Endocrine system

The endocrine system

The endocrine system

- The endocrine system involves the secretion of chemicals,
called hormones, by glands within the body. These chemicals control
bodily functions, often at locations very distant from the gland that
secreted the chemical.
- The opposite of endocrine is exocrine, which involves the secretion of
substances into spaces outside the body. The glands in the skin and
gastrointestinal tract are examples of exocrine organs.
- The lumen of the intestine is a space that technically isn’t “within” the
body, because it’s continuous with the outside environment via the
mouth and anus.
- The pancreas is unique in being both an endocrine gland and an
exocrine gland. The endocrine function is the secretion of substances
such as insulin, which metabolizes sugar. The exocrine function
involves the secretion of digestive enzymes into the duodenum.

Endocrine functions

- All endocrine glands secrete hormones in the form of proteins that
travel via the blood to the target organ for that hormone. The hormone
causes changes in the activity and in some cases the structure, of the
target organ.
- Hormones can be divided into three main groups:
o Peptide hormones
 hydrophilic, which means they can travel through blood
very easily. Most hormones fall in the peptide hormone
class.
o Steroid hormones
 made from cholesterol and are therefore hydrophobic.
These hormones have a difficult time traveling through
blood and must have a hydrophilic transport.
o Monoamine hormones
 made from amino acids and can be either hydrophilic or
hydrophobic, depending on the specific hormone.

Hypothalamus and pituitary gland

- hypothalamus works to control appetite, body temperature, and
wake-sleep cycles. It also links higher and lower brain centers with the
endocrine system by influencing the pituitary gland.

, - pituitary gland (also called the hypophysis) has a multitude of
functions, many of which involve control of other endocrine glands. The
pituitary gland consists of two parts, and each contains different types
of cells that secrete different substances.
- parts of the pituitary gland:
o Anterior pituitary
 epithelial tissue that comprises the anterior
pituitary wraps around the posterior pituitary gland and
communicates with the hypothalamus via the portal
system, a system of blood vessels.
o Posterior pituitary
 also called the neurohypophysis, is an outgrowth of
nervous tissue from the hypothalamus in the brain.
- hypothalamus produces hormones that help release or inhibit anterior
pituitary hormones. The hypothalamus also produces two
hormones, antidiuretic hormone (ADH) and oxytocin, that are then
stored in the posterior pituitary gland
- ADH is also called vasopressin and acts to improve water uptake in
the renal collecting duct by increasing its permeability to water.
- Oxytocin stimulates contractions of the uterus during labor and
mating. During mating, the oxytocin helps spermatozoa get to the
oviducts.
- Oxytocin also stimulates milk production in what’s termed milk
letdown
- stimulating hormones:
o Thyroid-stimulating hormone (TSH) stimulates thyroid gland
growth and secretion of hormones.
o Adrenocorticotrophic hormone (ACTH) stimulates adrenal
gland cortex growth and secretion of various hormones.
o Follicle-stimulating hormone (FSH) is involved in the growth
and development of follicles found in the female ovaries and
encourages secretion of estrogens from the follicle. In the male
animal, FSH stimulates spermatogenesis in the testes.
o Luteinizing hormone (LH) finishes the development of the
follicle, leading to ovulation and development of the corpus
luteum. The corpus luteum then produces progesterone. In the
male animal, LH stimulates interstitial cells to develop and
produce testosterone.
- Direct-acting anterior pituitary gland hormones include the
following: