- Understand the function of the endocrine system and its components
- Define the role of the sex hormones


[SLIDE 1]

The body has two types of glands, which are organs that secrete one or more chemical substances such as hormones, saliva, or milk. Some glands have ducts and other glands do not have ducts. A duct is a passageway that carries substances to specific locations. For example, saliva, sweat, tears, and breast milk all reach their destinations through ducts.

A number of substances secreted by ductless glands have effects on behavior and mental processes. The ductless glands make up the endocrine system and they release hormones into the bloodstream. Hormones act only on receptors in certain locations.

Much hormonal action helps the body maintain steady states, such as fluid levels, blood sugar levels, and so on. Bodily mechanisms measure current levels; when these levels deviate from optimal, they signal glands to release hormones. The maintenance of steady states requires feedback of bodily information to glands. This type of system is referred to as a negative feedback loop. When enough of a hormone has been secreted, the gland is signaled to stop.

Figure 2.13 above illustrates the endocrine system.


[SLIDE 2]

The pituitary gland and the hypothalamus work in close cooperation. The pituitary gland lies below the hypothalamus. It is only about the size of a pea, but is so central to the body's functioning that it is often called the master gland. The anterior (front) and posterior (back) lobes of the pituitary gland secrete hormones that regulate the functioning of many other glands.

<strong>Growth hormone</strong> regulates the growth of muscles, bones, and glands.

<strong>Prolactin</strong> regulates maternal behavior in lower mammals such as rats and stimulates production of milk in women.

As a water conservation measure, <strong>vasopressin</strong>, a antidiuretic hormone, inhibits production of urine when the body's fluid levels are low. Vasopressin is also connected with stereotypical paternal behavior in some mammals.

<strong>Oxytocin</strong> stimulates labor in pregnant women and is connected with maternal behavior in some mammals. Obstetricians can induce labor by injecting pregnant women with oxytocin. During nursing, stimulation of the nerve endings of the nipples signals the brain to secrete oxytocin, which then causes the breasts to eject milk.

The <strong>hypothalamus</strong> regulates much pituitary activity. The hypothalamus secretes a number of releasing hormones, or "factors," that stimulate the pituitary gland to secrete related hormones. For example, growth hormone releasing factor (hGRF) causes the pituitary to produce growth hormone. Blood vessels between the hypothalamus and the pituitary gland provide a direct route for these factors. 


[SLIDE 3]

The pineal gland secretes the hormone <strong>melatonin</strong>, which helps regulate the sleep-wake cycle. It may affect the onset of puberty and has been connected with the aging process. Melatonin is a mild sedative, so some people use it as a sleeping aid. Melatonin is also used to help people adjust to jet lag. 


[SLIDE 4]

The thyroid gland could be considered the body's accelerator. It produces <strong>thyroxin</strong>, which affects the body's metabolism, or the rate at which the body uses oxygen and produces energy.

Hypothyroidism is a condition that results from too little thyroxin. Thyroxin deficiency in children can lead to <strong>cretinism</strong>, a condition characterized by stunted growth and intellectual disability. Adults who secrete too little thyroxin may feel tired and sluggish and may put on weight. On the other hand, people who produce too much thyroxin may develop hyperthyroidism, which is characterized by excitability, insomnia, and weight loss. 


[SLIDE 5]

The adrenal glands, located above the kidneys, have an outer layer, or <strong>cortex</strong>, and an inner core, or <strong>medulla</strong>.

The adrenal cortex is regulated by the pituitary hormone <strong>ACTH</strong>, which stands for adrenocorticotrophic hormone. The adrenal cortex secretes hormones known as <strong>corticosteroids</strong>, or cortical steroids. These hormones regulate the heartbeat, increase resistance to stress, promote muscle development, and cause the liver to release stored sugar, making more energy available in emergencies.

<strong>Epinephrine</strong> and <strong>norepinephrine</strong> are secreted by the adrenal medulla. Epinephrine, also known as <strong>adrenaline</strong>, is manufactured exclusively by the adrenal glands, but norepinephrine, sometimes called noradrenaline, is also produced elsewhere in the body. Recall that norepinephrine acts as a neurotransmitter in the brain. The sympathetic branch of the autonomic nervous system causes the adrenal medulla to release a mixture of epinephrine and norepinephrine that helps arouse the body to cope with threats and stress.

Epinephrine is of interest to psychologists because it has emotional as well as physical effects. It intensifies most emotions and is central to the experience of fear and anxiety.


[SLIDE 6]

The testes and ovaries also produce steroids, among them <strong>testosterone</strong> and <strong>estrogen</strong>. Testosterone is also produced in smaller amounts by the adrenal glands.

About six weeks after conception, the male sex hormone testosterone causes the male's sex organs to develop. In fact, if it were not for the secretion of testosterone at this time, we would all develop the external genital organs of females.

During puberty, testosterone stokes the growth of muscle and bone and the development of primary and secondary sex characteristics. Primary sex characteristics are directly involved in reproduction and include the increased size of the penis and the sperm-producing ability of the testes. Secondary sex characteristics, such as the presence of a beard and a deeper voice, differentiate males from females but are not directly involved in reproduction.

The ovaries produce estrogen and progesterone as well as small amounts of testosterone. Estrogen is also produced in smaller amounts by the adrenal glands. Estrogen fosters female reproductive capacity and secondary sex characteristics such as accumulation of fatty tissue in the breasts and hips. <strong>Progesterone</strong> stimulates growth of the female reproductive organs and prepares the uterus to maintain pregnancy.

Estrogen and testosterone have psychological effects as well as biological effects, which we will explore in future lessons.


[SLIDE 7]

Chapter 2 describes the case study of professional wrestler Chris Benoit and Nancy Benoit and the double murder and suicide that took their lives and the life of their seven-year-old son. Steroids increase muscle mass, heighten resistance to stress, and increase the body's energy supply by signaling the liver to release glucose into the bloodstream. The steroid testosterone is connected with the sex drive in both males and females, since females secrete some testosterone in the adrenal glands.

Anabolic steroids are synthetic versions of the male sex hormone testosterone and they have been used, sometimes along with growth hormone, to enhance athletic abilities. Not only do these steroids enhance athletic prowess, but they appear to enhance self confidence and aggressiveness.

Anabolic steroids are generally outlawed in sports; however, many athletes, such as professional wrestler Chris Benoit, have used them. Benoit is best known for murdering his wife and his son before taking his own life – likely due to "roid rage" that comes with excessive use of anabolic steroids.