Ch. 8 Homeostasis of Gas Concentrations and Heart Rate

Question 1

What is the formula for cardiac input

Answer 1

HR x stroke volume

Question 2

What does b.p depend on (2)

Answer 2

o cardiac output- as cardiac output increases, blood pressure increases
o diameter of blood vessels- constriction of blood vessels increases pressure and dilation decreases blood pressure

Question 3

Six steps of heart contraction

Answer 3

1. SA send impulse that spreads over both atria
2. Atrium contracts
3. Stimulus reaches AV node
4. AV node sends out own impulse> travels down fibres in septum
5. Impulse spread through ventricles
6. Ventricles contract

Question 4

What system influences heart rate

Answer 4

• Influenced by ANS

Question 5

Explain the cardiac regulating systems role in influencing heart rate

Answer 5

o Medulla Oblongata sends impulse through network of cells (that have axons in heart and blood vessel walls)= cardiac regulating centre
o Reaches para/sympathetic neurons that carry impulses to the SA and AV

Question 6

what is the difference of the two ANS nerves in heart rate

Answer 6

• Sympathetic= noradrenalin > increase heart rate and stroke volume
• Parasympathetic= acetylcholine > decrease rate and strength of contractions

Question 7

at rest and during activity, which systems are dominant

Answer 7

o At rest: parasympathetic dominant

o Active: sympathetic dominant

Question 8

What acts on cardiac centre

Answer 8

Sensory impulses from receptors in cardiovascular system

- Some receptors = chemoreceptors in aortic and carotid bodies and in medulla oblongata

Question 9

during exercise, what response is brought on and what does it do

Answer 9

• Anticipatory response (brought about by ANS)> release adrenaline>
  o Diameter of blood vessel change, h.r. + stroke volume increase

Question 10

Explain glucose, breathing and heart rate effect of long distance race

Answer 10

o mental stress= blood glucose rise
o in anticipating of increased muscle activity= h.r. + b.p. increase
- race begins=
o breathing rate + depth increase
o cardiac output increase
o blood glucose= high level
o increase blood supply to skeletal (not to internal)

Question 11

What muscles cause air to move in and out and what stimulates each

Answer 11

1. Diaphragm= stimulated by phrenic nerve

2. Intercostal muscles= stimulated by intercostal nerves

Question 12

what occurs if theres an injury to phrenic or intercostal nerves

Answer 12

• origin at spinal cord at level of neck and thorax

o If injury to this region= complete paralysis in muscles that ventilate lungs

Question 13

does oxygen have a large role in regulation of breathing

Answer 13

no requires low levels for major effect

Question 14

What two receptors detect changes in oxygen levels

Answer 14

o Peripheral chemoreceptors (= groups of cells within walls of carotid and aortic arteries) = aortic and carotid bodies
o Central chemoreceptors (in medulla oblongata)

Question 15

Explain process when decrease in oxygen levels

Answer 15

1. Large decrease in [O2] stimulates central chemoreceptors >
2. Nerve impulses transmitted to respiratory centre >
3. Stimulate transmission of messages to diaphragm + intercostal muscles
4. rate of breathing

Question 16

Explain process when increase in co2 levels

Answer 16

1. Increase in both chemicals [ ]> stimulate central and peripheral chemoreceptors
2. Nerve impulse transmitted to respiratory centre
3. Increased breathing rate

Question 17

what is the two responses of co2

Answer 17

• Longer response (takes several minutes):
  o Most sensitive chemoreceptors= medulla oblongata
• Immediate response:
  o Stimulation of aortic and carotid bodies
  o Associated with hydrogen ion concentration

Question 18

what occurs when H content increases

Answer 18

ph decreases, breathing rate increases

Question 19

what does a decrease in pH stimulate

Answer 19

o chemoreceptors in aortic and carotid > transmit impulse to respiratory centre= breathing rate

Question 20

how are humans able to control breathing rate

Answer 20

o voluntary control via connections from cerebral cortex to descending tracts in spinal chord
o voluntary control // bypass respiratory centre
♣ protective device as enables to prevent irritating gases + water from entering lungs

Question 21

why can’t we stop breathing forever

Answer 21

o build-up of CO2 in blood stimulates inspiratory centre to send impulses to inspiratory muscles

Question 22

what is hyperventilating

Answer 22

extremely rapid or deep breathing; may result in dizziness and even fainting due to the loss of carbon dioxide from the blood

Question 23

what can cause hyperventilation

Answer 23

voluntarily, or physical stress or emotional pain

Question 24

why does hyperventilation correct itself

Answer 24

o usually corrects itself as [O2] means chemoreceptors not stimulated // no urge to breathe until CO2 normal