Chapter 10 - Homeostasis of Blood Sugar, Gas Concentrations and Blood Pressure Flashcards
1
Q
What is a Glycogen?
A
- It is a molecule made of long chains of glucose molecules.
- Glycogen is the form in which carbohydrate is stored in the body.
- Storage is mainly in the liver and muscle cells.
2
Q
How does the liver contribute to the regulation of blood sugar level?
A
•The liver stores glycogen, from which glucose can be made and added to the blood, or glucose can be removed from the blood and stored as glycogen.
3
Q
Give a summary of the glucose-glycogen conversions.
A
- When blood sugar level is high (after a meal) glucose is converted to Glycogen.
- When blood sugar level is low (during exercise) Glycogen is converted into glucose.
4
Q
Explain the regulation of blood sugar after nomnoms.
A
- After a meal, blood glucose concentration can rise sharply.
- Homeostatic mechanisms then begin to operate to reduce the blood glucose concentration and maintain it at the normal level.
- Any excess glucose in the blood must be removed and stored ready for use in cellular activities between meals.
5
Q
Where does most of the liver’s blood supply comes through?
A
The hepatic portal vein, which brings blood directly from the stomach, spleen, pancreas and small and large intestines.
-Thus, the liver has the first chance to absorb any of the nutrients from digested food.
6
Q
After consuming a typical meal containing a high proportion of carbohydrates, what happens to the products that is broken down?
A
Mainly glucose, are absorbed into the blood capillaries of the villi of the small intestine.
7
Q
The hepatic portal vein carries the glucose to the liver where a number of different things may occur:
A
- Glucose may be removed from the blood by the liver to provide energy for liver functioning.
- It may be removed by the liver and/or muscles and converted into glycogen for storage.
- It may continue to circulate in the blood where it is available for body cells to absorb and use as a source of energy.
- Glucose in excess of that required to maintain both the normal blood sugar level and the tissue glycogen level is converted into fat for long-term storage.
8
Q
The body is able to store 500g of glycogen, which part of the body are they stored?
A
- 100g is stored in the liver
- Remainder in skeletal muscle cells.
9
Q
Explain the process of Glycogensis.
A
- This process is stimulated by the pancreatic hormone Insulin.
- It is the process of Glucose molecules combining chemically in long chains to form glycogen molecules.
10
Q
Why can’t glycogen be used by cells?
A
It must be converted back into glucose or to other simple sugars.
11
Q
Where does the conversion of glycogen take place?
A
Glycogen stored in the liver is available for conversion into glucose to maintain blood sugar levels and supply energy for liver activity.
12
Q
What is the role of the glycogen stored in the muscle cells?
A
It provides the glucose requirement for muscle activity.
13
Q
What is Glycogenolysis?
A
- Stimulated by another pancreatic hormone, Glucagon.
- It occurs most frequently between meals.
- It is the process of converting glycogen back into glucose.
14
Q
What is one of the disadvantages of having Glycogen stored in the liver?
A
- It is a short-term energy supply.
- It can provide glucose for bode cell use for only about six hours if no other supply is available.
- If more energy is required, the body uses the energy reserves in the stored fat.
15
Q
What is a Pancreas?
A
- Pale grey gland
- 12-15cm long
- lying partly in the curve of the duodenum
16
Q
What lies within the Pancreas?
A
Within the pancreas are clusters of hormone-secreting cells called the Islets of Langerhans.
17
Q
What two types of cells are present in the islets?
A
- Alpha cells secrete glucagon
- Beta cells secrete insulin
-Both hormones are secreted into the bloodstream and are concerned with the control of blood sugar levels.
18
Q
How does insulin from the beta cells cause a decrease in blood sugar levels?
A
- It accelerates the transport of glucose from the blood into the cells, especially those of the skeletal muscles.
- It accelerates the conversion of glucose into glycogen.
+Insulin stimulates the conversion of glucose into fat in adipose tissue (fat storage tissue) and causes an increase in protein synthesis in some cells.
19
Q
How does the level of blood sugar regulate the secretion of insulin?
A
Negative Feedback System.
20
Q
What happens when blood sugar levels rise above normal?
A
- Chemical sensors in the beta cells of islets of Langerhans stimulate those cells to secrete insulin.
- As the level of blood sugar level decreases, the cells are no longer stimulated and production is reduced.
21
Q
What does the secretion of insulin (beta cells) specifically do?
A
- Enables entry of glucose into cells.
- Promotes conversion of glucose into glycogen in liver and muscles.
- Promotes fat storage.
- Promotes protein synthesis.
22
Q
What causes an increase in the blood sugar level?
A
-Glucagon from the alpha cells.
23
Q
How does Glucagon increase the blood sugar level?
A
- Glucagon does this by stimulating glycogenolysis - the conversion of glycogen into glucose - in the liver.
- The glucose formed is then released into the blood, and the blood sugar level rises.
24
Q
What is Gluconeogenesis?
A
It is when Glucagon stimulates the liver to produce new sugar molecules from fats and amino acids.
25
What other effects does glucagon have?
- It may have a mild stimulating effect on protein breakdown.
- The regulation of the secretion of glucagon, like that of insulin secretion, is directly determined by the level of sugar in the blood and is again based on a negative feedback system.
26
What happens when blood sugar levels drops below normal?
1. Chemical sensors in the alpha cells of the islets of Langerhans stimulate those cells to secrete glucagon.
2. As the level of blood sugar increases, the cells are no longer stimulated and production is reduced.
27
Explain the structure of the Adrenal Glands.
-Each gland is composed of two distinct parts:
1. Cortex (outer part)
2. Medulla (inner part)
28
What are the 3 main hormones involved in regulating blood sugar levels?
1. Glucocorticoids - Adrenal Cortex
2. Adrenaline (epinephrine) -Adrenal Medulla
3. Noradrenaline (norepinephrine) - Adrenal Medulla
29
How does the adrenal cortex secrete hormones?
They are stimulated by adrenocorticotrophic hormone (ACTH) from the anterior lobe of the pituitary.
30
What is the role of the Glucocorticoids (Cortisol)?
1. They regulate carbohydrate metabolism by making sure enough energy is provided to the cells.
2. In doing so, they stimulate the conversion of glycogen into glucose.
3. Increase the rate at which amino acids are removed from cells (mainly muscle cells) and transported to the liver.
4. Promotes the mobilisation of fatty acids from adipose tissue, allowing muscle cells to shift from glucose to fatty acids for much of their metabolic energy.
31
Define Glycogenesis, Glycogenolysis and Gloconeognesis.
1. Glycogenesis - is the formation of glycogen from other carbohydrates especially glucose (genesis: 'origin or creation')
2. Glycogenolysis - Breakdown of glycogen to glucose (lysis: 'to separate or break down'.)
3. Gluconeogenesis - Conversion of fats or proteins into glucose (neo: new)
32
What is the effect of Glucocorticoids (cortisol) on blood glucose levels? (AC)
1. Stimulate conversion of glycogen into glucose in liver.
| 2. Stimulate protein breakdown in muscles and conversion of amino acids into glucose in liver.
33
What is the effect of Adrenaline and Noradrenaline on blood glucose levels? (AM)
Stimulate breakdown of glycogen in liver and release of glucose into blood.
34
What muscles causes air to move in and out of the lungs ?
1. Diaphragm - a muscle that separates the thorax from the abdomen.
2. Intercostal Muscles - the muscles between the ribs.
35
What type of muscles are the Diaphragm and the Intercostal muscles?
They are skeletal muscles and require stimulation from nerve impulses to initiate contraction.
36
What specific nerves stimulate the Diaphragm and the Intercostal muscles ?
1. Diaphragm - phrenic nerve
| 2. Intercostal muscles - intercostal nerves (DUH!)
37
What type of nerves are the Phrenic nerve and Intercostal nerves ?
They are spinal nerves and they have their origin in the spinal cord at the level of the neck and thorax.
38
What happens if the spinal nerves are injured?
Complete paralysis of the muscles that ventilate the lungs.
-Death inevitably follows unless some form of artificial respiration is rapidly applied.
39
What controls the nerve impulses that travel to the diaphragm and intercostal muscles?
Respiratory Centre located in the medulla oblongata of the brain.
40
Explain the structure of the Respiratory centre.
There are two regions within the respiratory centre:
1. Controls expiration (breathing out)
2. Inspiration (breathing in)
41
How is breathing coordinated?
-To coordinate breathing, messages need to pass back and forth between the neurons in these two regions.
42
What two elements have an effect on breathing rate ?
- Oxygen
| - Carbon Dioxide
43
How does the concentration of Carbon Dioxide in the blood plasma affect the concentration of hydrogen ions?
When carbon dioxide dissolves in water it forms carbonic acid (H2CO3), which readily breaks down to form hydrogen ions (H+) and bicarbonate ions (HCO3-).
44
What happens when oxygen is consumed by the cells?
-Its concentration in the blood begins to fall. If concentration of oxygen falls below normal while other factors are held constant, the breathing rate increases.
45
Why does oxygen only play a little part in the regulation of breathing?
- Because within the normal range of blood oxygen concentration, the effect on breathing rate is only slight.
- The concentration has to fall to very low levels before it has a major stimulatory effect.
46
What role does the chemoreceptors, Aortic and Carotid Bodies play?
These are group of cells within the walls of the aorta and carotid arteries that are sensitive to changes in the concentration of oxygen in the blood plasma.
47
Are peripheral chemoreceptors the only receptors?
Nope, there are central chemoreceptors in the medulla oblongata.
48
What happens when there is a large decrease in oxygen concentration?
It stimulates the chemoreceptors and nerve impulses are transmitted to the respiratory centre. These nerve impulses stimulate the transmission of messages to the diaphragm and intercostal muscles so that the breathing rate increases.
49
What happens when there is a relatively small increase in the concentration of carbon dioxide?
It is enough to cause a marked increase in the rate of breathing.
50
How does the concentration of carbon dioxide cause an increase in breathing rate ?
1. The concentration of carbon dioxide in the plasma is associated with the concentration of hydrogen ions.
2. Any increase in carbon dioxide results in an associated increase in hydrogen ion concentration.
3. The increase in the concentration of both these chemicals in the blood results in the stimulation of the central and peripheral chemoreceptors.
4. These in turn transmit nerve impulses to the respiratory centre, resulting in an increase in breathing rate.
51
Which chemoreceptors are most sensitive to change in the concentration of carbon dioxide in the plasma?
Those located in the medulla oblongata.
52
How does the neurons making up the central chemoreceptors affect breathing rate?
- They are separate from, but communicate with, the neurons of the respiratory centre.
- These chemoreceptors are responsible for 70-80% of the increase in breathing rate that results rom an increase in the carbon dioxide concentration of the blood.
- However, this response takes several minutes.
53
What causes the immediate increase in breathing rate that occurs following an increase in the carbon dioxide concentration of the plasma?
- Stimulation of the aortic and carotid bodies.
| - These are stimulated by the associated increase in hydrogen ion concentration.
54
Explain how the concentration of hydrogen ion affects breathing rate.
- As the hydrogen ion concentration of the blood increases, the pH decreases, causing an increase in the breathing rate.
- A decrease in the pH directly stimulates chemoreceptors in the aortic and carotid bodies, which then transmit impulses to the respiratory centre, resulting in an increase in the breathing rate.
55
How does the concentration of Oxygen, Carbon Dioxide and Hydrogen Ion relate?
- None of the 3 factors is independent in the regulation of breathing rate.
- Each factor interacts with the others.
- Nor are these the only factors to play a role in the control of breathing.
56
Explain the action of stopping our breathing rate for a limited period.
1. This voluntary control comes via connections from the cerebral cortex to descending tracts in the spinal cord.
2. Voluntary control thus bypasses the respiratory centre in the medulla oblongata.
- This is a protective device as it enables us to prevent irritating gases and water from entering the lungs.
57
Why can't we stop breathing forever?
- The build-up of carbon dioxide in the plasma stimulates the inspiratory centre to send impulses to the inspiratory muscles.
- Thus, we are eventually forced to take a breath whether we want to or not.
58
What is hyperventilation?
It is the rapid, deep breathing and it can provide more oxygen than required and remove more carbon dioxide than necessary.
59
What are the characteristics of Hyperventilation?
- It can occur voluntarily or may be stimulated by physical stress such as severe pain or emotional stress such as extreme anxiety.
- Hyperventilation usually corrects itself because the reduction in carbon dioxide concentration means that the chemoreceptors are not stimulated and there is no urge to breathe until carbon dioxide levels return to normal.
60
How does hyperventilation before swimming under water allow a person to stay under water longer?
- This is not due to extra oxygen in the blood - it is due to the loss of carbon dioxide.
- This breadth-holding ability could be increased to such an extent that the individual loses consciousness from lack of oxygen to the brain before feeling the urge to breathe.
- This is very dangerous.
61
What happens to our breathing rate during exercise?
- During exercise the contracting muscle cells require large amounts of oxygen and produce large amounts of carbon dioxide.
- During heavy exercise, the volume of air going into and out of the lungs each minute may increase ten to twentyfold.
62
Define Heart Rate.
It is the number of times the heart beats per minute.
63
Define Stroke Volume.
It is the volume of blood forced from the heart with each concentration.
64
What is Cardiac Output?
- It is the combination of both the Heart Rate and Stroke Volume.
- It is the amount of blood leaving the heart every minute.
65
Define Venous Return.
It is the return of blood to the heart.
66
Why is Venous Return an important factor in cardiac output?
- Cardiac output could not increase unless the supply of blood returning from the veins was maintained at levels sufficient to ensure a satisfactory flow of blood to the heart.
- If this did not occur, any increase in stroke volume could be maintained.
67
Define Blood Pressure.
It is the force in which the blood presses on the walls of the blood vessels.
68
The blood pressure at a particular time depends on:
- The cardiac output - as cardiac output increases, blood pressure will increase.
- The diameter of blood vessels - constriction of blood vessels increases pressure and dilation decreases blood pressure.
69
What are the bundles of specialised cells controlling the heart's activity called?
1. Sinoatrial Node (SA Node)
| 2. Atrioventricular Node (AV Node)
70
Describe the function of the Sinoatrial Node.
- AKA Pacemaker because it is responsible for the rhythmical contractions of the heart.
- The SA node is located in the wall of the right atrium just below the opening of the superior vena cava.
- This node initiates each heartbeat with an impulse that spreads out over both atria, causing them to contract.
- As the impulse spreads over the atria, it eventually reaches the AV node.
71
Where is the Atrioventricular Valves located?
-This node is situated in the wall between the two atria near the atrioventricular valves.
72
Explain the structure of the conducting fibres that originate from the AV node.
- From the AV node, conducting fibres pass through the septum that separates the right and left ventricles of the heart.
- The fibres then divide into two branches, one branch going down each side of the septum.
- Within the muscle of the ventricles, these branches divide into a network of fine nerve fibres.
73
List the sequence of events that occurs when the heart beats.
1. The SA node sends out nerve impulses through the atria.
2. The stimulus reaches the AV node. At about this time, contraction of the muscle of the atrium begins.
3. Stimulation of the AV node causes it to send out its own impulses. These travel down the fibres in the septum between the ventricles.
4. The impulses then spread through the muscles of the ventricles. Atrial contraction is now complete and ventricular contraction begins.
74
What systems control the heart beat.
- Its activity is influenced by the autonomic nervous system.
- This system, with its sympathetic and parasympathetic divisions, has neurons that carry impulses to the SA and AV nodes as well as to the atria of the heart.
- The ventricles also receive such neruons but mainly from the sympathetic division.
75
Where do the neurons affecting the heart bring impulses from?
- These neurons bring impulses from the medulla oblongata of the brain.
- In the medulla there is a network of nerve cells with axons that extend to the heart and to the muscles in the walls of the blood vessels.
- This region within the medulla oblongata is known as the cardiac centre or cardiovascular regulating centre.
76
Where do the Sympathetic nerve fibres from the cardiovascular regulating centre travel?
Down a pathway in the spinal cord and then, as apart of the cardiac nerves, to the heart.
77
Explain the role of the sympathetic nerves in the heart.
- At the heart, these fibres make contact with the SA node, the AV node and parts of the cardiac muscle.
- Sympathetic fibres release the neurotransmitter noradrenaline which stimulates an increase in both heart rate and stroke volume.
78
Explain the role of the parasympathetic nerves in the heart.
- These are inhibiting impulses.
- Impulses from parasympathetic nerves cause the release of acetylcholine, which decreases the rate of heartbeat and the strength of contraction.
79
What is the autonomic control of the heart?
-It is the result of balancing the opposing influences of the stimulatory effects of the sympathetic neurons and the inhibitory effects of the parasympathetic neurons.
80
Summaries the autonomic control of the heart.
- At rest, parasympathetic activity is dominant.
- During exercise, however, the activity of the sympathetic neurons increases, while that of the parasympathetic neurons decreases, causing the heart to beat faster.
- Whenever one division is stimulated, the activity of the other is inhibited.
81
What are Pressoreceptors (Baroreceptors)?
- They respond to changes in blood pressure.
| - They send a message to the medulla oblongata.
82
What happens when Pressorecptors are stimulated and message is sent to the medulla oblongata?
- Within, the medulla, the cardiovascular regulating centre sends impulses via the parasympathetic neurons to decrease the rate and force of heart muscle contraction.
- With the subsequent decrease in cardiac output, the blood pressure returns to normal.
- On the other hand, if blood pressure falls, the cardiovascular regulating centre sends impulses via the sympathetic neurons and the heart beats faster and more forcefully, restoring the blood pressure to normal.
83
What determines the Stroke Volume?
- The force of contraction of the ventricles.
| - The more strongly the muscle fibres of the heart contract, the more blood is forced from the heart.
84
What are the 3 main factors that influence the volume of blood forced from the heart?
1. The length of diastole
2. The venous return
3. The sympathetic nervous system
85
Explain how the length of diastole affect the volume of blood forced from the heart?
- Diastole is the period of time the heart is relaxing between contractions.
- It affects the amount of blood that can enter the heart.
- The longer the period of diastole, the more time is available for the ventricles of the heart to fill with blood.
- However, as the rate of the heart beat increases, the length of diastole becomes shorter, and less time is available for the ventricles to fill with blood.
86
Explain how the venous return affect the volume of blood forced from the heart?
- Venous return is the volume of blood returning to the heart. It also has a major influence on stroke volume.
- Within limits, the contraction of the muscle fibres of the heart is more forceful when the fibres are stretched.
- The increased filling during diastole stretches the fibres of the ventricles, intensifying the force of contraction.
- That is, the increased volume of blood entering the heart is handled by an increased output through more forceful ventricular contractions.
87
What are factors that affect the venous return ?
- Activity of the skeletal muscles.
- The respiratory movements to ventilate the lungs.
- The tone of the walls of the veins.
- The ease with which blood flows from arteries to veins through skeletal muscles arterioles.
88
Explain how does the activity sympathetic nervous system affect the volume of blood forced from the heart?
- Noradrenaline released by sympathetic nerve fibres increases the force of contraction of cardiac muscle so that each ventricular contraction ejects a larger volume of blood.
- Thus stroke volume is increased by the activity of the sympathetic nervous system.
89
What are other factors that affect the heart rate?
- Age: Heart rate is fastest at birth, and it then slows somewhat as we grow older. It is still moderately fast during childhood and adolescences, before averaging out at 70-80 beats per minute in adulthood. In old age, it drops below this average.
- Sex: On average, males tend to have a slower heartbeat than females.
- Emotional State: Strong emotions such as anger, fear and anxiety increase heart rate and those such as depression and grief decrease heart rate.
90
Why must a change of blood flow have to occur during exercise?
To maintain the activity of the muscle cells during exercise, a large increase in blood flow is required to ensure an adequate supply of oxygen and nutrients, and to remove the carbon dioxide and heat produced.
-Thus cardiac output may increase from 5L per minute at rest to a maximum of 30L per minute in a trained athlete.
91
What has to happen to ensure that blood supply to the muscles is increased?
-The blood vessels in internal organs such as the alimentary canal have to constrict.
92
What happens when a person begins exercising?
- There is an anticipatory response brought about by the autonomic nervous system and by release of the hormone adrenaline.
- Heart rate and stroke volume increase and there is an increase in the blood flow to skeletal muscles.
93
Define Vasodilators.
Substances that produce a local widening, or dilation, of arterioles.
94
What do the wastes, including carbon dioxide and lactic acid from respiratory processes of cells act as ?
- Vasodilators.
- This results in an increased blood flow through the muscle tissues, ensuring the cells are adequately supplied with oxygen and nutrients for continued functioning.
95
What else does cellular respiration release?
- It also releases a lot of heat energy, which tends to increase blood temperature.
- This causes an increase in heart rate because it stimulates the heart to discharge impulses at a faster rate.
96
Give an example of how our behaviour can affect all of the variables described in this chapter.
- Suppose you are about to take part in a long distance race.
- The mental stress will cause blood glucose to rise and, in anticipation of the increased muscular activity, heart rate ad blood pressure will increase.
- When the race begins, breathing rate and depth will increase, cardiac output will rise further and blood glucose will continue to be at a high level.
- There will be an increase in blood supply to the working muscles and a corresponding decrease in supply to internal organs such as the stomach and intestines.
