Neural + Chemical control of breathing

Question 1

In the control of ventilation what is
* the respiratory control centers
*effectors
* sensors
involved? name them

Answer 1

respiratory control centers: pons, medulla (both in brainstem)
effectors: respiratory muscles, diaphragm
sensors: peripheral chemoreceptors, central chemoreceptors, pulmonary mechanoreceptors

Question 2

what is the brainstem made up of

Answer 2

Brainstem is composed of 3 sections in descending order: the midbrain, pons, and medulla oblongata. It is responsible for many vital functions of life, such as breathing, consciousness, blood pressure, heart rate + sleep

Question 3

What respiratory group is located in the pons and what is it made up of

Answer 3

Pontine respiratory group (PRG) in the pons made up of
* pneumotaxic center
* apneustic center

Question 4

What respiratory groups are located in the medulla and what respiratory muscles do they control

Answer 4

• ventral respiratory group (accessory respiratory muscles, internal intercostal muscle)
• dorsal respiratory group is located in the nucleus tractus solitarius (aka solitary tract nucleus) (external intercostal muscle, diaphragm)

Question 5

Basic rhythm set by central pattern generator in ___ (rostral region) pre-Bötzinger complex: sends pacemaker signals to ____

Answer 5

Basic rhythm set by central pattern generator in VRG (rostral region which means its closer to the nose)aka pre-Bötzinger complex: sends pacemaker signals to DRG

Question 6

DRG premotor neurons project to groups of spinal motor neurons, including ________ and _________

Answer 6

DRG premotor neurons project to groups of spinal motor neurons, including phrenic nerve (diaphragm) and intercostal nerves (external intercostals).

	* Activating these neurons causes inspiration
	
	* DRG receives information from various sensors via cranial nerves (CNs) X and IX, including chemoreceptors, lung and chest wall mechanoreceptors

• DRG also receives sensory information from higher brain centres

Question 7

Pontine Respiratory Centre does what?

Answer 7

Pontine Respiratory Centre (pneumotaxic and apneustic centres)

Limits lung expansion when we breathe

Decreasing transition from inspiration to expiration (increasing breathing rate) - shorter inspiratory phase leads to increased breathing rate

Question 8

which nerve innervates carotid sinus/ carotid bodies

Answer 8

cranial nerve 9, glossopharangeal nerve

Question 9

What nerve innervates the aortic arch baroreceptors + chemoreceptors

Answer 9

cranial nerve X (10) VAGUS NERVE
innervates baroreceptors + peripheral chemoreceptors in aortic arch

Question 10

Peripheral chemoreceptors—sense __,___ and ___ (we have these receptors in aortic arch)

Answer 10

Peripheral chemoreceptors—sense PO2, PCO2 and pH (we have these receptors in aortic arch)

Question 11

Central chemoreceptors sense ____ (primary stimulus) and ____

Answer 11

Central chemoreceptors sense pCO2 (primary stimulus) and pH

Question 12

cells within carotid body, that are found within peripheral chemoreceptors + what do these cells sense?

Answer 12

type 1 glomus cells (peripheral chemoreceptors) which sense low levels of partial pressure of o2 (mainly) and co2/pH

Question 13

what is the medical term for low partial pressure of o2 in arterial blood

Answer 13

hypoxaemia

Question 14

what is hypoxia

Answer 14

tissues having inadequate oxygen/ low levels of o2

Question 15

how do glomus cells sense hypoxaemia?

Answer 15

when theres hypoxaemia; glomus cell depolarises (potassium channels close), voltage gated calcium channels open, Ach released, triggering an action potential through afferent sensory nerve in glossopharyngeal nerve

n.b. Carotid body also supplied by parasympathetic + sympathetic efferent nerve fibres in glossopharyngeal and vagus nerves which control sensitivity to hypoxaemia as they stimulate the respiratory centres in medulla (DRG + VTG) these centres will respond by sending AP resulting in constricting/ dilating the capillaries in carotid body and thus regulating the partial pressure of oxygen in tissue aka it signal to body to increase/ decrease ventilation

Question 16

nerve impulse firing rate from carotid body is particularly sensitive to changes in arterial ___ in the range 8-4 kPa (usually rate is in kPa, but americans put in mmHg n.b. 100mmHg= 13.3kPa) a range in which haemoglobin saturation with _____ decreases rapidly

Answer 16

impulse rate is particularly sensitive to changes in arterial P o2 in the range of 8-4kPa, a range in which haemoglobin saturation with oxygen decreases rapidly

Question 17

with lower levels of oxygen curve is _____ (y axis ventilation per min; x axis pCo2 in alveoli) i.e. the sensitivity to Co2 is ______ in hypoxaemia

Answer 17

with lower levels of oxygen curve is steeper (y axis ventilation per min; x axis pCo2 in alveoli) i.e. the sensitivity to Co2 is INCREASED in hypoxaemia

Question 18

what is hypercapnia

Answer 18

Hypercapnia (aka hypercarbia) is when you have high levels of carbon dioxide in your blood.

Question 19

Main chemical drive to ventilation in normoxia is hypercapnia. Explain this in lay terms.

Answer 19

main driving force for normal o2 levels/conditions (aka normoxia) is an increase in co2 (hypercapnia)

Question 20

If peripheral chemoreceptors sense low PO2 and/or high PCO2 they will feed back to medulla respiratory centres to increase minute ventilation – this leads to increase in PO2 and decrease in PCO2

Peripheral chemoreceptors also increase firing in acidosis causing increased ventilation - how does increasing minute ventilation compensate for acidosis (low pH – high protons)?

Answer 20

Peripheral chemoreceptors (e.g. carotid and aortic bodies) detectchanges in the partial pressures of oxygen and carbon dioxide + pH of the blood.

In acidosis= low blood pH due to high levels of protons (H+ ions). chemoreceptors respond by increasing their rate of firing. This sends signals to the respiratory center in the brainstem, which then stimulates the respiratory muscles to increase the rate/depth of breathing (aka increased minute ventilation).

When you breathe faster and deeper:

• u get rid of more co2 every time you exhale. Since co2 can make your blood more acidic, breathing it out helps make your blood less acidic.
• More air moving in/out of lungs means better gas exchange, so your lungs can also take in more oxygen.
• By breathing out more carbon dioxide, your blood becomes less acidic, which is how your body balances out the high acidity from acidosis.

Question 21

what is acidosis

Answer 21

acidosis (a condition characterized by a low blood pH due to high levels of protons (H+ ions)

Question 22

CO2 strongly influences blood pH – based on WHICH reaction (write equation for it)

Answer 22

CO2 + H20 <-> H2C03 <-> HCO3- + H+

n.b. this is a reversible reaction; the rate of reaction depends on amounts of reactants + products (aka law of mass action)

Question 23

Blood pH is normally maintained between 7.35 and 7.45 via buffers – buffers required to adjust for changes from metabolism and nutrition.
1) why is acidosis (less than 7.45) dangerous
2) why is alkilosis (blood to alkaline aka more than 7.45) dangerous

Answer 23

• Acidosis: proteins denature
• Alkalosis disrupts function all excitable cells by decreasing levels free ionic calcium (calcium essential for APs in body)

Question 24

what happens to co2 levels in blood when u
1) hypoventilate
2) hyperventilate

Answer 24

1) hypoventilate (decreased ventilation) = co2 levels go up (H+ go up/ holding breath/ can lead to respiratory acidosis)
2) hyperventilate (increased ventilation) = co2 levels go down (H+ goes down/ breathing more/ can lead to respiratory alkalosis)

(fun fact) luckily if u hyperventilate from anxiety too much u will just faint body will not allow that

Question 25

to maintain pH at physiological range (7.35-7.45) what ratio shld u have of
HCO3-: pCO2

Answer 25

20 HCO3-: 1 pCO2
20:1

Question 26

_______ don’t normally diffuse, ______ diffuses freely through the Blood Brain Barrier into CSF (Cerebrospinal fluid). This reacts with water to form carbonic acid. The carbonic acid is converted into protons + bicarbonate by the enzyme ______ ______

Answer 26

charged/ big molecules e.g. H+, HCO3- don’t normally diffuse, however, co2 diffuses freely through blood brain barrier into CSF (Cerebrospinal fluid). This reacts with water to form carbonic acid. The carbonic acid is converted into protons + bicarbonate by the enzyme carbonic anhydrase.

Question 27

if co2 levels fall, the central chemoreceptors send signals to _____ ventilation

Answer 27

if co2 levels fall, the central chemoreceptors send signals to DECREASE ventilation

Question 28

Patients with COPD. Meaning co2 levels chronically high/ hypercapnia. How does there brain deal with their blood pH?

Answer 28

So if co2 levels chronically high kidney + CNS compensate. Specialised tissue within brain ventricles allows water + small ions to pass in + out in regulated manner; tissue is called CHOROID PLEXUS

Question 29

J receptors are a chemoreceptor that’s stimulated when we have a condition causing hypoxia, name some of these conditions

Answer 29

pulmonary edema, pulmonary embolism, pneumonia, barotrauma (all pathophysiological processes that decrease oxygenation)

Question 30

where are irritant receptors found and what do they do

Answer 30

mechanoreceptors found in lining of trachea + large bronchi
detect objects in airways too large to be carried away by mucus; they activate cough reflexes