Fifth Through Eighth Weeks of Stages Fetal Development /Weeks five through eight of gestation are characterized by the development of the major organ systems, including the circulatory, nervous, lymphatic, and gastrointestinal systems. During this time, the embryo is extremely susceptible to the effects of teratogens. Development Cardiovascular System The first organ system to develop during … [Read more…]
Fourth Week of Development of Embryo (the embryonic disc) will grow from about 2 to about 6 mm. The processes of the third week (neural tube formation, development of blood circulation) continue in the fourth week. At the same time, the amnion increases enormously in size, while the yolk sac does not. This is the … [Read more…]
Third Week of Development/The third week is concerned with establishing left and right handedness, the craniocaudal axis, as well as the conversion of the bilaminar disc into a trilaminar embryo. Additionally, there is further specialization of the extraembryonic structures that will continue to support the embryo during the intrauterine phase. Gastrulation During gastrulation, the embryo … [Read more…]
Trophoblast Development/Week 2 is often referred to as the week of twos. It’s the week when the embryoblast, extraembryonic mesoderm and trophoblast each separate into two distinct . Trophoblast Development Trophoblasts are the outer layer of cells that provide nutrients to the embryo and form part of the placenta. Key Points The trophoblast is subdivided into two layers, the inner cytotrophoblast, … [Read more…]
Oogenesis is the maturation of the female gametes through meiotic division. Key Points Oogenesis starts with the process of developing oogonia via the transformation of primordial follicles into primary oocytes, a process called oocytogenesis. Oocytogenesis is complete either before or shortly after birth in humans. During the menstrual cycle primary oocytes complete maturation through further … [Read more…]
The female reproductive system is made up of the internal and external sex organs that function in the reproduction of new offspring. In humans, the female reproductive system is immature at birth and develops to maturity at puberty to be able to produce gametes and to carry a fetus to full term. The internal sex organs are the uterus, Fallopian tubes, and ovaries. The uterus or womb accommodates the embryo which … [Read more…]
The Male sexual response cycle is a four-stage model of physiological responses to sexual stimulation, which, in order of their occurrence, are the excitement, plateau, orgasmic, and resolution phases. This physiological response model was first formulated by William H. Masters and Virginia E. Johnson, in their 1966 book Human Sexual Response.[rx][rx] Since that time, other models regarding human sexual response have been formulated by several scholars … [Read more…]
The male reproductive system consists of the internal structures: the testes, epididymis, vas deferens, prostate, and the external structures: the scrotum and penis. These structures are well-vascularized with many glands and ducts to promote the formation, storage, and ejaculation of sperm for fertilization, and to produce important androgens for male development.[rx] The major male androgen is … [Read more…]
Meiosis is a special type of cell division of germ cells in sexually reproducing organisms used to produce the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately result in four cells with only one copy of each chromosome (haploid). Additionally, prior to the division, genetic material from the paternal and maternal copies of each chromosome is crossed over, creating … [Read more…]
The reproductive system in females is responsible for producing gametes (called eggs or ova), certain sex hormones, and maintaining fertilized eggs as they develop into mature fetuses and become ready for delivery. A female’s reproductive years are between menarche (the first menstrual cycle) and menopause (cessation of menses for 12 consecutive months). During this period, … [Read more…]
Acid-base balance is the homeostatic regulation of the pH of the body’s extracellular fluid (ECF).[1] The proper balance between the acids and bases (i.e. the pH) in the ECF is crucial for the normal physiology of the body—and for cellular metabolism.[1] The pH of the intracellular fluid and the extracellular fluid need to be maintained at a constant level. The body’s balance between acidity and alkalinity is referred to as acid-base balance. The blood’s acid-base balance … [Read more…]
Body fluids, bodily fluids, or biofluids are liquids within the human body. In lean healthy adult men, the total body water is about 60% (60–67%) of the total body weight; it is usually slightly lower in women (52-55%).[rx][rx] The exact percentage of fluid relative to body weight is inversely proportional to the percentage of body fat. A lean 70 kg (160 pound) man, for example, … [Read more…]