Hormonal Communication - Module 5

What are Endocrine glands?

These secrete hormones into the blood which bind to target cells and tissues leading to a response

What is a gland

A group of cells that secrete substances?

What is a hormone?

A hormone is a chemical messenger produced by endocrine glands carried by blood

Describe endocrine communication by hormones?

Endocrine glands secrete hormones into the bloodstream, then transported in blood to target cells/tissues with complementary receptors to bring an effect

What is the structure and functions of the adrenal glands?

• The adrenal glands are located above the kidneys

• Made of adrenal cortex and adrenal medulla

• Adrenal cortex can secrete steroid hormones: glucocorticoids, mineralocorticoids, androgens, aldosterone and cortisol

• Adrenal Medulla secretes adrenaline in fight or flight situations

Describe Steroid hormones?

• Steroid hormones are lipid soluble so can diffuse through phospholipid bilayer and bind to receptor

• Then enter nucleus and act as transcription factors for gene expression

Describe Peptide hormones?

• Peptide horomes are not lipid soluble, so cannot enter via diffuion

• Instead it must bind to a complementary receptor on target cell

• This triggers the release of a second messenger inside cell which will acitvate gene expression or enzymes

What is a first messenger?

• This is the hormone whicn brings the information from endocrine gland to receptor on surface membrane

• Cannot enter cell

Describe the action of adrenaline?

1. Adrenaline 1st messenger binds to specific receptor on cell surface membrane of target cells

2. This activates a G protein which causes adenylyl cyclase to convert ATP to cAMP

3. cAMP then binds to and activates kinase which causes a series of enzyme - controlled reactions

4. breaking down glycogen to glucose glycogenolysis

How does nervous system differ from Endocrine system

• Releases messages from nerves vs glands

• Electrical impulse vs chemical hormone

• Transmitted across nerves vs in bloodstream

• Effectors are muscles/glands vs target cells/tissues

• Speed of transmission is very fast vs slower

• Length of effect short vs longer

what is the difference between endocrine and exocrine glands?

• Endocrine glands secrete hormones directly into bloodstream.

• Whereas exocrine glands release secretions via duct going to specific location

What is the exocrine function of the pancreas?

• To produce pancreatic juice with digestive enzymes to be delivered to small intestine via ducts to aid digestion

What is the endocrine function of the pancreas?

To produce the hormones glucagon and insulin

What is the section of the pancreas involved in endocrine function called?

The islets of Langerhans - producing hormones

What type of cells are contained in the islets of Langerhands and what do they do?

The islets of Langerhans contain beta cells which secrete insulin and alpha cells which secrete glucagon

What is histology?

The branch of biology which studies microscopic anatmony of tissues

How can glucose enter the blood stream

• Absorbed from digested carbohydrates

• Hydrolysed from Glycogen stores

• Non - carbohydrates converted to glucose

Which hormones regulate blood glucose conc?

• Inuslin

• Glucagon

What happens following a decrease in blood glucose conc below optimum?

1. This decrease is detected by alpha and beta cells

2. Alpha cells secrete glucagon and beta cells stop secreting insulin

3. Glucagon binds to receptors in cell surface membrane of liver cells

4. This causes conformational change in receptor activating G protein

5. G protein acitvates adenylyl cyclase which converts ATP to cAMP

6. cAMP binds to kinase activating it

7. Kinase causing a series of enzyme controlled reactions - catalysing glycogenolysis

8. Adrenaline is also relased binding to different receptors - causing same cascade

What happens following an increase in blood glucose conc above optimum?

1. This increaase is detected by alpha and beta cells

2. Glucose molecules move into beta cells via faccilitated diffusion

3. This causes cells to respire and release ATP

4. High conc of ATP cause potassium channels in beta cells to close chaning membrane potential

5. This causes voltage gate calcium channels to open causing an influx of calcium ions

6. These calcium ions causes insulin in beta cells to move towards cell surface membrane and fuse releasing insulin into bloodstream by exocytosis

Action of insulin

1. Insulin binds to specific receptors on target (muscle) cells to add more glucose transport protein on their cell surface

2. Release of insulin makes liver more permeable to glucose

3. Insulin stimulates glycogenesis in liver decreasing conc of glucose

4. Steep diffusion graident between blood and liver causes glucose to diffuse into liver

Descirbe negative feedback loop for blood glucose conc?

• Receptors (alpha/beta cells) detect if blood glucose conc is too low or high

• Information is communicated release insulin if too high glucagon if too low

• Recieved by effectors (liver cells and muscle cells) bring a repsonse

What is glycogenesis?

• This is when Glycogen molecules are made from glucose molecules

• After insulin is released

What is glycogenolysis?

• This is the hydrolysis of glycogen into glucose

• After glucagon is released

What is gluconeogenesis?

• This is the formation of glucose from non carbohydrate based molcules lipids/proteins

• After glucagon is released

What is diabetes?

This is a condition where the insulin function in the body is disrupted leading to spontaneous glucose conc rise and fall

What is Type 1 diabetes and how is it treated?

• Pancreas fails to create enough insulin

• Normally caused young age - autoimmune response attacking β cells

• High blood pressure - osmosis

• Insulin injections used for treatment

What is type 2 diabetes?

• Receptors have reduced sensitivty to insulin - reduced glucose uptake

• High blood glucose conc and insulin overproduced

• High blood pressure - osmosis

• More common and develops in older

• Treatment low carbohydrate diet + exercise

What are the potential treatments for diabetes?

• Producing insulin by genetically modifying bacteria with human insulin gene - extract

• Stem cells differntiate into pancreatic β cells - to create insulin