MODULE 5 SECTION 1 - COMMUNICATION AND HOMEOSTASIS (THIS DECK ONLY INCLUDES HORMONAL COMMUNICATION)

Question 1

What is the hormonal system?

Answer 1

• Hormonal system sends information as chemical signals.
• consists of glands and hormones
• Endocrine glands are specialised groups of cells that secrete hormones directly into the bloodstream.
• Hormones are chemical messengers, and some are proteins and peptides, some are steroids.
• Steroidal hormones can pass directly through the cell surface membrane of a cell and have a direct effect on the cell.
• Peptide hormones bind to specific complementary receptors on the cell surface membranes of target cells and induce a response inside the target cells.

Question 2

When and how are hormones secreted?

Answer 2

Hormones are secreted when endocrine glands are stimualted.

Glands are stimulated by:

• Change in concentration of a specific substance.
• Electrical impulses.

Question 3

How are hormones communicated around the body?

Answer 3

• When secreted, hormones directly diffuse into the blood and are taken around the body by the circulatory system.
• They diffuse out of blood all over body, but each hormone will only bind to specific complementary receptors found on the cell surface membranes of target cells.
• Target tissue: tissue containing target cells.
• When hormones bind to the specific complementary receptors on target cells, they induce/trigger a response in the target cells.

Question 4

Pathway of hormonal communication

Answer 4

Stimulus, receptors, hormone, effectors, response.

E.g increasing blood concentration when it is low:

• Stimulus: low blood glucose concentration.
• Receptors: Receptors on alpha cells in the pancreas detect the low blood glucose concentration.
• Hormone: Alpha cells produce and secrete glucagon into the bloodstream.
• Effector: Glucagon binds to specific complementary receptors on liver cells.
• Response: Liver cells convert glycogen into glucose. Glucose is released into the bloodstream; blood glucose concentration increases to normal levels.

Question 5

Action of hormones

Answer 5

• Hormone is a first messenger, as it carries a chemical message the first part of the way, from endocrine gland to receptor on target cell.
• When it binds, it activates an enzyme in the cell surface membrane.
• Enzyme catalyses production of signalling molecule.
• Signalling molecule is the second messenger as it carries the chemcal message the second part of the way, from receptor to other parts of the cell.
• Signalling molecules activate a cascade of reactions inside the cell
• A cascade is a chain of reactions.

Question 6

Action of the hormone adrenaline

Answer 6

Adrenaline is a hormone secreted by the arenal medulla. Secreted when there is low glucose concentration in blood, when you are stressed, when you exercise.
Adrenaline gets the body ready for action by making more glucose available for muscles to use to respire, such as by activating glycogenolysis.

• Adrenline is a first messenger. It binds to specific complementary receptors on cell surface membrane of many cells such as liver cells.
• This binding activates an enzyme called adenyl cyclase (found in the cell surface membrane).
• Activated adenyl cyclase catalyses the production of cAMP from ATP. cAMP is the secondary messenger.
• cAMP activates a cascade of enzyme reactions inside the cell; more glucose becomes available to the cell by catalysing the breakdown of glycogen into glucose (glycogenolysis).

Question 7

Adrenal glands

Answer 7

• An example of endocrine glands found just above the kidneys.
• Outer part called cortex, inner part called medulla.
• Cortex and medulla have different functions and hormones secreted by them induce different responses.
• E.g, they have different roles in our responses to stress - ‘fight or flight’ response.

Adrenal cortex:

• Outer part of the adrenal glands.
• Produces and secretes steroid hormones such as cortisol and aldosterone when stressed. These hormones have roles in both short-term and long-term responses to stress.
• Effects include:
• stimulating breakdown of proteins and fats into glucose. (Increases glucose available for brain and muscles to use).
• They increase blood volume and pressure by increasing uptake of sodium ions and water by kidneys.
• Suppressing the immune system.

Adrenal medulla:

• Inner part of the adrenal glands.
• Secretes adrenaline and noradrenlaine when stressed.
• These hormones have roles in short-term responses to stress:
• increasing heart and breathing rate.
• stimulating cells to break down glycogen to glucose.
• constricting blood vessels going to the skin and gut to divert and increase bloodflow to the brain and muscles.

Question 8

Structure of the pancreas

Answer 8

• Islets of Langerhans are the endocrine tissue found in the pancreas.
• Found in clusters around blood capillaries.
• They produce and secrete hormones directly into the bloodstream.

Two types of cells are present in the Islets of Langerhans (endocrine tissue):

• alpha cells: they produce and secrete glucagon directly into the bloodstream.
• beta cells: they produce and secrete insulin directly into the bloodstream.

These two hormones are involved in controlling blood glucose concentration.

Under a light microscope:

• alpha cells appear as pink stained cells.
• beta cells appear as purple stained cells.
• The alpha and beta cells can only be differentiated if a special stain is used to make them appear as different colours.

Question 9

Blood glucose concentration

Answer 9

• blood glucose concentration must be carefully controlled.
• controlled by cells in the pancreas.
• Blood glucose concentration increases after eating food containing carbohydrates.
• Blood glucose concentration falls after exercise, due to more glucose being used in respiration to release energy.

Question 10

Hormonal control of blood glucose concentration

Answer 10

• Blood glucose concentration is controlled by the hormonal system.
• Controlled by hormones insulin and glucagon.
• The endocrine tissue in the pancreas is called Islets of Langerhans, and they contain beta and alpha cells.
• Insulin is produced and secreted into bloodstream by beta cells.
• Glucagon is produced and secreted into bloodstream by alpha cells.

Question 11

Insulin

Answer 11

• Lowers blood glucose concentration when it is too high.

It does this by:

• Insulin binds to specific complementary receptors on cell surface membranes of liver cells and muscle cells, and increase the permeability of cell membranes to glucose, so that the cells take up more glucose.
• Insulin increases rate of respiration of glucose especially in muscle cells.
• Insulin also activates enzymes that convert glucose to glycogen. Glycogen stores are located in liver cells and muscle cells.
• Process of forming glycogen from glucose is called glycogensis.

Question 12

Glucagon

Answer 12

• Increases blood glucose concentration when it is too low.

It does this by:

• glucagon binds to specific complementary receptors on cell surface membranes of liver cells.
• activates enzymes to break down glycogen (stores) to glucose. This process is called glycogenolysis.
• Glucagon also promotes formation of glucose from glycerol and amino acids. Process of forming glucose from non-carbohydrate molecules is called gluconeogensis.
• Glucagon decreases rate of respiration of glucose in cells.

Question 13

glycogenesis

Answer 13

the conversion of glucose to glycogen, activated by insulin.

Question 14

glycogenolysis

Answer 14

the conversion of glycogen to glucose, activated by glucagon.

Question 15

gluconeogenesis

Answer 15

the conversion of fatty acids or amino acids to glucose, activated by glucagon.

Question 16

Negative feedback mechanisms and glucose concentrations - Rise in blood glucose concentration

Answer 16

• Pancreas detects high blood glucose concentration.
• Beta cells secrete insulin, alpha cells stop secreting glucagon.
• Insulin binds to specific complementary receptors on cell surface membrane of liver cells and muscle cells.
• The liver and muscle cells respond: insulin activates glycogenesis.
• Blood glucose concentration decreases and returns to normal levels.

Simplified version:

• rise in blood glucose concentration
• pancreas detects change
• beta cells secrete insulin, alpha cells stop secreting glucagon.
• liver cells and muscle cells respond by: glycogensis is activated, cells take up more glucose, cells respire more glucose.

This is a negative feedback mechanism.

Question 17

Negative feedback mechanisms and glucose concentrations - fall in blood glucose concentration.

Answer 17

• Pancreas detects low blood glucose concentration.
• Beta cells stop secreting insulin, alpha cells secrete glucagon.
• Glucagon binds to specific complementary receptors on cell surface membranes of liver cells.
• Liver cells respond: glucagon activates glycogenolysis and gluconeogenesis.
• Blood glucose concentration increases and returns back to normal.

Simplified version:

• fall in blood glucose concentration
• pancreas detects change
• alpha cells secrete glucagon, beta cells stop secreting insulin.
• liver cells respond by: glycogenolysis is activated, gluconeogenesis is activated, cells respire less glucose.

This is a negative feedback mechanism.

Question 18

What cells are involved when insulin or glucagon is secreted?

Answer 18

Insulin secreted - liver cells and muscle cells.

Glucagon scereted - liver cells.

Question 19

Beta cells structure in more detail

Answer 19

• They contain insulin stored in vesicles.
• K+ ion channels and Ca2+ ion channels in their membrane.

When blood glucose concentration is normal or lower:

• K+ channels open, Ca2+ channels closed.
• K+ diffuses out of cell through open K+ channels.
• This makes the inside of the cell membrane more negatively charged than outside, because outside contains more +ve ions than inside.
• Basically, membrane is polarised (as the inside is negatively charged).

Question 20

Insulin secretion in response to high blood glucose concentration in the beta cells steps

Answer 20

High blood glucose concentration is detected by beta cells:

• More glucose enters beta cells by facilitated diffusion.
• This increases production of ATP as more glucose increases rate of respiration in mitochondria.

Potassium ion channels close:

• Increase in ATP causes K+ ion channels in the beta cell cell surface membrane to close.
• This causes a build up of K+ inside the cell as they can no longer diffuse out of the cell.
• This makes the inside of the beta cell less negative (more positive) due to build up of positively charged K+ ions.
• Cell surface membrane of beta cell is depolarised.

Calcium ion channels open:

• Depolarisation of plasma membrane causes voltage-gated Ca2+ ion channels to open.
• Ca2+ ions diffuse into the beta cell.
• Influx of Ca2+ causes vesicles containing insulin to move to and fuse with the beta cell plasma membrane.
• Insulin is released by exocytosis.

Question 21

How is a beta cell (in pancreas) similar to a sensory receptor?

Answer 21

Membrane is polarised when at rest.

Question 22

What is another name for liver cells?

Answer 22

hepatocytes.

Question 23

What is diabetes mellitus?

Answer 23

Diabetes mellitus is a condition where blood glucose concentration cannot be controlled properly.

Two types:

• type 1
• type 2

Question 24

Type 1 diabetes

Answer 24

• It is an autoimmune disease.
• Immune system attacks and destorys beta cells in Islets of Langerhans, meaning that insulin cannot be produced.
• After eating, blood glucose concentration will increase and will remain high, which could result in death if left untreated.
• Kidney’s cannot reabsorb all of the glucose, so some glucose is excreted into the urine.
• Usually develops in children and young adults.
• Risk of developing it is slightly increased if there is family history of the disease.

Treatment options:

• Insulin therapy.
• Invovles regular insulin injections throughout the day.
• Also could involve using an insulin pump - A device that continuously delivers insulin into the body.

Other treament options:
- Islet cell transplantation: receiving healthy islet cells from a donor so their pancreas can produce some insulin, although they usually still require additional insulin therapy.

• Type 1 diabetes patients need to regularly monitor their blood glucose concentration and carefully control their diet and level of activity.
• Eating a healthy balanced diet reduces the amount of insulin that needs to be injected.
• Doing regular exercise also reduces amount of insulin that needs to be injected, becase more glucose will be used for respiration in periods of exercise.

Question 25

What is an autoimmune disease?

Answer 25

A disease resulting from the immune system launching an immune response against an organism’s own tissues.

Question 26

Type 2 diabetes

Answer 26

• Occurs when the beta cells do not produce enough insulin, or when the body cells do not respond properly to insulin.

Why do the cells not respond properly to insulin?

• insulin receptors on the cell surface membrane of body cells do not work properly, so cells do not take up enough glucose.
• Results in higher blood glucose concentrations than normal.
• Usually develops in older people, and is often linked with obesity.
• Risk of developing type 2 diabetes is increased in people of certain ethnic groups (african, asian), and in people with family history of the disease.

Treatment options:

• usually managed through lifestyle changes.
• Eating a healthy, balanced diet
• regular exercise
• lose weight.

If blood glucose concentration cannot be controlled by lifestyle changes alone, medication can be prescribed:

• drugs that act on liver cells to reduce amount of glucose released into the blood. Same drug also acts to increase sensitivity of body cells to insulin, so that glucose uptake by cells increases with the same amount of insulin.
• drugs that stimulate the pancreas to produce and secrete more insulin.
• There are other drugs that also increase sensitivity of body cells to insulin.

In some type 2 diabetes patients, the medications are not enough to control blood glucose concentration.
- Insulin therapy is used in addition to the medication, or it is used instead of the medication.

Question 27

Insulin from GM (genetically modified) bacteria

Answer 27

• Animal insulin used to be extracted from animal pancreases, but nowadays, human insulin can be made by genetically modified bacteria.

Why is GM bacteria better than animal pancreases to produce get insulin?

• Cheaper
• Large quantities of human insulin can be produced using GM bacteria.
• GM bacteria makes HUMAN insulin. More effective than using pig / cattle insulin. Human insulin produced by GM bacteria less likely to trigger allergic response, or be rejected by immune system.
• Some people prefer insulin from GM bacteria for ethical or religious reasons. E.g vegetarians may object the use of animals, some religious people may object use of insulin from pigs.

Question 28

Curing diabetes

Answer 28

• Stem cells could potentially cure diabetes.
• They could be grown into beta cells and implanted into the pancreas of a type 1 diabetes patient.
• This results in the person producing insulin as normal.
• This treatment method is still undergoing development.
• If stem cell treatment is effective, it will cure people with type 1 diabetes - they will no longer need insulin therapy.