By T. Jaffar. University of Wisconsin-River Falls. 2017.

The hypothalamic-pituitary-ovarian axis is suppressed by the high levels of sex steroids discount 20 mg levitra with mastercard. Conse- The Fetal Endocrine System Gradually Matures quently purchase levitra 20mg with visa, circulating gonadotropins are low, and ovulation does not occur during pregnancy. In contrast, the rising The protective intrauterine environment postpones the ini- levels of estrogens stimulate PRL release. PRL levels begin tiation of some physiological functions that are essential for to rise during the first trimester, increasing gradually to life after birth. For example, the fetal lungs and kidneys do reach a level 10 times higher near term (see Fig. Pi- not act as organs of gas exchange and excretion because tuitary lactotrophs undergo hyperplasia and hypertrophy their functions are carried out by the placenta. Constant and mostly account for the enlargement of the pregnant isothermal surroundings alleviate the need to expend calo- woman’s pituitary gland. The gastrointestinal duce growth hormone are reduced, and GH levels are low tract does not carry out digestive activities, and fetal bones throughout pregnancy. Being The thyroid gland enlarges, but TSH levels are in the exposed to low levels of external stimuli and environmental normal nonpregnant range. T3 and T4 increase, but thyrox- insults, the fetal nervous and immune systems develop ine-binding globulin (TBG) also increases in response to slowly. The parathyroid glands and their hor- Given that most protein and polypeptide hormones are mone, PTH, increase mostly during the third trimester. Notable exceptions are some of the and glucocorticoids increases, and plasma free cortisol is steroid hormones, which are produced by the fetoplacental higher because of its displacement from transcortin, the unit; they cross easily between the different compartments cortisol-binding globulin, by progesterone, but hypercorti- and carry out integrated functions in both the fetus and the solism is not apparent during pregnancy.

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Pituitary gland Right surrounded by Left posterior cerebral arterial posterior communicating a generic levitra 20 mg overnight delivery. The superficial temporal artery sup- plies blood to the parotid gland and to the superficial structures and Upper Extremity on the side of the head discount levitra 10 mg with mastercard. Pulsations through the temporal artery As mentioned earlier, the right subclavian artery arises from the can be easily detected by placing the fingertips immediately in brachiocephalic trunk, and the left subclavian artery arises di- front of the ear at the level of the eye (see fig. Each subclavian is frequently used by anesthesiologists to check a patient’s pulse artery passes laterally deep to the clavicle, carrying blood toward rate during surgery. The pulsations of the subclavian artery can Headaches are usually caused by vascular pressure on the be detected by pressing firmly on the skin just above the medial sensitive meninges covering the brain. From each subclavian sels serving the meninges are the meningeal branches of the occipi- artery arises a vertebral artery that carries blood to the brain (al- tal and maxillary arteries. Vasodilation of these vessels creates ready described); a short thyrocervical trunk that serves the thy- excessive pressure on the sensory receptors within the meninges, re- sulting in a headache. Circulatory System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 Chapter 16 Circulatory System 565 Ulna Radius Ulnar a. The costocervical trunk branches to serve the artery and curves posteriorly near the radial nerve to supply the upper intercostal muscles, posterior neck muscles, and the spinal triceps brachii muscle. A branch of the internal thoracic artery brachial, the anterior and posterior humeral circumflex arter- supplies blood to the muscles and tissues (mammary glands) of ies, form a continuous ring of vessels around the proximal por- the anterior thorax. The axillary artery is that portion of the major artery blood to the forearm and a portion of the hand and digits. Several small the arm, where it sends numerous small branches to the mus- branches arise from the axillary artery and supply blood to the cles of the forearm. The anterior interosseous artery extends tissues of the upper thorax and shoulder region. The radial recurrent artery serves the region of the axillary artery through the brachial region.