Fluid homeostasis

The family of apelin peptides is derived from a single gene, activate a single G-protein-coupled receptor and are substrates for the angiotensin converting enzyme-2 (ACE2). Apelins regulate cardiovascular function and fluid homeostasis. The apelin receptor also functions as a co-receptor for infection of CD4-positive cells by human immunodeficiency vims ( HIV). 

The renin-angiotensin-aldosterone system (RAAS) generates the peptide hormone angiotensin II and subsequently the mineralocorticoid aldosterone, which both exert considerable impact on blood pressure ( blood pressure control) and fluid homeostasis, and... 

Electrolytes are involved in many metabolic and homeostatic functions, including enzymatic and biochemical reactions, maintenance of cell membrane structure and function, neurotransmission, hormone function, muscle contraction, cardiovascular function, bone composition, and fluid homeostasis. The causes of electrolyte abnormalities in patients receiving PN may be multifactorial, including altered absorption and distribution excessive or inadequate intake altered hormonal, neurologic, and homeostatic mechanisms altered excretion via gastrointestinal and renal losses changes in fluid status and fluid shifts and medications. 

Ion transport processes of the cornea and the conjunctiva can play an important role in maintaining intra- and extracellular fluid homeostasis, signal transduction, and intercellular communication. As all these functions may contribute to the modulation of drug transport (see Section IV.B), it is essential that the baseline ion transport processes in the cornea and the conjunctiva be understood. 

Like nitric oxide, the discovery of the eicosanoid signalling molecules was a significant event in twentieth century physiology, due largely to research led by Sir John Vane (Nobel Prize 1982). The diverse actions of the eicosanoids include roles in muscle contraction, blood coagulation, salt and fluid homeostasis, inflammatory responses and pain sensitivity. 

The stratum corneum consists of separated, nonviable, cornified, almost nonpermeable corneocytes embedded into a continuous lipid bilayer made of various classes of lipids, for example, ceramides, cholesterol, cholesterol esters, free fatty acids, and triglycerides [6], Structurally, this epidermis layer is best described by the so-called brick-and-mortar model [7], The stratum corneum is crucial for the barrier function of the skin, controlling percutaneous absorption of dermally applied substances and regulating fluid homeostasis. The thickness of the stratum corneum is usually 10-25 /an, with exceptions at the soles of the feet and the palms, and swells several-fold when hydrated. All components of the stratum corneum originate from the basal layer of the epidermis, the stratum germinativum. 

Postsynaptic Hj- and Hj-receptors are responsible for a variety of processes in the CNS. Hi-receptors mediate the maintenance of wakeful states, while Hj- and Hj-receptors participate in the regulation of blood pressure, body temperature, fluid homeostasis, and pain sensation. Presynaptic Hj-receptors serve as feedback inhibitors of the release of histamine, norepinephrine, and other neurotransmitters. 

Aperia A, Broberger O, Thodenius K, Zetterstrom R. Development of renal control of salt and fluid homeostasis during the first year of life. Acta Pediatr Scand 1975 64 393-8. 

A. Renin-angiotensin family. The major function of renin-angiotensin system (RAS) in periphery is to maintain body-fluid homeostasis and regulate blood pressure. 

Birnbaumer M. The V2 vasopressin receptor mutations and fluid homeostasis (Review). Cardiovasc Res 2001 51 409-15. 

All workers, with one exception [248], found that enzymes and related substances were affected by phosgene, and in vitro studies have shown it to react with a number of tissue-specific amino acids and with some hormones e.g. insulin), as well as with enzymes [731]. It has been speculated [443] that it is the decrease in available energy (via ATP) for maintaining pulmonary ionic and fluid homeostasis which contributes to the formation of oedema fluid [731]. Further work on this topic is needed for clarification. 

Wangemann P (2006) Supporting sensory transduction cochlear fluid homeostasis and the endocochlear potential. J Physiol 576(Pt 1) 11-21... 

Norepinephrine (NE) and epinephrine (EPI) act as neurotransmitters and hormones in both the peripheral and central nervous systems (CNS). NE is released from neurons throughout the CNS and periphery to participate in a variety of physiological fimctions, while both NE and EPI are released from the adrenal medulla in response to stress. NE and EPI modulate fluid homeostasis, cardiac fimction, energy metabolism, and may play a role in depression. At the cellular level, these actions are mediated by multiple adrenergic receptor (AR) subtypes and second messenger systems. 

Another peptide, atrial natriuretic peptide, does not appear to be as specific as oxytocin and somatostatin. Central administration of atrial natriuretic peptide has been shown to attenuate both the increase in water intake caused by water deprivation and the increase in sodium intake caused by sodium depletion (Nakamura, Katsuura, Nakao, Imura, 1985 Tarjan, Denton, Weisinger, 1988 Weisinger, Blair-West, Denton, Tarjan, 1992). Atrial natriuretic peptide, a28-amino acid peptide, audits receptors are distributed widely throughout the brain including many of the areas thought to be involved in body fluid homeostasis (e.g., many of the brain areas that contain ANG II receptors such as the SFO, MnPO, OVLT, and PVN) (Mendelsohn, Allen, Chai, Sexton, Figdor, 1987 Quirion et al.. 1984),... 

AVP is a pituitary peptide hormone that plays an important role in regulation of renal water and solute excretion. AVP secretion is linked directly to changes in plasma osmolality, thus attempting to maintain body fluid homeostasis. The physiologic effects of AVP are mediated through the Via and V2 receptors. Via receptors are located in vascular smooth muscle and in myocytes, where their stimulation by AVP results in vasoconstriction and increased cardiac contractility, respectively. V2 receptors are located in the collecting duct of the kidney, where AVP stimulation causes reabsorption of free water. 

Skorecki KL, Brenner BM. Body fluid homeostasis. A contemporary overview. Am J Med 1981 70 77-88. 

Disturbances of gastrointestinal function are often accompanied by electrolyte imbalance due to fluid losses by emesis (vomiting), volvulus (dilation), diarrhea, or other perturbations of many varied mechanisms for electrolyte and fluid homeostasis (see... 

Rowland, N. E., B. E. Goldstein, and K. L. Robertson. 2003. Role of angiotensin in body fluid homeostasis of mice Fluid intake, plasma hormones and brain Fos. American Journal of Physiology Regulatory Integrative and Comparative Physiology 284 R 1380-1381. 

Silveira, P. R, J. Gil, L. Casis, and J. Irazusta. 2004. Peptide metabolism and the control of body fluid homeostasis. Current Medicinal Chemistry and Cardiovascular Hematology Agents 2 219-238. 

Fig. 4.10. Body fluid homeostasis (constant body water balance). Intake is influenced by availability of fluids and food, thirst, hunger, and the ability to swallow. The rates of breathing and evaporation and urinary volume influence water loss. The body adjusts the volume of urinary excretion to compensate for variations in other types of water loss and for variations in intake. The hormones aldosterone and antidiuretic hormone (ADH) help to monitor blood volume and osmolality through mechanisms regulating thirst and sodium and water balance.

The lymphatic system is a series of vessels for transporting back to the circulation, the fluid, cells and macromolecules that escape from the blood vascular system. It is therefore an essential part of the circulatory system. In normal physiology the lymphatics therefore play a key role in fluid homeostasis and immune cell trafficking. In pathological conditions aberrant lymphatic vessel function is associated with conditions such as lymphoedema and cancer (Baldwin et al 2002). 

Recently, Lautenschlager et al. (2010) described a multiparameter model in isolated rat intestinal segments to allow perfusion through the mesenteric artery and the gut lumen. In this model, blood vessels, lymphatics, interstitial space, and lumen are maintained, allowing the assessment of potential effects of drugs on fluid homeostasis, barrier functions, transport mechanisms, immtme responses, and gut motility in situ. 

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