ENDOCRINOLOGY

Endo means “Internal” and Crinos means “Secretion”So, endocrinology means internal secretion.

Endocrinology is the study of endocrine system which includes the endocrine glands and their hormones.

Endocrine System

Function of the body are regulated by two major control systems:

1. Nervous system

2. Hormonal or endocrine system

The endocrine system is made up of glands that produce and secrete hormones.

HormoneHormone is a chemical messenger that

transports a signal from one cell to another.

Made in glands or cellsTransported by bloodDistant or local target tissue receptorsActivates physiological responseComprises Endocrine System

Most hormones are proteins consisting of amino acid chains. Some hormones are steroids, fatty cholesterol-produced substances.

Classification of HormoneFunctional Classification:

Endocrine Hormones – Travel through the blood to act at a site distant from the secreting cell or gland

(e.g. Growth Hormone – Pituitary gland to circulation to be used up by the tissue to grow, Testosterone secreted from the testes acts as an endocrine agent to stimulate peripheral events - muscle growth )

Paracrine Hormones – Act on cells near the secreting cell (e.g. Testosterone as a paracrine agent to stimulate

spermatogenesis in the adjacent seminiferous tubules)

Autocrine Hormones – Act on the secreting cell. (e.g. Acetylcholine)

Neurocrine Hormones – Secreted by neural cellsNeurotransmitters (Dopamine, Serotonin) Neurohormones (Oxytocin, ADH,

Adrenocorticotropin Releasing Hormone)

Function of Hormone

Fetal development and differentiation

Cell growth Metabolism Cardiovascular function Renal function Skeletal function Reproductive function Immune function Central nervous system function

Anatomy of Endocrine GlandThe major glands of the endocrine system are:

Hypothalamus Pineal Gland Pituitary Thyroid Parathyroid Thymus Adrenal Pancreas Ovaries Testes

Anatomical position of endocrine glands

HypothalamusThe hypothalamus is located in the brain, near the optic chiasm. It secretes hormones that stimulate or suppress the release of hormones in the pituitary gland, in addition to controlling water balance, sleep, temperature, appetite, and blood pressure.

Pineal GlandThe pineal body is located below the corpus callosum, a part of the brain. It produces the hormone melatonin. Pineal body Involved with daily biological cycles.

Pituitary GlandThe pituitary gland is located at the base of the brain. It secretes hormones to stimulate the adrenals, thyroid, pigment-producing skin cells and gonads (ovaries and testes).

Hormone secretion from pituitary gland-

Anterior Pituitary: GH-Growth Hormone TSH-Thyroid Stimulating Hormone ACTH-Adrenocorticotrophic Hormone FSH-Follicle Stimulating Hormone LH-Leutining Hormone

Posterior Pituitary: Oxytocin Anti-diuretic hormone or vasopressin

Thyroid & Parathyroid

The thyroid and parathyroid glands are located in front of the neck, below the larynx. Thyroid gland - secretes thyroxin, triiodothyronine and calcitonin, which affect metabolism, body heat, and bone growth. Parathyroid glands - secretes a parathyroid hormone, which affects calcium levels in the blood.

Thymus Gland It is a relatively large organ at birth, centrally

placed in the upper chest behind the sternum, and extending into the neck. It grows with the child until puberty, then regresses to almost nothing in adulthood. It produces T-lymphocytes (white blood cells that fight infections and destroy abnormal cells). So, it plays a role in the body's immune system.

Adrenal GlandThe pair of adrenal glands are located on top of both kidneys. Adrenal cortex - secretes hydrocortisone, which affects metabolism. Also secretes androgen hormone and aldosterone, which affect blood pressure and saline balance.

PancreasThe pancreas is located across the back of the abdomen, behind the stomach. It secretes insulin and glucagon, which affect the body's absorption of glucose, the body's main source of energy.

Ovary

A woman's ovaries are located on both sides of the uterus, below the opening of the fallopian tubes. The ovaries secrete estrogen and progesterone, which affect many aspects of the female body, including menstrual cycles and pregnancy.

Testis

A man's testes are located in a pouch that hangs suspended outside the male body. The testes secrete testosterone, which stimulate sperm production and other male characteristics

Physiology The endocrine system is regulated by

feedback. For the hormones that are regulated by

the pituitary gland, a signal is sent from the hypothalamus to the pituitary gland in the form of a "releasing hormone," which stimulates the pituitary to secrete a "stimulating hormone" into the circulation.

The stimulating hormone then signals the target gland to secrete its hormone. As the level of this hormone rises in the circulation, the hypothalamus and the pituitary gland shut down secretion of the releasing hormone and the stimulating hormone, which in turn slows the secretion by the target gland.

This system results in stable blood concentrations of the hormones that are regulated by the pituitary gland.

Endocrine Disease/Condition

Sometimes the glands of the endocrine system are impaired and can cause a hormone imbalance. This hormone imbalance can affect the health in many ways, & some are more serious than others:

Cardiovascular Disorder Diabetes Mellitus Growth Disorders Menopause Osteoporosis Pituitary Disorders Polycystic Ovary Syndrome Reproductive Disorder Thyroid Conditions/Disorders Other Conditions

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