The Endocrine System Mrs. Hartley Anatomy and Physiology

Functions  Works with nervous system to control body activities  Primary role is to help maintain homeostasis  Communication using chemicals called hormones  Regulate processes including metabolism, growth and development, reproduction, and regulation of stress  Control of these processes is essential to survival

Composition of Endocrine System  Composed of organs that produce and secrete hormones  Perform a secretory function therefore are referred to as glands  Two types: endocrine and exocrine glands

Nervous vs. Endocrine  Often work together  Parts of the nervous sytem stimulate or inhibit the release of hormones and vice- versa  Endocrine system typically acts more slowly than the nervous system

Endocrine Glands  Secrete products into extracellular space surrounding the cells  Products = hormones that enter bloodstream  Pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pancreas, and gonads are primary endocrine glands  Pineal and thymus gland play small role  Hormones received by kidneys, stomach, small intestine, placenta

Hormones  Chemical units produced by endocrine glands  Means by which glands provide control of body activities  Hormones are released into the bloodstream which in turn delivers to all body cells  The cells that recognize a particular hormone will be the one to respond (target cell)

Hormonal Action  Released in very small quantities  Diffuse through bloodstream  Will have an effect only on a particular type of cell called the target cell  Effect limited to target cell because of protein molecules acting as receptors that are specific to a particular hormone  Cells other than the target cell are not affected by a hormone because they lack appropriate receptors

Hormonal Action Cont.  Hormone unites with receptor and exerts it’s effect (generally altering metabolic processes)  May change rate of activity, rate of protein synthesis, rate of secretion, etc largely determined by the nature of the hormone

LIPID BILAYER

Water Soluble Hormones  Include molecules that are composed of amino acids  Cannot pass through the lipid plasma membrane  How can they produce an effect on the cell then? They must use a second messenger system located in the cell.  Most common is cyclic AMP  Hormone (first messenger) activates second messenger which in turn exerts the effect in the cell.  Examples: epinephrine, norepinephrine (NE), antidiuretic hormone (ADH), oxytocin (OT), calcitonin (CT), and parathyroid hormone (PTH)

Lipid-Soluble Hormones  Include mainly steroid hormones  Can pass directly through the bilayer by diffusion to the target cell easily  Binds to receptor in cell which binds to the DNA of the nucleus  “Turns on” the synthesis of specific protein molecules by DNA  Activate genes to synthesize new proteins and enzymes  Examples: aldosterone, cortisol, testosterone, estrogen, thyroxine

Prostaglandins  Chemicals with regulating effect on cells  Act only on nearby cells whereas hormones can travel distances, often called “local hormones”  Interact with hormones to regulate activities  Reduce blood pressure and open airways OR stimulate smooth muscle contraction for the opposite effect

Hormonal Control  How does an endocrine gland “know” how much hormone to produce and release? - - Feedback is provided by way of chemical signals sent to the endocrine gland  Two systems: negative and positive feedback

Negative Feedback Systems  Provides a response in the opposite direction to that of the stimulus  Signal is secreted by the hormone or its products which exerts the negative effect on the endocrine gland

Decreased blood Level Ca2+ Stimulates Parathyroid gland Increased Blood level Ca2+ HOMEOSTASIS NORMAL BLOOD LEVEL Ca2+ Ca2+ Blood level Rises above normal Inhibits Parathyroid Gland Decreased Blood Level Ca2+ HOMEOSTASIS NORMAL BLOOD LEVEL Ca2+

Positive Feedback Systems  Regulate hormone secretion by providing a response in the same direction as the stimulus  Endocrine gland increases its rate of hormone release and more responses are stimulated  Cause extreme conditions in the body therefore quite unstable and uncommon

Positive-feedback mechanism of labor 1. The baby moves deeper into the mother's pelvic region. (See handout, Figure 29.16) 2.Special sensory nerve cells that are pressure receptors in the cervix are stimulated and send nerve impulses to the hypothalamus. 3. Specialized neurosecretory cells in the hypothalamus make oxytocin hormone that travels down long extensions of these cells into the posterior pituitary where it is stored. (See Fig. 5.3, p. 76 and read the text section titled Posterior Pituitary on p. 77.) 4. The posterior pituitary releases oxytocin hormone into the blood. 5. Oxytocin hormone stimulates the uterus muscle lining, the myometrium, to contract. 6. Uterine contraction pushes the baby deeper into the birth canal and pressure receptors in the cervix are again triggered.... see #2. This positive feedback loop continues until the baby is born. --> When doctors induce labor, the woman receives several doses of a synthetic oxytocin to get the positive feedback loop of labor going.

FYI  What triggers the start of the labor positive-feedback loop?  Doctors do not know, however, it has been the generally accepted hypothesis that the baby sends out the initial message. Most recently, scientists have discovered a protein released by the baby's lungs that acts as a hormone signaling mom to begin labor.

Pituitary Gland  Aka hypophysis  Located at base of brain  Connected to hypothalamus  Two portions: anterior lobe 75% and glandular; posterior composed of nerve tissue  Release of hormones regulated by hypothalamus

Anterior/Posterior Hormones  Growth Hormone (GH)  Prolactin (PRL)  Thyroid-stimulating hormone (TSH)  Adrenocroticotropic hormone (ACTH)  Follicle-Stimulating hormone (FSH)  Luteinizing hormone (LH)  Oxytocin (OT)  Antidiuretic hormone (ADH)  **Stored but not produced here!!!

Thyroid Gland  Prominent organ in neck made of two large lobes  Hormones: Thyroxine (T4), Triiodothyronine (T3), and Calcitonin (CT)

Parathyroid Glands  Four or five pea- shaped masses of glandular epithelium  Secrete one hormone called parathyroid hormone (PTH)

Adrenal Glands  Paired, triangular masses that lie on each kidney  Two areas: inner medulla and outer cortex  Function as distinct glands

Hormones of Medulla/Cortex  Medulla  Epinephrine  Norepinephrine  Cortex  Steroid hormones  Mineralocorticoids: aldosterone  Glucocorticoids: cortisol, corticosterone, cortisone  Sex hormones: androgens and estrogens

Pancreas  Part of endocrine and digestive system  Alpha cells secrete the hormone glucagon  Beta cells secrete the hormone insulin  ent_projects/2000/mnby 7lc2/factors_affecting_se cretion.htm ent_projects/2000/mnby 7lc2/factors_affecting_se cretion.htm ent_projects/2000/mnby 7lc2/factors_affecting_se cretion.htm

Gonads  Sex organs  Produce the sex cells and secrete primary sex hormones  Females = ovaries which secrete estrogens and progesterone  Males = testes which secrete testosterone

Pineal Gland  Small structure in cranial cavity associated with brain  Secretes one hormone called melatonin

Thymus Gland  Prominent in infants but diminishes in size with advancing age  Soft, irregulary shaped structure on the top of the heart  Early, secretes thymosin

Assignment: Create a powerpoint presentation for your assigned hormones  Presentation must answer the following questions:  From where does the hormone come?  What effects do these hormones have on the human body?  What organs do the hormones target?  Why are these hormones important to homeostasis in the body?  What are the feedback mechanisms and antagonistic hormones?  What happens when this gland does not work properly?  What can be medically done to correct malfunctions?  Presentation must include at least three illustrations/diagrams