Endocrine System
Anatomy & Physiology
I. Endocrine System
A. Cells of the nervous and endocrine systems work together
and monitor changes.
B. Nervous system performs crisis management by producing
rapid, short term and very specific responses to stimuli.
C. Endocrine cells release chemicals called hormones, which
are released into the bloodstream and distributed.
D. Hormonal effects may not be immediately apparent but will
be there for many days afterwards.
E. Endocrine system is very effective in regulating ongoing
metabolic processes.
F. Gradual changes in the pattern of hormones put together
such things as embryological development, growth, sexual
maturation, & reproduction
G. Hormones are classified by their chemical structures: amino
acid derivatives, peptide hormones & steroids.
H. Hormones have a physiological effect only upon a
restricted tissue or cell type (Target tissue/cell). These
cells possess specific receptor sites for the hormone
molecules.
I. Endocrine glands are ductless and secrete directly into
the blood. The endocrine glands include: pituitary,
thyroid, parathyroid, adrenals, pineal, thymus, &
gonads
J. Functions of the endocrine system are:
1. To regulate metabolic processes
2. To control the rate of certain chemical reactions within the
body
3. To aid in the transport of substances through the cell
membranes
4. To play vital roles in cell growth, water and electrolyte
balance
5. To control reproduction
II. Control of Hormonal Secretions
A. Controlled by a negative feedback system
B. Nerve control is done by the Hypothalamus by
releasing factors, which are chemicals that
stimulate the anterior pituitary to secrete its
hormones, & by inhibitory factors, which are
chemicals that inhibit the anterior pituitary
from secreting its hormones.
III. Glands and Hormones Secreted
A. Pituitary Gland (Hypophysis)
1. The “Master Gland” because its hormones
control the release of other hormones.
2. It is attached beneath the hypothalamus by a
slender stalk of tissue called the
Infundibulum.
3. Divided into 2 parts:
Anterior Pituitary (Adenohypophysis) &
Posterior Pituitary (Neurohypophysis)
4. Anterior Pituitary secretions
a. Growth Hormone (GH) - function: stimulate body cells
to increase in size and undergo rapid division
• release of GH controlled by the hypothalamus
• Dwarfism: not enough GH before and during puberty.
All body parts are abnormally proportional and some
need hormone therapy to develop sexually.
• Gigantism: too much GH before puberty.
• Acromegaly: secretion of GH after growth plate
closure of the long bones. Characterized by large
hands and feet, protruding jaw, large tongue and
nose.
b. Thyroid Stimulating Hormone (TSH) - function:
controls the secretion of thyroid hormones.
– release of TSH controlled by hypothalamus
– can be triggered to release by extreme cold or emotional
stress
c. Adrenocorticotrophic Hormone (ACTH) - function:
Stimulates the release of steroid hormones by the
adrenal cortex.
– Targets cells producing glucocorticoids, which effect glucose
metabolism.
– Highest levels in the morning as it is on a diurnal cycle.
d. Follicle Stimulating Hormone (FSH) – function:
stimulate gonad activities.
– In females: responsible for the growth and development of
the egg and stimulates the secretion of estrogen.
– In males: supports sperm production in the testes.
e. Luteinizing Hormone (LH) – function: stimulate
gonad activity & hormone release.
– In females: it induces ovulation and the
secretion of progesterone.
– In males it is responsible for testosterone
secretion.
f. Prolactin - function: causes milk production in the
pregnant female breast
– Galactorrhea - hypersecretion that causes
inappropriate lactation
g. Melanocyte-Stimulating Hormone (MSH) function: Promotes melanin production
5. Posterior Pituitary secretions - The
neurohypophysis does not synthesize hormones,
they are produced in the hypothalamus and then
transmitted to the posterior pituitary where they
are then secreted.
a. Antidiuretic Hormone (ADH) - function: inhibits urine
formation. It acts on the kidneys to reduce the amount
of water excreted.
•
•
Diabetes Insipidus: Pituitary no longer releases adequate
amounts of ADH, and excessive amounts of water are lost in
the urine. Individual is constantly thirsty and in severe cases,
fluid loss can be as much as 30 liters per day which causes
severe dehydration and could be fatal if not treated.
ADH production is inhibited by alcohol thus causing
increased micturation following its consumption.
b. Oxytocin - function: Contractions of the uterine wall &
milk ejection from mammary glands.
B. Thyroid Gland
1. Vascular organ that has 2 large lobes connected
by a broad isthmus. Located just below the
larynx on either side of the trachea
2. Secretions (all of which contain iodine)
a. Thyroxine & Triiodothyrine - functions:
Increase rate of metabolism.
b. Calcitonin – function: regulate calcium levels
in the blood by reducing osteoclast activity,
stimulating osteoblast activity, and
decreasing blood Ca levels.
3. Thyroid Disorders
a. Hypothyroidism: occurs when not enough thyroxin or
triiodothyrine is produced. Can be due to a lack of
iodine. 2 types
•
•
Cretinism: occurs in infants and children. stunted growth,
abnormal bone formation, retarded mental development,
low body temperature.
Myxedema: occurs after puberty. Low metabolic rate,
mentally slow, gain weight easily.
b. Hyperthyroidism (AKA Grave's Disease) - Eyes are likely
to protrude due to edema behind them. Thyroid is
likely to enlarge, elevated metabolic level, abnormal
weight loss.
c. Goiter: Enlargement of the thyroid. 2 types:
•
•
Toxic: due to over secretion of TSH from the anterior
pituitary.
Simple: due to lack of iodine in the diet.
C. Parathyroid Gland
1. Located on the posterior surface of the thyroid
2. There are usually 4 glands - 2 on each side
3. Secretes Parathormone - function: increase blood
calcium and decreases phosphorus levels in the blood
– Acts upon bones, intestines & kidneys.
D. Adrenal Gland
1. Located on the superior boarder of each kidney and embedded in
fat.
2. Has a pyramid shape and is very vascular.
3. Divided into 2 parts: Adrenal Cortex & Adrenal Medulla
a. Adrenal Medulla (inner portion) secretions.
– Epinephrine & norepinephrine: Both increase heart rate,
increase blood pressure, raises blood sugar, increases
breathing, dilation of air ways, decreases digestion activity
(fight/flight response)
b. Adrenal Cortex (outer portion) secretes more than 2 doz.
different steroids. There are three types of hormones secreted
by the cortex:
– Mineralocorticoids: regulate electrolyte composition of body
fluids.
– Glucocorticoids: regulate the metabolism of carbo’s.
– Androgens: affect the sexual characteristics of males and
females.
E.
Pancreas
1. Flattened globular organ just posterior to the stomach and small
intestine.
2. Exocrine (digestive juices) and endocrine cell types are found in the
pancreas.
3. Endocrine cells of the pancreas are in clusters called the Islets of
Langerhans, which have 2 types of secretary cells.
a. Alpha Cells: secrete glucagon, which converts glycogen to
glucose and elevates the blood glucose levels.
b. Beta Cells: secrete insulin, which facilitates the transport of
glucose into the cells, thus lowering the blood sugar levels.
4. Disorders of Islets
a. Diabetes Mellitus: insufficient secretion or total lack of insulin
being secreted. Too much glucose in blood and severe upset of
metabolism.
b. Hypoglycemia: to much insulin secreted at one time, causing a
very fast decrease of the blood sugar levels after a very quick
rise.
E. Pineal Gland
1. Located deep with the cerebral hemispheres of
the brain.
2. Function in doubt though it is thought to
secrete melatonin.
3. Melatonin: is thought to stimulate the secretion
of releasing factors from the hypothalamus.
4. May be associated with the menstrual cycle in
females.
5. May control the circadian rhythms: the periods
of wakefulness and sleeping in humans.
G. Gonads - Secrete separate hormones depending
on gender.
1. These hormones are responsible for the
secondary sex characteristics of each gender
and their reproductive capabilities.
2. Ovaries: female and they secrete estrogen and
progesterone.
3. Testes: male and they secrete testosterone.