Session 2 not done Flashcards
What is the functional unit of the kidney?
Nephron
Which germ layer are the kidneys derived from?
Intermediate mesoderm
How many kidney systems initially arise in the embryo? What are they called?
Three. Disappearance of one system marks the onset of development of the next developmental stage.
Pronephros 1st in the cervical region, mesonephros 2nd acts asembryonic kidney and metanephros 3rd, true kidney
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Describe the sequence of kidney development
Step 1: the pronephros
- First kidney system, never functions in humans but is structurally complete
- provided useful data on kidney development
- it’s DUCT is importnat
- pronephric duct extends from the cervical region to the cloaca where all three systems will drain and drives the development of the next developmental stage. Duct becomes duct of each subsequent stage
Step 2: the mesonephros
- Mesonephric tubules develop caudal to the pronephric region. These are primitive nephrons.
- Mesonephric tubules PLUS mesonephric duct = embryonic kidney
- No water conserving function so….need to upgrade
- Mesonephric duct sprouts the ureteric bud which induces development of the definitive kidney.
Step 3: The metanphric blastema is a small region of undifferentiated intermediate mesoderm, caudal to the mesonephros • Ureteric bud induces development of the true kidney, metanephros in this tissue.
The ureteric bud, which has the powerful ability to drive differentiation, makes contact with this intermediate mesoderm and it does two things, it branches and expands, and at the same time it drives differentiation so that this intermediate mesoderm becomes the parenchyma of the kidney.
- The collecting system is derived from the ureteric bud itself
- The excretory component (parenchyma) is derived from intermediate mesoderm under the influence of the ureteric bud. Within that excretory component is where we begin to develop the nephrons with their capacity to conserve and excrete the electrolytes needed. We also get investing of the parenchyma by sophisticated vascular arrangement including the glomeruli.
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What is the urogenital ridge?
• Region of intermediate mesoderm giving rise to both the embryonic kidney and the gonad. Created from hindgut by urorectal septum. Its continuous with umblicus.
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Describe the ascent of the kidney and the possible risk.
- The metanephric kidney first appears in the pelvic region
- Undergoes an apparent caudal to cranial shift, crossing the arterial fork formed by vessels returning blood from the foetus to the placenta. Direct branches of abdominal aorta resolve and new ones form as the kidneys ascend. Roughly 20-25% of people retain an excessive/accessory artery and as these are end arteries, if they become occluded then the region supplied by that artery can undergo hypoxia/necrosis.
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What is the positional change difference between the developing kidneys and the developing gonads?
Gonads descend whereas kidneys ascend.
What are the possible developmental problems that can occur with the kidney?
Renal agenesis - Ureteric bud fails to interact with intermediate mesoderm so kidney does not develop. Not compatible with life.
Ectopic ureter - Ureter doesn’t insert correctly into the bladder, instead it inserts somewhere else.
More than one ureteric bud can develop - Leads to duplication defects and then they can lead to ectopic ureters.
Horseshoe Kidney - As the two metanephric/true kidneys ascend, their caudal poles can touch and then fuse forming one horseshoe shaped kidney. This can limit their ascent as they will get stuck on the next unpaired aortic branch.
Splitting of the ureteric bud - Partial or complete - This can lead to duplication defects - Symptomatic consequence is ectopic ureteral opening E.g. straight into the urethra causing urinary incontinence; or into vagina
Pelvic kidney - When a kidney fails to ascend so remains in the pelvis.
How is the development of the GI urinary and reproductive system linked?
• To begin with, the reproductive tract, urinary tract and GI tract share a common caudal opening • Hindgut ends in a dilated structure – the cloaca • Closed to the outside by the cloacal membrane • no mesoderm
How is the urogenital sinus formed and what does it do?
Urogenital sinus • Created from hindgut by urorectal septum
Uro-genital tract separated from GI tract - Hindgut separated from cloaca by creation of urorectal septum (block of mesoderm which grows down).
UGS is continuous with umbilicus via the urachus which closes to become median umbilical ligament. Sometimes urachus (formerly allantois before urorectal septum forms) doesnt lose its patency so can cause issues.
Cloacal membrane ruptures as urorectal septum comes into contact with it to form perineum
Urogenital sinus • Superior part connects to umbilicus -patent during normal development • Majority of urogenital sinus differentiates to form the urinary bladder • Inferior part develops into the urethra • Sex differences in structural development of the urethra
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How the structures develop differently between men and women
Mesonephric ducts drop down to reach the urogenital sinus as theyre performin primite embryonic kidney function. They then give ureteric buds, UGS then begins to enlarge. So much so that the ureteric bud openings are consumed by the UGS itself so the ureteric buds, instead of draining through the mesonephric ducts, they now drain into the UGS so they drain into the bladder. Mesonephric ducts now not needed.
In the female, mesonephric ducts regress and disappear. Normal development of the ureters and bladder will proceed leaving us with bladder, two ureters, trigone of the bladder (smooth triangular region of the internal urinary bladder formed by the two ureteric orifices and the internal urethral orifice) and the urethral orifice. This happens because in the female, the mesonehric ducts are only needed to give ureters.
In males, Y chromosome is present so mesonephric ducts are supported and continue their development and make independent openings in the UGS. Mesonephric ducts then become vas deferens. Trigone of bladder, UGS and mesonephric ducts also work together to form the prostate and prostatic urethra.
How is the urethra divided and how does it develop?
- Female urethra is formed by the pelvic part of the urogenital sinus
- Male urethra is divided into 4 parts • Pre-prostatic (bladder to prsotate) • Prostatic (urethra enveloped by prostate gland) • Membranous (through perineum) • Spongy (in external genitalia)
The development of the male urethra
• Under the influence of androgens in particluar dihydrotestosterone, in the male the genital tract elongates & genital folds fuse to form the spongy urethra
What is Hypospadias?
- Defect in fusion of urethral folds (tissue which immediately surrounds the outlet of the urogenital sinus and under the influence of androgens those urethral folds will fuse to form spongy urethra)
- Urethra opens onto the ventral surface of the penis rather than at the tip of the glans penis
- Incidence increasing - not clear why - could be linked to increased environmental oestrogenic compounds from high concentrations of oral contraceptions in water.
The long axis of the kidney is parallel to what muscle?
psoas major
What is the first type of scan used to look at renal disease? Give information about what it’s used for in relation to urinary tract pathology.
Ultrasound as its quick, simple, non invasive and doesn’t use radiation. Uses soundwaves which are then transmitted back to the transducer. More dense structures like bone transmit more back as theyre harder to penetrate.
Can be used to identify structural problems, post renal causes of renal failure e.g urinary tract obstruction, infomations as to whether kidney disease is acute or chronic (often with chronic kidney dsease the kidney can get smaller/cortex is reduced), doppler function which enables you to look at velocity and direction of blood flow. Ultrasound can easily penetrate though fluid. So the bladder is hypoechoic and sonoluscent (allowing passage of ultrasonic waves without production of echoes) with posterior acoustic enhancement.
Cyst/renal abscess is an example of pathology that is sonoluscent. Adult polycystic disease has similar appearence.
Calculus (calcium stones) are an example of sonodense, hyperechoic pathology as they have low through transmission of US beam and posterior acoustic shadowing due to their density.
Collecting system not normally well seen. Seen more when blocked.
Renal biposies are usually under US guidance, occasionally CT - Targeted biopsy of mass• eg small tumour, • tissue prior to chemotherapy, • Multiple lesions • ?metastases/ lymphoma
