Development of Bladder, Urethra and Prostate – Urinary System and Kidney Development

by John McLachlan, PhD

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    00:00 Now, the bladder develops from part of the urogenital sinus.

    00:07 In this diagram, we can see the original cloaca, which is a large space dividing into two different components. The upper part, the more anterior part is known as the urogenital sinus.

    00:21 The anal canal or rectum is the posterior part of this process. Later on in life, the bladder and the urethra will both develop from the urogenital sinus. The cranial part of this urogenital sinus will give rise to the bladder. What we should know is that this is connected to the structure called the allantois. Now, this may seem rather mysterious and it certainly will not be the word that you’ve heard during your studies of adult anatomy. The reason for that is that the allantois is an evolutionary remnant. In our ancestors who existed inside eggs, one of the major problems was where to sequester waste products. And what [inaudible 00:10:32] developed inside eggs have evolved is a little impermeable sac called the allantois in which they store their waste products. It comes off from the hind end of the gut in the way that we’ve just seen. This of course is redundant in humans, and therefore, it will eventually become condensed to form a ligamentous like structure. So it will close down to form a structure like a ligament. And if you were to follow that forward, what you’d find is that that ligament now connected to the inside of the umbilical cord is called the urachus. By the time birth is taken place and development proceeds, eventually, it would be known as the medial umbilical ligament. So the name of the structure changes from allantois to urachus to medial umbilical ligament. You can readily imagine that this process of closing might not go completely properly. Therefore, it’s imaginable that in some babies, it will still be open at the time of birth. And if that were to happen, what would appear are little drops of urine appearing at the umbilicus which was normally fairly startling to individual, as we see it, but this is relatively simple to resolve surgically.

    02:24 But as we’re discussing these changes at this point, it’s worth pointing out that the process of separation between the urogenital sinus and the anal canal is also something which shows variation. There may be abnormal connections, fistulas, which join the rectum, the anal canal to the bladder or the urethra at some other point during the course of development.

    02:51 Let’s look at the insertions of these structures into the bladder. In the initial picture on the left hand side, we can see the mesonephric duct, and from it, the ureteric bud, and these two are still joined together but gradually, this will become separate. In this view, we’re looking at the posterior, the back wall of the bladder. We can see that they are gradually becoming separate in the nature of their insertions between the two. If we’re to follow this forward, what we would see is that the mesonephric duct is now quite separate from the ureter.

    03:25 In the male, the mesonephric duct will persist and form the vas deferens of the reproductive system.

    03:32 In the female, as we’ll see in another lecture, the mesonephric duct will degenerate.

    03:39 If we go back to the urogenital sinus, what we can see is that in the part just below the bladder, there will be little outgrowths that develop. In the female, these little outgrowths will form the urethral and paraurethral glands. However, in the male, this will give rise to the prostates and its supporting structures. The remainder of the urogenital sinus will form the membranous and penile urethra in the male. So the prostate gland is coming from these outgrowths from this lower part of the urogenital sinus just below the bladder.

    About the Lecture

    The lecture Development of Bladder, Urethra and Prostate – Urinary System and Kidney Development by John McLachlan, PhD is from the course System-Specific Embryology with John McLachlan.

    Author of lecture Development of Bladder, Urethra and Prostate – Urinary System and Kidney Development

     John McLachlan, PhD

    John McLachlan, PhD

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