Lecture 23 Flashcards
Describe the overview of breathing?
When you are breathing normal, the diaphragm is the only muscle that works. For 2seconds on the diaphragm contracts - normal inspiration - and for 3 seconds off the diaphragm relaxes - normal expiration. However with heavy breathing you have to use more muscles.
Describe the feedback loop?
You end a message to your breathing muscles, bronchi and secretory glands. You then motor your breathing and feed it back through receptors to your brainstem to decide what to do with your next breath. Every breath is modulated through this cycle.
What is the aim of control of breathing?
To keep your blood gases normal and pH normal. To meet the oxygen requirement of what is going on (exercising or sick etc). Oxygen in and CO2 out. Minimise work of breathing by keeping gas exchange extremely efficient.
What is Ondine’s Curse?
If falls asleep stop breathing. The breathing muscles are fine. Normal blood gases and so feedback to the centre is normal. there is a single point mutation in the Phox2b gene in the RTN. Responding to rise in carbon dioxide - virtually no response to carbon dioxide. When people are awake (with this curse) they are stimulating their breathing 100 different ways. However when you fall asleep you loos most things that are stimulating the oscillator ampulator. Falls asleep and CO2 drive is low, and CO2 does not stimulate her to breathe again. Can get hypoxic, and die. Rare - 1 in a million.
Describe rhyme generation?
Rhythm generation ahs to be able to cope with anything in your life - exercise etc. Amazingly complex and diverse system.
Describe Pons and medulla in regards to breathing?
In your medulla and pons is where the control of breathing happens. The stimulus to breathe is preBotC. NTS feeds in for breathing.
What is the current view of rhythmogenesis?
There has to be an inspiratory “off” switch to allow expiration and ability to switch an active expiration. It is an oscillator - inputs modulate output triggering inspiration. Has to do this to make a balanced system. There is a neuromodulator (e.d. adrenergic) input to the rhythm generator. The generator also has sensory modulators (e.g. lung volumes).
What is the current view of patternogenesis?
The pattern consists of:
- Frequency.
- Depth (tidal volume).
- Inspiratory/ expiratory timing (I/E ratio). The aim is to minimise the work of breathing.
Where do you sense hypoxia?
Sense hypoxia in chemoreceptors (carotid bodies).
Describe peripheral chemoreceptors?
Aortic bodies are weak chemoreceptors. Found in the aortic arch. There for controlling cardiovascular responses.
What are the mains sensors for hypoxia?
Carotid bodies. Counts for most of the hypoxic drive. Feeds via the 9th pharyngeal nerve to brainstem. Detects arterial pressure of oxygen in the plasma. Low [O2], high [CO2] and hight [H+] (low pH) lead to an increase in ventilation. Responds very rapidly and slowly through different transmitters. Hypoxic drive varies.
What does the carotid body sense?
Senses partial arterial pressure of oxygen not the content. This is due to very high blood flow and response hyperbolic (Vt»f). Powerful partial arterial pressure of carbon dioxide sensor if not suppressed by normal partial arterial oxygen threshold.
What is the carotid body prone to?
Surgical trauma (carotid endarterectomy). Only need one carotid body for adequate control of ventilation.
Describe regulation of ventilation in chemoreceptors?
When carbon dioxide pressure increases, then so does [H+]. Because hydrogen ions cannot get through into the brain as the blood-brain barrier stops it and lets CO2 through. Carbon dioxide then converts to H+ in the cerebrospinal fluid. The hydrogen ion then stimulates the central chemoreceptor to stimulate the respiratory control centre, which will increase the ventilation rate.
Describe the ventilatory response to CO2?
PCO2 responsiveness is variable between humans, but every human has it. As you increase the partial pressure of carbon dioxide, you increase the ventilation rate.
