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Thyroid Hormones and Calcium Metabolism
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The functional units of the thyroid gland are the follicles (acini). They are made up of a single layer of cuboidal epithelial cells with a central lumen filled with colloid, which is predominantly a glycoprotein, thyroglobulin. Parafollicular cells (C cells), which secrete calcitonin, are scattered between the follicles. Thyroid hormone synthesis and release is regulated by a negative feedback by the hypothalamic–pituitary–thyroid axis. Thyroid-releasing hormone is released from the median eminence of the hypothalamus and transported to the anterior pituitary gland, where it stimulates the release of TSH.
Central Nervous System Circuitry Involved in Blood Pressure Regulation
Published in Fuad Lechin, Bertha van der Dijs, Neurochemistry and Clinical Disorders: Circuitry of Some Psychiatric and Psychosomatic Syndromes, 2020
Fuad Lechin, Bertha van der Dijs, Jose Amat, Simon Villa, Alex E. Lechin
Locus coeruleus may also exert sympathoexcitatory effects through polysynaptic mechanisms. In effect, LC axons project to DR, amygdala, hippocampus, septum, and hypothalamic nuclei located outside the blood brain barrier (BBB), i.e., median eminence. All these central structures are involved in the regulation of autonomic functions.
Distribution and Characteristics of Brain Dopamine
Published in Nira Ben-Jonathan, Dopamine, 2020
The pituitary gland is suspended from the median eminence by the infundibulum (pituitary stalk) and is nested within the sella turcica of the sphenoid bone of the skull. The median eminence is one of the seven areas of the brain called circumventricular organs, which have fenestrated capillaries and are therefore devoid of the BBB [37]. As illustrated in Figure 3.9, the median eminence is composed of three distinct zones: ependymal, internal, and external. The ependymal zone forms the floor of the third ventricle and has several specialized features, including tight junctions between adjacent cells and highly specialized cells, the tanycytes. Tanycytes are glial-like cells that extend protrusions and microvilli into the cerebrospinal fluid (CSF) at their ventricular surface and long cytoplasmic processes into the body of the median eminence. Tanycytes are exposed to CSF from the third ventricle and also have an access to circulating hormones and various metabolites through the fenestrated capillaries [38]. Some of the tanycytes act as conduits for trafficking certain molecules into the brain parenchyma, while others act as neural stem/progenitor cells that supply the postnatal and adult hypothalamus with new neurons. During embryonic development, tanycytes also serve as a scaffolding for axons that enter the median eminence, guiding them to their ultimate destination in the external zone.
Possible roles of brain derived neurotrophic factor and corticotropin releasing hormone neurons in the nucleus of hippocampal commissure functioning within the avian neuroendocrine regulation of stress
Published in Stress, 2021
Hakeem J. Kadhim, Seong W. Kang, Wayne J. Kuenzel
In the PVN, CRH (Figure 3(D)), CRHR1 (Figure 3(E)) and BDNF mRNA (Figure 5(B)) levels were significantly elevated displaying a positive correlation in gene expression throughout the entire stress period. Importantly, BDNF within the PVN showed a significant increase in gene expression that preceded the significant increase of CRH and CRHR1 mRNA levels. In mammals, both acute and repeated immobilization stress increased BDNF mRNA by in situ hybridization in the PVN, lateral hypothalamus and APit (Smith et al., 1995a). Quantitative analysis of BDNF mRNA in hypothalamic tissue of rats subjected to immobilization showed rapid increases within 30 m (Tapia-Arancibia et al., 2004). Other studies in rats have shown rapid, significant increase in hypothalamic BDNF mRNA, release of ACTH and CORT all occurring at 15 m following immobilization with a peak increase in CORT occurring at 30 m. A follow up experiment injected BDNF intracerebroventricularly, showed a significant increase in ACTH and plasma CORT within 30 m and thereafter increased CRH mRNA; however, the first significant increase of the latter did not occur until 180 m when quantified by in situ hybridization. The authors suggested that BDNF may play two roles, one is that BDNF could be released from the median eminence after immobilization stress explaining its rapid involvement in the release of ACTH and CORT. A second, sustained role may be activating CRH mRNA within the PVN documented at 180 m and beyond (Givalois et al., 2004).
Hypophysitis related to immune checkpoint inhibitors: An intriguing adverse event with many faces
Published in Expert Opinion on Biological Therapy, 2021
Maria V Deligiorgi, Charis Liapi, Dimitrios T Trafalis
The aforementioned mechanisms may rationalize the predilection of ir hypophysitis for the anterior pituitary. An alternative explanation for this predilection is the distinct vascularity of the anterior pituitary, which renders it more vulnerable to immunotherapy compared to the posterior pituitary. The anterior pituitary is the most richly vascularized mammalian tissue receiving 0.8 ml/gr/min from a portal circulation linking the median eminence of hypothalamus with the anterior pituitary. Arterial blood is supplied by the superior, middle, and inferior hypophysial artery branches of the internal carotid arteries. The pituitary stalk and the posterior pituitary are supplied directly from branches of the middle and inferior hypophysial arteries [27]. Contrary to the anterior pituitary that produces and secretes ACTH, LH/FSH, TSH, GH, PRL, the posterior pituitary secrets AVP stored in the distal axon terminals of the hypothalamic magnocellular neurons, the cell bodies of which synthesize AVP as a large precursor peptide [28].
The autoimmune basis of hypopituitarism in traumatic brain injury: fiction or reality?
Published in British Journal of Neurosurgery, 2019
Viraat Harsh, Sukriti Jha, Hitesh Kumar, Anil Kumar
Animal models have permitted controlled infliction of trauma and helped discern the relationship between clinical results of TBI and dysfunction at cellular or molecular levels. A recent study by Osterstock et al described pathological alterations evident in the median eminence, which included disrupted tight junctions in tanycytes (special ependymal cells with processes extending upto hypothalamus), increased concentration of endogenous IgG near the third ventricle and increased permeability of third ventricle. What is important to note is that tanycytes are bipolar cells which provide a kind of passage between the CSF and blood in portal capillaries, transporting antigens and triggering immunological phenomena after TBI. This experimental model though still nascent, attempts to explain autoantibody development after TBI and resultant PTHP when both pituitary and stalk are normal.16–18