Human Development and Pregnancy

General Development

• Cell differentiation and overall development in humans is regulated by a combination of genetic, endocrine, and environmental factors.
• Prenatal development is categorized into three-month periods called trimesters.
• The embryonic period spans the first eight weeks, equivalent to two-thirds of the first trimester. Tremendous changes occur, such as cell division and redistribution, and the formation of tissues, organs and supporting structures for the developing embryo.
• The fetal period begins from the ninth week until birth, encompassing the final third of the first trimester and the second and third trimesters, during which rapid body growth and organ maturation transpire.

Pregnancy

• Pregnancy includes fertilization, implantation, membranes formation, embryonic/fetal development, and birth
• Key control mechanisms in these processes are hormones like progesterone, LH, hCG, prostaglandins, oxytocin, and prolactin

Fertilization

• Fertilization unites male and female gametes, creating a single cell with 23 chromosomes from each parent, totaling 46.
• The egg released from the ovary is swept into the fallopian tube, propelled towards the uterus via muscular contractions and cilia movement.
• Sperm must meet the egg within 12-24 hours of its release in the fallopian tube for fertilization to occur.
• Several hundred million sperm cells are released during ejaculation, navigating through the cervix and uterus to reach the correct fallopian tube
• Many sperm are eliminated by the vagina's acidic environment, and only a few dozen to hundreds reach the egg.
• The egg's plasma membrane has a zona pellucida, a protein/carbohydrate layer which in turn is surrounded by the corona radiata, follicle cells nourishing the egg within the ovary.
• Upon reaching, the acrosome of the sperm releases enzymes to digest a path through the corona radiata and zona pellucida using its flagellum to advance.
• This clearing requires the action of hundreds of sperm.
• Once one sperm enters the egg, the plasma membrane prevents further sperm binding or entry.
• Within approximately 12 hours the nucleus of the joined egg/sperm disappear
• The 23 chromosomes from sperm and egg combine
• Fertilization is complete, resulting in a diploid zygote containing 23 pairs of chromosomes (46 total).

Implantation

• After fertilization, the egg travels through the fallopian tube toward the uterus, marking the beginning of implantation.
• Upon reaching the uterus after 5-7 days, the zygote transforms into a blastocyst composed of an outer trophoblast layer and an inner cell mass.
• The blastocyst attaches to the endometrium with the inner cell mass positioned against it.
• Trophoblast cells secrete enzymes, digesting endometrial tissues and blood vessels as the blastocyst slowly sinks into the uterine wall. Implantation is complete by the tenth to fourteenth day, marking the start of pregnancy.

hCG

• Shortly after implantation, the trophoblast begins production of human chorionic gonadotropin (hCG).
• hCG mimics LH, supporting the corpus luteum beyond its typical degeneration time
• The maintenance of the corpus luteum leads to continuous estrogen and progesterone secretion, which is necessary for sustaining the endometrium and preventing menstruation cycles.
• hCG secretion remains high for about two months, then decreases by the end of the forth
• Post-first trimester, the placenta assumes primary responsibility for secreting estrogen and progesterone for endometrial maintenance, reducing the corpus luteum's significance/ hormone role.

Extra-Embryonic Structures

• During the second week, the blastocyst completes implantation, and the inner cell mass evolves, creating a space between it/the trophoblast.
• The amniotic cavity, filled with fluid, develops as the site where the baby will develop from the inner cell mass, enclosed by the amnion sac.
• Between the third and eighth weeks, embryonic internal organs develop, along with external membranes: the allantois, amnion chorion, and yolk sac.
• Protection, nutrition, respiration, and excretion of the embryo (later, the fetus) is handled by extra-embryonic membranes, placenta, and umbilical cord.
• At birth, the placenta, umbilical cord, and extra-embryonic membranes are expelled from the uterus.

Key Membrane functions and origins

• Amnion: A transparent sac from the embryonic disk enclosing the embryo with fluid to protect from trauma and temperature fluctuations while allowing movement.(fluid is called amniotic fluid)
• Yolk Sac: A sac suspended from the embryo's abdomen that contributes to digestive tract formation and produces the first blood and germ cells
• Allantois: Forms the foundation of the umbilical cord and later degenerates to become part of the urinary bladder
• Chorion: The outermost membrane enclosing other extra-embryonic membranes and the embryo

Placenta

• By the end of the second week post-fertilization, finger-like chorion projections extend into the uterine lining, establishing the placenta's foundations.
• The placenta as a blood vessel-rich, disk-shaped organ that attaches the embryo/fetus to the uterine wall to faciliate metabolic exchange
• It is fully developed by the tenth week and weighs about 600g
• The placenta originates from both the embryo and the mother, where the chorion tissue comes from the embryo and the blood pools from the mother's circulation.
• Maternal and embryonic blood systems remain separate but close allowing oxygen and nutrients to diffuse from mother and waste removed from baby
• The placenta filters substances such as alcohol, drugs, and nicotine which can diffuse across the membranes in the mother's blood, and can severely affect the developing baby
• Near week eight, the umbilical cord forms, averaging 60 cm long and 2 cm in diameter, connecting to the placenta's center as yolk sac shrinks and amniotic sac enlarges.
• The umbilical cord contains two arteries carrying oxygen-depleted blood to the placenta and one vein carrying oxygen-rich blood to the fetus

Placenta functions

• Nutritional: Transports nutrients (e.g., glucose, amino acids, fatty acids, minerals, vitamins) from mother's blood to the fetus and stores these, releasing them later as the baby needs.
• Excretory: Transports metabolic waste (urea, ammonia, creatinine) from fetal blood to the mother's blood
• Respiratory: Facilitates the transfer of oxygen from the mother to the fetus and carbon dioxide to the mother
• Endocrine: Secretes hormones (estrogen, progesterone, hCG) and allows hormone exchange between mother and fetus
• Immune: Transfers antibodies from the mother to the fetus, providing passive immunity

Parturition

• Parturition, or childbirth, is commonly called labour and typified by uterine contractions
• The uterus contracts continously during pregnancy, first at slight intensity every 15-20 mins for 20-30 seconds
• Nearing the end of term the contractions increase in frequency and strength
• Labour is determined by contractions occurring every 15-20 secs lasting 40 secs

Labour

• Positive feedback mechanisms drive the onset and progression of labour initiated by neural and hormone components

1. Cervix stretching causes oxytocin release from the posterior pituitary gland
2. Oxytocin stimulates uterine muscles directly and through prostaglandins
3. Contractions push the fetus down, stretching the cervix more
4. The cycle repeats until the baby is born

Delivery

• Physicians may perform a C-section (caesarean delivery) if a normal vaginal birth is unsafe or not feasible
• A C-section involves an incision through the mother's uterus and abdomen to remove the baby
• After normal breathing is established the umbilical cord is clamped, cut, tied, and the new born is now cut off from the source of protection and nutrients it has depended on for nine months
• The cord dries and shrivels, turning into what will be the belly button

Lactation

• Hormones regulate lactation. Milk is secreted from the mammary glands
• Prolactin, needed for milk product is not secreted during pregnancy due to suppression from high levels of progesterone and estrogen from the pituitary gland
• The anterior pituitary produces and secretes prolactin after birth
• Before milk production the breasts secrete colostrum, a similar and thin yellowish fluid with more protein and less fat then milk
• Milk and colostrum provide antibodies, that protect against disease

Lactation

• Baby Suckling->stimulates nerve endings in nipple and areola-> hypothalamic stimulation->posterior pituitary oxytocin release->mammary lobule contraction->milk flow to nipple through duct-> baby suckling maintains milk production/stopping will stop production in days

Embryonic and Fetal Development

• Embryonic development studies the development from fertilization to parturition.
• The stages are as fertilization/cleavage to produce zygote, then blastocyst stage->gastrulation, and then morphogenesis.
• The aim Is to identify major tissue and organ differentiations.
• As well as the morphological development of the ectoderm for the nervous system /epidermis.
• The skeleton/muscles/reproductive systems arise from the mesoderm.
• Lining of digestive organs and endocrine glands are produced from the endoderm

Cleavage

• The zygote divides 30 hours after fertilization by mitosis first to two new cells and then to four etc.
• The cells resulting from the dividing zygote become smaller but over all the size remains 0.1mm
• When the structure becomes a sphere of 16 cells it is called a morula

Blastocyst

• When the morula reaches the uterus in 3 to 5 days the fluid filled uterus diffuses into it
• The structure is now called a blastocyst which develops two groups of cells
• Forming an outer layer called a trophoblast
• The other group comes together within it to form the inner cell mass

Gastrulation

• The blastocyst attaches to the endometrium after 5–7 days post-fertilization – process termed implantation.
• During the second week the inner cell mass transforms forming aminiotic cavity which is the fluid environment for development
• The mass flattens to a distinct embryonic disk attached by a support/short stalk that links the blastocyst

Germ Layers

• Ectoderm is the outer layer, closer to the amniotic cavity surface.
• Innermost layer or endoderm
• Mesoderm develops between the endoderm ,which forms the three primary germ layers.
• Process is called gastrulation and the now developing embryo is gastrula. Ectoderm:
• Nervous System
• Epidermis
• Mesoderm:
• Skeleton
• Muscles
• Reproductive Structures
• Endoderm:
• Lining of Digestive System
• Lining of Respiratory Systems
• Endocrine Glands

Morphogenesis and Differentiation

• During gastrulation, morphogenesis (organ system forming events) begins, relies on the ability of embryonic cells ability to differentiate into cell types,.
• Differentiation is the process in which a cell develops a specific shape /function for other cells.
• The three primary germ layers is important as development and formation of structures come from these through cellular actions.

Embryonic Development

• Organ structure begins, as well as tissue folding because various cell division happens
• Body forms structure that start to form a recognizable human structure

3rd and 6th weeks

• 3rd week the mesoderm develops along the embryonic dick, going along the baby's back to form the skeleton
• The nervous system comes from the ectoderm just above
• Neurulation is the process of a developing neural tube becoming the brain/spinal cord
• Week three comes more organs/heart start
• About 0.6 cm / Blood vessels begin to form plus lungs
• In the sixth week, Brain rapid development and limbs extending as well as development of genitalia starts

Key periods in organogenesis

• Week seven-eight is marked by distictive structure and nervous connectivity
• Cartilage turns to skeleton formation
• Eyes formed but eyelids stuck together
• The 8th week has nostrill plugs of mucus to protect from uteral contaminants
• Undifferentiated external genitalia
• As the 8th week ends the embryo has reached paerclip size and 90& of its adult structures as well with the organs developing till birth

From the 9th week

• 9th week starts fetus development and difference in the stages relate to the organ systems, as things take shape it is now called a fetus rather then an embryo
• Fetus is present and organ continue, embryonic is when organs take shape
• A fetus is the growth and refinement of existing structures

First trimester is week 1-12

• Growth accelerates in body length while growth of the head has slowed
• Cartilage hardens in the skeletal system as well
• The external organs become distinguished as well

Second trimester week 13-24

• The fourth month is when heart beats
• Brain grows and nerves start to function
• Legs grow and development
• The baby becomes covered in fine soft hair

Third Trimester

• This is important for brain cells, connection and networks
• Male testes dissent to scrotum
• Fat layer developments
• System mature late in gestation

Last stage of gestation

• Nutrition is important for damgages to lead to low weight and retardation of development as well as learning differences and short stature
• Normal gestation of the 265 days after a single cell is formed to become a multi trillion cell being

Harmful external factors

• An agent that causes a structural irregularity via pregnancy from outside influence

Factor of contamination

• From what the dam in heels in or ingestion from body processes, in the first nine weeks organs develop
• Alcohol, or smoking and damage

Cigarette Smoking

• Damage causes constriction in blood delivery while being damaging to mothers and underweight babies
• Brain deficiencies as well as behavioural issues

Alcohol

• Fetus brain is targeted as wells and cns in regards of physiology development
• Can cause abnormalities of the Face as well, with challenges in learning or memory and aggression

Sterility And Fertility

• Male and obstruction, low sperm, erectile
• Female blocked follicles, fail to stimulate, endometic, damagers

Technologies in reproduction for fertility

• Includes artificial intimation, vitro fertilization, transfer of germ cells, for others

Artificial Insemination

• Sperm can be collected concentrated to deliver
• They can be donors either or the stranger in the sperm store.

Vitro

• Ultrasound and follicles close to ovulation
• Eggs can be taken and harvested from follicles
• After combining with sperm for implantation
• Development is continued in vitro

Gifting

• Germ cells transfer as an external method

Surrogate

• Have others that be contracted for in couples who suffer some sterility problems
• Where sperm or both sperm and Ova can be delivered to the womb from sperm donation and donor
• superovulation is done as multiple hormone treatments, that's done with rare ovulation in reproduction and

decreasing factors

• Are abstinence, sterilized, hormone treatments, chemical or biological barrier and natural regulation

Hormonal Contamination

• Hormone and the oral treatment
• FSH and LH which prevent ovulation

Pills in Hormones

• High progesterone and Estogen which prevent embryo
• Effectiveness goes down post
• As hours between increase, it drops

Birth Control Method

• Also by use of IUD inter uterine devices or by barrier or chemical including spermicide gels

Natural

• Natural is tracking which is based on
• Pull out control