The whitefish slide is from a blastula, an early stage in embryonic development. why do you think that this sample was chosen rather than a sample of adult tissue? hint: recall the discussion about how many times a cell must divide to create all of the cells in an adult human.

In the morula phase, the zygote begins to divide by mitosis, which is from one cell to two cells, two cells to four cells, four cells to 8 cells, and so on.

This cell division occurs continuously during the zygote journey to the uterus (approximately 4 days). This division produces daughter cells that are collected in a colony like a round ball, hereinafter called morula. In its growth, the morula will become a blastula that has cavities. This process of forming a morula is called morulation.

The blastula phase is a continuation of the formation of the morula which is continuously dividing. The shape of the blastula begins with irregularly curved cell changes. This blastula formation process is called blastulation. Inside the blastula, there is a cell fluid called the blastocoel. In the blastula wall, there is a sticky part that will help the process of attaching the zygote to the endometrium (uterine wall) or called the implanting process. Furthermore, the blastula will undergo a process of gastrulation or the process of cavity formation (gastrus).

Single-cell (which has been fertilized)

After initial fertilization, a diploid zygote nucleus is formed. Next will undergo mitotic division and begin the next stage of embryogenesis which is the formation of morula, blastula, gastrula, neurula, and ends in organogenesis)

Morula

After the initial cell division (cleavage), the cells in the embryo will divide miosis quickly into many small cells called blastomeres.

Blastula

Morula will experience a division that continues to form a cavity in the middle. This cavity is getting bigger and bigger with liquid. An embryo that has this cavity is called a blastula. This is called the blastocele.

Gastrula

Gastrula comes from the word gastric (stomach) because at this stage it will form a cavity that will become the digestive tract. The gastrula cavity is called a gastrosel (archenteron). After reaching the form of the blastula, cell mass increase still continues with the mitotic division.

Neurula

After the gastrula is formed, the embryo will differentiate, namely the change of cells that have not been specialized into cells that have a special structure and function. This means changes in physical properties and function of cells as cells multiply from the embryo to form different body structures.

Organogenesis

After neurulation, the embryo begins to reorganize to form a more perfect embryo through several stages, namely:

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Embryogenesis

several phases

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Class: College

Subject: Biology

Keyword: embryo, phases, cells

synovial joints are characterized by the presence of a joint cavity. the walls of this space are formed by the articular capsule, a fibrous connective tissue structure that is attached to each bone just outside the area of the bone’s articulating surface. the bones of the joint articulate with each other within the joint cavity.

friction between the bones at a synovial joint is prevented by the presence of the articular cartilage, a thin layer of hyaline cartilage that covers the entire articulating surface of each bone. however, unlike at a cartilaginous joint, the articular cartilages of each bone are not continuous with each other. instead, the articular cartilage acts like a teflon® coating over the bone surface, allowing the articulating bones to move smoothly against each other without damaging the underlying bone tissue. lining the inner surface of the articular capsule is a thin synovial membrane. the cells of this membrane secrete synovial fluid (synovia = “a thick fluid”), a thick, slimy fluid that provides lubrication to further reduce friction between the bones of the joint. this fluid also provides nourishment to the articular cartilage, which does not contain blood vessels. the ability of the bones to move smoothly against each other within the joint cavity, and the freedom of joint movement this provides, means that each synovial joint is functionally classified as a diarthrosis.

outside of their articulating surfaces, the bones are connected together by ligaments, which are strong bands of fibrous connective tissue. these strengthen and support the joint by anchoring the bones together and preventing their separation. ligaments allow for normal movements at a joint, but limit the range of these motions, thus preventing excessive or abnormal joint movements. ligaments are classified based on their relationship to the fibrous articular capsule. an extrinsic ligament is located outside of the articular capsule, an intrinsic ligament is fused to or incorporated into the wall of the articular capsule, and an intracapsular ligament is located inside of the articular capsule.

at many synovial joints, additional support is provided by the muscles and their tendons that act across the joint. a tendon is the dense connective tissue structure that attaches a muscle to bone. as forces acting on a joint increase, the body will automatically increase the overall strength of contraction of the muscles crossing that joint, thus allowing the muscle and its tendon to serve as a “dynamic ligament” to resist forces and support the joint. this type of indirect support by muscles is very important at the shoulder joint, for example, where the ligaments are relatively weak.

additional structures associated with synovial joints

a few synovial joints of the body have a fibrocartilage structure located between the articulating bones. this is called an articular disc, which is generally small and oval-shaped, or a meniscus, which is larger and c-shaped. these structures can serve several functions, depending on the specific joint. in some places, an articular disc may act to strongly unite the bones of the joint to each other. examples of this include the articular discs found at the sternoclavicular joint or between the distal ends of the radius and ulna bones. at other synovial joints, the disc can provide shock absorption and cushioning between the bones, which is the function of each meniscus within the knee joint. finally, an articular disc can serve to smooth the movements between the articulating bones, as seen at the temporomandibular joint. some synovial joints also have a fat pad, which can serve as a cushion between the bones.