PHYS - Week 5 [Endocrine System]

What’s the Pituitary gland & what are the 2 parts?

It’s a little lump that sits under brain at base of skull.

PARTS:

1) Anterior Pituitary (pinky colour - indicates it’s made of endocrine gland)

2) Posterior Pituitary (yellow colour - is partly an extension of neural tissue)

They are diff colours because they are made up of different types of tissue.

Hormones Released by the Anterior Pituitary

• ACTH (Adrenal corticotropin hormone)

  • tropin is a hormone that stimulates the release of another hormone.

• PRL, FSH, LH: These are important in reproduction

• TSH (Thyroid stimulating hormone): stimulates thyroid to do smt

• Growth Hormone: imp for growth

Hormones Released by the Posterior Pituitary

• Oxytocin: part of reproduction

• Vasopressin: part of renal (kidney) system

  • vaso = vessels, Pressin = squeeze/increase pressure - So Vasopressin squeezes blood vessels

  • Also called ADH (Anti-diuretic hormone): anti = against, Diuresis = water loss - So ADH stops u from peeing

Why Is the Pituitary Important?

The pituitary is part of something called the Hypothalamic Pituitary Adrenal Axis.

• There are 3 sections: Hypothalamus, Pituitary & Adrenal gland

Called axis bcs one goes to the next to the next and so on.

Tropic Hormones

The hypothalamus releases series of tropic hormones, which then travel into the pituitary - There are 2 pathways:

1) Posterior Pituitary Pathway: made up of axons from neurons that sit in the hypothalamus.

• neuron cell body in hypothalamus, Axon extends down, Ends in posterior pituitary

The neurons simply release substances directly into the bloodstream.

2) Anterior Pituitary Pathway: There is another set of cells in the hypothalamus. These release tropic hormones, which enter a special blood vessel network called Portal network (Portal = blood kind of bypasses the rest of the general circulatory system)

Why Use a Portal System in Anterior Pituitary Pathway?

Each of us has abt 5L of blood. If hypothalamus released tiny amounts of tropic hormones into all 5 litres, they would get rly diluted. Instead, hormones go from hypothalamus, Small portal blood supply, then Anterior pituitary.

• Bcs its only a small amt of blood, concentration stays really high.

Primary cause vs secondary cause for endocrine disorders:

Primary cause means the gland itself is abnormal.

Secondary cause means gland is normal, but signals telling it what to do are not.

Why does decreased hormone activity occur?

1) Hyposecretion: less hormone being released either bcs gland is abnormal or something else in pathway is abnormal.

2) Hormone gets Removed from blood Too Quickly, so doesn’t have enough time to do its job.

3) Target Tissue Doesn't Respond Properly: ex// Insulin insensitivity - pancreas may be releasing insulin perfectly, but Not enough receptors/Receptors aren't sensitive/Second messenger system isn't working, so response doesn’t happen

Increased Hormone activity causes

1) Hypersecretion: Too much hormone is being released.

2) Plasma binding proteins: Some hormones travel through the bloodstream attached to plasma binding proteins (theyre like taxis carrying hormones around). Normally, Hormone attached to protein = travelling, whilst Free hormone = able to act on target tissues. If There Are Fewer Binding Proteins, Less hormone is attached, so more hormone is free floating, Available to act & stimulate tissues = increased hormone activity

Cortisol regulation

1) Hypothalamus releases CRH (Corticotropin Releasing Hormone)

2) CRH Travels to the Anterior Pituitary & stimulates cells there.

3) Anterior Pituitary Releases ACTH (Adrenal Corticotropin Hormone) - its job is to go to adrenal gland & tell it to release cortisol

4) Adrenal Gland (specificaly adrenal cortex) Releases Cortisol

NEGATIVE FEEDBACK:

Cortisol levels are usually high in morning - as cortisl keeps rising, body says thats enough cortisol, so cortisol sends a msg back to hypothalamus urging it to release less CRH.

Quick Receptor Cheat Sheet

❤ Alpha 1

• Constriction

• Responds strongly to noradrenaline

❤ Alpha 2

• Inhibitory effects

• Important in the gut

💙 Beta 1

• Heart stimulation

• Responds to adrenaline and noradrenaline

💙 Beta 2

• Dilation

• Airways

• Responds mainly to adrenaline