8. Homeostasis of blood sugar and gas connections Flashcards
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Why do cells need a constant supply of glucose?
In order to undergo the basic cellular activities
What is the body’s source of glucose?
The food we eat as carbohydrates which are broken down and then absorbed through the small intestine
After a meal, what happens to blood glucose levels?
They rise sharply so homeostatic mechanisms come into play to reduce the glucose concentration.
They do this by removing the excess glucose and storing it for use in cellular activities between meals
What is glucose stored as?
It is stored as glycogen, a molecule made of long glucose chains
Stored mainly in the liver and muscle cells
What affects the level of glucose in the blood?
The pancreas and adrenal glands and then change whether the liver stores glycogen or takes excess glucose from the blood
What does Glucose + Oxygen create?
Carbon dioxide + water + energy
What does the liver do?
It’s the largest gland in the body and controls the blood sugar concentrations
It does this by converting glucose to glycogen for storage, or glycogen to glucose for release into the blood
Where does the livers main blood supply come from?
The hepatic portal vein which bring blood from the stomach, spleen, pancreas, and small intestine
What activities occur in the liver when it receives nutrient-rich blood?
Glucose may be removed from the blood to provide energy for the liver functioning
Glucose may be removed by the liver/muscles for storage
May continue to circulate in the blood, available for body cells to absorb and use as an energy source
Glucose may circulate in the blood
Glucose in excess of that required for normal blood sugar and tissue glycogen level is converted into fat for storage
How much glycogen is the body able to store?
500g
100g in the liver
The remainder in skeletal muscle cells
What is glycogenesis?
the process where glucose molecules are chemically combined in long chains to form glycogen molecule
Process is stimulated by insulin
Can glycogen be used by the cells?
No it has to be converted back into glucose to maintain blood sugar levels
What is glycogenolysis?
The process of converting glycogen back into glucose and most often occurs between meals
What are islets of Langerhans?
Clusters of hormone secreting cells in the pancreas
What are the two types of cells in the Islets of Langerhans?
Alpha cells which secrete glucagon
Beta sells which secrete insulin
What do beta cells do?
They cause a decrease in blood sugar
Accelerate transport of glucose from the blood into the cells
Accelerate conversion of glucose to glycogen
Causes an increase in protein synthesis in some cells
What does insulin stimulate the conversion of?
The conversion of glucose into fat in adipose tissue
What does the level of blood sugar regulate?
It regulates the secretion of insulin via a negative feedback system
When levels rise above normal, chemical sensors in the beta cells stimulate the secretion of insulin
What do alpha cells do?
Secrete glucagon
Cause an increase in blood sugar levels
Stimulate glycogenolysis in the liver, glucose then released into the blood
Stimulate the liver to produce more sugar molecules from fats and amino acids
May have mild stimulating effect on protein breakdown
Explain the negative feedback system for the regulation of glucagon
When blood sugar falls below normal, chemical sensors stimulate the cells to secrete glucagon, and as blood sugar levels increase, production is reduced
What does the adrenal cortex and adrenal medulla secrete?
Adrenal cortex- glucocorticoids
Adrenal medulla- adrenaline and noradrenaline
What stimulates the adrenal cortex to secrete hormones?
The adrenocorticotopic hormone (ACTH) from the APG
What is the most well know hormone of the glucocorticoid group?
Cortisol
What does the adrenal cortex do?
Regulate carbohydrate metabolism by ensuring enough energy is provided to the cells
Stimulate the conversion of glucose
Increase rate in which amino acids are removed from cells and transported to the liver
Promote the mobilisation of fatty acids from adipose tissue- muscle cells shift from glucose to fatty acids for their metabolic energy
What does the adrenal medulla do?
synthesise adrenaline and noradrenaline- produce the same effects as the sympathetic nervous system
Adrenaline evaporates blood glucose levels to counteract the effects of insulin, stimulates the production of lactic acid from glycogen in muscle cells- can be used by liver to manufacture glucose
What is the normal level of glucose in the blood?
4-6millimoles per litre
What muscles control breathing?
The diaphragm, intercostal muscles and muscles between the ribs
The skeletal muscles require stimulation from nerve impulses to initiate contraction
How are the diaphragm and intercostal muscles stimulated?
Diaphragm by impulses from the phrenic nerve
Intercostal muscles by impulses from the intercostal nerves
What are intercostal nerves?
They are spinal nerves and have origins in the spinal cord at the level of the neck and thorax
If they are damaged, the person could suffer complete paralysis
How are nerve impulses to the diaphragm and intercostal muscles controlled?
They are controlled by the respiratory centre in the medulla oblongata
What concentrations affect breathing rate?
Oxygen and carbon dioxide concentration levels in the blood
Under normal conditions, does oxygen play a big part in breathing regulation?
No oxygen doesnt and the concentration has to fall to very low levels before it has a major effect
Aortic and carotid bodies are sensitive to what?
They are sensitive to changes in the concentration of oxygen in the blood plasma and are in the walls of the aorta and carotid arteries
What happens to blood concentration as oxygen is consumed by the cells?
The blood concentration begins to fall, if it falls below normal, breathing rate increases
Chemoreceptors are stimulated when?
There is a large decrease in oxygen and the nerve impulses are transmitted to the respiratory sensor
What does the respiratory sensor stimulate?
The transmission of messages to the diaphragm and intercostal muscles so breathing rate increases
What does a relatively small increase in carbon dioxide do to the breathing rate?
It causes a large difference in the breathing rate and CO2 is the major factor regulating breathing rate
What does an increased amount of CO2 in the blood stimulate?
The increased level in the blood stimulates central and peripheral chemoreceptor, which stimulate the respiratory centre and increases breathing rate
Where are the most sensitive to CO2changes, chemoreceptors found?
In the Medulla oblongata
What are the immediate responses to increased CO2 stimulated by and what are they?
Increased breathing rate that follows the increased CO2 concentration of plasma is produced by Stimulation of the aortic and carotid bodies
Stimulated by increase in hydrogen ion concentration
What happens to the pH level when hydrogen ion concentration increases?
The pH decreases
An increase in breathing rate is seen
What does a decrease in pH stimulate?
Chemoreceptors in the aortic and carotid bodies
They transmit impulses to the respiratory centre, resulting in an increased breathing rate
What are hydrogen ion changes a result of?
Carbon dioxide concentrations
What is more sensitive, oxygen of Carbon dioxide?
Oxygen
What can we voluntarily control in our breathing?
Voluntarily control the rate and depth of breathing
How are we able to voluntarily control parts of our breaths?
Due to connection made between the cerebral cortex and descending tracts in the spinal cord
Voluntary control bypasses the respiratory centre in the medulla oblongata
Why is being able to control our breaths voluntarily important?
It’s important because it’s protective, preventing irritating gases and water from entering the lungs
What does the build up of CO2 in the plasma stimulate in the inspiratory centre?
It stimulates the inspiratory centre to send impulses to inspiratory muscles
We are eventually forced to take a breath
What is hyperventilation?
When rapid, deep breathing provides more oxygen than required and removes more carbon dioxide than necessary
How is hyperventilation corrected?
It usually corrects itself because the reduction of CO2 concentrations means the chemoreceptors aren’t stimulated, and there is no urge to breathe until CO2 levels return to normal
Why does the respiratory system increase both the rate and depth of breathing during exercise?
Because contracting muscles require large amounts of oxygen and produce large amounts of carbon dioxide
What is heart rate?
The number of times the heart beats per minute
What is stroke volume?
The volume of blood force from the heart with each contration
What is cardiac output?
A combination of both factors, the amount of blood leaving the heart each minute
What is blood pressure?
The force with which each the blood presses on the walls of the blood vessesl
How is blood pressure determined?
By the cardiac output (as CO increases, BP decreases)
Constriction of blood vessels increases pressure, dilation decreases BP
What are specialised cells in the heart capable of initiating?
They initiate nerve impulses to stimulate muscle contraction without any outside influence from the nervous system
What is the Sinoatrial node?
the ‘pacemaker’ responsible for rhythmic contractions of the heart
What is the Atrioventricular node?
The impulses that spread across the ventricles
Where is the SA node located?
In the wall of the right atrium, below the opening of the super vena cava
What does the SA node do?
It initiates each heartbeat with an impulse that spreads across both atria, causing them to contract
The impulse eventually reaches the AV node
Where is the AV node located?
In the wall between the two atria near the AV valves
What happens in a heartbeat?
- SA node sends impulse through the atria
- Stimulus reaches AV nod, contraction of atrium begins
- AV node sends out own impulses, which travel down the septum
- Impulses spread through the ventricle muscles, ventricles contract
Why cant the SA node create the heartbeat?
Although it can stimulate the heartbeat on its own, its activity is influenced by the ANS, which has neurons that carry impulses to the SA and AV nodes, as well as to the atria
What is the cardiac centre?
Where neurons bring impulses from the medulla oblongata to the body
Comes from a network of nerve cells with axons that texted to the heart and muscles of the blood
Autonomic control of the heart is a balance between what?
The stimulatory effects of the parasympathetic neurons and the inhibitory effects of the parasympathetic neurons
What division of the ANS is in control during rest and exercise?
At rest the parasympathetic activity is dominant
During exercise the sympathetic activity increases and causes the heart to beat faster
A balance between stimulation and inhibition is maintained in the heart how?
Sensory impulses from various receptors in the cardiovascular system act upon the cardiovascular regulating centre
Any increase in CO2 concentration or pH decrease influences the cardiac centre by increasing or decreasing cardiac output?
Increases
During exercise, why is a large increase in blood flow required?
To maintain muscle cell activity
Cardiac output may increase from 5Lper min to 30L per min
During exercise how do blood vessels in the internal organs, differ from blood vessels in the muscles?
Blood vessels in the internal organs constrict while blood vessels in the muscles dilate
What can the mental stress of activities do to blood glucose?
Can cause it to rise and blood pressure and heart rate to increase
During prolonged exercise what happens to homeostasis in the body?
During prolonged, steady exercise, heart and breathing rates are homeostatically controlled at a higher level than when at rest
