Medullary zones

The terminal portion of the proximal tubule leads into the descending thin limb of Henle in the region corresponding to the demarcation of outer and inner stripes of the outer zone of the medulla. The thin limb loops upward to form the ascending thin limb of Henle, which differentiates into the ascending thick limb of Henle at the intersection of the inner zone of medulla and the inner stripe of the outer medullary zone. This is characteristic of juxtamedullary nephrons that have long loops of Henle. In contrast, as noted earlier, cortical nephrons have short loops of... 

By GD 50, the primordial thymus contains a polymorphic cell population and is on an obvious differentiation into cortex and medullary zones. The first T-like cells can be identified histologically by GD 50 but do not show CD3-positive immunoreactivity (Buse et al., 2006). The first cells that have been identified immunohistochemically are those expressing Human Leukocyte Antigen-D Region (HLA-DR of the major histocompatibility complex, class... 

Uses NA Action -I- Medullary chemorec tor trigger zone Dose Adults. 

Mechanism of Action An antidote that acts centrally by stimulating medullary chemoreceptor trigger zone and locally by irritating gastric mucosa. Therapeutic Effect Produces emesis. 

We now turn to an anatomical description of lymph nodes. The lymph node is surrounded by a thick, fibrous capsule and is subdivided into compartments by trabeculae. Inside the capsule is the subcapsular or marginal sinus, which forms the entry point of lymphatic fluid into the node, via the afferent vessel. The lymph node cortex, which lies beneath the subcapsular sinus, is the location of the primary and secondary lymphoid follicles. The primary follicles are comprised of B-lymphocytes. An immune response stimulates B-cells to replicate and differentiate, converting the primary follicle into a secondary follicle or germinal center, surrounded by a zone of small lymphocytes. The paracortex surrounds the germinal centers and primary follicles and contains mostly T-lymphocytes. The medulla is composed of medullary cords, consisting of macrophages and plasma cells, and medullary sinuses. The medullary vessels include the arteries and veins, and the afferent and efferent lymphatic vessels, respectively, deliver the lymphatic fluid into and out of the lymph node. 

The anatomy of the tuber is shown diagrammatically in Figure 11.2. Parts that can be distinguished are the skin (periderm) with the lenticels, the eyes, the bud and stem ends, the cortex, the ring of vascular bundles, the perimedullary zone, and the pith with medullary rays which are homologous with the medulla of the stolon.7... 

These include infarcts in the territory of (1) the deep perforators of the MCA, anterior cerebral artery (ACA) and posterior cerebral artery (PCA), posterior communicating artery (PcomA), the lenticulo-striate arteries and the anterior choroidal artery (2) the superficial perforators (white matter medullary branches) of the superficial pial arteries (3) border-zone or junctional infarcts between 1 and 2 (4) combined infarcts. Small (< 1.5 mm infarcts - lacunes) are usually caused by single perforator disease while larger infarcts have a more diverse pathophysiology including embolism and MCA stenosis (Bang et al. 2002). 

The structure, organization, and ratio of matrix and fibrous proteins contribute to the physiochemical properties of keratinous tissues. For example, a primary difference between hair and nails is the arrangement of fibrous proteins and the concentration of matrix proteins present in each tissue. In cells destined to form the cortex of hair, fibrous proteins are oriented to form filaments which cluster to form fibrils. In the keratogenous zone, fibrils undergo lateral fusion to ultimately produce the cortex. The medulla also contains keratin which has been characterized as a collection of irregular fibrous proteins. Fibrous proteins form a trabecular framework comprising 95% of the medulla, and medullary proteins are less resistant to chemical degradation than proteins in the cortex. The cell membrane complex. 

Small deep infarcts in the subcortical white matter of the corona radiata may result from small vessel disease affecting the long medullary perforating arteries extending down from cortical branches of the middle cerebral artery or from embolism. Such centrum semiovale infarcts present as either a lacunar syndrome or, occasionally, as a partial anterior cirulation syndrome with cortical features (Read et al. 1998 Lammie and Wardlaw 1999). They are not, however, easy to classify or to distinguish from border zone infarcts deeper in the white matter lying between the arterial territories of the deep perforators from the first part of the middle cerebral artery and the superficial medullary perforators. 

By GD 60, the medullary and cortical regions can easily be distinguished microscopically. The medulla contains primarily CD3-positive cells and immature Hassall s bodies. The main zone of proliferation is the peripheral cortex. The identification of CD3 immunoreactivity signifies the onset of the prenatal thymus function of educating lymphocytes to discriminate self versus foreign proteins. From GD 70 onwards, macrophages (CD68) are observed in minute numbers evenly distributed over both cortex and medulla. By GD 85, B lym-... 

The antiemetic properties of metoclopramide appear to be a result of its antagonism of central and peripheral dopamine receptors. Dopamine produces nausea and vomiting by stimulation of the medullary chemoreceptor trigger zone (CTZ), and metoclopramide blocks stimulation of the CTZ by agents like levodopa or apomorphine that are known to increase dopamine levels or to possess dopaminelike effects. Metoclopramide also inhibits the central and peripheral effects of apomorphine and abolishes the slowing of gastric emptying caused by apomorphine. 

Perphenazine is thought to exert its antipsychotic effects by postsynaptic blockade of CNS dopamine receptors, thus inhibiting dopamine-mediated effects. The antiemetic effects of perphenazine are attributed to dopamine-receptor blockade in the medullary chemoreceptor trigger zone. Perphenazine has many other central and peripheral effects it produces both alpha and ganglionic blockade and counteracts histamine- and serotonin-mediated functions. It produces... 

Promazine (initially 50 to 150 mg IM) is indicated in the management of psychotic disorders. In addition, it has antiemetic and antivertigo properties and possesses antihista-minic actions, and hence may be used pre- or post-operatively (25 to 50 mg IM). The antiemetic effects of promazine may be due to its anticholinergic actions. Eur-thermore, promazine inhibits the medullary chemoreceptor trigger zone for emesis. The antipsychotic effects of promazine may be due in part to blockade of hyperactive dopaminergic transmission in the mesocortical and mesolimbic systems. 

The central anticholinergic and antihistaminic effects of promethazine causing inhibition of the medullary chemoreceptor trigger zone for emesis are responsible for its antiemetic and antivertigo effects (see also Figures 73 and 81). 

Trifluoperazine s antiemetic effects are attributed to dopamine-receptor blockade in the medullary chemorecep-tor trigger zone (see also Figure 73). 

Trimethobenzamide hydrochloride is an anticholinergic that is believed to directly affect the medullary chemoreceptor trigger zone to inhibit nausea. It is indicated in the prevention and treatment of nausea and vomiting. 

At the stem apex, alkaloids are present in all the young undifferentiated cells. According to Molle (6), the most recently formed cells have comparatively little, the precipitations increasing to a maximum density at a short distance behind the actual apex. The zone of tissue differentiation is also abundantly supplied, but as differentiation proceeds, alkaloids disappear from the vascular strands, and then from the central tissues of the pith. When differentiation is complete, the alkaloids are located principally in three concentric layers, in the epidermis and outer cortical layers just below it, in parenchyma within and adjacent to the phloem, and in the periphery of the pith just inside the xylem strands. The xylem parenchyma and medullary rays also possess alkaloids after they have disappeared from the conducting elements. 

Small B lymphocytes in mantle zone and cells within T-cell areas, medullary cells in thymus... 

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