Endocrine System
General description
The endocrine system is one of the most complicated of the body systems.It consists of glands widely separated from each other with no direct anatomical links. Many of its functions are understood,but some remain to be explained.This section describes the endocrine glands and the profound influences they exert on the growth and development as well as the activities of the human body.
The word “endocrine” means secreting internally. Endocrine glands perform their functions by extracting substances (raw materials) from blood and tissue fluids, and creating new substances called hormones. Hormones are secreted into the blood and lymph circulation, to be transported to the specific organs and structures, upon which they exert influence and control. They are often referred to as chemical messengers. The major glands of the endocrine system include the pituitary, thyroid and parathyroids, adrenals, Islets of Langerhans, and the gonads.
The pituitary
Situated in the brain, The pituitary acts together with the hypothalamus, to regulate the activity of most of the other endocrine glands. The pituitary is also called the hypophyseal or “master” gland. Substances produced and secreted by the pituitary act directly and indirectly.
Direct functions:
- Regulation of growth, development and sexual maturation of the young.
- Regulation of water excretion and retention.
- Regulation of lactation in the new mother.
Indirect functions (By regulating all other endocrine glands)
- Regulation of assimilation and metabolism of foods by action on the thyroid.
- Regulation of body composition, adaptation, and resistance to stress by action on the adrenal gland.
- Regulation of sexual development, activity and reproduction by action on the gonads.
- Regulation of respiration, circulation, digestion, urinary excretion, and muscular activity by combined actions of many hormones.
The influence of the pituitary gland is indeed “masterful” in the normal growth, development and activities of man and often referred to as the conductor of the endocrine orchestra.
Thyroid gland
Positioned in the front of the trachea, the thyroid gland produces and secretes substances important to the control and rate of certain metabolic processes, plus the normal growth and development of the young. It also helps to regulate blood calcium levels.Iodine is stored in the thyroid gland and is necessary for the production of thyroid hormones.
Parathyroids
There are four small glands, called the parathyroids, each about the size of a pea, situated in the lobes of the thyroid gland. Their primary functions include the maintenance of normal blood calcium levels and the regulation of phosphate metabolism.
Adrenal glands
There are two glands, called the adrenals, situated at the top of the kidneys that secrete hormones which help regulate fluid and electrolyte balance of the body. Some hormones released, including adrenalin, though not essential to life, are important in helping the body to respond to danger, stress and competitive activities. The adrenal steroids, however, are essential to life.
Islets of Langerhans
The islets of Langerhans are cell groups (islet cells) distributed throughout the pancreas, which secrete the hormone, insulin, and other hormones, which control the glucose level in the blood. The body must have insulin to use sugars and starch properly.
Ovaries
The ovaries release hormones in the female, essential to the normal cyclic changes
of menstruation, and preparation of the uterine lining for pregnancy
(see Section 10 on the Reproductive System).
Oestrogen
Oestrogen is a female hormone which controls development of the female characteristics and female sex libido.
Progesterone
The hormone, progesterone promotes gestation during the Menstrual cycle.
Testes
The male sex glands (testes) are located in the scrotum. They produce the steroid
testosterone, which stimulates development of male characteristics: body hair,
deepening voice, etc. The testes also produce spermatozoa.
Endocrine System
Glossary of Terms Endocrine System
Adrenal glands
(ad-re’nal) Two small endocrine glands, one located above each kidney.
Calcium
kal’se-um) An element which occurs naturally in all body tissues and fluids such as bones, teeth and blood.
Diabetes mellitus
(di-ah-be’tez) A condition in which cells of the pancreas, called Islets of Langerhans,
fail to produce enough insulin for proper metabolism of sugars and starches.
Ductless gland
A gland without excretory ducts or channels.
Electrolyte balance
Distribution of acids, bases and salts in tissue cells, fluids and blood plasma which helps maintain normal pH and control the passage of water between cell membranes.
Endocrine
(en’do-krin) Capable of secreting internally.
Endocrine gland
An organ which secretes hormones directly into the circulatory systems to influence and regulate numerous body processes.
Endocrine system
All the glands of internal secretion concerned with regulating and influencing organs and processes by the hormones they produce.
Exocrine
(eks’o-krin) Capable of external secretion.
Gastric
(gas’trik) Pertaining to the stomach.
Glucose
(gloo’kos) One form of sugar; it is a product of starch metabolism in the body.
Gonads
(gon’ads) Glands which produce sex hormones and germ cells necessary
for reproduction.
Hormone
(hor’mon) Chemical substance produced and secreted by an endocrine gland.
Hypophyseal gland
hi-po-fiz’e-al) The pituitary or “master” gland.
Insulin
(in’su-lin) Substance produced by the pancreas. Insulin is vital to normal glucose metabolism.
Islets of Langerhans
(lan’ger-hanz) Group of cells of the pancreas which secrete insulin.
Lymph system
(limf) A drainage network which assists the blood circulatory system in returning tissue fluids to the bloodstream.
Menstruation
(men-stroo-a’shun) Cyclic shedding of the uterine lining.
Metabolism
(me-tab’o-lizm) The physical and chemical processes by which ingested food and fluids are converted to energy or body tissues.
Mucosa
(mu-ko’sah) Mucous membrane.
Ovarian follicles
(o-va’re-an fol’li-kls) Blister like formations on the ovary which rupture when they
ripen and release the egg cell of reproduction.
Ovum
(o’vum) Egg cell.
Pancreas
(pan’kre-as) A gland which is both endocrine and exocrine; located behind the stomach,the pancreas produces secretions concerned with digestion.
Parathyroid glands
(par-ah-thi’roid) Two pairs of small endocrine glands usually attached to the back of the thyroid gland.
Phosphorus
(fos’fo-rus) A nonmetallic element normally found in the body.
Pituitary gland
(pi-tu’i-tar-e) The “master” gland of the body, so-called because of the many ways it controls and influences organs and body processes.
Puberty
(pu’ber-te) Onset of sexual maturity; appearance of adult secondary sex characteristics.
Scrotum
(skro’tum) Pouch which contains testes and accessory structures.
Testes
(tes’tez) The two male gonads in the scrotum which produce sex cells called spermatozoa.
Thyroid gland
(thi’roid) An endocrine gland located in the anterior neck at the trachea. Secretions
of the thyroid gland are important in certain metabolic processes.
Uterus
(u’ter-us) The womb. A muscular organ in which the fertilized ovum is implanted and develops.
Viscera
(vis’er-ah) Internal organs within the chest, abdominal and pelvic cavities.
Exercises on the Endocrine System
A. Write in the table below the medical terms for the numbered items in the diagram.Then check your answers against the fully labelled diagram in this section
B. Read the definitions of terms below. Each describes an organ, part or function of the endocrine system. You may refer to the preceding text to assign the appropriate word or phrase.
Definition
- The system consists of glands widely separated from each other, with no direct anatomical links.
- The substances which endocrine glands create and secrete directly into the blood and lymph circulation.
- Endocrine gland situated in front of the trachea, which is responsible for the control and rate of certain metabolic processes.
- The element stored in the thyroid gland necessary for the production of thyroid hormones.
- Four small glands situated in the lobes of the thyroid gland, whose primary function is to maintain normal blood calcium level.
- Two glands, each located on top of a kidney.
- One of the hormones released from the adrenal glands which helps the body to respond to danger.
- Secreted by the adrenal glands these hormones are Essential to life.
- Special groups of cells in the pancreas which secrete hormones.
- A hormone secreted by the Islets of Langerhans.
- A gland in the brain which regulates the activity of most other endocrine glands.
- Two small glands in females which produce hormones responsible for the development of female sex characteristics, and normal cyclic changes of menstruation.
- Two hormones produced by the ovaries.
- Male sex glands situated in the scrotum.
- Produced in the testes, this steroid stimulates Development of male characteristics.
C. Use a medical dictionary to look up the meaning of these terms which are commonly used in describing conditions related to the endocrine system.
acromegaly
Addison’s disease
aldosterone
alkalosis
cortisone
Cushing’s disease
diabetes insipidus
diabetes mellitus
electrolyte
exophthalmus
follicle stimulating hormone
goitre
glucagon
glucose
glycogen
homeostasis
hyperkinesia
hyperthyroidism
hypophysis
hypothyroidism
insulin
iodine
Ketosis
myxoedema
oestrogens
oxytocin
phenylketonuria
polydipsia
polyuria
progesterone
steroids