Pronunciation: [jˈə͡ʊk sˈaks] (IPA) 
The spelling of the word "yolk sacs" is fairly straightforward. "Yolk" is spelled with a "y" and an "o" and the "k" sound, while "sacs" is spelled with an "s" and a "c" and the "s" sound. The pronunciation is also quite simple, with "yolk" pronounced as /joʊk/ and "sacs" pronounced as /sæks/. Together, the words refer to the membranous sacs in the egg where the yolk is stored.
Yolk sacs are membranous structures present in the eggs of oviparous animals, particularly birds, reptiles, and monotremes (egg-laying mammals). They serve as a primary source of nourishment for the developing embryo during the early stages of development.
The yolk sac is typically attached to the embryo and acts as a storage site for nutrients such as proteins, lipids, and minerals, as well as vitamins required for the embryo's growth and development. It is formed from cells in the blastoderm, the outermost layer of the embryo, and consists of two layers: an outer layer called the vitelline membrane and an inner, more solid core called the yolk.
The yolk sac not only provides essential nutrients but also plays a role in waste removal, facilitating the transport of metabolic waste from the embryo. As development progresses, the yolk is gradually absorbed, and its nutrients are utilized by the growing embryo. Eventually, the yolk sac diminishes in size and may be discarded or incorporated into the digestive system of the embryo.
In summary, yolk sacs are critical structures in the early development of oviparous animals, providing vital nutrients to the developing embryo. They facilitate growth, development, and waste removal, playing a crucial role in the early stages of an animal's life before it hatches or is born.
The term "yolk sacs" is a compound word consisting of two parts: "yolk" and "sacs".
1. Yolk: The word "yolk" can be traced back to the Old English word "geoloca" or "geole", which means "the yellow part of an egg". It is related to the German word "Jolk" and the Dutch word "joo".
2. Sacs: The word "sac" is derived from the Latin word "saccus", which means "bag" or "pouch". It has been borrowed into English from Latin.
When combined, the term "yolk sacs" refers to the small membranous pouches or sacs that contain the yolk in an egg.
