ENDOCRINE SYSTEM

Chapter 16

ENDOCRINE GLANDS

Ductless glands that produce hormones that are released directly into the bloodstream and are transported throughout the body to regulate the metabolic function of other cells in the body.

Types of hormones: Paracrine Autocrine

Chemical Nature of Hormones

Amino-acid based hormones Amines=simple hormones derived from tyrosine

(example: Epinephrine) Protein and peptides=chains of amino acids hooked

together (example: ADH or Oxytocin)

Steroid-based hormones Progesterone Testosterone

Eicosanoids Hormone-like substances that act only on cells in the

immediate vicinity (example: prostaglandin)

Functions of Hormones

Integrative

Homeostatic

Growth

Mechanisms of Hormone Action

Lipid-soluble hormones Diffusion occurs Binds to intracellular

receptors Forms hormone-receptor

complexes Hormone-receptor complex

binds to specific receptor proteins on DNA

Initiates transcription of certain genes

Mechanisms of Hormone Action

Cyclic AMP signaling Hormone binds to cell

membrane receptor Hormone-receptor complex

binds to inactive G protein G protein becomes active by

GTP to GDP G protein binds adenylate

cyclase producing Cyclic AMP

Cyclic AMP activates protein kinase enzymes

Mechanisms of Hormone Action

PIP-calcium signaling Hormone binds to cell

membrane receptor Hormone-receptor

complex binds to inactive G protein

G protein becomes active and binds to phospholipase

Phospholipase splits to form IP3 and DAG which activate protein kinases and calcium

Control of Hormones

Feedback Mechanisms Negative feedback Positive feedback

Responsiveness to target cells Concentrations of hormones Number of receptors Interaction of other hormones

Control of Hormones

Major Endocrine Glands

Pituitary Gland

Thyroid Gland

Parathyroid Gland

Adrenal Gland

Thymus Gland

Pineal Gland

Other endocrine tissue

Pituitary Gland (Hypophysis)

Posterior lobe Oxytocin ADH

Anterior lobe GH TSH ACTH FSH LH PRL MSH

Thyroid Gland

Follicles and follicle cells

Thyroglobulin

Colloid

Thyroxine (T4)

Triiodothyronine (T3)

Calorigenic effect

Calcitonin produced by parafollicular cells

Parathyroid Gland

Produces parathyroid hormone (PTH)

Regulates calcium levels by targeting: Bones Intestine Kidneys

Adrenal Gland

Adrenal Cortex Zona glomerulosa

produces mineralcorticoids

Zona fasciculate produces glucocorticoids

Zona reticularis produces androgens or adrenal sex hormones

Adrenal Gland (continued)

Adrenal Medulla Chromaffin cells Epinephrine Norepinephrine Associated with stress

or “Fight or Flight” responses

Thymus and Pineal Gland

Thymus Gland Thymosin stimulates

T-cell maturation Immune system

Pineal Gland Pinealocytes Melatonin

Pancreas

Alpha Cells Produce glucagon Glycogen>>Glugacon>>Glucose

Beta Cells Produce insulin Enhances uptake of glucose by cells

as well as inhibits glycogenolysis and gluconeogenesis

Delta Cells Somatostatin

Acinar Cells Produces pancreatic enzymes but

are exocrine

Pancreas (continued)

Other Endocrine Tissues

Ovaries=produce estrogen and progesterone

Testes=produce testosterone and inhibin

Placenta=produces HCG

Heart=secretes ANP

Kidneys=secrete erythropoietin

Skin=produces choleocalciferol

Adipose tissue=releases leptin

Gastrointestinal tract=releases gastrin, secretin, serotonin, cholecystokinin and others

Homeostatic Imbalances

GigantismAcromegalyProgeriaPituitary dwarfismGalactorrheaGynecomastiaMyxedemaGoiterCretinism

Grave’s diseaseHyperparathyroidismHypoparathyroidismDiabetes insipidusDiabetes mellitusAldosteronismAddison’s diseaseCushing’s diseaseMasculinization

Thyroid Gland (continued)

Thyroid Gland (continued)

Cushing’s Disease

Cushing’ Disease

Acromegaly

Gigantism and Pituitary Dwarfism

Addison’s Disease