• The Endocrine System

I. Hormones:

A. Endocrine system produces hormones that are important in maintaining homeostasis & regulating reproduction & development.

B. A Hormone is a chemical messenger produced by a cell that effects specific change in the cellular activity of other cells (target cells).

C. Unlike exocrine glands that release their products at the body’s surface or into body cavities through ducts, the endocrine glands do not secrete substances into ducts instead their hormones are secreted directly into the surrounding extracellular space & then diffuse into nearby capillaries & are transported throughout the body in the blood.

• D. The endocrine & nervous systems often work together to maintain homeostasis.

• E. The nervous system uses neurotransmitters to act on cells (which is usually short-lived) to maintain homeostasis

• F. The endocrine system uses hormones (which effects last longer) to produce homeostasis.

• G. Hormones are classified into 2 basic categories: peptides (including amino acids, polypeptides, & proteins) & steroids (complex rings of carbon & hydrogen atoms)

• synthesized by cholesterol. Ex. Gonadal hormones adrenocortical hormones

Now we are going to look at each gland individually:

• These next few slides will be copied onto your paper but do not have blanks to fill in

• H. Pituitary – found in sella turcia pea-size, master gland. The Anterior pituitary has hormone production glandular portion. The Posterior pituitary neural portion & extension of hypothalamus. Ex. GH (bone & muscle) & TSH (growth of thyroid)

• I. Thyroid-Found in anterior throat overlying inferior border of larynx. One of the largest endocrine glands & has a heavy blood supply. Ex. Thyroid hormone T3 & T4 contain iodine.

• J. T3-T4 Function to 1) accelerate cellular metabolism, 2) tissue growth, 3) skeletal reproductive & nervous system development.

• K. Thyroid gland unique because it can store & slowly release its hormones (up to 3 months worth)

• L. Over active & uner active thyroid can cause severe disturbances. Ex. Hypothroid syndrome – goiter; Severe hypothyroidism – cretinism; Graves disease-most common.

• M. Parathyroid – 4 to 8 embedded in posterior aspect of thyroid gland. Ex. PTH important in controlling level of calcium in blood.

• N. Hyperparathyroidism- rare result of PTH deficiency untreated death may occur. Kidney stones, reflexes & skeletal muscle weakness.

• O. Adrenal glands almond size atop the kidneys.

1. Adrenal Medulla- epinephrine & norepinephrine

2. Adrenal cortex- corticosteroids

• P. Pancreas- located partially behind the stomach. Endocrine & exocrine – Islets of Langerhans-minute clusters of cells that produce pancreatic hormones. Ex. Insulin-lowers blood sugar levels: hypoglycemic; Glucagon-causes release of glucose into blood-major target cell are liver cells: hyperglycemic

• Q. Pineal located in brain secretes melatonin its fuction is unclear.

• The information on the next slides will be found on your notes papers

II. Hormone Action

• C. Hormones activate target cells by 1 of 2 methods, depending upon the chemical nature of the hormone:

• 1) peptide hormones {water soluble} that bind to a receptor protein on the plasma membrane of the cell. The receptor protein, then stimulates the production of a second messenger (either cAMP or calcium.)

II. Hormone Action

• 2) steroid hormones {lipid soluble} that diffuse through the plasma membrane of the target cell & bind to receptor protein present in the cytoplasm that activates a DNA segment that turns on specific genes

III. Control of Hormone Production

• A. Endocrine glands release hormones in response to 1 or more of the following stimuli:

• 1. Hormones form other endocrine glands• 2. Chemical characteristics of the blood• 3. Neural stimulation

III. Control of Hormone Production

• 4. most hormone production is regulated by negative feedback system.

• a. negative feedback: hormones secretion is triggered by some internal or external stimulus, then rising hormones levels inhibit further hormone release resulting in blood levels of many hormones varying only within a very narrow margin.

IV. Communication b/w the Hypothalamus & Pituitary Glands

• A. Communication b/w the hypothalamus & the Anterior Pituitary Gland occurs through chemicals that are produced by the hypothalamus & delivered to the ant. pituitary through blood vessels.

IV. Communication b/w the Hypothalamus & Pituitary Glands

• B. Communication b/w the hypothalamus & the Posterior Pituitary Gland occurs through neurosecretory cells that connect the 2 glands.

V. Antagonistic Hormones

• A. When the body hormone levels drop below normal homeostasis levels the antagonistic hormones are secreted to bring the body back to homeostasis.

• B. Ex. Bundles of cells in the pancreas called the islets of Langerhans contain 2 kinds of cells alpha (secrete glucagons) & beta (secrete insulin) cells, that control blood glucose concentrations by producing the antagonistic hormones insulin & glucagon

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VI. Major Endocrine Organs

Gland Hormone Released Target Tissue/Organ Chief Function of Hormone

Pineal

Hypothalamus

Anterior Pituitary

Posterior Pituitary

Thyroid

VI. Major Endocrine OrgansGland Hormone Released Target Tissue/

OrganChief Function of Hormone

Parathryroid

Thymus

Adrenal Gland

Adrenal Medulla

Adrenal Cortex

VI. Major Endocrine OrgansGland Hormone Released Target Tissue/

OrganChief Function of Hormone

Pancreas

Gonads

Ovaries

Testes

• THE END!!!!