Making of Human

 

Development of the human body is the process of growth to maturity. The process begins with fertilization, where an egg released from the ovary of a female is penetrated by a sperm cell from a male. The resulting zygote develops through mitosis and cell differentiation, and the resulting embryo then implants in the uterus, where the embryo continues development through a fetal stage until birth.

                                     Germinal Stage

 The germinal stage refers to the time from fertilization through the development of the early embryo until implantation is completed in the uterus. The germinal stage takes around 10 days. During this stage, the zygote begins to divide, in a process called cleavage. A blastocyst is then formed and implanted in the uterus. Embryonic development continues with the next stage of gastrulation, when the three germ layers of the embryo form in a process called histogenesis, and the processes of neurulation and organogenesis follow.

 

 Blastocyst Development

Blastocyst development is important stage for the formation of organs in embryo. The blastocyst stays inside a protective cover during maturation called zona pellucida, which could be described as an egg shell. The outer cells are located right below this cover, which will create the future placenta and surrounding tissues to support fetal development in the uterus. The inner cells of the blastocyst will become the different tissues and organs of the human body, such as bones, muscles, skin, liver, and heart.

 Embryo Development

As the blastocyst reaches the final steps in the implantation process into the inner lining of the uterus, it evolves into a structure called an embryo. This is the time when internal organs and external structures develop. The mouth, lower jaw, throat are emerging, while the blood circulation system starts its evolution and a heart tube is created. The ears arise and arms, legs, fingers, toes, and eyes are being shaped. The brain and the spinal cord are already formed, while the digestive tract and sensory organs start their development. The first bones are replacing the cartilage.

After ten-twelve weeks of pregnancy, the embryo moves into the final stage of development, a fetus.

Gastrulation

Gastrulation starts in the 3rd week, the inner cell or embryo starts differentiating into three germinal layers, i.e. ectoderm, endoderm and mesoderm. These cells transform and get differentiated to all the tissues and organs, like nerve, blood, muscle, bone, digestive tract, etc.

Ectoderm- nervous system, brain, spinal cord, epidermis, hair, nails, etc.

Mesoderm- connective tissue, muscles, circulatory system, notochord, bone, kidney, gonads

Endoderm- internal organs, stomach, liver, pancreas, bladder, lung, gut lining

 Fetal Development

By the twelfth week of fertilization the embryo moves into the final stage of development called the fetal stage. By now, the fetus has formed all of the organs and structures necessary for a baby, but those organs still need to grow and develop.

At three months of pregnancy, the upper and lower extremities of the fetus are completely developed. Ears and teeth are formed and the reproductive organs have evolved. At the end of this month, the fetus has completed the expansion of most of the circulatory and urinary systems and its length is about 5 inches.

At six months, the fetus can respond to sounds and is around 12 inches long. The fetus continues to develop and grow changing position and responding to sounds, and stimuli. The length of the little body can reach 14 inches.

The fetus becomes a baby at month eight. The brain is evolving quickly so the baby can see and hear, although the respiratory system requires maturation. The baby can weigh approximately 5 pounds. Close to the end of the pregnancy at month 9, the baby responds to stimuli, can move the whole body but space around the new human being is becoming too tight.

     

                                   

                                         PLACENTA

The interdigitated chronic villi of trophoblast and uterine cells form the placenta, which is the connection between the mother and the growing foetus.

The placenta provides nourishment and oxygen to the embryo and helps in removing carbon dioxide and waste produced by the embryo. It also acts as an endocrine gland and secretes various hormones like hCG (Human Chorionic Gonadotropin), estrogen, progestogens, etc. for maintenance of pregnancy.

                               Formation of Human Organ

1.The heart is the first functional organ to develop and starts to beat and pump blood at around 22 days.

2.The digestive system starts to develop from the third week and by the twelfth week, the organs have correctly positioned themselves.

3. The respiratory system develops from the lung bud, which appears in the ventral wall of the foregut about four weeks into development.

4. Brain developed around eight week

5. After12 week Male and female external genital differences observable

 Stages of Growth Month-by-Month in Pregnancy

First trimester

The first trimester will span from conception to 12 weeks. This is generally the first three months of pregnancy. During this trimester, your baby will change from a small grouping of cells to a fetus that is starting to have a baby’s features.

Second trimester

This middle section of pregnancy is often thought of as the best part of the experience. By this time, any morning sickness is probably gone and the discomfort of early pregnancy has faded. The baby will start to develop facial features during this month. You may also start to feel movement as your baby flips and turns in the uterus. During this trimester, many people find out the sex of the baby. This is typically done during an anatomy scan (an ultrasound that checks your baby’s physical development) around 20 weeks.

Third trimester

This is the final part of your pregnancy. You may be tempted to start the countdown till your due date and hope that it would come early, but each week of this final stage of development helps your baby prepare for childbirth. Throughout the third trimester, your baby will gain weight quickly, adding body fat that will help after birth.

  

Know The Making of Man and Woman

 

Child is a Father of man but which decides whether child becomes man or woman.We are  providing  here some interesting facts about  how biological activities determine the fetus future.

The normal human fetus of either sex has the potential to develop either male or female organs, depending on genetic and hormonal influences

Every fetus contains structures that are capable of developing into either male or female genitalia, and, regardless of the complement of sex chromosomes, all developing embryos become feminized unless masculinizing influences come into play at key times during gestation. 

    Most mammals, including humans, have an XY sex-determination system: the Y chromosome carries factors responsible for triggering male development. In the absence of a Y chromosome, the fetus will undergo female development. This is because of the presence of the sex-determining region of the Y chromosome, also known as the SRY gene. Thus, male mammals typically have an X and a Y chromosome (XY), while female mammals typically have two X chromosomes (XX). In humans, biological sex is determined by five factors present at birth: the presence or absence of a Y chromosome, the type of gonads, the sex hormones, the internal genitalia (such as the uterus in females), and the external genitalia.

 Chromosomal sex is determined at the time of fertilization; a chromosome from the sperm cell, either X or Y, fuses with the X chromosome in the egg cell. Gonadal sex refers to the gonads, that is the testis or ovaries, depending on which genes are expressed. Phenotypic sex refers to the structures of the external and internal genitalia.

A human fetus does not develop its external sexual organs until seven weeks after fertilization. The fetus appears to be sexually indifferent, looking neither like a male or a female. Over the next five weeks, the fetus begins producing hormones that cause its sex organs to grow into either male or female organs. This process is called sexual differentiation.

As we know In humans, each egg contains 23 chromosomes, of which 22 are autosomes and 1 is a female sex chromosome (the X chromosome). Each sperm also contains 23 chromosomes: 22 autosomes and either one female sex chromosome male sex chromosome (or one the Y chromosome).

Two precursor organs exist in the fetus: the Wolffian duct, which differentiates into the structures of the male genital tract, and the Müllerian duct, the source of the female reproductive organs. During the third month of fetal development, the Sertoli cells of the testes of XY fetuses begin to secrete a substance called Müllerian inhibiting hormone. This causes the Müllerian ducts to atrophy instead of develop into the oviducts (fallopian tubes) and uterus. In addition, the Wolffian ducts are stimulated by testosterone to eventually develop into the spermatic ducts (ductus deferens), ejaculatory ducts, and seminal vesicles. If the fetal gonads do not secrete testosterone at the proper time, the genitalia develop in the female direction

Males become externally distinct between 8 and 12 weeks, as androgens enlarge the phallus and cause the urogenital groove and sinus to fuse in the midline, producing an unambiguous penis with a phallic urethra, and a thinned, rugated scrotum. Dihydrotestosterone will differentiate the remaining male characteristics of the external genitalia.

A sufficient amount of any androgen can cause external masculinization. The most potent is dihydrotestosterone (DHT), generated from testosterone in skin and genital tissue by the action of 5α-reductase. A male fetus may be incompletely masculinized if this enzyme is deficient.

Know more about Sex Determination in Humans

                            Facts About Vaccine 

We are hearing these days that there is only solution to the Corona pandemic is vaccination.Here  we are trying to through some light on what is vaccine,history,its stage of development,and types.

                                  A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease.^[1] A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. The agent stimulates the body's immune system to recognize the agent as a threat, destroy it, and to further recognize and destroy any of the microorganisms associated with that agent that it may encounter in the future. Vaccines can be prophylactic (to prevent or ameliorate the effects of a future infection by a natural or "wild" pathogen), or therapeutic (to fight a disease that has already occurred, such as cancer).Edward Jenner hs developed the first vaccine Variolae vaccine (smallpox of the cow) known as the cowpox.His method underwent medical and technological changes over the next 200 years, and eventually resulted in the eradication of smallpox.

Louis Pasteur’s 1885 rabies vaccine was the next to make an impact on human disease. And then, at the dawn of bacteriology, developments rapidly followed. Antitoxins and vaccines against diphtheria, tetanus, anthrax, cholera, plague, typhoid, tuberculosis, and more were developed through the 1930s.

The middle of the 20th century was an active time for vaccine research and development. Methods for growing viruses in the laboratory led to rapid discoveries and innovations, including the creation of vaccines for polio. Researchers targeted other common childhood diseases such as measles, mumps, and rubella, and vaccines for these diseases reduced the disease burden greatly.

Innovative techniques now drive vaccine research, with recombinant DNA technology and new delivery techniques leading scientists in new directions. Disease targets have expanded, and some vaccine research is beginning to focus on non-infectious conditions such as addiction and allergies.

Different Types of Vaccines

Vaccines are made using several different processes. They may contain live viruses that have been attenuated (weakened or altered so as not to cause illness); inactivated or killed organisms or viruses; inactivated toxins (for bacterial diseases where toxins generated by the bacteria, and not the bacteria themselves, cause illness); or merely segments of the pathogen (this includes both subunit and conjugate vaccines).

Inactivated

Some vaccines contain inactivated, but previously virulent, micro-organisms that have been destroyed with chemicals, heat, or radiation.Examples include the IPV polio vaccine, hepatitis A vaccine, rabies vaccine and most influenza vaccines.

Attenuated

Some vaccines contain live, attenuated microorganisms. Many of these are active viruses that have been cultivated under conditions that disable their virulent properties, or that use closely related but less dangerous organisms to produce a broad immune response. Although most attenuated vaccines are viral, some are bacterial in nature. Examples include the viral diseases yellow fever, measles, mumps, and rubella, and the bacterial disease typhoid. The live Mycobacterium tuberculosis vaccine developed by Calmette and Guérin is not made of a contagious strain but contains a virulently modified strain called "BCG" used to elicit an immune response to the vaccine. The live attenuated vaccine containing strain Yersinia pestis EV is used for plague immunization. Attenuated vaccines have some advantages and disadvantages. Attenuated, or live, weakened, vaccines typically provoke more durable immunological responses. But they may not be safe for use in immunocompromised individuals, and on rare occasions mutate to a virulent form and cause disease.

Toxoid

Toxoid vaccines are made from inactivated toxic compounds that cause illness rather than the micro-organism. Examples of toxoid-based vaccines include tetanus and diphtheria. Toxoid vaccines are known for their efficacy. Not all toxoids are for micro-organisms; for example, Crotalus atrox toxoid is used to vaccinate dogs against rattlesnake bites.

Subunit

Rather than introducing an inactivated or attenuated micro-organism to an immune system (which would constitute a "whole-agent" vaccine), a subunit vaccine uses a fragment of it to create an immune response. Examples include the subunit vaccine against hepatitis B virus that is composed of only the surface proteins of the virus (previously extracted from the blood serum of chronically infected patients, but now produced by recombination of the viral genes into yeast) or as an edible algae vaccine, the virus-like particle (VLP) vaccine against human papillomavirus (HPV) that is composed of the viral major capsid protein, and the hemagglutinin and neuraminidase subunits of the influenza virus. A subunit vaccine is being used for plague immunization.

Conjugate

Certain bacteria have polysaccharide outer coats that are poorly immunogenic. By linking these outer coats to proteins (e.g., toxins), the immune system can be led to recognize the polysaccharide as if it were a protein antigen. This approach is used in the Haemophilus influenzae type B vaccine.

Heterotypic

Also known as heterologous or "Jennerian" vaccines, these are vaccines that are pathogens of other animals that either do not cause disease or cause mild disease in the organism being treated. The classic example is Jenner's use of cowpox to protect against smallpox. A current example is the use of BCG vaccine made from Mycobacterium bovis to protect against human tuberculosis. 

A number of innovative vaccines are also in development and in use:

·         Dendritic cell vaccines combine dendritic cells with antigens in order to present the antigens to the body's white blood cells, thus stimulating an immune reaction. These vaccines have shown some positive preliminary results for treating brain tumors  and are also tested in malignant melanoma.

·         DNA vaccination – The proposed mechanism is the insertion and expression of viral or bacterial DNA in human or animal cells (enhanced by the use of electroporation), triggering immune system recognition. Some cells of the immune system that recognize the proteins expressed will mount an attack against these proteins and cells expressing them. Because these cells live for a very long time, if the pathogen that normally expresses these proteins is encountered at a later time, they will be attacked instantly by the immune system. One potential advantage of DNA vaccines is that they are very easy to produce and store.

·         Recombinant vector – by combining the physiology of one micro-organism and the DNA of another, immunity can be created against diseases that have complex infection processes. An example is the RVSV-ZEBOV vaccine licensed to Merck that is being used in 2018 to combat ebola in Congo.

·         RNA vaccine is a novel type of vaccine which is composed of the nucleic acid RNA, packaged within a vector such as lipid nanoparticles. A number of RNA vaccines are under development to combat the COVID-19 pandemic.

·         T-cell receptor peptide vaccines are under development for several diseases using models of Valley Fever, stomatitis, and atopic dermatitis. These peptides have been shown to modulate cytokine production and improve cell-mediated immunity.

·         Targeting of identified bacterial proteins that are involved in complement inhibition would neutralize the key bacterial virulence mechanism.[50]

·         The use of plasmids has been validated in preclinical studies as a protective vaccine strategy for cancer and infectious diseases. However, in human studies, this approach has failed to provide clinically relevant benefit. The overall efficacy of plasmid DNA immunization depends on increasing the plasmid's immunogenicity while also correcting for factors involved in the specific activation of immune effector cells.

While most vaccines are created using inactivated or attenuated compounds from micro-organisms, synthetic vaccines are composed mainly or wholly of synthetic peptides, carbohydrates, or antigens.

Valence

Vaccines may be monovalent (also called univalent) or multivalent (also called polyvalent). A monovalent vaccine is designed to immunize against a single antigen or single microorganism. A multivalent or polyvalent vaccine is designed to immunize against two or more strains of the same microorganism, or against two or more microorganisms. The valency of a multivalent vaccine may be denoted with a Greek or Latin prefix (e.g., tetravalent or quadrivalent). In certain cases, a monovalent vaccine may be preferable for rapidly developing a strong immune response.

When two or more vaccines are mixed together in the same formulation, the two vaccines can interfere. This most frequently occurs with live attenuated vaccines, where one of the vaccine components is more robust than the others and suppresses the growth and immune response to the other components. This phenomenon was first noted in the trivalent Sabin polio vaccine, where the amount of serotype 2 virus in the vaccine had to be reduced to stop it from interfering with the "take" of the serotype 1 and 3 viruses in the vaccine. This phenomenon has also been found to be a problem with the dengue vaccines currently being researched.

Stages of Vaccine Development and Testing

Vaccine development and testing follow a standard set of steps. The first stages are exploratory in nature. Regulation and oversight increase as the candidate vaccine makes its way through the process.

Exploratory Stage

This stage involves basic laboratory research and often lasts 2-4 years. Federally funded academic and governmental scientists identify natural or synthetic antigens that might help 

prevent or treat a disease. These antigens could include virus-like particles, weakened viruses or bacteria, weakened bacterial toxins, or other substances derived from pathogens.

Pre-Clinical Stage

Pre-clinical studies use tissue-culture or cell-culture systems and animal testing to assess the safety of the candidate vaccine and its immunogenicity, or ability to provoke an immune response. Animal subjects may include mice and monkeys. These studies give researchers an idea of the cellular responses they might expect in humans. They may also suggest a safe starting dose for the next phase of research as well as a safe method of administering the vaccine.

Researchers may adapt the candidate vaccine during the pre-clinical state to try to make it more effective. They may also do challenge studies with the animals, meaning that they vaccinate the animals and then try to infect them with the target pathogen.

Many candidate vaccines never progress beyond this stage because they fail to produce the desired immune response. The pre-clinical stages often lasts 1-2 years and usually involves researchers in private industry.

Next Steps: Clinical Studies with Human Subjects

Phase I Vaccine Trials

This first attempt to assess the candidate vaccine in humans involves a small group of adults, usually between 20-80 subjects. If the vaccine is intended for children, researchers will first test adults, and then gradually step down the age of the test subjects until they reach their target. Phase I trials may be non-blinded (also known as open-label in that the researchers and perhaps subjects know whether a vaccine or placebo is used).

The goals of Phase 1 testing are to assess the safety of the candidate vaccine and to determine the type and extent of immune response that the vaccine provokes. In a small minority of Phase 1 vaccine trials, researchers may use the challenge model, attempting to infect participants with the pathogen after the experimental group has been vaccinated. The participants in these studies are carefully monitored and conditions are carefully controlled. In some cases, an attenuated, or modified, version of the pathogen is used for the challenge.

A promising Phase 1 trial will progress to the next stage.

Phase II Vaccine Trials

A larger group of several hundred individuals participates in Phase II testing. Some of the individuals may belong to groups at risk of acquiring the disease. These trials are randomized and well controlled, and include a placebo group.

The goals of Phase II testing are to study the candidate vaccine’s safety, immunogenicity, proposed doses, schedule of immunizations, and method of delivery.

Phase III Vaccine Trials

Successful Phase II candidate vaccines move on to larger trials, involving thousands to tens of thousands of people. These Phase III tests are randomized and double blind and involve the experimental vaccine being tested against a placebo (the placebo may be a saline solution, a vaccine for another disease, or some other substance).

One Phase III goal is to assess vaccine safety in a large group of people. Certain rare side effects might not surface in the smaller groups of subjects tested in earlier phases.

Vaccine efficacy is tested as well. These factors might include 1) Does the candidate vaccine prevent disease? 2) Does it prevent infection with the pathogen? 3) Does it lead to production of antibodies or other types of immune responses related to the pathogen?

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