Biology Chapter 26 Hormones and the Endocrine System by Emily Bower

26.1 Chemical signals Coordinate body Functions Animals rely chemical signals to regulate their body functions Hormone- is a chemical signal that is carried by the circulatory system (usually in blood) and communicates regulatory messages throughout the body Hormones are made and secreted by of endocrine glands Collectively known as the endocrine system. One of the two systems the body uses to communicate messages

Endocrine system makes slower but longer lasting responses then the nervous system Can take hours or day to act because of the time it takes for hormones to be made and transported, and because of cellular response time Hormones are important in controlling whole body activities and responses to stimuli (ex. Stress, dehydration, low blood glucose levels, and long term development process- growth, maturation, and reproduction

Secretory vesicles in the endocrine cell are full of molecules of the hormone The endocrine cell secretes the the molecules into the circulatory system From there hormones may travel to ALL parts of the body But only TARGET CELLS are equipped to respond A single hormone molecule may dramatically alter a target cell’s metabolism by turning on or off the production of a number of enzymes

Hormones are the body’s long distance chemical regulators, they convey info via the blood stream to target cells throughout the body Local Regulators- (other chemical signals) are secreted into the interstitial fluid and effect only nearby target cells Pheromones are another kind of chemical signal that carry messages between different individuals of the same species, as in mate attraction

Neurosecretory cells perform functions of both the nervous and the endocrine systems They conduct nerve cells but also make and secrete hormones in the blood Few chemicals serve as both hormones in the endocrine system and chemical signals in the nervous system (Epinephrine or adrenaline serves as both, allows fight or flight) Another example is the neurotransmitter- carries info from one nerve cell to another or from a nerve cell to another kind of a cell that will react. Unlike most hormones neurotransmitters usually do not travel in the bloodstream

26.2 Hormones affect target cells by two main signaling mechanisms There are 2 major classes of molecule functions in vertebrates 1.Amino acid derived hormones (proteins, peptides, and amines) they are all hydrophilic 2.Steroids which are all hydrophobic Regardless of the structure signaling by any of these molecules involves three key events- reception, signal transduction and response

1.Reception- when a hormone bonds to a specific receptor or on/in the target cell. The binding of a signal molecule to a receptor protein triggers events within the target cell. 2.Signal Transduction- that convert the signal from one form to another 3.Response- a change in the cells behavior. Cells that lack receptors for a particular chemical signal do not respond to hat signal While both hormones carryout the 3 steps above they do so in different ways

Water-soluble hormones are embedded in the plasma membrane of target cells and project outward from the cell surface 1.Hormone molecule binds to receptor protein- activating it 2.This initiates a signal transduction pathway, a series of changes in the cellular proteins that covert an extracellular chemical signal to a specific intracellular response 3.Molecule activates a protein that carries out the cell’s response either in the cytoplasm or in the nucleus. One hormone may trigger a variety of responses

Lipid soluble hormones bind to receptors inside the cell Steroid hormones- (sex hormones) are lipids made from cholesterol 1.The steroid hormone enters the cell. If it is a target cell then 2.Binds to a receptor protein in the cytoplasm or nucleus. The hormone receptor complex itself usually carries out the transduction of the hormonal signal. The complex acts as a gene activator 3.The hormone receptor complex attaches to a specific site on the cell’s DNA in the nucleus 4.The binding of the complex to DNA stimulates trasncroption of certain genes into RNA which is translated into new proteins. All steroid hormones react by turning on or off a gene. Different kinds of cells respond differently

26.4 The hypothalamus, which is closely tied to the pituitary, connect the nervous and endocrine system Hypothalamus- the part of the brain that receives info from nerves about the internal condition of the body and about the external environment. It responds by sending out the appropriate nervous or endocrine system. It dirrectly controls the Pituitary gland and thus exerts massive control over the endocrine system by using the pituitary to relay directives to other gland.

P ituitary gland- has two parts 1.Posterior Pituitary- nervous tissue and is an extension of the hypothalamus. Store and secretes two hormones made in the hypothalamus 2.Anterior Pituitary- endocrine cells that synthesize and secrete numerous hormones into the blood. Both are situated in a pocket of skull bone at the base of the hypothalamus. Releasing Hormones- stimulate the anterior pituitary to secrete hormones Inhibiting Hormones- induce the anterior pituitary to stop secreting hormones

There is a structural function between the hypothalamus and the pituitary A set of neurosecrtory cells extend form the hypothalamus into the posterior pituitary. The hormones in the body can be channeled through the neurosecretory cells into the posterior or anterior pituitary depending on what they are meant to do Thyroid-stimulating hormone (TSH)- a hormone secreted by the anterior pituitary that stimulates the thyroid gland to secrete its’ hormones Prolactin (PRL)- hormone secreted by the anterior pituitary that stimulates different effects in different species

Growth hormone (GH) - hormone secreted by the anterior pituitary that promotes development and growth and stimulates metabolism Endorphins- A pain inhibiting hormone produced by the brain and anterior pituitary, also serves as a neurotransmitter (natural painkillers & runners high) TSH-releasing hormone (TRH)- secreted by the hypothalamus. A peptide hormone that triggers the release of TSH which in turn stimulates the thyroid gland Precise regulations of the TRH-TSH-thyroxin system keeps the hormones at levels that maintain homeostasis

26.9 The adrenal glands mobilize responses to stress Adrenal Gland- One of the endocrine glands, located atop each kidney in mammals is made up of 2 parts 1.Adrenal Medulla-central portion. Produces the fight or flight hormone. Ensure rapid, short-term responses to stress. It secretes 2 hormones 1.epinephrine- adrenaline 2. norepinephrine- noradrenalin 2.Adrenal Cortex- outer portion of the adrenal gland. Controlled by the anterior pituitary, secretes hormones called glucocorticoids and mineral corticoids Both parts respond to stress

Stressful stimuli activate certain nerve cells in the hypothalamus 1.Cells send nerve cells via the spinal cord to the adrenal medulla 2.Stimulating it to secrete epinephrine and norepinephrine into the blood. Epinephrine and norepinephrine have somewhat different responses. Both contribute to short term response. Hormones secreted by Adrenal medulla are short-term and hormones secreted by the Cortex are long term. 3.The Hypothalamus secretes a hormone 4.Stimulates target cell in the anterior pituitary to secrete the hormone ACTH 5.In turn ACTH stimulates cells of the adrenal cortex to secrete the hormones that cause long-term stress

Short term stress response 1.Glycogen broken down to glucose; increased blood glucose 2.Increased blood pressure 3.Increased breathing rate 4.Increased metabolic rate 5.Change in blood-flow patterns, leading to increased alertness and decreased digestive and kidney activity

Long-term stress response Mineralocorticoids Glucocorticoids 1.Retention of sodium ions and water by kidneys 1.Proteins and fats broken down and converted to glucose, leading to increased blood glucose 2. Increased blood volume and blood pressure 2. Immune system may be suppressed

Mineralocorticoids- a corticosteroid hormone secreted by the adrenal cortex that helps maintain salt and water balance and may increase blood pressure in response to long term stress Glucocorticoids- a corticosteroid hormone secreted by the adrenal cortex that increases the blood glucose level and helps maintain the body’s response to long-term stress.