*E1 Human Physiology - Regulation of gas content in blood

Question 1

Importance of regulating gas content in blood

Answer 1

1. Constant oxygen supply
   - Provide oxygen to body cells to carry out aerobic respiration to release energy to support their metabolic activities
2. Removal of carbon dioxide at a rate that prevents accumulation of carbon dioxide in the body
   - Aerobic respiration of body cells produces carbon dioxide. When the rate of carbon dioxide formation in body is higher than the rate of carbon dioxide removal from body, there will be an accumulation of carbon dioxide in blood, decreases the pH of the blood

Question 2

Effect of carbon dioxide concentration in blood on the rate and depth of breathing

Answer 2

CO2 concentration increases:
1. When the carbon dioxide concentration in the blood increases, the high concentration of carbon dioxide is detected by chemoreceptors at carotid and aortic bodies
2. This stimulates the respiratory centre in the medulla to send out more nerve impulses to the intercostal muscles and diaphragm muscles
3. The intercostal muscles and diaphragm muscles are stimulated to contract faster and more forcefully
4. The rate and depth of breathing increases to remove more carbon dioxide out of the lungs
5. This helps lower the carbon dioxide concentration in blood back to normal

Question 3

Effect of oxygen concentration in blood on the rate and depth of breathing

Answer 3

O2 concentration decreases:
1. When the oxygen concentration in the blood decreases, the low concentration of oxygen is detected by chemoreceptors at carotid and aortic bodies
2. This stimulates the respiratory centre in the medulla to send out more nerve impulses to the intercostal muscles and diaphragm muscles
3. The intercostal muscles and diaphragm muscles are stimulated to contract faster and more forcefully
4. The rate and depth of breathing increase to breathe in more oxygen into the body
5. This helps increase oxygen concentration in blood back to normal

Question 4

How ventricular contraction is brought about

Answer 4

1. Sinoatrial node produces electrical impulses to initiate heartbeat
2. Impulses spread over the two atrial wall to cause them to contract at the same time
3. The impulses pass to the atrioventricular node
4. This relays signal down the septum to ventricular walls, initiating contraction of both ventricles

Question 5

Cardiac output

Answer 5

Heart rate: number of heartbeats per minute

Stroke volume: volume of blood pumped out of the ventricle in one heartbeat

Cardiac output: amount of blood pumped out of each ventricle per minute

Cardiac output = stroke volume x heart rate

Question 6

Nervous control of cardiac output

Answer 6

CO2 concentration increases:
- CO2 concentration increases
- Chemoreceptors in aortic and carotid bodies are stimulated
- Cardiovascular centre of medulla
- More nerve impulses through the sympathetic nerve to SA node
- Cardiac muscles are stimulated to contract faster and more forcefully
- Increase heart rate and stroke volume, hence cardiac output
- Restore CO2 concentration in blood

CO2 concentration decreases:
- CO2 concentration decreases
- Chemoreceptors in aortic and carotid bodies are stimulated
- Cardiovascular centre of medulla
- More nerve impulses through the parasympathetic nerve to SA node
- Cardiac muscles are stimulated to contract slower and less forcefully
- Decrease heart rate and stroke volume, hence cardiac output
- Restore CO2 concentration in blood

Question 7

Mechanisms involved during exercise

Answer 7

• During exercise, [stimulus] is detected by chemoreceptors. Cardiovascular centre of medulla oblongata is stimulated to send out more nerve impulses to the SA node through the sympathetic nerve. This stimulates the SA node to increase its activity, generating more electrical impulses that spread through the cardiac muscles. This causes the cardiac muscles to contract faster and more forcefully, increasing heart rate and stroke volume, hence increasing cardiac output for rapid supply of more blood carrying oxygen and nutrients to skeletal muscles to support vigorous contraction

An increase in cardiac output provide more blood carrying more nutrients and oxygen to skeletal muscles for aerobic respiration to produce more energy for more vigorous muscle contraction and to speed up removal of carbon dioxide from the body and lactic acid from the muscles to prevent their accumulation.

Question 8

Mechanisms involved at rest

Answer 8

• At rest, [stimulus] is detected by chemoreceptors. Cardiovascular centre of medulla oblongata is stimulate to send out more nerve impulses to the SA node through the parasympathetic nerve. This inhibits the SA node and causes the cardiac muscles to contract slower and less forcefully. Heart rate and stroke volume decreases hence cardiac output decreases.
• There is a decreased sympathetic output from the cardiovascular centre of medulla oblongata to the SA node and decreased sympathetic output from the cardiovascular centre of medulla oblongata to adrenal gland leading to decreased adrenaline secretion. Decreased sympathetic output and adrenaline secretion reduce the stimulatory effect on SA node activity.

Question 9

Hormonal control of cardiac output

Answer 9

• During exercise, cardiovascular centre of medulla oblongata is stimulated to send more nerve impulses to the adrenal gland through the sympathetic nerve.
• The adrenal gland is stimulated to release more adrenaline, which stimulates the cardiac muscles to contract faster and more forcefully, increasing heart rate and stroke volume, hence increasing cardiac output.

Question 10

Effect of blood pressure of cardiac output

Answer 10

Decrease in blood pressure:
- Decrease in blood pressure
- Detected by stretch receptors in carotid arteries and aorta
- Cardiovascular centre of medulla
- More nerve impulses through the sympathetic nerve to SA node
- Cardiac muscles are stimulated to contract faster and more forcefully
- Increase heart rate and stroke volume, hence cardiac output
- Restore CO2 concentration in blood

Blood pressure increases:
- Blood pressure increases
- Detected by stretch receptors in carotid arteries and aorta
- Cardiovascular centre of medulla
- More nerve impulses through the parasympathetic nerve to SA node
- Cardiac muscles are stimulated to contract slower and less forcefully
- Decrease heart rate and stroke volume, hence cardiac output
- Restore CO2 concentration in blood

Question 11

Effect of exercise on rate and depth of breathing

Answer 11

• There is a great demand of energy of skeletal muscles during vigorous exercise
• More sympathetic nerve impulses will be sent to intercostal muscles and diaphragm muscles for faster and stronger contractions
• This increases the rate and depth of breathing for rapid gas exchange and loading of oxygen to blood

Question 12

Anaerobic respiration in muscles during exercise

Answer 12

• During vigorous exercises, the oxygen delivered to the muscles is insufficient to support anaerobic respiration fast enough to produce enough energy to meet all the energy needed
• Skeletal muscles carry out anaerobic respiration to provide extra amount of energy within a short period of time to support more vigorous muscular contraction
• Lactic acids formed accumulates and causes muscle fatigue

Question 13

Repay of oxygen debt

Answer 13

• After exercise, the rate of depth of breathing is still higher than normal
• Extra oxygen has to be taken in to break down the lactic acid
• This helps restore the blood pH to normal

Question 14

Why is slow jogging better than sitting down after vigorous exercises?

Answer 14

• Higher breath rate / heartbeat
• More O2
• Helps break down lactic acid

Question 15

Effect of exercise on cardiac output

Answer 15

• Increase nervous output from cardiovascular centre of medulla to SA node
• Increase secretion of adrenaline from adrenal glands
• Increase cardiac output

Question 16

Effects of exercise on distribution of blood to different organs

Answer 16

Skeletal muscles
- More blood and hence more oxygen and nutrient supply to release more energy in aerobic respiration to support more vigorous muscular contraction

Heart muscles
- More oxygen and nutrient supply to heart muscles allows them to release more energy in aerobic respiration to support them to beat faster and more forcefully

Skin
- Faster blood flow to the skin facilitates heat loss by conduction, convection and radiation

Small intestine / Kidney
- Less blood is supplied to the small intestine and kidney so that more blood can be delivered to the organs that need more blood and oxygen and nutrient supply during exercise
- Digestion and absorption of food and urine production are reduced during exercise

Brain
- Brain will be damaged when there is a shortage of blood supply since the blood is sensitive to oxygen and glucose shortage, and brain cells depends on glucose for respiration, blood supply to brain remains unchanged

Question 17

Trained athlete vs normal person

Answer 17

Trained athlete:
- Lower resting heart rate
- Less increase in heart rate during exercise
- Lower blood lactate concentration during exercise

Question 18

Cardiac cycle + Pressure changes in the heart

Answer 18

Atrial systole
- Both atria contract
- Blood is pumped into the ventricles through the bicuspid and tricuspid valves
- Semilunar valves are closed
- More blood enter the ventricles, ventricular pressure increases

Ventricular systole
- Atria relax, ventricles contract
- Bicuspid and tricuspid valves closed to prevent backflow of blood into the atria
-When left ventricular pressure becomes higher than aortic pressure, bicuspid valve is closed
- Pressure in left atrium increases due to bulging of closed bicuspid valve into left atrium
- When the left ventricular pressure becomes higher than the aortic pressure, blood flows from the left ventricle to the aorta and the semilunar valve is forced to open
- The ventricles continue to contract
- Semilunar valves are forced to open and blood is pumped into the aorta and pulmonary artery

Diastole
- Both atria and ventricles relax
- Semilunar valves are closed to prevent the backflow of blood into the ventricles
- Blood from the vena caves and the pulmonary veins flows into the atria
- Blood from the pulmonary vein enters the left atrium, atrial pressure increases
- When the aortic pressure is higher than pressure in left atrium, semilunar valve is closed
- Pressure in aorta rises due to recoil of aorta when semilunar valve is closed
- The bicuspid and tricuspid valves are opened and blood starts to flow into the ventricles
- When atrial pressure is higher than the ventricular pressure, bicuspid and tricuspid valves opens
- The left ventricular pressure becomes lower than the left atrial pressure, blood flows from the left atrium to the left ventricle