The Endocrine System

Communication and Control

Endocrine System

Same general functions as the nervous system:

Nervous system – rapid, brief

Endocrine system – slow, longer-lasting

Intro Words to Know Tropic hormone – hormone that stimulates

another endocrine gland to grow and secrete its hormones

Melanocyte – specialized cells in the pigment layer that produces melanin (brown skin pigment)

Diuretic – substance that promotes or stimulates the production of urine

Antidiuretic hormone – hormone that accelerates reabsorption of water (reduces production of urine)

Objectives

Distinguish between endocrine and exocrine glands.

Define the terms hormone and prostaglandin.

Identify and locate the primary endocrine glands and list the major hormones produced by each gland.

Endocrine and Exocrine Glands

Endocrine – ductless; secrete hormones directly into bloodstream

Component of endocrine system Exocrine – discharge secretions into

ducts; sweat glands, salivary glands

Does not belong to endocrine system

Hormones and Prostaglandins

Hormones – chemicals secreted into intercellular spaces

Intercellular spaces..diffuse directly into

blood…target organ cell (hormone

molecule binds to receptor cell)

Prostaglandins – tissue hormone, diffuses only a short distance

Influence production of cyclic AMP?

Influence respiration, blood pressure, gastrointestinal secretions, and the reproductive system

Primary Endocrine Glands Pituitary 1. Cranial cavity 2. In small depression of sphenoid bone called

the sella turcica 3. Anterior lobe – growth hormone, TSH,

adrenocorticotropic hormone (ACTH), FSH, LH, melanocyte-stimulating hormone, prolactin

4. Posterior lobe – antidiuretic hormone and oxytocin

5. Often called “master gland”, but its secretions are actually controlled by the hypothalamus

Thyroid Gland

Lies in neck, just below the larynx Secretes thyroxine (T4), triiodothyronine

(T3), and calcitonin Increases body’s metabolic rate and helps

maintain homeostasis of blood calcium (decreases calcium concentration)

Parathyroid Glands

Four small glands on the back of the thyroid

Secrete parathyroid hormone Increases calcium concentration in blood

Adrenal Glands

Over the top of each kidney Adrenal cortex – mineralocorticoids,

glucocorticoids, and small amounts of sex hormones

Adrenal medulla – epinephrine and norepinephrine

Plays an essential part in maintaining blood pressure

Islands of Langerhans

Clumps of cells scattered among pancreatic cells

Alpha cells secrete glucagon Beta cells secrete insulin Insulin and glucagon are antagonists

Sex Glands

Ovaries of female (back of pelvic cavity) secrete estrogen and progesterone

Testes of male (in scrotum) secrete testosterone

Thymus

In mediastinum Not regulated by the pituitary gland Secretes thymosin ( a group of several

hormones) Essential role in the development and

function of the immune system

Placenta

Temporary endocrine gland formed during pregnancy

Secretes chorionic gonadotropin

Pineal Gland

Small cone-shaped gland Lies near the roof of the third ventricle of the

brain Secretes melatonin (thought to be involved in

regulating the onset of puberty and menstrual cycle in females)

“Third eye” – receives and responds to sensory information from the optic nerves

Helps regulate the body’s internal clock and sleep cycle

Hypothalamus and Atria

Hypothalamus (brain) – several releasing and inhibiting hormones that affect the hormone secretions of the anterior pituitary

Controls temperature, appetite, and thirst Atria (heart) – secretes atrial natriuretic

hormone (ANH) that regulates fluid and electrolyte homeostasis

Objective

Identify the principal functions of each major endocrine hormone and describe the conditions that may result from hypersecretion of hyposecretion.

Refer to pages 345-347 in text.

Objectives

Describe the mechanisms of steroid and protein hormone action.

Explain how negative and positive feedback mechanisms regulate the secretion of endocrine hormones.

Define diabetes insipidus, diabetes mellitus, gigantism, goiter, cretinism, and glycosuria.

Mechanisms of Hormone Action

Protein hormones (first messengers) bind to receptors on the target cell membrane, triggering second messengers (such as cyclic AMP) to affect the cell’s activities

Steroid hormones bind to receptor cells within the target cell nucleus and influence cell activity by acting on DNA

Negative Feedback Mechanisms

Negative – reverse the reaction of a change

Example: Pancreas releases insulin in response to elevation of sugar level in the blood. Blood sugar levels then decrease, which then causes endocrine cells in the pancreas to cease the production and release of insulin.

Positive Feedback Mechanisms

Positive – amplify the change, uncommon Example: When labor begins, the cervix

becomes distended and stimulates the synthesis of oxytocin, which stimulates the uterus to contract. As the contractions increase, the levels of oxytocin increase.

The cycle is broken by the birth of the baby.

Definitions

Diabetes insipidus – caused by hyposecretion of antidiuretic hormone produced by the posterior lobe of the pituitary gland

1. Eliminate extremely large volumes of water each day

2. Severe thirst, dehydration, electrolyte imbalance

Diabetes mellitus – Islets of Langerhans secrete too little insulin

1. Glucose cannot enter into cells, causing blood glucose to increase greatly

2. Excess sugar is filtered out of the blood into the kidneys to be lost along with urine.

Gigantism – too much growth hormone is produced by the pituitary gland

Goiter – painless enlargement of the thyroid gland caused by low dietary intake of iodine

Iodine is necessary for the synthesis of thyroid hormones

Cretinism – hyposecretion of thyroid hormones during the formative years

Low metabolic rate, retarded growth and sexual development

Frequently, mental retardation

Glycosuria – excess sugar in the urine

Occurs with diabetes mellitus (excess blood sugar is filtered out of the body by the kidneys to be transferred to urine)