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Box 24-2 A Closer Look Fetal Circulation: Routing Blood to Miss the LungsFetal Circulation: Routing Blood to Miss the Lungs he developing fetus has several adaptations in the cardio- into the systemic circulation through a small vessel virus 4 free trimox 500 mg for sale, the duc- Tvascular system that change at birth antibiotic home remedies buy trimox from india. The foramen ovale seals to Most of this blood joins the inferior vena cava by way of a become a depression called the fossa ovalis in the septum be- 24 small vessel antibiotics for uti gram negative order trimox from india, the ductus venosus, and is carried to the heart. DEVELOPMENT AND BIRTH ✦ 481 Placental Hormones In addition to maintaining the riages (loss of an embryo or fetus) frequently occur dur- fetus, the placenta is an endocrine organ. Beginning soon ing this critical time when hormone secretion is shifting after implantation, some embryonic cells produce the from the corpus luteum to the placenta. This hormone stimulates creted by the placenta during pregnancy, reaching a peak the ovarian corpus luteum, prolonging its life-span to 11 at term, the normal conclusion of pregnancy. It promotes endometrial secretion to nourish the function leads to an alternate name for this hormone: embryo, maintains the endometrium and decreases the human chorionic somatomammotropin. By the end of the fourth month, the fetus By the end of the second month, the embryo takes on is almost 15 cm (6 inches) long, and its external genitalia an appearance that is recognizably human. By the seventh bryos, the primitive testes have formed and have begun to month, the fetus is usually about 35 cm (14 inches) long secrete testosterone, which will direct formation of the and weighs approxoimately 1. During development, the fetal skin is protected by a ◗ The lungs provide more oxygen by increasing the rate layer of cheeselike material called the vernix caseosa and depth of respiration. The total period of pregnancy, from fertilization of the Nausea and vomiting are common discomforts in ovum to birth, is approximately 266 days, also given as early pregnancy. The specific cause of these food and oxygen for the fetus and eliminate its waste ma- symptoms is not known, but they may be a result of the great changes in hormone levels that occur at this time. They may reap- Amniotic sac pear late in pregnancy as the head of Amniotic fluid the fetus drops from the abdominal region down into the pelvis, pressing on the rectum and the urinary blad- der. The Use of Ultrasound in Ob- Fetus stetrics Ultrasonography (ul-trah- son-OG-rah-fe) is a safe, painless, and noninvasive method for studying soft Urinary tissue. An 24 Anus instrument called a transducer con- verts the reflected sound waves into Urethra Vagina Perineum electrical energy, and a computer is Cervix used to generate an image on a view- Figure 24-5 Midsagittal section of a pregnant uterus with intact fetus. Ultrasound scans can be used in 484 ✦ CHAPTER TWENTY FOUR The Four Stages of Labor The process by which the fetus is ex- pelled from the uterus is known as labor and delivery; it also may be called parturition (par-tu-RISH-un). The technique can placenta, the membranes of the amniotic sac, and the also show the presence of excess amniotic fluid and fetal umbilical cord, except for a small portion remaining abnormalities. The fourth stage begins after expulsion of the after- birth and constitutes a period in which bleeding is The exact mechanisms that trigger the beginning of uter- controlled. Increase in the relative amount Cesarean Section of estrogen as compared to progesterone stimulates A cesarean (se-ZAR-re-an) section (C section) is an inci- uterine contractions. A cesarean section may be required produce reflex secretion of oxytocin, which in turn in- for a variety of reasons, including placental abnormalities, creases the uterine contractions (an example of positive abnormal fetal position, disproportion between the head feedback. Like bone as bone marrow does, so there is less chance of transplant marrow, umbilical cord blood contains stem cells capable of rejection and graft-versus-host disease than with bone differentiating into all blood cell types. Whereas bone mar- source, only enough cells to treat a child or small adult can row collection is a surgical procedure, cord blood can be be harvested from a single donor. Triplets occurred much less frequently, usually once in several thousand births, whereas quadru- A pregnancy may end before its full term has been com- plets occurred very rarely. The term live birth is used if the baby breathes or sented a historic event unless the mother had taken fer- shows any evidence of life such as heartbeat, pulsation of tility drugs. After the 20th week of pregnancy, the fetus is con- ◗ Both breast milk and colostrum contain maternal anti- sidered viable, that is, able to live outside the uterus. Secretions from the Duct of lobe Adipose tissue lobes are conveyed through lactifer- Lactiferous ous (lak-TIF-er-us) ducts, all of which Pectoralis major ducts converge at the papilla (nipple) (Fig. Placental lactogen (hPL) helps to prepare the breasts for lacta- tion, and the hormone prolactin (PRL), produced by the anterior pitu- itary gland, stimulates the secretory Areola cells of the mammary glands.
The H1-antagonists are classified as either first- or this reaction is the basis for a skin test to quantify the second-generation compounds 90 bacteria 10 human 500mg trimox overnight delivery. The introduction of a specific antigen— First-generation antihistamines are well absorbed after usually in food or in injected material—into a sensitized oral administration antibiotics for acne and eczema cheap 250 mg trimox with amex, with peak blood levels occurring individual can cause the rapid release of mast cell con- within 1 to 2 hours; the therapeutic effect usually lasts 4 tents antimicrobial underpants buy 250 mg trimox with mastercard, producing a decrease in blood pressure, impaired to 6 hours, although some drugs are much longer acting respiratory function, abdominal cramps, and urticaria. These antagonists are generally metabo- Extreme and severe anaphylaxis is life threatening and lized in the liver through hydroxylation. Clinical Uses of Histamine The second-generation H1-receptor antagonists are Histamine has only minor uses in clinical medicine. In also rapidly absorbed, with peak plasma concentrations the past it was used to diagnose pernicious anemia, in being reached within 1 to 3 hours. Their duration of ac- which histamine fails to evoke the usual secretion of tion generally varies between 4 and 24 hours (Table gastric acid. Loratadine (Claritin) and its active metabolite, bronchial hyperreactivity, although this test may be desloratadine (Clarinex), undergoes extensive first-pass quite hazardous for asthmatics. Today the main clinical metabolism and is converted by CYP3A4 isozymes to use of histamine is as a positive control injection for al- an active metabolite. In contrast, cetirizine (Zyrtec) and fexofe- HISTAMINE ANTAGONISM AND nadine (Allegra) undergo little hepatic metabolism and HISTAMINE ANTAGONISTS are eliminated mainly as unchanged compounds in the urine and feces, respectively. The effects of histamine on body tissues and organs can The reduction in therapeutic effectiveness that can be diminished in four ways: inhibition of histamine syn- occur when antihistamines are given for long periods is thesis, inhibition of histamine release from storage probably related to an induction of hepatic drug- granules, blockade of histamine receptors, and physio- metabolizing enzymes. Of these ap- histamines more rapidly than adults, while individuals proaches, only the inhibition of histamine synthesis has with hepatic impairment may eliminate them more not been employed clinically. At therapeutic doses, the first- and second-generation antihistamines are equilibrium-competitive inhibitors of H1-receptor–mediated responses. Certain second- H1-Receptor Antagonists generation drugs are noncompetitive inhibitors at high The most common use of the H1-receptor antagonists is concentrations. Both first- and second-generation com- for the relief of allergic reactions such as rhinitis and ur- pounds have negligible abilities to block the H2-, H3-, or ticaria. The therapeutic effectiveness of these 454 V THERAPEUTIC ASPECTS OF INFLAMMATORY AND SELECTED OTHER CLINICAL DISORDERS TABLE 38. H1-antagonists generally produce sedation through an Adverse Effects effect on the CNS; however, excitation can occur when toxic dosages are ingested. Sedation is the most frequent adverse reaction to the Many of these drugs have effects that are not medi- first-generation antihistamines. The antimuscarinic ac- alertness and motor skills will result if alcohol or an- tivity of several first-generation H1-blockers may account other depressant is taken with these drugs. Anti- for their effectiveness in combating motion sickness and muscarinic effects caused by these drugs include dry their limited ability to suppress parkinsonian symptoms. Nausea, vomiting, constipation or diarrhea, adrenoceptors, whereas cyproheptadine (Periactin) is an dizziness, insomnia, nervousness, and fatigue also have antagonist at serotonin receptors. Drug allergy, especially after topical ap- (Benadryl), pyrilamine (Ryna), and promethazine (Phen- plication, is fairly common. Epidemiological 38 Histamine and Histamine Antagonists 455 studies have not shown such an association in humans. The most widely used H1-blocking The second-generation H1-antagonists are often re- drugs for sleep induction are diphenhydramine, pro- ferred to as nonsedating antihistamines; however, doses methazine, and pyrilamine. A more serious adverse effect of H2-Receptor Antagonists some earlier second-generation antihistamines is car- diotoxicity.
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