AP Biology Endocrine System and Hormones – Overall Function and Feedback Mechanisms

Signal Transduction Pathway

Kinases “turn on” processes Phosphotases “turn off” processes

A stimulus is recognized by the body. Basic Hormone Pattern Hormone – a chemical produced in one part of the body that travels to another part of the body (target tissue) and elicits a response. The basic mechanism of the endocrine system can be seen in the diagram to the left: A stimulus is recognized by the body. Endocrine cells release a hormone into the blood stream. The hormone travels throughout the body to the target tissue. The appropriate response is triggered. Pathway Example Low blood glucose Stimulus Receptor protein Pancreas secretes glucagon ( ) Endocrine cell Blood vessel Target effectors Liver Response Glycogen breakdown, glucose release into blood Simple endocrine pathway

Remember the “hands” on cell membranes? (In GREEN) Just as we discussed with the nervous system and the immune system, the endocrine system works through interactions between chemicals and protein receptors found on the surface of all cells throughout the body.

Hormonal System of Communication There are three majors parts to the hormonal system of communication: 1. Exocrine: a hormone is secreted by a gland, and the target is the outside of the body. Ex. Sweat and pheromones 2. Endocrine: a hormone is secreted by a gland, enters the blood stream and targets tissues in the body. Ex. Insulin, glycogen, ADH, Oxytocin, etc. 3. Neurosecretory: these are specialized neurons that can also secrete hormones. Ex. Hypothalamus, pituitary

LE 45-7 Hypothalamus Neurosecretory cells of the hypothalamus Axon Posterior pituitary Anterior pituitary HORMONE ADH Oxytocin TARGET Kidney tubules Mammary glands, uterine muscles

Cytokines IL 1 – Helper T to Cytotoxic T Cell IL2 – Helper T to B Cell

Different Types of Hormones The two major types of hormones found in living organisms are steroid hormones and peptide hormones. These work differently when targeting cells. 1. Steroid (lipid-based) hormones – steroid hormones are lipid-based, so they can easily pass through the phospholipid bilayer. Once in the cell, they target receptors deep in the cytoplasm or the nucleus. Ex. Testosterone, estrogen, aldosterone 2. Peptide (protein-based) hormones – peptide hormones are protein-based, so they can not pass directly through the phospholipid bilayer. These hormones must bind to a cell-surface receptor and then transmit their message into the cell. This follows the stereotypical signal transduction pathway. Ex. Prolactin, HGH, oxytocin, insulin, glucagon

Peptide and Monoamine Hormone Binding SECRETORY CELL SECRETORY CELL Hormone molecule Hormone molecule VIA BLOOD VIA BLOOD Peptide and Monoamine Hormone Binding Signal receptor Steroid Hormone Bonding TARGET CELL TARGET CELL Signal transduction pathway Signal receptor OR Cytoplasmic response DNA Signal transduction and response mRNA DNA Nuclear response NUCLEUS Synthesis of specific proteins NUCLEUS Receptor in plasma membrane Receptor in cell nucleus

Many hormones are involved in negative feedback loops Many hormones are involved in negative feedback loops. The most easily understood examples are insulin and glucagon. When changes in blood sugar are sensed by the body, these hormones are secreted to reverse the change. The secretion of the hormone stops the situation. TRH TSH

Positive feedback loops are also very important in living organisms Positive feedback loops are also very important in living organisms. These are the opposite of negative feedback. The production of a hormone causes continued production of a hormone, or the continuation of a behavior. Oxytocin and prolactin are examples of hormones that function through positive feedback.

Human Endocrine Glands Important Human Endocrine Glands: Hypothalamus – produces hormones that regulate the pituitary Pituitary Gland – major gland that produces hormones that travel throughout the body Thyroid Gland – produces hormones that regulate metabolism Pancreas – produces hormones that regulate blood sugar Thymus Gland – produces hormones that stimulate production of T-Cells Adrenal Glands – produces hormones that stimulate “fight or flight” and kidney function Ovaries – female sex hormones Testes – male sex hormones

Tropic Hormones of the Anterior Pituitary Tropic Effects Only FSH, follicle-stimulating hormone LH, luteinizing hormone TSH, thyroid-stimulating hormone ACTH, adrenocorticotropic hormone Neurosecretory cells of the hypothalamus Nontropic Effects Only Prolactin MSH, melanocyte-stimulating hormone Endorphin Portal vessels Nontropic and Tropic Effects Growth hormone Hypothalamic releasing hormones (red dots) Endocrine cells of the anterior pituitary Pituitary hormones (blue dots) HORMONE FSH and LH TSH ACTH Prolactin MSH Endorphin Growth hormone TARGET Testes or ovaries Thyroid Adrenal cortex Mammary glands Melanocytes Pain receptors in the brain Liver Bones