The Endocrine System

11.1- 11.2 Introduction

1. Made up of glands that produce and secrete hormones(chemical messengers)
2. Regulation of growth, metabolism, sexual development
3. Responses to stress and injury
4. Internal balance of body systems (homeostasis)

Major Glands

1. Hypothalamus
2. Pituitary
3. Thyroid
4. Parathyroid
5. Adrenals
6. Pineal Body
7. Reproductive organs (ovaries and testes
8. Pancreas


*HORMONES are chemical messengers that act on TARGET CELLS

Exocrine Glands – secrete outside the body through ducts and tubes (sweat)

11.3 Hormone Action

Steroids – insoluble in water, carried in the blood and released near the vicinity of the target cell

Nonsteroid hormones – binding site, activity site (cyclic AMP, cAMP = secondary messenger)

Prostoglandins – act locally, affecting only the organ where they are produces

11.4 Control of Hormonal Secretions

Negative Feedback

Regulated by Feedback

Hypothalamus (releasing hormone) --> Pituitary (stimulating hormone) --> Target Gland (secretes hormone) -->
hormone levels rise and releasing hormone is shut down

11.5 Pituitary Gland

pituitaryLocation: base of the brain, pituitary stalk (infundibulum) attaches it to the hypothalamus
Consists of an anterior pituitary and posterior pituitary

*Often called the “master gland” because of its great influence on the body organs

Anterior Pituitary Hormones

Prolactin or PRL - PRL stimulates milk production from a woman's breasts after childbirth and can affect sex hormone levels from the ovaries in women and the testes in men.

Growth hormone or GH - GH stimulates growth in childhood and is important for maintaining a healthy body composition. In adults it is also important for maintaining muscle mass and bone mass. It can affect fat distribution in the body.

Adrenocorticotropin or ACTH - ACTH stimulates production of cortisol by the adrenal glands. Cortisol, a so-called "stress hormone," is vital to survival. It helps maintain blood pressure and blood glucose levels.

Thyroid-stimulating hormone or TSH - TSH stimulates the thyroid gland to make thyroid hormones, which, in turn, control (regulate) the body's metabolism, energy, growth and development, and nervous system activity.

Luteinizing hormone or LH - LH regulates testosterone in men and estrogen in women. (gonadotropin)

Follicle-stimulating hormone or FSH - FSH promotes sperm production in men and stimulates the ovaries to release eggs (ovulate) in women. LH and FSH work together to allow normal function of the ovaries or testes. (gonadotropin)

Posterior Pituitary Hormones

Oxytocin - Oxytocin causes milk letdown in nursing mothers and contractions during childbirth.

Antidiuretic hormone or ADH - ADH, also called vasopressin, is stored in the back part of the pituitary gland and regulates water balance. If this hormone is not secreted properly, this can lead to problems of sodium (salt) and water balance, and could also affect the kidneys so that they do not work as well.

*Diuretics – increase urine production

11.6 Thyroid Gland


The thyroid is a small gland inside the neck, located in front of your breathing airway (trachea) and below your Adam's apple.

The thyroid hormones control your metabolism, which is the body's ability to break down food and store it as energy and the ability to break down food into waste products with a release of energy in the process.

Thyroid Hormones

Thyroxin (T4) & Tri-iodothyronine (T3) - both increase the rate at which cells release energy from carbohydrates

Calcitonin – regulates the blood concentration of calcium

BMR – basal metabolic rate : how many calories the body must consume to maintain life

Thyroid Disorders

Hypothyroidism (cretinism in infants) – stunted growth, mental retardation, sluggishness, weight gain in adults
Hyperthyroidism (Grave’s disease) - restlessness, weight loss, anxiety; can cause Goiter (enlarged thyroid)

11.7 Parathyroid Gland

parathyroidLocated behind the thyroid, four tiny glands that help maintain calcium and phosphorous levels

Parathyroid Hormone (PTH) - takes calcium from the bones to make it available in the blood

Hyperparathyroidism – can be caused by a tumor, increases PTH secretion; bones soften and too much calcium can cause kidney stones

Hypoparathyroidism – too little PTH, too little calcium affects nervous system


11.8 Adrenal Glands

adrenalEach adrenal gland is actually two endocrine organs located right above each kidney. The outer portion is called the adrenal cortex. The inner portion is called the adrenal medulla. The hormones of the adrenal cortex are essential for life. The types of  hormones secreted by the adrenal medulla are not.

Hormones of the Adrenal Medulla

Epinephrine & Norepinephrine – increased heart rate, breathing rate, elevated blood pressure (fight or flight, response to stress)

Hormones of the Adrenal Cortex

Aldosterone – a mineralcorticoid, helps kidneys conserve sodium and excrete potassium, maintaining blood pressure

Cortisol – glucocortoid, keeps blood glucose levels stable

Adrenal Sex Hormones - androgens (male) and estrogens (female)

Adrenal Disorders

Cushing’s Syndrome(hypersecretion of cortisol) – blood glucose remains high, retains too much sodium, puffy skin, masculinizing effects in women

Addison’s Disease (hyposecretion) – decreased blood sodium, dehydration, low blood pressure, increased skin pigmentation

11.9 Pancreas

pancreasThe pancreas is a large gland behind your stomach that helps the body to maintain healthy blood sugar (glucose) levels.
Contains islands of cells called the Islets of Langerhans which secrete glucagon and insulin

Glucagon – stimulates the liver to break down glycogen, raises blood sugar concentration

Insulin – decreases blood sugar concentrations, affects the uptake of glucose by cells

Disorders Related to the Pancreas

Diabetes Mellitus – results from an insulin deficiency, blood sugar rises (hypoglycemia) and excess is excreted in the urine.

Type I – insulin dependent diabetes mellitus or juvenile onset diabetes, often caused by inherited immune disorder that destroys pancreatic cells

Type II – mature onset diabetes (usually after the age of 40), often individuals are overweight, can be controlled with diet and exercise

Hypoglycemia – low blood sugar, can be caused by too much insulin

11.10 Other Endocrine Glands

Pineal Gland – located between the cerebral hemispheres, secretes melatonin, important for maintaining Circadian rhythms (light and dark activity)

Thymus Gland – large in young children, gradually shrinks with age, secretes thymosins, important to immune function

Reproductive Glands – testes and ovaries – testosterone, progesterone, estrogen

11.11 Stress and Health

Stressors can be physical (heat, cold, injuries, loud noises) or psychological (anxiety, grief, depression)

Hypothalamus (fight or flight)