Option H: H.1 – Hormonal Control

Hormones

• Chemical messenger secreted directly into the bloodstream– Secreted by endocrine cells or

neurosecretory cells (specialized neurons)

• Hormones are specific – they can only affect the actions of specific target cells.– Regulated by hormones binding to specific

receptors

Human Endocrine Glands

Types of Hormones

Classified based on chemical structure:• Steroids hormones - derived from

cholesterol– e.g. estrogen, testosterone

• Protein (Peptide) hormones – hormones derived from different amino acids.– e.g. insulin, ADH

• Tyrosine derivative hormones – derived from the amino acid tyrosin – e.g. Thyroxine

How Steroid Hormones Work

1. Steroids are lipid soluble and pass directly through the plasma membrane of their target cells.

2. Hormone binds to a receptor protein in the cytoplasm

3. Hormone-receptor complex moves into the nucleus and binds to recognition sites along the cell’s DNA

4. This induces or suppresses the expression of specific genes that code for specific proteins

How Steroid Hormones Work

How Steroid Hormones Work

• Steroid hormones can have different effects in different target cells:e.g. – estrogen stimulates uterine lining

growth and development of female secondary sex characteristics

• How is this possible?– The hormone-receptor complex binds to

different regulatory sites on the DNA and controls the expression of different genes.

How Protein Hormones Work

• Amino acid hormones are unable to pass through the plasma membrane of their target cells.– Therefore they must work from OUTSIDE

the cell.• Amino acid hormones use a signal-

transduction pathway to produce a response.– This requires two messengers:

• First messenger – hormone – extracellular• Second messenger – chemical signal -

intracellular

How Protein Hormones Work

1. Hormone binds to receptor on plasma membrane of target cell (first messenger)

2. Hormone-receptor stimulates action of effector to produce a chemical signal inside the cell (second messenger)

3. The second messenger induces or suppresses enzyme action within the cell, thus producing a response.

How Protein Hormones Work

Mode of Action of Protein & Steroid Hormones

Hypothalamus

• Located in the Lower part of the brain• Integrates nervous and endocrine systems

– Receives signal from neurons and initiates endocrine response.

• Neurosecretory cells in hypothalamus produce hormones in response to nerve impulse

• Regulates the activity of the pituitary gland

Hypothalamus

Pituitary Gland

• The “master,” gland – controls function of many other endocrine glands

Posterior Pituitary Gland:• Stores hormones produced in the

hypothalamus – e.g. oxytocin and ADHAnterior Pituitary Gland:• Synthesizes own hormones• Tropic hormones – hormones that target

and control other endocrine glands.• Only synthesizes hormones when

signaled by releasing hormones from the hypothalamus

Antidiuretic Hormone (ADH)

• Structure – it’s a protein hormone• Origin - produced in the hypothalamus by

neurosecretory cells– Stored and released from the posterior

pituitary gland

• Function – increases re-absorption of water into blood stream through collecting duct

• Regulation – osmotic changes in blood and osmoregulators in the hypothalamus

Control of ADH Secretion

Summary of Posterior Pituitary Hormones

Summary of Anterior Pituitary Hormones