Flashcards in Homeostasis of blood sugar and gas concentrations Deck (28)
What is the equation for cellular respiration?
Glucose + oxygen = carbon dioxide + water + energy
What is glucose?
A simple sugar
What is glycogen?
A molecule made of long chains of glucose molecules
The livers blood supply
- 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
Things that happen to glucose (in the liver)
- 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
What is glycogenesis?
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)
Can glycogen be used by the cells?
- it must be converted back to glucose or to other simple sugars in order to be used by the cells
What is glycogen stored in the liver used for?
- Conversion into glucose to maintain blood sugar levels
- Supply energy for liver activity
What is glycogen stored in muscles used for?
Provides the glucose required for muscle activity
What is glycogenolysis?
- the process of converting glycogen back into glucose
- Stimulated by the hormone glucagon
What are the islets of Langerhans?
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
What is the role of insulin?
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
What is the role of glucagon?
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
What is gluconeogenesis?
- The production of new sugar molecules from fats and amino acids
- Occurs in the liver
Role of the adrenal cortex
- Stimulated by adrenocorticotrophic hormone (ACTH) from the anterior lobe of the pituitary
- Secretes cortisol (glucocorticoids)
Role of cortisol
- 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)
Role of the adrenal medulla
- 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
What nerve stimulates the diaphragm?
The phrenic nerve
What nerve stimulates the intercostal muscles?
The intercostal nerves
The respiratory centre (role)
- Located in the medulla oblongata
- Carries nerve impulses to the diaphragm and intercostal muscles
- Controls two regions: expiration and inspiration
What is the regulation of breathing stimulated by?
Changes in the concentrations of:
- carbon dioxide
- hydrogen ions
- oxygen gas
- Located in the medulla oblongata
- Highly sensitive to high CO2 levels
Response to high carbon dioxide...
- 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
- 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
Main receptors responsible for changes in breathing rate
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
Immediate increase in breathing rate
- Caused by the stimulation of the aortic and carotid bodies
- Brought about by an increase in [H+]
- 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