Comprehensive Human Reproduction and Embryonic Development

Insemination

Insemination occurs when the male ejaculates, releasing sperm into the vagina at the entrance of the uterus.

Journey of sperm after insemination

After insemination, sperm travel through the cervix, into the uterus, and then into the uterine tubes.

Corona radiata

The corona radiata is a layer of follicle cells that surrounds a mature egg.

Sperm penetration of the egg

Sperm use enzymes contained in the acrosome to break down the cells surrounding the egg, requiring many sperm to achieve this.

Successful sperm entry into the egg

The entrance of one sperm into the egg stimulates the formation of a fertilization membrane, preventing any additional sperm from entering.

Changes in the egg after sperm entry

Once a sperm enters the egg, its tail is absorbed, and the head moves through the cytoplasm to form the male pronucleus, stimulating meiosis II in the egg.

Fusion of male and female pronuclei

When the male and female pronuclei fuse, fertilization is complete, resulting in the formation of a zygote.

Location of fertilization in the female reproductive system

Fertilization usually occurs about one-third of the way along the uterine tubes.

Zygote and its potential

A zygote is a single cell resulting from fertilization, with the potential to develop into a genetically unique human.

Cleavage in zygote development

Cleavage is the process by which the zygote immediately divides by mitosis after fertilization, resulting in progressively smaller cells until a solid ball of cells is formed.

Development of the zygote after fertilization

After fertilization, the zygote travels down the uterine tubes and begins mitosis, resulting in the formation of two cells and continuing to divide into a solid ball of cells called a morula.

Blastocyst

A blastocyst is a hollow ball of cells that forms after about 6 days of development when the zygote reaches the uterus.

Inner cell mass of a blastocyst

The inner cell mass, or embryoblast, is a group of about 30 cells on one side of the blastocyst that will develop into the embryo.

Implantation in early embryonic development

Implantation is the process where the blastocyst sinks into the endometrium and attaches to the wall of the uterus.

Nourishment after implantation

After implantation, the blastocyst absorbs nutrients from glands and blood vessels in the endometrium.

Role of hormones from the corpus luteum

Hormones from the corpus luteum maintain the endometrium, which is essential for the continued development of the blastocyst.

Trophoblast development

The trophoblast develops into the chorion and placenta, which are necessary to support and develop the fetus.

Stem cells

Stem cells are unspecialized cells capable of repeated division and can differentiate into any type of cell under the right conditions.

Proliferation in stem cells

Proliferation refers to the process where cells replicate themselves many times over.

Differentiation

The process by which unspecialized stem cells develop into a particular type of cell.

Zygote

A totipotent stem cell, meaning it has the potential to develop into any type of cell.

Pluripotent stem cells

Stem cells found in the inner cell mass of the blastocyst, capable of differentiating into most tissues of the body, except for the placenta and umbilical cord.

Multipotent stem cells

Stem cells that can form cells with specific functions, such as blood stem cells that give rise to red blood cells, white blood cells, and platelets.

Embryonic period

The first two months of development, after which the developing organism is referred to as a fetus.

Primary germ layers

Three layers formed during embryonic development: ectoderm, mesoderm, and endoderm.

Ectoderm

Gives rise to the nervous system, sensory epithelium of the eye, ear, and nose, epidermis and its appendages (nails and hair), and mammary glands.

Mesoderm

Forms connective tissue, cartilage, bone, striated and smooth muscles, heart walls, blood and lymph vessels, kidneys, and gonads.

Endoderm

Forms the lining of the alimentary canal and its glands, the lining of the bladder, and the respiratory system.

Amnion

Surrounds the embryo, secretes amniotic fluid which acts as a shock absorber, and helps maintain a constant temperature.

Chorion

Formed from the outer cells of the blastocyst and mesodermal cells, surrounds the embryo and the other three membranes, and forms the main part of the fetal placenta.

Yolk sac and allantois

The two additional membranes that become part of the umbilical cord.

Placenta

A combination of fetal and maternal tissues, formed from the chorion, with the fetal part developing from the chorionic membrane and the maternal portion from the endometrial lining.

Chorionic villi

Small finger-like projections that develop in the outer layer of the chorion, playing a crucial role in the exchange of nutrients and waste between the mother and fetus.

Role of the placenta

Supplies nutrients to the fetus, removes wastes, and produces hormones such as human chorionic gonadotropin (hCG) to maintain the corpus luteum at the beginning of pregnancy.

Nutrient and waste exchange

Occurs by diffusion and active transport, with the two blood supplies not mixing due to cellular separation.

Endocrine function of the placenta

The endocrine function of the placenta involves secreting hormones necessary for maintaining pregnancy, including hCG and progesterone.

Immune system contribution of the placenta

The placenta transports antibodies from the mother to the fetus, providing the fetus with immunity to some infectious diseases.

Excretory function of the placenta

The excretory function of the placenta transports nitrogenous wastes from the fetal blood to the mother's blood supply for excretion by the mother's kidneys.

Nutritional role of the placenta

The nutritional role of the placenta involves transporting nutrients from the mother's blood to the fetal blood and storing essential nutrients early in pregnancy to release later when demand is greater.

Respiratory function of the placenta

The respiratory function of the placenta includes transporting oxygen from the mother to the fetus and carbon dioxide from the fetus to the mother.

Umbilical cord function in fetal circulation

The umbilical cord contains two umbilical arteries that carry blood from the fetus to the chorionic villi and one umbilical vein that transports blood from the placenta to the fetus.

Development of the embryo after one month

After one month, the embryo shows muscle segments that will become the spinal cord and brain, and features such as the heart, liver, and early formation of facial structures.

Key features of the embryo by the end of four weeks

By the end of four weeks, the embryo has about 30 pairs of muscle segments, and the brain, heart, and liver begin to form, along with the development of a tail and pharyngeal arches.

Appearance of arm and leg buds in the embryo

Arm and leg buds become apparent by the fifth week of embryonic development.

Changes in fetal length and weight at 3 months

At 3 months, the fetus doubles in length, with a length of approximately 18 cm and a weight of about 100 g.

Development of limbs and sensory features at 4 months

By 4 months, the arms and hands are fully shaped, and the skeleton is complete.

Fine hair and reflexes development during the 5th month

Yes, during the 5th month, fine hair covers the body, gripping reflexes develop, and growth increases, with kicking and turning felt.

Changes in respiratory and digestive functions at 6 months

At 6 months, respiratory movements begin, digestive glands start functioning, and eyebrows grow, indicating obvious signs of pregnancy.

Growth pattern observed during the 7th month of fetal development

The 7th month is characterized by the greatest growth of the fetus.

Changes in fat accumulation and growth rate during the 8th month

In the 8th month, there is an accumulation of fat under the skin, and growth slows down.

Physical features and reflexes present at 9 months of fetal development

At 9 months, the eyes are open, the nose is well formed, sucking and grasping reflexes are apparent, and fine body hair is shed.

Effect of maternal antibodies on the fetus during the 9th month

During the 9th month, maternal antibodies cross the placenta, providing temporary immunity to the fetus.

Fetal movement by the end of the 9th month

By the end of the 9th month, movement stops due to lack of space.