2014 Group Project 2

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The Group assessment for 2014 will be an online project on Fetal Development of a specific System. This page is an undergraduate science embryology student and may contain inaccuracies in either description or acknowledgements.

Renal

--Mark Hill (talk) 15:11, 26 August 2014 (EST) No subheadings yet and I even had to add your project title! Get moving.

--Mark Hill (talk) 16:00, 6 September 2014 (EST) OK some sub-headings and a few refs. No content yet expelling the feral component or how the references you have selected relate to the topic.

Introduction

The renal system's main function is the production, storage and elimination of urine, and to maintain the balance of chemicals and water of the body. Kidneys are the primary organ of the renal system, and consist of smaller units known as nephrons - which filter the blood to remove urea and other wastes, and reabsorb or excrete excess water according to the needs of the body as directed by hormones released by the pituitary glands. Nephrons are made up of glomeruli to filter the blood, tubules to reabsorb any solutes or fluids, and more tubule networks to carry the urine to the bladder and outside the body. Small amounts of urine is released from the kidneys every 1 ~ 15 seconds into the ureter, which carry the urine to the bladder. (Kim Ann Zimmermann, 2013). The bladder is a hollow organ which has the ability to change its epithelium according to how full the bladder is of urine. "The bladder's walls relax and expand to store urine, and contract and flatten to empty urine through the urethra. The typical healthy adult bladder can store up to two cups of urine for two to five hours.” (Standford, 2014) Two sphincter muscles are present at the base of the bladder, and two more at the end of the urethra (internal & external) to voluntarily control the excretion of urine.

Development of these components begin during the embryonic phase, and continue to develop and mature throughout the fetal stages. During the fetal stages, some abnormalities may form. During the embryonic period and fetal periods, the mother's placenta work to remove wastes from the fetus.

Abnormalities may arise during the embryonic and fetal stages of development of the renal system, such as Hereditary renal adysplasia, or polycystic kidney disease. Hereditary renal adysplasia is an inherited condition, where there is malformations in organs derived of the embryonic mesoderm. (Acién P, Galán F, Manchón I, Ruiz E, Acién M, Alcaraz LA. 2010. Polycystic kidney disease is a fairly common genetic disorder in which fluid-filled cysts displace normal renal tubules. (Chapin HC, Caplan MJ. 2010)

Stanford (2014). “Anatomy of the urinary system” http://www.stanfordchildrens.org/en/topic/default?id=anatomy-of-the-urinary-system-85-P01468

Kim Ann Zimmermann (2013). “Urinary System: Facts, Functions & Diseases” Feb 11 2013 http://www.livescience.com/27012-urinary-system.html

Hannah C Chapin, Michael J Caplan The cell biology of polycystic kidney disease. J. Cell Biol.: 2010, 191(4);701-10 PMID:21079243

Pedro Acién, Francisco Galán, Irene Manchón, Eva Ruiz, Maribel Acién, Luis A Alcaraz Hereditary renal adysplasia, pulmonary hypoplasia and Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome: a case report. Orphanet J Rare Dis: 2010, 5;6 PMID:20388228

Current research models

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Kidney

Early Development

The kidneys first develop in the embryo by a process called nephrogenesis, in which self-renewing mesenchymal renal stem cells produce nephrons, the main functional unit, and form a simple embryonic kidney called the pronephros. This process of nephron formation is stimulated by the signaling between the ureteric buds and these stem cells, named progenitor cells and located at the tips of the ureteric buds, causing nephrons to develop and the ureteric buds to branch.

While it is not well known the mechanisms by which nephron number is determined, the causes of several disorders and diseases, such as renal disease and hypertension, have been attributed to a low nephron count. It has been determined that a decrease in the number of progenitor cells, a possible result of genetic abnormalities, toxic insults, and nutritional deficiencies, can result in fewer branching of the ureteric buds, leading to impaired kidney growth. Therefore, nephron number is important as it can show the success/extent of nephrogenesis, and thus be used to determine if any and what genes and environmental factors may aid this process.

When sufficient development has occurred during week 3 of gestation, two pronephri are produced and nephrotomes, a series of tubules, begin to fuse together with the pronepheric duct. As the pronephri continue to develop, they elongate and induce the nearby mesoderm to form mesonephri, and the pronepheric duct to become the mesonephric (Woffian) duct. Towards the bottom of this duct, close to where it connects to the cloaca, is the ureteric bud connected by the ureter. Surrounding this bud is a mass of metanephric mesoderm (blastema), the two of which react together to form the metanephros which goes on to form the mature kidney. The cells of the ureteric bud differentiate to form the major and minor calyces as well as the collecting tubules, while the cells of the metanephrogenic blastema develop into the renal tubules and glomeruli. This process begins from as early as week 3 and continues until week 8 of gestation. The development of the nephrons however, continue through to week 32-36 of gestation.

A drawing of the following picture will be made and uploaded as a direct copy is prohibited under copyright. It shows the formation of the kidney during the embryonic development:http://renalsystem.weebly.com/uploads/1/4/9/9/14997296/9282501_orig.jpg?1

Fetal Development

There are a number of factors that occur in regards to the kidneys during the fetal period of development, the most important of which is the continued generation of nephrons. There are specific genes expressed as well as hormones released for their generation, with vasculature created to supply the newly formed kidneys. There are certain events that occur for the kidneys to achieve their correct anatomical position before they are fully formed, as well as further growth post-natally before the kidneys are fully matured.

An embryonic gene named gremlin (GREM1) has been found to play a key role in the formation of the kidneys and nephrogenesis in general. When fully formed, the expression of this gene is relatively low in an adult. However, it is thought that many renal diseases and their progressions are linked to an overexpression of this gremlin gene.

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At birth, although the infant’s kidneys are developed enough to maintain homeostasis and are sufficient for growth and development, their functional capabilities are decreased. This is a result of the transition from depending on the placenta to maintain homeostasis of fluid and electrolyte balance while in-utero, to maturation of the neonatal glomeruli once born.

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Urine Formation during the fetal period

The amniotic fluid is mainly composed of nutrients that will supply the fetus, and its components fluctuate during pregnancy according to the fetal development. [5] As the fetus develops, it excretes fetal urine into the amniotic sac.

Polyhydramnios and oligohydramnios

amniotic fluid: not just urine anymore [5]

Sebe. P., Schwentner. C., Oswald. J., Radmayr. C., Bartsch. G., Fritsch. H. Fetal development of striated and smooth muscle sphincters of the male urethra from a common primordium and modifications due to the development of the prostate: an anatomic and histologic study. Prostate (2005) [1]

Werff. V. D., Nievelstein. R.A, Brands. E., Luijsterburg. A.J., Vermeij-Keers. C. Normal development of the male anterior urethra. Teratology (2005) [2]

Sebe. P., Fritsch. H., Oswald. J., Schwentner. C., Lunacek. A., Bartsch. G., Radmayr. C. Fetal development of the female external urinary sphincter complex: an anatomical and histological study. J urol (2005) [3]

Ludwikowski B, Hayward OI, Brenner E, Fritsch H. The development of the external urethral sphincter in humans. BJU Int. 2001 Apr;87(6):565-8. [4]

Bladder

The urinary bladder develops in the first 12 weeks of gestation from the urogenital sinus and the surrounding splanchnic mesenchyme, these development events are controlled by by complex epithelial–mesenchymal signals. The vesical part of the urogenital sinus is attached to the allantois and goes on to form the bladder.

During foetal development the bladder is supplied by an increasing number of nerves in the detrusor muscle, as the gestational period continues different peptide containing nerves are observed.

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During development the bladder only produces immature reflexes rather than the voluntary bladder control that is only seen once the infant is toilet trained. It is suggested that the switch between involuntary reflexes and voluntary contractions is due to the development of the central and peripheral neural pathways that control the contraction of the bladder.

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Abnormalities

Renal agenesis

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The overexpression of the gremlin gene (GREM1) has been found to be a cause of renal disease.

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