Endocrine system

What are the functions of the endocrine system?

• Regulate long term growth

• Regulate development

• Regulate reproduction

What are hormones?

Chemical messengers which travel in the blood stream used by the endocrine system

How is an endocrine gland structured?

• Ductless gland made of endocrine cells

• Have good blood supply

• Secrete hormones into the blood stream

How do hormones work?

• They bind to the receptors (binding sites) in the target cells (cells with receptors)

• This stimulates gene expression or protein synthesis to control physiological functions

What is a hormone receptor?

Protein located in or on a cell surface which binds to a specific hormone

What is the target cell?

A cell with a binding site containing a hormone receptor

What are anabolic steroid hormones?

Hormones which have receptors in muscles which stimulate muscle protein production

What are the 3 hormone types?

• Amino acid derivative

• Peptide derivative

• Lipid derivative

What are amino acid derivative hormones?

Small molecules, similar structure to amino acids

What are peptide derivative hormones?

Consists of a chain of amino acids, the largest hormone

What are lipid derivative hormones?

Fat soluble hormones

Which types of hormones are lipid soluble?

Thyroid and steroid hormones

What is the dissolvability of lipid hormones?

Good for cell membranes, bad for bloodstream

What is the dissolvability of water hormones?

Good for bloodstream, bad for cell membrane

What location can hormone receptors be?

• Cell membrane = This triggers G proteins on the cell membrane surface. This then activates second messengers within the cell, which alters the cell activity

• Inside the cell = includes all receptors for thyroid and steroid hormones

How does hormonal action through cell membrane receptors work?

1. Hormone has a receptor on the cell membrane, which is bound to an inactive G protein

2. This activates the G protein, which activates enzyme adenylate cyclase

3. Adenylate cyclase converts ATP into cAMP, which is a secondary messenger

4. cAMP activates kinase enzymes, affected the cell

How does hormonal action through intracellular receptors work (STEROID)?

1. Hormone diffuses into the cell through the membrane, binding to a receptor

2. The hormone receptor complex binds to DNA in the nucleus

3. This activates genes which increases transcription rates

4. This increases mRNA production, leading to increase translation and protein synthesis

How does hormonal action through intracellular receptors work (THYROID)?

• Same steps as steroid hormones, but the mitochondria also have hormone receptors

• This increases ATP production

What 2 things can happen to hormones after secretion?

• Free hormone = either bind to target cell receptor or broken down

• Steroid + Thyroid = remain in circulation and require special transport proteins

What is the hypothalamus?

• Interface between nervous and endocrine system

• Has regulatory hormones which affect pituitary function

How does the hypothalamus regulate activity?

1. Production of oxytocin and ADH, which is passed down to the posterior pituitary

2. Secretion of hormones to control activity of anterior pituitary

3. Neuron travel down the preganglionic motor fibres to the adrenal gland to stimulate production of catecholamines

What is the structure of the pituitary gland?

• Anterior lobe = made of endocrine cells

• Posterior lobe = made of neural tissue

Separated by the pars media

What does the posterior pituitary lobe release?

ADH and oxytocin

What does the pars media release?

MSH

What does the anterior pituitary lobe release?

Pituitary hormone

What are some examples of the hypothalamus providing homeostasis?

Prolactin = use of PRF and PIF

Growth hormone = use of GH-RH and GH-IH

Where is growth hormone produced and what is its function?

• Anterior pituitary lobe

• Acts on the liver to promote the release of somatomedins, stimulating tissue growth and increased protein synthesis

• This stimulate cell division in epithelial and connective tissue, stimulating liver glycogen breakdown triglyceride breakdown in adipocytes

Where is ADH produced and its function?

• Produced in posterior pituitary lobe and secreted by osmoreceptors

• Reduces fluid loss by increasing reabsorption, increasing blood pressure and volume

What is the function of the pineal gland?

• Contains pinealocytes which secrete melatonin

• Melatonin affects the circadian rhythm

What is the function of the thyroid gland?

• Stores thyroid hormones T3 + T4

• This increases sodium potassium ATP production

What effects do thyroid hormones have?

• Increase HR

• Increase O2 and energy consumption

• Stimulates RBC production

• Increase sensitivity to SNS

• Increases bone turnover

What is the structure of a thyroid follicle?

• Spherical unit filled with colloid

• Lined by cuboidal epithelial cells

• Surrounded by capillaries for iodine uptake and hormone release

How do thyroid follicles produce T3 and T4?

• Follicular cells synthesise thyroglobulin and transport iodine into the colloid

• Iodine binds to thyroglobulin → forms T3 and T4

What are C cells?

• Produce calcitonin which is important in calcium homeostasis

• They reduce serum calcium, which increases bone formation

What happens when calcium levels are low?

• Detected by parathyroid hormone (PTH)

• Stimulates osteoclasts to breakdown bones to release calcium into bloodstream

• Increases production of calcitriol, increasing the absorption of calcium in the digestive system

Where is the parathyroid gland?

Small gland on the posterior of the thyroid gland

What does the adrenal medulla produce?

Catecholamines e.g. adrenaline

What does the adrenal cortex produce?

Steroid hormones

What does the zona reticularis produce?

Androgens, which provide an anabolic effect?

What does the zona fasciculata produce?

Glucocorticoids, which promote glucose synthesis, breakdown fat and protein

What does zona glomerulosa produce?

Produces mineralocorticoids, which effect electrolyte balance in the body

What is the pancreatic acini?

Exocrine cells which secrete hormones into the digestive tract

What is the pancreatic islet made up of?

2 types of endocrine cells:

• Alpha cells

• Beta cells

What do pancreatic alpha cells do?

Produce glucagon and increase blood glucose level

What do pancreatic beta cells do?

Produce insulin and reduce blood glucose levels

What jobs does insulin do?

• Moves glucose from the blood into the cells to reduce blood glucose levels

• Increases glycolysis rates,

• Conversion of glucose to glycogen

• Increase protein synthesis and amino acid absorption

What jobs does glucagon do?

Stimulates breakdown of glycogen and fatty acids

What is diabetes mellitus?

Disease where blood glucose levels are abnormally high

What is type 1 diabetes mellitus?

• When pancreatic insulin production is inadequate

• Requires an insulin pump

What is type 2 diabetes mellitus?

• Caused by reduced tissue response to insulin

• Can be managed by exercise and diet

What are the aims of growth hormones?

Stimulate protein synthesis and cell growth

What are the aims of thyroid hormones?

Nervous system development

What are the aims of insulin hormone?

Supply of energy and nutrients

What are the aims of parathyroid and calcitonin?

Calcium absorption and deposition in bones

What are the aims of reproductive hormones?

Cell growth and differentiation, and secondary sexual characteristics

What is the exhaustion phase?

The collapse of vital systems including:

• Exhaustion of lipid reserves

• Inability to produce glucocorticoids

• Failure of electrolyte balance

• Structural and functional damage of vital organs