Endocrine system.docx

Endocrine system is a system of glands that secrete signalling molecules in the bloodstream. Gland is an organ that can release a substance with a specific function into the body. 2 types are: Endocrine- ductless and releases hormones Exocrine- has ducts which targets specific areas close by and r...

Endocrine system is a system of glands that secrete signalling molecules in the bloodstream. Gland is an organ that can release a substance with a specific function into the body. 2 types are: Endocrine- ductless and releases hormones Exocrine- has ducts which targets specific areas close by and release mucus, digestive juices, swear etc. Some organs can do both above e.g., pancreas. Examples of glands include: Pineal Hypothalamus Pituitary Thyroid Thymus Parathyroid Direct intercellular communication Gaps junctions- 2 cells are directly in contact and communicate. Direct link up cell surface markers e.g., in the blood/immune system In endocrine system, it is indirect cellular communication. Paracrine signalling- targets neighbour’s cells by releasing the signal into extracellular fluid- doesn’t go into the blood. Can be hormone or neurotransmitters. Autocrine signalling- targets itself (self-signalling) Most neuronal signalling is paracrine- releasing of neurotransmitter as a signal to communicate. E.g., neurotransmitter is released into the extracellular fluid where it then binds to local target cells Key difference between endocrine, paracrine, and autocrine is that endocrine communicates over long distances via bloodstream. Neuroendocrine releases the neurotransmitter in the bloodstream, it then travels through and effects a distant cell. Hormones Involved in; Metabolism Reproduction Appetite and digestion Cardiac rhythms Types of hormones- different classifications of different hormones Hormones can be peptides, amines, and steroids. Peptides are the most abundant. Hormones can be hydrophilic or lipophilic. Water loving or fat loving. Site of action (receptor on cell surface or to genes in nucleus) Mechanism of action (secondary messengers) Common drugs that target endocrine systems Insulin HRT Levothyroxine Steroids Hormone concentration is controlled using feedback loops. Neurotransmitter concentration is controlled by storing in vesicles and releasing in very specific areas. Positive and negative feedback loop- important for maintaining homeostasis. One gland may secrete multiple hormones. One hormone may be secreted by multiple glands. One hormone may have multiple target cells (different effects) One target cell may be targeted by multiple hormones. Rate of secretion can vary. Same molecule can act as a hormone or a neurotransmitter. Some endocrine organs have additional functions. Effects are proportional to concentration in the blood therefore plasma concentration needs to be monitored by: Rate of secretion= how much is being secreted out in the blood. Metabolic activation or conversion= some hormones need to undergo activation step to have their intended affects. Inactivation or excretion= inactivation by the liver or kidneys or the enzymes in the blood. Extent of binding to plasma proteins= lipophilic hormones need to circulate in the blood bound to plasma membrane- only hormones that are not bound to protein can interact. Tropic hormones- hormone that regulates the secretion of another hormone. Hypothalamus and pituitary gland are endocrine glands. Pituitary gland secretes 9 hormones and controlled by the hypothalamus. Anterior pituitary Hypothalamus synthesises releasing or inhibitory hormones. The connecting stalk contains a special capillary network that connect the hypothalamus and anterior pituitary gland called hypothalamic-hypophyseal portal. Distinct cell populations in the anterior pituitary stimulated to produce different hormones. Also termed adenohypophysis as it contains glandular epithelial tissues. Secretion or inhibition of hormones released by anterior pituitary gland is stimulated by hypophysiotropic hormones. most hormones released are tropic. Posterior pituitary Extension of hypothalamus Neuronal cell bodies in the hypothalamus and they send axons directly down to posterior pituitary. An AP in hypothalamus sends signals down to the nerve endings in the posterior pituitary where it releases hormones directly into blood stream. E.g. oxytocin and vasopressin Also termed neurohypophysis due to all the nerve tissues present. Endocrine axes- sequential activation of organs to produce hormone and finally have an effect. e.g.- Hypothalamus pituitary adrenal axis