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Kidney Lect 2
Development of the Urinary System
| Question | Answer |
|---|---|
| gastrulation, subdivision of the mesodermal germ layer into paraxial, intermediate, and lateral mesoderm | Week 3 |
| formation of the pronephric duct (subsequently called mesonephric duct) appearance and regression of pronephric tubules appearance of mesonephric tubules | Week 4 |
| appearance of adult kidney precursors (metanephric mesenchyme and ureteric bud) | Week 5 |
| cranial (thoracic) mesonephros undergoes massive regression caudal (lumbar) mesonephric tubules function metanephric excretory units begin to form kidneys begin to ascend | Week 6 |
| division of the cloaca complete regression of the allantois urogenital component of the cloacal membrane ruptures | Week 7 |
| kidneys reach a lumbar position mesonephros ceases to function and regresses metanephric kidney begins to function | Week 9-10 |
| At three and a half weeks of development, the ___ ___ extends on each side of the embryo from cervical to sacral regions. | intermediate mesoderm |
| This mesoderm gives rise to three paired sets of excretory structures but only the ___ components will develop into adult kidneys. Excretory structures in the ____ and ___ regions are transient. | sacral; cervical; thoraco-lumbar |
| During the 4th week of development, an elongated duct forms within the intermediate mesoderm on each side of the embryo and extends from the ___ ___ to the expanded end of the ____. | cervical region; hindgut (the cloaca). |
| On each side of the embryo, interactions between this duct and the ___ ___ ___ lead to the differentiation of excretory tubules. | adjacent intermediate mesoderm |
| The pronephric kidney (pronephros) | consists of small epithelial clusters or rudimentary tubules in the cervical region. The pronephros is nonfunctional in humans and present only during the 4th week. |
| At early stages of the pronephric kidney, the associated duct is called the ___ duct. At later stages, this duct is known as the ___ or ___ duct as its primary association is with the ___. | pronephric; mesonephric or Wolffian; mesonephros |
| The mesonephric kidney (mesonephros) | consists of clusters of tubules that form a large swelling in the thoraco-lumbar region. |
| Mesenephronic duct | (the original pronephric duct) duct associated with mesonephric kidney tubules |
| ____ tubules resemble simplified versions of adult excretory tubules and appear to function during the 2nd month of evelopment. | Mesonephric tubules resemble simplified versions of adult excretory tubules and appear to function during the 2nd month of development. |
| What happens to the cranial mesenephros? | The tubules of the cranial mesonephros undergo extensive regression shortly after they form. |
| What happens to the tubules of the caudal mesonephros? | The tubules of the caudal mesonephros ultimately regress as well, but some of their cellular components contribute to the gonads in males. |
| What happens to the mesonephric ducts? | The mesonephric ducts regress in females but form the epididymis and vas deferens in males. |
| The metanephric kidney (metanephros) | definitive kidney |
| What are the two embryonic components that contribute to the formation of each adult kidney? | ureteric bud and the metanephric mesenchyme. |
| Ureteric bud | ureteric bud emerges as a bud off the distal end of the mesonephric duct. Each bud penetrates intermediate mesoderm in the sacral region. |
| Metanephric mesenchyme | This intermediate mesoderm is called the metanephric mesenchyme or metanephric blastema. |
| The ureteric bud and its branches ultimately give rise to what structures (5)? | The ureter, renal pelvis, the calyses, and the collecting ducts and tubules. |
| What (3) major events mark the morphogenesis of the ureteric bud and the metanephric mesenchyme? | 1) The ureteric bud emerges from the mesonephric duct; undergoes repeated branching and elongation 2) Mesenchyme condenses around tips of ureteric bud + branches 3) Mesenchymal cells transform into epithelial cells + differentiate into nephrons. |
| Derivatives of the metanephric mesenchyme include what (3) structures? | the renal corpuscle (except the blood vessels), the loop of Henle, and the proximal and distal convoluted tubules. |
| the differentiation of the ureteric bud and the metanephric mesenchyme depend on __ ___ signals. | mutually inductive |
| How do the metanephric mesenchyme and ureteric bud signal to each other during development? | Signals from metanephric mesenchym induce elongation and branching of the ureteric bud. Signals from the ureteric bud induce the aggregation of metanephric mesenchyme cells and their subsequent differentiation into nephrons. |
| Describe the ascent of the kidneys and changing arterial blood supply. | Late embryogenesis: kidneys ascend from a sacral position to a lumbar position; the metanephric kidneys are supplied by segmental arteries that originally supplied the mesonephros. Usually, these vessels reduced to single pair of renal art's in adult. |
| * * ____ signaling drives ureteric bud outgrowth and branching. What secretes it? | GDNF-Ret (Glial cell line derived growth factor); it is a secreted factor produced by metanephric mesenchyme. |
| How/on what does GDNF act? | It activates the RET receptor (a tyrosine kinase) and its co-receptor, GFRA1, located on mesonephric duct and ureteric bud cells. |
| Studies in animal models suggest that GDNF drives ureteric bud outgrowth and branching by influencing cell ___ and ___. | movement, proliferation |
| What can mutations in RET lead to? | A study in which stillborn fetuses were examined found mutations in RET in 37% of fetuses with bilateral agenesis and in 20% with unilateral agenesis (Skinner et al., 2008). |
| * * Mutations in transcription factors that regulate ___ signaling are associated with several human syndromes affecting kidney development. | GDNF |
| Syndrome: Branchio-oto-renal (BOR); what is the gene and the defect? | Gene: EYA1: Defect: Renal agenesis or hypoplasia |
| Syndrome: Renal Coloboma; what is the gene and the defect? | Gene: PAX2, Defect: Renal hypoplasia |
| Syndrome: Townes-Brocks; what is the gene and the defect? | Gene: SALL1, Defect: Renal hypoplasia, |
| How do Hox genes influence kidney development? | Studies in animal models suggest that Hox genes (particularly Hox11 genes) also influence GDNF expression and are necessary for specifying metanephric identity (as opposed to pronephric or mesonephric identity). |
| What limits expression/function of GDNF to sacral regions? | Signaling via SLIT2 and its receptor ROBO2 may repress GDNF expression levels at more cranial levels; BMP4 signaling may inhibit RET signaling in cranial parts of the mesonephric duct. |
| What defects are seen in patients with ROBO2 mutations? | Mutations in a ROBO2 have been found in patients with vesicoureteral reflux (VUR), megaureter, and dysplastic kidneys |
| What does Gremlin do? | The BMP inhibitor, Gremlin, blocks BMP signaling in the metanephric mesenchyme (i.e. allows outgrowth in the right region). |
| What defects are seen in patients with BMP4 mutations? | Mutations in BMP4 have been identified in patients with congenital anomalies of the kidney and urinary tract (CAKUT). |
| * * ___ proteins appear to be the primary initiators of metanephric mesenchyme condensation and epithelial cell polarization | Wnt |
| What are WNT proteins? | WNT (Wingless-related) proteins are secreted molecules that signal via multiple pathways. |
| Describe the canonical pathway in which WNT acts (receptor, downstream effects) | WNT binding to the Frizzled receptor leads to an accumulation of β-catenin in the cytoplasm, its translocation to the nucleus, and ultimately its regulation of target genes including those influencing cellular proliferation and differentiation. |
| Wnts expressed in the ureteric bud serve as major inducers of ___ ___ aggregation and promote a ___ to ___ transition. They may also function in the maintenance/upregulation of ___. | metanephric mesenchyme; mesenchymal to epithelial transition(Wnt9b); GDNF (WNT 11) |
| Wnt4: where is it expressed and what does it do? | Wnt4 is expressed in metanephric mesenchyme and is involved in the formation and polarization of epithelial cells of the nephron. |
| * * Wilms tumor gene 1 (WT1) | ___ is involved in early and late phases of metanephric kidney development. |
| What does WT1 do in the early stages of metanephron development? At later stages? | At early stages, WT1 appears to regulate GDNF and promote the survival of metanephric mesenchyme progenitors. At later stages, WT1 may inhibit proliferation of these cells, leading instead to differentiation. |
| Mutations in WT1 are present in about ___% of Wilms tumors. | 5-10% |
| ___ tumor is the most common pediatric kidney cancer. | Wilms |
| These tumors are thought to develop from clusters of mesenchyme (nephrogenic rests) that may represent arrested nephrogenic progenitors or stem cells. | Wilms tumors |
| Describe the proposed pathphysiology of Wilms tumors | The loss of WT1 may arrest nephron precursors in multipotent progenitor state. Subsequently, additional genetic events may transform these cells and cause uncontrolled growth. |
| The central player in the development of the bladder and urethra is the expanded end of the primitive gut tube, the ___(Latin, sewer) | cloaca |
| The cloaca is continuous with the ____, a thin diverticulum that extends into the connecting stalk, and the ___. | allantois; hindgut |
| Between the 4th and 7th weeks the cloaca is partitioned into the ____ ____(continuous with the hindgut) and the ____ ___ (continuous with the allantois). How is this done? | anorectal canal; urogenital sinus (or UGS); This is accomplished by the growth and rearrangement of mesoderm between and around the allantois and hindgut (originally called the urorectal septum) |
| Initially the ___ ____ separates the cavity of the cloaca from the amniotic cavity. | cloacal membrane |
| What happens to the cloacal membrane? | The cloacal membrane breaks down during the 7th and 8th weeks, thus opening the cavities of the urogenital sinus and the anal canal to that of the amnion. |
| The cranial part of the urogenital sinus expands to form the ____. | bladder |
| The more caudal part of the urogenital sinus (the pelvic or genital portion) gives rise to the _____ in the male and the ____ and ______ in the female. | urethra; urethra and vestibule of the vagina |
| Only the internal linings of these structures are derived from the endoderm of the urogenital sinus. ___ ___ tissue forms the muscles and connective tissues. In addition an epithelial tag of tissue contributes to the ___ ___ of the ___ ___. | Lateral mesodermal; distal tip of the male urethra |
| As the bladder is forming, the ___ become displaced from the mesonephric ducts to the bladder wall. | ureters |
| How do the ureters become distinct from the vas deferens? | First, the ureters acquire a distinct and separate entry into the bladder. Second, the entry of the mesonephric duct (presumptive vas deferens) becomes positioned inferior to that of the ureter. |
| The ___ and ___ ___ regress during the second embryonic month. The remnants become a ligamentous band called the ___ or ___ ___ ___. | allantois; bladder apex; urachus or median umbilical ligament |
| Where does the prostate gland originate from? | originates as buds from the prostatic region of the urethra. |
| Where does the lower part of the vagina originate from? | derived from solid endodermal outgrowths of UGS |
| renal agenesis: definition | failure of formation or degeneration of the ureteric bud; In the absence of appropriate signals the metanephric mesenchyme does not differentiate |
| renal agenesis: possible causes | Renal agenesis may be associated with mutations in RET or EYA1. |
| If renal agenesis is bilateral, _____can occur and the fetus/neonate may show ___ __ or syndrome. | oligohydramnios; Potter sequence |
| What is oligohydramnios | (an insufficiency in amniotic fluid volume) |
| renal agenesis: associated abnormalities | Abnormalities include clubbed feet, craniofacial abnormalities, and pulmonary hypoplasia. |
| duplication of the ureter: definition/description | premature bifurcation of the ureteric bud or formation of two ureteric buds: one ureter may open normally, one may open lower (bladder neck or urethra). |
| duplication of the ureter: symptoms/complications | Ureter may become enlarged due to obstructed urine flow. There may also be back-flow of urine (vesicoureteral reflux, VUR) and frequent infections. |
| renal hypoplasia: description, possible cause | kidney contains fewer than normal nephrons. May be associated with PAX2, SALL1 mutations |
| renal dysplasia: description, possible cause | kidney contains undifferentiated tissue and/or cysts. May be associated with PAX2, SALL1mutations. |
| accessory renal arteries: description | transient embryonic renal arteries fail to regress |
| pelvic kidney: description | failure of kidney to ascend |
| horseshoe kidney: description; possible cause | fusion of the inferior poles of the kidneys on each side. Likely cause: abnormality in the kidney capsule. Ascent of kidney is blocked by the inferior mesenteric artery. |
| hydronephrosis and hydroureter: description, possible cause | increased diameter/dilation of renal pelvis and ureter which can be associated with uteropelvic junction obstruction (UPJ). May be caused by abnormal development of smooth muscle and can be part of BOR syndrome |
| Polycystic kidney disease (PKD) | characterized by the formation of fluid filled cysts and kidney enlargement. The timing of cyst formation ranges from the prenatal period through adulthood. |
| Underlying PKD (as well as other renal cystic diseases) are mutations in proteins localized to what cells/structures? | non-motile cilia or ciliary basal bodies |
| What protein mutations are associated with polycystic kidney disease? | polycystins 1 and 2 (autosomal dominant PKD) and fibrocystin (autosomal recessive PKD) |
| What do non-motile cilia or ciliary basal bodies do normally? | In kidney epithelia, these solitary cilia appear to function as mechanosensors that detect and transmit signals about fluid flow in tubules to the cell body, a process involving the elicitation of a calcium signal. |
| How could non-motile cilia mutations lead to PKD? | During growth and development, these cilia may regulate cell polarity, the cell cycle, and Wnt signaling. How mutations in ciliary proteins lead to cyst formation unknown but may involve increase in cell proliferation and a loss of oriented cell division. |
| urorectal atresia/ fistula: description, possible cause | abnormal communication between the rectum and the urethra, vagina, or bladder. Possible cause: ectopic positioning and/or size of the cloaca. |
| urachal fistula, cyst, or sinus: description | persistence of part or all of the lumen of the urachus or allantois |
| exstrophy of the bladder: description, possible cause(s) | bladder open at anterior body surface, resulting from defect in the anterior body wall. Possible causes: insufficient tissue proliferation in anterior body wall, abnormally large cloacal membrane |
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karkis77
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