Endocrine glands produce and secrete hormones into the blood (process called "Secretion").
Hormones are chemical messengers that travel throughout the body, targeting sensitive parts known as "Target Cells".
The endocrine system acts as a communication system throughout the body, slower than the nervous system but capable of significant prolonged changes.
Blood circulates throughout the body, mixing with hormones, but only specific cells with appropriate receptors respond to these hormones.
Paracrines: Send signals to neighboring cells (not in blood).
Autocrines: Target the same cells that produced them.
Pineal Gland: Produces melatonin for sleep.
Hypothalamus: Controls the pituitary gland and produces important hormones.
Pituitary Gland (Hypophysis):
Anterior Pituitary: Produces at least 6 hormones.
Posterior Pituitary: Stores hormones produced by the hypothalamus (Oxytocin & ADH).
Thyroid Gland:
Largest pure endocrine gland, produces Thyroid hormones (T3 and T4) and Calcitonin.
Parathyroid Glands: Produce parathyroid hormone to regulate calcium levels in bones.
Thymus: Produces thymulin and thymopoietins, largest when a child.
Adrenal Glands (on kidneys):
Adrenal Medulla: Releases adrenaline and noradrenaline (fight or flight response).
Adrenal Cortex: Divided into three layers producing corticosteroids (mineralocorticoids, glucocorticoids, gonadocorticoids).
Pancreas: Functions as both an exocrine (digestive enzymes) and endocrine (insulin and glucagon) gland.
Gonads: Ovaries produce estrogens and progesterone; testes produce testosterone.
Placenta: During pregnancy, produces hormones like human chorionic gonadotropin (hCG).
Thyroid Hormones (T3/T4): Major hormones for metabolism; T4 (Thyroxine) is the most commonly released form.
Insulin: Lowers blood sugar by allowing glucose into body cells.
Glucagon: Raises blood sugar by stimulating the breakdown of glycogen.
ADH: Regulates water retention in the kidneys; excess can cause edema and headaches.
Hormone release is regulated through three types of stimuli:
Humoral Stimuli: Respond to blood levels (e.g., insulin in response to high glucose).
Neural Stimuli: Release due to nerve impulses (e.g., catecholamines during stress).
Hormonal Stimuli: Hormone release triggered by other hormones (e.g., hypothalamic hormones stimulate the pituitary).
Infundibulum: Connects hypothalamus to pituitary gland.
Hypothalamic hormones: Releasing and inhibiting hormones that regulate anterior pituitary hormones:
TSH (Thyroid-Stimulating Hormone): Stimulates thyroid hormone release.
ACTH (Adrenocorticotropic Hormone): Stimulates cortisol release from adrenal cortex.
FSH (Follicle-Stimulating Hormone) and LH (Luteinizing Hormone): Control gonadal function.
Prolactin: Stimulates breast milk production.
GH (Growth Hormone): Stimulates growth through IGFs (Insulin-like Growth Factors).
High levels of thyroid hormone stop TRH release from hypothalamus, thus regulating hormone production.
Production of Thyroid Hormones: Requires iodine; TH is crucial for metabolism.
Conditions:
Hypothyroidism: Results in low TH levels (e.g., Myxedema, Goiter).
Hyperthyroidism: High TH levels (e.g., Graves' Disease, symptoms include high metabolic rate).
Adrenal Medulla: Releases catecholamines in response to sympathetic nervous activation.
Adrenal Cortex: Divided into three zones producing different corticosteroids:
Zona Glomerulosa: Produces aldosterone (mineralocorticoids).
Zona Fasciculata: Produces cortisol (glucocorticoids).
Zona Reticularis: Produces gonadocorticoids (androgens).
Medical Conditions:
Cushing's Syndrome: Excess cortisol. (buffalo hump/moon face)
Addison's Disease: Low cortisol levels. (too little aldosterone)
Islets of Langerhans: Alpha cells produce glucagon; beta cells produce insulin.
Diabetes Mellitus: Results from insulin levels issues:
Type 1: No insulin production.
Type 2: Insulin resistance.
Symptoms: Polydipsia (excess thirst), Polyuria (excess urine), Polyphagia (excess hunger).
Nonsteroidal Hormones: Use G protein relay systems (e.g., cyclic AMP) as second messengers.
Steroid Hormones: Lipid-soluble, enter target cells directly and bind to receptors to influence gene expression.
Regulates calcium levels in the blood through PTH (Parathyroid Hormone).
Medical Issues:
Hyperparathyroidism: High Ca2+ levels, risks of kidney stones.
Hypoparathyroidism: Can cause muscle twitching and possible respiratory failure.
Ensure to study each gland's specific functions, associated hormones, and related medical conditions for a comprehensive understanding.