2 Flashcards
What is the functional unit of a kidney?
Nephron
How many kidney systems form in development? In what way?
3 systems develop sequentially
-disappearance of one system marks the onset of development of the next developmental stage
Where and from what do the kidney and ureter form from?
Intermediate mesoderm at the urogenital ridge
Where does the first system appear and what is it called? When does it appear and regress? Is it functional? Why have it?
- appears in the cervical region
- the pronephros
- appears at start of week 4
- regresses end of week 4
- not functional but provides useful data on kidney development
- has the pronephros duct which extends to the cloaca and drives development of the next developmental stage
What is the urogenital ridge?
-region of intermediate mesoderm which gives rise to both the embryonic kidney and the gonad
What is the mesonephros? Describe it
- Appears at end of week 4
- Regresses at end of week 8
- is functional but has no water conserving mechanism
- pronephros gives rise to mesonephric tubules; differentiate from intermediate mesoderm
- tubules are primitive nephrons that act like kidney
- mesonephric tubules + mesonephric ducts = embryonic kidney
- mesonephric ducts are important for male reproductive tract
- they also sprout the “ureteric bud” which is the primordial of the collecting system of the definitive kidney
- ureteric bud develops into ureter and has the capability to drive undifferentiated mesoderm close to it
Describe the ureteric bud and its importance
- undifferentiated intermediated mesoderm, caudal to mesonephros
- ureteric bud induces development of the true kidney, metanephros in this tissue
How do the ureteric bud and metanephros work together?
- metanephros appears at week 5
- is functional from the end of the first trimester
- becomes the definitive kidney and collecting system which develops from the ureteric bud
- ureteric bud contacts metanephric blastema (undifferentiated intermediate mesoderm)
- bud expands an branches which drives the blastema to become parenchyma of the kidney
How does the excretory system develop?
- develops from “metanephric tissue cap”
- derived from intermediate mesoderm under the influence of the ureteric bud
Explain the migration of the kidney
- metanephric kidney first appears in the pelvic region
- undergoes a dramatic caudal to cranial shift (pelvis to abd)
- crosses the arterial fork formed by vessels returning blood from the fetus to the placenta
- as the cavity expands kidney and gonads swap places basically
- 1: cranio-caudal shift from L4 to L1/T12
- 2: lateral displacement (meeting with adrenal glands in the process)
- 3: 90 degrees rotation so the renal pelvis faces the midline
Why do 25% of the population have an extra renal artery?
- branch of aorta rises as the kidney rises cranially
- can sometimes end up forming an extra artery which is an end artery to renal system
What happens when the ureteric bud fails to interact with the intermediate mesoderm?
- renal agenesis (no development of a true kidney)
- migration goes awry
- duplication defects
- ectopic ureter
- cystic disease
What are some structural anomalies related to migration?
- pelvic kidney: kidney does not ascend
- horseshoe kidney: tru kidneys start moving but the caudal poles touch each other and fuse
- this prevents ascent as the kidney will stop at the first branched artery
Explain duplication defects and ectopic ureteric orifices
- splitting of the ureteric bud, which can be partial or complete (two are formed
- symptomatic consequence is ectopic ureteral opening
- additional kidney or lobes are formed
- the opening of the duplex kidney can possibly go into the vagina since it develops at the same time as the bladder
- could also go into the urethra
Explain the development of the urogenital and GI tracts
- all derived from hindgut
- hindgut ends in the cloaca in which all the tracts drain into
- closed to the outside by cloacal membrane (no mesoderm)
