chapter 42 guyton

Question 1

what is the respiratory centre composed of

Answer 1

• several groups of neurons located bilaterally in medulla oblongata and pons of the brain stem

Question 2

dorsal respiratory group location and function

Answer 2

• dorsal portion of medulla
• inspiration

Question 3

ventral resp grp location and function

Answer 3

• ventrolateral part of the medulla
• expiration

Question 4

pneumotaxic centre location and function

Answer 4

• dorsally in superior portion of the pons
• control of rate and depth of breathing

Question 5

where are most neurons of dorsal resp grp found

Answer 5

nucleus of tractus solitarius NTS

Question 6

role of NTS

Answer 6

• sensory termination of vagal and glossopharyngeal nerves, transmits sensory signals into the respiratory centre from:
  1. peripheral chemoreceptors
  2. baroreceptors
  3. receptors in the liver, pancreas and multiple parts of the git
  4. several types of receptors in the lungs

Question 7

role of dorsal resp grp in rhythm

Answer 7

• repetitive bursts of inspiratory neuronal action potentials; one neurone excites a second set which inhibits the first.
• this then repeats

Question 8

explain RAMP signal

Answer 8

• nervous signal transmitted to diaphragm is not instantaneous;
• rather increases steadily in ramp manner for 2 seconds
• ceases abruptly, turns off excitation for the next 3 seconds
• allows elastic recoil of lungs and chest wall to cause expiration
• inspiratory signal repeats again for another cycle

Question 9

advantage of ramp signalling

Answer 9

• causes steady increase in lung volume instead of inspiratory gasps

Question 10

what 2 qualities of the ramp signal are controlled

Answer 10

• control of the rate of increase of the ramp signal; heavy resp ramp increases rapidly
• control of limiting point at which ramp suddenly ceases ; ceases earlier = shorter inspiration=shorter exp= increased frequency

Question 11

which nucleus is pneumotaxic centre located in

Answer 11

nucleus parabrachialis of upper pons

Question 12

what does a strong pneumotaxic signal cause

Answer 12

• limits inspiration, short as 0.5s
• has secondary effect of increasing resp rate as it also shortens expiration

Question 13

weak pneumotaxic signal causes what?

Answer 13

• allows inspiration to continue for 5/more seconds
• secondary effect of reducing rate of resp

Question 14

which nucleus is ventral grp located in

Answer 14

• nucleus ambiguus rostrally
• nucleus retroambiguus caudally

Question 15

how does ventral resp grp differ to dorsal

Answer 15

1. totally inactive during normal quiet breathing
2. dont ppt in rhythm
3. involved in inspiration and expiration. especially imp in powerful expiratory signals to diaphragm during heavy expiration.
   - therefore functions as overdrive mechanism when increased pulmonary ventilation is req eg during exercise

Question 16

explain the hering-breuer inflation reflex

Answer 16

• stretch receptors in muscular portion of bronchi and bronchioles transmit signals through vagi into dorsal resp grp when overstretched
• function in same way as pneumotaxic centre; switches off the inspiratory ramp, stops further inspiration
• inc rate of resp
• not activated until tidal volumes is 3x normal, so more of a protective mechanism to prevent excess lung inflation

Question 17

what is the primary stimulus for the chemosensitive area

Answer 17

H+ concentration

Question 18

why does co2 have more effect on chemosensitive area than H+

Answer 18

• H+ cannot easily cross BBB
• co2 passes very easily through BBB
• reacts with water to form carbonic acid
• dissociates into HCO3- and H+
• H+ then have potent direct stimulatory effect on chemosensitive area

Question 19

explain attenuation of stimulatory effect of co2

Answer 19

• co2 effect gradually declines after 1 or 2 days
  1. renal adjustment; increasing HCO3- in cerebrospinal fluid which binds with h+
  2. HCO3- slowly diffuses across BBB and binds with H+
• therefore CO2 has potent acute effect but weak chronic effect

Question 20

where are carotid bodies located

Answer 20

bilaterally in the bifurcations of the common carotid arteries

Question 21

afferent nerve fibres of carotid bodies

Answer 21

• pass through herings nerves to glossopharyngeal nerves and to dorsal respiratory grp

Question 22

aortic bodies location

Answer 22

arch of aorta

Question 23

afferent nerve fibres of aorta

Answer 23

pass through vagi ti dorsal respiratory grp

Question 24

arterial supply of carotid and aortic bodies

Answer 24

• directly from adjacent arterial trunk, therefore exposed at all times to arterial blood

Question 25

mechanism of stimulation of peripheral chemoreceptors

Answer 25

• glomus cells have 02-sensitive K+ channels
• inactivation of channels = depolarise
• opens voltage gated ca2+ channels
• inc in intracellular ca2+ ions
• stimulate release of neurotransmitter
• activates afferent neurons - send signals to CNS and stimulate respiration

Question 26

what neurotransmitter is involved in peripheral chemoreceptors

Answer 26

ATP

Question 27

what levels stimulate peripheral chemoreceptors

Answer 27

• o2 mainly
• co2 and h+ – not as strong as central but more RAPID

Question 28

acute hypoxia vs chronic hypoxia responses

Answer 28

• acute hypoxia: peripheral chemoreceptors increase ventilation, but central still sensitive to pco2 and ph
• chronic hypoxia: central chemoreceptors lose sensitivity, peripheral increase ventilation greatly to compensate

Question 29

regulation of respiration during exercise

Answer 29

• po2, pco2 and ph levels remain almost exactly same
• when brain transmits impulses to exercising muscles, also transmits collateral signals to brain stem to excite respiratory centre
• this allows for almost adequate o2 levels
• chemical factors make the final adjustments

Question 30

what are J lung receptors

Answer 30

• sensory nerve endings in alveolar walls in juxtaposition to pulmonary capillaries
• stimulated when capillaries become engorged w/ blood or due to pulmonary oedema
• excitation may give feeling of dyspnea

Question 31

effects of brain oedema on respiratory centre

Answer 31

• depressed or inactivated by brain oedema resulting from concussion.
• swelling of brain tissues compress cerebral arteries against cranial vault, blocking blood supply

Question 32

how are effects of brain oedema relieved

Answer 32

• IV injection of hypertonic solution, eg highly concentrated mannitol solution, which osmotically remove some fluid of brain, relieving intracranial pressure and re establishing respiration

Question 33

effects of anaesthetics and narcotics overdosage on respiration

Answer 33

• depresses respiratory centre

Question 34

cheyne stokes breathing

Answer 34

• slow waxing and waning respiration occurring every 40-60 seconds
• hyperventilation, then hypoventilation then apnea
• cycle repeats

Question 35

causes of cheyne-stokes breathing

Answer 35

• severe cardiac failure: causes slow blood flow, delays transport of gases from lungs to brain
• damage to respiratory centres causing increased negative feedback gain; brain damage switches off respiratory centre for a few seconds and low co2 levels switch it back on with force. often prelude to death from brain malfunction

Question 36

apnea definition

Answer 36

absence of spontaneous breathing

Question 37

sleep apnoea

Answer 37

• frequency and duration of apneas greatly increased during sleep, lasting 10s or longer and occurring between 300-500 times a night

Question 38

obstructive sleep apnoea cause

Answer 38

• blockage of airway; muscles of pharynx relax
• narrow pharynx = complete blockage
• elder obese people
• large tongue
• large tonsils
• nasal obstruction

Question 38

treatment for obstructive sleep apnoea

Answer 38

• surgery to:
• remove excess fat tissue from throat
• remove tonsils
• create opening in trachea (tracheotomy)
• nasal ventilation with CPAP

Question 39

central sleep apnoea causes

Answer 39

• neural drive in respiratory centre is transiently abolished
• caused by damage to the respiratory centre or insensitivity. treated with continuous positive airway pressure

Question 40

what is fvc + how to obtain

Answer 40

forced expiratory vital capacity
- pt inspires maximally to TLC then exhales rapidly + w/ max expiratory effort
- represented by total distance of downslope of lung volume