Bio132- Endocrine Part 2

Hormones circulate throughout the body to only affect what?

Target cells that possess specific hormone receptors

The Effect of hormones is to alter what?

Target cell activity

What are the common hormone effects on target cells

• stimulating synthesis of enzymes or other proteins within the cell

• activating or deactivating enzymes

• inducing secretory activity

• stimulating mitosis (cell division)

• changing membrane permeability (and/or membrane potential) by opening or closing ion channels

Most amino acid-based hormones target what on cell surfaces

Plasma membrane receptors

What is water soluble?

Amino acid-based hormones (except thyroid hormones)

If it’s water-soluble then what can it not do?

It cannot cross the phospholipid bilayer of plasma membrane

When hormones bind to a membrane receptor then what is activated?

G protein that is coupled to intracellular second messengers (non-protein molecules)

When the G protein is activated what does the second messengers do?

It leads into a cell response

For second messenger systems, a small and brief amount of hormone outside the cell can trigger what?

Amplified and pronounced changes inside the target cell

What is the correct order of the G Protein-coupled hormone receptor and cyclic AMP second messenger mechanism?

Read aloud to remember properly.

1. Receptor activated G protein

2. Adenylate cyclase converts ATP to cAMP (2nd messenger)

3. cAMP activated protein kinases leading to cell response

4. 1st messenger hormone binds to the membrane receptor

5. G protein activated adenylate cyclase

4-1-5-2-3

What are each shape in this picture represent?

Hormone

Receptor

G protein

Enzyme

2nd messenger

what do Lipid-soluble steroid hormones do?

Diffuse across the plasma membrane

Bind to intracellular receptors

Activated hormone-receptor complex directly activates what?

Specific genes that lead to protein synthesis

Do thyroid hormones have similar functions to steroids?

Yes

What is the correct order of Direct Gene Activation by Lipid-Soluble Hormones?

1. Hormone-receptor complex enters the nucleus

2. Binding initiates transcription of the gene to mRNA

3. mRNA directs synthesis of new proteins

4. Hormone-receptor complex binds a specific DNA region

5. Steroid hormone diffuses through the plasma membrane and binds to an intracellular receptor

5-1-4-2-3

Half-life is what?

Length of time for blood level of a substance (hormone, drug, etc.) to decrease by half

Skin is a source of what?

cholecalciferol (the inactive form of Vitamin D)

What is the active form of vitamin D?

Calciferol

What is the half life in blood for lipid soluble hormones?

Long length of time (mostly metabolized by the liver)

What is the half life in blood for water-soluble hormones?

Short length of time (Mostly removed by kidneys)

Location of receptors for lipid-solubles hormones

Intracellular

Location of receptors for water-solubles hormones

Plasma Membrane

Mechanism of action at target cells for lipid-soluble hormones

Directly activates genes, causing synthesis of new proteins

Mechanism of action at target cells for water-soluble hormones

act through second-messenger systems

Transport in blood in lipid-soluble hormones

Bound to the plasma proteins

Transport in blood in water-soluble hormones

Free in plasma

Lipid-soluble hormone sources

Adrenal cortex, gonads, thyroid gland, and skin

Water-soluble hormone sources

All other endocrine glands

Lipid-soluble hormones

Steroid hormones and thyroid hormones

Water-soluble hormones

Amino acid-based hormones (except thyroid hormone)

What are the three types of stimuli that triggers endocrine glands to synthesize and release hormones?

Humoral stimuli, Neural stimuli, and hormonal stimuli

Humoral Stimuli

Secretes hormones in direct response to levels of key ions or nutrients in the blood

Involves negative feedback

Negative feedback example

Parathyroid glands monitor blood calcium levels

• Low blood calcium causes parathyroid glands to secrete parathyroid hormones (PTH), which functions to increase blood calcium

• Elevated blood calcium inhibits parathyroid glands from secreting PTH

Humoral stimulus

Changing levels of key ions or nutrients in body fluids (humors) triggers hormone release

Neural Stimuli

Hormone release may be stimulated by the nervous system

Example of Neural stimuli

Neurons of the sympathetic nervous system stimulate the adrenal medulla to release epinephrine (E) and norepinephrine (NE) (adrenalin) into the bloodstream

Neural Stimulus

Hormone release caused by neurons

Hormonal stimuli

Tropic Hormones: hormones that control other endocrine glands

Releasing hormones and inhibiting hormones from the hypothalamus regulate the anterior pituitary

Likewise, many hormones secreted by the anterior pituitary control other endocrine organs

Hormonal stimulus

Hormone release caused by other hormones