Endocrine System
The endocrine system is
the system of glands, each of which secretes different
types of hormones directly
into the bloodstream (some of which are transported along nerve tracts[citation
needed]) to
maintain homeostasis. The endocrine system is in contrast to the exocrine system, which secretes its chemicals using ducts. The word endocrine derives from the Greek words "endo" meaning inside, within, and "crinis" for secrete. The endocrine system is an information
signal system like the nervous system, yet its effects and mechanism are
classifiably different.
The endocrine system's effects are slow to
initiate, and prolonged in their response, lasting from a few hours up to
weeks. The nervous system sends information very quickly, and responses are
generally short lived. Hormones are substances (chemical mediators) released
from endocrine tissue into the bloodstream where they travel to target tissue
and generate a response. Hormones regulate various human functions, including metabolism, growth and development, tissuefunction, sleep, and mood.
The field of study dealing with the endocrine
system and its disorders is endocrinology, a branch of internal medicine.
Pituitary gland
In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland about
the size of a pea and weighing 0.5 grams (0.018 oz) in humans. It is a
protrusion off the bottom of the hypothalamus at
the base of the brain, and rests in a small, bony cavity (sella turcica) covered by a dural fold
(diaphragma sellae). The pituitary gland is functionally connected
to the hypothalamus by
the median eminence via
a small tube called the infundibular stem (Pituitary stalk). The pituitary fossa, in which the pituitary
gland sits, is situated in the sphenoid bone
in the middle cranial fossa at
the base of the brain. The pituitary gland secretes nine hormones that
regulate homeostasis.
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Pituitary gland
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Located at the base of the brain, the pituitary gland is protected
by a bony structure called the sella turcica of the sphenoid bone.
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Hormones
A hormone (from Greek ὁρμή,
"impetus") is a chemical released by a cell, a gland, or an organ in
one part of the body that affects cells in other parts of the organism.
Generally, only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that
transports a signal from one cell to another.[1] All multicellular organisms produce
hormones; plant hormones are
also called phytohormones. Hormones in animals are
often transported in the blood. Cells respond to a hormone when they express a
specificreceptor for
that hormone. The hormone binds to the receptor protein, resulting in the activation of a signal transduction mechanism
that ultimately leads to cell type-specific responses.
Thyroid Gland
The thyroid gland or simply, the thyroid /ˈθaɪərɔɪd/, in vertebrate anatomy, is one of the largest endocrine
glands. The
thyroid gland is found in the neck, below the thyroid
cartilage (which
forms the laryngeal
prominence, or
"Adam's apple"). The thyroid gland controls how quickly the body uses
energy, makes proteins, and controls how sensitive the body is to otherhormones. It participates in these processes by producing
thyroid hormones, the principal ones being triiodothyronine (T3) and thyroxine which
can sometimes be referred to as tetraiodothyronine (T4).
These hormones regulate the growth and rate of function of many other systems
in the body. T3 and
T4 are synthesized from iodine and tyrosine. The thyroid also producescalcitonin, which plays a role in calcium
homeostasis.
Parathyroid
The parathyroid glands are
small endocrine glands in
the neck that produce parathyroid hormone. Humans usually have four parathyroid glands,
which are usually located on the rear surface of the thyroid gland, or, in rare cases, within the thyroid gland
itself or in the chest. Parathyroid glands control the amount of calcium in the
blood and within the bones.
Testosterone
Testosterone is a steroid hormone from the androgen group and is found in mammals,
reptiles,[1] birds,[2] and
othervertebrates. In mammals,
testosterone is primarily secreted in the testicles of males and the ovaries of females,
although small amounts are also secreted by the adrenal glands. It is the principal male sex hormone and an anabolic steroid.
In men, testosterone plays a key role
in the development of male reproductive tissues such as the testis and prostate as well as promoting secondary sexual
characteristics such as increased muscle, bone mass, and the growth of body hair. In
addition, testosterone is essential for health and well-being as well as the prevention of osteoporosis.
Progesterone
Progesterone also known as P4 (pregn-4-ene-3,20-dione) is a C-21 steroid hormone involved in the female menstrual cycle,pregnancy (supports gestation) and embryogenesis of humans and other species. Progesterone belongs to a class
of hormones called progestogens, and
is the major naturally occurring human progestogen.
