Chemical Coordination: Endocrine System

Chemical Coordination and Integration

• Chemical coordination and integration involve the endocrine system
• This system uses hormones to transmit information
• It complements the nervous system's rapid but short-lived communication via electrical impulses

Endocrine Glands

• Endocrine glands secrete hormones directly into the bloodstream
• They lack ducts, and are different from exocrine glands that secrete through ducts

Hypothalamus

• The hypothalamus links the nervous and endocrine systems
• It contains neurosecretory cells that produce hormones
• These hormones regulate the pituitary gland

Pituitary Gland

• The pituitary gland is divided into the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis)
• The anterior pituitary produces growth hormone (GH), prolactin (PRL), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH)
• The posterior pituitary stores and releases oxytocin and vasopressin, which are produced by the hypothalamus
• Growth hormone (GH) stimulates body growth
• Prolactin (PRL) regulates mammary gland growth and milk production
• Thyroid-stimulating hormone (TSH) controls thyroid hormone synthesis and release
• Adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex to release glucocorticoids
• Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) control gonadal activity, leading to the production of sex hormones

Pineal Gland

• The pineal gland secretes melatonin
• Melatonin regulates the sleep-wake cycle and influences body temperature

Thyroid Gland

• The thyroid gland produces thyroxine (T4) and triiodothyronine (T3), which regulate metabolism
• Iodine is essential for thyroid hormone synthesis
• Calcitonin, also secreted by the thyroid, lowers blood calcium levels

Parathyroid Glands

• The parathyroid glands secrete parathyroid hormone (PTH)
• PTH increases blood calcium levels
• It does this by stimulating bone resorption and calcium reabsorption in the kidneys

Thymus

• The thymus gland secretes thymosins
• Thymosins play a role in T-cell maturation and immune response

Adrenal Glands

• The adrenal glands consist of the adrenal cortex and adrenal medulla
• The adrenal cortex secretes glucocorticoids (e.g., cortisol) and mineralocorticoids (e.g., aldosterone)
• Glucocorticoids regulate carbohydrate, protein, and fat metabolism
• Mineralocorticoids regulate electrolyte and water balance
• The adrenal medulla secretes epinephrine and norepinephrine in response to stress

Pancreas

• The pancreas functions as both an exocrine and endocrine gland
• The endocrine part, the islets of Langerhans, contains alpha cells that produce glucagon and beta cells that produce insulin
• Insulin lowers blood glucose levels by promoting glucose uptake by cells
• Glucagon increases blood glucose levels by stimulating glycogen breakdown

Testes

• The testes produce androgens, mainly testosterone
• Testosterone regulates the development of male secondary sexual characteristics and spermatogenesis

Ovaries

• The ovaries produce estrogen and progesterone
• Estrogen regulates the development of female secondary sexual characteristics
• Progesterone supports pregnancy

Hormones from Other Tissues

• The heart secretes atrial natriuretic factor (ANF), which decreases blood pressure
• The kidneys secrete erythropoietin, which stimulates red blood cell production
• The gastrointestinal tract secretes hormones like gastrin, secretin, and cholecystokinin (CCK) that regulate digestion

Mechanism of Hormone Action

• Hormones bind to receptors on or in target cells
• Peptide hormones typically bind to cell surface receptors
• Steroid hormones bind to intracellular receptors, affecting gene expression