L25 Embryology of the Kidney Flashcards
How does the mesoderm reorganise at day 17?
Into paraxial mesoderm, intermediate mesoderm and lateral plate mesoderm. The paraxial mesoderm will go on to develop into the vertebrae - the sclerotome and myotome. The lateral plate mesoderm forms the lining of the body wall - in the abdomen, it forms the peritoneum. The intermediate mesoderm will from the gonads, internal reproductive tracts as well as the kidneys.
When does the pronephros develop?
Week 4
What is the structure of the pronephros?
It forms from the intermediate mesoderm from cervical condensations
In human development, they develop and regress. They are non-functional. Development of the pronephros, sets of a caascade leading to the development of the second structure. It disappears by day 25. Lateral to the condensements is a duct system - mesonephric duct.
When does the mesonephric duct form?
The mesonephric duct grows caudally, at 26 days it eventually joins with the cloaca - the common point at with the GU and urinary system empty.
How does the mesonephric duct form?
Canalisation commences from the caudal end (through apoptosis it forms a lumen). The pronephros induces the mesonephric duct to form. Development of the mesonephric duct induces formation of mesonephric buds from mesenchyme. The cascade occurs as the mesonephric duct secretes signalling factors to the intermediate mesoderm to develop.
What a mesonephric tubules?
The mesonephric buds start to elongate to form an S shape structure, then form tubules. Tubules are formed in a craniocaudal fashion
What is the urogenital ridge?
Development of the mesonephros forms to a urogenital ridge. Gonadal development takes place on the medial aspect of the mesonephric ridge.
When does the metanephros develop?
It appears in the 5th week of development and becomes functional around the 12th week.
What is the stucture of the metanephros?
Ureteric bud bifurcates in a specific pattern as it penetrates the metanephric mesenchyme
Renal ampulla -> Renal pelvis -> Major Calyces -> Minor Calyces -> Collecting Ducts. The ureteric bud develops a sprouting fashion,. The “roots” join together to form major calyces, they sprout again to form minor calyces. They sprout again to form collecting tubules, the smallest collecting part of the kidney.
How does the collecting system of the metanephros develop?
From the mesonephric duct, from the caudal region a ureteric bud sprouts which will go onto form the collecting portion. As it sprouts, it grows into mesonephric mesenchyme. There is therefore reciprocal interaction between the mesenchyme and the ureteric bud: they communicate, signal and induce one another to develop. From the mesenchyme we from condensements called renal vesicles induced from signals from the ureteric bud. The ureteric buds signals the renal vesicles to elongate. As they elongate they form the nephron. These two structures will then join together.
How does duplication of the ureter occur?
The ureteric bud comes from the mesonephric duct. As it pierces the metanephric mesenchyme, the signals from the mesenchyme, it splits. However before it pierces the mesenchyme, it can split prematurely. Depending however early it splits, or how many time, we can develop a number of collecting systems. Duplication so the ureter, means both structures go onto form separate ureters. Depending how early or how it splits, we can get misconfiguration (on the proximal part has two parts) or two separate ureters. We can also end up with an ectopic ureter, where it attaches to structures where it shouldn’t e.g. the vagina or the urethra (instead of the bladder).
What is renal agenesis?
The kidney fails to form. If one of the kidneys fails to form, we have unilateral agenesis which is usually asymptomatic. The second kidney just undergoes hypertrophy and takes over the function. If we have bilateral renal agenesis, the foetus usually dies or the baby does after birth. This is formed by degeneration of the ureteric bud or failed interaction between ureteric bud and metanephric tissue cap.
What is PKD?
Polycystic Kidney Disease
What are the two forms of PKD?
There is an autosomal recessive type. Cysts form from the collecting ducts. Kidneys are enlarged and renal failure occurs in childhood. It is more progressive. The nephrons are disruptive leading to renal failure. Eventually patients require a transplant. here is an autosomal type - adult polycystic disease which usually does not present until later in life - it is slightly more common. Cysts form on all parts of the nephron. Usually not as progressive. When the cysts form the kidney tries to heal itself and make more structures leading to enlargement of the kidneys.
When do the kidneys relocate?
The metanephric mesenchyme is in the sacral region. In an adult, the kidneys reside in the posterior abdominal wall and so the kidneys must relocate. They ascend because the spine grows at different rates. In the foetal position, the foetus straightens out pulling the kidney into the abdominal region. As it ascends into the abdomen, it creates a new blood supply. As it ascends more, it loses that blood supply and makes one further up. However sometimes it may not lose that blood supply, and so it is not uncommon for people to have multiple renal arteries - the original blood supply does not regress.
