ENDOCRINE SYSTEM An Introduction

• Series of glands that produce hormones to help maintain homeostasis.

• Hormones: Chemical regulators that affect target cells in other parts of the body.

– eg: insulin, growth hormone, testosterone

The Endocrine System

• Some glands produce one hormone, some produce many kinds and even other chemicals.

• All hormones are transmitted by blood to target cells which have hormone specific receptor sites

HORMONES• Cells must have a specific receptor • Two types of hormones:

– Steroid hormones: made from cholesterol, complex ring structures, fat soluble

• eg., sex hormones, cortisol

– Protein hormones: amino acid chains • eg., insulin, growth hormone

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Steroid Hormones (LIPID Soluble):

– hormones diffuse out of blood stream and into the target cells

– cross target cell membranes to combine with receptor molecules in cytosol

– hormone-receptor complex activates a gene, initiating transcription & protein synthesis.

Mechanism of Action

Mechanism of Action• PROTEIN Hormones (WATER Soluble):

– hormones diffuse out of blood stream – attach to receptors on the membrane of target cells – the receptor-hormone complex activates a series of

reactions within target cells to turn on genes – target cells begin their specific cellular functions.

Hormones and Feedback Mechanisms

• One gland responds to a stimulus to produce a hormone (A)

• This hormone stimulates a second gland to produce other hormone(s) (B) to generate homeostatic responses.

• The second hormone (B) also inhibits the hormone production of the original gland.

The Endocrine Glands

Hypothalamus• Region of the brain - therefore part of the nervous sys. • Governs physiological functions (eg: sensory of temperature,

thirst, hunger, sleep, sex drive chemistry) • Contains neurones that produce hormones (neurohormones) • Hormones transferred by blood to the pituitary gland. • —> releasing or inhibiting hormones

Pituitary Gland

• MASTER GLAND • Region outside of the brain -but

in the cranium • Secretes several hormones to

the other glands around the body.

• Two parts -anterior & posterior

Posterior Pituitary Gland

• Receives and stores two hormones made in the hypothalamus

• ADH controls kidney function (stimulated by salty blood)

• Oxytocin stimulates milk release and labour contractions (in women)

Anterior Pituitary Gland

• The front part & most active part • Receives neurohormone signals from the hypothalamus • Eight major hormones produced

Growth Hormone (GH)

Prolactin (PRL)

Gonadotropins (FSH and LH)

Thyroid- stimulating hormone (TSH)

Melanocyte-stimulating-Hormone (MSH)

Adrenocorticotropic Hormone (ACTH)

Endorphins