The Endocrine System

introduction

Endocrine v Nervous Endocrine system Releases hormones into interstitial fluid  blood  general circulation Effectors: virtually any type of body cell; can have widespread effects on diverse aspects of metabolism Slower, longer-lasting responses as hormones linger in blood

Hormone Action Hormones are carried in blood stream Only certain cells can be affected by hormones These target cells have 1000’s of receptors specific for a particular hormone. Response determined by target cell: different cells may respond differently to the same hormone.

Location of Endocrine Glands

Hormone chemistry

Lipid-Soluble Hormones Steroids, such as testosterone, estrogens Thyroid hormones: T3 and T4 Nitric oxide (NO)

Lipid-Soluble Hormones 1 Lipid-soluble hormone diffuses into cell Blood capillary Activated receptor-hormone complex alters gene expression Nucleus Receptor mRNA Newly formed mRNA directs synthesis of specific proteins on ribosomes DNA Cytosol Target cell Transport protein Free hormone Ribosome 2 3

Water Soluble Hormones Amino acid derivatives, such as epinephrine, norepinephrine Peptides: antidiuretic hormone (ADH), oxytocin Proteins: insulin and growth hormone

Water Soluble Hormones Receptor cAMP serves as a second messenger to activate protein kinases G protein Protein kinases cAMP Activated protein Protein— Second messenger Phosphodiesterase inactivates cAMP Activated adenylate cyclase converts ATP to cAMP Activated protein phosphorylate cellular proteins Millions of phosphorylated proteins cause reactions that produce physiological responses Blood capillary Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase Adenylate cyclase Target cell P ADP Protein ATP 1 2 6 4 3 5

Control of Secretions Release occurs in short bursts Regulated by Signals from nervous system Example: epinephrine Chemical changes in blood Example: blood Ca2+ affects PTH Other hormones Example: ACTH from pituitary stimulates release of cortisol from adrenal cortex

Hypothalamus & pituitary

Anterior Pituitary Also called the adenohypophysis; it produces: hGH (somatotropin) IGF (Insulinlike Growth Factor) TSH – Thyroid Stimulating Hormone FSH – Follicle Stimulating Hormone

Anterior Pituitary LH – Luteinizing Hormone PRL – Prolactin ACTH – Adrenocorticotropic Hormone MSH – Melanocyte Stimulating Hormone These are all regulated by release factors made in the hypothalamus

Posterior Pituitary Also called the neurohypophysis; it stores and releases: Oxytocin ADH – Antidiuretic Hormone These substances are produced by the hypothalamus

Glands of the body

The Thyroid Gland Produces thyroxin (T4) and triiodothyronine (T3) Actions: Increases BMR (rate of O2 consumption) → body temp Body growth and development Also produces calcitonin Lowers blood levels of Ca, P

The Parathyroid Glands Produces Parathyroid Hormone (PTH) Increases blood levels of Ca, P, Mg

The Pancreas Pancreas is both endocrine and exocrine (digestive enzymes) Islets of Langerhans produce glucagon and insulin Glucagon increases blood levels of glucose Insulin decreases blood glucose levels

The Adrenal Glands Adrenal Cortex Mineralocorticoids such as Aldosterone – regulates Na+ (reabsorption) and K+ (excretion) Glucocorticoids such as Cortisol – breaks down proteins and triglycerides; anti-inflammatory

The Adrenal Glands Adrenal Medulla Produces epinephrine and norepinephrine Stress response; Fight-or-flight

The Pineal Gland Produces melatonin Biological clock Levels increase in darkness and during sleep Levels high in infants and young children; lower in adults