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Circadian regulation of sleep during ontogenesis in humans
Grieblová, Adéla ; Sumová, Alena (advisor) ; Soták, Matúš (referee)
The circadian system has evolved as an adaptation to periodically changing conditions on Earth. In mammals, and therefore in humans, the circadian system consists of the central and perip- heral oscillators generating a circadian rhythm. One of the most significant process exhibiting circadian rhythm is the sleep-wake cycle. Sleep is regulated by cooperation of circadian and homeostatic process. There are changes in circadian regulation of sleep during ontogenesis in human. The changes mainly releate to chronotype, i.e., to the diurnal preferences of activity and sleep. In the first years of life, there is a typical morning chronotype. In the end of first decade of life, the circadian phase begins to delay and reaches its maximal eveningness during ado- lescence. In adulthood, the preference changes again toward morning chronotype and reaches extreme morningness in elderly. Changes in circadian regulation of sleep during ontogenesis depend not only on age, but also on sex. 1
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Circadian regulation of glucocorticoid secretion
Tejkal, Karel ; Sumová, Alena (advisor) ; Soták, Matúš (referee)
Glucocorticoids belong to a family of steroid hormones synthesized in the adrenal gland. They fulfill a variety of functions related to metabolism, immune response and ontogenesis. Glucocorticoids function as the end-effector of hypothalamic-pituitary-adrenal (HPA) axis and as such, their levels in blood are elevated after exposure to stressors. The basal levels of glucocorticoid also show a pronounced diurnal rhythm, suggesting involvement of the circadian clock in the regulation of HPA axis. Studies have shown that other regulatory mechanisms apart from the HPA axis are involved in regulation of diurnal glucocortioid secretion. The disturbances of the regulatory mechanisms may lead to serious pathological conditions. This thesis describes the rhythmic nature of glucocorticoid release and mechanisms by which the circadian clock exerts its influence over the rhythm. Thereafter, the feedback of glucocorticoids onto the clock system is briefly explained. Finally, some examples of a role of abnormal glucocorticoid secretion in selected pathologies are provided.
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Endothelin system and the role of salt in hypertension
Čejková, Soňa ; Vaněčková, Ivana (advisor) ; Soták, Matúš (referee)
Although hypertension is studied for several decades, this problem is still not solved. Moreover, its incidence increases. Most cases of secondary hypertension is associated with the kidneys, the most important organ regulating the volume and ionic composition of body fluids. If the kidneys are damaged, or intake of salt is excessive, they are unable to fulfill their role and blood pressure (BP) increases. Especially salt contributes to secondary hypertension. Excessive salt intake increases the volume of body fluids and subsequently increases BP, and secondary act on the mechanisms regulating BP, mainly the renin-angiotensin system (RAS) and endotelin (ET) system. Endothelin-1 (ET 1) is the main active peptide of the ET system. ET-1 is one of the most potent vasoconstrictors. It acts through ET receptors type A and B (ETA and ETB receptors), which belong to the family of receptors coupled with G-proteins. The effects of ETA and ETB receptors differ depending on the type of cells where they are located. For example, ETB receptors in vascular smooth muscle contribute to vasoconstriction, whereas the same receptors on endothelial cells of blood vessels mediate vasodilation (stimulating the production of NO). In the kidney, ET system affects excretion of Na+and water and contribute to the regulation...
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