The endocrine system

How does the nervous system control bodily functions?

It fires neurotransmitters, the effects are almost instantaneous but short lasting

How does the endocrine system control bodily functions?

It uses hormones that travel through the blood stream, the effects take a while to appear but are long lasting

What is the route of hormone secretion via the blood?

1. Secreted into the interstitial fluid

2. To the blood capillaries

3. To the heart via veins

4. Through the rest of the blood through arteries

5. Hormones diffuse out of the blood into the ISF and bind to target cell receptors

What are the different types of signaling used by the endocrine system?

Classic endocrine signals, paracrine signals, and autocrine signals

What are the types of local signals used by the endocrine system?

Paracrine and autocrine signals, they are secreted into the interstitial fluid

What do paracrine signals do?

They are signals secreted into the ECF that target nearby cells

What do autocrine signals do?

They are signals secreted into the ECF that target the same cell

How are all endocrine organs alike?

They all regulate other cell types with hormones

Exocrine glands use what?

Ducts!! Onto a surface

What are the 7 major organs of the endocrine system?

The anterior pituitary gland, thyroid gland, parathyroid gland, adrenal cortex, pancreas, thymus, and ovaries/testes

What are secondary glands?

Secondary glands are organs that are not apart of the endocrine system but still produce hormones; they are made up of nervous tissue

List the secondary organs/neuroendocrine organs

Adrenal medulla, hypothalamus, pineal gland, and posterior pituitary gland (neuroendo)

Other: heart, kidneys, small intestine, and adipose tissue

What are the basic classes of hormones according to chemical structure?

Amino acid based, steroid based, and peptide based

Amino acid based hormones have a structure that is

Dervived from amino acids, they are hydrophilic other than the thyroid

What are the glands that make amino acid based hormones?

Hypothalamus, adrenal medulla, and thyroid

What class do most hormones fall into?

Peptide hormones, they are amino acids linked by peptide bonds

What are some examples of glands that make peptide based hormones?

Hypothalamus, pancreas, anterior pituitary gland, thyroid gland, and parathyroid gland

What are steroid hormones?

They are hormones dervived from cholesterol with a hydrocarbon ring core, they are hydrophobic

What are the endocrine glands that make steroid based hormones?

The adrenal cortex, testes, and ovaries (can be stored in adipose tissue)

What are the ways that hormones can travel through the blood?

Freely or bound to proteins in plasma

Free hormones

Small, amino acid or peptide based hormones that can freely interact with water; they can travel freely through the plasma

Bound hormones

Form complexes with binding proteins in the plasma, they are hydrophobic so they cannot associate with water in plasma

Why is protein binding important?

• It allows hydrophobic hormones to be transported safely in the blood

• serves as a hormone reservoir (prevents concentration of free hormones from experiencing large fluctuations)

• Extends the life of a hormone in the blood

What are receptors?

• Proteins with 3D shapes that are highly specific for hormones

• hormones can cause different effects depending on what receptor they bind to

What does the location of a receptor depend on?

The solubility of the hormone (if it's hydrophobic or hydrophilic)

Where do hydrophilic hormones bind to?

Receptors on the surface of the plasma membrane, they cannot bypass the fatty acid tails of the plasma membrane

What are hydrophilic receptors associated with?

Proteins (ion channels, enzymes, or peripheral proteins)

Where do hydrophobic hormones bind to?

Receptors in the plasma membrane, cytosol, or nucleus

What does the number of receptors in the target cell depend on?

The body’s needs, if hormone levels are low there will be more receptors (upregulation), if hormone levels are high there will be fewer receptors (down regulation)

Second messenger system

Used by hydrophilic amino acids

Hormone binds to receptor (first messenger) →G- protein changes shape and splits → G- protein subunits activates adenylate cyclade → cAMP forms as a second messenger → kinase A activates → phosphorylated proteins

Phosphorylation

Transfering a phosphate group from ATP to another substance

Hydrophobic hormones diffusion across the plasma membrane

When hydrophobic hormones bind to an intracellular receptor they form a hormone receptor complex that binds to hormone response elements (region of DNA) that changes the rate of protein synthesis

What are the effects of hormone actions?

• Stimulating secretion from an endocrine or exocrine cell

• Activating or inhibiting enzymes

• Stimulating or inhibiting mitosis

• Opening or closing ion channels

• Altering membrane potential

• Activating or inhibiting transcription and translation

Synergistic hormones

Different hormones act on the same target cell to exert the same effect to create more profound effects

Half life

The anount of time it takes for the plasma concentration of the hormone to reduce by half, longest in hydrophobic hormones

What effects hormone secretion?

Hormonal stimuli, humoral stimuli, and neural stimuli/negative feedback loops

Hormonal stimuli

Endocrine cells increase or decrease their secretions in response to other hormones (hypothalamic releasal of TRH)

Humoral stimuli

Endocrine cells respond to the concentration of a certain ion or compound in the blood or ECF (glucose or calcium)

Neural stimuli

Cells respond to signals from the nervous system (adrenal medulla is stimulated by the SNS)

Tropic hormones

Control the hormonal secretion from other endocrine glands (TRH from hypothalamus)

Hypothalamic-hypophyseal portal system

A specialized blood supply between the hypothalamus and pituitary gland where capillaries merge together to travel through the infudibulum (transports hormones)

What is the process for secretion of ADH?

Hypothalamic neurons make ADH → portal tract in infudibulum → stored in axon terminals of p.pituitary → secreted into the capillaries in the posterior pituitary when the hypothalamus fires action potentials

What does ADH do?

It is stimulated by low blood pressure or dehydration to increase water retention in the kidneys by decreasing urine production

How does ADH increase the amount of water in the body?

It inserts aquaporins into the plasma membrane of the kidney tubules, allowing water in the tubules to enter the cytosol of the kidneys, from there water moves into the ISF into the blood

Osmorecptors

Cells of the hypothalamus that monitors changes in blood solute concentration, when solute concentration increases they stimulate the release of ADH

Diabetes insipidus

A lack of ADH causing extreme thirst, dehydration, and a high solute concentration of the blood because the body cannot conserve water

Treated with ADH administration

Oxytocin

Targets the mammary glands and uterus, stimulates milk ejection (not production) aka the milk let-down reflex