Animal Hormones

30.1 Messengers of the Endocrine System Endocrine cells—cells that secrete endocrine signals Endocrine glands—secretory organs composed of aggregations of endocrine cells Hormones are “long-distance” endocrine signals that are released into the bloodstream and circulate throughout the body. Target cells—cells that have receptors for the chemical signals The same hormone can have a variety of different target cells, all distant from the site of release.

30.1 Protein Hormones Peptide and protein hormones—water-soluble, transported in blood with receptors on exterior of target cells

30.1 Steroid Hormones Steroid hormones—synthesized from cholesterol; lipid-soluble; bound to carrier proteins in blood; receptors inside target cells

30.1 Amine Hormones Amine hormones—synthesized from single amino acids; may be lipid-soluble or water-soluble, depending on the charge of the amino acid

30.1 Hormonal Control in Invertebrates Chemical communication was critical for evolution of multicellular organisms. Plants, sponges, and protists all use chemical signals. Signaling molecules are highly conserved, but their functions differ.

30.1 Molting Shedding of exoskeleton Control of molting in arthropods Rhodnius prolixus Growth stages between molts are called instars.

30.1 Control of Molting Two hormones regulate molting: PTTH (prothoracicotropic hormone), from cells in the brain, is stored in the corpora cardiaca PTTH stimulates the prothoracic gland to secrete ecdysone. Ecdysone diffuses to target tissues and stimulates molting. A third hormone, juvenile hormone, is also released from the brain—prevents maturation to adult form. Control of development by juvenile hormone is important in insects with complete metamorphosis.

30.2 Peptide Receptors Three domains of membrane bound hormone receptors: Binding domain—projects outside plasma membrane Transmembrane domain—anchors receptor Cytoplasmic domain—extends into cytoplasm, initiates target cell response

30.2 Steroid and Amine Receptors Lipid soluble, and can diffuse through plasma membrane Within target cells cytoplasm Hormone receptor moves to target nucleus, where it alters gene expresion

30.2 Fight or Flight Similar hormones cause different responses Depends on: which receptors present, and what cellular responses are triggered

30.2 Link between Nervous and Endocrine Nervous system stimulates endocrine cells Adrenal glands Epinephrine – Norepinephrine -

30.2 -Adrenergic Response Blood vessels constrict Shut off secretion of digestive enzymes Decrease blood flow

30.2 -Adrenergic Receptors Arterioles in skeletal muscles to dilate Increase blood flow to skeletal muscles Breakdown of glycogen into glucose for quick energy

30.2 Hormone Receptors are Regulated Downregulation – continuous high regulation of a hormone causes a decrease in the number of its receptors. Cell less sensitive to hormones Upregulation – hormone secretion is chemically low, cells respond to low signal level by creating more receptor for hormone.

30.3 Endocrine and Nervous System Link The nervous system communicates via molecules—neurotransmitters. The endocrine system communicates via molecules released into the blood. The systems are complementary—nervous system is rapid and specific, endocrine system is broader and longer-term Nervous system controls activity of many endocrine glands. Some neurons secrete hormones directly—neurohormones.

30.3 What is the Endocrine System Composed of? The pituitary gland connects the nervous and endocrine systems. The pituitary gland is attached to the hypothalamus of the brain. Two parts—the anterior pituitary and posterior pituitary

30.3 Oxytocin Stimulates the uterine contraction during birth. Promotes Pair Bonding and Trust. Cuddle Hormone

30.3 Anterior Pituitary Releases 4 tropic hormones. Tropic Hormones: Direct and control the activities of endocrine glands. 1. Thyroid Stimulating Hormone. 2. Luteinizing hormone 3. Follicle stimulating Hormone. 4. Adrenocorticotropic Hormone.

30.3 Anterior Pituitary Growth hormones: Promotes Growth. Stimulates Protein Synthesis Stimulates liver to produce signals Gigantism: Caused by Overproduction Dwarfism: Underproduction.

30.3 Anterior Pituitary Hormones are under control Hypothalamus receives info. On external Environment by secreting neurohormones. Portal Blood vessels carries neurohormones. Negative Feedback Loops Control Pituitary Hormones.

30.4 Metabolic rate regulated by Thyroxine The thyroid gland contains two cell types that produce two different hormones, thyroxine and calcitonin. In or near the thyroid gland are the parathyroid glands, which produce parathyroid hormone. Thyroxine (T4) is synthesized from the amino acid tyrosine and iodine. T3 is a similar hormone that is more active.

30.4 Metabolic rate regulated by Thyroxine In birds and mammals, thyroxine raises metabolic rate. Thyroxine regulates cell metabolism by acting as a transcription factor for many genes and is crucial during development. Hypothalamus releases thyrotropin-releasing hormone (TRH), which causes anterior pituitary to secrete thyroid-stimulating hormone (TSH). TSH causes the thyroid to produce thyroxine.

30.4 Control of Thyroxine Goiter is an enlarged thyroid gland. Hyperthyroidism (thyroxine excess) is often caused by an autoimmune disease. Antibody-binding activates TSH receptors on follicle cells and increases thyroxine. Thyroid remains stimulated and grows bigger.

30.4 Calcium Concentration Regulation Blood calcium concentration is controlled by calcitonin, calcitriol (from vitamin D), and parathyroid hormone (PTH). Mechanisms for changing calcium levels: Deposition or absorption by bone Excretion or retention by kidneys Absorption of calcium from digestive tract

30.4 Calcium Concentration Regulation Calcitonin, released by thyroid, lowers blood calcium (Ca2+) by regulating bone turnover. Osteoclasts break down bone, increasing blood Ca2+. Ca2+ is deposited into bone by osteoblasts; levels of Ca2+ in blood decrease. Calcitonin decreases osteoclast activity and favors adding calcium to bones.

30.4 Vitamin D and Calcitrol Vitamin D (calciferol) is synthesized from cholesterol in skin cells by UV light. Once synthesized it is converted to calcitriol, a hormone that stimulates calcium absorption from food. If light is insufficient, vitamin D must be obtained from diet or supplements.

30.4 Parathyroid The parathyroid glands secrete parathyroid hormone (PTH). PTH raises blood calcium levels: Stimulates osteoclasts and osteoblasts Stimulates kidneys to reabsorb calcium Activates synthesis of calcitriol from vitamin D

30.4 Adrenal Glands and the Stress Response Each of the two adrenal glands is a gland within a gland. The core, or adrenal medulla, produces epinephrine and norepinephrine. Release of these neurohormones is under control of the nervous system and is very rapid in the stress response.

30.4 Gonads and Sex Steroids Gonads produce sex steroids. Androgens—male steroids, testosterone Estrogens and progesterone—female steroids Both sexes use both types, in varying levels.

30.4 Gonads and Sex Steroids In embryos, sex hormones determine sex of fetus; at puberty, they stimulate maturation and secondary sex characteristics. Sex hormones exert their effects by the seventh week of human development. If a Y chromosome is present, gonads begin producing testosterone and MIS (Müllerian-inhibiting substance)—these produce male reproductive organs and inhibit female reproductive structures. Without androgens, female reproductive structures develop.

30.4 Increase in Production of Sex Homrmones At puberty, production of sex hormones increases. Controlled by tropic hormones called gonadotropins from the anterior pituitary: Luteinizing hormone (LH) Follicle-stimulating hormone (FSH)