Endocrine System• Remember: Your nervous system senses

impulses over a system of wire-like neurons that carry messages from one cell to another

• The term endocrine comes from Greek because endon = within and krinein = to secrete

• The endocrine system is made up of glands that release their products into the blood stream. These products broadcast messages throughout the body.

Hormones• Hormones = “Chemical messengers” • Hormones travel through the bloodstream and affect the

activities of other cells by binding to specific chemical receptors on those cells

• Cells that have receptors for a particular hormone = target cells

• If a cell does not have the specific receptors for a hormone, that hormone will have no effect on that cell

• Responses to hormones are slower and last longer than responses to nerve impulses

Glands• Gland = organ that

produces and releases a substance or a secretion

• Exocrine glands = release their secretions through tube-like structures called ducts (sweat, tears, and digestive juices)

• Endocrine glands = release their secretions (hormones) directly into the bloodstream

ENDOCRINE VS. EXOCRINE GLAND (copy chart)

GLAND SECRETION METHOD OFTRANSPORT

WHERESECRETIONFUNCTIONS

EXOCRINE(DUCTGLAND)

JUICE,OFTENCONTAINING

ENZYMES

DUCT ORGANNEARGLAND

ENDOCRINE(DUCTLESSGLAND)

HORMONE BLOOD-STREAM

ORGANDISTANTFROMGLAND

EXAMPLES OF ENDOCRINE AND EXOCRINE SECRETIONS

EXOCRINE:• SALIVA• SWEAT• BILE• TEARS

ENDOCRINE:• INSULIN• ADRENALINE

Feedback Example• Thyroid gland produces thyroxine, which affects

activity of cells• More thyroxine makes cells more active, less

thyroxine makes cells less active• The thyroid gland is controlled by the

hypothalamus and anterior pituitary glands• The hypothalamus secretes thyroid-releasing

hormone (TRH), which stimulates the anterior pituitary to secrete thyroid-stimulating hormone (TSH), which stimulates the thyroid gland to release thyroxine, which inhibits the hypothalamus to maintain balance

Human Endocrine Glands

• Pituitary gland• Hypothalamus• Thyroid gland• Parathyroid glands• Adrenal glands• Pancreas• Reproductive glands

HypothalamusThe hypothalamus makes hormones that control the pituitary gland. In addition, it makes hormones that are stored in the pituitary gland.

Pituitary glandThe pituitary gland produces hormones that regulate many of the other endocrine glands.

Parathyroid glandsThese four glands release parathyroid hormone, which regulate the level of calcium in the blood.

ThymusDuring childhood, the thymus releases thymosin, which stimulates Tcell development.

Adrenal glandsThe adrenal glands release epinephrine and nonepinephrine, which help the body deal with stress.

Pineal glandThe pineal gland releases melatonin, which is involved in rhythmic activities, such as daily sleep-wake cycles.

ThyroidThe thyroid produces thyroxine, which regulates metabolism.

PancreasThe pancreas produces insulin and glucagon, which regulate the level of glucose in the blood.

OvaryThe ovaries produce estrogen and progesterone. Estrogen is required for the development of secondary sex characteristics and for the development of eggs. Progesterone prepares the uterus for a fertilized egg.

Testis The testes produce testosterone, which is responsible for sperm production and the development of male secondary sex characteristics

Section 39-1Figure 39–2 The Endocrine Glands

Pituitary gland• Bean-sized structure that dangles on tissue at the base of

the skull within the brain• The pituitary gland is divided into two parts: anterior

pituitary and posterior pituitary

• “Master gland” because secretes nine hormones that directly regulate many body functions and controls the actions of several other endocrine glands– Growth hormone (GH)– Thyroid-stimulating hormone (TSH)– Luteinizing hormone (LH)– Follicle-stimulating hormone (FSH)

Hypothalamus• Part of the brain above and attached to the

pituitary gland• Controls the secretions of the pituitary gland• Connects nervous system and endocrine

system

Thyroid gland• At the base of the neck and wraps

around the upper part of the trachea• Regulates the body’s metabolism• Produce thyroxine, which affects cellular

respiration rates producing energy• Hyperthyroidism = too much thyroxine

(increased temperature, increased heart and metabolic rates, increased blood pressure, and weight loss)

• Hypothyroidism = too little thyroxine (low temperature, low metabolic rates, lack of energy, weight gain and sometimes goiter)

• Needs enough iodine to produce normal amounts of thyroxine

Parathyroid gland• Four glands found on the back of the thyroid • Maintain homeostasis in blood calcium levels• Secrete parathyroid hormone (PTH), which

regulates calcium levels in the blood

Adrenal glands• Two pyramid-shaped structures that

sit on top of the kidneys (one gland on each kidney)

• Help the body prepare for and deal with stress by secreting adrenaline

• Has two parts:– Adrenal cortex: outer part secretes

over 24 hormones (corticosteroids, aldosterone, corisol)

– Adrenal medulla: inner part secretes epinephrine and norepinephrine producing the “fight or flight” response to stress by increasing heart rate, blood pressure and blood flow

Pancreas

• Right side of the body behind the stomach• Remember: the pancreas secretes enzymes through a duct to

help break down food = exocrine gland• Different cells in the pancreas release hormones into the blood =

endocrine gland• Clusters of cells that resemble islands = islets of Langerhans

that secrete insulin and glucagon that help keep the level of glucose in the blood stable

• Insulin stimulates cells in liver and muscles to remove sugar from the blood and store sugar as glycogen or fat

• Glucagon stimulates the liver to break down glycogen and release glucose back into the blood• Diabetes mellitus = too little insulin (high blood glucose

levels)