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)
How is the bladder formed?
- hindgut derivative
- derived from the caudal portion of the primitive gut tube formed during the embryonic folding in the 4th week of development
- caudal portion is the cloaca, separated from outside by cloacal membrane
- allantois: superoventral diverticulum of the hindgut which extends into the umbilical cord
- lumen of allantois becomes obliterated to become the urachus (medial umbilical ligament in adults)
- cloaca becomes divided by the urorectal septum into the urogenital sinus (future bladder and urethra) and anorectal canal (future rectum and anal canal)
What is the urogenital sinus?
- created from hindgut by urorectal septum
- UGS is continuous with umbilicus which becomes the urachus (patent during development but is closed up after birth)
- urorectal septum separates hindgut into urinary tract an rectum
- superior part of UGS connects to umbilicus and majority of it differentiates into urinary bladder
- inferior part of UGS develops into urethra (develops differently dependant on sex)
What is the urorectal septum?
- large wedge of mesoderm
- separates hindgut into urinary tract and rectum
How does the urethra develop?
- formed from lower bit of UGS
- females: urethra opens into the vestibule because urethral folds do not fuse
- mesonephric ducts reach UGS, ureteric bud sprouts from MD, UGS begins to expand and MD begins to regress, ureteric bud opens into UGS
- male: distal urethra is elongated (becomes spongy urethra) as the penis develops from fusion of the urethral folds under the influence of androgens
- MD reach UGS, UB sprouts from MD, smooth musculature begins to appear and UGS begins to expand, UB and MD make independent openings into UGS, MD converted into vas deferens, prostate and prostatic urethra formed
What is the female urethra formed from?
-pelvic part of UGS
What are the 4 parts if the male urethra and explain its development?
- pre-prostatic (from narrowed lower segment of UGS)
- prostatic (from narrowed lower segment of UGS)
- membranous (narrowed lower segment of UGS)
- spongy (phallic portion which is enclosed by urethral folds)
- GT elongates and genital folds fuse to form spongy urethra
- see diagram
What is hypospadias?
- defect in fusion of urethral folds
- urethra opens onto the ventral surface rather than at the end of the glands
- more prevalent these days possibly due to bad substances in the water
Why is ultrasound the first choice for renal investigation?
- helps to see post renal cause such as hydropnephrosis
- structural problems ex. APKD
- acute/chronic: reduced kidney size, cortical thickness, echogenicity
- Doppler function
- high frequency sound waves transmitted through body
- soundwaves are either transmitted back to transducer or pass through body tissues
Which investigation is best to detect stones?
-CT scan
Explain a PUJ obstruction
- narrowing of the junction between the renal pelvis and the ureter
- causes: idiopathic but usually congenital, retroperitoneal fibrosis, secondary to trauma or infections
- aetiology is unknown but factors may be: aberrant lower pole vessels, persistent fetal urothelial fold
- symptoms: pain (esp. after alcohol) and urine infection
- more common in men
- affect L kidney more than R
What should you do about renal imaging?
LOOK AT THE SHITTY LECTURE
