2.19 : 内分泌系统

The endocrine system is composed of glands that secrete hormones, which are chemical messengers crucial for bodily functions.

These hormones circulate through the bloodstream, attach to specific cell receptors, and trigger cellular responses such as cell division, secretion of secondary messengers, or gene expression.

Some of the major endocrine glands include the pituitary, thyroid, adrenal glands, the pancreas, and gonads.

The pituitary gland serves a crucial role in regulating hormone secretion from other glands in the body and is controlled by the hypothalamus.

It secretes several hormones, including growth hormones, oxytocin, and endorphins.

The thyroid gland releases hormones that control growth, metabolism, and appetite.

The adrenal glands produce hormones such as epinephrine and norepinephrine, which are vital for stress responses.

The pancreas is crucial for blood sugar regulation by releasing insulin to lower blood glucose and glucagon to raise it.

Lastly, the gonads produce sexual hormones crucial for reproductive functions and behaviors. The female ovaries secrete estrogen and progesterone, while the male testes produce testosterone.