The Endocrine System

VS 223

Dr. Noland

Endocrine Glands

• Secrete their product directly into bloodstream

• Known as “ductless” glands

Hormones

• Act on target organs due to specific receptors located on the target plasma membrane

Neuroendocrine Reflex

• Nerve input on the afferent end

• Hormonal input on the efferent end

• Suckling reflex

• Induced ovulation in cats, rabbits

Endocrine Glands

• Discrete gland - Adrenal gland

• Organ – Duodenum

• Combo of Exocrine/Endocrine - Pancreas

Classification of Hormones

• Peptides – chains of amino acids–Most hormones

• Amines – tyrosine derivatives–Catecholamines, T4

• Steroids – cholesterol derivatives–Gonadal hormones and adrenal

cortical hormones

Mechanisms of Action

• Hormones circulate in the bloodstream and bind with target organ cell receptors to affect a change in the target cell

Hydrophilic HormonesPeptides and

Catecholamines

Lipophilic HormonesSteroids and Thyroid

Hormonal Action

Feedback Regulation