Week 2 - Development of the urinary system + histology Flashcards
What is the pronephros?
- The first kidney system
- Never functions in humans
- Appears at the start of week 4
- Regresses at the end of week 4
- Produces the pronephric duct
- – Extends from the cervical region to the cloaca
- – Drives the development of the next stage
What is the mesonephros?
- Appears at the end of week 4
- Regresses at the end of week 8
- It is functional but has no water conserving mechanism
- The mesonephric duct has an important role in the development of the male reproductive tract
- The mesonephric duct sprouts the ureteric bud
- Sprouts tubules that develop caudal to the pronephric region
- – These tubules + mesonephric duct = embryonic kidney
What is the metanephros? (definitive kidney)
- Appears in week 5
- Does not regress
- Functional
- The ureteric bud sprouts from the mesonephric duct
- – Induces the development of the definitive kidney within the intermediate mesoderm of the caudal region of the embryo that lies closest to it
- – Then expands and branches into this differentiated intermediate mesoderm, forming the definitive kidney’s structure
- Collecting system develops from the ureteric bud and the excretory system develops from metanephric tissue cap
Where does the embryonic kidney and gonad develop from?
The urogenital ridge
- A region of intermediate mesoderm
What is the ascent of the kidneys?
- The metanephric kidney first appears in the pelvic region
- It then undergoes an apparent caudal to cranial shift, crossing the arterial fork formed by vessels returning blood from the foetus to the placenta
- The kidneys don’t actually move:
- – Development is cranial to caudal, and the trunk just extends downwards, making it appear as though the kidneys move
What is renal agenesis?
The ureteric bud fails to interact with the intermediate mesoderm
- Can affect 1 or both of the kidneys
What are some migration defects of the kidney?
- If a kidney fails to cross the arterial fork, it ends up much lower than it should do
- During their ascent, the kidneys lie extremely close to each other
- – If they both get caught on the arterial fork, they can fuse and form a horseshoe kidney
What are some duplication defects of the kidney?
Splitting of the ureteric bud, either partial or complete can lead to abnormalities
- The systemic consequence is an ectopic opening bypassing the bladder and causing incontinence
- – Opening may by into the vagina or urethra
- May cause 1 kidney to have 2 urethras
What is the bladder derived from?
- A hindgut derivative
- Derived from the caudal portion of the primitive gut tube formed during embryonic folding in the 4th week of development
- – A dilated, blind pouch called the cloaca
- – Separated from the outside by the cloacal membrane
- – Divided by the urorectal septum into the urogenital sinus (future bladder and urethra) and anorectal canal (future rectum and anal canal)
- The allantois is also involved
- – It is a superoventral diverticulum of the hindgut
- – Extends into the umbilical cord
- – Lumen on the allantois becomes obliterated to become the urachus, which is the median umbilical ligament in adults
Describe how the male bladder is formed
- Mesonephric ducts (MD) reach the urogenital sinus (UGS)
- – Drains Embryonic urine into the cloaca
- Ureteric Bud (UB) Sprouts from MD
- – Ureteric bud will become ureter opening into the bladder
- Smooth musculature begins to appear
- UGS begins to expand
- UBs and MDs make independent openings in UGS
- Prostate and prostatic urethra formed. MD is maintained in the male, forming the prostate and ducts of the male reproductive system.
Describe how the female bladder is formed
The female bladder develops in much the same way as the male, but without male hormones the Mesonephric duct regresses
- So females do not form prostates or the tubes of the male reproductive system
What forms the female urethra?
The pelvic part of the urogenital sinus
What are the different parts of the male urethra?
- Pre-prostatic
- Prostatic
- Membranous
- Spongy
What is exstrophy of the bladder?
- A congenital anomaly
- Part of the bladder is present outside the body
- Occurs due to maldevelopment of the lower abdominal wall, leading to a rupture that causes the bladder to communicate with the amniotic fluid
- May be due to a urachal fistula
- – A patent urachus
- – If it remains as a duct, it will connect the bladder to the umbilicus (belly button!)
What is hypospadia?
- A defect in fusion of the urethral folds
- The urethra opens onto the ventral surface of the penis, rather than at the end of the glans
