Major Endocrine Organs Hypothalamus Pineal Gland Pituitary Gland Thyroid Gland Thymus Gland Adrenal Glands Pancreas Ovaries (Female) Testis (Male) Chapter 8.2 The Endocrine System The endocrine system is run by the hypothalamus. Hormones in the hypothalamus stimulate the pituitary gland, which starts a chain reaction that impacts organs and hormones throughout the endocrine system. Hypothalamus Very small gland found deep inside the brain Part of both the nervous and endocrine systems Collects information from the body systems and regulates responses of nervous and endocrine system to maintain homeostasis Helps regulate: Metabolism Heart rate Energy level Body temperature Thirst Nutrient intake Blood pressure Blood composition Emotions Sleep President of the endocrine system Main controller of endocrine system Produces hypothalamic releasing and non-releasing hormones that stimulate or inhibit the release of hormones from the pituitary gland Pituitary Gland Pea-sized gland with two lobes Anterior pituitary Stores and releases hormones from the hypothalamus; hormones kept in anterior pituitary until the hypothalamus stimulates their release Posterior pituitary
Posterior pituitary is actually an extension of the hypothalamus; it does not produce hormones, but stores two hormones that are produced by the hypothalamus Hangs from hypothalamus by the infundibulum Hormones secreted by the pituitary gland have two functions: Act on target tissues to cause a specific metabolic response Stimulate other endocrine glands to release their own hormones Tropic hormones: hormones secreted by pituitary gland to stimulate other glands Anterior pituitary hormones Growth hormone (GH) Helps with growth and development of muscles, cartilage, and bones Helps to break down fats for use as fuel GH stimulated by exercise; exercise causes glycogenesis, in which fats and proteins are metabolized by the liver; allows for prolonged physical activity Prolactin (PRO) Stimulates growth of mammary glands and milk production in a nursing mother Present in males as well, however its function in males is unclear Adrenocorticotropin hormone (ACTH) ~ tropic hormone Acts on the adrenal cortex to stimulate the release of steroid hormones Thyroid-stimulating hormone (TSH) ~ tropic hormone Acts on the thyroid gland to stimulate the release of two thyroid hormones: thyroxine and triiodthyronine Follicle-stimulating hormone (FSH) ~ gonadotropic Stimulates the production of estrogen and eggs in females and the production of sperm in males Luteinizing hormone (LH) ~ gonadotropic Acts of ovaries to produce progesterone and estrogen in females Signals for egg release in females Stimulates the interstitial cells of the testes to produce testosterone in males Posterior pituitary hormones Antidiuretic hormone (ADH) Acts on kidneys to decrease urine output which increases body fluid volume Regular physical activity causes upregulation (increased sensitivity) to ADH and a higher volume of blood plasma The hypothalamus triggers the release of ADH by humoral control when blood plasma volume decreases from dehydration and profuse sweating Also secreted when solid particles in the blood become more concentrated Plays a role in blood pressure regulation by narrowing arteries to raise blood pressure and by increasing blood volume
Inhibited by alcohol consumption, which leads to increased urination, resulting in dehydration and dry mouth Also inhibited by caffeine and foods such as asparagus Oxytocin Produced by pregnant women during labor Levels of oxytocin will stay in mother s bloodstream until she finishes breastfeeding Causes the uterus to contract during labor Release stimulated by labor and the sucking mechanism of a nursing baby Thyroid Gland Inferior to the larynx Butterfly shaped and about two inches long Two lobes connected by isthmus Secretes two hormones Thyroid hormone Two separate hormones: thyroxine (T4) and triiodothyronine (T3) Responsible for: Energy metabolism Heat production Growth Development Maturation Iodine is required for T3 and T4 production Every cell in the body is impacted by thyroid hormone Calcitonin Regulates calcium homeostasis with the help of parathyroid hormone When blood calcium levels rise, the thyroid gland releases calcitonin, which causes calcium in the blood to be absorbed by bones Once a human reaches adulthood and bones are fully developed, very little calcitonin, if any, is secreted Parathyroid Glands Two pairs of glands, each about the size of a grain of rice Located on posterior part of thyroid gland Secrete parathyroid hormone which works with calcitonin to maintain calcium levels in blood Removes calcium from bones and puts it into the blood by stimulating the breakdown of bone tissue by osteoclasts which moves calcium from the bone to the blood Only occurs when blood-calcium levels are decreased Results in increased calcium absorption in the intestines with the help of vitamin D, along with calcium reabsorption from urine by kidneys and the excretion of phosphorus
Thymus Gland Functions as an endocrine gland and a lymphatic organ Located right ender the sternum and in front of the heart Shrinks with age; begins to shrink at the onset of puberty and is barely visible by late adulthood Secretes thymosin Aids in the development of immune system Essential for the development of white blood cells (T-lymphocytes of T-cells) Pineal Gland Pinecone-shaped gland in brain Secretes melatonin Exact function is unclear Secreted when the body is exposed to darkness Causes drowsiness Adrenal Glands Pair of glands Sit on top of kidneys Actually two organs: Adrenal cortex Makes up the outer layer of each adrenal gland and has three layers of its own Gland that produces three types of steroid hormones Mineralocorticoids Aldosterone: stimulates kidneys to reabsorb sodium and water from urine Glucocorticoids Cortisone and cortisol: maintain blood glucose levels through gluconeogenesis; convert fat and amino acids into glucose Sex hormones Estrogen (females) Androgens (males): testosterone Adrenal medulla Part of the nervous system Secretes epinephrine and norepinephrine Released in times of physical or emotional stress Produces adrenaline rush or fight-or-flight response which results in: Increased respiratory rate Increased heart rate Increased blood flow to heart and skeletal muscles Decreased blood flow to internal organs Dilated pupils
Pancreas Long, thin gland Posterior to the stomach Functions as both an endocrine and exocrine gland Endocrine: secretes hormones that secrete blood glucose levels Exocrine: secretes digestive enzymes to the small intestine Contains structures called islets of Langerhans Made of alpha cells and beta cells Alpha cells Secrete glucagon Increase blood glucose levels Glucagon causes the liver to break down glucogen into glucose Beta cells Secrete insulin Decrease blood glucose levels Insulin targets almost every cell in the body and promotes glucose uptake Insulin is the only tool for getting insulin into body cells Gonads Testes Testosterone Sperm production Secondary sexual characteristics: body hair, deep voice Ovaries Estrogen Secondary sexual characteristics: body curvature (hips), breast development Progesterone Helps control the menstrual cycle