Endocrine System |Anatomy & Physiology|

Endocrine System

Regulates long-term changes in homeostasis using chemical messengers (hormones).

Homeostasis

Nervous system regulates short-term changes. Endocrine system regulates long-term changes.

Direct Communication

Occurs between two cells of the same type in extensive physical contact, typically through gap junctions.

Paracrine Communication

Chemical messengers transfer information within a single tissue (e.g., local hormones like prostaglandins).

Synaptic Communication

Neurons release neurotransmitters to target cells at synapses.

Endocrine Communication

Hormones travel through the bloodstream to distant target cells, influencing cell activity by altering protein production.

Amino Acid Derivatives

Small molecules related to amino acids, also known as biogenic amines.

Tyrosine Derivatives

Include thyroid hormones, epinephrine, norepinephrine.

Tryptophan Derivatives

Include melatonin.

Peptide Hormones

Chains of amino acids.

Glycoproteins

Peptide hormones with sugar side chains (e.g., TSH, LH, FSH).

Non-glycoproteins

Peptide hormones without sugar side chains (e.g., ADH, oxytocin, growth hormone).

Lipid Derivatives

Hormones derived from lipids.

Eicosanoids

Small molecules with a five-carbon ring, involved in coordinating cellular activities (e.g., prostaglandins, leukotrienes).

Steroid Hormones

Lipids similar to cholesterol (e.g., estrogens, androgens, corticosteroids).

Receptors

Molecules that bind hormones to initiate their effects.

First Messengers

Hormones that bind to receptors on the cell surface.

Second Messengers

Intracellular molecules (e.g., cAMP) that trigger cellular changes after the first messenger binds.

G-proteins and cAMP

G-proteins activate adenylate cyclase, which converts ATP to cAMP (a second messenger).

cAMP

Activates enzymes, such as those that convert glycogen to glucose.

Calcium Pathway

G-proteins trigger calcium release, which activates protein kinase C and other proteins involved in cellular functions.

Hormone Action in the Nucleus

Steroid hormones enter cells, bind to intracellular receptors, and alter DNA transcription (e.g., testosterone).

Thyroid Hormones

Cross plasma membranes by transport mechanisms and bind to nuclear or mitochondrial receptors, changing gene expression.Hypothalamic control of adenohypophysis

Mechanism of Releasing hormone

Releasing hormone from hypothalamus shows negative feedback when concentrations of hormone 2 become too high.

Hormones of adenohypophysis

Hormones of adenohypophysis are termed tropic hormones because they "turn on" other endocrine glands.

Thyroid-stimulating hormone (TSH)

Triggers release of hormones from thyroid.

Adrenocorticotropic hormone (ACTH)

Stimulates release of steroid hormones by the cortex of the suprarenal glands.

Gonadotropins

Regulates activities of the gonads under stimulation of gonadotropin-releasing hormone from hypothalamus.

Follicle-stimulating hormone (FSH)

Promotes follicle development in females (part of oogenesis).

Luteinizing hormone (LH)

Induces ovulation in females.

Prolactin (PRL)

Stimulates mammary gland development and milk production in females.

Growth hormone (GH)

Stimulates cell growth and replication by accelerating protein synthesis.

Neurohypophysis

Posterior portion of pituitary gland.

Antidiuretic hormone (ADH)

Released when blood solute concentration becomes high or drop in blood plasma volume.

Oxytocin

In women, stimulates smooth muscle contractions during labor.

Thyroid gland

Lies inferior to the larynx.

Functions of thyroid hormones

Thyroid hormones bind to receptors in cytoplasm, mitochondria, and nucleus.

C cells of thyroid gland

C cells (parafollicular cells) produce calcitonin.

Parathyroid glands

Embedded in posterior portion of thyroid gland.

PTH effects

Inhibits osteoblasts and increases osteoclast numbers.

Adrenal glands

Sits on superior surface of kidneys.

Adrenal cortex

Produces corticosteroids.

Zona glomerulosa

Produces mineralocorticoids like aldosterone.

Zona Fasciculata

Produces glucocorticoids (e.g., cortisol, corticosterone).

Zona reticularis

Stimulation of ACTH causes release of androgens.

Adrenal medulla

Releases epinephrine and norepinephrine.

Pancreas

Endocrine clusters known as islets of Langerhans.

Insulin

Secreted when blood glucose levels are high.

Glucagon

Released when glucose levels fall.

Diabetes Mellitus

Characterized by high glucose concentrations in blood.

Diabetes Mellitus risk factors

Insulin resistance may run in families.

Organs with endocrine function

Kidneys produce calcitriol and erythropoietin (EPO).