Endocrine system General mechanisms: Hypothalamus→ Anterior Pituitary→ Endocrine gland→ Target cells

Hypothalamus: Release hormones that connect the CNS and endocrine System

Anterior Pituitary: Stimulating hormones that prompt endocrine Glands

Endocrine gland: Hormones that regulate endocrine and nonendocrine targets

Repeated Negative feedback loop

Pituitary gland has two lobes:

Anterior Pituitary • Glandular Tissue • Hormone release is stimulated by local secretions from neurosecretory cells projecting from the hypothalamus

Posterior Pituitary • Neurosecretory Tissue • Neurosecretory cells projecting from the hypothalamus secrete directly into the circulatory system

Neurons synthesize release stimulating hormones targeting endocrine cells of the anterior pituitary

Active neurons excrete release stimulating hormones into local capillary system of the anterior pituitary

Release stimulating hormones travel in local capillary system to endocrine cells clusters of the anterior pituitary

In response to release stimulating hormones, the anterior pituitary secretes hormones into general circulation

Hormones of anterior pituitary: Growth Hormone (GH) Thyroid-stimulating Hormone (TSH) or Thyrotropin Adrenocorticotropic hormone (ACTH) Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) Prolactin (PRL)

Posterior pituitary lobe • Outgrowth of hypothalamic neural tissue. Composed of neurosecretory neurons synthesizing and releasing hormones • Oxytocin • Antidiuretic Hormone (ADH) Hormones are directly secreted by the neurosecretory cells into blood capillaries and general circulation

Hypothalamic neurons synthesize Oxytocin or Antidiuretic Hormone (ADH). Posterior lobe of pituitary Hypothalamus Oxytocin and ADH are transported in axons to the posterior pituitary. Oxytocin and ADH are stored in axon terminals and released into the circulatory system

Oxytocin Peptide Hormone Released during childbirth to stimulate uterine contractions Controls milk production and lactation Acts as a neurotransmitter in brain

ADH (Vasopressin) Peptide Hormone Regulates water balance Release also triggered by pain, low blood pressure, and certain drugs (antidiuretics) Release is inhibited by alcohol, which is a diuretic

Growth hormone: Hypothalamus- Growth Hormone Releasing Hormone Anterior Pituitary- Growth Hormone Liver- Insulin Like Growth Factors (non-hormonal) Many Tissues Stimulates Regulates growth hormone secretion

Direct actions on metabolism • Increases fatty acid levels in the blood • Encourages the use of fatty acids for fuel • Increases protein synthesis • Increases blood glucose levels

Indirect actions on metabolism • Mediates the release of Insulin-like growth factors (IGFs) • Uptake of nutrients and synthesis of DNA and proteins • Formation of collagen and deposition to bone matrix

Homeostatic Imbalances Hypersecretion - In children results in Gigantism - In adults results in Acromegaly Hyposecretion - In children results in Pituitary Dwarfism

Thyroid Hormone • Major metabolic hormone • Increases metabolic rate and heat production • Regulates tissue growth and development • Development of skeletal and nervous systems • Reproductive capabilities • Maintenance of blood pressure

• Composed of follicles that produce a glycoprotein • Thyroglobulin • Colloid (fluid with thyroglobulin + iodine) fills the lumen of follicles • Colloid is the precursor to Thyroid Hormone • Parafollicular cells produce the hormone calcitonin

Homeostatic Imbalances Hyposecretion in adults • Myxedema • Goiter due to lack of iodine Hyposecretion in infants - Cretinism

Homeostatic Imbalances Hypersecretion • Graves' Disease • Autoimmune disorder caused by thyroid-stimulating immunoglobulin antibodies mimicking thyroid stimulating hormone Typical symptoms: • Bulging eyes • Anxiety, difficulty sleeping and/or insomnia • Elevated blood pressure • Fatigue • Tremors and muscle weakness • Rapid or irregular heartbeat

Endocrine System Adrenal gland and corticoids ACTH Adrenocorticotropic hormone (Corticotropin)

Adrenocorticotropic Hormone (Corticotropin) Hypothalamus Ant. pituitary Adrenal cortex Corticotropin Release Hormone Adrenocorticotropic hormone Cortisol Target tissue

Mineralocorticoids Regulate electrolytes (Na+ and K+) - Na+ affects blood volume and blood pressure - K+ sets the VM (membrane potential) of cells

Aldosterone most potent mineralocorticoid - Stimulates Na+ reabsorption and water retention by kidneys - Elevates blood volume and blood pressure - Elimination of K+ increases cellular excitability

Glucocorticoids (cortisone and corticosterone) • Stabilize blood glucose levels • Maintain blood pressure by controlling vasoconstriction

Cortisol (Hydrocortisone) - Increases gluconeogenesis - Formation of glucose from fats and protein - Promotes rise in blood glucose, fatty acids, and amino acids for energy - Vasoconstriction raises blood pressure and increases the speed at which energy is distributed

Homeostatic Imbalances of glucocorticoids Hypersecretion • Cushing’s syndrome • Depressed cartilage and bone formation • Inhibits inflammation • Depresses immune system • Disrupts cardiovascular, neural, and gastrointestinal functions

Hyposecretion • Addison's Disease • Decrease in glucose and Na+ levels • Weight loss, severe dehydration, and hypotension

Peptide Hormone • Synthesized by endocrine ɴ cells of “islets of Langerhans” in the pancreas

Glucagon is another peptide hormone • Synthesized by endocrine ɲ cells of “islets of Langerhans” Insulin and Glucagon are “antagonists” that control blood sugar level • Insulin triggers glucose remove from the blood into storage • Glucagon triggers glucose release from storage into the blood

DNA encoded peptide sequence, • Raw peptide chain with 4 regions • P, C, B and A • Preproinsulin • Posttranslational modification of preproinsulin involves enzymatic cleavage of regions C and P from peptide • Remaining A&B are Insulin • C fragment has no known function and is used as a clinical marker for insulin production • Insulin (and C subunit) is released by exocytosis as required

Three Principal Types: Type 1 Diabetes (10%); Inability to produce Insulin • Sudden onset, diagnosed mainly in children and adolescent youth • Treated with insulin injections • Mostly hereditary

Type 2 Diabetes (90%); Inability to produce sufficient insulin quantities or use insulin (no receptors) • Gradual onset, diagnosed in adults and increasingly in children • Can be treated by dietary changes and medications • Obesity & stress (lifestyle) and genetic risk factors Gestational Diabetes; Temporary diabetes during pregnancy • < 4% of pregnancies • Increased risk for diabetes Type 2 for mother and child down the road