Development of the kidney and ureters Flashcards
From which mesoderm does the urinary system develop?
The intermediate mesoderm, situated between the paraxial and lateral plate mesoderm
What is the origin of the intermediate mesoderm?
- During early development, small coelomic spaces (small cavities) appear in the lateral mesoderm, which eventually merge to form the intraembryonic cavity (coelom “horseshoe cavity”) This process divides the mesoderm into:
1) Paraxial mesoderm (contributed to somites and the musculoskeletal structures
2) Intermediate mesoderm (gives rise to the urogenital system, kidneys and gonads)
3) Lateral plate mesoderm (splits into somatic and splanchnic layers, contributing to the cardiovascular system and body wall structure
The intraembryonic cavities form which cavities?
- Pericardial cavity
- Pleural cavity
- Peritoneal cavity
What are the stages of the development of the urinary system?
- Three stages
1) Pronephrons
2) Mesonephrons
3) Metanephrons (the permanent kidney)
What happens in the pronephron stage (forekidney)?
- Starts at the beginning of the 4th week
- It is a functionless, transitory structure
- It makes the appearance of the urinary system opposite to the cervical segment
- They are about 5:7 pairs of horizontally arranged segments (nephrotomes)
- Each pronephric tubule has 2 ends (one end opens into the intraembryonic coelom and is invaginated by small branches of the dorsal aorta forming an internal and external renal corpuscle), while the second end bends causally and all of the unite together and becomes canalized to form longitudinal ducts called the pronephric duct
When do the pronephric tubules disappear?
At the end of the 4th week of development
What is the fate of the pronephric duct?
It grows caudally beyond the level of the tubules until it opens into the cloaca and receives the opening of the mesonephric tubules to become the mesonephric duct
What is the general function of the pronephrons?
Forming the mesonephric duct is formed for the next stage (mesonephrons), and thus the pronephrons, is a temporary functionless structure, and there is no urine secretion at this stage
What happens in the mesonephron (midkiney) “Wollfian body stage”?
- It is the second kidney to appear at the end of the 4th week
- It is a temporary functioning structure
- It starts the development as masses of cells called the mesonephric masses, which appear opposite to the thoracic region left to the level of the 3rd lumber
- Each mass becomes hallowed into a vesicle, elongated to form a tubule, and then bends to become an S shape
- Its lateral end joins the mesonephric duct (continuation of the previous stage)
- Its medial end becomes invaginated by blood capillaries to form a renal corpuscle
During which stage of development does the kidney start to function?
The second stage (mesonephric stage) as during this stage they become a temporary functioning structure
What are the functions of the mesonephrons?
- They are the primary kidneys of amphibians
2) In humans, mesonephrons function and produce small amounts of urine between the 6th and 10th weeks, and it is degenerated by the end of the 10th week
During which intraembryonic period does the mesonephron function?
Between the 6th and 10th week, after that they degenerate
What structures do the mesonephric structures give rise to in males?
- Vasa efferentia
- Vas deferens
- Seminal vesicles
- Ejaculatory ducts
What structures do the mesonephric structures give rise to in females?
- Epoophoron
- Paraophoron (located near the ovary)
What happens to the medial end of the mesonephron?
It becomes hollow to form a vesicle and receive an artery to form a corpuscle
What happens to the lateral end of the mesonephron?
- Its lateral end joins the mesonephric duct (continuation of the previous stage), by elongating and bending to form an S-shape
What happens during the metanephron stage (Hind kidney)
- It is the permanent kidney of humans
- It starts to appear at the end of the fourth week
- It has a double origin: 1. Ureteric bud: gives rise to the collecting system, and 2) Metapheric cap: Gives rise to the excretory unit.
- The ureters that originate from the ureteric bud originally open into the mesonephric duct, but at a later stage, the lower part of the mesonephric duct becomes absorbed into the wall of the developing urinary bladder and so the ureter will open directly into the urinary bladder (this is what gives rise to the trigone region)
- The metanephric cap will develop to form different part of the nephron
What is the origin of the metanephrons (hind kidney)?
- It has a double origin:
1) Ureteric bud: gives rise to the collecting system
2) Metapheric cap: Gives rise to the excretory unit
From where does the ureteric bud arise?
- It arises from the distal end of the mesonephric duct close to the cloaca
- It elongates up through the intermediate mesoderm
- The ureteric bud appears as a diverticulum
- Its upper end dilates to form the pelvis of the ureter while its proximal part (the greater part) forms the ureter
- The pelvis of the ureter divides into 2/3 major calyces and then to the minor calyces, which branches into a great number of collecting tubules
What is the embryological origin of the ureter?
The ureteric bud, the pelvis of the ureter, calyces all of them
What is the embryological origin of the PCT?
The metanephric cap
Which structure gives rise to the trigone region?
The part of the mesonephric duct that gets absorbed into the cloaca (when the metanephron ureter opens into the bladder)
From which dermal layer does the urinary bladder arise?
It is primarily derived from the endoderm, except for the trigone, which originates from the intermediate mesoderm
HOW IS THE METANEPHRIC CAP FORMED?
- The mesoderm of the metanephrons surrounds the upper part of the ureteric bud
- The mesoderm of the metanephric cap gets segmented into cell clusters in relation to the termination of the collecting tubules, these cell clusters change into vesicles (known as renal vesicles), which elongate to form different parts of the nephron
- The DCT will then join the nearest collecting tubule to form a complete uriniferous tubule
What are the different parts of the nephron that form from the metanephric cap?
- Bowman’s capsule
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule (DCT will join the nearest collecting tubule “formed by the ureteric bud”)
What is the origin of the (bowman’s capsule, PCT, loop of Henle, and the DCT)?
Metanephric cap
What forms the uriniferous tubule?
The joining of the DCT (formed by the metanephric cap) with the collecting tubule (formed by the ureteris bud)
Summarize the key events of the mesonephron stage
- Diverticulum appears in the disytal end of the mesonephric duct (AKA ureteric bud)
- The ureteric bud joins the metanephric cap
- The ureteric bud dilates to form the (1. Ureter, 2. Renal pelvis, 3. Major calyces, 4. minor calyces, 5. Collecting tubules)
- The metanephric cap becomes segmented into cell clusters, and each cluster forms the (1. Bowman’s capsule, 2. PCT, Loop of Henle, 4. DCT)
- DCT will join the nearest collecting tubule to form a complete urinephron tubule
What are the structures formed by the ureteric bud?
1) Ureter
2) Renal pelvis
3) Major calyces
4) minor calyces
5) Collecting tubules
Describe the process of kidney ascending
- At first, the kidney lies at the sacral region; it will then ascend to the lumbar region due to:
1) Growth of the body in the lumbar and sacral region
2) Straightening of the body curvature
3) Differential growth of the surrounding organs
- Due to the large size of the right lobe of the liver, the right kidney is slightly lower than the left
What is the blood supply of the kidney?
- Supplied by the nearest artery during its ascend
- It is supplied by the median sacral, internal iliac, and common iliac, during their ascend to the abdomen. (During development, the kidneys initially form low in the pelvis. As the embryo grows, the kidneys “ascend” or move upwards to their final position in the abdomen)
- Initially, the kidneys receive their blood supply from arteries located lower in the body. These include the median sacral artery (a small artery in the midline), the internal iliac arteries (which supply the pelvic organs), and the common iliac arteries (which branch from the aorta to supply the legs and pelvis)
- Finally, once in the abdomen, the renal artery supplies it, which develops at the lumbar vertebra
What is the lobulation of the kidney
- The fetal kidney is lobulated, but this lobulation disappears before birth
- If the fetal lobulation persists, it is considered a congenital anomaly, however, it is usually harmless a long as the kidney function remains normal
Describe the rotation of the kidneys
- At the beginning, the hilus is directed anteriorly, then the kidney rotates 90 degrees medially so that the hilum faces the medial side
What are the congenital anomalies of the kidneys?
1) Anomalies of number
2) Anomalies of site
3) Anomalies in form and fusion (shape)
4) Anomalies in rotation
5) Anomalies in volume and structure
6) Anomalies in lobulation
7) Anomalies of renal vasculature
What are the number of anomalies of the kidney?
- Agenesis of the kidney
- Supernumerary kidney (multiple kidneys)
What is meant by the Agenesis of the kidney?
- Failure of the development of the ureteric bud or failure to develop the nephrogenic ridge, it might be:
- Unilateral renal agenesis
- Has no specific symptoms because the other kidney undergoes compensatory hypertrophy and does the function of the missing one
- Bilateral renal agenesis
- The 2 kidneys are absent
- The ureters are either wholly or partially absent
- The trigone of the bladder is poorly formed
- It is incompatible with postnetal life
- It is associated with oligohydraminos because little or no urine is excreted into the amniotic fluid
What is meant by supernumerary kidney (multiple kidneys)?
It is due to:
- Early splitting of the ureteric bud
- Branching from the initial ureteric bud
- There is more than one kidney in one or both sides
- The additional kidney is normal in shape
What are the anomalies of the site of the kidney?
- Simple renal ectopia
What is the cause and the different types of simple renal ectopia?
It occurs due to:
- Defective development of the metanephric cap
- Failure of the metanephric cap to induce the ascent which might be:
1- Pelvic kidney: Opposite the acrum, below the aortic bifurcation
2- Lumbar kidney: In the iliac fossa opposite the sacral promontory
3- Abdominal kidney: Above the iliac crest opposite the 2nd lumbar vertebra
What are the different anomalies in the formation and fusion of the kidney?
Horse - Shoe kidney
What is meant by horseshoe kidney?
- The lower poles of both kidneys are connected by an isthmus, usually formed of renal tissue, and may pass in front of the aorta and the IVC
- The hilum in such cases usually faces anteriorly
- The ascending of the horseshoe kidney is arrested by the origin of the inferior mesenteric artery (IMA arises from the abdominal aorta at the level of L3), and thus the isthimus is usually located below L3
- It produces no symptoms as the collecting system developed normally
What are the different anomalies of the rotation in the kidneys?
- Normally, the hilum is facing medially
1) Non-rotation
2) Incomplete rotation
3) Reversed rotation
What is meant by non-rotation?
The hilum is directed forward
What is meant by incomplete rotation?
The hilum is directed anteromedially
What is meant by reversed rotation?
The hilum is directed anterolaterally
What are the anomalies in the volume and structure of the kidney?
1) Hypoplasia
2) Polycystic kidney
What is meant by kidney hypoplasia?
- Due to the incomplete development and differentiation of the ureteric bud
- The kidneys are small in one or both sides
What is meant by polycystic kidney?
- It might be:
1) Congenital polycytic kidney: Due to hereditary causes
2) Adult polycystic kidney: Due to failure of the connection between the collecting tubules of the ureteric bud and the DCT of the metanephric cap, it usually appears around the age of puberty (patient presents with complete renal failure)
3) Solitary cyst of the kidney
- Accumulation of urine in the convoluted tubule results in the formation of retention cysts
- The normal nephrons are compressed by the nearby cysts
What is meant by lobulation anomaly?
When the fetal lobulation persists after birth
What are the anomalies of the renal vasculature?
1) Multiple renal arteries
2) Accessory renal artery
What is meant by multiple renal arteries?
- The kidneys are supplied by multiple arteries due to the failure of the degeneration of the primitivbe arterial supply
- The additional artery could be the median sacral artery, internal iliac artery, and the common iliac artery (which provides blood supply to the kidney as it ascends from the pelvis to the lumbar)
What is meant by the accessory renal artery?
2 or more arterial branches supplying the same renal segment
What are the congenital anomalies of the ureters?
1) Anomalies in number
- Ureteral agenesis
- Duplication of the ureter
2) Anomalies in termination
- Ectopic ureteric orifice
3) Anomalies in course
- Retrocaval/retroiliac ureter
4) Anomalies in structure (Caused by varying degrees of failure of ureteral bud development and canalization)
- Mega ureter
- Atresia and hypoplasia
- Ureteral stenosis and stricture.
- Folds of the ureters
- Ureteral Valves
- Ureteral diverticula
What is meant by ureteral agenesis?
- Complete failure of the ureteral bud development
- It occurs in the bilateral renal agenesis
- Associated with renal agenesis
What is meant by the duplication of the ureter?
- The most common ureteral anomaly
- It occurs due to the premature division of the ureteric bud
- It is hereditary (autosomal dominant trait), and it might show:
1) Double pelvis of the ureter: Due to the premature division of the ureteric bud near termination
2) Bifid ureter (partial duplication): Double pelvis and double ureters, but they open through a common orifice into the urinary bladder
3) Double ureter (complete duplication, “more than 2 ureters”):
- Development of two ureteric buds from a single mesonephric duct
- The two ureters open independently into the bladder
- The orifice of the lower ureter occupies the more cranial and lateral position, and that of the upper ureter
What is meant by ectopic ureteric orifice?
- A second ureteric bud that arises from a single mesonephric duct near its termination
- In males, the additional ureter might open into the bladder, prostatic urethra, or even the ejaculatory duct
- In females, the additional ureter may open into the urethra or even into the vagina
What is meant by retrocaval/retroiliac ureter?
- It is a development disorder of the inferior vena cavs
- In this abnormality, the right ureter traces out an S shape at the L4 level behind the vena cava (retrocaval ureter). In the case of retrocaval ureter, sometimes these patients can suffer from renal obstruction or ureteric obstruction if we have increased venous return
- In a similar fashion, the ureter can also run behind the common iliac artery at the level of L5 (retroiliac)
What is meant by mega ureter?
- Caused by an obstruction to urine flow
- Mega-ureter, the ureter is very huge and wide in diameter
What are the other structural anomalies of the ureters?
- Atresia and hypoplasia (the ureter has developed proximally and can end blindly distally)
- Ureteral stenosis and stricture
- Fold of the ureters
- Ureteral valves
- Ureteral diverticula
