EYES

 

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Zonules: ring of fibrous strands connecting the ciliary body with the crystalline lens of the eye

Cornea: front sixth clear layer in which all light must pass first when it enters the eye

Iris: colored part of the eye; an adjustable diaphragm around an opening called the pupil

Lens: clear, bi-convex structure which changes shape because it is attached to muscles in the ciliary body to fine-tune vision

Ciliary body: muscular area attached to the lends which contracts and relaxes to control the size of the lens for focusing

Optic nerve: conducts the electrical impulses from the light entering the eye to the brain

Choroid: second layer of the eye that contains the blood vessels that supply blood to structures of the eye

Sclera: tough, outermost layer of the eye which maintains the shape of the eye

Retina: innermost layer and light-sensing portion of the eye which contains rod cells (responsible for vision in low light) and cone cells (responsible for color vision and detail)

Macula: center of the retina which contains the fovea centralis (contains only cones and is responsible for seeing fine detail clearly

Myopia vs. hyperopia

Near-sightedness vs. far-sightedness

Myopia is a refractive defect of the eye in which light produces an image in front of the retina which translates to you are better at seeing objects close up than far away. Hyperopia is literally the exact opposite. Thus, the image is produced behind the retina which means that you can see objects better far way than close up. Myopia usually occurs with an eyeball that is longer or a cornea that is steeper than normal. Hyperopia usually occurs with an eyeball is shorter or the cornea has too little curvature.

LASIK surgery:

LASIK surgery is performed with a laser programmed to remove a defined amount of tissue from the cornea. The doctor will cut a flap on the top layer of the cornea which allows access to the deeper layers of the eye. They layer is used again to flatten certain tissue or to make the tissue steeper, depending on the needs of the patient. Finally, the flap is folded back into place and will heal on its own. This procedure corrects vision because it makes up for the discrepancies of the eye making sure the image will be focused on the retina, not ahead or behind it.

SLEEP

Neurotransmitters and the circadian clock:

Neurotransmitters are chemical messengers between nerve cells and allow communication between the brain and other organs. Sleep is influenced by neurotransmitters and hormones. There are two types of neurotransmitters: excitatory (epinephrine, norepinephrine, dopamine, glutamate, PEA, histamine) and inhibitory (GABA and serotonin). They are involved in all aspects of sleep (waking, transitions, etc.). An imbalance in one or more of these chemical messengers can lead to sleep difficulty. The sleep cycle stems from the interaction between the circadian clock and a separate sleep-wake homeostatic process. The circadian rhythm relates to a periodicity of 24 hours. It is linked to fluctuations of behavioral and physiological functions such as sleep and awaking. It is our internal sleep regulation process.  We use light as cues as well.

REM vs. nREM sleep:

Sleep is prompted by natural cycles of activity in the brain and consists of two basic states: rapid eye movement (REM) sleep and non-rapid eye movement (nREM) sleep which consists of four stages. During sleep, the body cycles between nREM and REM sleep. Usually, we begin the sleep cycle with nREM sleep followed by a short period of REM sleep. Dreams occur only in the REM stages of sleep. During nREM sleep, the body repairs and regenerates tissues, builds bone and muscle, and appears to strengthen the immune system.

Sleep disorders:

Insomnia: a disorder that can make it hard to fall asleep, hard to stay asleep, or both; insomniacs may lie awake for hours before falling asleep; insomniacs may wake up too early and be unable to drift off again, or may wake up repeatedly throughout the night

Sleep apnea: a disorder characterized by abnormal pauses in breathing; people with sleep apnea may stop breathing many times while they sleep and the breathing pauses last several seconds which trigger a switch from deep sleep to light sleep

Restless leg syndrome: a sleep disorder characterized by discomfort which induces the urge to move the legs at rest which makes it difficult to fall asleep; some experience twitching motions during sleep that cause brief awakenings

Narcolepsy: extreme sleepiness during the day; people find it hard to function without naps despite spending enough time in bed at night; narcoleptics enter REM sleep almost immediately without the nREM sleep stages which normally lead up to dream sleep.

Effects from a lack of sleep: fatigue, lethargy, lack of motivation, moodiness, irritability, reduced creativity and problem-solving skills, inability to cope with stress, reduced immunity (frequent colds and infections), concentration and memory problems, weight gain, impaired motors skills and increased risk of accidents, difficulty making decisions, increased health risks and problems

How much sleep should I get?

Average Sleep Needs
Age	Hours
0-2 months	12-18
3 months-1 year	14=15
1-3 years	12-14
3-5 years	11-13
5-12 years	10-11
12-18 years	8.5-10
18+ years	7.5-9

OVARIAN AND UTERINE CYCLES

Ovarian cycle: cycle where an oocyte will mature, erupt from an ovary, and travel down the oviduct to the uterus

Uterine cycle: cycle where the lining of the uterus grows and prepares for an embryo to implant, but if an oocyte is not fertilized then menstruation occurs

GnRH: gonadotropin releasing hormone stored in the hypothalamus triggers the release of FSH and LH
LH: luteinizing hormone produced by an implanted embryo; when released it causes the follicle to release the egg (ovulation); triggers remaining follicle cells to differentiate into the corpus luteum (which secretes estrogen and progesterone)
FSH: follicle-stimulating hormone produced in the pituitary gland; stimulates ovarian follicles to grow which begins the secretion of estrogen

Estrogen: increased levels of estrogen serve as a source of positive and negative feedback to regulate the levels of FSH and LH

Progesterone: secretion from a follicle that released an egg; responsible for the thickening of the endometrium and preparing to support embryonic development

hCG: human chorionic hormone is secreted once the egg has been fertilized and is detected in pregnancy tests

Positive Feedback Loops: An increase in the hormone levels after the release of an egg into the ovary because more hormones are needed to aid in the proper development of the zygote to a fetus (when fertilized)
Negative Feedback Loops: a decrease in the hormone levels within the body which decreases GnRH levels

Menstruation vs. Pregnancy: hormone levels are much lower during menstruation than during pregnancy which is an easy source for differentiating between the two processes

Fetal development

First trimester: zygote is turning into a fetus; embryo is made of three layers; organs in the fetus are in their first stages

            Second trimester: fetus continues to grow and develop; brain and lungs form

            Third trimester: fetus is growing the most rapidly

IMMUNE SYSTEM

The ABC's about your immune system...
Pathogens (Germs): an infectious agent

            Examples: virus, bacteria, fungus, prion

Macrophage: Type of white blood cell that attacks foreign invaders in the body; help destroy bacteria, tumors, etc. via phagocytosis

Antigen: Any foreign substance that can enter the body

Helper T cell: Type of white blood cell that recognizes antigens releasing cytokines that active B+ killer T cells

B cell: Lymphocytes that will release antibodies to fight off antigens; important role in immune system responses

Antibody: Proteins that bind to an antigen and neutralize it

Killer cell: Destroy antigens that are discovered by antibodies

Cytoxic T cell: Type of T-cell which kills cells that are infected with viruses and other pathogens

Memory cell: Immune cells with a long lifespan which remembers attacks by certain antigens; when those antigens return, memory cells trigger a quick immune response before the body experiences the symptoms  

Innate vs. adaptive vs. passive immunity
Innate immunity is a type of general protection which everyone is born with. It includes the external barriers of the body such as the skin and mucous membranes (lining of the nose, throat, gastrointestinal tract, etc.). These are the first lines of defense in preventing antigens from entering the body. It this is broken, the membranes attempt to heal quickly and specialize immune cells attack invading germs. The next type of protection is adaptive or active immunity. This develops throughout our life and involves the lymphocytes. As we are exposed to diseases or immunized against diseases through vaccination, adaptive immunity develops. Finally passive immunity is the last type of protection. It is a borrowed immunity from another source and only lasts for a short time

Immune Disorders

DiGeorge syndrome (thymic dysplasia): a birth defect and a primary T-lymphocyte disease in which children are born without a thymus gland (where T lymphocytes mature)

Chediak-Higashi syndrome (chronic granulomatous disease): the inability of the neutrophils (a type of white blood cells) to function normally as phagocytes (cells that digest foreign organisms)

EXERCISE PHYSIOLOGY

An exercise physiologist studies the acute responses and chronic adaptations of physical exercise conditions. Specifically, they focus on the effect of exercise on pathology (study and diagnosis of disease) and the mechanisms by which exercise can reduce disease progression. When working with athletes, the monitor and assess cardiovascular and metabolic effects and mechanisms of exercise, replenishment of fluids during physical activity, and exercise for cardiac and musculoskeletal rehabilitation.

Common terms:

Aerobic respiration: Requires oxygen to generate energy in the form of ATP; occurs in fives steps (glycolysis, oxidation of pyruvate to Acetyl Coenzyme A, Krebs cycle, electron transport chain, and oxidative phosphorylation)
Anaerobic respiration: A form of respiration without the use of oxygen
ATP: Adenosine Triphosphate transports chemical energy within cells; it is produced via cellular respiration and is known as the energy currency of cells

Carbohydrates: Main fuel source for high intensity exercise and main fuel source for muscle contractions

CP: Creatine Phosphate is a molecule that serves as a reserve of high-energy phosphates in the skeletal muscle and brain; it can anaerobically supply a phosphate grout to ADP in order to form ATP during the first 2-7 seconds following an intense muscular effort

Fats: Main fuel source for long duration, low to moderate intensity exercise and help access stored carbohydrates during high intensity exercise
Glycolysis: The first stage of both aerobic and anaerobic respiration; glucose is converted into a 3 carbon sugar (pyruvate) in ten reduction/oxidation reactions; energy released is used to for ATP and NADH
Lactic acid: A chemical compound playing a significant role in many biochemical processes; byproduct of anaerobic respiration

Protein: Biochemical compound that is a sequence of amino acids that are the building blocks of the body; proteins repair and rebuild muscle that is broken down during exercise and to help optimize carbohydrate storage in the form of glycogen

VO₂ max: The maximum capacity of a person’s body to transport and use oxygen during periods of exercise; reflects physical fitness of a person

Energy Pathways
The body cannot easily store ATP, so the body needs to continually for ATP during exercise through aerobic or anaerobic respirtaiton.

1.      ATP-CP: the phosphate system; the combination of ADP and CP which are both stored in muscles create ATP, but it only lasts about 2-3 seconds and the re-synthesis of ATP from CP will continue unto CP storage are depleted

2.      Anaerobic Metabolism: glycolysis and lactic acid production; production of ATP without oxygen once the CP reserves are depleted; it makes energy for a short amount of time during high intensity activity or until lactic acid build-up reaches a threshold with muscle pain and fatigue

3.      Aerobic Metabolism: endurance exercise energy production; oxygen from the Krebs cycle and the electron transport chain manufacture ATP from glucose; it is the prime energy source during endurance activities, but it is slower than anaerobic enrgy because it relies on the circulatory system to transport oxygen to muscle cells to generate ATP

AGING

Aging is inevitable. It happens to everyone and there is no way to around it. We may try to use cosmetic serums to deceive society, but aging is a natural, physiological process that everyone and every living organism endures over time (time lengths vary immensely). Unfortunately, both genetics and lifestyle are to blame for the process of aging.

Some basic factors:

HDL: Cholesterol is generally seen as a harmful food component, but, in reality, it is an essential nutrient. The key factor is which cholesterol is consumed and the amount of cholesterol consumed. High-density lipoprotein (HDL) is known as “good cholesterol” because it is able to remove cholesterol from arteries and transport that cholesterol to the liver for excretion or re-utilization. On the other hand, low-density lipoprotein (LDL) is known as “bad cholesterol” because high levels of LDL promote heart problems and cardiovascular disease. Thus, people with higher levels of HDL in their body have a higher chance of living longer because they have a decreased risk of cardiovascular issues.

Aging and sirtuins: Sirtuins are a class of proteins that possess either histone deacetylase or monoribosyltransferase which influence aging and regulation (transcription, apoptosis, stress resistance, etc.). Harvard’s David Sinclair works closely with siruins and their effect of longevity on yeast and other organisms.

Telomere: Telomeres is a region of repetitive DNA at the end of a chromosome which protects the ends of chromosomes from deterioration. Aging occurs on a cellular level. Eventually cells lose the ability to divide and repair itself. The loss of this ability to divide is known as cellular senescence. As we age, telomeres decompose or decay. Thus, the cell continues to divide, but the telomeres shorten. Sooner or later, the telomeres become so short that essential parts of DNA can be damaged in the replication process. Leonard Hayflick found that a human cell replicates 50 times before the telomeres become too short. If the telomeres are two short, the cell will stop replicating and dividing altogether.

Pharmaceutical companies: Resveratol is a possible sirtunis. It is believed to assist in the repair of DNA and regulate genes that undergo altered expression with age. Scientists speculate that this natural phenol could extend lifespan. This hypothesis is still in dispute and in the experimentation phases, though. In 2003, Howitz and Sinclair report in the journal Nature that resveratol significantly extends the lifespan of yeast (Saccharomyces cerevisiae). They also found that it prolong the lifespan of worms (Caenorhabditis elegans) and fruit flies (Drosophila melanogaster). Pharmaceutical companies are working endless hours with this natural phenol to find a product that can conceivably reverse the effects of aging.

Genetics are not the only component of aging. Lifestyle decisions are also to blame when it comes to aging. Exercise, eating habits, stress levels, hygiene, personal health, and drug abuse can all impact the lifespan of humans. A healthy diet and exercise have influenced the increased life expectancy rate throughout the world in the past century. A lack of exercise increase the risk of cardiovascular disease and type II diabetes. There has also been a relationship found between telomere length and smoking. The habit of smoking decreases the length of telomeres faster than their natural rate of decay. These are just a few negative lifestyle habits that decrease an individual’s life span.

References

Leonard Hayflick Proposes The Cellular Theory Of Aging Based On The Limited Replicative Lifespan Of Primary Human Cells. (n.d.). Science of Aging. Retrieved March 19, 2011, from http://science-of-aging.healthaliciousness.com/timelines/hayflick-cells-limited-lifespan.php

Sedentary Lifestyles Associated With Accelerated Aging Process. (n.d.). Science Daily: News & Articles in Science, Health, Environment & Technology. Retrieved March 19, 2011, from http://www.sciencedaily.com/releases/2008/01/080128165734.htm

Your Kids Could Reach 100 - Health Checkup: How to Live 100 Years - TIME. (n.d.). Breaking News, Analysis, Politics, Blogs, News Photos, Video, Tech Reviews - TIME.com. Retrieved March 19, 2011, from http://www.time.com/time/specials/packages/article/0,28804,1963392_1963367,00.html

STRESS

Stress is extremely common. Everyone experiences it at one point or another. By definition, stress is a physical and emotional reaction that everyone experiences as he or she encounters changes in life. These reactions can have positive (when it makes us deal constructively with daily problems and meet the challenges) or negative effects (when it becomes continues which can lead to depression and heart disease).

Symptoms of stress include increased heart rate, tense muscles, increased blood pressure, fear, confusion, anger, and sweating. These physical and emotional reactions may help us by focusing our concentration and other bodily functions to prepare for a challenge. Our ancestors experienced these symptoms when faced with a wild animal in front of them, but nowadays stress is not manifested in the same ways.

In my life stress comes in all different shapes and sizes. School is a constant source of stress. A full schedule, plus extracurricular activities becomes overwhelming at times. Also, uncertainty about my future and the major changes that lie ahead (college) has been a more current stressor.

Relationships, schoolwork, and personal responsibilities can be both positive and/or negative stressors. After meeting a challenge, the body relaxes as the heart rate, muscle tension, and blood pressure return to normal. This gives the body a chance to recover physically and for the person to feel emotionally rewarded for overcoming the challenge.  

Studies have shown that certain symptoms such as sweat and an increased heart rate is an advantage for acute stress or good stress. However, when physical and emotional stress reactions are non-stopping or perceived as non-stopping, the body never gets a chance to relax, knotted stomach constant tense muscles. This is known as chronic stress or bad stress.

Some risks associated with chronic stress include high blood pressure. This can lead to heart problems and even heart attacks. Migraine headaches, back pain, and ulcers are also frequently associated with stress. The immune system may also be weakened or compromised which makes the individual more susceptible to illness.

Sadly, many individuals with chronic stress may try to relieve chronic stress with illegal drugs, smoking, or alcohol. These stimulants may seem to reduce stress but the feeling will only last a short while and the person is likely to become addicted.

My Survival Guide to Stress

-a stressor is situation that causes stress

-it is necessary and imperative to identify what causes stress in order to try to control it

-common symptoms: headaches, tense muscles, shaky hands, fatigue, insomnia, heartburn

-emotions: nervous, fearful, confused, worried, irritable, hostile, inability to concentrate (these changes in behavior may cause one to snap at others, have accidents, and/or compulsively tap fingers)

-Preventing stress

1.      Avoid controllable stressors

2.      Plan major lifestyle changes: avoid taking on too much at one time

3.      Realize your limits: learn to say NO to new responsibilities you’re not sure you can fulfill

4.      Prioritize: don’t rush, do things one at a time and well

5.      Improve communication

6.      Share your thoughts

7.      Develop a positive attitude

8.      Reward yourself

9.      Exercise

10.  Eat and sleep well: can help develop a healthier lifestyle that is conducive to less stress

-Managing Stress

1.      Plan by visualizing expected events

2.      Think positively: put things into perspective

3.      Imagine potential negative big events: have a back-up plan in case things go differently than expected

4.      Relax with deep breathing

5.      Relax by clearing your mind

6.      Relax your muscles

7.      Relax with stretching and exercise

8.      Relax with massage therapy

9.      Ask for help

10.   Find professional help if needed

HEART SURGERIES

HEART SURGERIES

Patient: John Doe
Age: 47
Height: 6’0”
Weight: 257 lbs.

History: Mr. Doe has been a smoker for 27 years. He is a lawyer and has recently taken on a high profile case which comes with an increased amount of pressure. This has led to an increase in working hours and a strain on his 18 year marriage. His wife recently filed for divorce after being separated for a year. These events have encouraged the consumption of fast-food for nourishment during his long work hours and separation. He is frequently experiencing anxiety and shortness of breath. He has been in the hospital 6 times in the last 3 months due to fainting and chest pain (angina).

Family History: His grandfather and mother had diabetes and hypertension.

Tests: Physical examination illustrated his hypertension. The EKG test had abnormal results which indicated an underlying disease. Then we did an electron-beam computed tomography (EBCT) to look for the calcium in the lining of the arteries which was severe. The Angiocardiography (test using x-rays and dyes to produce images of the heart’s chambers and blood vessels) determined the extent and location of coronary artery disease.

Angiocardiography of Mr. Doe with several areas of disease.

http://www.smm.org/heart/videos/top.html#replacement

Diagnosis: Mr. Doe has coronary heart disease, which is the result of a sow buildup of plaque inside the heart’s arteries, and hypertension.

Treatment: Due to the extent of the disease, Mr. Doe has the option of stents or bypass surgery. Stents (simplest way to treat a heart attack is to open up the blocked artery using stents, which are permanent, tiny, metal, mesh tubes, to hold it open and improve blood flow) or bypass surgery (a piece of healthy artery or vein can be taken from other parts of the body, one end is attached to the aorta and the other end is grafted [process of joining one thing to another] to the diseased artery just below where it narrows). It he refuses to get treatment and continues to live the way he is currently living, he has a very high risk of heart attack and will eventually need a heart transplant. Also, he was strongly encouraged  reduce the amount of sodium (salt) he eats, quit smoking, get regular exercise and maintain a healthy weight, and eat a healthy diet. He was prescribed ACE inhibitors to lower blood pressure and nitrates to stop chest pain and improve blood supply to the heart.

ARTIFICIAL ORGANS

ARTIFICIAL ORGANS (REGENERATIVE MEDICINE)

Scientists are calling regenerative medicine the "Holy Grail" of stem-cell research! The field of regenerative medicine works under the theory that organs can be grown outside the body. This science could revolutionize organ transplants.

Regenerative medicine is the process of creating living, functional tissues to repair or replace a tissue or an organ function lost due to damage, or congenital defects. This field holds the promise of regenerating damaged tissues and organs in the body by stimulating previously irreparable organs to heal themselves.

Regenerative medicine also empowers scientists to grow tissues and organs in the laboratory and safely implant them when the body cannot heal itself. Regenerative medicine has the potential to solve the problem of the shortage of organs available for donation compared to the number of patients that require life-saving organ transplantation, as well as solve the problem of organ transplant rejection, since the organ's cells will match that of the patient.

An artificial organ is a man-made device that is implanted or integrated into a human to replace a natural organ, for the purpose of restoring a specific function or a group of related functions so the patient may return to as normal a life as possible.

Let’s take a look at an artificial bladder.

On April 4, 2006, it was announced that a team of biologists at the Wake Forest University School of Medicine, led by Professor Anthony Atala, had created the world's first lab-grown organ, a bladder, and transplanted it into a human. Seven people between the ages four and 19, received transplants. The bladders were grown from a small sample of the patients' own bladder tissue, so there was no risk of transplant rejection. Usually, damaged urinary bladders are stitched back together using other tissue from the stomach or intestine. Patients with bladders made of intestinal tissues suffer unpleasant side-effects because intestinal tissues reabsorb chemicals that are meant to be eliminated through the urine.

Professor Atala and his team successfully extracted muscle and bladder cells from several patients’ bodies, cultivated these cells in petri dishes, and then layered the cells in three-dimensional molds that resembled the shape of bladders. Within a few weeks, the cells in the molds began functioning as regular bladders which were then implanted back into the patients’ bodies.

Artificial Organs
Pros	Cons
Allows the patient to possibly conquer a disease or illness	Possible presence of latent or hidden disease or illness in the base tissue (if the foreign body tissue used to reconstruct a particular organ or tissue is infected or hiding a disease)
Has the possibility of prolonging life and making the general quality of life better	Ethical issues
Can help burn victims regenerate skin
Organ transplant lists will become unnecessary
Solve the problem of organ transplant rejection because the organ’s cells with match that of the patient
Solve the problem of the shortage of organs available for donation compared to the number of patients that require life-saving organ transplantation

STEM CELLS

Stem cells have been a very controversial topic since they were discovered in the mid 1970s. The use of embryonic stem cells has caused many moral and practical dilemmas. Embryonic stem cell research requires the creation, usage, and destruction of human embryos. But today scientists are researching new ways to cure diseases without the use of embryonic stem cells.

Glossary

Stem cells: cells with the ability to divide for indefinite periods in culture and to give rise to specialized cells

Embryonic stem cells: undifferentiated cells derived from a 5-day preimplantation embryo that are capable of dividing without differentiating for a prolonged period in culture and are known to develop into cells and tissues of the three primary germ layers

Induced pluripotent stem cells (iPSC): a pluripotent stem cells artificially derived from a non-pluripotent cell, typically a somatic cell, by inducing a forced expression of specific genes which preprograms the cell to enter and embryonic stem cell-like state

Adult stem cells (somatic stem cells): a relatively rare undifferentiated cell found in many organs and differentiated tissues with a limited capacity for both self renewal (in the laboratory) and differentiation

Pluripotency: the capacity to morph into any tissue in the body

Preimplantation: embryo has not yet implanted in the wall of the uterus

Some depth

Stem cells have the potential to develop into many different cell types in the body during early life and growth. They may for tissues that serve as a sort of internal repair system, dividing essentially without limit to replenish other cells. Each new stem cell, when it’s dividing, has the potential to either remain and stem cell or become another type of cell with a more specialized function. Two fundamental properties of stem cells are that they are capable of renewing themselves through cell division, sometimes after long periods of inactivity, and they can be induced to become tissue-specific or organ-specific cells with specialized functions, under certain experimental conditions.

iPSCs demonstrate important characteristics of pluripotent stem cells. They include the expression of stem cell markers, the formation of tumors contain cells from all three germ layers, and the ability to contribute to many different tissues when injected.

Somatic cells vs. embryonic stem cells: Both types of stem cells have potential for cell-based regenerative therapies. However, there are some major differences. Embryonic stems cells are pluripotent. Somatic stem cells are thought to be more limited to differentiating into different cell types of their tissue of origin. Embryonic stems cells can be grown relatively easily in culture while somatic stem cells are rare. Embryonic stem cells have a higher chance of rejection than somatic stem cells because somatic stem cells contain the host’s DNA so they are perfect matches as opposed to an embryo.

Medical experiments

Parkinson’s disease: Researches have created embryonic stem cells to become the types of cells damaged by this neurodegenerative disease and grafted them into the appropriate brain area of mice (who were injected with a deficit similar to Parkinson’s disease). Results showed that the neurons integrated themselves into the mice’s tissue and made proper connections. However, some cells were cancerous because they had a high potential to divide.

Spinal cord injury: Researches grafted human neural stem cells into mice with spinal cord injuries. The results produced appropriately differentiated cells and helped the mice recover motor function. But this stem cell therapy will take years before a clinical therapy is available for humans.

Experimental heart repair: Stem cells are currently used in a human clinical trial to repair the heart muscle that was damaged or destroyed during heart attacks. These stem cells come from bone marrow and circulating blood. Data suggests that these cells may help make moderate repairs, but there is no significant date to make a conclusion yet.

Differentiation

Scientists can harvest and maintain stem cells and they can cause stem cells to differentiate in to many different lineages, but some types of differentiation are hard to control. For example, the proper differentiation and growth of neurons are still difficult to perform, whereas the differentiation to muscle is easier. Scientists use growth additives to encourage differentiation. For example sonic hedgehog and retinoic acid are used to tell cells what to do. Also, activin is similar in function to sonic hedgehog. Hormonal environments also affect the path a stem cell can take in its differentiation.

EMBRYOLOGY

Embryology, what exactly is embryology? It is the science concerning the development of an embryo form the fertilization of the ovum to the fetus stage. Fertilization occurs in a series of steps: contact between the sperm and egg, entry of sperm into the egg, fusion of egg and sperm nuclei, and activation of development .During fertilization, a sperm must fuse with and penetrate the female egg for a successful fertilization. Fusing is the easy part, but penetrating through the egg’s hard protective shell is a problem for sperm. Thus, sperm go through a process called the acrosome reaction. An acrosome reaction is the reaction that occurs in the acrosome of the sperm as it approaches the egg. The acrosome is a cap-like structure over the frontal (anterior) half of the sperm’s head. As the sperm approaches the zona pellucid (glycoprotein membrane) of the egg, which initiates the acrosome reaction, the memebrane surrounding the acrosome fuses with the plasma membrane of the sperm. The contents (surface antigens and enzymes to break through egg’s hard shell) are exposed allowing fertilization to occur. The cortical reaction occurs directly after the acrosomal reaction. It happens when a sperm cell fuses with the egg’s plasma membrane which alters the zona pellucid preventing other sperm from binding and entering the egg. It is the exocytosis of the egg’s cortical granules (secretory vesicles below the plasma membrane). When the sperm is in contact with the egg’s plasma membrane, calcium is released from storage sites in the egg triggering the fusion of cortical granule membranes with the egg plasma membrane. The wave of calcium surrounds the egg and a wave of cortical granule fusion results.

Cleavage is the first step in development for all multicellular organisms. It converts a single-celled zygote into a multicelled embryo via mitosis. It is the division of cells in the early embryo. The blastula is produced by mitosis of the zygote. A blastula is a ball of cells surrounding the blastocoel (fluid-filled cavity). As a result of rapidly dividing cells, their size decreases. However, it increases their surface area to volume ratio to increase allowing more efficient oxygen exchange between cells and their environment. The blastula receives RNA and information carrying molecules to start the differentiation of cells and early development.

Grastrulation occurs next. It is a series of cell migration to positions where they will form three primary cell layers: ectoderm (outer layer), endoderm (inner layer), and mesoderm (middle layer). This single-layered blastula is reorganized into a gastrula. The ectoderm forms tissues such as skin, hair, sweat glands, and epithelium. It also develops the brain and nervous system. The mesoderm forms structures associated with body movement and support. Mesoderm structures include muscles, cartilage, bone, and blood. It also forms kidneys and reproductive organs. Reproductive organs are also developed by the archenteron. The archenteron is the primitive gut that forms during gastrulation in the developing blastula. Lastly, the endoderm forms tissues and organs that aid in digestion and respiration. Endocrine structures such as the thyroid and parathyroid glands are formed by the endoderm. The liver, pancreas, and gall bladder are also developed by the endoderm.

Organogenesis is summed up by its name, the creation of organs. It is the process by which the ectoderm, endoderm, and mesoderm develop into internal organs. For humans, this process usually occurs between the third and eighth week in utero. The germ layers in organogenesis differ by three processes. These three processes are folds, splits, and condensation.  

Let’s take a closer look at fertilization in sea urchins.

Fertilization is external. Most sea urchins have their eggs free floating in the sea, but others keep them on their spines for protection. To prevent the sperm and egg from being washed away they have evolved mechanisms to bring the gametes together. When a sperm cell encounters an egg of the same species, components of the jelly coat bind to specific egg receptors in the plasma membrane. This triggers the release of calcium that facilitates fertilization.

In the sea urchin, early cell divisions are rapid. The proteins that are synthesized during cleavage utilize mRNA found in the cytoplasm provided by the mother. The first three cell divisions bisect the embryo equally; the fourth cleavage divides the cells in the top half equally, but those in the bottom half unequally. The cells continue to divide until the form the blastula.

A sea urchin embryo has ten cycles of cell division to make a single epithelial layer enveloping a blasteocoel. The embryo then begins grastrulation, a multipart process which dramatically rearranges and invaginizes cells to produce three germ layers.

The fertilized egg develops into a free-swimming blastula embryo in as little as twelve hours! The simple blastula transforms into a cone-shaped echinopluteus larva which has elongated arms, nutrients, a cilia to capture food particles. It may take several months for the larva to be fully developed. The larva sinks to the bottom of the sea after development is completed and metamorphoses into an adult in as little as one hour.