endocrine system
Summary
The endocrine system is a network of glands that release hormones into the blood to act on distant target cells that have matching receptors. Compared with the nervous system, its effects are usually slower but longer-lasting, and the hypothalamus–pituitary link joins the two systems.
Detail
Meaning: The endocrine system is a set of glands, including the hypothalamus, pituitary, thyroid, adrenals, pineal gland and gonads, that secrete hormones into the blood. Cells respond when they have matching receptors, so one hormone can affect distant targets. Signaling usually starts more slowly and lasts longer than nervous signaling. The hypothalamus controls the pituitary, which links the two systems. Biology covers the same system in more detail, with feedback loops and hormone chemistry.
On the MCAT: Stress is the classic setup. The hypothalamus releases CRH, the anterior pituitary releases ACTH, and the adrenal cortex releases cortisol (the HPA axis). Separately, sympathetic input to the adrenal medulla releases epinephrine for fight-or-flight. Other examples: testosterone with aggression and sex drive, oxytocin with bonding, and melatonin from the pineal gland with sleep-wake cycles. Questions ask you to compare speed and duration with the nervous system, or to predict a behavioral change when a hormone level rises or falls.
Common confusion: Hormones do not simply cause behavior. The influence runs both ways: experience and environment can change hormone levels, and hormones bias behavior rather than dictate it. The two systems also overlap: epinephrine and norepinephrine act as hormones in the blood and as neurotransmitters at synapses.
Sources
- Psychology
- Psychological Science
- Discovering Psychology
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.