Endocrine System

Standards:

SAP 1 – Students will analyze anatomical structures in relationship to their physiological functions.

SAP 3 – Students will assess the integration and coordination of body functions and their dependence on the endocrine and nervous systems to regulate physiological activities.

The endocrine system is a group of glands that transmit chemical messengers (hormones) throughout the body

Glands with ducts (tubes) are exocrine glands

Examples: sweat glands

digestive glands - pancreas and liver (bile duct)

Glands without ducts secrete hormones directly into the blood are endocrine glands

Most hormones are proteins or shorter protein-like molecules

Others are fat-like molecules called steroids

Glands

I. Pituitary Gland – master gland

Location – attached to hypothalamus at base of brain

• direct link between endocrine and nervous system

• 2 major lobes: anterior and posterior

A. Anterior Pituitary Hormones

1. GH – (growth hormone) – regulates growth

• if too much is released during childhood = giant

ex. Andre the Giant

• if too little is released during childhood = midget (perfectly proportioned

individual, only smaller

• if too much is released during adulthood, a condition called acromegaly results

These individuals exhibit a thickening of the bones of the hands, feet, cheeks, and jaw

Age 16 Age 33 Age 52

Age 16

Age 42Age 37Age 29Age 24

Age 52Age 33

Acromegaly Normal

2. ACTH – (adrenocorticotropic hormone) – stimulates adrenal cortex to

secrete cortisol

3. TSH – (thyroid stimulating hormone) – stimulates the thyroid gland to secrete thyroxine

4. FSH – (follicle stimulating hormone) – stimulates egg growth and the

secretion of estrogen in females and sperm growth in males

5. LH – (luteinizing hormone) – stimulates the ovaries to produce estrogen and stimulates ovulation in females

Stimulates the testes to produce testosterone in males

6. PRL – (prolactin) – stimulates milk production in pregnant females

• some evidence that PRL enhances testosterone production in males

B. Posterior Pituitary Hormones

1. Oxytocin – stimulates the uterus to contract during childbirth

2. ADH – (antidiuretic hormone) or vasopressin – stimulates kidneys to return water to the blood

II. Thyroid Gland

Location – in neck near lower part of larynx

thyroid gland

larynx

• butterfly shaped

1. Thyroxine – regulates metabolism; necessary for normal growth

• if too much thyroxine is produced, you have hyperthyroidism – which causes nervousness, sleep disorders, irregular heart rate, and weight loss

• if too little thyroxine is produced, you have hypothyroidism

Adults with hypothyroidism will tire easily, have dry skin, and experience weight gain

Infants with hypothyroidism are said to have cretinism – which results in stunted growth and mental retardation

• If your diet contains too little iodine you may develop a goiter (= enlarged thyroid gland)

Goiter is largely a condition of the past – today, goiter is prevented by adding iodine to table salt

2. Calcitonin – helps regulate the amount of calcium in the bloodstream

• when the level of calcium in the blood is high, the thyroid gland releases calcitonin

• calcitonin causes calcium to be deposited in bone tissue, removing it from the bloodstream

III. Parathyroid Glands

Location – embedded in the back of the thyroid gland

• pea-sized

parathyroid glands

thyroid gland

1. PTH – (parathyroid hormone) – works with calcitonin to regulate the levels of calcium in the blood

• PTH is released if there is too little calcium in the bloodstream – causes bone tissue to be broken down, releasing calcium into the bloodstream

IV. Adrenal Gland

Location – top of each kidney

• they can be separated into 2 regions: the adrenal cortex (outer portion) and the adrenal medulla (inner portion)

• adrenal cortex secretes a group (about 30) hormones called corticosteroids which aid metabolism, helps maintain salt and water balance, and suppresses inflammation

A. Adrenal Cortex Hormones

1. Aldosterone – increases salt concentration in the bloodstream by causing Na+ to be absorbed from the filtrate by the kidneys

2. Cortisol – stimulates metabolism of carbohydrates, lipids, and proteins

Individuals with this disease suffer from weight loss, muscular weakness, and mental lethargy

• hyposecretion of aldosterone and cortisol causes Addison’s disease

B. Adrenal Medulla Hormones

1. Adrenaline - epinephrine

2. Norepinephrine

• they cause an increase in heart rate, an increase in respiration rate, the pupils to dilate, an increase in blood pressure, restrict blood flow to the skin and digestive system, and stimulate the liver to release glucose, prepares the body for action (fight or flight)

• these hormones are released anytime you are placed in a stressful situation

V. Thymus

Location – just behind the sternum

thymus

• unusual in that it is very large in children, but decreases in size as we age

1. Thymosins – aid in T cell lymphocyte maturation

VI. Islets of Langerhans

Location – a group of scattered cells throughout pancreas

• the pancreas is unusual in that it functions both as an exocrine gland and endocrine gland

• most of its cells are exocrine in function – they secrete digestive enzymes into the duodenum

1. Insulin – lowers blood sugar levels by stimulating liver and muscle cells to remove glucose from the bloodstream and store it in the form of glycogen

• hypoglycemia – excess insulin production results in too little blood glucose

Individuals with hypoglycemia feel tired and dizzy

• diabetes mellitus – too little insulin is being produced, causing too much glucose to remain in the bloodstream

• two types of diabetes mellitus – type I and type II

Type I diabetes occurs when the islets of Langerhans are producing too little or no insulin

• this type of diabetes is often called juvenile onset diabetes because individuals who develop it usually young

In type 2 diabetes, the levels of insulin being produced are normal. However, cells do not respond to it because there is something wrong with their insulin receptors

• this type of diabetes is often called adult onset diabetes because it usually does not develop until later in life

• it is not known what causes type 2 diabetes; however, we do know that heredity, obesity, and smoking are contributing factors in its occurrence

• type 2 diabetes is not as severe as type 1 diabetes. Type 1 can be treated only with daily insulin injections. Type 2 can be treated by a controlled diet

Symptoms of Type I diabetes include:Frequent urinationConstant thirstExtreme hungerWeight lossFatigue Irritability

Symptoms of Type II diabetes include:Those of Type I +Frequent infectionsBlurred visionSlow healing cuts and bruisesTingling or numbness in the hands or feetRecurring skin or bladder infections

2. Glucagon – raises blood sugar levels by stimulating liver cells to convert stored glycogen to glucose and release it into the bloodstream

VII. Pineal Gland

Location – at the top of the brain stem (above the pituitary)

1. Melatonin – function in humans is not known. However, it is believed to be involved in establishing daily biorhythms and moods

• may be remnant from species in which day length was important in selecting optimum breeding times

VIII. Gonads – Testes and Ovaries

Testes

Location – in scrotum outside the body cavity (where temperature is lower – for normal sperm production)

• testosterone stimulates development of male secondary sex characteristics (deepening of the voice, beard growth, body hair, broadening of the chest, etc.) during puberty

1. Androgens – the group of hormones that the testes secrete. The main androgen is testosterone

Ovaries

Location – in the pelvic cavity

1. Estrogen – stimulates development of female secondary sex characteristics (growth of breasts, widening of hips, body hair, etc.) during puberty

2. Progesterone – prepares the uterus for implantation of a fertilized egg (maintains uterine lining)