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Endocrine System

Modified from:http://www2.kumc.edu/instruction/nursing/nrsg812/endocrine/

Images from:

http://www.endocrineweb.com/

gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookENDOCR.html

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Mechanisms of Hormone Action

• Certain secretory cells release chemical agents (hormones) for the purpose of mediating biologic responses in distant Target Cells.

• Hormones sources

– Single amino acid (catecholamines)

– Chains amino acids (peptide hormones of hypothalamus)

– Cholesterol (steroids)

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Mechanisms of Hormone Action• Hormones control and integrate many body functions

with this system.

• In general, hormonal control regulates the metabolic functions of the body, the types of effects that occur inside the cell and determined the character of the cell itself.

• The endocrine system works with the nervous system to regulate: metabolism, water and salt balance, blood pressure, response to stress, and sexual reproduction.

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3 Forms of Hormonal Communication1. Endocrine = hormones are secreted into blood to

regulate the function of distant target cell

2. Paracrine = endocrine cells secrete into surrounding extracellular space. Target cells are neighbors

3. Neuroendocrine = Directly into blood (norepin), & into brain interstitial space (Vasopressin)

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Endocrine System

• Endocrine System Hormones/Glands whose functions are solely endocrine include:

• pituitary (hypophysis)

• pineal

• thyroid

• parathyroids

• adrenals

• pancreas

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Hypothalamus and Pituitary• Pituitary has direct

neural and blood connection to the hypothalamus

• Hypothalamus sends releasing factors to anterior pituitary

• Hypothalamus stimulates posterior pituitary via neural pathway

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Hypothalamus• Hypothalamus can synthesize and release hormones from its

axon terminals into the blood circulation. • controls pituitary function and thus has an important,

indirect influence on the other glands of the endocrine system.

• exerts direct control over both the anterior and posterior portions of the pituitary gland.

• regulates pituitary activity through two pathways: a neural pathway and a portal venous pathway.

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Hypothalamus

• Neural pathways extend from the hypothalamus to the posterior pituitary lobe, where the hormones are stored and secreted.

• Portal venous pathways connect the hypothalamus to the anterior pituitary lobe, carry releasing and inhibiting hormones

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Pituitary Gland• Pituitary Gland is located at the base of the

skull in an indentation of the sphenoid bone.

• Is joined to the hypothalamus by the pituitary stalk (neurohypophyseal tract) and consists of the anterior pituitary and the posterior pituitary

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Anterior pituitary gland (adenohypophysis)• Called the master gland, because its anterior lobe

has direct control over the secretion of:

• ADH - antidiuretic hormone (vasopressin)

• ACTH - adrenocorticotrophic hormone

• TTH - thyrotrophic hormone

• GH - growth hormone

• FSH - follicle stimulating hormone

• LH - leutinizing hormone

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Posterior pituitary• Stores and secretes hormones made in the

hypothalamus and contains many nerve fibers.

• ADH (Antidiuretic Hormone/Vasopressin), which controls the rate of water excretion into the urine

• Regulates Na+ & K+ reabsorption in the kidneys this influences blood volume & blood pressure

• Oxytocin, which, among other functions, helps deliver milk from the glands of the breast.

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Adrenal Glands• Adrenal Glands

have an outer cortex and an inner medulla.

• The adrenal cortex and medulla are major factors in the body's response to stress.

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Kidneys—Renal Hormones• Renin is an hormone/enzyme

(released from juxtaglomerular cells)

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Thyroid Gland• Thyroid function is regulated by the

hypothalamus and pituitary, feedback controls an intrinsic regulator mechanism

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Thyroid Problems• Thyroid gland enlargement may or may not be

associated with abnormal hormone secretion.

• An enlarged thyroid gland can be the result of:

• iodine deficiency (Goiter)

• inflammation, or

• benign or malignant tumors

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Parathyroid Glands• There are 4 parathyroid glands

located behind the thyroid.

• Parathyroid Glands are important in calcium metabolism phosphorus metabolism

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Pancreas

• endocrine gland, secreting the hormones insulin and glucagon, exocrine gland, producing digestive enzymes.

• Secretes insulin, glucagon (regulate blood sugar)

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Cellular Mechanisms of Hormone Action• Hormonal interaction with target cells begin with

reversible binding to specific receptors

1. Interactions with membrane receptor (protein)2. Interactions with nuclear receptors (steroid)

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Amino Acid Based Hormones• Bind to receptor sites on cell membranes

• Amino acid hormone binding causes changes to occur receptor can activate carrier molecules which transport substances across the membrane

• receptor can activate second messengers

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Second Messengers• Second Messengers set a series of reactions in

motion

• Activate adenylate cyclase, generates cAMP from ATP

• cAMP activates other proteins within the cell increases glycogenolysis & lipolysis

• Open Ca2+ ion channels, activates calmodulin

• Hydrolyzes phospholipase C into inositol triphosphate & diacylglycerol

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Steroid Hormones• Steroid hormones are produced

by chemical modification of cholesterol

•Major classes steroid hormones•glucocorticoids (cortisol)•mineralocorticoids (aldosterone)•androgens (testosterone)•estrogens (estradiol)•Vitamin D metabolites

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Steroid Hormones

• Diffuse into cell and influence DNA

• Bind to a protein associated with DNA

• Cause DNA to increase synthesis of specific amino acids

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Feedback Loops• The release of a hormone is often triggered by a

change in the concentration of some substance in the body fluids.

• Each hormone has a corrective effect, eliminating the stimulus, which then leads to a reduction in hormone secretion.

• This process is called a negative feedback homeostatic control system to keep hormones at normal levels. (if levels increased it would be called positive feedback)

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Blood Sugar Control• Insulin and glucagon are produced by small groups

of cells in the pancreas (islets of Langerhans).

• Beta cell make insulin (beta cells) and Alpha cells that make glucagon

• Insulin is released when the blood sugar rises too high. Insulin tells the cells to use sugar.

• Glucagon is produced when the blood sugar is falling too low. Glucagon tells the liver to release sugar that was stored there when the blood sugar was higher.