The renal system
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella in Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
The kidneys are essential excretory organs that remove the waste products of metabolism from the body. In addition to their role in excretion, the kidneys also function in regulation of blood pressure, blood volume and erythropoiesis. The nephron is the functional unit of the kidney. Each nephron is comprised of a glomerulus, which acts as a selective filter, and the renal tubules, which selectively absorb and secrete solutes between the filtrate and blood. In order for the nephrons to function normally, three things must occur. First, there must be adequate blood flow through the glomerular capillaries. Second, the glomerular capillaries, which selectively filter blood, must be intact. Normal glomeruli allow fluids and small solutes to be filtered into the renal tubules but not proteins or blood cells. Third, the tubules of the kidney must be able to selectively reabsorb essential substances from the filtrate while excreting other substances into the filtrate to be eliminated in the final urine.
Fluid balance and continence care
Barbara Smith, Linda Field in Nursing Care, 2019
The kidneys are positioned against the posterior abdominal wall, lying close to the aorta and inferior vena cava, to which they are joined by blood vessels (see Figure 6.3). The most important function of the kidney is to maintain constant composition and volume of body fluids, primarily the blood, from which the other fluids are formed. The functional unit of the kidney is the nephron, which is responsible for filtering the blood and removing metabolic waste. In an average adult, 1200 mL of blood (about 21 per cent of the cardiac output) passes through the kidneys every minute (Kozier et al.,2004, 2014). Each kidney contains about one million nephrons. The filtration process through the nephrons results in the production of urine. Approximately 1500 mL of urine is produced and excreted daily.
Practice Paper 9: Answers
Anthony B. Starr, Hiruni Jayasena, David Capewell, Saran Shantikumar in Get ahead! Medicine, 2016
Antidiuretic hormone (ADH, also known as arginine vasopressin) is secreted from the posterior pituitary gland in response to a high plasma osmolality, hypovolaemia or stress. Its main function is to stimulate the reabsorption of water from the collecting ducts of the nephron into the circulation. This results in a reduction in plasma osmolality and urine output and an increase in urine osmolality and blood pressure. Diabetes insipidus (DI) is a condition caused by either an absolute lack of ADH secretion (cranial DI) or renal insensitivity to its actions (nephrogenic DI). DI usually presents with massive polyuria, as water cannot be reabsorbed from the collecting ducts. As a result, patients with DI are often dehydrated, and consume massive amounts of water to maintain their fluid balance. Other conditions that may present in a similar manner include diabetes mellitus, hypercalcaemia and psychogenic polydipsia. DI is usually diagnosed using the water deprivation test. This involves measuring the patient’s urine volume, concentration and plasma osmolality while depriving the patient of water. A positive result is recorded when water deprivation fails to concentrate urine due to a lack of ADH or insensitivity to its actions. If the initial test is positive, the patient is given a dose of desmopressin – a synthetic ADH analogue. If the patient concentrates their urine in response to desmopressin, the defect must be central and a diagnosis of cranial DI can be made. If, however, the urine is not concentrated following desmopressin administration, there is end-organ resistance to ADH, i.e. nephrogenic DI.
Advances in understanding vertebrate nephrogenesis
Published in Tissue Barriers, 2020
Joseph M. Chambers, Rebecca A. Wingert
Following IM specification, the progression of vertebrate renal development involves the stepwise generation and degeneration of several kidney forms: the pronephros, mesonephros, and metanephros. Each kidney iteration develops along the anterior-posterior embryonic axis, where each subsequent version becomes more structurally complex than the previous structure. The pronephros emerges first, and while it is vestigial/nonfunctional in mammals, it is functional in other vertebrates such as fish and frogs.23 The mesonephros is further developed and partially functional in mammals, while serving as the final kidney form in amphibians and fish.24 However, the fully formed and functional version of this vital organ in mammals is the metanephros, which develops through branching morphogenesis events that result in an arborized structure essential for fluid homeostasis. Importantly, all three vertebrate kidney forms share the overall structure of the kidney’s functional unit: the nephron. Broadly, the nephron is composed of a blood filter, a segmented tubule, and a collecting duct system to shuttle urine to the bladder.
A novel role of HIF-1α/PROX-1/LYVE-1 axis on tissue regeneration after renal ischaemia/reperfusion in mice
Published in Archives of Physiology and Biochemistry, 2019
Nephron formation is an important stage of kidney development in neonates. In adults, the number of nephrons in the kidney is consistent. Once kidney function is lost, it can only be partially recovered (Hartman et al.2007, Humphreys et al.2008). To date, the source of progenitor cells, the associated-cooperation procedure, and signal transduction for renal tissue repair remain controversial. It is worthwhile to study these signals in kidney development and apply the information in therapeutic strategies of repair renal injury or disease. Several critical factors have been noted recently. First, prospero homeobox-1 (PROX-1) is a transcriptional factor for embryonic morphogenesis and it regulates the formation and development of organs (Elsir et al.2012). Specifically, it reportedly is required in the development of the lymphatic vascular system (Wigle and Oliver 1999, Wigle et al.2002), regulates hepatocyte growth (Sosa-Pineda et al.2000, Wilting et al.2002), and involves in the development of cardiac size (Risebro et al.2009) In addition, PROX-1 reportedly regulates the thin limb cell fate in kidney and prolongs the expression of the renal papilla and maturation of the Henle’s loop (Kim et al.2015).
The effect of cholesterol overload on mouse kidney and kidney-derived cells
Published in Renal Failure, 2018
Shoko Honzumi, Miho Takeuchi, Mizuki Kurihara, Masachika Fujiyoshi, Masashi Uchida, Kenta Watanabe, Takaaki Suzuki, Itsuko Ishii
In the kidney of the HCD mice, the gap between glomerulus and the surrounding Bowman’s capsule decreased (Figures 1(A,B)). Tomizawa et al. [24] have reported that HCD mice showed significantly higher levels of blood urea nitrogen, creatinine and uric acid compared to the ND mice. In HCD mice, Tomizawa et al. showed that the quantity of glomerulus filtration decreased. It is considered that the decrease in quantity of glomerulus filtration causes the filtration pressure of the remaining individual nephrons to rise [27], which may have affected the size of the gap between the glomerulus and the surrounding Bowman’s capsule. It is reported that the damage of podocyte causes leakage of protein from the basement membrane, inducing further damage to the podocyte and causing loss of podocyte, leaving bare basement membrane. Parietal epithelial cells attach to the bare basement membrane, leading to the formation of a tuft adhesion to the Bowman’s capsule [28,29]. LeHir and Kriz [30] proposed that cellular adhesion was formed predominantly by injured podocytes. From the above, there is a possibility that the decreased gap between the glomerulus and the Bowman’s capsule by cholesterol overload enhances the adhesion to Bowman’s capsule.
Related Knowledge Centers
- Kidney
- Renal Corpuscle
- Capillary
- Glomerulus
- Bowman'S Capsule
- Epithelium
- Lumen
- Endothelium
- Basement Membrane
- Podocyte