China
Africa
Explore chapters and articles related to this topic
Occupational toxicology of the kidney
Published in Chris Winder, Neill Stacey, Occupational Toxicology, 2004
The cells of the distal tubule contain numerous mitochondria, but do not have a well-developed brush border or lysosomal system. Specialised cells in the macula densa, which is part of the juxtaglomerular apparatus and found adjacent to the glomerulus, provide a feedback loop triggered by increased solute concentration. This signal results in decreased blood flow into the glomerulus, thereby decreasing GFR in the nephron (tubuloglomerular feedback). The distal tubule is relatively impermeable to water. The distal tubule and collecting duct reabsorb sodium chloride and water, and acidify urine.
Kidney Structure and Physiology
Published in Joseph D. Bronzino, Donald R. Peterson, Biomedical Engineering Fundamentals, 2019
Joel M. Henderson and Mostafa Belghasem
glomerulus. Blood ows into the glomerulus via the aerent arteriole and enters the glomerular capillaries. e glomerular capillary walls are highly permeable to water and small solutes, and a substantial proportion of the uid owing through the glomerulus (about 20%) crosses this barrier. e resulting ultraltrate accumulates in the space surrounding the glomerular capillary tu, called Bowman’s space, and is collected by a cup-like structure that surrounds and closely approximates the tu called Bowman’s capsule. Bowman’s space is continuous with the lumen of the tubule, thus accumulating ultraltrate ows into the tubular lumen. e ow continues radially inward along the tubule, where the ultraltrate is processed further through reabsorption and secretion by the tubular epithelial cells. e initial tubular segment, the proximal convoluted tubule, meanders in the vicinity of its associated glomerulus. As the tubule continues, it becomes directed toward the deeper kidney and transitions into a thin-walled tube with attened epithelium, which penetrates the medulla. In nephrons arising deep in the cortex, this tube penetrates the medullary pyramids and is responsible for establishing the countercurrent ow needed to recover the ltered water. is thin tube, the loop of Henle, eventually turns 180° and reemerges in the cortex. ere, the tubule redevelops a thickened cuboidal epithelium, and again meanders in the vicinity of its corresponding glomerulus, becoming the distal convoluted tubule. is portion of the tubule passes next to the vascular pole of the glomerulus at one point, where a small patch of specialized tubular epithelial cells called the macula densa are positioned. e basal aspect of these cells makes contact with a small collection of cells adjacent to the arterioles at the glomerular vascular pole, called the juxtaglomerular apparatus. ese structures play an important role in the regulation of glomerular perfusion through the regulation of constriction of the arterioles serving the glomerulus. e distal convoluted tubule continues toward the medulla, and eventually coalesces with other tubules to form larger collecting ducts. e collecting ducts continue radially through the medullary pyramid to the papilla, where they open into the adjacent calyx. e processed ultraltrate, now called urine, ows out of the collecting ducts at the papilla into the calyx, and the adjoining renal pelvis.
Effects of continuous and pulsatile flows generated by ventricular assist devices on renal function and pathology
Published in Expert Review of Medical Devices, 2018
Takuma Miyamoto, Jamshid H. Karimov, Kiyotaka Fukamachi
Under physiologic conditions, the RAA system is activated in response to decreases in blood pressure or salt and extracellular fluid volume [59]. At the organ level, secretion of renin from juxtaglomerular cells is controlled by a number of factors that become active in the direct vicinity of renin-secreting cells [60]. These factors comprise neurotransmitters released from sympathetic nerve endings, which are found at high density around renin-secreting cells, angiotensin II, autacoids released from endothelial or macula densa cells, various hormones, and the intraluminal blood pressure in afferent arterioles. Renin secretion from the kidneys is inversely related to renal perfusion pressure. Renal baroreceptor mechanisms not only regulate acute renin secretion but also the long-term transformation of vascular SMCs into renin producers.