A&p 2 Endocrine System

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4 principle avenues of cell to cell communication

Back 1

gap junctions, neurotransmitters, paracrines, hormones

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Gap Junctions

Back 2

specialized intercellular connection between many cell types. Enable cells to pass nutrients, electrolytes, signaling molecules directly between cytoplasm

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Neurotransmitters

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chemicals released by neurons, diffuse across a narrow synaptic cleft and bind to receptors on surface of next cell

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Paracrines

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chemicals secreted by one cell diffuse to nearby cells in the same tissue. Sometimes referred to as local hormones.

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Hormones

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chemical signals carried throughout the body in the bloodstream. Main component of the endocrine system.

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Main functions of the endocrine system

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regulation of the body's growth, regulation of metabolism, regulation of sexual development

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Exocrine Glands

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glands that secrete their products into ducts which lead directly to a surrounding environment

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Endocrine Glands

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do not have ducts. Secrete their products (hormones) directly into the bloodstream

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Steroid hormones

Back 9

synthesized from cholesterol which forms a four ring backbone in their molecular structure

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Peptide hormones

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protein based hormones

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Hypothalamus

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region of the brain that regulates functions including water balance, thermoregulation, sex drive, and child birth..many of these functions are carried out by the pituitary gland

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2 components of the pituitary gland

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anterior and posterior

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Anterior pituitary gland

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no nerve connection to the hypothalamus, but is connected through a complex of blood vessels called the hypophyseal portal system which allows endocrine communication between the 2 structures

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Posterior pituitary gland

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contains many nerve fibers that arise in the hypothalamus. These fibers traverse the infundibulum in bundles known as the hypothalamo-hypophyseal* tract which ultimately terminate within the posterior pituitary

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Hormones secreted by the hypothalamus

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CRH, GHRH, GnRH, PIH, PRH, TRH

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Hormones secreted by the anterior pituitary

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ACTH, FSH, GH, LH, PRL, TSH

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Hormones secreted by the posterior pituitary

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ADH and OT

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Thyroid

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largest endocrine gland. Wrapped around front and sides of the trachea.
In response to TSH from the pituitary, it secretes triiodothyronine (T3) and thyroxine (T4), collectively referred to as thyroid hormones (TH)

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calcitonin

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secreted when blood calcium levels rise

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Parathyroid glands secrete..

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parathyroid hormone (PTH)*, which increases calcium in the blood

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Adrenal Glands

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cap like structures on the superior pole of the kidneys

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catecholamines

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secreted by the adrenal medulla to prepare the body for heightened physical activity

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mineralocorticoids

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secreted by the adrenal cortex and control electrolyte balance

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glucocorticoids

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secreted by the adrenal cortex and involved in fat and glucose catabolism

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sex steroids

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also secreted by the adrenal cortex ..androgens and estrogens

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Pancreas

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contains endocrine cell clusters called pancreatic islets which secrete insulin, glucagon, and somatostatin

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Insulin

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Stimulates cells to absorb glucose and amino acids

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Glucagon

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Increases glucose availability

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Somatostatin

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inhibits digestive functions, insulin, and glucagon

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Ovaries

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are both endocrine and exocrine glands. Exocrine product is an egg. Endocrine products are gonadal hormones such as estradiol and progesterone which are implicated in the development of the reproductive system

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Testes

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also both endocrine and exocrine glands. Exocrine product is sperm. Endocrine products are gonadal hormones such as testosterone, weaker androgens and estrogen

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Thymus

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located superior to the heart. Regulates the development and activation of T-lymphocytes

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Stomach and small intestine

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possess enteroendocrine cells which secrete enteric hormones* which coordinate the regions and glands of the digestive system

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Heart

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produces atrial natriuretic peptide (ANP).

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Pineal gland

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located within the brain. Produces serotonin by day and melatonin by night

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Liver

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EPO (erythropoietin). EPO stimulates bone marrow to produce red blood cells. Also secretes the hormone precursor, angiotensinogen, which is involved in the RAA system.

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Negative Feedback

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occurs when the concentration of one hormone increases and then acts to inhibit the secretion of a second hormone that is responsible for stimulating the first hormone’s production

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The axis

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designates a relationship between the hypothalamus, pituitary and one more remote endocrine gland