Communication And Homeostasis Flashcards
(171 cards)
0
Q
What is a response
A
A change in behaviour or physiology as a result of a change in the environment
1
Q
What is a stimulus
A
Any change in the environment that causes a response
2
Q
What conditions need to be maintained in order to keep the enzymes in cells working
A
- A suitable temperature
- A suitable pH
- An aqueous environment that keeps the substrates and products in solution
- Freedom from toxins and excess inhibitors
3
Q
How do organisms internal environments change?
A
As cells undergo their metabolic activities they use up substrates and produce products. Some of these may be unwanted or even toxic
4
Q
Why is a build up of CO2 in the tissue fluid bad?
A
It changes the pH, disrupting enzymes
5
Q
The accumulation of excess waste or toxins in the internal environment…
A
Acts as a stimulus, causing removal of the wastes so the cell can survive. The stimulus may act directly on the cells causing them to reduce activities and produce less waste. This may not be good for the organism.
6
Q
How is the composition of the tissue fluid maintained?
A
Blood flows throughout the body, transporting substances to and from cells. Any wastes or toxins enter the blood and are carried away
7
Q
What are the requirements of a good communication system?
A
It should:
•cover the whole body
•enable cells to communicate with each other
•enable specific communication
•enable rapid communication
•enable both short and long term responses
8
Q
Why is a multicellular organism more efficient than a single-called organism?
A
It’s cells can be differentiated, and specialised to perform particular functions, forming tissues and organs.
9
Q
How do cells communicate with each other?
A
By cell signalling: one cell releases a chemical which is detected by another cell, provoking a response
10
Q
What are the two major systems of communication dependent on cell signalling?
A
The neuronal system and the hormonal system
11
Q
What is the neuronal system?
A
An interconnected network of neurones that signal to each other across synapse junctions
12
Q
How does the hormonal system work?
A
It uses blood to transport its signals. Cells in an endocrine organ release the signal (a hormone) into the blood. It is carried all over the body but is only recognised by specific target cells.
13
Q
How fast do the neuronal and hormonal systems work?
A
Neuronal system conducts signals very quickly, enabling rapid responses to stimuli that may be changing quickly.
Hormonal system enables long term responses to be coordinated
14
Q
What conditions need to be kept constant inside the body of living organisms?
A
Body temperature Blood glucose concentration Blood salt concentration Water potential of the blood Blood pressure Carbon dioxide concentration
15
Q
Define homeostasis
A
The maintenance of the internal environment in a constant state despite external changes
16
Q
What is negative feedback?
A
A process that brings about a reversal of any change in conditions, ensuring that an optimum steady state can be maintained
17
Q
What processes must occur in order to maintain homeostasis?
A
Any change in the internal environment must be detected.
The change must be signalled to other cells.
There must be a response to reverse the change.
18
Q
What is the pathway of structures required for negative feedback?
A
Stimulus-receptor-communication pathway (cell signalling)-effector-response
19
Q
What is a harmful example of positive feedback?
A
When the body gets too cold,enzymes become less active meaning exergonic reactions slow down and less heat is released
20
Q
What is a beneficial example of positive feedback?
A
At the end of pregnancy; as the cervix begins to stretch the change is signalled to the anterior pituitary gland, stimulating it to secrete the hormone oxytocin. Oxytocin increases the uterine contractions, stretching the cervix more and causing more oxytocin to be secreted
21
Q
What is positive feedback?
A
A process which increases any change detected by the receptors. It tends to be harmful and does not lead to homeostasis.
22
Q
What is an ectotherm?
A
An organism that relies on external sources of heat to regulate it’s body temperature
23
Q
What is an endotherm?
A
An organism that can use internal sources of heat, such as heat generated from metabolism in the liver, to maintain it’s body temperature
24
Advantages of being an ectotherm
* Ectotherms use less food in respiration
* they need to find less food and may be able to survive long periods without eating
* a greater proportion of energy can be used for growth
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Disadvantages of being an ectotherm
* Ectotherms are less active in cooler temperatures, and may need to warm up in the morning before becoming active, putting them at greater risk of predation
* May not be capable of activity during the winter, so need to have sufficient energy stores to survive.
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When an ectotherm is cold it will...
...change it's behaviour or physiology to increase absorption of heat from its environment
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When an ectotherm is hot it will...
Change it's behaviour or physiology to decrease absorption of heat and increase loss of heat to its environment
28
How will exposing it's body to the sun help an ectotherm to regulate its temperature, and what is an example of an ectotherm that does this?
It enables more heat to be absorbed, snakes do this
29
How will orientating its body to the sun help an ectotherm to regulate its temperature, and what is an example of an ectotherm that does this?
It exposes a larger surface area, for more heat absorption, locusts do this.
30
How will orientating its body away from the sun help an ectotherm to regulate its temperature, and what is an example of an ectotherm that does this?
It exposes a lower surface area so that less heat is absorbed, locusts do this
31
How will hiding in a borrow help an ectotherm to regulate its temperature, and what is an example of an ectotherm that does this?
Reduces heat absorption by keeping out of the sun, lizards do this
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How will altering its body shape help an ectotherm to regulate its temperature, and what is an example of an ectotherm that does this?
It exposes more or less surface area to the sun, horned lizards do this
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How will increasing breathing movements help an ectotherm to regulate its temperature, and what is an example of an ectotherm that does this?
Evaporates more water, causing heat loss, locusts do this
34
Advantages of being an endotherm
* A fairly constant body temperature
* activity is possible when external temperatures are cool - night, early in the morning, during the winter
* ability to inhabit colder parts of the planet
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Disadvantages of being an endotherm
* a significant part of the energy intake is used to maintain body temperature in the cold
* more food required
* less energy from food is used for growth/more food is required for growth
36
How do sweat glands in skin respond to maintain core body temperature?
If core temperature is too high, more sweat will be secreted onto skin; water in sweat evaporates, heat from blood is used to supply latent heat of vaporisation. If temperature is too low less sweat is secreted
37
How do lungs, mouth and nose respond to maintain core body temperature?
When core body temperature is too high, panting increases evaporation from lungs, tongue and other moist surfaces, using latent heat as above. When temperature is too low the animal does not pant
38
How do hairs on skin respond to maintain a constant body temperature?
When core temperature is too high, hairs lie flat l, providing little insulation so that heat can be lost by convection and radiation. When temperature is too low, hairs are raised to trap a layer of insulating air, reducing loss of heat from the skin
39
How do arterioles leading to capillaries in skin respond to maintain core body temperature?
If core temperature is too high, vasodilation allows more blood to flow into capillaries near the skin surface so more heat can be radiated from the skin. If core temperature is too low, vasoconstriction reduces the flow of blood through capillaries near the surface of skin; less heat radiated
40
How do liver cells respond to maintain constant body temperature?
If core temperature is too high the rate of metabolism is reduced, less heat is generated from exergonic reactions such as respiration. If core temperature is too low, rate of metabolism is increased, generating more heat, which is transferred to the blood
41
How do skeletal muscles respond to maintain constant body temperature?
If core temperature is too low, spontaneous contractions generate heat as muscle cells respire more
42
What behavioural mechanisms do endotherms have if their core temperature is too hot?
* move into shade or hide in burrow
* orientate body to decrease surface area exposed to sun
* remain inactive and spread out limbs to increase surface area
43
What behavioural mechanisms do endotherms have if their core temperature is too cold?
* Move into sunlight
* orientate body to increase surface area exposed to sun
* move about to generate heat in muscles (except in extreme cold, when it's better to roll into a ball to decrease surface area)
44
Where do endotherms monitor the temperature of their blood?
The thermoregulatory centre in the hypothalamus
45
How do peripheral temperature receptors in the skin help maintain body temperature?
They provide an early warning to the hypothalamus; if the extremities start to cool down or warm up it is an indication that core body temperature may soon change, so the brain can initiate behavioural mechanisms for maintaining body temperature, preventing too much variation.
46
What are sensory receptors?
Specialised cells that can detect changes in our surroundings. They are energy transducers that convert one form of energy to another.
47
What proteins does a neurone have in it's cell surface membrane?
Gated channel proteins specific to either sodium or potassium
Proteins that actively transport 3 sodium ions out of the cell for every 2 potassium ions they transport in (sodium/potassium ion pumps).
48
What is a polarised membrane?
A membrane that has a potential difference across it. This is the resting potential
49
What is depolarisation?
The loss of polarisation across the membrane. It refers to the period when sodium ions are entering the cell, making the inside less negative compared to the outside
50
How is a nerve impulse created in a neurone?
By altering the permeability of the nerve cell membrane to sodium ions, allowing sodium ions into the cell and depolarisation to occur
51
When does an action potential happen?
An action potential happens in response to a stimulus which causes sodium ions to be transported into the cell, reducing the potential difference across the membrane which causes gated sodium channel proteins to open
52
Why is an action potential called an "all-or-nothing" event?
Because if the stimulus is large enough to reach the "threshold potential" an action potential will be generated, but if not then there will be no action potential, and all action potentials are the same size.
53
What is a generator potential?
A small depolarisation caused by sodium ions entering the cell
54
What is the resting potential across the cell surface membrane of a neurone?
About -60mV
55
at resting potential what do the proteins in the cell surface membrane of the neurone do?
The gated channel proteins are closed, with the exception of a few potassium channels, which let potassium flow into the cell, down it's concentration gradient
The sodium/potassium pumps are working
56
What different types of neurones are there?
Sensory neurones
Motor neurones
Relay neurones
57
What do sensory neurones do?
Carry the action potential from a sensory receptor to the CNS
58
What do motor neurones do?
Carry an action potential from the CNS to an effector, such as a muscle or a gland
59
What do relay neurones do?
Connect sensory and motor neurones
60
What specialised features do neurone cells have?
* very long to transmit action potential over a long distance
* Cell surface membrane has many gated ion channels to control entry and exit of ions
* maintain a potential difference across their cell surface
* surrounded by a fatty sheath called the myelin sheath
* have a cell body that contains the nucleus, mitochondria and ribosomes
* sensory and motor neurones have numerous dendrites connected to other neurones
61
What is the structure of a sensory neurone?
A long dendron carrying the action potential from a sensory receptor to the cell body, which is positioned just outside the CNS. A short axon carrying the action potential into the CNS
62
What is the structure of a motor neurone?
The cell body is in the CNS, with a long axon to carry the action potential out to the effector
63
What is the myelin sheath and what is it composed of?
An insulating layer of fatty material which sodium and potassium ions cannot diffuse through, meaning that the ionic movements that create an action potential cannot occur at myelinated parts of the neurone. The myelin sheath consists of a series of Schwann cells
64
How is a resting potential of -60mV maintained in a neurone?
Sodium/potassium pumps actively transport 2 sodium ions out of the cell for every 2 potassium ions in (both types of ion are positively charged)
Some potassium channels remain open when the neurone is at rest, allowing some of the potassium ions pumped into the cell to diffuse out again
The cell cytoplasm contains large organic (negatively charged) anions
65
What causes a generator potential?
In the generator region of receptor cells the sodium gated channels are opened by energy changes in the environment, rather than by changes in voltage across the membrane
66
What does the term "threshold potential" mean?
Threshold potential is the potential difference across the membrane at which an action potential will be triggered (about -50mV). If the depolarisation of the membrane by the generator potential does not reach the threshold potential, no action potential will be created.
67
What are voltage gated channels?
Channels in the cell membrane that allow the passage of charged particles or ions. They have a mechanism called a gate, which can open or close the channel. In these channels the gates respond to changes in the potential difference across the membrane
68
What is an action potential?
The action potential is a depolarisation of the cell membrane so that the inside is more positive than the outside, with a potential difference of +40mV. This can be transmitted along the axon or dendron plasma membrane
69
What is the resting state of a neurone membrane?
Polarised, with the inside of the cell being -60mV compared to the outside
70
What happens when the potential difference across the cell surface membrane of a neurone reaches +40mV during an action potential?
The inside of the cell is positive compared to the outside. The sodium ion channels close and potassium ion channels open. Potassium ions diffuse out of the cell, bringing the polarisation back to negative inside compared with out. This is called repolarisation. The potential difference overshoots slightly, making it hyperpolarised.
71
Why can an action potential only travel along a neurone in one direction?
Because after repolarisation has occurred there is a refractory period, during which it is impossible to stimulate another action potential in the same part of the membrane, as the sodium and potassium ions are in the wrong places, and must be restored by the action of the sodium/potassium ion pumps.
72
What are local currents?
The movements of ions along the neurone. The flow of ions is caused by an increase in concentration at one point, which causes diffusion away from the region of higher concentration
73
How does an action potential move along a neurone?
When an action potential occurs, the increase in concentration of sodium ions at the point where sodium channels have opened creates a concentration gradient along the neurone, and sodium ions diffuse along, reducing the potential difference across the membrane further down the neurone and causing more action potentials
74
What are gaps in the myelin sheath called?
Nodes of Ranvier
75
Why can action potentials only occur at the nodes of Ranvier in myelinated neurones?
Because sodium and potassium ions cannot diffuse through the myelin sheath, so the ionic movements that create an action potential cannot happen unless there is a gap in the myelin sheath.
76
Why is transmission so much faster in myelinated neurones than unmyelinated neurones?
Because the local currents are elongated and sodium ions diffuse along the neurone from one node of Ranvier to the next, with action potentials occurring much less frequently, and appearing to jump from one node to the next. This is called saltatory conduction
77
What is saltatory conduction?
Saltatory conduction means 'jumping conduction'. It refers to the way that the action potential appears to jump from one node of Ranvier to the next.
78
How fast can a myelinated neurone conduct an action potential?
Up to 120m/s
79
What is a neurotransmitter?
A chemical that diffuses across the cleft of the synapse to transmit a signal to the postsynaptic neurone
80
What is a cholinergic synapse?
A synapse which uses acetylcholine as it's transmitter substance
81
What is a synaptic knob?
A swelling at the end of the presynaptic neurone
82
What is a synapse?
A junction between two or more neurones, where one neurone can communicate with, or signal to, another.
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What is the gap between two neurones called and how big is it?
The synaptic cleft, approximately 20nm wide
84
How is the synaptic knob specialised to perform its job?
It contains:
•many mitochondria, producing ATP
•a large amount of smooth endoplasmic reticulum
•vesicles containing acetylcholine, the neurotransmitter.
•voltage gated calcium ion channels in the membrane
85
How is the postsynaptic membrane specialised?
It contains specialised sodium ion channels that can respond to the presence of acetylcholine
86
How does the synaptic knob respond to the arrival of an action potential?
Voltage gated calcium ion channels open and calcium ions diffuse into the synaptic knob, causing the synaptic vesicles to move and fuse with the presynaptic membrane. Acetylcholine is released by exocytosis
87
What happens when acetylcholine is released into the synaptic cleft?
It diffuses across the cleft and binds to receptor sites on the sodium ion channels in the postsynaptic membrane, causing the channels to open, and sodium ions to diffuse into the postsynaptic neurone, creating a generator potential and, if large enough, an action potential
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What is acetylcholinesterase?
An enzyme in the synaptic cleft which breaks down the neurotransmitter acetylcholine
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What does acetylcholinesterase do?
It breaks down acetylcholine to acetate and choline, stopping the transmission of signals so that the synapse does not continue to produce action potentials in the postsynaptic neurone. The acetate and choline diffuse back into the synaptic knob and are recombined to acetylcholine using ATP
90
What is summation?
Summation is a term that refers to the way that several small potential changes can combine to produce one larger change in potential difference across the membrane
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Why do several presynaptic neurones sometimes converge to one postsynaptic neurone?
To allow signals from different parts of the nervous system to create the same response. This could be useful where several different stimuli are warning us of danger
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Why might one presynaptic neurone diverge to several postsynaptic neurones?
This would allow one signal to be transmitted to several parts of the nervous system. This is useful in a reflex arc. One postsynaptic neurone elicits the response while another informs the brain
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How do synapses ensure that signals are transmitted in the right direction?
Only the presynaptic knob contains vesicles of acetylcholine
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How do synapses filter out low level signals?
If a low level stimulus creates an action potential in the presynaptic neurone it is unlikely to pass across a synapse to the next neurone because several vesicles of acetylcholine must be released to create an action potential in the postsynaptic neurone
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How can low level signals be amplified by a synapse?
By the process of summation - if a low level stimulus is persistent it will generate several successive action potentials in the presynaptic neurone. The release of many vesicles of acetylcholine over a short period of time will enable the postsynaptic generator potentials to combine together to create an action potential. Summation can also occur when several presynaptic neurones each release small numbers of vesicles into one synapse
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How do synapses allow acclimatisation to background stimuli?
After repeated stimulation a synapse may run out of vesicles containing the transmitter substance. The synapse is said to be fatigued, and the nervous system no longer responds to the stimulus. This may also help avoid overstimulation of an effector, which could damage it
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The creation of specific pathways in the nervous system is thought to be...
...the basis of conscious thought and memory
98
How do neurones inform the central nervous system on the strength or intensity of a stimulus?
When the stimulus is at higher intensity the sensory receptor will produce more generator potentials, causing more frequent action potentials in the sensory neurone. When these arrive at a synapse they will cause more vesicles to be released, causing a higher frequency of action potentials in the postsynaptic neurone, which is detected by the brain
99
How is the arrangement of Schwann cells in myelinated neurones different to in non-myelinated neurones?
In myelinated neurones the Schwann cells are wrapped around the neurone, so the sheath consists of several layers of membrane and thin cytoplasm. In non-myelinated neurones the Schwann cells are only loosely wrapped, and may enshroud several neurones rather than just one
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What is the advantage of myelination?
Myelinated neurones can transmit an action potential much more quickly than non myelinated neurones can, enabling a more rapid response to a stimulus.
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What are myelinated and non myelinated neurones used for?
Myelinated neurones carry signals from sensory receptors to the CNS and from the CNS to effectors. They carry signals over long distances. Non myelinated neurones tend to be shorter and carry signals over only a short distance. They are used in coordinating body functions such as breathing and the action of the digestive system, so speed is not important
102
What are hormones?
Molecules that are released by endocrine glands directly into the blood. They act as messengers, carrying a signal from the endocrine gland to a specific target organ or tissue
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What is an endocrine gland?
A gland that secreted hormones directly into the blood. Endocrine glands have no ducts.
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What is an exocrine gland?
A gland that secretes molecules into a duct that carries the molecules to where they need to be
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What is the difference between endocrine and exocrine glands?
Endocrine glands release their secretion directly into the blood, allowing it to be transported all over the body, but exocrine glands have ducts that take their secretion to a specific place
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What is a target cell?
A cell that possesses a specific receptor on its plasma membrane, which is complementary to the shape of a specific hormone molecule
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What is adenyl cyclase?
An enzyme associated with the receptor for many hormones, including adrenaline. It is found on the inside of the cell surface membrane.
108
Why can the endocrine system be used to send signals all over the body at the same time, but also very specific signals?
Because it releases hormones directly into the blood, so they travel all over the body, but only target cells are affected, so depending on the hormone, all cells in the body could be affected or only a small group of them
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What are the two types of hormones?
Protein/peptide hormones (adrenaline, insulin etc), and steroid hormones (eg sex hormones)
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What is the difference between the two types of hormones?
Protein hormones are not soluble in the phospholipid membrane and do not enter the cell. Steroids however can pass through the membrane and enter the cell, to have a direct effect on the DNA in the nucleus
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How does adrenaline effect the action of its target cells?
It is an amino acid derivative so it is unable to enter the target cell. It therefore binds to the receptor on the outside of the cell, which is associated with an enzyme on the inner surface of the membrane called adenyl cyclase
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What does the term "first messenger" refer to?
The hormone that transmits a signal around the body
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What does the term "second messenger" refer to?
The substance (cyclic AMP) which is used to transmit a signal inside the cell
114
What does adenyl cyclase do when activated?
It converts ATP to cyclic AMP (cAMP), which can cause an effect inside the cell by activating enzyme action.
115
Where are the adrenal glands found and what is their structure?
Just above the kidneys on either side of the body. Each gland consists of a medulla region and a cortex region
116
What is the function of the adrenal medulla?
It manufactures and releases the hormone adrenaline in response to stress such as pain or shock
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What is the function of the adrenal cortex?
It uses cholesterol to produce certain steroid hormones, which have a variety of roles in the body.
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What are the effects of adrenaline?
The effects are to prepare the body for activity and include: •relaxing smooth muscle in the bronchioles •increasing stroke volume & heart rate •causing vasoconstriction to raise blood pressure •stimulate conversion of glycogen to glucose •dilate pupils •inhibit action of the gut •cause body hair to erect
119
Where is the pancreas located and why is it unusual?
It is located below the stomach and is unusual because it has both endocrine and exocrine functions
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What is the exocrine function of the pancreas?
The manufacture and release of digestive enzymes
121
What is the arrangement of the cells in the pancreas that perform its exocrine function?
The cells are found in small groups surrounding tiny tubules into which they secrete digestive enzymes. The tubules join to make the pancreatic duct, which carries the fluid containing the enzymes into the first part of the small intestine
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What are the exocrine cells in the pancreas called?
Acinar cells
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What do the enzymes carried along the pancreatic duct to the duodenum do?
They digest food in the duodenum, eg amylase breaks down starch to glucose. The fluid containing the enzymes also contains sodium hydrogen carbonate, which is alkaline and helps to neutralise the acidic contents of the digestive system
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Where can the endocrine tissues of the pancreas be found?
In areas called the islets of langerhans
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What two types of cell can be found in the islets of langerhans and what do they do?
Alpha cells manufacture and secrete the hormone glucagon
| Beta cells manufacture and secrete the hormone insulin
126
Where do the enzymes secreted by the Acinar cells in the pancreas go?
Along the pancreatic duct to a part of the small intestine called the duodenum
127
What effect does insulin have on blood glucose levels?
It causes blood glucose levels to go down
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What effect does glucagon have on blood glucose levels?
It causes blood glucose levels to rise
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Where is the concentration of blood glucose monitored from?
From the alpha and beta cells in the islets of langerhans
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What happens if blood glucose rises too high?
The high concentration is detected by the beta cells, which secrete insulin into the blood
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What are the target cells for insulin?
Hepatocytes, muscle cells, some other body cells including the brain
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What are hepatocytes?
Liver cells
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What effects does insulin have on it's target cells?
* more glucose channels are placed into the cell surface membrane
* more glucose enters the cell
* glucose in the cell is converted to glycogen for storage (glycogenesis)
* more glucose is converted to fats
* more glucose is used for respiration
134
What happens if blood glucose drops too low?
The low concentration is detected by the alpha cells, which respond by secreting the hormone glucagon
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What are the target cells of glucagon?
Hepatocytes
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What are the effects of glucagon on its target cells?
* conversion of glycogen to glucose (glycogenolysis)
* use of more fatty acids in respiration
* the production of glucose by conversion from fats and amino acids (gluconeogenesis)
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What is glycogenesis?
The conversion of glucose to glycogen
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What is glycogenolysis?
The conversion of glycogen to glucose
139
What is gluconeogenesis?
The production of glucose from fats and amino acids
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What is hypoglycaemia?
The state in which the blood glucose concentration is too low
141
What is thought to be the cause of type I diabetes?
It is thought to be the result of an autoimmune response in which the body's own immune system attacks the beta cells, meaning that the body can no longer manufacture sufficient insulin and cannot store excess glucose as glycogen
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What is diabetes mellitus?
A disease in which blood glucose concentrations cannot be controlled effectively
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What is hyperglycaemia?
The state in which blood glucose concentration is too high
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What is the difference between type I and type II diabetes?
In type I diabetes the body cannot produce insulin, in type II diabetes the body can produce insulin but may produce less of it, and the target cells can no longer respond to insulin in the blood
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What factors can lead to type II diabetes?
* old age
* a diet high in sugars
* being of Asian or Afro-Caribbean origin
* family history
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How is type I diabetes treated?
Using insulin injections; the blood glucose concentration must be monitored and the correct dose of insulin administered to ensure that the blood glucose concentration remains fairly stable
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How is type II diabetes treated?
By careful monitoring and control of diet. Care is taken to match carbohydrate intake and use. This may eventually be supplemented by insulin injections or use of other drugs which slow down the absorption of glucose from the digestive system
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How are beta cells specialised for insulin secretion?
The cell membranes contain both calcium and potassium ion channels; the potassium channels are normally open and the calcium channels are closed. There is a resting potential of about -70mV across the membrane. The cell also contains vesicles of insulin.
149
How does a high blood glucose concentration lead to insulin secretion by the beta cells?
When glucose concentrations are high, glucose diffuses into the cell and is used in metabolism to produce ATP. This ATP causes potassium channels to close, meaning that potassium can no longer diffuse out, and the potential difference becomes less negative, causing calcium ion channels to open. Calcium ions enter the cell and cause the vesicles of insulin to move towards the surface membrane, and insulin to be released by exocytosis
150
What is the source of insulin for treating type I diabetes?
It used to be extracted from animals, usually pigs, but is now produced by bacteria that have been genetically modified to produce human insulin
151
What are the advantages of using insulin from genetically modified bacteria rather than extracting it from animals?
* it is an exact copy of human insulin, so is faster acting and more effective
* there is less of a chance of developing tolerance to the insulin.
* lower risk of infection
* cheaper to manufacture than animal insulin
* people are less likely to be morally against it, as animals are not harmed
152
What does myogenic mean?
Muscle tissue that is myogenic can initiate it's own contractions
153
What is the pacemaker?
A region of tissue in the heart's right atrium wall that can generate an impulse, and initiates the contraction of the chambers
154
What is the medulla oblongata and where is it found?
It is found at the base of the brain. It is the region of the brain that coordinates the unconscious functions of the body such as breathing rate and heart rate
155
What is the cardiovascular centre?
A specific region of the medulla oblongata that recieves sensory inputs about levels of physical activity, blood carbon dioxide concentration and blood pressure. It sends nerve impulses to the SAN in the heart to alter the frequency of excitation waves
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Why does the heart need to adapt it's activities?
To meet the requirements if the cells, which vary according to their activity levels.
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How does the heart adapt to supply more oxygen and glucose to the body?
* increased heart rate
* increased strength of contractions
* increased volume of blood pumped per beat (stroke volume)
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What factors can control heart rate?
* the heart muscle is myogenic
* the heart contains it's own pacemaker, the sinoatrial node.
* the heart is supplied by nerves from the medulla oblongata of the brain, which connect to the SAN and can affect frequency of contractions
* the heart muscle responds to the presence of adrenaline in the blood
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How does the sinoatrial node (SAN) work to cause contraction of the heart?
It initiates an action potential, which travels as a wave of excitation over the atria walls, through the atrioventricular node (AVN) and down the purkyne fibres to the ventricles, causing them to contract
160
How does the medulla oblongata work to increase heart rate?
By sending an action potential down the accelerator nerve
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How does the medulla oblongata work to reduce heart rate?
By sending an action potential down the vagus nerve
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How is the heart rate controlled under resting conditions?
By the SAN, which has a set frequency varying from person to person
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What are the factors that lead to increased or decreased heart rate?
* movement of limbs
* CO2 production
* blood pH
* stress, shock, anticipation or excitement
* blood pressure
164
How does movement of limbs affect heart rate?
Movement is detected by stretch receptors in the muscles, which send impulses to the cardiovascular centre that extra oxygen may soon be needed. This leads to increased heart rate
165
How does increased CO2 production affect heart rate?
The extra carbon dioxide produced by muscles during exercise reacts with water in the blood plasma and reduces it's pH, which is detected by chemoreceptors in the carotid arteries, aorta and brain. The chemoreceptors send impulses to the cardiovascular centre, increasing heart rate.
166
How do reduced CO2 levels affect heart rate?
When we stop exercising the concentration of carbon dioxide in the blood falls. This reduces the activity of the accelerator pathway. Therefore heart rate declines
167
How does stress, shock, anticipation or excitement affect heart rate?
They cause adrenaline to be secreted from the adrenal glands, and the presence of adrenaline in the blood increases the heart rate. This helps to prepare the body for activity
168
How does blood pressure affect heart rate?
Blood pressure is monitored by stretch receptors in the walls of the carotid sinus. If blood pressure rises too high, perhaps during vigorous exercise, the stretch receptors send signals to the cardiovascular centre, which responds by increasing heart rate
169
What do stretch receptors detect?
Movement of limbs and blood pressure
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What do chemoreceptors detect?
pH levels, which are affected by CO2 production
