Endocrine System Overview and Hormonal Functions

Exocrine glands

Secrete products into ducts which carry these secretions to their target site. Examples include sweat, oil, mucus, and digestive glands.

Endocrine glands

Secrete products (hormones) into interstitial fluid of secretory cells, which then diffuse by capillaries and are taken away by blood. Examples include pituitary, thyroid, adrenal, and pineal glands.

Hormones

Chemical messengers released in one part of the body that act somewhere else, targeting specific cells with specific receptors.

Circulating hormones

Travel in blood and act on distant target cells, needing blood to carry them to their destination.

Local hormones

Do not need to travel in blood; they travel in extracellular space.

Paracrine

Local hormones that go from one cell to a close target cell.

Autocrine

Local hormones released from one part of the cell with receptors on a different part of the same cell.

Mechanisms of hormone action

Hormones bind to their receptors, which can be on the cell surface or inside the target cell, leading to various cellular actions.

Lipid-soluble hormones

Bind to transport proteins to be carried in blood; examples include steroids, thyroid hormones, and nitric oxide.

Water-soluble hormones

Circulate freely in plasma without needing a transporter; examples include amines, peptides, proteins/glycoproteins, and eicosanoids.

Amplification of Hormone Effects

One hormone binding to a receptor activates about 100 G-proteins, each of which activates many adenylate cyclases, producing thousands of cyclic cAMP.

Three Types of Stimuli

Humoral: response to changes in body fluids; Neural: nerve stimulates hormone release; Hormonal: release of a hormone in response to another hormone.

Pituitary Gland

Known as the master gland, it regulates most aspects of growth, development, metabolism, and homeostasis.

Hypothalamus

The link between the nervous and endocrine systems, controlling the pituitary gland with 9 different releasing and inhibiting hormones.

Specific target cells

Cells that have specific receptors for hormones, allowing for targeted action.

Hormone regulation

Hormones are highly regulated and can work in very small concentrations.

Hormonal action

Can involve synthesizing molecules, changing membrane permeability, or altering rates of reactions.

Fat-soluble hormones

Have a harder time being transported to the cell but can easily pass through the lipid bilayer and go directly to the nucleus for gene activation.

G-proteins

Proteins activated by hormone binding that play a role in amplifying hormone effects.

cAMP

Cyclic adenosine monophosphate, a secondary messenger activated by G-proteins that can activate protein kinases.

Transport proteins

Proteins that carry lipid-soluble hormones in the blood.

Maturation

Growth process of an organism.

Reproduction

Biological process of producing offspring.

Metabolism

Chemical processes that occur within a living organism to maintain life.

Circulation

Movement of blood through the heart and blood vessels.

Bone metabolism

Process involving the formation and resorption of bone.

Body temperature

The degree of heat maintained by the body.

Water balance

The equilibrium between water intake and output in the body.

Anterior lobe

Larger, lower part of the pituitary gland that releases more hormones.

Posterior lobe

Smaller part of the pituitary gland with no direct blood link to the hypothalamus.

Growth hormone (GH)

Hormone released by the anterior pituitary essential for normal growth.

Thyroid stimulating hormone (TSH)

Hormone that stimulates the thyroid gland to produce T3 and T4.

Adrenocorticotropic hormone (ACTH)

Hormone that stimulates the adrenal cortex to release cortisol.

Prolactin (PRL)

Hormone that stimulates mammary glands for milk production.

Follicle stimulating hormone (FSH)

Hormone that stimulates the growth of ovarian follicles in females.

Luteinizing hormone (LH)

Hormone that triggers ovulation and stimulates testosterone production in males.

Hypophyseal portal system

Direct blood link between the hypothalamus and anterior pituitary.

Oxytocin

Hormone released by the posterior pituitary that stimulates uterine contractions.

Antidiuretic hormone (ADH)

Hormone that promotes water retention in the kidneys.

Hypothalamic releasing hormones

Hormones that control the release of hormones from the anterior pituitary.

Insulin-like growth factors (IGF)

Hormones that stimulate growth and regulate metabolism.

Thyroid gland

Gland located on the anterior trachea that produces T4, T3, and calcitonin.

Basal metabolic rate (BMR)

Rate of energy expenditure at rest.

Hyperthyroidism

Condition characterized by excessive thyroid hormone production, leading to weight loss and irritability.

Hypothyroidism

Condition characterized by insufficient thyroid hormone production, leading to weight gain and fatigue.

Calcitonin

Hormone that regulates calcium homeostasis by lowering blood calcium levels.

Parathyroid hormone

Hormone that increases blood calcium levels by stimulating bone resorption.

Renin-angiotensin-aldosterone system (RAAS)

Hormonal system that regulates blood pressure and fluid balance.

Adrenal glands

Glands located on top of the kidneys that produce various hormones.

Cortisol

Stress hormone produced by the adrenal cortex that regulates metabolism.

Epinephrine

Hormone produced by the adrenal medulla that increases heart rate and energy availability.

Norepinephrine

Hormone produced by the adrenal medulla that affects blood pressure and blood flow.

Insulin

Hormone produced by pancreatic beta cells that promotes glucose uptake.

Glucagon

Hormone produced by pancreatic alpha cells that promotes glucose release into the blood.

Diabetes mellitus

Condition characterized by high blood sugar levels due to insulin issues.

Hypothalamic-pituitary-gonadal axis

Regulatory system for reproductive functions in both males and females.