Chemical Control of the Animal Body: The Endocrine System

pineal gland hypothalamus pituitary gland thyroid gland thymus adrenal glands (one at each kidney) Figure: 23-03 Title: Major mammalian endocrine glands. Caption: pancreas gonads testis ovary

II. Hormones—chemical signals of change A. Classes of animal hormones 1. Peptide hormones 2. Amino acid derivatives 3. Steroid hormones

(a) hormone: (1st messenger) (plasma membrane) 1 (extracellular fluid) (cytoplasm) activates (nuclear membrane) 2 cAMP- synthesizing enzyme active enzyme Figure: 23-02a Title: Modes of action of hormones Caption: (a) Peptide and amino-acid hormones, which are not soluble in lipids, (1) bind to receptors on the outside of the target cell's plasma membrane. (2) Hormone-receptor binding activates an enzyme that triggers the synthesis of cyclic AMP (cAMP) from ATP. (3) Cyclic AMP activates enzymes that (4) promote specific cellular reactions, producing new products. product 4 hormone receptor protein (2nd messenger) 3 activates enzyme inactive reactant (nucleus)

(b) steroid hormone (plasma membrane) 1 (extracellular fluid) (nuclear hormone-receptor complex 2 DNA 3 (cytoplasm) Figure: 23-02b Title: Modes of action of hormones Caption: (b) Lipid-soluble steroid hormones (1) diffuse readily through the plasma membrane into the target cell and into the nucleus, (2) where they combine with a receptor molecule. (3) The hormone-receptor complex binds to DNA and facilitates the binding of RNA polymerase to promoter sites on specific genes, accelerating (4) the transcription of DNA into messenger RNA (mRNA), which moves out into the cytoplasm. (5) The mRNA then directs protein synthesis. RNA polymerase ribosome hormone receptor protein 5 gene 4 mRNA protein synthesized (nucleus)

II. Hormones—chemical signals of change B. Function of animal hormones 1. Binding to surface receptors 2. Binding to intracellular receptors 3. Negative feedback as a regulatory mechanism for hormone synthesis and release

Hormone is distributed throughout the body. Endocrine cells release hormone. Hormone is distributed throughout the body. capillary Hormone enters bloodstream. receptor on target cell Figure: 23-01 Title: Endocrine glands, hormones, and target cells. Caption: The cells of endocrine glands secrete hormones into the extracellular fluid, from which they diffuse into the capillaries. A hormone binds to (and influences) only those cells with receptors for it. Muscle cells but not nerve cells have receptors for the particular hormone shown here. hormone- receptor complex SKELETAL MUSCLE TISSUE binding occurs, hormonal effects appear NEURAL TISSUE no binding, no hormone effects

The mammalian endocrine system Major endocrine glands Hypothalamus– pituitary complex Anterior pituitary hormones Posterior pituitary hormones

secreted into the blood by neurosecretory cells. PITUITARY in hypothalamus HYPOTHALAMUS hormone artery direction of blood flow Oxytocin or ADH is secreted into the blood by neurosecretory cells. Figure: 23-04 Title: The hypothalamus controls the pituitary. Caption: Neurosecretory cells of the hypothalamus control hormone release in the anterior lobe of the pituitary by producing hormones (left). These hormones are secreted into a capillary network that carries them to the anterior pituitary. There, each hormone from the hypothalamus stimulates endocrine cells with appropriate receptors to secrete that hormone while leaving other types unaffected. The posterior lobe of the pituitary (right) is an extension of the hypothalamus. Neurosecretory cells in the hypothalamus have cell endings on a capillary bed in the posterior lobe, where the cells release oxytocin or antidiuretic hormone (ADH). PITUITARY (anterior lobe) PITUITARY (posterior lobe) capillary bed capillary bed Hormone is secreted into the blood by pituitary cells. endocrine cells artery vein

Figure: 23-T01-1 Title: Mammalian endocrine glands and hormones. Caption: Mammalian endocrine glands and hormones. From "hypothalamus" through "pancreas."

Figure: 23-T01-2 Title: Mammalian endocrine glands and hormones. Caption: Mammalian endocrine glands and hormones. From "ovaries" through "fat cells."

hypothalamus Hypothalamus sends impulses to posterior pituitary. hunger posterior pituitary Oxytocin is released and carried in blood to the breast. Nerve impulses are sent to Hypothalamus. Muscles contract and squeeze out milk. Suckling stimulates nerves in breast. Figure: 23-06 Title: Hormones and breastfeeding. Caption: The control of milk letdown by oxytocin during breastfeeding is regulated by feedback between an infant and its mother. The cycle begins with the infant’s suckling and continues until the infant is full and stops suckling. With the nipple no longer being stimulated, oxytocin release stops, the muscles relax, and milk flow ceases. milk gland muscle cells duct milk-producing cells nipple

Figure: 23-05 Title: When the anterior pituitary malfunctions. Caption: An improperly functioning anterior pituitary produces either too much or too little growth hormone. Too little causes dwarfism; too much causes gigantism.

The mammalian endocrine system Thyroid and parathyroid glands a. Thyroxine and metabolism b. Hyperthyroidism and Graves' disease

(a) larynx thyroid gland esophagus trachea (b) Figure: 23-07 Title: The thyroid gland. Caption: (a) The thyroid gland wraps around the front of the larynx in the neck. (b) Goiter, a condition in which the thyroid gland becomes greatly enlarged, is caused by an iodine-deficient diet.

The mammalian endocrine system 3. Pancreas as an endocrine gland a. Regulation of blood glucose levels by insulin and glucagon b. Insulin insensitivity and diabetes mellitus

insulin-producing cells glucagon-producing cells glucose glycogen eating insulin-producing cells pancreas glucagon-producing cells glucagon insulin Figure: 23-08 Title: The pancreas controls blood glucose levels. Caption: The pancreatic islet cells contain two populations of hormone-producing cells: one producing insulin; the other, producing glucagon. These two hormones cooperate in a two-part negative feedback loop to control blood glucose concentrations. glucose glycogen liver

The mammalian endocrine system 4. Sex organs and steroid hormones a. Puberty and secondary sex characteristics b. Gamete production

The mammalian endocrine system Adrenal glands a. Adrenal medulla 1) Produces adrenaline and noradrenaline a) Released in response to stress or emergency situations b. Adrenal cortex 1) Produces glucocorticoids a) Steroid hormones that help regulate glucose metabolism b) Glucocorticoids and sports medicine 2) Produces aldosterone Steroid hormone that regulates the sodium content of the blood by affecting the kidneys and sweat glands 3) Testosterone synthesis and the bearded lady

adrenal medulla (epinephrine, norepinephrine) adrenal gland adrenal cortex (glucocorticoids, testosterone, aldosterone) Figure: 23-09 Title: The adrenal glands. Caption: Atop each kidney sits an adrenal gland, which is a two-part gland composed of very dissimilar cells. The outer cortex secretes steroid hormones; the inner medulla secretes epinephrine and norepinephrine. kidney

The mammalian endocrine system Kidneys a. Erythropoietin 1) Response to low oxygen content in the blood 2) Stimulates the production of RBC in the bone marrow b. Renin 1) Response to low blood pressure 2) Activates the production of angiotensin, which constricts arterioles