Lesson 1 - Mechanisms of Hormone Regulation

What are the functions of hormonal regulation?

• Fetal development; Differentiate reproductive system and CNS

• Stimulation of growth and development during childhood and adolescence

• Coordination of male and female reproductive systems

• Maintenance of internal homeostasis (e.g. glucose, water balance)

• Adaptation to stress and emergency (fight or flight)

• Regulation of metabolism and energy balance

What are the different secretion patterns of hormones?

• Diurnal

• Pulsatile

• Cyclic

How is hormone secretion controlled/regulated?

• feedback systems; mostly negative feedback loops

What characteristic of hormonal secretion describes how target cells have specific receptors?

• Specificity

What organ are hormones excreted and metabolized by?

• Excreted by kidneys

• Metabolized in the liver

What triggers hormone release?

• Changes in the body’s environment or needs

How does hormone secretion maintain homeostasis?

• Regulates substances or other hormones

What are the factors that regulate hormone secretion?

• chemical, hormonal, neural signals

• Primarily regulated by negative feedback mechanisms

Hormones are released into the _________ by _______ _______

• Bloodstream, endocrine glands

How is receptor sensitivity regulated?

• Up regulation and down regulation of receptors

What are the types of hormonal effects?

• Direct effects

• Permissive effects

What are ‘direct effects’ of hormones?

• Hormones have direct impact on target cells (e.g., insulin lowers blood glucose)

What are ‘permissive effects’ of hormones?

• One hormone enhances the action of another (e.g., thyroid hormones make tissues more responsive to epinephrine by increasing receptors specific to epinephrine)

Describe Lipid-soluble hormones

• Primarily bound to carrier proteins in blood

• Have longer-lasting effects

• Can cross the plasma membrane and bind to intracellular receptors

Describe water-soluble hormones

• circulate in free, unbound form

• act quickly and are short-lived

• Bind to surface receptors on target cells

Compare and contrast the structural differences between water-soluble and lipid-soluble hormones

• Water-soluble hormones

  • Large, hydrophilic; can’t cross plasma membrane

• Lipid-soluble hormones

  • Small, hydrophobic molecules that diffuse across the membrane

Describe the signal transduction for water-soluble hormones

• first messenger is the hormone itself, binds to receptor protein, triggering secondary messengers

• Second messengers - intracellular molecules (Ca2+, cAMP) that amplify the signal and activate protein kinases

• Short-lived cellular changes (enzyme activity or membrane channels)

Describe the signal transduction of lipid-soluble hormones

• They are steroid hormones; derived from cholesterol

• Exert effects by binding to nuclear or cytosolic receptors

• Hormone-receptor complex attaches to DNA, turning on/off specific genes

• Changes in protein synthesis occur, alters cell activity

• Slower to start, but longer lasting effects

What is the Hypothalamic-Putuitary axis?

• Describes how the hypothalamus is the master regulator of endocrine function; controls trophic hormone release from the pituitary gland which affects all other endocrine glands

Differentiate between the anterior vs. Posterior pituitary gland

• Anterior pituitary

  • Pars distalis, pars tuberalis, pars intermedia

  • Secrete tropic hormones that regulate other endocrine glands

• Posterior pituitary

  • Pars nervosa and pituitary stalk

  • Stores and releases hormones produced in the hypothalamus

What are the tropic hormones released by the anterior pituitary?

• Adrenocorticotrophic hormone (ACTH)

• Melanocyte-stimulating hormone (MSH)

• Follicle-stimulating hormone (FSH)

• Luteinizing hormone (LH)

• Thyroid-stimulating hormone (TSH)

What are the somatropic hormones released by the anterior pituitary

• Growth hormone

• Prolactin

What are the hormones of the posterior pituitary

• ADH

• Oxytocin

Role of ADH

• Water conservation

• Electrolyte balance

• Blood vessel constriction

Role of Oxytocin

• Breast smooth muscle contraction; milk ejection in lactating women

• Uterine smooth muscle contraction (childbirth)

• Orgasm

• Social recognition & maternal bonding

• Sperm movement & testosterone levels in testes

Describe the role of the pineal gland

• located near center of the brain

• Secretes melatonin

  • Regulates circadian rhythms

  • Influences reproductive systems and puberty onset

  • Role in immune regulation

Describe the thyroid gland

• Located on either side of trachea

• Two lobes connected by isthmus

• Two cells types:

  • Follicles (contain colloid)

  • Parafollicular cells (secretes calcitonin)

Describe the parathyroid glands

• located behind thyroid

• Secretes parathyroid hormone (PTH)

What hormones does the thyroid gland release?

• Thyroid hormones T3 and T4

What does thyroid hormones do

• regulates growth, metabolism, heat production, and oxygen consumption

What is the role of PTH?

• increases serum Ca2+ levels; bone resorption

• Opposite of calcitonin

• Vitamin D is cofactor

What are the islets of langerhans

• Alpha cells

• Beta cells

• Delta cells

• F cells

What do alpha cells release?

• glucagon

What do beta cells release?

• insulin and amyloid

What do delta cells release?

• somatostatin and gastric

What do F cells release?

• pancreatic polypeptide

What is the function of Insulin?

• facilitates the rate of glucose uptake into cells of body

What is the insulin precursor?

• Proinsulin

What is the functions of Amylin

• peptide hormone co-secreted with insulin

• Delays nutrient uptake

• Suppresses glucagon secretion

What is the function of glucagon

• secreted when blood glucose is low to increase blood glucose by increasing glycogenolysis, gluconeogenesis, lipolysis, amino acid catabolism

What are “other” pancreatic hormones

• somatostatin - regulates alpha and beta cell activity

• Gastric - stimulates gastric secretion

• Ghrelin - stimulates hunger

• Pancreatic polypeptide - regulates pancreatic secretion

Where are the adrenal glands located

• on top of kidneys

What are the two main parts of the adrenal glands

• Adrenal cortex

• Adrenal medulla

Describe glucocorticoid hormones

• stimulated by ACTH

• Regulate carbohydrate metabolism, inflammation, and immune response

What is the most potent glucocorticoid?

Cortisol

What are mineralcorticoids?

• steroid hormones produced in adrenal cortex, regulates body’s salt & water balance via controlling electrolyte levels (Na+ & K+)

What is the function of Aldosterone

• affects ion transport by epithelial cells

  • Increases activity of sodium pump of epithelial cells

  • Causes sodium retention and potassium & H+ loss

• Stimulated by RAAS

What is the most potent naturally occurring mineralcorticoid

• Aldosterone

What are adrenal androgens

• sex hormones

• Weak androgens are converted to stronger androgens like testosterone in peripheral tissues

What are adrenal estrogens

• female sex hormone

• secreted in smaller amounts but contribute to estrogenic effects

What kind of cells are in the adrenal medulla?

• Chromaffin cells that secrete catecholamines

What are catecholamines?

• stress-related hormones made by adrenal medulla

• Epinephrine (majority), norepinephrine (minority)

• Involved in fight or flight response and hyperglycemia