ENDOCRINE SYSTEM

INTRODUCTION

Along with nervous system it controls and coordinates activity of body

Instead of nerve impulses, it uses hormones Hormones are chemical messengers that are

released into blood or lymph

2 Types of Horomones:1. Steroid=lipid soluble2. Amino Acid based=water soluble

FUNCTIONS OF ENDOCRINE SYSTEM

1. Reproduction

2. Growth and development

3. Mobilization of body defenses

4. Maintenance of homeostasis

5. Regulation of metabolism

EXTENT OF HORMONE ACTIVITY IS DEPENDENT UPON…

1. Blood level of hormones

2. Number of receptors on target cells

3. Strength of binding between hormone and receptors

HORMONES ACT ON TARGET CELLS IN FOUR WAYS

1. Change permeability of plasma membrane

2. Synthesize proteins (enzymes) in cell

3. Activate or inactivate enzymes

4. Stimulate mitosis

ENDOCRINE VS. EXOCRINE

Exocrine Contains ducts that

empty into membranous surfaces

Non-hormone products

Ex: Sweat glands

Endocrine Ductless glands that

empty into blood or lymph

Hormonal products

Ex: Thyroid gland

CONTROL OF HORMONE RELEASE

Negative feedback (usually)

Stimulus or low levels of hormones will trigger the release of hormones

Hormone release stops once an appropriate level in blood is reached

THREE TYPES OF STIMULI THAT ACTIVATE ENDOCRINE ORGANS

1. Hormonal (most common) Endocrine system is activated by other hormones Example: Hypothalamus will stimulate anterior

pituitary to secrete hormones->makes other glands secrete hormones

2. Humoral Changing levels of blood ions cause release of

hormones PTH will be secreted as Ca2+ in blood decreases

3. Neural (Rare) Nerve fibers release hormones Sympathetic NS stimulation will release epinephrine

MAJOR ENDOCRINE GLANDS AND ORGANS

Pituitary Thyroid Parathyroid Adrenal Pancreas Pineal Thymus Gonads Placenta

PITUITARY GLAND Size of a grape

Located on inferior side of hypothalamus

Surrounded by Turks saddle

Two parts:1. Anterior pituitary-

glandular tissue2. Posterior pituitary-

nervous tissue

ANTERIOR PITUITARY

1. Growth hormone (GH) Stimulates cells of skeletal muscles and long bones

to increase in size. Increases rate of mitosis Concentration decreases with age Secretion is greater at night Homeostatic imbalance: Hyposecretion can lead to

pituitary dwarfism. Hypersecretion can lead to gigantism. If hypersecretion occurs after bone growth has stopped the result is acromegaly, or abnormal bone growth (usually occurs in facial bones)

2. Adrenocorticotropic hormone (ACTH) Stimulates production of cortisol (stress hormone)

by adrenal glands

ANTERIOR PITUITARY

3. Thyroid stimulating hormone (TSH) Stimulates thyroid to grow and make thyroid

hormones

4. Follicle stimulating hormone (FSH) In men it promotes the production of sperm. In

women, FSH will stimulate development of a follicle.

5. Luteinizing hormone (LH) Triggers ovulation of an egg and then causes

ruptured follicle to become a corpus luteum which then produces progesterone and estrogen (promotes pregnancy)

ANTERIOR PITUITARY

6. Gonadtropic hormones Regulates hormonal activity in ovaries and

testes

7. Prolactin Stimulates breast milk development and milk

production during pregnancy. Its function in males is unknown

POSTERIOR PITUITARY

Doesn’t make hormones Releases hormones that are made by

hypothalamus Not strictly an endocrine gland

Remember it doesn’t make hormones, it only releases them

POSTERIOR PITUITARY

1. Oxytocin Stimulates contractions in women and causes milk

letdown in nursing mothers Pitocin-synthetic oxytocin given to mothers to increase

labor Positive feedback- Doesn’t oppose a change

2. Antidiuretic hormone (ADH) Will inhibit urine production if solute concentration in

blood is too high (retain water) Urine volume will decrease, blood volume will increase. In large

amounts it increases blood pressure by constricting arterioles. Because of this, it is often referred to as a vasopressin.

Alcohol inhibits ADH Diuretics increase urine production Homeostatic imbalance: Hyposecretion of ADH will lead to

diabetes insipidus (excessive urine)

THYROID GLAND

Located in front of trachea, just below the larynx (Adam’s apple)

Composed of two hormones that contain active iodine

Iodine is very important to help make other hormones

THYROID GLAND1. Thyroxin/T4

Secreted by thyroid follicles

2. T3 Converted to T4 at the target cell

Homeostatic imbalance- Without iodine (food you eat contains enough iodine) a goiter can develop. A goiter is an enlarged thyroid. TSH will call for T3, the thyroid will expand trying to put T3 out but without iodine the body will only make the non-functional part of T3, this will fail to stop TSH, making the body put out more TSH.

3. Calcitonin Decreases blood calcium levels by

allowing calcium to be deposited into bones. It’s the antagonist to the PTH.

HOMEOSTATIC IMBALANCES OF T3 AND T4-HYPERTHYROIDISM AND HYPOTHYROIDISM

Cretinism Deficiency of TH,

causes dwarfism and occurs in infants

Myxedema Physical and mental

sluggishness in adults; results in puffiness of face, fatigue, poor muscle tone, and low body temperature

Graves disease Rapid heartbeat,

weight loss, nervous and agitated behavior and inability to relax

Hypothyroidism Hyperthyroidism

Cretinism

Myxdema

Graves Disease

PARATHYROID GLAND Tiny tissues that are found on the

posterior surface of the thyroid gland.

Homeostatic imbalance-If blood calcium levels fall too low, neurons will become overactive and cause tetany, or uncontrolled spasms. This is why doctors try to leave part of the thyroid gland if there are problems.

1. Parathyroid Hormone (PTH) Increases blood calcium by

stimulating osteoclasts to break bone down, releasing calcium into blood. It also stimulates the kidneys and intestines to absorb more calcium.

ADRENAL GLAND

Two bean shaped glands that curve over the top of each kidney. Outer portion is the cortex and the inner portion is the medulla.

ADRENAL GLAND- CORTEX Aldosterone

Mineralocorticoid Helps kidney conserve sodium and

excrete potassium, maintains blood pressure.

Promotes reabsorption of sodium which results in water retention. This increases blood volume and, in turn, blood pressure

Cortisone/Cortical Glucocorticoid Promotes normal cell metabolism

and helps body resist long term stressors by increasing blood glucose levels. It reduces swelling and imflammation by inhibiting immune system

Sex hormones Produces both sex hormones (male

and female) in low levels. Mostly androgens (male) but trace amounts of estrogen (female)

Homeostatic imbalance: Hyposecretion of all adrenal

cortex hormones will result in Addison’s Disease, which causes a bronze color of skin, decreased sodium levels and as a result, water retention as awell as low blood pressure.

Homeostatic imbalance: Hypersecretion will cause

Cushing’s Syndrome, blood glucose will remain high, too much sodium will be retained, skin will become puffy and it has a masculinizing effect in women.

ADDISON’S CUSHING’SDISEASE SYNDROME

ADRENAL GLAND-MEDULLA

Epinephrine/Adrenaline and Norepinephrine/Nonadrenaline Sympathetic Nervous System, increase blood

pressure, heart rate, blood glucose levels and dilate passageways of lungs

PANCREAS

Located behind stomach, contains specialized calls called islets, or islets of Langerhans, which secrete glucagon and insulin

PANCREAS

1. Insulin Lowers blood glucose levels. High glucose will cause

beta cells of islets to release insulin. Insulin will decrease blood glucose concentrations by causing cells to uptake glucose and allowing liver to store it as glycogen.

Homeostatic imbalance- Diabetes mellitus (means sweet) Blood glucose is too high, spilling into urine because kidneys cannot absorb it fast enough. As glucose leaves, water follows causing dehydration. Type I (juvenile), II (mature onset). Hypoglycemia-low blood sugar

2. Glucagon Raises blood glucose levels. Low blood glucose will

cause alpha cells of islets to stimulate the liver to break down glycogen to glucose.

PINEAL GLAND

Found in brain1. Melatonin

Maintains Circadian Rhythm (sleep cycles). Levels of melatonin are higher at night.

THYMUS

Located in upper thorax, posterior to sternum

1. Thymosin Mature t-

lymphocytes (a type of white blood cell) that is important to immune function.

Larger in children, shrinks as you age

GONADS Ovaries1. Estrogen

Stimulates development of secondary sex characteristics, stimulates uterine lining during pregnancy

2. Progesterone Promotes growth of

uterine lining Testes1. Testosterone

Development of adult male sex characteristics, necessary for sperm production

PLACENTA

Temporarily formed in uterus, produces human chorionic gonadotropin (hCG) Hormone that over the counter pregnancy tests

test for

Stimulates the ovaries to continue to produce estrogen and progresterone so that the lining of the uterus is not sloughed off.