EMBRYOL Chapter 1 - Embryology: History and Concepts

His studies are significant for us because they represent a shift from superstition and conjecture toward observation

Learned much about the structure of relatively advanced fetuses when the development of the microscope allowed the study of early stages of embryos

In Holland, the human sperm was first seen in 1677 by

In 1672, ovarian follicles were described by

Contended that the sperm contained the new individual in miniature and was merely nourished in the ovum

Argued that the ovum contained a minute body, which was stimulated to grow by the seminal fluid

Discovered in 1745 that the eggs of some insects can develop parthenogenetically (without the participation of sperm), which strengthened the ovists' cause

A German biologist that wrote a thesis setting forth the conception of epigenesis

His work during 1828 in Estonia first emphasized the fact that the more general basic features of any animal group appear earlier in development than do the special features that are peculiar to different members of the group (von Baer's law)

The foundation of modem embryology was laid down and embryology as a science began because of the formulation of the cell theory by German biologists

The zygote has a dual origin from two gametes

Refers to the time of fertilization that represents the starting point in an individual's life history; Individual's entire life span

German biologist that made the important distinction between the soma (body) and the germ-cell line (gametes)

Weismann: All-important for perpetuation of the species

Weismann: Vehicle for protecting and perpetuation the germ plasm

The period starting with fertilization and ending with metamorphosis in Amphibia, hatching in birds, and birth in mammals.

Also deals with the development and maturation of gametes

The development and maturation of gametes

Between 1880 and 1890, the new techniques of serial sections and of making three-dimensional wax plate reconstructions from them provided the basis for

Arose late in the 19th century. A great interest in evolution was a driving force behind the development of this field. Provided the insight for the concept that "ontogeny recapitulates phylogeny"

The acquisition of detailed structural information on embryos paved the way for the growth of this field. They seek to understand causative factors in development by posing hypotheses and testing them by manipulating the embryos.

One of the pioneers of experimental embryology who performed an experiment that ushered in the era of this field. He destroyed one cell (blastomere) of a two-cell frog embryo with a hot needle.

This showed that if the cells of a two-cell frog embryo are entirely separated, each cell is capable of giving rise to a complete individual. This experiment provided proof of the untenability of the preformationist doctrine and laid the foundations for a new field

Roux coined the German word Entwicklungsmechanik which means

Development is brought about by a series of causal interactions between the various parts; and also reminds one that genetic factors are among the most important determinants of development

During the 1930s and 1940s newly emerging chemical and biochemical techniques led to the establishment of this field, which provided descriptive information about chemical and physiological events in the embryo

The branch of embryology concerned with the study of malformations

The rapid growth of research related to problems of conception and contraception has led to the establishment of a discipline that is commonly called

A popular way of looking at embryonic development is through the approach known as ____. This field includes not only embryonic development, but also postnatal processes such as normal and neoplastic growth, metamorphosis, regeneration, and tissue repair at levels of complexity ranging from the molecular to the organismal

A technique that allowed childless couples to have children from their own genetic heritage. It is used in cases where both the mother and father are capable of producing viable eggs and sperm cells, but because of a blockage in the women’s uterine tubes the ovulated eggs are unable to be fertilized in her body and then become transported to her uterus

Just before the eggs would normally be shed from the ovary, a doctor, using a technique called

Some women who are able to produce fertile eggs but are unable to carry an embryo to term in their own uteri have made arrangements with other women to act as

This technique makes it possible to determine the sex of a baby before it is born and to detect the presence of genetic conditions that could lead to a defective child

This technique allows the diagnosis of many anatomical defects in fetuses. Some of these can be dealt with by means of intrauterine surgery

[Intracellular Synthesis and Its Regulation] In an interphase cell (one between mitotic divisions) certain portions of the nuclear DNA molecule are free of restricting proteins that bind to the DNA and can direct the synthesis of messenger RNA (mRNA).

The newly formed RNA molecules commonly contain regions (exons) that code for specific segments of a protein molecule and other regions (introns or intervening sequences) that appear to contain no information directly involved in the amino acid sequence of the protein to be formed

[Intracellular Synthesis and Its Regulation] The introns are enzymatically cut out and the remaining exons are spliced together to form the definitive mRNA molecule. After processing, the newly formed mRNA molecules migrate from the nucleus into the cytoplasm of the cell via pores in the nuclear membrane

[Intracellular Synthesis and Its Regulation] Once in the cytoplasm, the mRNA molecules may follow either of two chief pathways, depending on the type of

[Intracellular Synthesis and Its Regulation] For the formation of protein molecules that are destined to function within the cell (structural proteins and most enzymes), the mRNA molecules link up with ribosomes to form _______, the length of which varies according to the size of the protein that is being made

[Intracellular Synthesis and Its Regulation] If, however, the mRNAs are coding for proteins that will be secreted from the cell (e.g., collagen, immunoglobulins), the mRNA forms complexes with the rough endoplasmic reticulum. These are called

The polypeptide chains that are formed in the rough endoplasmic reticulum are then transported to the Golgi apparatus, where they are commonly linked with ________.

From the Golgi complex, the finished proteins are then brought to the cell membrane within vesicles and emptied into the medium surrounding the cell

Many extracellular influences of regulatory mechanisms are mediated by ______ located at the cell surface

In __________, messenger RNA is first transcribed on the DNA template

(1). After processing within the nucleus

(2), the mRNA leaves the nucleus through nuclear pores

(3). The synthesis of intracellular proteins

(4) is accomplished by polysomes, which consist of molecules of mRNA associated with ribosomes. Synthesis of proteins for export from the cell is accomplished on the rough endoplasmic reticulum

(5). From there they are transported

(6) to the Golgi apparatus

(7), where they may be complexed with newly synthesized polysaccharides. Small membrane-bound vesicles containing the proteins leave the Golgi apparatus

(8) and, when they reach the cell membrane

(9), fuse with it and release the protein molecules by a process called exocytosis

Extracellular signaling substance

The overall sequence of events from the binding of an extracellular signaling substance (called a ligand) by cell-surface receptors to the activation of specific genes or the stimulation of other intracellular processes is commonly called

Receptors that develop active intracellular enzyme activity (e.g., tyrosine-specific protein kinase) when bound to their ligand

Receptors that activate cellular processes through an intermediate protein

A cell's plasma membrane is composed of a

A component of the cell surface that has at least 130 varieties, constitute about 5% of the lipid molecules in the outer surface of the plasma membrane

A type of junctional complexes that bind epithelial cells together in small spots. Also serve as focal points for the attachment of fibrillar intracellular proteins

Another spot-like junction which mediates communication and the exchange of small molecules between two cells

Found along the surface of many epithelia which bind adjacent cells together, forming an impermeable barrier to the outside. It also prevents the mingling of membrane proteins on either side of the junction

An important property of most embryonic structures. A number of crucial experiments have shown that like cells tend to stick together and sort out from cells of a different sort.

This person demonstrated cell adhesion by squeezing a sponge through a silk mesh and dissociating it into individual cells. The dissociated cells later reaggregated and ultimately formed a new sponge

In later work, when two species of sponges were thus treated, the disaggregated cells sorted out according to species, and the two original types of sponge re-formed

1. Ca⁺⁺-mediated adhesion

2. N-CAM (neural cell adhesion molecule)

3. Lock and key fashion (heterophilic binding) between complementary saccharides

The surface morphology of cells can be examined with

At a finer level, the surface morphology of cells is examined using the technique

Cells are embedded in or rest upon this part which is a macromolecular meshwork that varies in composition from one tissue to the next and from one developmental period to the next

Epithelial-cell layers rest upon a thin sheet-like form of extracellular matrix

Embedded in a massive extracellular matrix designed to support great weight

The spaces between different tissues are filled with this extracellular matrix that serves as both a biological packing material and a means of transmitting mechanical tension

Represents an extreme example of an extracellular matrix designed to transmit powerful mechanical forces from a muscle to a bone

The generic term for a family of glycoproteins that are characterized by having glycine as every third amino acid and also by possessing two amino acids, hydroxyproline, and hydroxylysine, which are rarely found in other proteins

Basic unit of collagen

Involved in attaching cells to other components of the extracellular matrix. In developmental processes characterized by the migration or extension of cells, these are an important feature of the substrates through which the cells move

I. Fibronectin (skin, bone, tendons, teeth, cornea, ligaments, interstitial connective tissue (about 90% of collagen is type I))

II. Chondronectin (Cartilage, notochord, vitreous body (eye), cornea (chick))

III. Fibronectin (Skin, blood vessels, sclera, many organs, skeletal muscle)

IV. Laminin (Basal laminae)

V. Fibronectin (Placenta, blood vessels, smooth muscle)

X. Chondronectin (Hypertrophying cartilage)

Best understood of the attachment glycoproteins; a dimer with similar polypeptide subunits of 220-250,000 daltons.

Accounts for the fibronectin's cell-binding properties

The RGD sequence of fibronectin attaches to a specific cell-surface binding protein that is a member of a large family of binding proteins

Sites of fibronectin attachment to cells are also areas upon which bundles of ___, an important intracellular contractile protein, converge

A glycoprotein with an analogous function; mediates the attachment of chondrocytes (cartilage cells) to type II collagen in cartilage matrix

A major attachment glycoprotein that is cross-shaped molecule composed of three A chains of 200,000 daltons each and one B chain of 400,000 daltons. Laminin is a major component of basal laminae, where it binds cells to type IV collagen and other matrix molecules

Shaped like an irregular 6-pointed star which is found in much more restricted circumstances in development than either fibronectin or laminin, displays different degrees of adhesiveness to several types of cells

It is formerly called mucopolysaccharides, constitute another of the fundamental groups of extracellular matrix molecules. Although they are large molecules, most consist of repeated disaccharide units.

It bind large amounts of water, which is important in maintaining the physical and mechanical properties of different types of extracellular matrix. The water-binding properties of hyaluronic acid make it particularly important in early developmental processes

These are immense molecules of the extracellular matrix with molecular weights in the millions. Consists of a brush-like monomer, with a protein core and numerous glycosaminoglycan branches