Transcript The Endocrine System Human Anatomy Chapter 25 • This system includes all the glands of the body that secrete hormones directly into the blood stream.

The Endocrine System
Human Anatomy
Chapter 25
• This system includes
all the glands of the
body that secrete
hormones directly
into the blood
stream. They do not
contain ducts, some
glands may be both
endocrine and
exocrine (ex:
pancreas). The
hormones are
chemical stimulants
that control changes
in the body.
Endocrine glands
may be stimulated
by the nervous
system or chemical
changes in the body.
I. The endrocrine system: an
overview
• Endocrine glands are studied
by endocrinologist. These
scientists have determined that
despite the fact that hormones
travel all over the body through
the blood stream and that all
tissues are exposed to them
not all are affected. Hormones
affect specific tissues called
target tissues. The cells of
these organs have receptors
that bind the specific hormone
and are stimulated by that
reaction.
• A. Endocrine organssome organs are “pure”
in that the entire
structure is composed
of endocrine cells, these
include: the pituitary
gland, the pineal gland,
the thryroid and
parathryroid gland, and
the adrenal glands. The
following perform
functions in other
system asides from the
endocrine: pancreas,
thymus, testes, ovaries,
and hypothalamus.
Endocrine glands have
a high supply of blood
and lymph vessels.
• B. Hormones- each hormone type had its own chemical
structure and thus performs different actions.
• 1. Classes of hormones- amino acid-based hormones
contain amino acids or small proteins as part of their
structure. Steroids are hormones that contain a
cholesterol group as part of its structure.
• 2. Basic hormone action- Cells have receptors on their
surface that bind only specific types of hormones. When
receptor binding occurs a program response/reaction
takes place. Hormones do not carry information but are
only released to stimulate a chemical reaction. Tropic
hormones are secreted by an endocrine to stimulate the
activity of another endocrine gland.
• .
•
•
•
•
•
3. Control of hormone secretion- the following list condition under which an
endocrine gland releases hormones:
a. Humoral stimuli: gland responds to chemical changes in the body such as
changing levels or ions or nutrients in the blood.
b. Neural stimuli: some glands are signal by nervous system (sympathetic
nerves) to release hormones in order to induce physiological changes.
c. Hormonal stimuli: some endocrine glands are controlled by other
endocrine glands and thus respond to hormone.
d. Feedback loops: hormone levels are also controlled by feedback loops
that either stimulate or halt the production of a hormone
PG 361
II. Major endocrine organs
Be familiar with the location of each gland, the hormones they release and
its function.
A. The pituitary gland: is also called the hypophysis and is located within the
cranium inferior to the brain. It sits on the hypophyseal fossa of the sella
turcica (sphenoid bone). This gland connects to the hypothalums through a
stalk called the infundibulum, the infundibulum connect to the tuber
cinereum of the hypothalamus.
Pituitary Gland and visible leukocytes
•
1. Adenohypophysis: also known as the
anterior pituitary gland. The majority of the
hormones produced are amino acid based
hormones. Different cell types produce
different hormones including:
a. Growth hormone (GH)- signals growth of
the body
b. Somatotropic hormone(SH) or
somatotropin- signals growth of the
body
c. Prolactin- stimulates the breast tissue to
produce milk
d. Thyroid-Stimulating hormone- stimulates
the thyroid gland to secrete hormones that
influence our metabolism.
e. Adrenocorticotropic hormone (ACTH)stimulates adrenal gland to signal its
hormones that help us deal with stress.
f. Melanocyte-stimulating hormone (MSH)stimulates melanocytes of the epidermis to
produce more melanin, thus darkening the
skin.
g. Follicle stimulating hormone (FSH)- act
on testes or ovaries an stimulate the
maturation of egg/sperm and induce
secretion of sex hormones
h. Leutinizing hormone (LH)- During the
menstrual cycle it signals ovulation
•
2. Hypothalamic control of
hormone secretion from the
adenohypophysis: the
hypothalamus had neurons that
produce hormones and release
them much like
neurotransmitters are released.
These travel through the
hypophyseal portal system into
the anterior pituitary and
stimulate its hormone
secretion. The hypophysial
portal system involves two
beds of capillaries connected
by a vein. It allows a high level
of horomone concentration
within a small region and it is
designed so that the hormones
released by the hypothalamus
travel directly to the anterior
pituitary and it in turn release
hormones into systemic
circulation.
• 3. Neurohypophysis: also known
as the posterior pituitary gland, it is
technically part of the brain and it
composed of neurons. Rather
than making hormones it stores
those produced by the
hypothalamus and releases them
when it receives a neural impuls.
The hormones produced by the
hypothalamus but released by the
neurohypophysis are:
a. Antidiuretic hormone (ADH)stimulates the collecting tubules of
the kidney to concentrate the urine
in order to reduce water loss.
b. Oxytocin- induces contractions
of smooth muscle of the sexual
organs, such when a mother
experiences contractions of the
uterus during labor.
•
•
•
B. The thyroid gland: located just inferior to the larynx, it has two lobes that
give it the appearance of butterfly wings. It is the largest endocrine gland and it
releases thyroid hormones and calcitonin.
a. Thyroid hormone: T4 and T3, amino acid based hormones that contain iodine,
main function is to increase metabolic rate.
b. Calcitonin- reduces excessive levels of calcium ion in the blood by slowing
down osteoclast activity, actively secreted during childhood.
Histology of Thryroid and
Parathyroid Gland
• C. The parathyroid gland: yellowish in color, lie posterior or the thyroid
gland. There are at least two pairs of glands but some may have as many as
four pairs. The hormone it releases is parathyroid hormone (PTH) which has
the opposite effect if calcitonin. It increase calcium ion levels in the blood by
either activating the osteoclast, stimulating the kidney to reabsorb more
calcium, or activation vitamin D production for calcium to be absorbed from
food.
•
D. The adrenal (suprarenal) gland: These are two glands located
superiorly to the kidney and are actually two different glands within one
structure.
•
1. adrenal medulla: considered part of the autonomic nervous system, it
releases adrenaline or epinephrine to assist in the “fight or flight” response.
•
2. adrenal cortex: secretes steroids called corticosteroids. Aldosterone
(mineralocorticoid) is secreted in response to a decrease in blood volume or
blood pressure stimulating the kidneys to reabsorb more water or sodium.
Another group of hormones is called the glucocorticoids which include
cortisol. These hormones keep blood glucose levels high to maintain brain
activity during stressful situations. They can direct lymphocytes, or
decrease inflammation.
• E. The pineal gland: also located in the brain and controlled by the
hypothalamus, it is composed of endocrine cells that secrete
melatonin which regulates the internal body clocks: it induces sleep.
•
F. The pancreas: located in the abdominal cavity it contains endocrine cells
called the islets of Langerhans that produce amino acid based hormones.
The cells release insulin which stimulates absorption of glucose by tissue
cells when blood glucose levels are high, and also releases glucagon that
stimulates the liver to release sugar into the blood when blood glucose
levels are low.
Histology of the pancreas
•
•
G. The thymus: located in lower neck, anterior thorax, and posterior to the
sternum. It secretes amino acid based hormones called thymic hormones
like thymopoeitin and thymosin that stimulate T-lymphocytes to become
immunocompetent.
H. The gonads: testes and ovaries are organs that secret steroid sex
hormones. Androgens released by these glands are changed into
testosterone, estrogen, and progesterone. They maintain primary and
secondary sex characteristics and cells involved in reproduction.
III. Other endocrine structures:
• A. The heart has sensory cells in the atria that stimulate the kidneys
to produce more urine containing salt. Getting rid of the excess fluid
and salt reduces excess blood volume and salt blood levels, and
reduces blood pressure.
• B. The GI tract has scattered cells that release amino acid/peptide
hormones chemically similar to neurotransmitters. They affect
functions related to regulating digestion, blood chemistry, and blood
flow.
• C. The placenta is produced only when conception occurs, it secrets
hormones that prevent the uterus from getting rid of the nutrient
layer to which it is attached. It also produces other steroid
hormones: estrogen, progesterone, corticotropin-releasing hormone,
and human chorionic gonadotropin.
• D. The kidneys release rennin which regulates blood pressure and
erythropoietin which stimulates erythrocyte production.
• E. When exposed to UV rays, the skin produces a steroid hormone
precursor to vitamin D. Vitamin D helps in the absorption of calcium.
A woman with Cushins Disease