The Endocrine System Allied Health Sciences I Unit P.

The Endocrine System

Allied Health Sciences I

Unit P

Functions of the Endocrine System

• Secrete hormones

• Hormones are chemical messengers that coordinate and direct target cells and organs.

• Hormone control– Negative feedback = drop in hormone level triggers a chain

reaction

• Blood level of hormone falls

• Brain gets message and sends out hormone to stimulate gland

• Gland secretes more hormone

• When blood level of hormone increases, brain hormones stop

Functions of Endocrine System

• Nervous control– In some cases, sympathetic nervous system

causes direct release of hormone from gland (for example, when stress causes the adrenal medulla to secrete adrenalin)

Two types of glands

• Endocrine– Secrete hormones

directly into the bloodstream

– ductless

• Exocrine– Secrete substance

through a duct

– Sweat, salivary, lacrimal and pancreas

Structures of the Endocrine System

• Anterior Pituitary Gland

• Posterior Pituitary Gland

• Thyroid Gland• Parathyroid glands• Thymus Gland

• Adrenal Glands• Ovaries• Testes• Pancreas• Pineal Gland

The Anterior Pituitary Gland

• The entire pituitary gland is the size of a grape.

• It is located on the underside of the brain in the sella turcica.

• The anterior lobe secretes 7 hormones:– Growth hormone or GH or somatotrophin-responsible for growth

and development.

– Prolactin hormone or PRL: responsible for stimulating milk production after childbirth

– Thryroid-stimulating hormone or TSH: stimulates growth and secretion of the thyroid gland

The Anterior Pituitary Gland

• Hormones cont.:– Adrenocorticotropic hormone or ACTH: stimulates growth and

secretion of the adrenal cortex

– Follicle-stimulating hormone or FSH: stimulates the growth of the graafian follicle and production of estrogen in the female and production of sperm in the male

– Luteinizing hormone or LH: stimulates ovulation and formation of the corpus luteum which produces progesterone in the female

– Interstitial-cell stimulating hormone or ICSH: needed for the production of testosterone in the male

The Posterior Pituitary Gland

• The posterior pituitary gland produces two hormones:– Vasopressin: this converts to ADH in the

bloodstream. ADH helps with water balance.– Oxytocin: causes contractions of the uterus

during childbirth and during breastfeeding

The Thyroid Gland

• It is located behind the cricoid cartilage in the neck and is about 2 inches long.

• It produces three hormones:– Thyroxine (T4) and triiodothyronine (T3):

controls the rate of metabolism, protein synthesis and the breakdown of liver glycogen.

– Calcitonin: controls the calcium level in the bloodstream when it gets too high

The Parathyroid Glands

• There are four of these and are the size of a grain of rice. They are attached to the posterior side of the thyroid gland.

• It secretes one hormone:– Parathormone: also controls the calcium level

when it gets too low

The Thymus Gland

• The thymus gland is located beneath the sternum and decreases in size after puberty.

• It secretes several hormones but the most important is:– Thymosin: stimulates lymphoid cells to

produce T cells which help with immunity

The Adrenal Glands

• There are two adrenal glands located on the top of each kidney.

• There are two parts: the cortex and the medulla.• The cortex secretes three corticoids (which act as

antiinflammatory agents):– Mineralocorticoids: mainly aldosterone which speeds

sodium and water reabsorption in the kidneys– Glucocorticoids: mainly cortisone and cortisol,

increases the amount of glucose in the blood– Androgens: male sex hormones that produce male

sexual characteristics

The Adrenal Glands (cont.)

• The medulla of the adrenal gland produces one hormone:– Epinephrine: increases heart rate, blood

pressure and flow of blood; decreases intestinal activities

The Ovaries

• They are located in the female pelvis.

• They produce two hormones:– Estrogen: promotes growth of primary and

secondary sexual characteristics– Progesterone- develops excretory portion of

mammary glands, aids in maintaining pregnancy

The Testes

• They are located in the male scrotum.

• They produce one hormone:– Testosterone: develops primary and secondary

sexual characteristics; stimulates maturation of sperm

The Pancreas

• The pancreas is located behind the stomach.

• It produces two hormones:– Insulin: essential to the metabolism of

carbohydrates, reduces blood sugar level– Glucagon: stimulates the liver to release

glycogen and converts it to glucose to increase blood sugar levels

The Pineal Gland

• The pineal gland is located at the base of the brain.

• It produces one hormone:– Melatonin: relates to the sleep cycle

Prostaglandins

• Hormones called prostaglandins are secreted in various tissues. What the prostaglandins do depend on which tissue is secreting them. Some may cause constriction while others cause dilation. Prostaglandins can be used to induce labor and cause severe muscular contractions of the uterus.

Acromegaly

• This occurs when hypersecretion of the growth hormone occurs.

• Overdevelopment of the bones of the face, hands and feet occur.

• Patients may have lethargy and headaches.

• Tx. is drug therapy and radiation therapy.

Gigantism

• This is an overgrowth of the long bones leading to excessive tallness.

• This is due to hyperfunctioning of the pituitary gland during preadolescence.

• Tx. is drug therapy and radiation therapy

Dwarfism

• Hypofunctioning of the pituitary gland during childhood leads to dwarfism.

• The body of a dwarf is normally proportioned and intelligence is normal.

• Tx. Is early diagnosis and injections of the human growth hormone.

Hyperthyroidism

• Hyperthroidism is an overactivity of the thyroid gland.

• The gland becomes enlarged.• Patients may feel hot, have fast

growing, rough fingernails, increased blood pressure and heart beat.

• Patients may exhibit goiter and exopthalmos.

• Tx. is partial or total removal of the thyroid, drugs to reduce thyroxine, radiation

Hypothyroidism

• The thyroid gland does not secrete enough thyroxine.

• Iodine deficiency may cause adult hypothyroidism.

• Myxedema causes the face to swell, weight gain and memory failure. Tx. is the thyroid hormone.

• Occuring in infancy and early childhood, cretinism causes mental retardation and lack of physical growth. Tx. Is the thyroid hormone; however complete recovery is not possible.

Cushing’s Disease

• This results from hypersecretion of the glucocorticoid hormones from the adrenal cortex. It may be caused by a tumor or prolonged use of prednisone.

• The most common characteristics are a “moon” face and a “buffalo” hump.

• Tx. Is removal of the tumor or gradual decrease of use of the prednisone.

Addison’s Disease

• It is caused by decreased functioning of the adrenal cortex.

• It is characterized by a “bronzing” of the skin.

• Tx. is replacement of the deficient hormones.

Tetany

• Caused by hypoparathyroidism, decreased calcium levels affect functions of nerves

• Symptoms = convulsive twitching develops, person dies of spasms in the respiratory muscles

• Rx = vitamin D, calcium and parathormone

Diabetes Mellitus

• This is caused by decreased secretion of insulin in the islets of Langerhans.

• There are two types: Type I- children and young adults and Type II- adults.

• Type I requires insulin to control the glucose levels.

• Type II may be controlled through diet and oral meds or may require injections.

• Polyuria, polydypsia and polyphagia are typical symptoms.

Diabetes Insipidus

• This is caused by a drop in the ADH (antidiuretic hormone) secondary to dysfunction of the posterior lobe of the pituitary gland. The person has excessive thirst.