The Endocrine System Chapter 15

Hormones Secreted by endocrine glands, endocrine cells, and certain neurons Travel through the bloodstream to nonadjacent target cells

Other Signaling Molecules Neurotransmitters Local signaling molecules Pheromones

Discovery of Hormones Bayliss and Starling severed nerves to dog’s intestine; left blood vessels intact Pancreas still responded Extracts of glandular epithelium also provoked pancreatic response Extracts contained secretin

Hormone Interactions Opposing interaction Synergistic interaction Permissive interaction

Endocrine System Main Sources Pituitary gland Adrenal glands Thyroid gland Parathyroid glands Pineal gland Thymus gland

Responses to Hormones Vary Different hormones activate different responses in the same target cell Not all types of cells respond to a particular hormone

Two Main Hormone Types Steroid hormones –Derived from cholesterol –Estrogens, progestins, androgens (such as testosterone), cortisol, aldosterone Peptide hormones –Peptides, proteins, or glycoproteins –Glucagon, ADH, oxytocin, TRH, insulin, somatotropin, prolactin, FSH, LH, TSH

Steroid Hormones receptor hormone-receptor complex gene product hormone Most diffuse across the plasma membrane and bind to a receptor Hormone-receptor complex acts in nucleus to inhibit or enhance transcription

Protein Hormone Hormone binds to a receptor at cell surface Binding triggers a change in activity of enzymes inside the cell glucagon receptor cyclic AMP+ P i ATP cAMP activates protein kinase A glucagon Protein kinase A converts phosphorylase kinase to active form and inhibits an enzyme required for glucagon synthesis.

The Hypothalamus Region in the forebrain Contains hormone- secreting cells Interacts with pituitary hypothalamus pituitary gland

Pituitary Gland Pea-sized gland at base of hypothalamus Two lobes –Posterior lobe stores and secretes hormones that were synthesized in the hypothalamus –Anterior lobe produces and secretes its own hormones

Posterior Lobe Antidiuretic hormone (ADH) Oxytocin (OCT) cell body in hypothalamus axons to the general circulation

Anterior Pituitary ACTH TSH FSH LH PRL STH

Normal Hormone Production Generally, the body produces only very small amounts of hormones To isolate 1 milligram of TRH, researchers dissected 7 metric tons of hypothalamic tissue

Abnormal Somatotropin Output Gigantism Pituitary dwarfism Acromegaly

Feedback Mechanisms Negative feedback –An increase in concentration of a hormone triggers activities that inhibit further secretion Positive feedback –An increase in concentration of a hormone triggers activities that stimulate further secretion

Cortisol Cortisol secretion –Inhibits blood glucose uptake by muscle and other tissues –Causes breakdown of proteins to amino acids and conversion to glucose –Causes degradation of adipose tissue to fatty acids for use as energy source

Feedback Control of Cortisol Secretion Hypothalamus senses rise in glucose and secretes less releasing hormone (CRH) Anterior pituitary responds by secreting less ACTH Adrenal cortex slows its secretion of cortisol

Localized Feedback in Adrenal Medulla Norepinephrine secreted by neurons in the medulla accumulates in the synaptic gap Some molecules bind to receptors on the axon endings that secreted them This prevents further secretion of norepinephrine by that axon

Thyroid Gland Disorders Goiter Hyperthyroidism Hypothyroidism

Calcium Regulation Parathyroid hormone (PTH) is the main regulator of calcium in the blood It is secreted when calcium levels drop PTH causes bone cells to digest bone tissue and release calcium PTH also stimulates calcium reabsorption by the kidneys and absorption by the gut

Control of Glucose Metabolism insulin Glucose rises Glucose falls Glucose is absorbed Cells use glucose glucagon Glycogen to glucose Glucose uptake Glucose to glycogen

Diabetes Mellitus Disease in which excess glucose accumulates in blood, then urine Effects include –Excessive urination –Constant thirst –Weight loss –Ketone formation and acid-base imbalances

Two Types of Diabetes Type 1 Autoimmune disease Usually appears in childhood Treated with insulin injections Type 2 Target cells don’t respond Usually appears in adults Treated with diet, drugs

The Pineal Gland Photosensitive gland embedded in brain In the absence of light, secretes melatonin Affects the human biological clock May also play a role in human puberty and in seasonal affective disorder

Local Signaling Molecules Prostaglandins –Produced and secreted in response to local changes –Sixteen types with a variety of effects Growth factors –Affect cell division rates in tissues