Morphological and functional features of gametes - eggs and sperm

Size and shape

The egg cell (or ovum, or oocyte) is the largest human cell. She measures 0.15 to 0.2 mm and is just visible to the naked eye. She is also the roundest cell, she is almost perfectly round (Fig. 4). She therefore has the largest volume in relation to her surface. The cell consists of a large amount of cytoplasm (= cell fluid) in which the nucleus is dissolved (and therefore invisible) until just before conception.

Sperm cells are the smallest human cells. They are no more than a nucleus with a small amount of cytoplasm, some mitochondria (the energy suppliers of the cell) and a long tail. They have hardly any content and are the straightest cells.
Egg cell and sperm are each others opposite. Large versus small, round versus straight, cytoplasm versus nucleus. The differences are great, at the same time they belong together if we perceive the ovum as a sphere and the straight sperm as the corresponding radius.

 

Mobility
The cytoplasm of a normal body-cell is in movement, the nucleus is not. The two gametes (= germ cells) show different features. The egg cell consists primarily of cytoplasm, she is internally mobile. The nucleus is outspread, the chromosomes are unwound (not folded up). The cell is internally active and mobile. The sperm cells have hardly any cytoplasm and are concentrated in their nuclear DNA. They have a crystalline structure. These cells are internally structured and rigid.

In contrast, the ovum is externally not active. After her release, she is passively moved by the fluid-flow in the oviduct (uterine tube), while the sperm cells are active, using their tails to swim against the stream of fluid in the oviduct. They are externally active and mobile.

The ovum is internally mobile and externally passive, this is a polarity. The sperm shows the opposite: internally passive and externally mobile. Egg cell and sperm have a polarity and are opposite to each other, we see a double polarity.
Metabolism
An egg cell is a metabolically active cell; substances are absorbed and released. E.g. nutrients are absorbed, substances that affect the uterus and substances that attract the sperm are released. An egg cell lives only 12 to 24 hours in her own environment and cannot be preserved. The egg cell can easily be destroyed. She is an active cell and open to the environment.

Sperm cells do not absorb or release substances. There is no interaction with the environment. They live about 3 to 5 days in the womb and can be preserved and frozen at temperatures below 60 °C. They are not easy to destroy. They are closed off from the environment and metabolically passive.

The open and vulnerable state of the egg cell is polar to the closed and robust state of the sperm cells.
Number
For a conception one ovum and millions of sperm are required. The one ovum is worth as much as all those millions of sperm. A man with less than 20-40 million sperm in an ejaculation is barren. Such great numbers are necessary because most sperm do not reach the ovum. Also, for a conception more than one spermatozoon is necessary. See the page Conception.

The ovum is alone and the sperm are with millions. One sperm cell is nothing, one ovum determines everything. One is polar to millions. One comprises everything, it is all there is, whereas the millions of sperm cells are infinitive, have no importance on their own.

Location
The egg cell develops in one of the two ovaries in the warm abdominal cavity, the sperm develop in the testicles just outside the body in a relatively cold environment.

The ovum develops in warm- and sperm in relative cold conditions.

Development
Egg cells are produced well before birth in a huge number of so called primordial egg cells (primordial oocytes). From the beginning on, there is a continuous process of dying, so that at birth 2 million (!) are left. That process of dying goes on after birth. At the onset of puberty there remain about 40,000 ova. Then every four weeks a number of them begin a process of maturation. Of these, only one (sometimes two or three) ovum matures, the rest dies. In total about 400 ova mature (13 per year for 30 years). At menopause, no primordial egg cells are left.
In men, a very different process is going on. The first sperm cells are formed only from puberty on, before that they are not produced. Then the production goes on and on and never stops, hundreds per second, millions each day. Sperm cells are constantly being newly formed.

Egg cells are old cells that became mature. Primordial oocytes are in a process of dying. Sperm cells are newly formed and are young. The maturation process of ova is an expiring process, it stops. The formation of the sperm is a vital process, it never stops.

39) Basic approaches and principles of gene therapy. Gene therapy ex vivo, in vivo, in situ.

Gene therapy is the use of DNA as a pharmaceutical agent to treat disease. It derives its name from the idea that DNA can be used to supplement or alter genes within an individual's cells as a therapy to treat disease. The most common form of gene therapy involves using DNA that encodes a functional, therapeutic gene to replace a mutated gene. Other forms involve directly correcting a mutation, or using DNA that encodes a therapeutic protein drug (rather than a natural human gene) to provide treatment. In gene therapy, DNA that encodes a therapeutic protein is packaged within a "vector", which is used to get the DNA inside cells within the body. Once inside, the DNA becomes expressed by the cell machinery, resulting in the production of therapeutic protein, which in turn treats the patient's disease.

Gene therapy may be classified into the two following types:

[edit] Somatic gene therapy

In somatic gene therapy, the therapeutic genes are transferred into the somatic cells, or body, of a patient. Any modifications and effects will be restricted to the individual patient only, and will not be inherited by the patient's offspring or later generations. Somatic gene therapy represents the mainstream line of current basic and clinical research, where the therapeutic DNA transgene (either integrated in the genome or as an external episome or plasmid) is used to treat a disease in an individual.

[edit] Germ line gene therapy

In germ line gene therapy, germ cells, i.e., sperm or eggs, are modified by the introduction of functional genes, which are integrated into their genomes. This would allow the therapy to be heritable and passed on to later generations. Although this should, in theory, be highly effective in counteracting genetic disorders and hereditary diseases, many jurisdictions prohibit this for application in human beings, at least for the present, for a variety of technical and ethical reasons

This can be accomplished in three ways: ex vivo, in situ, or in vivo. Ex vivo involves removing cells from the patient, altering the genetic material, and placing them back into the patient. In situ requires the vector be placed directly into the affected tissues. In vivo gene therapy involves injecting the vector into the bloodstream.