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Metanephros
Kidney development, or nephrogenesis, describes the embryologic origins of the kidney, a major organ in the urinary system. This article covers a 3 part developmental process that is observed in most reptiles, birds and mammals, including humans. Nephrogenesis is often considered in the broader context of the development of the urinary and reproductive organs. Phases The development of the kidney proceeds through a series of successive phases, each marked by the development of a more advanced kidney: the archinephros, pronephros, mesonephros, and metanephros. The pronephros is the most immature form of kidney, while the metanephros is most developed. The metanephros persists as the definitive adult kidney. Archinephros The archinephros is considered as hypothetical or primitive kidney. Pronephros The pronephros develops in the cervical region of the embryo. During approximately day 22 of human gestation, the paired pronephri appears towards the cranial end of the intermediate m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Development Of The Urinary And Reproductive Organs
The development of the urinary system begins during prenatal development, and relates to the development of the urogenital system – both the organs of the urinary system and the sex organs of the reproductive system. The development continues as a part of sexual differentiation. The urinary and reproductive organs are developed from the intermediate mesoderm. The permanent organs of the adult are preceded by a set of structures which are purely embryonic, and which with the exception of the ducts disappear almost entirely before birth. These embryonic structures are on either side; the pronephros, the mesonephros and the metanephros of the kidney, and the Wolffian and Müllerian ducts of the sex organ. The pronephros disappears very early; the structural elements of the mesonephros mostly degenerate, but the gonad is developed in their place, with which the Wolffian duct remains as the duct in males, and the Müllerian as that of the female. Some of the tubules of the mesonephro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Intermediate Mesoderm
Intermediate mesoderm or intermediate mesenchyme is a narrow section of the mesoderm (one of the three primary germ layers) located between the paraxial mesoderm and the lateral plate of the developing embryo. The intermediate mesoderm develops into vital parts of the urogenital system (kidneys, gonads and respective tracts). Early formation Factors regulating the formation of the intermediate mesoderm are not fully understood. It is believed that bone morphogenic proteins, or BMPs, specify regions of growth along the dorsal-ventral axis of the mesoderm and plays a central role in formation of the intermediate mesoderm. Vg1/Nodal signalling is an identified regulator of intermediate mesoderm formation acting through BMP signalling. Excess Vg1/Nodal signalling during early gastrulation stages results in expansion of the intermediate mesoderm at the expense of the adjacent paraxial mesoderm, whereas inhibition of Vg1/Nodal signalling represses intermediate mesoderm formation. A li ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Embryology
Embryology (from Greek ἔμβρυον, ''embryon'', "the unborn, embryo"; and -λογία, '' -logia'') is the branch of animal biology that studies the prenatal development of gametes (sex cells), fertilization, and development of embryos and fetuses. Additionally, embryology encompasses the study of congenital disorders that occur before birth, known as teratology. Early embryology was proposed by Marcello Malpighi, and known as preformationism, the theory that organisms develop from pre-existing miniature versions of themselves. Aristotle proposed the theory that is now accepted, epigenesis. Epigenesis is the idea that organisms develop from seed or egg in a sequence of steps. Modern embryology, developed from the work of Karl Ernst von Baer, though accurate observations had been made in Italy by anatomists such as Aldrovandi and Leonardo da Vinci in the Renaissance. Comparative embryology Preformationism and epigenesis As recently as the 18th century, the prevailin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amphibian
Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial animal, terrestrial, fossorial, arboreal or freshwater aquatic ecosystems. Thus amphibians typically start out as larvae living in water, but some species have developed behavioural adaptations to bypass this. The young generally undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a secondary respiratory surface and some small terrestrial salamanders and frogs lack lungs and rely entirely on their skin. They are superficially similar to reptiles like lizards but, along with mammals and birds, reptiles are amniotes and do not require water bodies in which to breed. With their complex reproductive needs and permeable skins, amphibians are often ecological indicators; in re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kidneys
The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blood exits into the paired renal veins. Each kidney is attached to a ureter, a tube that carries excreted urine to the bladder. The kidney participates in the control of the volume of various body fluids, fluid osmolality, acid–base balance, various electrolyte concentrations, and removal of toxins. Filtration occurs in the glomerulus: one-fifth of the blood volume that enters the kidneys is filtered. Examples of substances reabsorbed are solute-free water, sodium, bicarbonate, glucose, and amino acids. Examples of substances secreted are hydrogen, ammonium, potassium and uric acid. The nephron is the structural and functional unit of the kidney. Each adult human kidney contains around 1 million nephrons, while a mouse kidney contains only ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ureters
The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually long and around in diameter. The ureter is lined by urothelial cells, a type of transitional epithelium, and has an additional smooth muscle layer that assists with peristalsis in its lowest third. The ureters can be affected by a number of diseases, including urinary tract infections and kidney stone. is when a ureter is narrowed, due to for example chronic inflammation. Congenital abnormalities that affect the ureters can include the development of two ureters on the same side or abnormally placed ureters. Additionally, reflux of urine from the bladder back up the ureters is a condition commonly seen in children. The ureters have been identified for at least two thousand years, with the word "ureter" stemming from the stem relating to urinating and seen in written records since at least the time of Hippocrates. It is, however, onl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Urinary Bladder
The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters the bladder via the ureters and exits via the urethra. The typical adult human bladder will hold between 300 and (10.14 and ) before the urge to empty occurs, but can hold considerably more. The Latin phrase for "urinary bladder" is ''vesica urinaria'', and the term ''vesical'' or prefix ''vesico -'' appear in connection with associated structures such as vesical veins. The modern Latin word for "bladder" – ''cystis'' – appears in associated terms such as cystitis (inflammation of the bladder). Structure In humans, the bladder is a hollow muscular organ situated at the base of the pelvis. In gross anatomy, the bladder can be divided into a broad , a body, an apex, and a neck. The apex (also called the vertex) is directed forward ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Connecting Tubule
The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis. The collecting duct system is the last part of nephron and participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and vasopressin (antidiuretic hormone). There are several components of the collecting duct system, including the connecting tubules, cortical collecting ducts, and medullary collecting ducts. Structure Segments The segments of the system are as follows: Connecting tubule With respect to the renal corpuscle, the connecting tubule (CNT, or junctional tubule, or arcuate renal tubule) is the most proximal part of the collecting duct system. It is adjacent to the distal convoluted tubule, the most distal segment of the renal tubule. Connecting tubules from several adjacent nephrons merge to form cortical collecting tubules, and th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Renal Tubule
The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure called Bowman's capsule. The renal tubule extends from the capsule. The capsule and tubule are connected and are composed of epithelial cells with a lumen. A healthy adult has 1 to 1.5 million nephrons in each kidney. Blood is filtered as it passes through three layers: the endothelial cells of the capillary wall, its basement membrane, and between the foot processes of the podocytes of the lining of the capsule. The tubule has adjacent peritubular capillaries that run between the descending and ascending portions of the tubule. As the fluid from the capsule flows down into the tubule, it is processed by the epithelial cells lining the tubule: water is reabsorbed and substances are exchanged (some are added, others are removed); first with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Renal Pelvis
The renal pelvis or pelvis of the kidney is the funnel-like dilated part of the ureter in the kidney. It is formed by the covnvergence of the major calyces, acting as a funnel for urine flowing from the major calyces to the ureter. It has a mucous membrane and is covered with transitional epithelium and an underlying lamina propria of loose-to-dense connective tissue. The renal pelvis is situated within the renal sinus alongside the other structures of the renal sinus. The renal pelvis is the location of several kinds of kidney cancer and is affected by infection in pyelonephritis. Clinical significance The renal pelvis is the location of several kinds of kidney cancer and is affected by infection in pyelonephritis. A large "staghorn" kidney stone may block all or part of the renal pelvis. The size of the renal pelvis plays a major role in the grading of hydronephrosis. Normally, the anteroposterior diameter of the renal pelvis is less than 4 mm in fetuses up to 32 weeks ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Renal Calyx
The renal calyces are chambers of the kidney through which urine passes. The minor calyces surround the apex of the renal pyramids. Urine formed in the kidney passes through a renal papilla at the apex into the minor calyx; two or three minor calyces converge to form a major calyx, through which urine passes before continuing through the renal pelvis into the ureter. Function Peristalsis of the smooth muscle originating in pace-maker cells originating in the walls of the calyces propels urine through the renal pelvis and ureters to the bladder. The initiation is caused by the increase in volume that stretches the walls of the calyces. This causes them to fire impulses which stimulate rhythmical contraction and relaxation, called peristalsis. Parasympathetic innervation enhances the peristalsis while sympathetic innervation inhibits it. Clinical significance A "staghorn calculus" is a kidney stone that may extend into the renal calyces. A renal diverticulum is diverticulum of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Collecting Duct System
The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis. The collecting duct system is the last part of nephron and participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and vasopressin (antidiuretic hormone). There are several components of the collecting duct system, including the connecting tubules, cortical collecting ducts, and medullary collecting ducts. Structure Segments The segments of the system are as follows: Connecting tubule With respect to the renal corpuscle, the connecting tubule (CNT, or junctional tubule, or arcuate renal tubule) is the most proximal part of the collecting duct system. It is adjacent to the distal convoluted tubule, the most distal segment of the renal tubule. Connecting tubules from several adjacent nephrons merge to form cortical collecting tubules, and the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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