Hormonal Communication

Question 1

What is the purpose of the endocrine system

Answer 1

Communication around the body
- Hormones travel round the circulatory system to target cells

Question 2

2 types of hormone

Answer 2

• protein/peptide hormone
  E.g. adrenaline, insulin, ADH
• steroid hormone
  E.g. oestrogen, testosterone

Question 3

Protein hormones

Answer 3

• not soluble through the phospholipid bilayer
• They bind to receptors on the cell surface membrane and release a second messenger inside the cell

Question 4

Steroid hormones

Answer 4

• Steroid hormones can pass through the membrane, enter the cell and the nucleus
• They have a direct effect on the DNA in the nucleus.

Question 5

When are hormones secreted

Answer 5

When the gland is stimulated
- this can be done by a change in concentration or stimulated by electrical impulses

Question 6

2 types of gland

Answer 6

Endocrine and exocrine

Question 7

Endocrine gland

Answer 7

Are a group of cells that release a hormone directly into the blood
E.g. thyroid, adrenal, pancreas, pituitary

Question 8

Exocrine gland

Answer 8

Are a group of cells which surround a duct and secrete their hormones into this
E.g. salivary glands, liver (bile)

Question 9

The pancreas contains endocrine glands and contains cells that produce digestive enzymes. Why are the cells that produce digestive enzymes described as exocrine?

Answer 9

Because digestive enzymes are released into ducts

Question 10

Pathway from stimulus to respomse

Answer 10

Stimulus —> receptors —> hormone —> effectors —> response

Question 11

First messengers

Answer 11

Non steroid hormones
- signalling molecules that bind to receptors (glycoproteins) on the cell surface membranes and initiate an effect
- usually cause the release of another signalling molecule (second messenger)

Question 12

Second messenger

Answer 12

Stimulates a change in the activity of the cell

Question 13

What is a G protein

Answer 13

Activated when the hormone binds to the receptor
- the G protein

Question 14

Example: adrenaline

Answer 14

1. Adrenaline is a first messenger.
2. It binds to specific receptors on the plasma cell membrane of many cells e.g. hepatocytes
3. When adrenaline binds it activates an enzyme in the membrane called adenylyl cyclase.
4. Activated adenylyl cyclase catalyses the production of a second messenger called cyclic AMP (cAMP) from ATP.
5. cAMP activates a cascade eg: a cascade of enzyme reactions to make more glucose available to the cell by catalysing the breakdown of glycogen into glucose

Question 15

Adrenaline

Answer 15

• produced in medulla of adrenal gland
• peptide hormone / non steroid hormone

Question 16

Structure of adrenal gland

Answer 16

Cortex (broken into 2 sections)
Medulla
Blood vessels

Question 17

Effects of adrenaline / noradrenaline

Answer 17

• increase HR
• increase blood flow
• increase blood pressure
• Glycogenolysis (glycogen broken down into glucose)
• dilating of pupils

Question 18

Aldosterone (mineralocorticoids)

Answer 18

• produced in cortex (outermost layer)
• steroid hormone
  Role:
• sodium and potassium ions reabsorption in kidneys
• control of blood pressure

Question 19

Cortisol (glucocorticoids)

Answer 19

• produced in cortex (middle layer)
• steroid hormone
  Roles:
• regulating metabolism of carbohydrates, fats and proteins
• released in response to stress and as a result of low BGL

Question 20

How do steroid hormones work

Answer 20

• Passes through the cell surface membrane of the target cell.
• Binds with a receptor in the cytoplasm.
• The receptor-steroid hormone complex enters the nucleus of the target cells and binds to a receptor on the chromosomal material.
• This binding stimulates the production of mRNA which code for the production of proteins

Question 21

Androgens

Answer 21

Regulation of sexual characteristics and cell growth

Question 22

Pancreas

Answer 22

• endocrine tissue in the pancreas is called islets of Langerhans
• they are found in cluster around capillaries
• made up of 2 types of cell: alpha cells and **beta cells*

Question 23

What do alpha cells secrete

Answer 23

GLUCAGON

Question 24

What do beta cells secrete

Answer 24

INSULIN

Question 25

What do ducts always have on a micrograph

Answer 25

White space around it

Question 26

What do electron micrographs of pancreas cells look like

Answer 26

Islets of Langerhans- largest circle, very pale pink/white Ducts always have white space around it Alpha cells are pink Beta cells are purple *acini are also visible and are just pancreatic cells*

Question 27

What is diabetes

Answer 27

A condition in which the homeostatic control of blood glucose has failed / deteriorated

Question 28

What happens to the kidneys when someone has diabetes

Answer 28

- their insulin function is disrupted which allows the glucose concentration in the blood to rise - the kidneys are unable to filter out this excess glucose in the blood and so it often **appears in the urine** - the increased glucose conc also causes the kidneys to produce large quantities of urine, making the individual feel thirsty due to dehydratiom

Question 29

What are the 2 types of diabetes

Answer 29

Type I and Type II

Question 30

Type I diabetes

Answer 30

- begins in childhood due to an **autoimmune response** where the body’s immune system (T cells) attacks the **beta cells* of the islets of Langerhans in the pancreas - the pancreas fails to produce sufficient insulin to control BGL - the lack of insulin also affects glycogen stores which results in an individual feeling fatigued - may experience a ‘hypo’- if BGC reaches a dangerously high level after a meal, organ damage can occur

Question 31

Type II diabetes

Answer 31

- more common than type I - usually develops in this 40+ - pancreas still produces insulin, but receptors have reduced in numbers or no longer respond to it. This reduced sensitivity to insulin occurs in the liver and fat storage tissues - lack of response to insulin means there is a reduced glucose uptake which leads to an uncontrolled high blood glucose concentration. This can cause the B cells to produce larger amounts of insulin which ultimately damages them

Question 32

Risk factors for type II diabetes

Answer 32

- obesity - physical inactivity - high BP - high blood cholesterol - genetics - specific ethnic groups are more likely to develop the condition

Question 33

Diabetes and blood pressure

Answer 33

- individuals with poorly controlled diabetes often suffer from high blood pressure - the high blood glucose concentration lowers WP of the blood which causes more water to move from the tissues into the blood vessels by osmosis - as a result, there is a larger volume of blood within the circulatory system which causes BP to increase

Question 34

Which of the following is not an endocrine gland or does not contain endocrine tissue: A- gall bladder B- ovaries C- pancreas D- pituitary

Answer 34

A- gall bladder

Question 35

3 ways glucose can enter the bloodstream

Answer 35

1. Absorption in the gut following carbohydrate digestion 2. Hydrolysis of glycogen stores 3. Lipids/lactate and amino acids converted into glucose

Question 36

2 hormones which help regulate BGL

Answer 36

Insulin and glucagon

Question 37

What do alpha and beta cells act as

Answer 37

Receptors - detect level of blood glucose *not receptors on cell surface membrane*

Question 38

What happens when BGL are too low

Answer 38

1. Alpha cells secrete glucagon, beta cells stop secreting insulin 2. Glucagon binds to receptors in the cell surface membranes of liver cells 3. This binding causes a conformational change in the receptor protein that activated a G protein 4. This activated G protein activated the enzyme **adenylyl cyclase** 5. Active adenylyl cyclase catalyses the conversion of ATP to cAMP (second messenger) 6. cAMP binds to Protein Kinase A enzymes, activating them, leading to an **enzyme cascade** resulting in the breakdown of glycogen to glucose

Question 39

BGL too low (simplified)

Answer 39

1. Glucagon binds to liver cells membrane receptors 2. G protein is activated 3. Adenylyl cyclase converts ATP to cAMP 4. cAMP initiates enzyme cascade

Question 40

BGL too high

Answer 40

1. High BGL detected by beta cells in the pancreas 2. Glucose molecules enter B cells by facilitated diffusion 3. Cells respire the glucose and produce ATP 4. High concentration of ATP causes K⁺ channels in the B cells to close, causing a change in membrane potential 5. Causes voltage gated Ca⁺ channels to open 6. Increase in calcium ions causes B cells to secrete insulin 7. Insulin containing vesicles move to cell surface membrane and release insulin into the capillaries by exocytosis 8. Insulin (hormone) enters the blood stream and circulates around the body 9. BGL returns to normal

Question 41

Action of insulin

Answer 41

Target cells: muscle cells, fat storage cells, adipose tissue and liver cells - They have glucose transporter proteins in their surface membranes - These membrane proteins allow for the uptake of glucose molecules via facilitated diffusion - The rate of glucose uptake for these cells is limited by the number of glucose transporter proteins present - Insulin binds to specific receptors on the membranes of target cells, which stimulates them to activate/add more glucose transporter proteins to their cell surface membrane which increases the permeability of the cells to glucose.

Question 42

Role of the liver

Answer 42

- plays a vital role converting glycogen to glucose - both insulin and glucagon have specific receptors on the membranes of hepatocytes

Question 43

Insulin and glucagon result in different responses:

Answer 43

**Glycogenesis** synthesis of glycogen from glucose **Glycogenolysis**the breakdown of glycogen to glucose **Gluconeogenesis** synthesis if glucose from non carbohydrate molecules

Question 44

What does insulin trigger

Answer 44

Glycogenesis (Glycogen to glucose)

Question 45

What does glucagon trigger

Answer 45

**Glycogenolysis** (Breakdown of glycogen to glucose) **Gluconeogenesis** (Synthesis of glucose from non-carbohydrate molecules)

Question 46

What is the function of acini

Answer 46

Secrete digestive enzymes

Question 47

Type 1 diabetes

Answer 47

- get from early childhood - pancreas doesn’t produce insulin - no cure - must inject insulin - autoimmune response ee

Question 48

Type 2 diabetes

Answer 48

- get later in life - both environmental and genetic - cells become resistant to insulin - diet and exercise to help control - physical inactivity and obesity are risk factors

Question 49

Type 2 diabetes treatments

Answer 49

Lifestyle changes: 1. Regular exercise 2. Losing weight 3. Healthy diet with less sugary food Medications: - metformin- reduces amount of glucose that liver cells release, increases cell sensitivity to insulin - sulfonylureas- stimulates the pancreas to produce more insulin

Question 50

Type 1 diabetes treatments: past

Answer 50

Insulin therapy: inject with insulin 4-6 times per day _advantages_ - tried and tested method - effective way of lowering BGL- early treatment kept people alive _disadvantages_ - expensive to produce - doesn’t produce a lot - needs to be purified - risk of rejection since pig insulin is different to human insulin - ethical concerns

Question 51

Type 1 diabetes treatments: Present

Answer 51

• Insulin injections, monitor BGL levels (made by GM bacteria) • insulin pump therapy- a small device constantly pumps insulin into the bloodstream through a needle that is permanently inserted under the skin • Islet cell transplantation- healthy beta cells from the pancreas of a donor are implanted into the pancreas of the person with diabetes • Complete pancreas transplant _Advantages_ - faster to produce - larger quantities produced - less likely to trigger allergic response or be rejected - fewer ethical concerns - cheaper to produce _disadvantages: transplant_ - not enough donors to keep up with demand - donor must be dead - risk of rejection - risks of surgery and infection

Question 52

Type 1 diabetes treatments: future

Answer 52

Stem cells to grow new islets of Langerhans in the pancreas Immunotherapy- treatment aims to stop the immune system from attacking the body’s own insulin producing cells Stem cell therapy: involves using stem cells to create insulin producing cells that can be transplanted into patients _Advantages_ - improved quality of life - no need for injections daily - reduce risk of hypos _disadvantages_ - immunosuppression - lack of available donors - ethical issues with stem cells - high cost