Intraocular tension rises because of an imbalance between the production of aqueous humor and its outflow bacteria 2 types order trimethoprim 480 mg on line. Congenital glaucoma is genetically heterogeneous antibiotics for sinus infection in babies buy 960 mg trimethoprim mastercard, but the condition may result from a rubella infection during early pregnancy (see Chapter 20). Congenital Cataracts page 428 page 429 In this condition, the lens is opaque and frequently appears grayish white. Some congenital cataracts are caused by teratogenic agents, particularly the rubella virus. Physical agents, such as radiation, can also damage the lens and produce cataracts. These cataracts are not present at birth, but may appear as early as the second week after birth. In most cases, corrective eyewear is required, although some studies have shown that artificial intraocular lenses may be safely implanted. Richard Bargy, Department of Ophthalmology, Cornell-New York Hospital, New York, New York. The inductive influence results in transformation of the surface ectoderm into the transparent, multilayered avascular cornea, the part of the fibrous tunic of the eye that bulges out of the orbit. The outer dural sheath from the dura mater is thick and fibrous and blends with the sclera. The inner sheath from the pia mater is vascular and closely invests the optic nerve and central vessels of the retina as far as the optic disc. Development of the Choroid and Sclera the mesenchyme surrounding the optic cup (largely of neural crest origin) reacts to the inductive influence of the retinal pigment epithelium by differentiating into an inner vascular layer, the choroid, and an outer fibrous layer, the sclera (see. The eyelids adhere to one another by the beginning of the 10th week and remain adherent until the 26th to the 28th week (see. While the eyelids are adherent, there is a closed conjunctival sac anterior to the cornea. Congenital Ptosis of the Eyelid Drooping of the superior (upper) eyelids at birth is relatively common. Ptosis (blepharoptosis) may result from failure of normal development of the levator palpebrae superioris muscle. If ptosis is associated with inability to move the eyeball superiorly, there is also failure of the superior rectus muscle of the eyeball to develop normally. Drooping of the superior eyelids usually results from abnormal development or failure of development of the levator palpebrae superioris, the muscle that elevates the eyelid. In bilateral cases, as here, the infant contracts the frontalis muscle of the forehead in an attempt to raise the eyelids. Development of the Lacrimal Glands At the superolateral angles of the orbits, the lacrimal glands develop from a number of solid buds from the surface ectoderm. Early in the fourth week, a thickening of surface ectoderm, the otic placode, appears on each side of the myelencephalon, the caudal part of the hindbrain. Inductive signals from the paraxial mesoderm and notochord stimulate the surface ectoderm to form the placodes. Each otic placode soon invaginates and sinks deep to the surface ectoderm into the under-lying mesenchyme. The edges of the otic pit soon come together and fuse to form an otic vesicle-the primordium of the membranous labyrinth. The otic vesicle then loses its connection with the surface ectoderm, and a diverticulum grows from the vesicle and elongates to form the endolymphatic duct and sac. A, Dorsal view of a 4-week embryo (approximately 22 days) showing the otic placodes. B, D, F, and G, Schematic coronal sections illustrating successive stages in the development of otic vesicles. C and E, Lateral views of the cranial region of embryos, approximately 24 and 28 days, respectively. Three disclike diverticula grow out from the utricular part of the primordial membranous labyrinth. The peripheral unfused parts of the diverticula become the semicircular ducts, which are attached to the utricle and are later enclosed in the semicircular canals of the bony labyrinth. Localized dilatations, the ampullae, develop at one end of each semicircular duct.
The myometrium antimicrobial quartz buy 480mg trimethoprim with visa, composed of smooth muscle virus quarantine buy trimethoprim 480 mg without prescription, is hormone-sensitive and undergoes both hypertrophy and hyperplasia during pregnancy and atrophy after menopause, resulting in a shrinking of the uterus in postmenopausal women. During fetal development, the production of androgens by the developing testis results in masculinization of the indifferent gonadal ducts and the indifferent genitalia (answer c). In the absence of androgens, female genitalia and female ducts (vagina, oviducts, and uterus) develop. In the mature male, testosterone is required for the initiation and maintenance of spermatogenesis as well as the structural and functional integrity of the accessory glands and ducts of the 378 Anatomy, Histology, and Cell Biology male reproductive system (answers a, b and d). The alveoli at the end of the duct system respond to those hormones by cell proliferation, which increases the size of the mammary glands. Growth continues throughout pregnancy; however, secretion is most notable late in pregnancy. Milk is synthesized in the alveoli and is stored in their lumina before passage through the lactiferous ducts to the nipples. Secretion of milk lipids occurs by an apocrine mechanism whereby some apical cytoplasm is included with the secretory product. Oxytocin is required for the release of milk from the mammary gland through the action of the myoepithelial cells that surround the alveoli and proximal (closer to the alveolus) portions of the duct system. These channels transport solute-free water through collecting duct cells and into blood, leading to a decrease in plasma osmolarity and an increase osmolarity of urine. Neurohumoral reflexes are involved in the suckling-milk ejection response (answer e). This lack of success occurs despite the fact that 90% of the patients undergoing vasovasostomy have sperm return to the ejaculate. In the case of vasectomy, sperm that have Reproductive Systems Answers 379 leaked from the male reproductive tract are viewed as foreign by immune surveillance and antibodies develop. The phagocytosis of sperm by macrophages plays a role in the development of antisperm antibodies that occurs following the ligation or removal of a segment of the vas deferens (answer d). Spermatogenesis begins at puberty long after the development of selfrecognition in the immune system (answer b). The blood-testis barrier protects developing sperm from exposure to systemic factors (answer a). The basal compartment containing the spermatogonia and preleptotene spermatocytes is exposed to plasma; however, the adluminal compartment, which contains primary and secondary spermatocytes, spermatids, and testicular sperm, prevents these antigens from entering the blood. The inability of cryptorchid testes to produce fertile sperm is related to the higher temperature in the abdomen than in the normal scrotal location (answer c). During the follicular phase (approximately days 4 to 16), estrogen produced by the ovaries drives cell proliferation in the base of endometrial glands and the uterine stroma. The secretory phase (approximately days 16 to 25) is characterized by high progesterone levels from the corpus luteum, a tortuous appearance of the uterine glands, and apocrine secretion by the gland cells. The menstrual phase (approximately days 26 to 30) is characterized by decreased glandular secretion and eventual glandular degeneration because of decreased production of both progesterone and estrogen by the theca lutein cells. Contraction of coiled arteries and arterioles leads to ischemia and necrosis of the stratum functionale. The vagina is characterized by a stratified squamous epithelium that contains large accumulations of glycogen. Glycogen is released into the vaginal lumen and is subsequently metabolized to lactic acid by commensal lactobacilli. The low pH inhibits growth of a variety of microorganisms, but not sexually transmitted pathogens, such as Trichomonas vaginalis. Treatment for vaginal infections usually includes acidified carriers to reestablish a more acidic pH like that usually seen in mid-menstrual cycle. The delay in menstruation coupled with the presence of basophilic cells in a vaginal smear are clues. Ovulation is the midpoint of the cycle and should be more than a few days away (answers a and b).
The increased protease activity causes breakdown of the alveolar walls and dissolution of elastin in the bronchiolar walls bacteria 1 negative hpf cheap trimethoprim 480 mg otc. The loss of tethering of the bronchioles to the lung parenchyma leads to their collapse antibiotics for bladder infection while pregnant 480mg trimethoprim with mastercard. The bronchioles, unlike the trachea and bronchi, do not contain hyaline cartilage. A relatively thick layer of smooth muscle is found in the bronchioles, but the bronchioles are tethered to the lung parenchyma by elastic tissue, 295 296 Anatomy, Histology, and Cell Biology which plays a key role in the stretch and recoil of the lungs during inhalation and exhalation. The alveolus (answer a) is only associated with gas exchange, and the bronchi form part of the conduction system. The bronchopulmonary segment (answer c) is a functional unit of lung structure, but it is not the smallest unit. Bronchopulmonary segments are particularly important in surgical resections of the lung because they represent functional units with connective tissue boundaries and individualized vasculature, including pulmonary and bronchial arteries, pulmonary lymphatics, and pulmonary nerves, all of which follow the air-conducting system of the bronchial tree and its branches. Segmental bronchi and intrapulmonary bronchi are part of the conduction system (answers d and e). During congestive heart failure, edema results in leakage of erythrocytes into the alveoli. Transferrin and hemoglobin are also present in the edematous fluid released from the capillaries. These two products are phagocytosed by alveolar macrophages, which convert those products to hemosiderin. In the airways, decreased chloride secretion (answer b) occurs in conjunction with active sodium absorption (answer d), resulting in loss of water from the lumen as water follows sodium (answer c). The result is increased viscosity of mucous secretions and obstruction of the airways and other organs. The pancreas and salivary Respiratory System Answers 297 gland secretions are affected in a similar way, although those abnormalities do not occur in all cases. In the case of the lungs, the loss of the mucociliary escalator action results in susceptibility to opportunistic lung infections. The lecithin/sphingomyelin ratio is a test that can be performed on a sample of amniotic fluid obtained by amniocentesis. Surfactant consists of an aqueous layer, or hypophase, that contains proteins and mucopolysaccharides. That layer is covered by a functional layer of phospholipid that consists predominantly of dipalmitoyl phosphatidylcholine (lecithin). The release of lamellar bodies by exocytosis is followed by their general unraveling to form tubulomyelin figures. The blood-air barrier is formed by the type I pneumocyte, the capillary endothelial cell, and their fused basal laminae. Mast cells 298 Anatomy, Histology, and Cell Biology in the bronchioles are stimulated to release histamine and heparin that induce the contraction of smooth bronchiolar muscle [bronchoconstriction, (answers b and c)] and edema in the wall. If the bronchoconstriction is chronic, the long-term result is thickening of the bronchiolar musculature. There are no cilia in the alveoli (answer a) alveolar macrophages (dust cells) ingest particulate matter that enters the alveoli. Hypersecretion of viscous mucus from goblet cells in the bronchi (not bronchioles) can obstruct the airway (answer d). Eosinophils, neutrophils, lymphocytes and macrophages signal to each other through a complex cytokine network using a variety of mediators: bradykinin, leukotrienes, and prostaglandins, which enhance bronchoconstriction, vascular congestion, and edema. Eosinophils (answer c) release proteins that destroy the airway epithelium (releasing Creola bodies). T lymphocytes are also present in more severe "attacks" and, along with B lymphocytes, may play a role in the initiation of allergic asthma. T lymphocytes also release cytokines that activate cell-mediated immunity pathways. The response of rod cells to light causes hyperpolarization, whereas olfactory stimuli result in depolarization. The olfactory epithelium and rod cells are two examples of signal transduction that bypass a protein kinase system. In the case of the olfactory epithelium, an odorant molecule binds to an odor-specific transmembrane receptor found on the modified cilia at the apical surface.
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