9.1: Endocrine System

Purpose

  • endocrine and nervous control and facilitate communication between cells

  • endocrine glands secrete chemical messengers called hormones directly into the bloodstream

  • endocrine system = glands and heir hormones

  • slower and longer acting effects compared to rapid actions of nervous system

Endocrine Glands

  • >200 hormones or hormone like chemicals secreted by glands

  • exclusively endocrine glands = pituitary, pineal, thyroid, parathyroid, adrenal

  • tissues and organs with different functions can also secrete hormones

    • hypothalamus, thymus, pancreas, testes, ovaries

Hormone Action on Target Cells

  • when hormones are secreted, they action certain target cells to elicit a response

  • each target cell contains specific receptor proteins for various hormones

Lipid-Soluble Hormones

  • aka steroid hormones

  • diffuse through cell membrane of target cell

  • ex. testosterone, estrogen, cortisol

  • bind to receptor proteins and result in gene expression

Water-Soluble Hormones

  • cannot diffuse across cell membranes

  • hormones made from amino acid/polypeptides

  • bind to receptor proteins on surface of target cells

binding starts cascade of reactions inside target cells, amplifying the effect of the hormone

Action of Epinephrine

  • when epinephrine reaches the liver, it stimulates the conversion of ATP to cAMP

  • cAMP triggers an enzyme cascade that results in many molecules of glycogen being broken down into glucose

  • once a hormones message has been delivered, enzymes inactivate the hormone

  • a single molecule of epinephrine in the liver can trigger the conversion of glycogen into 1 million molecules of glucose

Regulating the Regulators

  • pituitary gland releases hormones that control many other endocrine glans

  • near hypothalamus

  • secretion of hormones from the pituitary gland is regulated by the hypothalamus

  • secretion of hormones from the pituitary glans is regulated by the hypothalamus

  • hypothalamus receives signals from sensors in the body

  • to maintain homeostasis, the hypothalamus secretes releasing hormones

  • hormones from hypothalamus stimulate the pituitary gland to secrete other hormones that act on other endocrine glands

  • tropic hormones = hormones that target endocrine glands to secrete other hormones

Coordination of Endocrine and Nervous Systems

  • maintain homeostasis

  • some nervous system structures release hormones

    • cells in hypothalamus

  • some chemicals act as hormones and neurotransmitters

    • epinephrine

  • both endocrine and nervous regulated by feedback loops

  • some psychological processes require both systems to operate