Homeostasis of blood sugar and gas concentrations

Question 1

What is the equation for cellular respiration?

Answer 1

Glucose + oxygen = carbon dioxide + water + energy

Question 2

What is glucose?

Answer 2

A simple sugar

C6H12O6

Question 3

What is glycogen?

Answer 3

A molecule made of long chains of glucose molecules

Question 4

The livers blood supply

Answer 4

• From the hepatic portal vein
• Brings blood directly from the stomach, spleen, pancreas and small and large intestines
• Absorbs lots of nutrients from digested food

Question 5

Things that happen to glucose (in the liver)

Answer 5

• Glucose may be removed from the blood stream by the liver to provide energy for liver functioning
• It may be removed by the liver and/or muscles and converted to glycogen for storage
• It may continue to circulate in the blood, available for body cells to absorb and use as a source of energy
• Glucose in excess of that required to maintain normal blood sugars and tissue glycogen levels is converted to fat for storage

Question 6

What is glycogenesis?

Answer 6

When glucose molecules are chemically combined in long chains to form glycogen molecules
- This is stimulated by insulin (secreted from the beta cells of the islet of Langerhans in the pancreas)

Question 7

Can glycogen be used by the cells?

Answer 7

No

- it must be converted back to glucose or to other simple sugars in order to be used by the cells

Question 8

What is glycogen stored in the liver used for?

Answer 8

• Conversion into glucose to maintain blood sugar levels

- Supply energy for liver activity

Question 9

What is glycogen stored in muscles used for?

Answer 9

Provides the glucose required for muscle activity

Question 10

What is glycogenolysis?

Answer 10

• the process of converting glycogen back into glucose

- Stimulated by the hormone glucagon

Question 11

What are the islets of Langerhans?

Answer 11

A cluster of hormone secreting cells
- Alpha cells: secrete glucagon
- Beta cells: secret insulin
Both hormones are secreted into the blood stream and are concerned with blood sugar levels

Question 12

What is the role of insulin?

Answer 12

It decreases blood sugar levels

• Accelerates the transport of glucose into the cells
• Accelerates the conversion of glucose to glycogen (glycogenesis)
• Stimulates the conversion of glucose into fat
• Increase in protein synthesis

Question 13

What is the role of glucagon?

Answer 13

Increases blood sugar levels

• Stimulates glycogenolysis. The glucose formed is then released into the blood
• Stimulates the liver to produce new sugar molecules from fats and amino acids, this is known as gluconeogenesis

Question 14

What is gluconeogenesis?

Answer 14

• The production of new sugar molecules from fats and amino acids
• Occurs in the liver

Question 15

Role of the adrenal cortex

Answer 15

• Stimulated by adrenocorticotrophic hormone (ACTH) from the anterior lobe of the pituitary
• Secretes cortisol (glucocorticoids)

Question 16

Role of cortisol

Answer 16

• Regulates carbohydrate metabolism by making sure enough energy is provided to the cells
• Increases the rate at which amino acids are removed from cells (mainly muscle cells) and transported to the liver. Amino acids may be converted into glucose by the liver if glycogen and fat levels are low (gluconeogenesis)

Question 17

Role of the adrenal medulla

Answer 17

• Secretes adrenaline and nor adrenaline
• Produces the same effects as those brought about by the sympathetic division of the autonomic nervous system
• Increases blood sugar levels
• Stimulates the production of lactic acid from glycogen in muscle cells, and the lactic acid can then be used by the liver to manufacture glucose

Question 18

What nerve stimulates the diaphragm?

Answer 18

The phrenic nerve

Question 19

What nerve stimulates the intercostal muscles?

Answer 19

The intercostal nerves

Question 20

The respiratory centre (role)

Answer 20

• Located in the medulla oblongata
• Carries nerve impulses to the diaphragm and intercostal muscles
• Controls two regions: expiration and inspiration

Question 21

What is the regulation of breathing stimulated by?

Answer 21

Changes in the concentrations of:

• carbon dioxide
• hydrogen ions
• oxygen gas

Question 22

Central chemoreceptors

Answer 22

• Located in the medulla oblongata

- Highly sensitive to high CO2 levels

Question 23

Response to high carbon dioxide…

Answer 23

• The respiratory centre is stimulated to send a nervous impulse along the intercostal nerve to contract the external intercostal muscles
• The phrenic nerve is also stimulated causing the diaphragm to contract
• This results in inhalation, followed by exhalation to decrease CO2 levels

Question 24

Peripheral receptors

Answer 24

• Aortic body
• Carotid body
• Detect pH and oxygen concentrations
• When these cells detect a decrease in [O2] and a decrease in pH as a result of increased [H+], nerve impulses are sent to the respiratory centre to stimulate breathing

Question 25

Main receptors responsible for changes in breathing rate

Answer 25

Chemoreceptors in the medulla oblongata are responsible for 70-80% of the increase in breathing rate that results from an increase in the carbon dioxide concentrations in the blood
- Although, this takes several minutes

Question 26

Immediate increase in breathing rate

Answer 26

• Caused by the stimulation of the aortic and carotid bodies

- Brought about by an increase in [H+]

Question 27

Stretch receptors

Answer 27

• Neurons located in the lungs which are stimulated by stretching (inflation) of the lungs
• When the lungs inflate, stretch receptors send impulses to the medulla which inhibits inspiration
• Prevents the lungs from over-inflating

Question 28

Hyperventilation

Answer 28

• Rapid deep breathing that increases the amount of oxygen in the blood and decreases the amount of carbon dioxide
• We need carbon dioxide to regulate our breathing
• A person may then pass out due to a lack of oxygen