Endocrine System

Homeostasis Maintaining internal balance in the body Regulation Organisms must keep internal conditions stable even if environment changes Regulation Nervous system Nerve signals control body functions Endocrine system Hormones Chemical signals control body functions

Endocrine System includes the organs of the body that secrete hormones directly into body fluids such as blood Regulates chemical reaction in cells and therefore control functions of the organs, tissues, and other cells

Hormones Endocrine glands Hormones Ductless Release hormones Into bloodstream to be carried to target tissues Hormones Chemicals secreted by a cell that affect the functions of other cells Growth hormones Sex hormones Response hormones Metabolism hormones And more…

Negative & Positive Feedback Loops Control Hormone Levels Negative feedback loop Hormone release stops in response to decrease in stimulus Stimulus (eating) raises blood glucose levels Pancreas releases insulin in response to elevated blood glucose Blood glucose decreases as it is used by the body or stored in the liver Insulin release stops as blood glucose levels normalize

Negative & Positive Feedback Loops As long as stimulus is present, action of hormone continues Infant nursing at mother’s breast stimulates hypothalamus stimulates posterior pituitary Oxytocin released stimulates milk production & ejection from mammary glands Milk release continues as long as infant continues to nurse

Endocrine Glands Pineal gland & thymus gland are ductless but little is know about their endocrine function Pineal gland Secretes melatonin Supports body’s biological clock Thought to induce sleep Thymus gland Produces thymosin Important in the development of immune responses in newborns

Endocrine Glands Thyroid Gland Composed of right & left lobe on either side of trachea Major hormones Thyroid hormone Stimulates protein synthesis & increase metabolism Calcitonin Lowers blood calcium levels

Endocrine Glands Parathyroid Glands Four small oval bodes located on the dorsal aspect of the thyroid gland Major hormone Parathyroid hormone (PTH) Agonist to calcitonin by raising blood calcium levels

Endocrine Glands Adrenal Glands Glands on top of kidneys Adrenal Cortex (outer) Increases blood glucose Increases salt reabsorption Sexual characteristics Adrenal medulla (inner) Epinephrine (adrenaline) & Norepinephrine (noradrenaline) Sympathomimetic Mimic the actions of the sympathetic nervous system

Endocrine Glands Pancreas Located near & partly behind the stomach islets of Langerhans Hormone-producing cells Produce insulin Lowers blood sugar Produce glucagon Raises blood sugar

Endocrine Glands Pituitary Gland (hypophysis) “Master Gland”- controls several other endocrine glands Pea-sized gland located at the base of the brain Consists of an anterior lobe (adenohypophysis) & posterior lobe (neurohypophysis)

Endocrine Glands Ovaries Testes Produce the ovum & hormones responsible for female sex characteristic & regulation of the menstrual cycle Estrogen Female sex characteristics Progesterone Maintains pregnancy Testes Produce the spermatozoa & testosterone Testosterone is an androgen Stimulates secondary sex characteristics

Common Diseases and Disorders Disease/Disorder Description Acromegaly Too much growth hormone produced in adults; enlargement of bones and thickened skin Addison’s disease Adrenal gland fails to produce enough corticosteroids Cretinism Extreme form of hypothyroidism present prior to or soon after birth Cushing’s disease Hypercortisolism; over-production of cortisol Diabetes insipidus Kidneys fail to reabsorb water, resulting in excessive urination; hyposecretion of ADH

Acromegaly Cushing’s disease

Common Diseases and Disorders (cont.) Disease/Disorder Description Diabetes mellitus Type I Type II Gestational Chronic disease characterized by elevated blood glucose levels Insulin-dependent diabetes mellitus; usually develops in childhood Noninsulin-dependent diabetes mellitus; primarily in adults but increased incidence in teens Occurs during pregnancy; usually temporary Dwarfism Too little growth hormone (somatotropin) produced during childhood

Common Diseases and Disorders (cont.) Disease/Disorder Description Gigantism Too much growth hormone produced during childhood Goiter Enlargement of thyroid gland, causing swelling in neck; deficiency of iodine in diet Grave’s disease Hyperthyroidism; antibodies attach to thyroid gland, causing it to produce too much thyroid hormone Myxedema Thyroid gland produces inadequate amounts of thyroid hormone; common in females over 50

Gigantism Goiter