Physiology 6 Flashcards
What 2 factors control respiration?
NeuralHormonal
What control the rhythmicity (inspiration followed by expiration) of breathing?
Neural control
What are the 3 parts of the brainstem?
The midbrainPonsMedulla oblongata
What part of the brain is the major rhythm generator?
Medulla
What are the respiratory centres of the pons? (2)
Pneumotaxic centreApneustic centre
What are the respiratory centres of the medulla? (3)
Pre-Botzinger complexDorsal respiratory groupVentral respiratory group
What 2 parts of the brain stem have respiratory control centres in them?
Pons respiratory centresMedullary respiratory centres
What network of neurones generates the breathing rhythm?
Pre-botzinger complex
What are pacemakers?
a group of cells or a body part (as the sinoatrial node of the heart) that serves to establish and maintain a rhythmic activity e.g. the neurones of the pre-botzinger complex display pacemaker activity
What does the Pre-botzinger complex do with the rhythm it generates?What does this cause?
Excites dorsal respiratory group neurones which fire in bursts leading to contraction of inspiratory muscles = inspiration
What causes passive expiration?
When the firing from dorsal respiratory group neurones stops
Is the dorsal respiratory group neurones concerned with inspiration or expiration?
Inspiration
What causes “active” expiration during hyperventilation?
Increased firing of dorsal neurones excites the ventral respiratory group neuronesThese excite internal intercostal muscles and muscles in the abdominal wall causing forceful expiration
What are the major muscles of inspiration? (contract every inspiration; relaxation causes passive expiration)
External intercostal musclesDiaphragm
Accessory muscles of inspiration? (contract only during forceful inspiration)
ScalenusSternocleidomastoid
What ar the muscles of active expiration (contract only during active expiration)?
Internal intercostal musclesAbdominal muscles
What is the purpose of the pons respiratory centres?
To modify the rhythm generated in the medulla
What does stimulation of the pneumotaxic centre do?When is the PC stimulated?
Terminates inspirationWhen dorsal respiratory neurones fire
What is breathing like without a functioning pneumotaxic centre?
Prolonged inspiratory gasps with brief expiration called apneusis
What is the purpose of the apneustic centre?
To excite inspiratory area of medulla prolonging inspiration
What are some examples of stimuli influencing the respiratory centre? (7)
Higher brain centres e.g. cerebral cortex, limbic centreStretch receptors in the wall of bronchi and bronchiolesJuxtapulmonary (J) receptorsJoint receptorsBaroreceptorsCentral chemoreceptorsPeripheral chemoreceptors
What is an example of a reflex due to the stretch receptors in the walls of the bronchi and bronchioles?What does this protect against?
The inflation Hering-Breuer reflexGuards against hyperinflation(involuntary modification of breathing)
What stimulates juxtapulmonary (J) receptors? (3)What does this cause?
Stimulated by pulmonary capillary congestion, pulmonary oedema and PECauses rapid shallow breathing
what stimulates joint receptors?What is this important in?
Joint movement increases breathing reflexlyExercise(involuntary modification of breathing)
What does stimulation of baroreceptors cause?
Increased ventilatory rate in response to decreased blood pressure
What 4 factors cause involuntary increase in ventilation during exercise?
Reflexes originating from body movementAdrenaline releaseImpulses from the cerebral cortexIncrease in body temperatureLater accumulation of CO2 and H+ generated by active muscles
Is the cough reflex a voluntary or involuntary modification of breathing?
Involuntary
How does the Hering-breur reflex work?When is this activated?
Pulmonary stretch receptors are activated during inspiration Afferent discharge inhibits inspiration through the hearing-breur reflexAt tidal volumes»_space;1L meaning they don’t tend to switch off respiration during the normal respiratory cycleMay prevent over inflation of the lungs during hard exercise or in new born babies
What activates the cough reflex? (2)
Irritation of airways or tight airways e.g. in asthma
Where is the centre that controls coughing located?
In the medulla
What type of control system is the chemical control of respiration?
Negative feedback system
What are the controlled variables in the chemical control of respiration?What senses the values of these?
Blood gas tensions (especially CO2)Chemoreceptors
Where are the peripheral chemoreceptors located?What do these sense?
Carotid bodiesAortic bodiesTension of O2, CO2 and [H+] in the blood - mainly O2 levels
Where are the central chemoreceptors located?What do these sense?
Near the surface of the medulla in the brainstem[H+] of the cerebrospinal fluid (CSF) - CO2 levels
What separates CSF from blood?What is this impermeable to?
Blood brain barrierImpermeable to H+ and HCO3- (CO2 diffuses readily)
Is the CSF more or less buffered than blood?
Less as it contains less proteins
What is hypercapnia?
An abnormally high level of CO2 in the blood
Why can you not raise your breath for a long period of time?
The system is very sensitive to PCO2 meaning CO2 will rise and diffuse into the CSF causing the [H+] to rise leading to the stimulation of central chemoreceptors = increased respiratory rate
What happens to ventilation rate when hypoxia is extremely severe?
Neurons will be depressed meaning ventilation rate decreases
When can your peripheral chemoreceptors be stimulated?
When PO2 is less than 8.0kPa
Is changes in our respiratory rate normally based on our O2 or CO2 concentration?
Changes in our CO2 concentration (detected by our central chemoreceptors) - increase in CO2 = increase in rate and depth of breathing
What happens to the control of respiratory rate in patients with conditions such as COPD?
Over time the central chemoreceptors become insensitive to the chronically high levels of CO2. This therefore leads to the peripheral chemoreceptors controlling ventilation rate through the levels of O2
What is hypoxia?
Deficiency in the amount of O2 reaching the tissues
What is the hypoxic drive?
A type of respiratory drive in which the body uses oxygen (peripheral) chemoreceptors instead of CO2 receptors (central chemoreceptors) to regulate the respiratory cycle
When is hypoxic drive stimulated?
When arterial PO2 falls below 8.0kPa
Apart from in COPD patients with chronic CO2 retention, when else is the hypoxic drive important?
In high altitudes
What is hypoxia at high altitudes caused by?
Decreased partial pressure of inspired oxygen (PiO2)
What is the acute response to hypoxia at high altitudes?
Hyperventilation (due to the hypoxic drive) and increased cardiac output
What are the symptoms of acute mountain sickness?
Headache fatiguenauseaTachycardiadizzinesssleep disturbanceexhaustionSOBunconsciousness(all due to a lack of O2)
What are some chronic adaptions to high altitude hypoxia? (5)
RBC production (polycythaemia) - O2 carrying capacity of the blood is increased2,3 BPG produced within RBCs - O2offloaded more easily into tissuesIncreased number of capillaries - blood diffuses more easilyIncreased number of mitochondria = O2 can be used more efficientlyKidneys conserve acid - arterial pH increases
Does H+ move readily across the blood brain barrier
No - CO2 does
What is the [H+] respiratory drive?
When there is acidosis caused by the addition of non-carbonic acid H+ to the blood e.g. lactic acid or diabetic ketoacidosis, peripheral chemoreceptors cause hyperventilation increasing elimination from the body (central chemoreceptors do not do this as H+ doesn’t diffuse across the blood brain barrier - CO2 does)
