Endocrine SystemPart II

Bio 219Napa Valley College

Dr. Adam Ross

Endocrine System

Secondary Endocrine

• GI Organs• Hormones that affect GI motility

• Heart• ANP

• Kidneys• EPO

• Liver, Skin• Vitamin D3

Hypothalamus and Pituitary Gland

• Hypothalamus is part of the diencephalon, controls the pituitary gland

• Pituitary gland- major endocrine gland in the body

Posterior pituitary (neurohypophysis)

• Direct neural connection to hypothalamus

• Actually part of the brain

• Neurosecretory cells originate in hypothalamus, axons in infundibulum

• Axon terminals in posterior pituitary secrete neurohormones• ADH (vasopressin) and oxytocin

Anterior Pituitary (adenohypophysis)

• Circulatory connection to hypothalamus via hypothalamic-hypophyseal portal system

• Neurosecretory cells in hypothalamus secrete releasing hormones into portal system• These control hormone release from the anterior pituitary

• Anterior pituitary secretes trophic hormones that control other endocrine glands and tissues• GH, TSH, ACTH, LH, FSH and PRL

Hypothalamus-Anterior Pituitary Axis

hypothalamus anterior pituitary target endocrine gland/tissue

TRH + TSH thyroid gland

CRH + ACTH adrenal cortex

GnRH + FSH & LH ovaries/testes

GHRH + growth hormone liver, bone, muscle, etc.

somatostatin – growth hormone

PRH + prolactin breasts

dopamine – prolactin

Thyroid Gland

• Responsible for production of thyroid hormones T3 and T4 (Thyoxine)

• Effects of Thyroid Hormone (TH)• Increased basal metabolic rate

• Stimulate protein synthesis (need for growth)

• Developmental effects: nervous and reproductive systems

Feedback control of Thyroid Hormone secretion• Decrease in T3, T4 or low body temp is sensed by hypothalamus

• Hypothalamus releases TRH, sends to anterior pituitary (via portal system)

• Anterior pituitary releases Thyroid Stimulating Hormone (TSH)

• TSH stimulates thyroid to release T3 and T4• Increased metabolism increases body temp

• Normal levels achieved, signal turned off

HPA Axis (Hypothalamus, Pituitary, Adrenal Gland)• Adrenal Cortex:

• Adrenal gland is located on top of kidneys, cortex is the outer part

• Three types of hormones:• Mineralocorticoids: Aldosterone- affects kidney

• Glucocorticoids: Cortisol- stress hormone promotes gluconeogenesis

• Androgens: Testosterone

• Adrenal Medulla: Inner part of adrenal gland• Connection to sympathetic nervous system

• Chromaffin cells secrete epi and norepi

Testosterone

• Steroid sex hormone• Crosses membrane, binds to cytoplasmic receptor

• Hormone-receptor complex (dimer) enters nucleus and causes changes in gene expression

• Increases expression of genes that give male sex characteristics

Epi and Norepi

• Epi and NE act via adrenergic receptors on target cells• α1 → constriction of blood vessels

• β1 → increase in heart rate and contractility

• β2 → bronchodilation, vasodilation

Pancreas

• Endocrine portion consists of islets of Langerhans (pancreatic islets)• Beta cells secrete insulin

• Secretion of insulin when blood sugar is high

• Alpha cells secrete glucagon• Secreted when blood sugar is low

• Major regulators of homeostasis

Paracrine Factors

• A number of signaling molecules that are not themselves hormones can affect the function and activity of the endocrine system

• Interleukins

• Platelet Derived Growth Factor (PDGF)

Second messengers