endocrine system

endocrine system

is composed of endocrine glands and specialized endocrine cells located throughout the body

hormones

Endocrine glands and cells secrete very small amounts of chemical messengers called — into the bloodstream, rather than into a duct

target tissues

The hormones diffuse into the blood to be transported to their target. Hormones circulate through the bloodstream to specific sites called — or effectors

1. autocrine chemical messengers

2. paracrine chemical messengers

3. neurotransmitters

4. endocrine chemical messengers

the study of the endocrine system includes several of the following categories (classes of chemical messengers) :

autocrine chemical messengers

• chemical messenger stimulates the cell that originally secreted it

• have local effect on same cell type

• ex. eicosanoids and secreted by white blood cells

paracrine chemical messengers

• chemical messengers act locally on neighboring cells

• released by cells that affect other cell types in close proximity

• ex. somatostatin and histamine

neurotransmitter (and neuromodulators)

• chemical messengers secreted by neurons that activate an adjacent cell, whether it is another neuron, a muscle cell, or a glandular cell

• secreted by nerve cells

• ex. nervous system function

endocrine chemical messenger (hormones and neurohormones)

• secrete into blood and bind to receptors on target tissues

• ex. epinephrine and insulin

1. lipid-soluble hormones

2. water-soluble hormones

Hormones fit into one of two chemical categories:

lipid-soluble hormones

• are nonpolar, and include steroid hormones

• thyroid hormones, and fatty acid derivative hormones, such as certain eicosanoids.

• hormones bind to nuclear receptors due to their lipid solubility and small molecular size allowing to easily pass through the cell membrane

water-soluble hormones

• are polar molecules and cannot pass through the cell membrane

• they include protein hormones, peptide hormones, and most amino acid derivative hormones.

• bind to membrane-bound receptors.

1. humoral

2. neural

3. hormonal

Three types of stimuli regulate hormone release:

humoral stimuli

• Blood-borne chemicals can directly stimulate the release of some hormones.

• These chemicals are referred to as —- because they circulate in the blood

hormonal stimuli

It occurs when a hormone is secreted that, in turn, stimulates the secretion of other hormones

1. negative feedback

2. positive feedback

Two major mechanisms maintain hormone levels in the blood within a homeostatic range:

negative feedback

• Most hormones are regulated by a — mechanism, whereby the hormone’s secretion is inhibited by the hormone itself once blood levels have reached a certain point

• it is a self-limiting system.

positive feedback

• Some hormones, when stimulated by a tropic hormone, promote the synthesis and secretion of the tropic hormone in addition to stimulating their target cell. In turn, this stimulates further secretion of the original hormone.

• Thus, it is a self-propagating system.

pituitary gland

• It is a small gland about the size of a pea

• controlled by hypothalamus

• divided into 2 regions: anterior and posterior

hypothalamus

serves as a control center for the autonomic nervous system as well as the endocrine system

anterior pituitary gland

synthesizes hormones under the control of the hypothalamus

posterior pituitary gland

stores and releases hormones produced by neuroendocrine cells in the hypothalamus

1. growth hormone

2. thyroid-stimulating hormone

3. adrenocorticotropic hormone

4. melanocyte-stimulating hormone

5. luteinizing hormone

6. follicle-stimulating hormone

7. prolactin

anterior pituitary gland hormones

growth hormone

• target tissues: most tissues

• Functions: stimulates growth of bones, muscles, and organs

giantism

too much growth hormone causes —

pituitary dwarfism

too little growth hormone causes

thyroid-stimulating hormone

• binds to membrane-bound receptors on cells of the thyroid gland and stimulates the secretion of thyroid hormone

• target tissue: thyroid gland

thyroid gland enlarges (goiter)

too much thyroid-stimulating hormone causes —

thyroid gland shrinks

too little thyroid-stimulating hormone causes—

adrenocorticotropic hormone

• binds to membrane-bound receptors on cells of the adrenal cortex.

• increases the secretion of corticosteroids

luteinizing hormone

• females: promotes the secretion of the reproductive hormones, estrogen and progesterone, from the ovaries

• males: stimulates interstitial cells of the testes to secrete the reproductive hormone testosterone

follicle-stimulating hormone

• female: follicle in ovaries and estrogen secretion

• male: sperm production

prolactin

• binds to membrane-bound receptors in cells of the breast, where it helps promote development of the breast during pregnancy

• stimulates the production of milk following pregnancy.

melanocyte-stimulating hormone

binds to membrane-bound receptors on melanocytes and causes them to synthesize melanin

darken

The structure of MSH is similar to that of ACTH, and over secretion of either hormone causes the skin to

1. antidiuretic hormone

2. oxytocin

hormones of the posterior pituitary gland

antidiuretic hormone

• target tissues: kidney

• function: conserve water

diabetes insipidus

• A lack of ADH secretion

• which is the production of a large amount of dilute urine

• can lead to dehydration and thirst

oxytocin

• target tissue: uterus

• function: increases uterine contractions during labor

thyroid gland

• one of the largest glands

• require iodine to function

1. thyroid hormone

2. calcitonin

thyroid gland secretes —

thyroid hormones

• secreted by follicular cells

• Target tissues: most tissues

• Functions: regulates metabolic rates and is needed for growth

calcitonin

• secreted by parafollicular cells:

• Target tissues: bone and some other tissues

• Function: reduces blood calcium level when high

hypothyroidism

• lack of thyroid hormones

• Decreased metabolism

• Weight gain, reduced appetite, fatigue

• Low temp. and pulse

• Dry, cold skin

• Myxedema in adults

• Cretinism in infant

hyperthyroidism

• elevated rate of thyroid hormones

• increased metabolism

• Weight loss, increased appetite, nervousness

• Higher temp. and pulse

• Warm, flushed skin

• Graves’ disease is autoimmune disease that cause —

parathyroid glands

Four tiny — are embedded in the posterior wall of the thyroid

parathyroid hormone

• target tissues: bones and kidneys

• functions: essential for the regulation of blood calcium levels

adrenal gland

are two small glands located superior to each kidney

adrenal medulla

adrenal gland inner part

adrenal cortex

adrenal gland outer part

epinephrine and norepinephrine

• adrenal medulla secrete 2 hormones —

• are called the fight-or-flight hormones. They prepare the body for intense physical activity.

1. aldosterone

2. cortisol

3. androgens

adrenal cortex hormones

aldosterone

• type of mineralocorticoid

• target tissues: kidneys

• functions: regulate ion balance, causes Na+ and H2O to be retained and K+ to be secreted, indirectly involved with blood pressure and blood volume

cortisol

• type of glucocorticoid

• target tissues: most

• functions: increases breakdown of fat and protein for energy uses reduces inflammatory and immune responses

androgens

• males: which stimulate the development of male secondary sex characteristics.

• female: sex drive

pancreas

is a mixed gland, with an exocrine portion and an endocrine portion

pancreatic islets (islets of Langerhans)

The endocrine part of the pancreas consists of —-, which are dispersed throughout the exocrine portion of the pancreas

1. alpha cells

2. beta cells

3. delta cells

• The islets consist of three cell types, each of which secretes a separate hormone

• These three hormones regulate the blood levels of nutrients, especially glucose

alpha cells

secretes glucagon

beta cells

secrete insulin

delta cells

secrete somatostatin

insulin

• target tissues: liver, skeletal muscle, adipose tissue

• Functions:

• regulates blood glucose levels

• after a meal glucose levels are high and — is secreted

diabetes mellitus

• Causes: too little insulin or faulty insulin receptors

• Symptoms: hyperglycemia, exaggerated appetite, excess urine, dehydration, thirst, fatigue

type 1 diabetes mellitus

• occurs when too little insulin is secreted from the pancreas

• insulin dependent (daily injections required)

type 2 diabetes mellitus

• is caused by either too few insulin receptors on target cells or defective receptors on target cells

• insulin independent, often found in obese people and can be treated with diet

glucagon

• is released from the alpha cells when blood glucose levels are low

• target tissues: liver

• between meals glucose levels drop and —is secreted

• allows glycogen to be broken down into glucose

testosterone

• which is secreted by the testes.

• It regulates the production of sperm cells by the testes and the development and maintenance of male reproductive organs and secondary sexual characteristics

estrogen and progesterone

• In the female, two main classes of reproductive hormones, secreted by the ovaries, affect sexual characteristics

• involved in uterine and mammary gland development and menstrual cycle

thymus

lies in the upper part of the thoracic cavity and is important in the function of the immune system

thymosin

• The thymus secretes a hormone called—

• which aids the development of white blood cells called T cells

• promotes immune system development and function

pineal gland

is a small, pinecone-shaped structure located superior and posterior to the thalamus of the brain

melatonin

• pineal gland produces a hormone called

• plays a role in onset of puberty and controls circadian rhythms.

• Light affects its function