Chapter 3 Section 3: The Endocrine System

The endocrine system consists of glands that secret substances, called hormones, into the bloodstream. Hormones stimulate growth and many kinds of reactions such as changes in activity levels and moods.

Because hormones affect behavior and emotional reactions, psychologists who study the biology of behavior are also interested in the endocrine system.

Hormones have specific receptor sites. Although various hormones circulate throughout the body, they act only on hormone receptors in certain places. Hormones are produced by glands, such as the pituitary gland, thyroid gland, adrenal glands, and the testes and the ovaries.

The Pituitary Gland Lies just below the hypothalamus (a region of the forebrain- autonomic nervous system). Size of a pea Stimulated by the hypothalamus, is responsible for the secretion of many different hormones that affect various aspects of behavior. Growth hormone regulates that growth of muscles, bones, and glands.

Hormones also affect females in relation to pregnancy and mothering. Prolactin stimulates production of milk in nursing women. Oxytocin stimulates labor in pregnant women.

The Thyroid Gland Produces thyroxin Thyroxin affects the body’s metabolism- its rate of converting food to energy.

Hypothyroidism Production of too little thyroxin. Often causes people to be overweight

Cretinism Occurs in children with not enough thyroxin. Stunted growth

Hyperthyroidism Production of too much thyroxin. Excitability, inability to sleep, and weight loss.

The Adrenal Glands Located above the kidneys. The outer layer, or cortex, of the adrenal glands secretes cortical steroids. Cortical steroids increase resistance to stress and promote muscle development. Also cause the liver to release stored sugar, making energy available for emergencies.

The adrenal glands also produce adrenaline and noradrenaline. During a stressful situation, the sympathetic nervous system causes the adrenal glands to release a mixture of adrenaline and noradrenaline. These hormones help arouse the body, enabling the person to cope with a stressful situation.

Adrenaline also plays a role in the emotions people experience. Can intensify emotions such as fear and anxiety. Noradrenaline can raise blood pressure and in the nervous system it also acts as a neurotransmitter.

The Testes and the Ovaries Testes (males) Ovaries (females) These glands produce the hormones testosterone, estrogen, and progesterone.

Testosterone Male sex hormone Females have small amounts of this hormone as well. Produced by the testes in males. Small amounts of it are also secreted by the ovaries in females.

Testosterone plays an important role in development, particularly during the prenatal period and during adolescence. Prenatal Period Testosterone influences development of the sex organs. Six weeks after fertilization, if testosterone is secreted, it stimulates development of male sex organs. If not secreted, female organs develop.

Adolescence Testosterone aids the growth of muscle and bone, as well as the development of primary and secondary sex characteristics. Primary sex characteristics are directly involved in reproduction. Secondary sex characteristics, such as beard growth, distinguish males and females but are not directly involved in reproduction.

Testosterone is a kind of steroid. Steroids affect muscle mass, heighten resistance to stress, and increase the body’s energy supply.

Estrogen and Progesterone Female sex hormones Low levels are found in males as well. Ovaries in females produce estrogen and progesterone Estrogen is also produced in smaller amounts by the testes in males.

Estrogen fosters the development of primary and secondary sex characteristics, such as breast enlargement. Progesterone Stimulates growth of the female reproductive organs Helps prepare the body for pregnancy Together, estrogen and progesterone regulate the menstrual cycle.