Chapter 9: The Endocrine System UNIT 4 Chapter 9: The Endocrine System Chapter 9: The Endocrine System How do body systems, including the endocrine system, interact to maintain homeostasis? Imagine you’re about to bungee jump off a bridge. Your heart is racing, and your breathing rate has increased. The hormones epinephrine and norepinephrine are coursing through your body – preparing your body for action.

9.1 The Glands and Hormones of the Endocrine System UNIT 4 Chapter 9: The Endocrine System Section 9.1 9.1 The Glands and Hormones of the Endocrine System The body systems that facilitate cellular communication and control are the nervous and endocrine systems. Endocrine glands secrete chemical messengers called hormones directly into the bloodstream. Together, the glands and hormones make up the endocrine system. It has slower and longer acting effects compared to the rapid actions of the nervous system.

The Endocrine Glands UNIT 4 Chapter 9: The Endocrine System Section 9.1 The Endocrine Glands Over 200 different hormones or hormone-like chemicals in the human body are secreted by endocrine glands. (ie. endocrine glands= pituitary, pineal, thyroid, parathyroid, and adrenal glands)

Hormone Action on Target Cells UNIT 4 Chapter 9: The Endocrine System Section 9.1 Hormone Action on Target Cells When hormones are secreted, they act on target cells to elicit a response. Each target cell contains specific receptor proteins for the various hormones. Most hormones are distributed by the bloodstream to target cells. Target cells have receptors for the hormone, and the hormone combines with the receptor the same way a key fits a lock.

Steroid (Lipid-Soluble) Hormones UNIT 4 Chapter 9: The Endocrine System Section 9.1 Steroid (Lipid-Soluble) Hormones Steroid hormones, such as testosterone, estrogen, and cortisol, are lipid-based. They are also known as lipid-soluble hormones because they can diffuse through the lipid bilayer of the membranes of the target cells.  Once steroid hormones are inside the target cells, they bind to their receptor proteins. This binding activates specific genes, causing changes in the cells such as cell growth.

Water-Soluble Hormones UNIT 4 Chapter 9: The Endocrine System Section 9.1 Water-Soluble Hormones Water-soluble hormones, such as the amino acid-based epinephrine, cannot diffuse across cell membranes.   Water-soluble hormones bind to receptor proteins on the surface of the target cells. This binding starts a cascade of reactions inside the target cells, amplifying the effect of the hormones.

Regulating the Regulators UNIT 4 Chapter 9: The Endocrine System Section 9.1 Regulating the Regulators The secretion of the numerous hormones from the pituitary gland is regulated by the hypothalamus. After receiving signals from sensors in the body, the hypothalamus secretes releasing hormones. These hormones stimulate the pituitary gland to secrete other hormones that act on other endocrine glands. Hormones that target endocrine glands to secrete other hormones are called tropic hormones. Tropic hormones act on other endocrine glands. In these loops, the hormone secreted by the target gland will affect other tissues in the body, such as the bones and muscles. Continued…  

Regulating the Regulators UNIT 4 Chapter 9: The Endocrine System Section 9.1 Regulating the Regulators A specific example of hormone regulation is the negative feedback system that controls thyroid-stimulating hormone (TSH), shown in example B.

UNIT 4 Chapter 9: The Endocrine System Section 9.1 Working Together The nervous system and the endocrine system work together to maintain homeostasis. The functions of these two systems often overlap: some nervous system structures (such as cells in the hypothalamus) release hormones some chemicals (epinephrine) act as both neurotransmitters and hormones both the endocrine and nervous systems are regulated by feedback loops some physiological processes require both systems to operate (e.g., breastfeeding a baby involves nerve messages and the hormone oxytocin)