The Endocrine System

Major functions of the Endocrine System By releasing chemicals called hormones into the bloodstream, Endocrine glands control: Metabolism Growth Development Puberty Tissue function Mood

Exocrine vs. Endocrine Endocrine Glands Exocrine Glands Secrete into the blood Secrete into the external environment or an organ Ductless (no ducts) Have ducts Secrete hormones Secrete other stuff (sweat, oil, enzymes etc.)

The Endocrine System: a Gland System Endocrine glands utilize blood vessels to transport hormones as a means of regulating hundreds of physiologic processes, maintaining homeostasis.

Endocrine Glands

The Hypothalamus The hypothalamus is an incredibly complex portion of the midbrain which bridges the gap between the nervous system and the endocrine system. It secretes a number of different “releasing” hormones which, in turn, activate Pituitary Gland function.

The Hypothalamus (cont.) The Hypothalamus is connected to the pituitary via a funnel shaped stalk called the infundibulum. In addition to ‘releasing hormones,’ the hypothalamus secretes inhibitory hormones which halt the secreation of various stimulatng hormones into the capillary beds of the pituitary.

Endocrine Glands: The Master Gland About the size of a walnut, the Pituitary Gland receives messages from the hypothalamus and releases many different hormones into the bloodstream in response. These hormones target other glands, organs and/or tissues usually elliciting a cascade of responses.

Pituitary Gland Hormones Abbreviation Target Effect Growth Hormone GH Bones and muscles Growth/ cell reproduction Prolactin N/A Mammary Glands Milk production Adrenocorticotropic Hormone ACTH Adrenal Glands Releases androgens Melanocyte Stimulating Hormone MSH Melanocytes (in the dermis) Produces melanin Follicle Stimulating Hormone FSH Ovaries/Testes puberty Luteinizing Hormone LH Ovaries ovulation Oxytocin Uterus Uterine contraction during pregnancy Antidiuretic Hormone ADH Kidneys Water retention Thyroid Stimulating Hormone TSH Thyroid Metabolism regulation

Pituitary/Hypothalamus Interaction

Classification of Hormones: 3 Basic Categories The simplest group of hormones are modified amino acids. Hormones may also include much more larger and intricate protein complexes. Finally, some lipid hormones are considered steroids, and actually diffuse across cell membranes. EXAMPLES

The Pineal Gland The pineal gland is about the size of the tip of your little finger, and is located deep inside the brain. Secretes melatonin, which regulates sleep patterns. Its other functions remain a mystery….

Did You Know?... The Pineal Gland is the smallest of all your organs.

The Thyroid Gland Located at the base of the throat, and shaped like a butterfly, the Thyroid Gland is actually 2 glands in one… Secretes the hormone thyroxine to regulate metabolism of carbohydrates, fats, and proteins in the bloodstream. Iodine is an integral element in this hormone. Secretes calcitonin to regulate Calcium (Ca+) and phosphate ion levels in blood and bone.

The Thyroid (cont.) C Cells- (extrafollicular cells): Calcitonin follicular cells surrounding lumen filled with thyroglobulin T3, T4

The Parathyroid glands Embedded in the posterior surface of the thyroid, there are 4 raisin sized parathyroid glands. Parathormone (PTH) governs osteoblast and osteoclast activity, while aiding the thyroid maintaining appropriate calcium concentration in the blood.

Challenge Question: What is a “goiter?”

The Thymus Gland the thymus is located in the upper anterior portion of the chest cavity just behind the sternum. Its primary function is to provide an area for Immune cell maturation, and is vital in immune system development. The thymus secrets a hormone called Thymosin, which controls T-Lymphocyte maturation.

The Pancreas The Pancreas acts as both an endocrine and an exocrine gland. Its endocrine function regulates blood sugar levels by releasing insulin (lowers blood sugar) and/or glucagon (raises blood sugar) into the bloodstream.

The Adrenal Glands Located on the top of the kidneys, the adrenal glands secrete adrenaline and cortisol. These hormones initiate the “Fight or Flight” response as part of the sympathetic nervous system.

Adrenal Glands (cont.) Cortex Zona glomerulosa: mineralcorticoids Zona fasciculata: glucocorticoids Zona reticularis: sex steroids Medulla: epinepherine and norepinepherine

The Testes testes are components of both the reproductive system and the endocrine system. The respective functions of the testes are: producing sperm producing male sex hormones of which testosterone is the best-known. Testosterone is responsible for the appearance of secondary sex characteristics in males.

The Ovaries Just like the testes, the ovaries have both a reproductive function as well as endocrine. Producing eggs Secretion of estrogen and progesterone Estrogen is responsible for the appearance of secondary sex characteristics in females at puberty as well as the development and maintenance of the reproductive organs

The Endocrine System and Interdependence: Negative Feedback Loops The primary function of the Endocrine System is to maintain homeostasis (equilibrium) among all body systems by using “negative feedback” to control hormone secretion.

Negative Feedback: Blood Sugar

Negative Feedback: Calcium

Negative Feedback: Temperature

Negative Feedback: Metabolism

Practice Quiz: Name These Glands 1. 3. 2. 4. 5. 6. 7. 8. 9.