E N D O C R I N E S I G N A L S A R E P R O D U C E D B Y
E N D O C R I N E C E L L S T H A T R E L E A S E
S I G N A L I N G M O L E C U L E S , W H I C H A R E
S P E C I F I C A N D C A N T R A V E L L O N G D I S T A N C E S
T H R O U G H T H E B L O O D T O R E A C H A L L P A R T S
O F T H E B O D Y

 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

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

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 2 nd hormone).
Synaptic Signaling and
Neuroendocrine Signaling




Reception
Signal transduction
Response
Receptor Location Varies with
Hormone

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

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

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

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
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 iodinecontaining hormones: triiodothyronine
(T
3
(T
4
) and thyroxine
)
The thyroid is regulate by Thyroid
Stimulating
Hormone (TSH) from the antior pituitary

Thyroid Gland
Triiodothyroxine (T
3
) called T3 because it has three iodine atoms thyroxine (T
4
) 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

Luteinizing Hormone and Follicle Stimulating Hormone
Male Females

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



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
+
Pathway
Stimulus
Example
Suckling
Sensory neuron
Hypothalamus/ posterior pituitary
Neurosecretory cell
Blood vessel
Posterior pituitary secretes oxytocin ( )
Target cells
Response
Smooth muscle in breasts
Milk release


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