Regulation of Gas Concentration

Where does cellular respiration occur? Why?

In the cells to provide energy for its functions.

What is the cellular respiration equation?

6O₂ + C₆H₁₂O₆ → 6CO₂ + 6H₂O + energy

What gas do cells need a constant supply of?

Oxygen

What gas do cells produce?

Carbon dioxide

What system(s) is responsible for the intake and excretion of O₂ and CO₂?

Respiratory system and circulatory system.

Primarily lungs.

Which muscles cause air to move in and out of the lungs?

• the diaphragm, a muscle that separates the thorax from the abdomen

• the intercostal muscles, the muscles between the ribs

What type of muscles are the diaphragm and intercostal muscles?

Skeletal muscles; require stimulation from nerve impulses to iniate contraction

From which nerve do impulses stimulate the diaphragm?

Phrenic nerve

From which nerve do impulses stimulate the intercostal muscles?

Intercostal nerves

Where is the respirator centre located?

Medulla oblongate (in the brain)

What are the two regions of the respiratory centre?

1. controls expiration (breathing in)

2. controls inspiration (breathing in)

Neurons between the regions coordinate breathing.

What chemicals affect breathing?

• CO₂

• H⁺ ions

• O₂

What are the two types of chemoreceptors?

• peripheral chemoreceptors: groups of cells within walls of aorta and carotid arteries sensitive to changes in concentration of O₂ , CO₂ , H⁺ ions in blood plasma

• central chemoreceptors: located in medualla oblongate, sensitive to changes in concentration of CO₂ in blood and H⁺ ions in cerebrospinal fluid

Is oxygen concentration in blood plasma a major regulator of breathing?

No

• concentration of blood oxygen has to be very low to have major stimulatory effect

• if within normal range, effect is minimal (slight)

What happens if there is a large decrease in oxugen concentration?

Stimulates chemoreceptors and nerve impulses transmitted to respirator centre.

• nerve impulses stimulate transmission of messages to diaphragm and intercostal muscles → increasing breathing rate and depth

Which gas concentration in blood plasma is the major factor in the regulation of breating rate?

Carbon dioxide

• small increase → increase in rate and depth of breathing

What happens if CO₂ in blood plasma increases?

• H⁺ ion concentraion increases

• central and peripheral chemoreceptors stimulated → increase breathing rate and depth

Which chemoreceptors are responsible for most of breathing rate and depth increases?

Central chemoreceptors in medulla oblongate - 70-80%.

Response take several mins.

What causes immediate increase in breathing rate and depth follwing increase of CO₂?

Stimulation of the aortic and carotid bodies → stimulated by associated increase in H⁺ ion concentration

What happens to pH as H⁺ ion concentration in the blood increases?

pH decreases

How does an increase in H⁺ ion concentration stimulate chemoreceptors?

increase H⁺ ion concentration → decrease in pH → stimulates chemoreceptors in the aortic and carotid bodies → transmits impulses to respirator centre → increases breathing rate and depth

How do humans volunatarily control rate and breathing depth?

connections from the cerebral cortex to descending tracts in spinal cord and therefore bypasses respiratory centre in meduall oblongata

Why do humans need to be able to hold our breath?

Swimming

Is it possible to hold our breath forever?

No. Build up of carbon dioxide in plasma stimulates inspiratory centre → sends impulses to inspitatory muscles → breathing

What is hyperventilation?

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

How does hyperventilation occur?

Volunatrily or stimulated by physical stress such as severe pain or emotion stress (i.e. anxiety)

How does hyperventilation correct itself?

reduction of CO₂ concentration → chemoreceptors not stimulated → reducing rate and depth of breahing until CO₂ normal

Why does breathing rate increase during exercise?

Contracting cells require large amounts of oxygen and produce large amounts of carbon dioxide → breathing rate and depth increases