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)