Hormones and the endocrine system 1 The endocrine

Hormones and the endocrine system 1) The endocrine system and the nervous system act individually and together in regulating an animal’s physiology 2) Hormones and other chemical signals bind to target cell receptors, initiating pathways that culminate in specific cell responses 3) The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system 4) Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior

The body’s long-lasting regulators Concert of chemical signals – complete change of body form e. g. metamorphosis Hormone – from the Greek „horman“ – to excite Elicits specific responses from target cells only

The endocrine system and the nervous system act individually and together in regulating an animal’s physiology 2(3) systems of internal communication - different tasks – different signals All hormone-secreting cells – endocrine system Endocrine gland => messengers => extracellular fluid

The endocrine system and the nervous system act individually and together in regulating an animal’s physiology Overlap between endocrine and nervous regulation Specialized neurons - neurosecretory cells => neurohormones In insects, vertebrates Epinephrine – in both systems – neurotransmitter and hormone

The endocrine system and the nervous system act individually and together in regulating an animal’s physiology Control pathways and feedback loops Stimulus => receptor/sensor => control center => comparing incoming information to a set point => efferent signal => effector => response Negative feedback – connecting response to initial stimulus Effector response reduces the initial stimulus Positive feedback reinforces stimulus (release of milk)

The endocrine system and the nervous system act individually and together in regulating an animal’s physiology - summary Overlap between endocrine and nervous regulation The endocrine and nervous systems often function together in maintaining homeostasis, development, and reproduction. Endocrine glands and various organs with primarily nonendocrine functions secrete hormones, and specialized secretory cells derived from nervous tissue secrete neurohormones. Both classes of hormonal signals circulate through the body to their target tissues, functioning as long-distance regulators. Control pathways and feedback loops There are three major types of hormonal control pathways: endocrine, neurohormone, and neuroendocrine. The basic components of a biological regulatory system are present in each kind of pathway. Negative feedback regulates many hormonal pathways involved in homeostasis.

Hormones and other chemical signals bind to target cell receptors, initiating pathways that culminate in specific cell responses Hormones through bloodstream Local regulators – near secreting cells pheromones – message to other individual by air Three major classes – as hormones: 1) Proteins and peptides, 2) Amines from AA, 3) Steroids (not water soluble) Reception (binding), signal transduction, and response Receptors in or on the target cells Transduction – activation of enzyme, cascade of changes, direct or indirect regulation of transcription of specific genes

Hormones and other chemical signals bind to target cell receptors, initiating pathways that culminate in specific cell responses Intracellular receptors for small hydrophobic molecules coupled with transduction/transcription factor in nucleus m. RNA => new protein Different effects in different species – thyroxine In mammals - regulates metabolism In frogs – triggers metamorphosis of tadpoles

Hormones and other chemical signals bind to target cell receptors, initiating pathways that culminate in specific cell responses Particular hormone (signal) may cause diverse responses – different receptors => different transduction => different response e. g. epinephrine distribution of energy to muscles

Local regulators – diffusion within second Neurotransmitters Cytokines Growth factors (cell proliferation and differentiation) Gas - nitric oxide NO produced in O 2 insufficiency => dilates vessels => improves blood flow Prostaglandins (PGs) modified fatty acids Regulation of nearby cells in various ways e. g. excitation of uterine muscles, induction of fever and inflammation, aggregation of platelets, sensation of pain, in respiratory system antagonists PGs E and F

Hormones and other chemical signals bind to target cell receptors, initiating pathways that culminate in specific cell responses - summary Cell-surface receptors for water-soluble hormones Peptide/protein hormones and most of those derived from amino acids bind to receptors embedded in the plasma membrane. Hormone binding triggers an intracellular signal transduction pathway leading to specific responses in the cytoplasm or changes in gene expression. The same hormone may have different effects on target cells that have different receptors for the hormone, different signal transduction pathways, or different effector proteins. Intracellular receptors for lipid-soluble hormones Steroid hormones, thyroid hormones, and the hormonal form of vitamin D enter target cells and bind to specific protein receptors in the cytoplasm or nucleus. The hormone-receptor complexes then act as transcription factors in the nucleus, regulating transcription of specific genes. Paracrine signaling by local regulators Various types of chemical signals elicit responses in nearby target cells. Local regulators include neurotransmitters, cytokines and growth factors (proteins/peptides), nitric oxide (a gas), and prostaglandins (modified fatty acids).

The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system Major (20) human glands and hormones

The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system Hormone-secreting cells also in : Heart, thymus, liver, stomach, small intestine, kidney, placenta

The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system Relationship between the hypothalamus and pituitary gland Hypothalamus plays an integrating role in vertebrate endocrine and nervous systems Information from whole body and brain through nerves Hypothalamus then triggers the release e. g. reproductive hormones Hypothalamus - two sets of neurosecretory cells 1) Posterior pituitary – neurohypophysis Stores and secretes: ADH – excretory syst. Oxytocin – uterine muscles, milk ejection

The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system 2) Anterior pituitary – adenohypophysis (roof of embryonic mouth) Several hormones – other endocrine glands as their targets = tropic hormone Neurosecretory cells => releasing and inhibiting hormones – tropic hormones for anterior pituitary Tropic hormones: glycoprotein gonadotropins ACTH – peptide => Adrenal cortex Nontropic: PRL - great diversity of effects MSH – regulates pigment cells, hunger in mammals Beta-endorphin – dull the pain perception Both: GH => IGFs

The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system - summary Relationship between the hypothalamus and pituitary gland The hypothalamus, a region on the underside of the brain, contains different sets of neurosecretory cells. Some produce direct-acting hormones that are stored in and released from the posterior pituitary. Other hypothalamic cells produce tropic hormones that are transported by portal blood vessels to the anterior pituitary, an endocrine gland. These tropic hormones control release of hormones from the anterior pituitary. Posterior pituitary hormones The two hormones released from the posterior pituitary act directly on nonendocrine tissues. Oxytocin induces uterine contractions and milk ejection, and antidiuretic hormone (ADH) enhances water reabsorption in the kidneys. Anterior pituitary hormones Both tropic and nontropic hormones are produced by the anterior pituitary. The four strictly tropic hormones are thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and adrenocorticotropic hormone (ACTH). Each acts on its target endocrine tissue to stimulate release of hormone(s) with direct metabolic or developmental effects. Prolactin, melanocyte-stimulating hormone (MSH), and beta-endorphin are nontropic anterior pituitary hormones. Prolactin stimulates lactation in mammals but has diverse effects in different vertebrates. MSH influences skin pigmentation in some vertebrates and fat metabolism in mammals. Endorphins inhibit the perception of pain. Growth hormone (GH) promotes growth directly and has diverse metabolic effects; it also stimulates the production of growth factors by other tissues (a tropic effect).

Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior Thyroid gland (ventral surface of the trachea) => thyroid hormones Tri- and tetra- iodothyronine In mammals - T 4 > T 3, in target cells – T 4 converted to T 3 Vertebrate metabolism, development, and maturation

Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior Disorders: Deficiency => cretinism (retarded skeletal growth and mental development) Deficiency in diet => goiter - through negative feedback on the hypothalamus Excessive secretion => hyperthyroidism (high body temperature, high blood pressure, sweating, weight loss, fluid accumulation behind the eyes)

Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior Parathyroid hormone and calcitonin: control of blood calcium Blood calcium (Ca 2+) level - essential for all body cells Set point - 10 mg/ 100 ml From food or skin vitamin D => in liver and then in kidneys stimulated by PTH => active D

Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior Insulin and glucagon: control of blood glucose Endocrine cells in islets of Langerhans (1 -2 % of pankreas weight) Islet: Alpha cells – glucagon (protein) Beta cells – insulin (protein) Diabetes mellitus (sugar in urine) Type I – (insulin dependent) autoimmune disorder against beta cells Type II – changes in insulin receptors (90% of people)

Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior Adrenal hormones: Response to stress In mammals: Adjacent to kidneys - fused endocrine and neuroendocrine gland Fight or flight response Catecholamines – from AA tyrosine Epinephrine Norepinephrine (sustaining blood pressure) Signals by sympathetic autonomic nervous system

Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior

Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior summary Thyroid hormones The thyroid gland produces iodine-containing hormones (T 3 and T 4) that stimulate metabolism and influence development and maturation. Secretion of T 3 and T 4 is controlled by the hypothalamus and pituitary in a complex neuroendocrine pathway involving two negativefeedback loops. The thyroid also secretes calcitonin, which functions in calcium homeostasis. Parathyroid hormone and calcitonin: control of blood calcium Two antagonistic hormones, calcitonin and parathyroid hormone (PTH), play the major role in calcium (Ca 2+) homeostasis in mammals. Calcitonin, secreted by the thyroid, stimulates Ca 2+ deposition in bones and excretion by kidneys, thereby decreasing blood Ca 2+ levels. PTH, secreted by the parathyroid glands, has the opposite effects on bones and kidneys, thereby increasing blood Ca 2+ levels. PTH also has an indirect effect, stimulating the kidneys to activate vitamin D, which in turn promotes intestinal uptake of Ca 2+ from food. Insulin and glucagon: control of blood glucose Two types of endocrine cells in the pancreas secrete insulin and glucagon, antagonistic hormones that help maintain glucose homeostasis. Insulin (from beta cells) reduces blood glucose levels by promoting the cellular uptake of glucose, glycogen formation in the liver, protein synthesis, and fat storage. Glucagon (from alpha cells) increases blood glucose levels by stimulating the conversion of glycogen to glucose in the liver and the breakdown of fat and protein to glucose. Diabetes mellitus, which is marked by elevated blood glucose levels, may be caused by inadequate production of insulin (type I) or loss of responsiveness to target cells to insulin (type II).

Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior – summary Adrenal Hormones: response to stress Neurosecretory cells in the adrenal medulla release epinephrine and norepinephrine in response to stress-activated impulses from the nervous system. These hormones mediate various fight-or-flight responses. The adrenal cortex releases three functional classes of steroid hormones. Glucocorticoids, such as cortisol, influence glucose metabolism and the immune system; mineralocorticoids, primarily aldosterone, affect salt and water balance. The adrenal cortex also produces small amounts of sex hormones. Gonadal sex hormones The gonads – testes and ovaries – produce most of the body’s sex hormones: androgens, estrogens, and progestins. All three types are produced in males and females but in different proportions. Melatonin and biorhythms The pineal gland, located within the brain, secretes melatonin. Release of melatonin is controlled by light/dark cycles. Its primary functions appear to be related to biological rhythms associated with reproduction.