Regulation and Reproduction
INTRODUCTION TO REGULATORY SYSTEMS
lymphatic system: a system in the body that acts as a drainage system that collects and transports lymph throughout the body
The lymphatic system is crucial in tying all system components together and transports lymph throughout hr body
lymph: fluid carrying wastes, immune cells, proteins and excess tissue
The immune system does not have single central organ but it is made up oof several primary organs and tissues essential for the immune function.
Immune System
tonsils and adenoids: contains cells to help protect against respiratory and oral infections as they enter the body
thymus: develops specific types of white blood cells
lymph nodes: contain immune cells and filter lymph
peyer’s patch: contain immune cells and monitor the gut for pathogens and foreign substances
appendix: contains immune cells
bone marrow: production site of all of the body’s blood cells, including B and T cells which are vital for immunity
spleen: acts as a blood filter and stores immune cells
INTRODUCTION TO THE REPRODUCTIVE SYSTEM
gametes: mature haploid male or female cell which is able unite with anoother of the opposite type to form a zygote
The reproductive system is responsible for producing gametes. Gametes include sperm in males and eggs in females. The reproductive system als helps manage the human body’s development throughout life’s stages.
Main Organs of the Male and Female Reproductive System
Male:
testicle - produces sperm and secretes testosterone
epididymis - coiled tube located on the surface of each testicle to store sperm
vas deferens - a muscular tube that carries sperm from the epididymis to the urethra
seminal vesicles - glands that produce a significant portion of the seminal fluid, which nourishes and supports sperm
prostate - gland that produces prostate-specific antigen and other fluid to regulate pH
penis - external male reproductive organ
Female:
ovary - produces eggs for fertilization and secretes estrogen and progesterone
fallopian tubes - slender tubes that are the site of fertilization
uterus - a muscular organ that provides a nourishing environment for an egg to develop
cervix - lower, narrow portion of the uterus
fimbriae - entrance to fallopian tibe
vagina - muscular canal that connects the cervix the external body
SUPPORTING GROWTH AND DEVELOPMENT
innate immunity: the innate system provides immediate defenses against pathogens; newborns depend on this innate immunity the most and breast feeding promotes these immunities from the mother
ex: skin, nose hairs, mucus-filled passages
adaptive immunity: is more specific and takes time to develop. Some of it is given from the mother and the rest will evolve as the body is exposed to different environments. Medical treatments such as vaccines are vital to help the immune system adapt to fighting pathogens and thus promote health
Reproductive and Endocrine Systems:
The reproductive system produces hormones like estrogen and testosterone, these hormones various roles in bone development and muscle growth. The endocrine system secretes these hormones throughout the body.
Reproductive and Skeletal Systems:
Puberty is initiated by the activation of the reproductive system and is a critical period for growth and development. Hormones released during puberty stimulate the growth plates in bones, leading to increased height and overall development.
Reproductive and Immune Systems:
During fetal development, the immune system is not fully developed. The fetus relies on the immunity that the mother passes the the baby. Immune cells are present in the reproductive organs to help protect against infections by responding to potential threats.
LYMPHATIC SYSTEM BASICS
nodes: a small mass or lump of body tissue
When blood circulates through your body, some of the blood plasma leaks through the blood vessels walls and into the surrounding tissues. Most plasma moves back into the blood vessels but some fluid is left behind. This fluid carrying wastes, immune cells, proteins, and excess tissues is called lymph.
The lymphatic system is a network of vessels, nodes and organs. Lymphatic vessels transport lymph throughout the body. The lymphatic system also supports the fluid balance within the body as a whole by removing extra fluids from tissues and into the lymph (this stops them from swelling).The extra fluids leave the body in the urine. This promotes immunity and resistance to infections and disease.
The lymphatic system relies in the circulatory system to support the body. Blood vessels (capillaries) facilitate the exchange of nutrients, oxygen and waste products between the bloodstream and surrounding tissues. The circulatory system assists in transporting immune cells produced in bone marrow, and lymphatic organs such as the spleen and thymus to various parts of the body through the bloodstream. The relationship between the circulatory and lymphatic systems ensures proper immune function, tissue health and overall health.
FUNCTION OF THE LYMPHATIC SYSTEM
Lymph contains lymphocytes (cells that attack pathogens and other diseases cells). Lymphatic organs include lymph vessels, ducts and small round structures called lymph nodes. These nodes are gathered in clusters around the neck, armpit, grooin, and inside the chest and abdomen. The body’s movement encourages lymph to circulate in the body and eventually drain into the bloodstream, When a person lack mobility, gentle and rhythmic massage can encourage lymphatic flow and help move excess fluid, toxins and waste products from the tissues and into the lymph.
Removing Lymphatic Fluid from the Body
when an infectious agent enters a lymph node, white blood cells like lymphocytes increase in number to help fight infection
once the lymph is filtered, muscle contraction move it into larger lymph vessels called lymphatics. these lymph vessels contain valves that prevent lymph from flowing backward.
the lymphatics converge into lymph trunks that drain back into the blood through the subclavian veins of the circulatory system
blood is eventually filtered by the kidneys and waste products are excreted as urine
Other Lymphatic Tissues
Thymus: located under the neck and is made up of two lobes of lymphoid tissues: medulla and surrounding cortex. Immature lymphocytes enter the cortex to become T cells and mature in the medulla
Spleen: located in the upper left side of the abdomen, just under the ribs. It removes old or damaged red blood cells from the blood and releases lymphocytes in reaction to infection and disease
Tonsils: three sets of tonsils are located in the back of the throat. they help fight infection but are susceptible to becoming infected due to their constant exposure to pathogens
Peyer’s Patches: located in the mucosa and submucosa of the small intestine. they contain mostly B cells which initiate the humoral immune response against infectious agents
LYMPHATIC SYSTEM INTERACTIONS
cytokines: any number of substances secreted by certain cells of the immune system that have an effect on other cells
antigens: inherited proteins or carbohydrate structure on the surface of the red blood cell, or a toxin or other foreign substance which induces an immune response in the body
The lymphatic system primarily uses chemical signals, cytokines and immune cells to communicate within the body. These mechanisms are essential for monitoring for pathogens. The goal is for the signals to initiate the removal of pathogens and foreign substances that are found in the body.
Cytokines and Chemokines
These proteins signal nearby cells to become activated, coordinate immune cell movement and control the intensity and duration of immune response.
Cell-Cell Interactions
Interactions between cells involve cell surface receptors, adhesion molecules and antigen recognition. These mechanisms facilitate communication and coordination of immune responses.
Lymphatic Vessel Flow
The movement of lymph is driven by muscle contraction and other factors. This helps distribute immune cells and signaling molecules throughout the lymphatic system, facilitating immune monitoring and responses.
Antigen Presentation
Cells communicate by presenting antigens to other immune cells. This process activates specific immune responses against detected threats.
Interactions with Other Body Systems
Immune System:
Lymph nodes, the spleen, the tonsils, and other lymphoid organs are strategically located throughout the body. Immune cells within these organs monitor and respond to pathogens, toxins, and abnormal cells present in the lymph.
Digestive System:
Plays a significant role in fat absorption within the digestive system. Specialized lymphatic vessels called lacteals in the small intestine absorb dietary fats and fat-soluble vitamins, transporting them to the bloodstream; this process is essential for nutrient absorption
Integumentary System:
It is involved in maintaining the health of the skin and subcutaneous tissues. It helps remove excess tissue fluid, debris, and pathogens from the skin, contributing to its health and immune function.
Respiratory System:
Lymphatic vessels exist in the lungs and help drain excess fluid from lung tissues, ensuring healthy gas exchange and lung health.
Endocrine System:
The lymphatic system can interact with the endocrine system indirectly by helping to remove waste products and hormones that need to be eliminated from the body. This interaction contributes to hormone balance.
Nervous System:
Not a direct interaction, but the lymphatic system can indirectly influence the nervous system by helping to regulate inflammation. Inflammatory responses mediated by immune cells within the lymphatic system can affect the nervous system, contributing to the perception of pain or discomfort.
IMMUNE SYSTEM BASICS
pathogens: a bacterium, or another microorganism that can cause disease
bacteria - single-celled organisms with structures that can help them evade the immune system and adhere to host tissues. Many bacteria produce toxins that can damage cells or tissues. Bacteria can reproduce rapidly, leading to exponential growth within the host
ex: Streptococcus pyogenes causes strep throat, with symptoms including fever, sore throat, and difficulty swallowing; Escherichia coli causes nausea, vomiting, diarrhea, abdominal cramps, and fever
viruses - are not alive and rely on host cells to replicate. Once inside a host cell, viruses hijack the cell’s machinery to produce more virus particles. Viruses can mutate, rapidly leading to new strains that may be better at avoiding the immune system.
ex: the coronavirus (viruses can lay dormant in the body and appear later in life, such as human immunodeficiency)
protozoans - single-celled complex organisms. Some have specialized structures to facilitate movement and invasion. Some protozoa can change their surface antigens to avoid detection by the host immune system. Others can break into small sections to re-infect a host.
ex: naegleria fowleri is a protozoan that lives in soil and warm fresh water. It can cause a brain infection when water containing the protozoan goes up the nose
fungi - some grow structures throughout the host tissue layers. Fungi can produce toxins or simply damage the tissue as they grow.
ex: Tinea spp also called ringworm causes red itchy and circular rashes or scaling and flaking skin
NONSPECIFIC IMMUNE RESPONSE
innate immunity: the immune defenses a person is born with
nonspecific immune response: innate immunity that provides protection against a wide range of pathogens
Inflammatory Response
redness, swelling and heat occur at the site of damagge or infection
caused by blood rushing to the site to bring immune cells to protect the affected area
can cause pus to build up as infection is attacked
Fever
pathogens thrive at body temperature
body increases temperature
pathogens cannot survive
Physical Barriers
skin blocks all pathogens
mucus and small hairs help catch pathogens in the nasal passage and respiratory tract
lining of the stomach helps kill pathogens before they reach the bloodstream
Neutrophils, basophils and eosinophils are white blood cells that circulate in the blood, looking for foreign invaders in the body. They use phagocytosis to engulf the pathogen or attack and break down a pathogens cell membrane. They are also macrophages that use phagocytosis and stay within the tissues of the body and natural killer cells that destroy viruses.
Phagocytosis: the ingestion of cells or other materials by certain immune cells
natural killer cell - kills tumor cells and body cells that are infected with a virus using enzymes
macrophages - uses phagocytosis to protect the body’s tissues; it does not circulate like neutrophils
neutrophil - white blood cell that circulates in the bloodstream and responds to bacterial fungal infections using phagocytosis
basophil - white blood cell that responds to allergic attacks and helps destroy cancer cells; also releases histamines that promote fever and inflammation
histmaines: a compound that causes contraction of smooth muscle and dilation of capillaries in response to injuries or allergens
eosinophil - white blood cell that responds to parasitic attacks
SPECIFIC IMMUNE RESPONSE
specific immune response: adaptive immunity that is highly specialized and targets specific pathogens by producing antibodies and activating specific immune system cells such as B-cells and T-cells
B-cells
type of white blood cell
identify antigens on pathogens and trigger the production of antibodies, proteins that recognize and neutralize specific pathogens
called humoral immunity
T-cells
type of white blood cells
cytotoxic T cells directly kill infected or abnormal cells
helper T cells assist in coordinating immune responses and activating other immune cells
called cell-meditated immunity
Memory cells
made from B and T cells after exposure to a pathogen
remembers the specific pathogen and can start a quicker and more robust immune response if that pathogen is seen again
provides long-lasting immunity
Step to Destroying Pathogens
recognition of pathogen: the immune system recognizes the presence of the pathogen through immune cells
activation of nonspecific immune cells: inflammation causes blood to rush to the area, bringing macrophages and natural killer T cells which can destroy some pathogens
activation of specific immune cells: helper T cells recognize the antigens of remaining pathogens and become activated. If the pathogen is inside of body cells, killer T cells destroy the pathogen. If the pathogen is outside of the body, B cells are activated and identify the antiggens displayed on the pathogens surface. Activated B cells then produce antibodies specific to the pathogen to break down
memory cell formation: throughout the immune response, some B cells and T cells differentiate into memory cells. These memory cells ‘remember’ the specific pathogen for future attacks
When a vaccinated person encounters a pathogen for which they've been vaccinated, the B and T cells of their immune system can quickly mount an effective defense, preventing or reducing the severity of illness or disease.
BIOTECHNOLOGY ADVANCEMENTS
Antibiotics
Bacteria create antibodies to kill off their competition which are other bacteria. When antibodies enter our body, they target only bacteria cells and nothing else, so the antibiotics don’t kill our own cells but it also means they can’t destroy viruses, thus meaning, taking a antibiotic medication for a flu virus won’t get you any better. For viruses you must vaccinate beforehand to avoid getting sick
Vaccines
Vaccines expose the immune system to a safe form of a virus to initiate a specific immune response. This response creates memory cells that will remember the virus and act quickly if the body is exposes to the full virus later. Vaccines are created by identifying the disease-causing pathogen, such as a virus or bacteria and studying it characteristics. Scientists then develop a vaccine candidate, often using weakened or inactivated forms of the pathogen or pieces of it. These candidates undergo rigorous testing to make sure they are safe and effective. Once a candidate shows promise it progresses to human clinical trials, with phases that assess safety, immune response, and real-world effectiveness. If successful, the vaccine is manufactured, approves by regulatory agencies, and distributed for public use
Health Considerations
Postive
vaccines have been instrumental in preventing and controlling infectious diseases like polio, measles, and hepatitis
high vaccination rates in population can provide herd immunity, protecting vulnerable individuals who cannot be vaccinated such as those with certain medical conditions ot allergies
antibodies have saved countless lives. They are essential for treating various illnesses from common bacterial infections to life threatening conditions
Negative
vaccine hesitancy prevents herd immunity putting more individuals at risk for infection
ensuring access to vaccines across all segments of society remains challenging, with undeserved population often having limited access to vaccination
the overuse and misuse of antibodies have led to the development of antibiotic resistant bacteria
UNDERSTANDING HUMAN REPRODUCTION
fertilization: the process of combining a sperm cell with an egg cell to create a zygote
gametes: mature haploid male or female cell which is able to unite with another of the opposite type to form a zygote
sperm: a gamete produced in the sex organs of a male
haploid: having a single set of chromosomes without a pair
zygote: a diploid cell resulting from the fusion of two haploid gametes (a sperm and an egg)
The reproductive system focuses on ensuring fertilization of an egg and fostering the development of new life. The reproductive system also influences growth and development. To support fertilization the reproductive system produces, nourishes and transports gametes (contains a haploid set of chromosomes that carry genetic information)
Males produce sperm cells also called spermatozoa and females produce egg cells called ova.
For humans the haploid number of chromosomes is 23 for egg cells and 23 for sperm cells. During fertilization, the 23 chromosomes in the egg combine with the 23 chromosomes of the sperm cell resulting in a zygote containing 46 chromosomes.
Reproductive Hormones
menstrual cycle: the process of an egg maturing and being released, along with changes in the uterus and other female reproductive organs in preparation to support a fetus
gestation: the process or period of time between conception and birth
Estrogen: regulates the menstrual cycle and is essential for maintaining reproductive health
Testosterone: responsible for the production of sperm and the development of facial/body hair. It deepens the voice and increases muscle mass
Progesterone: prepares the uterus to hold the egg; levels rise in the second half of the menstrual cycle and during pregnancy to support gestation
Follicle-stimulating hormone: In females, FSH stimulates the growth and development of the ovaries. It also helps regulate the menstrual cycle. In males, FSH supports the growth of sperm.
Luteinizing Hormone: In females, LH triggers the release of an egg from an ovary and plays a role in progesterone production. In males, LH stimulates the testes to produce testosterone.
FEMALE REPRODUCTIVE SYSTEM
Puberty is the period of life when an individual becomes sexually mature and capable of reproduction. Physical and chemical changes occur differently for females and males.
growth of pubic and underarm hair
widening of hips to prepare for potential childbirth
changes in texture and appearance of skin; becomes smoother and softer compared to male skin
changes in voice; higher-pitched
emotional and behavioral changes including the development of maternal instincts and nurturing behaviors
sexual development of internal and external genitalia
Structures in the Menstrual Cycle
One typically lasts for about 28 days (give or take).
Steps:
Menstruation - the breaking downs if the uterine lining as the body begins a new menstrual cycle
Proliferative phase - forms a new layer of endometrial tissue in the uterus - estrogen levels begin to increase to prepare the uterus lining for a potential pregnancy; estrogen also regulates FSH and LH levels
Ovulation - FSH stimulates the production of estrogen and maturation of eggs within the ovarian follicles - once estrogen levels reach a certain threshold they trigger a surge in LH which then triggers the release of a mature egg from the ovary; the egg moves through the fallopian tube
Secretory phase - an increase in progesterone prepares the endometrium of the uterus for egg implantation - a fertilized egg can adhere to the lining of the uterus - if fertilization does not occur progesterone levels drop back to normal, triggering the start of a new menstrual cycle
As an Egg Matures…
Oogenesis: the process of female germ cells, called oocytes or egg cells developing and maturing within the ovaries
Each ovary contains about 200,000 small egg sacs called follicles, each follicles contains an immature egg. As puberty approaches the follicles mature into egg ready to be released during ovulation. When the egg sac matures it follicle moves to the surface of the ovary, breaks open and releases the egg (ovulation). The egg then travels to the fallopian tube, then the uterus, where the fetus will grow. The cervix is the opening into the vagina, which leads to the outside of the body.
MALE REPRODUCTIVE SYSTEM
The main functions are to produce and deliver sperm. Sperm cells are built to swim through the female reproductive tract, locate an egg, and deliver their genetic material to create a zygote. The male reproductive system also produces male sex hormones; testosterone which is responsible for the development of male characteristics and the regulation of sexual function.
growth of facial, pubic, and underarm hair that can be darker and coarser than the hair on the scalp
more pronounced jawline ana a broader forehead (male secondary characteristics)
increased muscle mass and strength
toughening of skin as facial hair develops; increase of oil production with facial hair
vocal cord development; deeper voice in males than in females
enlargement of the Adam’s apple as a result of the growth of the larynx
emotional and behavioral changes; increased aggression and competitive behavior
growth spurt leading to an increase in height and overall body size
sexual development of internal and external genitalia
Production of Sperm
Acrosome: a part of sperm that contains enzymes that help the sperm penetrate the outer layers of the egg during fertilization
The head of a sperm contains 23 chromosomes and a covering called the acrosome: this contains enzymes that help the sperm penetrate the outer layers of the egg during fertilization. The midpiece is rich in mitochondria that provide the energy needed for movement. Sperm are produced in the testes and are contained in the sac-like scrotum (testosterone is also generated in the testes). Each testis consists of small, coiled tubes called seminiferous tubules, there are between 300 and 600 tubules in each testis. Sperm cells are produced in the seminiferous tubules but then are moved to the epididymis where they mature and are stored. Mature sperm exit the epididymis through a tube called the vas deferens, where they empty to the urethra. As sperm enter the urethra the seminal vesicles, cowper glands, and the prostate gland secrete fluids into the urethra that nourishes and protects the sperm. That fluid mixture is called semen.
SUPPORTING REPRODUCTION
embryo: the initial stage of development of a multicellular organism
Female:
fallopian tubes provide a pathway for sperm to meet the egg in a safe location
the cilia in the fallopian tubes help move the egg and sperm toward each other
around ovulation mucus in the cervix becomes thinner and more slippery facilitating the movement of sperm into the uterus
Male:
muscles in the penis cause it to becomes erect allowing beneficial entry of sperm into the vagina
glands provide sperm with fluid that supplies nutrients to sustain energy and neutralize the pH of the female reproductive tract
millions of sperm are produced to increase the chance of fertilization
The female body must sustain the growing embryo until birth. The gestation period of a human is divided into three time periods, or trimesters. The female’s body changes with each trimester.
Trimester One: Weeks 1-12
After fertilization the zygote travels to the uterus and implants into a nourishing uterine lining. The body then ensures the developing embryo receives nutrients and oxygen. Hormonal changes including the production of progesterone, maintain the uterine lining, prevent menstruation, and promote early embryonic growth.
Trimester Two: Weeks 13-27
During the second trimester the mother’s body supports the growing baby by allowing for rapid fetal growth and development including the maturation of the respiratory, digestive and nervous systems. Estrogen and progesterone levels rise, maintaining the uterine lining and supporting fetal development.
Trimester Three: Weeks 28-40
The mother’s body continues to support the growing fetus by experiencing frequent uterine contractions, cervical changes, and the loosening of pelvic bones in preparation for childbirth. The body produces hormones that initiate labor while breasts prepare for breastfeeding through mammary gland development and milk production.
After birth the breasts produce milk to nourish the baby and provide innate immune cells to the baby. Hormones are released to increase the mother and baby bonding. Estrogen and progesterone which were elevated during pregnancy significantly decrease after childbirth. The drop in hormones temporarily suppresses ovulation and menstruation in breastfeeding woman.
UNDERSTANDING FETAL CIRCULATION
placenta: a structure that develops during pregnancy to support fetal circulation and allows the fetus to obtain oxygenated blood and nutrients
As human embryo develops into a fetus organ systems complete their development. Some organs, however, will not work as intended until the baby is born (ex: lungs). During pregnancy fetal circulation replaces the lungs and other organs by providing oxygenated blood and nutrients, along with removing wastes for the growing fetus. Fetal circulation occurs through an important structure inside the uterus called the placenta. The placenta functions as the lungs, G1 tract, liver and kidneys until after birth.
PLACENTA AND UMBILICAL CORD
Fetal support begins as soon as the zygote is implanted into the uterine wall and continues through birth.
These structures are…
Placenta: a temporary organ that develops during pregnancy, made of fetal blood vessels (layer of cells forming a barrier between the maternal and fetal bloodstreams and maternal blood vessels
Amniotic sac: a membrane that protects the fetus from impacts and forms a protective barrier against the pathogens
Amniotic fluid: the fluid in the amniotic sac that helps maintain a stable environment for the fetus to grow
Maternal vessels: blood vessels of the mother that supply blood to the uterine wall, this allows for gas exchange without direct mixing of blood between mother and fetus
Umbilical cord: connects the placenta to the fetus; contains two arteries that carry carbon dioxide and waste products away from the fetus and one vein that carries oxygenated blood and nutrients to the fetus
Umbilical vein: a vein present during fetal development that carries oxygenated blood from the placenta into the growing fetus
Umbilical artery: carries deoxygenated blood from fetal circulation to the placenta
Fetal Heart
Ductus arteriosus: a pathway in the fetal heart that connects the pulmonary artery to the aorta. This allows the blood from the right ventricle to bypass the nonfunctioning fetal lungs
Foramen ovale: a hole between the two atria; this opening allows most of the oxygen-rich blood from the placenta to flow from the right atrium into the left atrium, bypassing the nonfunctioning fetal lungs
Ductus venosus: a pathway that directs oxygenated blood from the placenta directly to the fetus’s inferior vena cava
FETAL CIRCULATION AT BIRTH
Fetal circulation relies on specialised structures to support development and bypass organs that cannot yet function on their own. However, after birth the fetal circulatory pathways change and adapts to support body systems through the lungs and heart
After birth…
clamping of the umbilical cord removes oxygen and nutrient transfer from the mother
lungs expand and blood supply increases to the lungs
the ductus arteriosus, ductus venosus, and foramen ovale close off
the fetus begins to get oxygen from their own respiratory system
blood, nutrients, and waste begin absorption and filtration through the cardiac and lymphatic system
UNDERSTANDING FERTILIZATION TO BIRTH
blastocyst: a group of dividing cells that make up a fertilized egg
gestation period: the process or period of time between conception and birth
Reproductive systems produce haploid gametes and fertilization is the process of combining sperm cell with an egg cell to create a zygote. Sperm travels up the vaginal canal and fuses with the egg in the female’s fallopian tube. The fertilized egg, called a zygote, travels down the fallopian tube and becomes a larger ball of cells called a blastocyst. Then the blastocyst implants itself inside the wall of the uterus. Here the cells differentiate to from the placenta and embryo and eventually develop into a fetus.
Human fertilization to birth occurs during a gestational period of three trimesters. The first trimester is months 1-3, the second is months 4-6, and the third is months seven through nine.
Twins
Sometimes more then one egg is released during ovulation. If two eggs are fertilized by sperm, it can result in fraternal (nonidentical) twins. Identical twins occur when one fertilized egg splits into two before cells begin dividing. This means that the cells of identical twins have identical chromosomes.
GESTATION IN TRIMESTER ONE
The three layers are germ layers, eventually give rise to specific body tissues and organs. The outer layer is the ectoderm, develops into the nervous system and skin. The middle layer, the mesoderm, develops into the muscles, bones, kidneys, heart, blood vessels, and reproductive system. And the endoderm, the inner layer, gives rise to the liver, lungs, certain glands, and the digestive system.
Following the development if the germ layers, a more complex embryo forms which has two outer membranes: the chorion and amnion. The chorion contributes to an important structure called the placenta through which gases, nutrients, and wastes are exchanged between the mother and the embryo.
The umbilical cord is a tube that connects the embryo to the placenta. Because many dangerous substances such as nicotine, drugs, and alcohol can negatively impact the development of the embryo, pregnant mothers are discouraged from using these substances that can be transferred to the embryo.
From the ninth week of development until birth the developing embryo is referred to as a fetus. By the ninth week the major body systems have developed. By 14 weeks, the hands, arms, legs, feer, nose, eyes, and ears have developed.
Month 1: After the blastocyst implants into the uterus, the cells divide quickly. Some of the cells begin to develop into specialized tissues, while others develop into tissues that support and protect the embryo as it grows.
Cells divide into three cells layers…
Ectoderm: develops into the nervous system and skin
Mesoderm: develops into the muscles, bones, kidneys, heart, blood vessels, and reproductive system
Endoderm: develops into the liver, lungs, certain glands, and digestive system
Month 2: Neurulation is the first step in the development of the nervous system. During this process, part of the ectoderm thickens and folds to form a neural tube that eventually develops into the brain and spinal cord.
Specialized membranes form to protect and nourish the growing embryo. A sac filled with amniotic fluid surrounds the embryo to cushion and protect it. Other membranes form the placenta and umbilical cord to connect the embryo to the mother. Throughout the pregnancy, it is through these organs that the fetus receives its oxygen and nutrients and disposes of waste.
Month 3: At the end of the first trimester the embryo is now referred to as a fetus. Most of the major organs of the fetus are fully formed. However, many tissues and organs are far from ready to function on their own. The fetus is about eight centimeters long and can move and show signs of reflexes.
GESTATION IN TRIMESTER TWO
Month 4: Facial features, limbs, and digits develop. Fingerprint patterns begin to form. Eyebrows and eyelashes grow in. Brain development occurs rapidly during this stage, with the formation of complex brain structures. Sensory organs, such as the eyes and ears, continue to develop. By the end of the second trimester, the eyes can open and close, and the baby many start to hear sounds from the outside world.
Month 5: The fetus begins to kick, move, and turn from side-to-side as muscle development increases. The mother may begin to feel these movements. The heart is now large enough for heartbeats to be heard with a stethoscope. Respiratory organs continue to develop. The fetus begins making rhythmic breathing movements although the lungs are not yes fully functional.
Month 6: A waxy substance known as the vernix caseosa begins to cover the skin of the fetus. This serves as a protective barrier as wells as hydration for the skin. Fine hair known as laugo covers the baby’s body. This hair helps to regulate the body temperature. In females, o varian follicles begin forming. In males the prostate gland begins developing. Gender can be determined through ultrasound, usually around the 20th week of gestation.
GESTATION IN TRIMESTER THREE
Cesarean Section (C-section): the surgical removal of a baby through a cut in the abdomen and uterus of the mother
Month 7: Eyes open and can be sensitive to light. Vision is fuzzy until 3-6 months after birth. Sound recognition occurs and the fetus may respond to certain sounds. Surfactant increases and is an essential mixture of molecules necessary for preventing lung collapse and is crucial for breathing after birth.
Month 8: All organs continue to mature. Fetal development continues with an increase in size and weight. Muscles continue to develop and fat accumulates under the skin. The fetus usually begins to position itself head-down, often known as engage, in preparation for birth.
Month 9: The fetal brain almost triples in weight as neural connections develop and refine. The bones and the skull remain soft in preparation for travelling through the birth canal. The average length of a newborn baby is 19 to 21 inches. The average weight of a newborn baby ranges from 6 to 9 pound at birth.
Changes at Birth
A combination of physical and chemical factors triggers the process of birth. Hormones stimulate the movement of involuntary muscles that begin rhythmic contractions known as labor. As the labor continues the opening of the cervix expands until it is large enough for the baby’s head too pass through. During this process, the amniotic sac around the fetus breaks and contractions oof the uterus push the baby, usually head first out through the vagina.
In some cases, babies are born through cesarean section; the surgical removal of a baby through a cut in the abdomen and uterus of the mother
Babies born earlier then 37 weeks are considered preterm. Some preterm babies may have incomplete lung development.