Download Urinary system 2008

Embryology 12- Urinary
1. Discuss the three stages of kidney development
a. Pronephros system- forms by 3rd week according to Dr. Bateman’s lecture, according to book
forms by the fourth week. This system only has 7-10 solid cell groups, is located in the cervical
region. Forms and then regresses, (is gone by the end of the fourth week) and is thought to be
nonfunctional.
b. Mesonephros system- Forms from intermediate mesoderm early in the fourth week of
development. This system is made up of mesonephric ducts and mesonephric excretory units.
This system also ends up regressing.
c. Metanephros system- This is the permanent kidney and appears in the fifth week. Develops from
the meanephric mesoderm. This is where all the ducts and tubules for the adult kidney occur.
i. Collecting system- the collecting ducts will develop from the ureteric bud, this is an
outgrowth of the mesonephric duct close to the entrance of the clocal. The bud pushes
into the metanephric tissue moving inferiorly (starts at the renal pelvis and deeps dividing
until it reaches the calyxes. These buds will eventually from the renal pyramid, ureter,
renal pelvis, major and minor calyces, and 1-3 million collecting tubules. (pg 232)
ii. Excretory system- the tubules have metanephric tissue caps- after further development
these eventually from the glomeruli, nephrons, bowmans capsules, proximal convoluted
tubule, loop of Henle, and distal convoluted tubules. (pg 233)
2. Discuss the changes in the kidney that occur with development
a. Migration of the kidney- the kidney is initially in the pelvic region and later ascends to the
abdomen. The ascent occurs because of the growth of the body in the lumbar and sacral regions.
b. Blood supply- while in the pelvis the metanephros system gets its arterial supply from a pelvic
branch of the aorta, during its ascent it becomes vascularized by arteries coming from the aorta at
higher levels.
c. Rotation- Normally the developing metanephros rotates from dorsomedial to a more lateral
position relative to the collecting system. In otherwords your collecting ducts are medial and the
cortex part of the kidney will be lateral.
3. Describe the development of the urinary bladder
a. Weeks 4-7 the cloaca divides into the urogenital sinus (anterior) and the anal canal (posterior).
Mesodermal layer between the anal canal and the rogenital sinus is the urorectal septum,
eventually this will form the perineal body.
b. Urogenital sinus has three parts
i. Urinary bladder- the urinary bladder is continuos with the allantois, allantois will
disappear and the urachus will connect the bladder with the umbilicus. Medial umbilical
ligament comes from the urachus.
ii. Pelvic part of urogenital sinus (not discussed in class) gives rise to the prostatic and
membranous parts of urethra
iii. Phallic part (not discussed in class) differs greatly in men and women
4. Discuss common malformations of the urinary system
a. Polycystic Kidney disease: cysts from in the kidneys, if the disease is autosomal recessive the
cysts form in the collecting ducts and renal failure occurs in infancy or childhood. In autosomal
dominant polycystic kidney disease cysts from from all segmaents of the nephron and do not
cause renal failure until adulthood.
b. Renal agenesis: when one kidney fails to develop, a more serious form found in the book but
not discussed in class is potters sequence where not only do the kidneys fail to form, but ther can
also be absence or abnormailities of the vagina and uterus, vas deferens, and seminial vesicles.
c. Pelvic kidney: This is a kidney that did not ascend to the level of L1-L2. Note that the adrenal
gland will still be in the right place, it is not dependant on the kidney.
d. Horseshoe Kidney: In this malformation the kidneys are fused in the center, these kidneys are
found low in the abdomen because when they go to ascend they end up getting stuck on the
inferior mesenteric artery
e. Bifed Ureter- This abnormality results from the early splitting of the ureteric bud. Splitting may
be partial or complete and metanephric tissue may be divided intow two parts, each with its own
renal pelvis and ureter. Sometimes the two parts have a number of lobes in common as a result of
intermingling of collecting tubules.
f. Exstrophy of Bladder- is a ventral body wall defect in which the bladder mucosa is exposed.
Epispadias is a constant feature and the open urinary tract extends along the dorsal aspect of the
penis through the bladder to the umbilicus. Ghis can be caused by a lack of mesodermal
migration into the region between the umbilicus and genital tubercle, followed by rupture of the
thin layer of ectoderm.
g. Urachal Fistula- occurs when the lumen of the intraembryonic portion of the allantois persists,
causing urine to drain from the umbilicus.
h. Urachal cyst- similar to urachal fistula, this occurs if only a local area of the allantois persists,
and secretory activity of its lining results in a cystic dilation.