling of the lungs.
What is Boyle’s law?
At any constant temperature the
pressure exerted by a gas varies
inversely with the volume of the gas
aka. as the volume of a gas increases the pressure exerted by the gas decreases
What are the two forces that link the lungs to the thorax?
- The intrapleural fluid cohesiveness
- The negative intrapleural pressure
How does the intrapleural fluid cohesiveness hold the lungs and thorax together?
The water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart. Hence the pleural membranes tend to stick together.
How does the negative intrapleural pressure hold the thorax and lungs together?
the sub-atmospheric intrapleural pressure create a transmural(across the wall) pressure gradient across the lung wall and across the chest wall. So the lungs are forced to expand outwards while the chest is forced to squeeze inwards
Which 3 pressures are important in ventilation?
- Atmospheric pressure
- Intra-alveolar(intrapulmonary) pressure
- Intrapleural (intrathoracic) pressure
True/false, the atmospheric pressure is the same as the intrapleural pressure?
false, the atmospheric pressure is the same as the intra-alveolar pressure
Which muscles are involved in inspiration?
Diaphragm and external intercostal muscels
What happens to intra-alveolar pressure when the lungs expand? Why does this happen?
Intra-alveolar pressure falls, this is because air molecules become contained in a larger volume
Inspiration/Expiration is a passive/active process
Inspiration is an active process
Expiration is a passive process
What is alveolar surface tension?
- Attraction between water molecules at liquid air interface
- In the alveoli this produces a force which resists the stretching of the lungs
- If the alveoli were lined with water alone the surface tension would be too strong so the alveoli would collapse
What reduces alveolar surface tension?
Surfactant
What is pulmonary surfactant composed of ?
Pulmonary surfactant is a complex mixture of lipids and proteins secreted by type II alveoli
What does surfactant do? and why does it do this?
Surfactant lowers the surface tension of smaller alveoli more than that of large alveoli
This prevent the smaller alveoli from collapsing and emptying their air contents into the larger alveoli
How does surfactant lower surface tension inside alveoli?
by interspersing between the water molecules lining the alveoli
What is pneumothorax?
When you have air inside the pleural space
In pneumothorax, where does the air come from?
Ari comes from the lungs or from outside
Symptoms of pneumothorax
- Shortness of breath
- Chest pain
Physical signs of pneumothorax
- hyperresonant percussion note
- decreased/absent breath sounds
What are the 3 forces that help keep the alveoli open?
- Pulmonary surfactant
- The alveolar interdependence
- Transmural pressure gradient
Explain how alveolar interdependence works to keep alveoli open?
If an alveolus start to collapse the surrounding alveoli are
stretched and then recoil exerting expanding forces in the
collapsing alveolus to open it
2 forces promoting alveolar collapse
- Elasticity of stretched lung connective tissue
- Alveolar surface tension
Pulmonary ventilation
Is the volume of air breathed in and out per minute Pulmonary Ventilation (L) = tidal volume (L/breath) x Respiratory Rate (breath/min)
Alveolar ventilation
Is the volume of air exchanged between the atmosphere and alveoli per minute
Alveolar Ventilation = (tidal volume – dead space volume) x Respiratory Rate = (0.5 – 0.15) x 12 = 4.2 L/min under resting conditions.
Why is alveolar ventilation less than pulmonary ventilation?
Alveolar Ventilation is less than pulmonary ventilation because of the presence of anatomical dead space.
List non-respiratory functions of the respiratory system
- Route for water loss and heat elimination
- Enhances venous return (Cardiovascular Physiology)
- Helps maintain normal acid-base balance (Respiratory and Renal Physiology)
- Enables speech, singing, and other vocalisations
- Defends against inhaled foreign matter
- Removes, modifies, activates, or inactivates various materials passing through the pulmonary circulation
- Nose serves as the organ of smell
True/false blood flow and ventilation vary from bottom to top of lungs?
True
Blood flow/ventilation is lower/higher at the top of the lungs
Blood flow is lower
Ventilation is higher
Alveolar dead space
Ventilated alveoli which are not adequately perfused with blood are considered as alveolar dead space
The partial pressure of gas is:
The pressure that one gas in a mixture of gases would exert if it were the only gas present in the whole volume occupied by the mixture at a given temperature
Dalton’s law of partial pressures state..
The Total Pressure exerted by
a gaseous mixture =
The sum of the partial pressures of
each individual component in
the gas mixture
PAO2
PiO2
PaCO2..
are the abbreviations for?
PAO2 = Partial pressure of O2 in alveolar air PiO2 = Partial pressure of O2 in inspired air PaCO2 = Partial pressure of CO2 in arterial blood
What is the solubility of gas in membranes known as?
The solubility coefficient
True/false CO2 has a solubility coefficient that is 20 times that of O2
True, CO2 is much more soluble in membranes than O2
What does a big gradient in PAO2 and PaO2 indicate
A big gradient between PAO2 and PaO2 would indicate problems with gas exchange in the lungs or a right to left shunt in the heart
Fick’s Law of diffusion
The amount of gas that moves across a sheet of tissue in unit time is proportional to the area of the sheet but inversely proportional to its thickness
What does the respiratory system provide to facilitate effective gas exchange?
- The lungs provide large surface area and thin membranes
- The airways divide repeatedly to increase the surface area for gas exchange
- The small airways form outpockets (the alveoli). This help increase the surface area for gas exchange in the lungs
- The lungs have a very extensive pulmonary capillary network
Effect of partial pressure on gas solubility
This means that if the partial pressure in the gas phase is increased the concentration of the gas in the liquid phase would increase proportionally
Explain the differences between foetal haemoglobin and adult haemoglobin
- Foetal haemoglobin differs in structure form adult haemoglobin, it has 2 alpha subunits and 2 gamma subunits.
- HbF interacts less with 2,3- Biphosphoglycerate in red blood cells
- Hence, HbF has a higher affinity for O2 compared to adult haemoglobin (HbA)
- This would allow O2 to transfer from mother to foetus even if the PO2 is low
Oxygen is present in the blood in which two forms?
- Bound to haemoglobin (98.5%)
- Physically dissolved (1.5%)
What is the primary factor which determines the percentage saturation of haemoglobin with O2?
PO2
True/false, decreased PO2 = increase saturation of haemoglobin with oxygen
False, increased PO2 = Increase saturation of haemoglobin with oxygen
What is the O2 content of arterial blood determined by?
The O2 content of arterial blood is determined by the haemoglobin concentration [Hb] and the saturation of Hb with O2
What can oxygen delivery to tissues be impaired by?
Decreased partial pressure of inspired oxygen
Respiratory disease
Heart failure
Anaemia
What shape is the graph of oxygen binding to haemoglobin?
Sigmoidal because of the co-operativity of subunits and flattens when all 4 subunits are occupied
Where is myoglobin present in the body?
Skeletal and cardiac muscle cells
How is myoglobin different to haemoglobin?
- One haem group per myoglobin molecule
- No cooperative binding of O2
- Dissociation curve hyperbolic, not sigmoidal
- Myoglobin releases O2 at very low PO2
- Provides a short-term storage of O2 for anaerobic conditions
What does the presence of myoglobin in the blood suggest?
The presence of myoglobin in the blood indicates muscle damage
In what form is CO2 mostly carried in the blood as?
bicarbonate
What are the 3 forms that CO2 can be transported in the blood as?
- Solution
- Bicarbonate
- Carbamino compounds
How is bicarbonate formed in the blood?
CO2 and water react to form carbonic acid, catalysed by carbonic anhydrase.
Carbonic acid then dissociates into hydrogen ions and bicarbonate. This occurs in red blood cells.
Bicarbonate then moves out of cells into blood plasma and chloride ions come into the cells.
How are carbamino compounds formed?
Carbamino compounds formed by combination of CO2 with terminal amine groups in blood proteins
What do the Boher effect and the haldane effect work in synchrony to facilitate?
O2 liberation and uptake of CO2 & CO2 generated H+ at tissues
Explain the Haldane effect
Removing O2 from Hb increases
the ability of Hb to pick-up CO2 and
CO2 generated H+
In what form is CO2 mostly carried in the blood as?
bicarbonate
What are the 3 forms that CO2 can be transported in the blood as?
- Solution
- Bicarbonate
- Carbamino compounds
How is bicarbonate formed in the blood?
CO2 and water react to form carbonic acid, catalysed by carbonic anhydrase.
Carbonic acid then dissociates into hydrogen ions and bicarbonate. This occurs in red blood cells.
Bicarbonate then moves out of cells into blood plasma and chloride ions come into the cells.
How are carbamino compounds formed?
Carbamino compounds formed by combination of CO2 with terminal amine groups in blood proteins
What do the Boher effect and the haldane effect work in synchrony to facilitate?
O2 liberation and uptake of CO2 & CO2 generated H+ at tissues
Explain the Haldane effect
Removing O2 from Hb increases
the ability of Hb to pick-up CO2 and
CO2 generated H+
What happens when Hb picks up oxygen?
it weakens its ability to bind CO2 and H+, so they are released
What happens when Hb picks up oxygen?
it weakens its ability to bind CO2 and H+, so they are released
What makes the inspiratory muscles contract and relax rhythmically?
Pre-Botzinger complex
How could the expiratory muscles be called on during active expiration?
When the increased firing of dorsal neurones excite a second group of neutron complex: Ventral respiratory group neurones.
This excites internal intercostals, abdominals etc. which leads to forceful expiration.
How could the arterial PO2 and PCO2 be maintained within narrow limits?
Chemoreceptors (peripheral and central)
What is the role of the respiratory system in regulating blood H+ concentration?
Maintaining acid-base balance?
What is the breathing rhythm generated by?
the breathing rhythm is generated by a network of neurons called the Pre-Botzinger complex
Where are the pre-botzinger complex neurones located? and what kind of activity do they display?
These neurons display pacemaker activity. They are located near the upper end of the medullary respiratory centre
Examples of involuntary modifications of breathing
- Pulmonary Stretch Receptors Hering-Breuer Reflex
- Joint Receptors Reflex in Exercise
- Stimulation of Respiratory Centre by Temperature,
- Adrenaline, or Impulses from Cerebral Cortex
- Cough Reflex
The mechanism of the cough reflex (stimulated by afferent discharge)
Short intake of breath, followed by closure of the larynx, then contraction of abdominal muscles (increases intra-alveolar pressure), and finally opening of the larynx and expulsion of air at a high speed
?
The Pneumotaxic Centre is stimulated when dorsal respiratory neurones fire, stimulation results in inhibition of inspiration.
In the Apneustic Centre, impulses from these neurones excite the inspiratory area of medulla, this results in prolonged inspiration.
What is hypoxia at high altitudes caused by? and what is the acute response to this?
Decreased partial pressure of inspired oxygen (PiO2)
Acute response: hyperventilation & increased cardiac output
True/false, H+ can pass the blood-brain barrier
False, H+ cannot pass the blood-brain barrier but CO2 can and CO2 can generate H+
Hypercapnia
increase in CO2 levels in body
True/false, central chemoreceptors respond to H+ of the cerebrospinal fluid
True
True/false, CSF is more buffered than blood?
False, CSF is less buffered than blood as it contains less proteins than blood
True/false, peripheral chemoreceptors sense tension of oxygen and carbon dioxide; and H+ in the blood
True
Factors That May Increase Ventilation During Exercise
- Reflexes originating from body movement
- Adrenaline release
- Impulses from the cerebral cortex
- Increase in body temperature
- Later: accumulation of CO2 and H+ generated by active muscles
