homeostatic regulation of blood carbon dioxide conc

Question 1

what are the stimuli for breathing?

Answer 1

1. pH of blood
2. carbon dioxide concentration of blood
3. hydrogen ions concentration
4. signals from higher brain centres

Question 2

what is the control of breathing?

Answer 2

1. gas exchange is vital the survival of multicellular organisms
2. O2 is vital for aerobic respiration, CO2 is a by-product of cellular respiration. it is toxic if it builds up in cells.
3. the respiratory system is responsible for removing CO2 from the blood and replacing it with O2.
4. the ANS is responsible for detecting and responding to changes in O2 and CO2 levels in the blood and telling the respiratory system on how to respond.

Question 3

what are the receptors in blood vessels and brain?

Answer 3

1. the respiratory centre in medulla oblongata detects carbon dioxide conc in the blood
2. chemoreceptors detect the carbon dioxide conc. in the blood and cerebrospinal fluid (CSF).
3. chemoreceptors in the carotid arteries and aorta detect blood CO2 and pH.

Question 4

how is breathing rate regulated?

Answer 4

stimulus: high concentration of CO2 in the blood
receptor: chemoreceptors in the artery and respiratory centre in the medulla oblongata
there will be an increase in nerve impulses to chest cavity
effector: intercostal and diaphragm muscles
response: increased breathing rate and depth results in lower CO2 conc in the blood
there will be negative feedback

Question 5

how does a high CO2 conc. decrease the pH of blood and CSF?

Answer 5

CO2 breaks down into water, forming carbonic acid. acids have low pH

Question 6

why is high CO2/low pH harmful for cells?

Answer 6

it drops the pH below the optimal level. enzymes outside their optimal pH will denature and become non-functional. w/o functioning enzymes, the cells cannot carry out metabolic reactions and eventually die.

Question 7

why can O2 and CO2 move in and out of the capillary by simple diffusion?

Answer 7

both O2 and CO2 are very small, nonpolar molecules, they are small enough to diffuse directly through the phospholipid bilayer with simple diffusion, down their concentration gradients

Question 8

what are the advantages of a) a network of capillaries surrounding each alveolus and b) the one-cell thick wall of alveoli and capillaries

Answer 8

a) reduces the distance of gases like co2 and o2 needed to travel, thus speeding up gas exchange
b) the thinner the wall of both the alveoli and capillary, the shorter the distance the gases need to diffuse. this increases the speed of gas exchange between the blood and lungs

Question 9

what are the other factors that affect breathing?

Answer 9

1) O2 conc.
peripheral chemoreceptors in the carotid arteries and aorta detect o2 conc in blood. if the conc falls below the threshold, they signal the respiratory centres. the response is to increase the breathing rate and depth until o2 blood conc returns to normal
2) mechanoreceptors
mechanoreceptors in the lungs, diaphragm and intercostal muscles tell the brain how much these organs have stretched. as lungs stretch during inspiration, they signal the respiratory centres. the response is to inhibit further inspiration and to trigger expiration. this feedback prevents damage to the lungs caused by over-inflation
3) cerebral cortex
nerve cells in the hypothalamus and cerebral cortex also influence the activity of resp. centres. during pain or strong emotions, the hypothalamus tells the respi. centres to increase the BR. cerebral cortex deliberatly tells the diaphragm contractions to speed up, slow down or stop. chemical stimuli like pH, o2, co2 conc override any conscious control
4) chemical irritants
nerve cells in airways sense the presence of unwanted substances in the airways like pollen, dust or dangerous gases or cigarette smoke. these cells signal the respiratory centres to contract the respi. muscles strongly, causing you to sneeze or cough which removes unwanted substances

Question 10

what is intrinsic and extrinsic controls of breathing?

Answer 10

intrinsic
1. smooth muscle of bronchioles are sensitive to changes in co2 conc.
2. increase in co2 causes the muscle in the bronciole to relax
3. this increases the diameter of bronchioles and allows more co2 to be expired
4. decrease in co2 has the opposite effect
extrinsic
1. respiratory centre in brain, receptors are in the brain stem
2. receives input from chemoreceptors and stretch receptors throughout the body.