THE ENDOCRINE SYSTEM

 
The Endocrine System

• plays a major role in the various changes that occur in the body. These changes are triggered by chemicals, called hormones, which are secreted by the endocrine glands.
• one function of this system is to regulate reproduction
• the endocrine system provides integration of the different organs and tissues
• the endocrine system is made of many glands—groups of cells that release chemical substances called hormones into the bloodstream. Hormones influence and regulate diverse activities such as metabolism, growth, mental development, and emotional behavior.

The Glands

Gland – is an organ that develops a secretion which performs a specific function

Two Kinds:

1. exocrine glands – external secretion
2. endocrine glands – internal secretion

Exocrine glands

• pass through a channel or duct to the site where they take effect
• examples are the salivary glands of the mouth and the gastric glands of the stomach

Endocrine glands

·      secrete their products directly into the bloodstream

·      the term ductless indicates that no duct leads from the glands.

·  their products or secretions are called hormones also known as chemical messengers

·     they regulate and integrate body functions

·  sometimes called ductless glands because they have no ducts connecting them to specific body parts

 

The Hormones

• are formed from substances taken from the blood
• are able to regulate the body processes, such as growth, development, metabolism, and response to critical situations
• are defined as chemical messengers formed in an organ or glands that is send to a target tissue or organ through the blood to influence the activity of the target tissue
• if hormones are no longer needed, they are:

1.    removed from the blood by the target tissue or organ;

2.    excreted out by the kidney; and

3.    broken down to anything simpler and usable by the liver

The Endocrine Glands

The primary glands that make up the human endocrine system are the pituitary, thyroid, parathyroid, thymus, adrenal, pancreas, and reproductive glands—the ovary and testis

 1. Pituitary gland
 

·      is a pea-sized gland located at the base of the brain

·      it weighs only about 4 grams

·      the chief of the ductless glands

·      also known as hypophysis

• the pituitary gland is a pea-sized gland located in the center of the skull. The pituitary  gland acts as a master controlling gland, releasing a number of hormones that activate other glands.  
•   it controls the functioning of almost all the endocrine glands 
•  acts as a master controlling gland, releasing a number of hormones that activate other glands. 
• Diabetes insipidus is caused by a deficiency of vasopressin, one of the antidiuretic hormones (ADH) secreted by the posterior lobe of the pituitary gland which controls the amount of urine secreted by the kidneys. 
• The symptoms of diabetes insipidus are marked thirst and the excretion of large quantities of urine, as much as 4 to 10 liters a day
•  it is often called the master gland because it controls all the endocrine glands

2. Thyroid gland

· is a soft, brownish-red organ shaped like a butterfly

· it is situated beneath the larynx

· the thyroid gland, located in the neck, secretes the hormone thyroxine

· it secretes the hormones thyroxine and calcitonin

Thyroxine

 

· it increases the oxygen consumption, or speeds up the metabolic rate, of nearly all the cells in the body

· the effects of the hormones include increased appetite, weight loss, and slight rise in body temperature

· thyroxine increases body metabolism, in which food is broken down and converted into heat and energy. Too little thyroxine in the blood produces lethargy and fatigue, while too much thyroxine results in overactivity, nervousness, and weight loss.

· if the thyroid failed to develop, you could be sluggish, or be both physically and mentally retarded. This condition is called cretinism; it usually occurs in early childhood

· thyroid hormone contains iodine

Calcitonin

 

· it prevents the release of calcium from the bones, thus lowering the levels of phosphate and calcium in the blood

3. Parathyroid glands

 

· are four, small glandular bodies about the size of a small pea attached to the back of the thyroid gland

· these glands secrete a hormone that regulates the body’s use of calcium and phosphorus to maintain healthy bones. Parathyroid hormone also affects muscle contraction and the conduction of nerve impulses.

· the hormone they secrete is the parathyroid hormone, or parathormone, which makes sure that calcium and phosphate ions are provided properly to the bones, muscles, and nerves.

· these glands secrete a hormone that regulates the body’s use of calcium and phosphorus to maintain healthy bones. Parathyroid hormone also affects muscle contraction and the conduction of nerve impulses.

 4. Thymus gland

·      is located at the upper part of the chest, below the neck

·      it performs a vital function in early months of life before puberty

·   it manufactures WBC that make it possible for the body to develop immunity against infection

·      the hormones it secretes are the promine, which promotes growth; and retine, which retards growth

 5. Adrenal glands

 

· a small gland on top of each of the kidneys

· these two glands consist of an inner core, called the adrenal medulla, and an outer area, known as the adrenal cortex.

· releases epinephrine and norepinephrine, which help the body deal with stress

                  · the adrenal medulla releases the hormone epinephrine

· the adrenal cortex releases hormones that control the level of salts and water in the blood and help regulate the use of sugar. It also secretes small amounts of male sex hormones, or androgens, in both males and females.

· of the two parts of the adrenal glands, only the adrenal cortex is under the control of the pituitary gland.

 · the adrenal cortex secrets the hormone cortisiol

Cortisol

· regulates the metabolism (storage and use) of proteins, fats, and carbohydrates

·    also controls the amount of water the body retains or excretes. It acts as “watcher” of the important body salts

·      it influences the growth and development

• the adrenal medulla secretes two important hormones, the emergency glands – adrenaline and nonadrenaline

Adrenaline

·   also called epinephrine, is the hormone secreted during times of anger, stress, pain, excitement, or cold

·     it raises the blood pressure and body temperature

·    speeds up heart rate and increases blood pressure to help the body cope with emergencies.

Nonadrenaline

·      also called norepinephrine

·      it supplements the actin and complex functions of the nervous system

6. Pancreas

 

·  the pancreas is a long, narrow gland located in the abdomen behind the stomach and beneath the liver.

· the pancreas produces insulin and glucagon, which regulate the level of glucose in the blood

·   hormone-secreting cells are found in the islets of Langerhans, located all over the pancreas

·    the pancreas secretes insulin, a hormone that regulates the body’s use of sugar. When too little insulin is produced, the body tissues cannot use or store sugar, and a disease known as diabetes mellitus develops.

Glucagon

· it converts glycogen (stored body sugar in liver) to glucose

· this happens when the blood glucose concentration becomes low

Insulin

· controls the storage of sugar in the liver and sugar breakdown in the tissues

· if you do not produce enough insulin, a condition called diabetes mellitus results

· when too little insulin is produced, the body tissues cannot use or store sugar, and a disease known as diabetes mellitus develops.

 7. Gonads

 

·    the male and female reproductive systems also contain glands

·    in males, the prostate gland and the Cowper’s gland may be found

·    in females, glands are also present, and these glands line the mucus membrane of the uterus

· Females have sex glands called ovaries that release hormones called estrogens and progesterone

· Males have sex glands called testes that secrete androgens, male sex hormones. In addition to contributing to male sexual characteristics, androgens contribute to the production of sperm and the development of the prostate gland.

 

Estrogen

· these hormones contribute to the development of female sexual characteristics, including skin, hair, and breast development. Estrogens work with certain pituitary hormones to control the menstrual cycle.

·      is required for the development of eggs

Progesterone

·      the principal function of progesterone is the preparation of the mucous membrane of the uterus for the reception of the ovum.

·      the hormone also stimulates the formation of saclike structures in the lacteal glands in preparation for their function of producing milk, and inhibits the release in the pituitary of prolactin hormone.

·      prepares the uterus for a fertilized egg

Androgen

·      the male sex hormones, substances that induce and maintain secondary sex characteristics in males

·      the principal androgen is testosterone, which is responsible for sperm production and the development of male secondary sex characteristics

·      testosterone circulates in the blood and is excreted in the urine.

·      androgens function principally, beginning at puberty, in the stimulation of such male secondary sex characteristics as development of the genital organs and maturation of sperm, growth of body hair, and changes in the larynx that lower the voice.

·      androgens have an anabolic effect—that is, they stimulate protein synthesis and inhibit protein breakdown, enhancing the growth of muscle and bone tissue in the developing male.

·       an excess of androgens can lead to a variety of disorders, including the accentuation of male secondary sex characteristics in both males and females. Less frequently, an excess of androgens may cause testicular tumors.

 

Gland	Location	Secreted Hormones	Hormonal Function
Thyroid	Beneath the larynx	Thyroxine Calcitonin	Speeds up metabolism rate Prevents release of calcium from the bones
Parathyroid	At the back of the thyroid	Parathormone	Controls calcium and phosphate ions
Pituitary	Base of the brain	THS (thyroid stimulating) Prolactin ACTH (adrenocorticotropic) GH (growth hormone) LH (leutenizing hormone) FSH (follicle stimulating) Oxytocin	Controls all other glands for proper utilization of nutrients
Adrenal	On top of kidneys	Cortisol epinephrine norepinephrine	For adaptation in times of stress
Pancreas	Below the stomach	Insulin	Allow sugar to enter the cell from blood vessel
Thymus	Upper part of the chest	Promine Retine	Promotes growth Retards growth
Testes	In the scrotum	Testosterone	For sexual development
Ovaries	Side of the pelvic cavity	Estrogen Progesterone	Vital to the menstrual cycle and sexual growth