By S. Kafa. McKendree College.
It is called the au- (F13) is registered by sensory organs (F10) 400 mg flagyl free shipping antibiotics for sinus infection and sore throat, tonomic (visceral flagyl 250mg generic bacteria gumball, or vegetative) nervous which return the corresponding informa- system (ANS), and consists of two com- tion via afferent nerves (F11) to the CNS ponents which often have opposing func- (F12) (reafference, or external feedback). De- tions: the sympathetic nervous system and the pending on whether or not the result meets parasympathetic nervous system. The interac- thedesiredtarget,theCNSsendsoutfurther tion of these two systems keeps the interior stimulating or inhibiting signals (F13). Nervous activity is based on a vast number In vertebrates, the somatic nervous system of such functional circuits. It is re- supply of the intestines), we can subdivide sponsible for conscious perception, for vol- the motor system into an environment- untary movement, and for the processing of oriented ecotropic somatomotor system information (integration). Note that most (striated, voluntary muscles) and an idio- textbooks include the peripheral nerves of tropic visceromotor system (smooth intestinal the autonomic nervous system in the PNS. The CNS develops from the neural plate (D4) of the ectoderm which then transforms into the neural groove (D5) and further into the Kahle, Color Atlas of Human Anatomy, Vol. Development of the Nervous System, Functional Circuits 3 A–C Models of primitive nervous systems (according to Parker and Bethe) 1 1 1 3 3 2 2 A Sensory cell with B Nerve cell connecting process to a a sensory cell and a muscle cell muscle cell C Diffuse neural network 10 11 12 4 9 5 15 13 16 6 14 E Functional circuit: response of an organism to environmental stimuli 7 8 14 13 12 17 7 8 11 7 10 D Embryonic development 8 of the central nervous system: F Functional circuit: influence of an spinal cord on the left, brain on organism on its environment the right Kahle, Color Atlas of Human Anatomy, Vol. The anterior the Body (A, B) division is called the forebrain (gray) (B8). The central nervous system (CNS) is The divisions of the brain stem, or encephalic divided into the brain, encephalon (A1), and trunk, have a common structural plan (con- the spinal cord (SC), medulla spinalis (A2). Genuine peripheral by a bony capsule; the spinal cord in the nerves emerge from these divisions, as they vertebral canal is enclosed by the bony do from the spinal cord. Both are covered by they are supported by the chorda dorsalis meninges that enclose a cavity filled with a during embryonic development. Thus, the CNS is features distinguish the brain stem from the protected from all sides by bony walls and forebrain. The subdivision chosen here the cushioning effect of a fluid (fluid cush- differs from the other classifications in ion). The peripheral nervous system (PNS) in- cludes the cranial nerves, which emerge The forebrain, prosencephalon, consists of through holes (foramina) in the base of the two parts, the diencephalon and the telen- skull, and the spinal nerves, which emerge cephalon or cerebrum. In the mature brain, through spaces between the vertebrae (in- the telencephalon forms the two hemi- tervertebral foramina) (A3). At the entry points of the afferent nerve fibers lie ganglia (A6); these are small oval bodies containing sensory neurons. When describing brain structures, terms like “top,” “bottom,” “front,” and “back” are inaccurate, because we have to distinguish between different axes of the brain (B). Owing to the upright posture of humans, theneuraltubeisbent;theaxis ofthespinal cord runs almost vertically, while the axis of the forebrain (Forel’s axis, orange) runs hori- zontally; the axis of the lower brain divi- sions (Meinert’s axis, violet) runs obliquely. The positional terms relate to theses axes: the anterior end of the axis is called oral or rostral (os, mouth; rostrum, beak), the pos- terior end is called caudal (cauda, tail), the underside is called basal or ventral (venter, abdomen), and the upper side is called dor- sal (dorsum, back). The lower brain divisions, which merge into the spinal cord, are collectively called Kahle, Color Atlas of Human Anatomy, Vol. Position of the Nervous System 5 1 9 2 4 4 3 6 5 5 A Position of the central nervous system in the body dorsal 8 oral (rostral) caudal oral (rostral) ventral dorsal 7 ventral B Axes of the brain: caudal median section through the brain Kahle, Color Atlas of Human Anatomy, Vol. A deep transverse sulcus (B15) is formed between the cerebellar an- Development of the Brain (A–E) lageandthemedullaoblongataasaresultof The closure of the neural groove into the the pontine flexure; the underside of the neural tube begins at the level of the upper cerebellum comes to lie in apposition to the cervical cord. From here, further closure membrane-thin dorsal wall of the medulla runs in the oral direction up to the rostral (p. The telencephalon, developmental events in the CNS proceed in which initially lagged behind all other brain the same directions. Thus, the brain’s divi- divisions in its development, now exhibits sions do not mature simultaneously but at the most intense growth (p. During the sixth month, the insula cephalon (yellow and red); the caudal ves- still lies free (D). The first grooves and con- icles are the future brain stem, encephalic volutions appear on the previously smooth trunk (blue). The initially tube appear at this time: the cephalic thin walls of neural tube and brain vesicles flexure (A1) and the cervical flexure (A2). They Although the brain stem still shows a uni- contain the neurons and nerve tracts that form structure at this early stage, the future make up the brain substance proper.
Cellularity may Signal intensity of GRE sequences is also dependent also be increased in patients suffering from chronic bac- upon magnetic susceptibility purchase flagyl 250 mg otc prophylactic antibiotics for uti guidelines, allowing for differentiating terial infectious spondylitis (Fig purchase flagyl 250 mg fast delivery antibiotic not working for uti. In these cases, tumor infiltration with and without trabecular destruc- MR imaging signal intensity alterations are probably due tion. This situation can be found in tumor infiltration of to reactive bone marrow stimulation. The subtraction placed by non-neoplastic stimulated, bone marrow cells, of fat and water signal on opposed GRE sequences pro- which are necessary for the production of white blood vides a perfect background with low signal intensity to cells in chronic infection. Stäbler Imaging Diffuse Bone Marrow Abnormalities When there are diffuse abnormalities of the bone marrow signal in hematologic neoplasias and myeloproliferative diseases but no focal disease is present, a pathologic sig- nal intensity of the bone marrow can be overlooked. In this situation, a homogenous diffuse decrease of signal intensity over all vertebral bodies on T1-weighted spin- echo images results from a homogenous replacement of fat cells by cellular marrow or an accumulation of iron in the bone marrow in hemolytic disorders. In the presence of diffuse neoplastic bone marrow in- filtration or bone marrow stimulation, low homogenous SI on T1-weighted images is seen, in addition to increased SI on STIR-images. The percentage enhancement following Gadolinium injection is increased (Fig. On the STIR-image multiple metastasis are outlined with high signal intensity. The lo- cation of the metastasis, which is of risk for a neuro- logic complication by com- pressing the spinal cord, is easily recognized a b Fig. Diffuse neoplastic bone marrow infitration in a patient enhanced T1-weighted image (a). On unenhanced T1-weighted image a diffuse quency selective fat suppression creates a low intensity back- low SI is present in all vertebrae (a). Gadolinium enhancement is ground to highlight the enhancing metastasis (b) heavily increased indicating the diffuse tumor infiltration (b) Bone Marrow Disorders 79 Multiple Myeloma The “salt-and-pepper” pattern is characterized by an irregular bone marrow structure with irregular areas of Multiple myeloma is characterized by bone marrow infil- high and low signal intensity on T1-weighted spin-echo tration with neoplastic plasma cells. Hyperintense areas cretory and Bence Jones plasmacytoma, these cells pro- on T1-weighted spin-echo images represent focal fat de- duce monoclonal immunglobulins, recognizable in serum posits, whereas hypointense areas correlate with electrophoresis. The “salt-and-pepper” pattern correlates up to ten years in cases of smoldering myeloma. Bone marrow biopsy is essential for diagnosis of mul- When minimal plasma cell infiltration is present, this tiple myeloma and gives direct proof for atypical plasma is usually accompanied by a normal or even increased cells. Because of the small size of the biopsy sample, amount of marrow fat cells. In malignant tumors with dif- however, the result is not always representative of the en- fuse bone marrow infiltration, there is rapid displacement tire bone marrow, especially in cases of nodular involve- of fat cells by tumor cells. At the beginning of interstitial ment, in which the correlation of bone marrow biopsy tumor infiltration in multiple myeloma, monoclonal plas- and MRI is low. Laboratory parameters, such as serum- ma cells arrange themselves in such a way as to not dis- paraprotein, β2-microglobulin and the labeling index, are place the fat cells. Apparently, these cells produce factors indirect criteria, but correlate well with tumor mass and which inhibit normal hematopoesis, thus increasing the survival times. Therefore, despite tumor cell in- plasmacytoma, these parameters may be negative. When filtration and replacement of hematopoetic cells, bone “solitary” plasmacytoma is present, MR imaging can de- marrow fat may be normal or even increased without sig- tect or exclude additional marrow abnormalities. As long as there is no crit- ical shift in the water to fat ratio of the bone marrow, myeloma remains undetected in MR imaging. Differentiation of acute osteoporotic In diffuse plasma cell infiltration, no contrast to unin- and tumor-related vertebral fractures volved bone marrow is present. Patients with a diffuse infiltration pattern in multiple myeloma are generally in On T1- and T2-weighted spin echo as well as STIR im- stage II or III disease which is prognostically unfavor- ages and following contrast enhancement, acute benign able. Bone marrow edema as well as normal bone marrow by neoplastic plasma cells with or tumor infiltration exhibit hypointense signal on non-en- without trabecular destruction. Myelomatous foci in gen- hanced T1-weighted spin echo-images and increased eral show low signal intensity on T1-weighted spin-echo signal intensity on T2-weighted spin echo or STIR-im- images, but they can be isointense or hyperintense com- ages. Especially, if the whole vertebral body is affected pared with surrounding bone marrow. On opposed GRE due to bone marrow edema and if a malignant tumor is and STIR images, focal plasmocytoma nodules exhibit a known in the patient´s medical history, differential diag- high or very high signal intensity with pronounced in- nosis can be difficult. There exist morphologic criteria crease of signal intensity, if Gadolinium is added.
Estradiol formed from exposure of the testes to elevated temperature cheap flagyl 500 mg free shipping antibiotics for uti uti, fever generic flagyl 250mg otc 3m antimicrobial foam mouse pad, or testosterone by aromatase also has an inhibitory effect on thermoregulatory dysfunction can lead to temporary or per- GnRH secretion. Acute testosterone treatment does not al- manent sterility as a result of a failure of spermatogenesis, ter pituitary responsiveness to GnRH, but prolonged expo- whereas steroidogenesis is unaltered. The testes are encapsulated by a thick fibrous connec- Removal of the testes results in increased circulating lev- tive tissue layer, the tunica albuginea. Replacement therapy with physiologi- contains hundreds of tightly packed seminiferous tubules, cal doses of testosterone restores LH to precastration levels ranging from 150 to 250 m in diameter and from 30 to 70 but does not completely correct FSH levels. The tubules are arranged in lobules, separated by tion led to a search for a gonadal factor that specifically in- extensions of the tunica albuginea, and open on both ends hibits FSH release. Examination of a cross section of a testis eventually isolated from seminal fluid. Inhibin is produced reveals distinct morphological compartmentalization. Inhibin is ous tubules, whereas testosterone is produced by the Ley- composed of two dissimilar subunits, and , which are dig cells, which are scattered in a vascular, loose connective held together by disulfide bonds. There are two subunit tissue between the seminiferous tubules in the interstitial forms, called A and B. Each seminiferous tubule is composed of two somatic bound by a disulfide bridge to the B subunit and is the cell types (myoid cells and Sertoli cells) and germ cells. The physiologically important form of inhibin in the human seminiferous tubule is surrounded by a basement membrane male. Inhibin acts directly on the anterior pituitary and in- (basal lamina) with myoid cells on its perimeter, which de- hibits the secretion of FSH but not LH. On the inside of the basement mem- Activin is produced by Sertoli cells, stimulates the se- brane are large, irregularly shaped Sertoli cells, which ex- cretion of FSH, has an approximate molecular weight of 30 tend from the basement membrane to the lumen (Fig. The tight junctions divide each tivin A (two A subunits linked by a disulfide bridge), ac- tubule into a basal compartment, whose constituents are tivin B (two B subunits), and activin AB (one A and one exposed to circulating agents, and an adluminal compart- B subunit). The major form of activin in the male is cur- ment, which is isolated from bloodborne elements. The rently unknown although both Sertoli and Leydig cells tight junctions limit the transport of fluid and macromole- have been implicated in its secretion. Thus, the deactivation of activin by binding to follis- germ cells at various stages of division and differentiation. Follistatin is apparently Mitosis of the spermatogonia (diploid progenitors of sper- produced by Sertoli cells and acts as a paracrine factor on matozoa) occurs in the basal compartment of the seminifer- the developing spermatogenic cells. The early meiotic cells (primary spermatocytes) move across the junctional complexes into the adluminal compartment, where they mature into sper- matozoa or gametes after meiosis. The adluminal compart- THE MALE REPRODUCTIVE ORGANS ment is an immunologically privileged site. Spermatozoa The testes produce spermatozoa and transport them that develop in the adluminal compartment are not recog- through a series of ducts in preparation for fertilization. Consequently, males The testes also produce testosterone that regulates devel- can develop antibodies against their own sperm, resulting in opment of the male gametes, male sex characteristics, and infertility. Sperm antibodies are often present after vasec- CHAPTER 37 The Male Reproductive System 653 Spermatogonium Spermatozoon Lumen Sertoli cell Basement membrane Leydig cell surrounding the seminiferous tubule The testis. Receptors for FSH, present only where the adluminal compartment is ruptured, allowing on the plasma membranes of Sertoli cells, are glycoproteins sperm to mingle with immune cells from the circulation. FSH exerts mul- tiple effects on the Sertoli cell, most of which are mediated by cAMP and protein kinase A (Fig. FSH stimulates Sertoli Cells Have Multiple Functions the production of androgen-binding protein and plasmino- Sertoli cells are critical to germ cell development, as indi- gen activator, increases secretion of inhibin, and induces cated by their close contact. As many as 6 to 12 spermatids aromatase activity for the conversion of androgens to es- may be attached to a Sertoli cell. The testosterone receptor is within the nucleus of residual bodies (excess cytoplasm resulting from the trans- the Sertoli cell.
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