Class Notes (836,267)
Canada (509,734)
Physiology (1,062)

Endocrine System.doc

9 Pages
Unlock Document

Physiology 2130
Sarah Mc Lean

Endocrine System The endocrine system consists of a series of glands that secrete different hormones into the blood. These hormones then travel throughout the body to their target site to initiate their effect. Function - maintenance of internal environment - adaptation to stress - control of growth - metabolism - control of reproduction Actions of endocrine system are slower to take effect than nervous system but they last longer and are generally more widespread throughout the body. Glands - group of specialized cells that synthesize, store and release hormones - hormones circulate throughout the body to specific target cells that have receptors for the hormone Hormones 1) Tyrosine (thyroxine, triiodothyronine)  thyroid gland 2) Protein (calcitonn, parathyroid, pituitary and pancreatic) hypothalamus 3) Steroid (cortisol, aldosterone, estrogen, progesterone and testosterone)  cholesterol Protein Hormones  Hydrophilic = circulate freely in blood = cannot diffuse through the cell membrane  Receptor = must be located on the cell membrane of target cell Steroid/Thyroid Hormones  Hydrophobic = require a protein carrier to help circulate = diffuse easily  Receptor = located inside target cell - Hormones are secreted into the blood in pulses by a very specific stimulus and in amounts that vary with the strength of stimulus. Receptors - Unique structure in or on a cell that interacts with hormone Hydrophobic Hormones o can diffuse through the cell membrane, the receptor will be located in the cytoplasm or in the nucleus o hormone must be released by its carrier protein before it can enter cell Hydrophilic Hormones o unable to diffuse through the cell membrane o hormone attaches to the receptor and initiates a sequence of chemical reactions that will eventually alter the activity of the cell o 3 ways: through second messenger, G protein, tyrosine kinase Second messenger • when hormone binds to its receptor, it causes a G-protein nd on the inside of the membrane to produce a 2 messenger • cAMP is most common Tyrosine Kinase • hormone receptor complex activates tyrosine kinase on the inside surface of the membrane • tyrosine kinase then alters existing proteins that will then alter activity of cell Ion Channels - when hormone attaches to its receptor, a G protein is activated that lies within the cell membrane - G-protein can then open adjacent ion channels Control of secretion - controlled by negative feedback Hypothalamus Structure/Function - located at the base of the brain just above pituitary gland and below thalamus - receives information from all over the brain - involved with homeostatic mechanisms: temperature, water balance, energy production, behavioural drives (thirst, hunger, sexual) Hormones and releasing factors - secretion of many types of hormones:  Prolactin Releasing Hormone (PRH)  Prolacting Inhibiting Hormone (PIH)  Thyrotropin Releasing Hormone (TRH)  Corticotropin Releasing Hormone (CRH)  Growth Hormone Releasing Hormone (GHRH)  Growth Hormone Inhibiting Hormone (GHIH)  Gonadotropin Releasing Hormone (GnRH) I.e. Prolacting Releasing hormone is secreted from the hypothalamus to cause the ‘release’ of the hormone prolactin from the anterior pituitary. Pituitary Gland Structure - divided into two distinct regions (anterior and posterior) Anterior: o develops from tissue that forms the roof of the mouth o made up of endocrine tissue  endocrine cells secrete pituitary hormones directly into blood o Regulated by circulatory system: hypothalamic-hypophyseal portal system o Communicates with anterior pituitary by secreting releasing/inhibiting hormones Posterior: o Develops from neural tissue at the base of the brain o Contains axons and nerve terminals of neurons whose cell bodies lie in the hypothalamus (hypothalamic-hypophyseal tract) o Neurons produce neurohomrones (antidiuretic and oxytocin) o Secreted into posterior in response to AP Function - hormones from anterior pituitary control metabolic functions - two other anterior hormones control growth of the ovaries and testes and regulate their reproductive functions - hormones from posterior pituitary regulate water reabsorption in kidney and milk release from the breasts + contraction of uterus Regulation by Negative Feedback - Hypothalamus secretes a releasing hormone (H1) which causes the release of an anterior pituitary hormone (H2) into the blood - Hormone (H2) can feed back to the hypothalamus to decrease the release of hormone (H1) in a ‘short loop’ - The anterior pituitary hormone (H2) will circulate to an endocrine gland to cause the release of (H3) - (H3) can feed back to the hypothalamus and pituitary to decrease the release of H1 and H2 in a ‘long loop’ Thyroid Gland Structure - lies directly below the larynx and consists of two lobes that almost completely surround the trachea - made up of follicles (functional units of gland) - follicles consist of a central region of colloid surrounded by epithelial cells Function - produce triiodothyronine (T3) and thyroxine (T4)  regulating basal metabolic rate - hormones are made from tyrosine (hydrophobic)  require protein carrier to circulate in the blood Production of T3 and T4 - produced inside the follicles of the thyroid gland by combining iodine and tyrosine with the help of a glycoprotein called thyroglobulin - epithelial cells take up molecules of tyrosine from the circulation, then they combine with thyroglobulin. - Epithelial cells also actively take up iodine (from diet) - As the tyrosine-thyroglobulin complex is secreted into the colloid, one or two molecules of iodine attach to each tyrosine - In colloid, two tyrosine molecules will join together while attached to the thyroglobulin - Depending on number of iodine molecules attached to tyrosine  T3 or T4 Secretion of T3 and T4 - Thyroid stimulating hormone (TSH) is released from anterior pituitary gland - TSH binds to a receptor on membrane of epithelial cell which will stimulate rxn - Reactions:  Trapping and taking up of circulating iodine (in order to form hormones)  Stimulating endocytosis of the T3/T4 thyroglobulin complex into the cells  Enzymatic removal of thyroglobulin from T3/T4 in epithelial cells and stimulating the secretion of T3/T4 into the blood - TSH also stimulates the thyroid to grow  Hyperplasia Regulation of Secretion (T3/T4) - hormones will feed back to the hypothalamus and pituitary to ultimately inhibit the release of thyrotropin releasing hormone + TSH - With less TSH circulating to the thyroid  less T3/T4 will be released into blood Circulation of T3/T4 - 90% of hormones released from the thyroid gland consist of T4 - 10% is T3 - Most of T4 is converted to T3 (T3 is more biologically active) Effects of T3 and T4 hormones - Receptors for hormones are found within the nucleus of almost all cells in the body and can alter the transcription of genes to form many different proteins - Responsible for regulating body’s basal metabolic rate (BMR), proper development of nervous system in foetus - Help maintain person’s alertness, responsiveness, and emotional state o Increase in thyroid hormone will:  Increase body temperature  Increase cardiac output  Increas
More Less

Related notes for Physiology 2130

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.