Cells communicate with each other through direct contact with other cells or from a distance via chemical signaling Endocrine signals are produced by endocrine cells that release signaling molecules, which are specific and can travel long distances through the blood to reach all parts of the body

Endocrine Communication Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body Hormones reach all parts of the body, but only target cells are equipped to respond

Two systems coordinate communication throughout the body: the endocrine system and the nervous system The endocrine system secretes hormones that coordinate slower but longer-acting responses including reproduction, development, energy metabolism, growth, and behavior The nervous system conveys high-speed electrical signals along specialized cells called neurons; these signals regulate other cells

Endocrine signals (hormones) are secreted into extracellular fluids and travel via the bloodstream Endocrine Signaling

Paracrine and Autocrine Signaling Local regulators are chemical signals that travel over short distances by diffusion Local regulators help regulate blood pressure, nervous system function, and reproduction Two types Paracrine signals act on cells near the secreting cell Autocrine signals act on the secreting cell itself Paracrine and Autocrine Signaling

Synaptic Signaling and Neuroendocrine Signaling At synapses, neurons often secrete chemical signals called neurotransmitters that diffuse a short distance to bind to receptors on the target cell Neurohormones are a class of hormones that originate from neurons in the brain (i.e. hypothalamus) and diffuse through the bloodstream to act on target cells (possibly an endocrine gland to produce a 2nd hormone). Synaptic Signaling and Neuroendocrine Signaling

Receptor Location Varies with Hormone Signaling by any of these hormones involves three key events: Reception Signal transduction Response Receptor Location Varies with Hormone

One Hormone – Different Effects The same hormone may have different effects on target cells that have Different receptors for the hormone Different signal transduction pathways Different proteins for carrying out the response A hormone can also have different effects in different species One Hormone – Different Effects

Major endocrine glands: Fig. 45-10 Major endocrine glands: Hypothalamus Pineal gland Pituitary gland Organs containing endocrine cells: Thyroid gland Thymus Parathyroid glands Heart Liver Adrenal glands Stomach Figure 45.10 Major human endocrine glands Pancreas Testes Kidney Kidney Small intestine Ovaries

A negative feedback loop inhibits a response by reducing the initial stimulus Negative feedback regulates many hormonal pathways involved in homeostasis

Insulin & Glucagon: control blood glucose Pancreas contains clusters of endocrine cells known as Islets of Langerhans Islets of Langerhans contain alpha and beta cells Beta cells secrete insulin which triggers uptake of glucose from the blood Alpha cells secrete glucagon which promotes the release of glucose into the blood Hormones secreted into the interstitial fluid and enter circulatory system

Insulin & Glucagon Insulin – stimulates nearly all body cells to take up glucose; Insulin – slows glycogen breakdown in liver and glucose production Glucagon –targets cells in liver to increase glycogen hydrolysis – release glucose into the bloodstream Negative Feedback – stimulus leads to release of hormone which works on target cell to bring about response; response shuts off hormone

Diabetes Melitus Causes: Deficiency of insulin Decreased response to insulin Results in increased blood glucose levels Body forced to use fat as main fuel – can result in acidic metabolite build up lowering pH Kidney can’t handle high level of glucose in blood = sugar in urine leading to frequent urination and extreme thirst Diabetes Melitus

Insulin-dependent diabetes is an autoimmune disorder in which the immune system destroys the beta cells of the pancreas Often thought of as childhood diabetes Destroys a person’s ability to produce insulin Treatment = insulin injections Type I Diabetes

Target cells fail to respond to insulin – blood glucose levels remain high Develops with age – usually around 40 Excess weight and lack of exercise can contribute to type 2 diabetes Most common form of diabetes Type 2 Diabetes

Human Growth Hormone Releasing hormones from hypothalamus trigger anterior pituitary to secrete growth hormone Growth Hormone has Tropic effects (regulates other endocrine cells) and Nontropic effects (targets nonendocrine cells) Major target of GH is the liver which secretes IGF’s (insulin-like growth factors) which stimulate bone and cartilage growth

Gigantism Hypersecretion of GH during childhood can lead to gigantism Person grows unusually tall Results in overgrowth of extremities in adults (acromegaly)

Dwarfism Hyposecretion of GH in childhood retards long-bon growth and can pituitary dwarfism If diagnosed before puberty, can be treated with HGH

Thyroid Hormones The thyroid gland consists of two lobes on the ventral surface of the trachea It produces two iodine- containing hormones: triiodothyronine (T3) and thyroxine (T4) The thyroid is regulate by Thyroid Stimulating Hormone (TSH) from the antior pituitary

Thyroid Gland Triiodothyroxine (T3) called T3 because it has three iodine atoms thyroxine (T4) called T4 because it has four iodine atoms Both have basically the same effect: Bone and nerve cell development Help maintain normal blood pressure, heart rate, muscle tone, digestion & reproductive function

Hyperthyroidism Hyperthyroidism, excessive secretion of thyroid hormones, causes high body temperature, weight loss, irritability, and high blood pressure Graves’ disease is a form of hyperthyroidism in humans In Grave’s disease, the body's natural defense (immune) system attacks the thyroid gland. The thyroid fights back by making too much thyroid hormone

Hypothyroidism Hypothyroidism, low secretion of thyroid hormones, causes weight gain, lethargy, and intolerance to cold

Goiter – Excess TSH enlarge the thyroid gland results in a large swelling just above the breast bone. Rarely, it may constrict the trachea (windpipe) or esophagus and cause difficulty breathing or swallowing. The rest of the symptoms come from thyroxin or the lack of it. Iodine Deficiency Severe iodine deficiency causes problems because the thyroid can never produce enough T3 and T4 but is still continually stimulated by TSH resulting in elargement childhood can cause cretinism Adulthood can cause goiter Cretinism – congenital condition due to thyroid hormone deficiency during fetal development and marked in childhood by dwarfed structure, mental retardation dystrophy of the bones, and low basal metabolism

Antidiuretic Hormone Neurosecretory cells extend from the hypothalamus into the posterior pituitary where ADH is released into the blood stream Antidiuretic hormone (ADH) enhances water reabsorption in the kidneys

Luteinizing Hormone and Follicle Stimulating Hormone Male Females

Estrogen Estrogens, most importantly estradiol, are responsible for maintenance of the female reproductive system and the development of female secondary sex characteristics

Testosterone The testes primarily synthesize androgens, mainly testosterone, which stimulate development and maintenance of the male reproductive system Testosterone causes an increase in muscle and bone mass and is often taken as a supplement to cause muscle growth, which carries health risks

Hypothalamus/ posterior pituitary Fig. 45-16 Pathway Example Stimulus Suckling + Sensory neuron Hypothalamus/ posterior pituitary Neurosecretory cell Posterior pituitary secretes oxytocin ( ) Positive feedback Blood vessel Figure 45.16 A simple neurohormone pathway Target cells Smooth muscle in breasts Response Milk release

Positive Feedback Hormones Oxytocin induces uterine contractions and the release of milk Suckling sends a message to the hypothalamus via the nervous system to release oxytocin, which further stimulates the milk glands