Module 5.1 - Communication and Homeostasis

Question 1

What is any change in the internal or external environment called?

Answer 1

A stimulus.

Question 2

What are receptors and what is their function?

Answer 2

Receptors detect stimuli and they are specific, only detect one particular stimulus. Some receptors are cells or proteins.

Question 3

What are effectors?

Answer 3

Cells that bring about the response to a stimulus, to produce an effect.

Question 4

Give some examples of effectors?

Answer 4

Muscle cells and found in glands such as the pancreas.

Question 5

Where can cell signalling, communication occur between?

Answer 5

Between adjacent cells or between distant cells.

Question 6

Define homeostasis?

Answer 6

The maintenance and regulation of a stable internal environment within narrow limits despite the environment changing.

Question 7

Why is keeping your internal environment constant important?

Answer 7

Vital for cells to keep on functioning normally and prevent them being damaged.

Question 8

What is one thing that would happen if the core body temperature increases or decreases too much?

Answer 8

It would affect enzyme activity which control the rate of metabolic reactions.

Question 9

Describe the negative feedback mechanism?

Answer 9

The effectors respond to counteract the change of certain levels being too high or too low and bring the levels back to normal.

Question 10

What is a positive feedback mechanism?

Answer 10

The effectors respond to further increase the level away from the normal level, amplifying the change. Is useful to rapidly activate something.

Question 11

Give two examples where positive feedback is useful?

Answer 11

> Blood clotting - platelets become activated releasing a chemical which triggers the activation of more platelets and so on. Platelets very quickly form a blood clot at the injury site. The process ends with negative feedback, when the body detects the blood clot has been formed.
Labour – Oxytocin is released causing contractions and cervix to stretch, resulting in more oxytocin being released.

Question 12

What do sensory neurones do?

Answer 12

Transmit nervous impulses from receptors to the CNS – brain and spinal cord.

Question 13

What do motor neurones do?

Answer 13

Transmit nervous impulses from the CNS to effectors.

Question 14

What do relay neurones do?

Answer 14

Transmit nervous impulses between sensory and motor neurones.

Question 15

What happens when a nerve impulse reaches the end of a neurone?

Answer 15

Chemicals called neurotransmitters take the information across to the next neurone, which then sends a nervous impulse.

Question 16

Describe the CNS reflex mechanism?

Answer 16

Stimulus – receptor – sensory neurone – CNS – motor neurone – effectors – response.

Question 17

Describe the differences between ectotherms and endotherms?

Answer 17

> Ectotherms can’t control their body temperature internally but endotherms control their body temp. internally by homeostasis.
Ectotherms’ internal temp. depends on the external temp. of their surroundings but endotherms internal temp. is less affected by the external temp. (in limits).
Ectotherms’ activity level depends on the external temp. (more active at high temp. and vice versa) whereas, endotherms’ activity level is largely independent of the external temp., can be active at any temp.
Ectotherms have a variable metabolic rate and generate very little heat themselves but endotherms have a high metabolic rate and generate a lot of heat from metabolic reactions.

Question 18

Give examples of an ectotherm?

Answer 18

Reptiles, fish.

Question 19

Give examples of an endotherm?

Answer 19

Mammals, birds.

Question 20

Describe the similarities between endotherms and ectotherms and give examples?

Answer 20

Both can control their temperature by changing their behaviour:
>In ectotherms, reptiles gain heat by basking in the sun.
>Endotherms cool down by finding shade.

Question 21

List a few mechanisms to reduce body temperature?

Answer 21

> Sweating
Hairs lie flat
Vasodilation

Question 22

List a few mechanisms that increase body temperature?

Answer 22

>Shivering 
>Much less sweat
>Hairs stand up/erect
>Vasoconstriction 
>Hormones

Question 23

Describe how sweating reduces body temperature?

Answer 23

More sweat is secreted from the sweat glands when the body is hot. The water in sweat evaporates from the surface of the skin and takes heat from the body. The skin is cooled.

Question 24

Describe how vasodilation reduces body temperature?

Answer 24

When it’s hot, arterioles near the surface of the skin dilate. More blood flows through the capillaries in the surface layers of the dermis. This means more heat is lost from the skin by radiation and the temperature is lowered.

Question 25

Describe how hormones can help increase body temp.?

Answer 25

The body releases adrenaline and thyroxine. These increase metabolism and so more heat is produced.

Question 26

Describe how shivering increases body temperature?

Answer 26

When it’s cold, muscles contract in spasms. This makes the body shiver and more heat is produced from increased respiration for as the muscles contract they need to respire to produce the energy to contract.

Question 27

How is body temperature maintained at a constant level in mammals?

Answer 27

By a part of the brain called the hypothalamus.

1) Receives information about temp. from thermoreceptors - which detect internal temp. (blood) and from the skin detecting external temp. (temp of skin)
2) Thermoreceptors send impulses to the hypothalamus via the sensory neurone which sends neurones along the motor neurones to effectors.
3) The effectors respond to restore the body temp. back to normal.

Question 28

What is a hormone?

Answer 28

Hormones are chemical messengers (many are proteins or peptides).

Question 29

Give 2 examples of how hormones can be stimulated?

Answer 29

> Glands can be stimulated by a change in concentration of a specific substance (sometimes another hormone).
Electrical impulses.

Question 30

Describe using adrenaline the process of hormones triggering second messengers?

Answer 30

> The hormone adrenaline is a first messenger.
It binds to specific receptors in the cell membranes of many cells.
When adrenaline binds it activates an enzyme in the membrane called adenylyl cyclase.
Activated adenylyl cyclase catalyses the production of a second messenger called cyclic AMP (cAMP) from ATP.
cAMP activates a cascade, e.g - a cascade of enzyme reactions.

Question 31

What hormones do the cortex in the adrenal glands secrete?

Answer 31

The cortex secretes steroid hormones (cortisol/aldosterone when stressed). These hormones have a role in both the short-term and the long-term responses to stress.

Question 32

What effects do the stress hormones such as cortisol have?

Answer 32

> Stimulate the breakdown of proteins and fats into glucose - increasing the amount of energy available so the brain and muscles can respond to the situation.
Increasing blood volume and pressure by increasing the uptake of sodium ions and water by the kidneys.
Suppressing the immune system.

Question 33

What hormones do the medulla in the adrenal glands secrete?

Answer 33

Catecholamine hormones (modified amino acids) - acts to make more energy available in the short term.

Question 34

How do the catecholamine hormones make more energy available in the short term?

Answer 34

> Increasing heart and breath rate
Causing cells to break down glycogen into glucose.
Constricting some blood vessels so that blood is diverted to the brain and muscles.

Question 35

What are the islets of Langerhans and where are they found?

Answer 35

The areas of the pancreas that contain endocrine tissue. They’re found in clusters around blood capillaries.

Question 36

What do the islets of Langerhans do?

Answer 36

Secrete hormones directly into the blood.

Question 37

How do the islets of langerhans help control blood glucose concentration?

Answer 37

They are made up of two types of cell:
>Alpha cells that secrete glucagon
>Beta cells secrete insulin
Glucagon and insulin act as effector to restore the blood glucose concentration to the normal level.

Question 38

Describe how insulin lowers blood glucose concentration when its too high?

Answer 38

1) Insulin binds to specific receptors on the cell membranes of liver and muscle cells.
2) Increases the permeability of cell membranes to glucose, so the cells take up more glucose.
3) Insulin also activates enzymes that convert glucose into glycogen.
4) Cells are able to store glycogen in their cytoplasm, as an energy source.
5) The process of forming glycogen from glucose is called glycogenesis.
6) Insulin also increases the rate of respiration of glucose, especially in muscle cells.

Question 39

Does glucagon raise or lower blood glucose concentration and how does it do so?

Answer 39

It raises blood glucose concentration when it’s too low.

1) Glucagon binds to specific receptors on the cell membranes of liver cells.
2) Glucagon activates enzymes that break down glycogen into glucose.
3) The process of breaking down glycogen is called glycogenolysis.
4) Glucagon also promotes the formation of glucose from fatty acids and amino acids.
5) The process of forming glucose from non-carbohydrates is called gluconeogenesis.
6) Glucagon decreases the rate of respiration of glucose in cells.

Question 40

How do beta cells secrete insulin?

Answer 40

1) When blood glucose conc. is high, more glucose enters the beta cells by facilitated diffusion.
2) More glucose in a beta cell causes the rate of respiration to increase, making more ATP.
3) The rise in ATP triggers the K+ channels in the beta cell plasma membrane to close.
4) This means K+ ions can’t get through the membrane - so they build up inside the cell.
5) This makes the inside of the beta cell less negative because there are more positively-charged potassium ions inside the cell - so the plasma membrane of the beta cell is depolarised.
6) Depolarisation triggers calcium ion channels to open, so calcium ions diffuse into the beta cell.
7) This causes the vesicles (contain insulin) to fuse with the beta plasma membrane, releasing insulin (by exocytosis).

Question 41

What causes Type 1 diabetes and why is it so dangerous?

Answer 41

Is an auto-immune disease where the body attacks and destroys the beta cells in the islets of Langerhans so they don’t produce insulin.
>After eatign, blood glucose conc. rises and remains high which can result in death if untreated.

Question 42

Give 2 ways of treating Type 1 diabetes?

Answer 42

> Insulin therapy - regular insulin injections, insulin pump.
Islet cell transplantation - receive healthy islet cells from a donor so their pancreas can produce insulin.

Question 43

What do patients with diabetes (Type 1 and 2) both have to monitor?

Answer 43

Lifestyle -
>Healthy balanced diet (carefully planned for Type 1 diabetes to manage the amount of glucose they are taking in).
>Regular exercise.
>Losing weight only for Type 2.

Question 44

Describe the onset of Type 2 diabetes?

Answer 44

Usually acquired later in life than Type 1 and often linked with obesity.

Question 45

Give some examples of medication that can be prescribed to help control blood glucose concentrations in people with Type 2 diabetes?

Answer 45

> Metmorfin - acts on liver cells to reduce the amount of glucose that they release into the blood and to increase the sensitivity of cells to insulin so more glucose can be taken up with the same amount of insulin.
Sulfonylureas - stimulate the pancreas to produce more insulin
Thiazolidinediones - Make the body more sensitive to insulin.
For some people with Type 2 diabetes these types of medication aren’t enough so need insulin therapy as well or instead of.

Question 46

Give two ways insulin can be produced for insulin therapy for people suffering with diabetes?

Answer 46

> Insulin used to be extracted from animal pancreases.

>From genetically modified (GM) bacteria.

Question 47

What are the advantages of using GM to produce insulin?

Answer 47

> Cheaper
Larger quantities can be produced.
Make human insulin which is more effective than pig/cattle insulin (for it’s slightly different) and less likely yo trigger an allergic response or be rejected by the immune system.
Ethical/religious reasons - Vegetarians etc.

Question 48

How could stem cells be used to cure diabetes?

Answer 48

> Stem cells could be grown into beta cells.
The beta cells would then be implanted into the pancreas of a person with Type 1 diabetes.
This means the person would be able to make insulin as normal.

Question 49

What are the two types of hormones?

Answer 49

> Protein and peptide hormones and derivatives of amino acids (e.g. adrenaline, glucagon).
Steroid hormones (e.g. oestrogen, testosterone).

Question 50

What is the difference between protein/peptide hormones and steroid hormones?

Answer 50

Proteins are not soluble in the phospholipid membrane and do not enter the cell. Protein hormones need to bind to the cell surface membrane and release a 2nd messenger inside the cell. Steroid hormones, however, can pass through the membrane and enter the cell and nucleus, to have a direct effect on the DNA in the nucleus.