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

Cells communicate with each other through direct contact with other

cells or from a distance via chemical signaling

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 Signaling

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

Paracrine and AutocrineSignaling

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

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).

Receptor Location Varies with Hormone

Signaling by any of these hormones involves three key events:

Reception Signal

transduction Response

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

Fig. 45-10Major endocrine glands:

Adrenalglands

Hypothalamus

Pineal gland

Pituitary gland

Thyroid glandParathyroid glands

Pancreas

Kidney

Ovaries

Testes

Organs containingendocrine cells:

Thymus

Heart

Liver

Stomach

Kidney

Smallintestine

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 & GlucagonInsulin – 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:

1.Deficiency of insulin

2.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

Type I Diabetes

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 2 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

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 GlandTriiodothyroxine (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:

1.Bone and nerve cell development

2.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

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

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.

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

MaleMale FemalesFemales

Luteinizing Hormone and Follicle Stimulating Hormone

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

Fig. 45-16

Suckling

Pathway

Stimulus

Hypothalamus/posterior pituitary

Posi

tive

feed

back

Example

Sensoryneuron

Neurosecretorycell

Bloodvessel

Posterior pituitarysecretes oxytocin ( )

Targetcells

Response

Smooth muscle inbreasts

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