Glandular cells

The function of a neuron is to communicate or relay information to another cell by way of an electrical impulse. A synapse is the site at which the impulse is transmitted from one cell to the next. A neuron may terminate on a muscle cell, glandular cell, or another neuron. The discussion in this chapter will focus on neuron-to-neuron transmission. At these types of synapses, the presynaptic neuron transmits the impulse toward the synapse and the postsyn-aptic neuron transmits the impulse away from the synapse. Specifically, it is the axon terminal of the presynaptic neuron that comes into contact with the cell body or the dendrites of the postsynaptic neuron. Most neurons, particularly in the CNS, receive thousands of inputs. As will become evident, the transmission of the impulse at the synapse is unidirectional and the presynaptic neuron influences activity of the postsynaptic neuron only. 

Experiment 8. The observation of the secretory hairs and their secretion Cell-donor of allelochemicals releases the substances out. The process may be seen with the help of LSCM technique as the study of the fluorescence of various external secretory structures. Such structures are glandular cells, which contained many potentially fluorescent substances (Roshchina and Roshchina, 1993). One of the example is shown for secretory leaf hair of allelopathically active species Solidago virgaurea L. (Fig.ll). 

Fig. 13.1 Triple immunostaining of a normal duct epithelium for K14 (Ckl4, pink), K5 (Ck5/6, red), and K8/18 8 (Ckl8, green). Note that few progenitor cells are stained only for K5 and/or K14 (1), whereas most are stained both for basal (usually K5) and glandular keratins K8/18. These cells represent intermediary glandular cells. Few cells stained only for K8/18 are differentiated glandu lar cells...

Fig. 13.8 Triple staining of a usual ductal hyperplasia for K5 (red), K8/18 (green) and SMA (pink). Note that the proliferating cells are only glandular cells. Myoepithelial cells are seen only in the outer layer (pink) and do not participate in the proliferation process...

Each hormone is the center of a hormonal regulation system. Specialized glandular cells synthesize the hormone from precursors, store it in many cases, and release it into the bloodstream when needed (biosynthesis). For transport, the poorly water-soluble lipophilic hormones are bound to plasma proteins known as hormone carriers. To stop the effects of the hormone again, it is inactivated by enzymatic reactions, most of which take place in the liver (metabolism). Finally, the hormone and its metabolites are expelled via the excretory system, usually in the kidney (excretion). All of these processes affect the concentration of the hormone and thus contribute to regulation of the hormonal signal. 

Hormones transfer signals by migrating from their site of synthesis to their site of action. They are usually transported in the blood. In this case, they are said to have an endocrine effect (1 example insulin). By contrast, tissue hormones, the target cells for which are in the immediate vicinity of the glandular cells that produce them, are said to have a paracrine effect (2 example gastrointestinal tract hormones). When signal substances also pass effects back to the cells that synthesize them, they are said to have an autocrine effect (3 example prostaglandins). Autocrine effects are often found in tumor cells (see p. 400), which stimulate their own proliferation in this way. 

The cholesterol required for biosynthesis of the steroid hormones is obtained from various sources, it is either taken up as a constituent of LDL lipoproteins (see p. 278) into the hormone-synthesizing glandular cells, or synthesized by glandular cells themselves from acetyl-CoA (see p. 172). Excess cholesterol is stored in the form of fatty acid esters in lipid droplets. Hydrolysis allows rapid mobilization of the cholesterol from this reserve again. 

The hydrophilic hormones are derived from amino acids, or are peptides and proteins composed of amino acids. Hormones with endocrine effects are synthesized in glandular cells and stored there in vesicles until they are released. As they are easily soluble, they do not need carrier proteins for transport in the blood. They bind on the plasma membrane of the target cells to receptors that pass the hormonal signal on (signal transduction see p.384). Several hormones in this group have paracrine effects—i.e., they only act in the immediate vicinity of their site of synthesis (see p. 372). 

These transmitters are synthesized from the amino-acid L-tyrosine (see Fig. 4). In the axon and the glandular cells of the adrenal medulla L-tyrosine... 

Noradrenaline is not only present in the sympathetic nerve endings but in the glandular cells of the adrenal medulla as well. The contents of noradrenaline in the medulla is dependent on the functional state of the gland and the species. Noradrenaline is always the precursor of adrenaline. In the central nervous system there are regions with a high noradrenaline content the hypothalamus and vegetative centers. 

Adrenaline is the main hormone released from the adrenal medulla. The glandular cells in this structure correspond to the second, postganglionic neuron of the sympathetic nervous system. Furthermore, adrenaline can be found in chromaffin cells in various tissues. For the better understanding of the function of noradrenaline it is important to realize that this substance, as a neuronal transmitter, affects only the innervated target structure, that is it acts mainly locally. Among these effects are the activation of the musculus dilatator to widen the pupillae in response to a reduced light intensity, an increase in heart rate as a response to a blood pressure drop due to a reduction of the peripheral resistance or constriction... 

The functional unit of the central nervous system (CNS) is the neuron, and most neuropharmacological agents have the neuron as their primary site of action. CNS neurons are capable of transmitting information to and receiving information from other neurons and peripheral end organs, such as muscle cells, glandular cells, and specialized receptors, for example, those involved with proprioception, temperature sensing, and so on. 

Brossut, R. and Roth, L. M. (1977). Tergal modifications associated with abdominal glandular cells in the Blattaria. Journal of Morphology 151 259-297. 

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