Hormones & the Endocrine System

Hormones & the Endocrine System

Hormones & the Endocrine System Hormones Hormone: a chemical signal that is secreted into the extracellular fluid, is carried by the circulatory system (in blood or hemolymph) and communicates a regulatory message within the body Thus, a given hormone Hormones can travel throughout entire traveling through the the body elicits specific

responses to , body, but only target cells are equipped such as a change in respond metabolism , from its target cells while other cell types remain unaffected by that particular hormone Regulation of Animal Physiology Animals have 2 systems of internal communication

Endocrine system: the collection of hormone secreting cells Nervous system: conveys high speed electrical signals along specialized cells called neurons The endocrine system and the nervous system act individually and together in regulating an animals physiology Hormones Hormones coordinate slower but longer lasting responses to stimuli such as stress, dehydration, and low blood glucose levels Regulate long term developmental processes by informing different parts of the body how fast to grow or when to develop

characteristics that Distinguish male from female Distinguish juvenile from adult Endocrine Glands Secrete their chemical messengers (hormones) directly into the extracellular fluid allowing for quick diffusion and circulation Overlap Between Endocrine & Nervous Regulation Neurosecretory cells blur the line between nervous and endocrine regulation

Release hormones into the blood via the extracellular fluid Some hormones function as both endocrine hormones and and chemical signals in the nervous system Sometimes called neurohormones to distinguish from classic hormones Epinephrine fight or flight Nervous system plays a role in sustained responses by

increasing or decreasing secretion from endocrine glands Feedback Loops: Back to Basics A receptor on/in a cell is bound by a molecule Signal transduction pathways allow the cell to detect the stimulus and sends the information to its control center The incoming information is compared to a desired value, and the control center sends out a signal that directs an effector to respond Control Pathways and Feedback Loops Now apply this to hormones In endocrine and neuroendocrine pathways, the outgoing signal, called an efferent signal

is a hormone or neurohormone which acts on particular effector tissues and elicits physiological or developmental changes There are about 20 different hormones we will be learning about, and each acts via one of the 3 following pathways Basic Patterns of Simple Hormonal Control Pathways Simple Endocrine Pathway Simple Neurohormone Pathway Simple Neuroendocrine Pathway In each pathway a receptor (blue) detects a change in some internal or external variable - the stimulus- and informs the control center (gold) The control center then sends out an efferent signal

Hormone (red circles) Neurohormone (red squares) Endocrine cells carry out both receptor and effector functions Control Pathways & Feedback Loops Feedback loops connect the response to the initial stimulus Negative feedback: the effector response reduces the initial stimulus

Prevents overreaction by the system and wild fluctuations in the variable being regulated Operates in many endocrine and nervous pathways, especially those necessary for maintaining homeostasis! Control Pathways & Feedback Loops Feedback loops connect the response to the initial stimulus Positive Feedback: reinforces the stimulus and leads to an even greater response Example: the neurohormone pathway regulating the

release of milk by a nursing mother Suckling stimulates sensory nerves in the nipple Nipple sends nervous signals to hypothalamus (control center) Hypothalamus triggers release of neurohormone oxytocin from the posterior pituitary gland Oxytocin causes mammary gland to secrete more milk Release of milk leads to more suckling, stimulating pathway more 3 Major Classes of Molecules Function as Hormones Proteins and peptides

Water Soluble Amines derived from amino acids Steroids (not soluble in water) 3 Key Events in Hormone Signalling Reception of the signal: occurs when signal molecule binds receptor protein in/on target cell Receptors usually bound to plasma membrane or nuclear envelope Signal Transduction: usually via signaling cascades involving phosphorylation of proteins OR direct up-regulation of transcription of target

genes Response: via change in cells behavior or phenotype Cell Surface Receptors for Water Soluble Hormones Receptors for most water soluble hormones are embedded in the plasma membrane projecting outward from the cell surface Binding of hormone to its receptor initiates a signal transduction pathway A series of changes in cellular proteins that converts the extracellular chemical signal to a specific intracellular response

Activation of an enzyme Changes in uptake or secretion of molecules Rearrangement of cytoskeleton Regulation of transcription Cell Surface Receptors for Water Soluble Hormones: Example The ability of frogs to change the color of their skin is an adaptation that helps camouflage the frog in changing light Skin cells called melanocytes contain dark brown pigments called melanin in cytoplasmic organelles called melanosomes The frogs skin appears light when

melanosomes cluster tightly around the cell nuclei and darker when melanosomes spread throughout the cytoplasm Camouflaging a Frog A peptide hormone called melanocyte stimulating hormone controls the arrangement of melanosomes Adding MSH to the interstitial fluid causes melanosomes to disperse Direct injection into a cell

does not WHY? Intracellular Receptors for Lipid Soluble Hormones Steroid hormones are small, nonpolar (hydrophobic) molecules that diffuse easily through the hydrophobic interior of the plasma membrane Intracellular proteins / receptors function as receptors for

Steroid hormones Thyroid hormones Hormonal form of vitamin D usually perform the vital task of transducing a signal within a target cell Usually the hormone-receptor complex acts as a transcription factor Usually located in the nucleus Paracrine Signaling by Local Regulators Paracrine Signaling: local regulators that convey messages to neighboring cells

Takes seconds or milliseconds to elicit a response Some have cell surface receptors, others use intracellular receptors Examples of Paracrine Signaling Molecules Neurotransmitters Cytokines Growth factors Nitric oxide Prostaglandins In Case you didnt get this, paracrine signalling is the OPPOSITE of endocrine

signaling Paracrine Signaling Nitric Oxide (NO) When blood O2 levels fall it activates enzymes that relaxes smooth muscle vessel dilation increased blood flow Increases blood flow to the penis during male sexual arousal

Prostaglandin (PG) Modified fatty acids derived from lipids in the plasma membranes 1st discovered in semen secreted from the PROSTATE the GLAND (henceRelease the name) Prostaglandins

Help stimulate contraction of !! the the uterine wall to help swimmers make it to the egg (also during child birth to increase contractions) Immune response: increased fever & inflammation Also involved in blood clotting What you need to learn Physiological Effects of the Primary Vertebrate Hormones The Role of endocrine signaling in adjusting the bodies activities to changing environmental and developmental conditions Memorize Table 45.1 on page 949

Relationship Between the Hypothalamus & the Pituitary Gland Hypothalamus plays an important role in integrating the endocrine and nervous system Hypothalamus receives info from other parts of brain or body and initiates appropriate endocrine responses Example: brain passes sensory info about seasonal changes and mate availability to the hypothalamus via nerve signals; hypothalamus then triggers release of reproductive hormones Contains 2 sets of neurosecretory cells whose

hormonal secretions are stored in or regulate the pituitary Pituitary: Composed of 2 fused glands located at the base of the hypothalamus Posterior Pituitary An extension of the hypothalamus stores and secretes 2 hormones (made by the hypothalamus) both of which function via the simple neurohormone pathway Antidiuretic Hormon (ADH): acts on kidneys increasing water retention and thus decreasing urine volume

Helps regulate osmolarity of blood Negative feedback pathways Oxytocin: induces in uterus to contract in child birth, and causes mammary glands to eject milk Positive feedback pathways Anterior Pituitary Consists of endocrine cells that synthesize and secrete at least 6 different hormones Tropic hormones: are hormones produced and secreted All 4 anterior pituitary tropic hormones by the anterior pituitary that target endocrine glands. participate in complex neuroendocrine

Thyroid-stimulating hormone (TSH ) promotes normal pathways inthyroid which signals the tothyroid the brain development of the and stimulates gland to LH,thyroid & TSH hormone are all similar glycoproteins make andFSH, release stimulate release of an anterior pituitary Luteinizing hormone (LH) stimulates the release of steroid

FSH & hormone; LH are also called gonadotropins because theyits stimulate tropic which then acts on target hormones in gonadsthe ovary and testes activities of the gonads Follicle-stimulating hormone (FSH) stimulates the maturation of endocrine tissue, stimulating secretion of yet eggs and production of sperm.

another hormone that )exerts systemic Adrenocorticotropic hormone (ACTH a peptide hormone that stimulates the adrenal cortex to release glucocorticoids metabolic or developmental effects Nontropic Hormones of the Anterior Pituitary Prolactin (PRL): stimulates mammary gland

growth & milk synthesis in vertebrates Melanocyte-stimulating hormone (MSH): regulates activity in pigment containing cells in the skin of some fishes, amphibians, and reptiles In mammals acts on neurons in the brain inhibiting hunger My MSH is defective Endorphins: bind receptors in the brain and dull the perception of pain

Responsible for runners high One More Anterior Pituitary Hormone: Growth Hormone Acts on a wide variety of tissues exhibiting both tropic and nontropic effects Signals liver to release Insulin Like Growth Factors (IGFs): circulate in the blood and directly stimulate bone and cartilage growth Necessary for proper skeletal development Thyroid Gland Thyroid gland : one of the largest endocrine glands in the body.

Produces 2 hormones, both derived from the amino acid tyrosine, which both bind to the same receptor located in the target cells nucleus Triiodothyronine (T3) Thyroxine (T4) Hypothalamus & anterior pituitary control secretion of thyroid hormones Thyroid Hormones The thyronines act on nearly every cell in the body. increase the basal metabolic rate affect protein synthesis Basically he thyroid

help regulate long bone growth and neuronal maturation controls howto quickly the increase the body's sensitivity s adrenaline are essential to body uses energy, proper development andmakes differentiation of all cells of the human body. proteins, and controls

regulate protein, fat, and carbohydrate metabolism ,affecting how sensitive the body how human cells use energetic compounds. stimulate vitamin should be to other metabolism Thyroid hormone plays hormones an important role in the hibernation cycles of mammals and the moulting behaviour of birds. Thyroid Malfunction Goiter: is a swelling in the thyroid gland, which can lead to a swelling of the neck or larynx (voice box).

most common cause for goiter is iodine deficiency Deficiency of iodine in diet prohibits the thyroid from making adequate amounts of T3 and T4 This results in low blood levels of T3 & T4 which cant exert the usual negative feedback on the hypothalamus & anterior pituitary Consequently, the pituitary continuse to secrete TSH TSH stimulates the thyroid to grow, forming a goiter Other Problems of the Thyroid Hypothyroidism (underactive thyroid)

Hyperthyroidism (overactive thyroid) Graves' disease is an autoimmune disease where the thyroid is diffusely enlarged and overactive, producing an excessive amount of thyroid hormones caused by autoantibodies to the TSH-receptor (TSHRAb) that activate that TSH-receptor, thereby stimulating thyroid hormone synthesis and secretion and thyroid growth Parathyroid Hormone & Calcitonin Ca2+ ions are critical to functioning of all cells, so control of blood calcium levels must be maintained If Ca2+ are too low, muscles contract convulsively in a

condition known as tetany If uncorrected its fatal Parathyroid hormone & Calcitonin have opposing actions that regulate blood Ca2+ levels Parathyroid hormone (PTH) produced by parathyroid gland Converts Vitamin D to its active hormone form which stimulates uptake of Ca2+ from food Calcitonin produced by thyroid has opposite effects of PTH and lowers levels of Ca2+ in blood

Pancreas The pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including Insulin Glucagon somatostatin as well as an exocrine gland, secreting pancreatic juice containing digestive enzymes that pass to the small intestine

Islets of Langerhans Clusters of endocrine cells called Islets of Langerhans (about 1-2% 0f the pancreas) are scattered throughout the exocrine tissue (98-99% of pancreatic tissue) Each Islet has a population of cells which produce glucogon cells which produce insulin Both of these proteins are secreted to the extracellular fluid

and enter the circulatory system They are antagonistic hormones that regulate concentration of glucose in the blood Metabolic homeostasis requires maintaining blood glucose concentrations near about 90 mg/100 mL Insulin & Glucagon Insulin lowers blood glucose levels by stimulating virtually all body cells except those of the brain to take up glucose from the blood, and also slows down break down of glycogen in the liver Diabetes Mellitus

a condition in which a person has a high blood sugar either because the body doesn't produce enough insulin, or because body cells don't properly respond to the insulin The most common types of diabetes are: Type 1 diabetes: results from the body's failure to produce insulin, and presently requires the person to inject insulin. Type 2 diabetes: results from insulin resistance, a condition in which cells fail to use insulin properly, sometimes combined with an absolute insulin deficiency. Gestational diabetes: is when pregnant women with no history of diabetes, have a high blood glucose level during pregnancy.

Test for diabetes include direct testing of blood sugar levels via finger prick or testing for sugar levels in the urine High levels of sugar in urine may give it a sweet odor Adrenal Glands triangular-shaped endocrine glands that sit on top of the kidneys. They are chiefly responsible for releasing hormones in conjunction with stress through the synthesis of corticosteroids and catecholamines, including cortisol and adrenaline (epinephrine)

Catecholamines (see p957) released by the adrenal glands in response to stress. They are part of the sympathetic nervous system epinephrine (adrenaline): is a hormone and neurotransmitter it increases heart rate, contracts blood vessels and dilates air passages and participates in the fight-or-flight response norepinephrine (noradrenaline): is a hormone and neurotransmitter is a stress hormone affects parts of the brain where attention

and responding actions are controlled. underlies the fight-or-flight response, directly increasing heart rate, triggering the release of glucose from energy stores, and increasing blood flow to skeletal muscle Adrenal Hormones: Response to Stress Steroid Hormones from the Adrenal Cortex Catecholamines Epinepherine Norepinephrine Corticosteroids

Glucocorticoides Mineralocorticoides Sex Hormones All synthesized from cholesterol Mainly androgens (male hormones) some estrogens and progestines (female hormones) Steroid Hormones from the Adrenal Cortex Hormones from the adrenal cortex function in response to stress induced endocrine signals Stressful stimuli cause hypothalamus to release a hormone that stimulates the anterior pituitary to release ACTH When ACTH reaches adrenal cortex via blood stream it stimulates the endocrine cells to

synthesize and secrete corticosteroids Corticosteroids work via negative feedback to suppress ACTH secrtetion 2 Main Types of Corticosteroids Glucocorticoids: class in the regulation of the metabolism of glucose and are part of the feedback mechanism in the immune system that turns immune activity (inflammation) down Cortisol Used to treat autoimmune diseases and arthritis Mineralocorticoid: influence on salt and water

balances Stimulates kidneys to reabsorb sodium ions and water Evidence suggests both are involved in the bodys ability to maintain homeostasis over extended periods of stress Gonadal Sex Hormones Gonads are the primary source of sex hormones Gonads produce and secrete 3 major classes of steroid hormones

Androgens Estrogens Progestins All 3 types are found in both males and females, just proportions are different Androgens Testes produce mainly androgens Main androgen is testosterone Androgens stimulate development and maintenance of the male reproductive system At puberty high concentrations of androgens are responsible for development of human male secondary sex characteristics

Patterns of hair growth Low voice Increased muscle and bone mass Estrogens & Progestins Both are components of complex neuroendocrine pathways Synthesis is controlled by gonadotropins FSH & LH Estrogens: Most importat is estradiol Responsible for maintenance of female reproductive system and development of female secondary sex

characteristics Progestins: include progesterone Primarily involved in preparing and maintaining the uterus which supports growth and development of an embryo Melatonin & Biorythyms Pineal gland: synthesizes and secretes the hormone melatonin, a modified amino acid Depending on the species the pineal gland contains light sensitive cells or has nervous connections from the eyes that control its secretory activity Melatonin regulates functions related to light and seasons marked by changes in day length

Is secreted at night Decreases the activity of certain neurons in the brain, and thus mediates rhythyms Invertebrate Regulatory Systems Invertebrate regulatory systems also involve endocrine and nervous system interactions We know the most about invertebrate hormones involved in reproduction Hydra have a hormone that stimulates budding while preventing sexual reproduction In molluscs specialized nerve cells secrete a neurohormone that that stimulates the laying of

thousands of eggs and also inhibits feeding and locomotion (activities that interfere with reproduction) In Arthropods Molting is Triggered by a Hormone Most insects go through a series of larval stages, controlled by hormones, with each molt leading to a larger larva. Molting of the final larval stage gives rise to a pupa, in which metamorphosis produces and adult. Three hormones control insect development Brain Hormone (BH): stimulates release of ecdysone Ecdysone: promotes molting and development of adult

characteristics Juvenile Hormone (JH): promotes retention of larval (juvenile) characteristics In Arthropods Molting is Triggered by a Hormone 1. Neurosecretory cells in the brain produce BH which is stored in the corpus cardiacum until release 2. BH stimulates its main target organ the prothoracic , to produce the hormone ecdysone 3. Ecdysone secretion is episodic with each release stimulating a molt

JH secreted by the corpora allata, determines the result of the molt. At relatively high concentrations of JH, ecdysone-stimulated molting produces another larval stage. JH supresses metamorphosis. But when levels are low a pupa forms at the next ecdysoneinduced molt. The adult insect emerges from the pupa

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