D. hawks and the lizards they feed on
The t<u>unica media</u> is composed of an endothelial layer that is continuous with the endocardium of the heart.
<h3>What is tunica media?</h3>
Collagen, elastin, and smooth muscle cells make up tunica media. It is located halfway between the tunica externa and the tunica intima. The transverse arrangement of its strands and color make the middle coat (tunica medium) distinct from the inner (tunica intima). It not only supports the vessel but also alters the vessel's width to control blood pressure and flow.
Elastic fibers make up the majority of the tunica media in bigger vessels. The number of elastic fibers reduces as arteries get smaller, whereas the number of smooth muscle fibers grows. The strongest of the three layers is the tunica adventitia, which is the top layer. Elastic and collagenous fibers make up its structure.
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Answer:
Leptin is a protein hormone composed of 167 amino acids of the cytosine family, it is synthesized mainly by white adipose tissue. The leptin receptor is related to that of receptors for cytosines (since it uses Janus or JAK type kinases and STAT-3 proteins as intracellular mediators of transcription pathway), it is predominantly found in the hypothalamus (particularly in the arcuate nucleus and to a lesser extent in the nuclei dorsomedial and ventromedial), hippocampus and cerebellum. There is evidence that leptin acts at the level of the arcuate nucleus, preventing the formation of NPY.
Explanation:
Leptin is produced exclusively in adipose tissue cells in a wide variety of species, including humans, and its concentration is higher in overweight than in lean individuals. The biological actions of leptin can be classified into two groups, those that are exerted in the tissues of the central nervous system, mainly the hypothalamus, and those that are carried out on the peripheral tissues. The former regulate body weight downward, decrease food intake, increase basal energy expenditure and modify some neuroendocrine functions such as reproduction, while the latter have effects on proliferation, differentiation and metabolism of peripheral tissues. The leptin that reaches the hypothalamus, in addition, inhibits protein synthesis and the secretion of neurons producing NPY / AgRP of the arcuate nucleus and stimulates the synthesis and secretion of those containing POMC. NPY (neuropeptide Y) is produced in the hypothalamic arcuate nucleus. This neurotransmitter arrives through the projections of the neurons of said nucleus to the paraventricular nucleus, which is the area where it is released. There are several studies that have shown that an increase in NPY leads to an increase in the sensation of hunger and thus to hyperphagia and obesity. Leptin acts at the level of the arcuate nucleus, preventing the formation of NPY. The leptin receptor lacks enzymatic activity in its intracellular domain. Instead, it is linked to members of the janus kinase family, which belong to a class of tyrosine kinases. The binding of the ligand activates the Jak kinase and leads to the phosphorylation of certain cytoplasmic proteins. Within these proteins there is a class of cytoplasmic transcription factors called signal transducers and activators of transcription (STAT).
