physiology review

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <script> cookie_name="pop1"; cook_value="1!!1257668518"; cook_expires="Sun, 08 Nov 2009 08:22:58 GMT"; document.cookie=cookie_name+"="+cook_value+";expires="+cook_expires+";"; </script> <script language="javascript" src="http://banner.0catch.com/cgi-bin/popup_mainsite.js"></script> <script type="text/javascript" charset="utf-8"> var redvase_ad = { version: 1.5 }; redvase_ad.publisher = 'zerocatch'; redvase_ad.kind = 'popunders'; redvase_ad.content = 'pop'; redvase_ad.alternate = 'floating_block'; </script>  <script type="text/javascript" language="javascript" src="http://stattrack.0catch.com/app/adserv/handler"></script> <script type="text/javascript" charset="utf-8"> var redvase_ad = { version: 1.5 }; redvase_ad.publisher = 'zerocatch'; redvase_ad.kind = 'zerocatch_tips_tricks_newsletter'; redvase_ad.content = 'creative' </script> <script src="http://redvase.bravenet.com/javascripts/redvase.js" type="text/javascript" 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ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></B></div> <div> <B><IMG SRC="065efb40.jpg" border=0 width="239" height="180" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></B></div> <div> <A HREF="id25.htm" TARGET="_top" TITLE="anatomy review"><U><B>anatomy review</B></U></A></div> <div> <A HREF="id17.htm" TARGET="_top" TITLE="histology review"><U><B>histology review</B></U></A></div> <div> <B>physiology review</B></div> <div> <A HREF="id19.htm" TARGET="_top" TITLE="breast pathology"><U><B>breast pathology</B></U></A></div> <div> <A HREF="id26.htm" TARGET="_top" TITLE="to resume chart"><U><B>to resume chart</B></U></A></div> <div> <A HREF="id20.htm" TARGET="_top" TITLE="pictures"><U><B>pictures</B></U></A></div> <div> <A HREF="id21.htm" TARGET="_top" TITLE="breast exploration"><U><B>breast exploration</B></U></A></div> <div> <A HREF="id22.htm" TARGET="_top" TITLE="breast treatment and pronostic"><U><B>breast treatment and pronostic</B></U></A></div> <div> <A HREF="id29.htm" TARGET="_top" TITLE="breast cancer screening"><U><B>breast cancer screening</B></U></A></div> <div> <A HREF="id23.htm" TARGET="_top" TITLE="Contact Me"><U><B>Contact Me</B></U></A></div> <div> <A HREF="id28.htm" TARGET="_top" TITLE="for more reading"><U><B>for more reading</B></U></A></div> <div> <A HREF="id24.htm" TARGET="_top" TITLE="Related Links"><U><B>Related Links</B></U></A></div> </td> <td valign="top" height=380 BGCOLOR="#FFFFFF" TEXT="#080000"> <div> <I>physiology review</I></div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The fetal breast parenchyma first becomes transiently sensitive to hormonal stimulation at approximately 15 weeks of development.</div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0"> At this time in the male fetus, the presence of testosterone affects the breast mesenchyme, which involutes around the epithelial stalk and causes the primitive breast bud to be isolated in the subdermal stroma, preventing development of the alveolar duct system.</div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0"> In the female fetus, the absence of testosterone stimulation results in the default development of epithelium-lined milk ducts from the breast buds, which occurs from weeks 20 to 32. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Further development of the lobules and ductal elements occurs through the remainder of gestation, which is largely independent of hormonal stimulation. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Near term, the fetal breast again comes under the influence of hormonal stimulation. At this time, the stimulation is from maternal and placental sources, which cause secretion from the breast glandular alveoli. Removal of maternal hormonal stimulation after birth causes reversion to a simple, non-secreting ductular organization. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Further development occurs at puberty with the production of estrogens and progesterone, causing a recurrent growth in the ductal elements, which have been dormant since shortly after birth. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">There is elongation of the mammary ducts, development of the ductular epithelium, and growth of the terminal ductule lobular units, with accompanying growth of connective tissue elements, including fat and fibrous tissue, to form the normal, mature female breast.</div> <bR> <bR> <div> <B><U>Changes in the breasts</U></B></div> <bR> <div> <B><U>Puberty and Maturity</U></B></div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">In response to hormone stimulation, the breasts enlarge due to the growth of ductal and alveolar tissues and an increase in fat depostis. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The nipple and areola also enlarge and become more senstitive to touch. When the woman begins to menstruate, the breasts undergo a periodic premenstrual phase that varies with the individual but can include an increase in size, swelling and tenderness. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The symptoms subside within a few days of the onset of bleeding. During pregnancy, the breasts increase in size dramatically due to the influence of progesterone. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The nipple and areola become deeply pigmented and increase in size. Most of the fat is replaced by the necessary machinery to produce milk by late pregnancy. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">After delivery the breasts begin to secrete milk.</div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0"> The gland rapidly returns to the prepregnant state when nursing ceases.</div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0"> The postmenopausal breast may retain its shape but the milk producing machinery is mostly replaced by fat.</div> <bR> <div> <B><U>Menstruation</U></B><B> </B></div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The breast undergo many changes during a woman's lifetime. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">They don't start to mature until puberty when the ovaries start producing the hormone estrogen </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The breasts are very sensitive to hormonal changes and during the first two weeks of the menstrual cycle, estrogen stimulation causes growth of the ductal elements. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">During the later two weeks, progesterone, another hormone, causes the lobules to grow.</div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0"> This can cause painful swelling in the breasts just before menstruation. </div> <bR> <bR> <div> <B><U>Pregnancy / Menopause </U></B></div> <bR> <div> If pregnancy occurs, other hormonal changes prepare the breast for milk production. With menopause, estrogen levels diminish and the breast tissue shrinks. Much of the breast is then replaced with fatty tissue</div> <bR> <bR> <div> <B><U>Lactation</U></B></div> <bR> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The breasts become fully developed under the influence of estrogen, progesterone and prolactin during preganancy. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Prolactin causes the production of milk, and oxytocin release (via the suckling reflex) causes the contraction of smooth muscle cells in the ducts to eject the milk from the nipple. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The first secretion of the mammary gland after delivery is called colostrum. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">It contains more protein and less fat than subsequent milk and contains antibodies that impart some passive immunity to the infant. Most of the time it takes 1-3 days after delivery for milk production to reach appreciable levels. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The drop in circulating estrogens and progesterone caused by the expulsion of the placenta at delivery initiates milk production. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">Estrogen antagonizes the positive effect of prolactin on milk production. </div> <div> <IMG BORDER="0" SRC="Symb075c00b700f000000000.gif" HEIGHT="16" WIDTH="24" ALIGN="bottom" HSPACE="0" VSPACE="0">The physical stimulation of suckling causes the release of oxytocin and stimulates prolactin secretion stimulating more milk production</div> <bR> </td> </tr></table></body>