Embryology Biology 441 Spring 2011 Albert Harris
Tissues and organs that develop from endoderm
What parts of the body develop from endoderm?Salivary glands: (note, these develop partly from stomodeum epithelium; and stomodeum is traditionally regarded as part of the ectoderm)
Pharyngeal pouches: : "gill slits"
Our very distant ancestors were fish, and had gills.
Except, of course, in mammals, birds etc.
these gill-like structures develop into organs with other functions.
The third and fourth pair develop partly into the parathyroid gland (which is an endocrine gland that secretes parathyroid hormone)
And other parts of the third and fourth pharyngeal pouches develop into the thymus "gland", which is a very important part of the immune system (rather than a gland).
Its true function was discovered over the last few decades, and more will be learned.
Mutations that cause the third and fourth pharyngeal pouches not to develop result in animals with very weak immune systems.
The best example are "nude mice". For some unknown reason, their hair does not develop, in addition to failure of development of the third and fourth pharyngeal pouch. It is not yet known whether this is two effects of the same gene, or whether two separate, but very closely-linked, genes control development of hair and of those pharyngeal pouches.
Thyroid gland forms as an outpocketing of the floor or the endoderm behind the throat, that then disconnects from the surface, but remains as a series of hollow sacks, full of mucus.
Hepatic diverticulum (--> liver) gallbladder
Cloaca --> Bladder (these separate in mammals)
Birds, reptiles & amphibia continue to have cloacas
In amphibian embryos, the anus develops from the blastopore.
Instead, they form a posterior infolding called the proctodeum
The proctodeum is an infolding of the somatic ectoderm, equivalent to the stomodeum at the other end.
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