Stem cells

Stem Cells

I. Introduction:

                                Stem cells are a class of undifferentiated cells that are able to differentiate into specialized cell types.  These cells have the remarkable property to get developed into many different cell types in the body during early life and growth. They may even show unlimited division resulting in internal repair and prevention from injury in some cases. As these cells are undifferentiated, each cell has a choice either to be an undifferentiated cell (stem cell) or get converted into other type of specialized cell having specific function like a nerve cell, a blood cell or any other cell for that matter.

                            Stem cells are different from other cells as they are the cells which are unspecialized but can renew themselves or can take up a special function under certain conditions. Their properties of differentiation also depend on type of organs or tissue they are present in. For instance in organs like bone marrow, Stem cells divide regularly too repair and replace the dead and worn out cells while in organs such as pancreas and the heart, stem cells only divide under special conditions.

 Commonly, stem cells come from two main sources:

•     Embryos formed during the blastocyst phase of embryological development (embryonic stem cells) and

• Adult tissue (somatic or adult stem cells).

Both types are generally characterized by their potential to differentiate into different cell types (such as skin, muscle, bone, etc.). Scientists discovered ways to derive embryonic stem cells from early mouse embryos more than 30 years ago, in 1981. The detailed study of the biology of human stem cells however came into existence as late as, in 1998. Embryos used in these studies were created for reproductive purposes. When they were no longer needed for that purpose, they were donated for research with the informed consent of the donor. Afterwards scientists have found many applications of these stem cells and their banking. One such application is to completely reprogram some specialized cells to get converted into stem cell like state, which can be a revolution. These stem cells as are induced, so named induced pluripotent stem cells.  

 In the 3- to 5-day-old embryo, called a blastocyst, the inner cells give rise to the entire body of the organism, including all of the many specialized cell types and organs such as the heart, lungs, skin, sperm, eggs and other tissues. In some adult tissues, such as bone marrow, muscle, and brain, discrete populations of adult stem cells generate replacements for cells that are lost through normal wear and tear, injury, or disease.

Due to these unique properties, stem cells have great futuristic aspects as they can be used to treat many diseases like Diabetes, thallesemia and much other deadly disease. Although these aspects still need to be researched heavily and yet to be tested properly but theoretically it is indeed a possibility.

Laboratory studies of stem cells enable scientists to learn about the cells’ essential properties and what makes them different from specialized cell types. Scientists are already using stem cells in the laboratory to screen new drugs and to develop model systems to study normal growth and identify the causes of birth defects.

Embryonic stem cells

Embryonic stem cells are derived from a four- or five-day-old human embryo that is in the blastocyst phase of development. Sexual reproduction begins when a male's sperm fertilizes a female's ovum (egg) to form a single cell called a zygote. The single zygote cell then undergo  a series of divisions, forming 2, 4, 8, 16 cells, etc. After four to six days - before implantation in the uterus - this mass of cells is called a blastocyst. The blastocyst consists of an inner cell mass (embryoblast) and an outer cell mass (trophoblast). The outer cell mass becomes part of the placenta, and the inner cell mass is the group of cells that will differentiate to become all the structures of an adult organism. This latter mass is the source of embryonic stem cells - totipotent cells (cells with total potential to develop into any cell in the body).   In a normal pregnancy, the blastocyst stage continues until implantation of the embryo in the uterus, at which point the embryo is referred to as a fetus. This usually occurs by the end of the 10th week of gestation after all major organs of the body have been created.

 

Somatic  stem cells

                                   Adult or somatic stem cells exist throughout the body after embryonic development and are found inside of different types of tissue. These stem cells have been found in tissues such as the brain, bone marrow, blood, blood vessels, skeletal muscles, skin, and the liver. They remain in a quiescent or non-dividing state for years until activated by disease or tissue injury.

Adult stem cells can divide or self-renew indefinitely, enabling them to generate a range of cell types from the originating organ or even regenerate the entire original organ. It is generally thought that adult stem cells are limited in their ability to differentiate based on their tissue of origin, but there is some evidence to suggest that they can differentiate to become other cell types.

Stem cell cultures

  Stem cells are either extracted from adult tissue or from a dividing zygote in a culture dish. Once extracted, scientists place the cells in a controlled culture that prohibits them from further specializing or differentiating but usually allows them to divide and replicate. The process of growing large numbers of embryonic stem cells has been easier than growing large numbers of adult stem cells, but progress is being made for both cell types.

Stem cell lines

Once stem cells have been allowed to divide and propagate in a controlled culture, the collection of healthy, dividing, and undifferentiated cells is called a stem cell line. These stem cell lines are subsequently managed and shared among researchers. Once under control, the stem cells can be stimulated to specialize as directed by a researcher - a process known as directed differentiation. Embryonic stem cells are able to differentiate into more cell types than adult stem cells.

Potency

Stem cells are categorized by their potential to differentiate into other types of cells. Embryonic stem cells are the most potent since they must become every type of cell in the body. The full classification includes:

•   Totipotent - the ability to differentiate into all possible cell types. E.g. zygote formed at egg fertilization and the first few cells that result from the division of the zygote.

• Pluripotent - the ability to differentiate into almost all cell types.

                              E.g. embryonic stem cells and cells that are derived from the mesoderm, endoderm, and ectoderm germ layers that are formed in the beginning stages of embryonic stem cell differentiation.

•   Multipotent - the ability to differentiate into a number of closely related cells. e.g.  hematopoietic stem cells that can become red and white blood cells or platelets.

•   Oligopotent - the ability to differentiate into a few cells. e.g. include (adult) lymphoid or myeloid stem cells.

•   Unipotent - the ability to only produce cells of their own type.E.g. muscle stem cells.

Embryonic stem cells are considered pluripotent instead of totipotent because they do not have the ability to become part of the extra-embryonic membranes or the placenta.

10 most common myths about dieting

Being physically fit and having toned and good figure is the dream of everybody but the modern lifestyle doesn’t allow everyone to have the same. Not everybody has the time to go to gym and workout so an option of dieting is what we are left with so as to reduce body weight. Don’t eat after 8 pm, stop eating rice, avoid bananas and potatoes, no tea and coffee! How many times you have been advised to make these changes in your diet by your friends and relatives when you said you wish to lose weight? Almost all the time! Right?  And you end up following the advice without realizing that it may not do any good to you.

In reality, we are surrounded by many misconceptions when it comes to dieting and that’s the reason many dieters fail to achieve their goal even if they are highly motivated. Let’s look at 10 such myths associated with dieting and the impact they have on you.

     1.       Low fat does not necessarily mean less calories

                                                    Low-fat diet simply doesn’t mean low-calorie diet and so it’s not like that you can have as much of it as you want. If you pile up your plate with low-fat, you may end up eating more calories than if you had a one serving of chips. In order to make products low in fat, manufacturers add substituting ingredients like flour, sugar, starch, etc. to improve taste and this adds calories. Therefore the best way to know about how healthy your food product is check the nutritional label, and know how many calories, fat, sugar you are getting.

      2.      Skip potatoes, rice and bananas

                                                    Learn to make smart choices and include these foods in your diet without letting them hamper your calorie count. For example, banana in the morning will not only provide you with a dose of potassium, fibre, vitamin C, etc.  but will also provide you with energy which will help you keep going throughout the day.

Rice contains methionine which helps mobilise fat from the liver. Where you need to be careful is stop mindless eating and control portion size when it comes to eating rice based preparations.

Potatoes are loaded with nutrients too but we make it unhealthy by using faulty cooking treatments like deep frying (chips, cutlet, French fries, etc). If included sensibly in diet it can protect against cardiovascular disease and cancer due to high potassium and Vitamin B6.

      3.       Late night meals result in overweight

                                                 Your weight is a result of what you eat throughout the day and not just at night. This might be true for people who keep skipping meals at day time and binge at night. The idea is keep a gap of at least an hour before hitting bed and eat something light as you don’t need too many calories in the night.  

      4.       Do not eat junk food while dieting

                                                 Most fast foods are unhealthy but not all, and if you choose your options carefully you can include them in your healthy diet. Tips you can follow:

·         Avoid high-calorie toppings like cheese, butter, mayonnaise; instead you can go for salsa, garlic dip, etc.

·         Pick fresh fruit juice or milkshake rather than aerated drinks.

·         Choose salad based wraps and burgers.

·         Ask for steamed, baked or grilled items rather than deep fried.

      5.       Skipping meals or reducing intake of diet

                                                 If you eat less or skip meals you will end up binging later on when you feel extremely hungry. And therefore you gain more weight and your efforts get wasted. Moreover, if you keep yourself on extremely low-calorie diet for longer period of time, your metabolism gets altered and restricting yourself from essential nutrients also poses great health threats.

      6.      Bye bye snacks?    

                                                While mindless snacking can gift you with several extra kilos, thoughtful snacking can help you reduce several kilos. People who have small, frequent meals with snacks are more likely to get better weight loss results. Choose snacks which are low in calorie and high in protein so that they can curb your hunger pangs in a healthy way.  

      7.      Vegetarians are devoid of good protein sources

                                                False, there are plenty options for vegans too. Include at least three servings of milk and milk products (one glass milk, one cup curd, 40g paneer), two servings of pulses especially soybean, one serving of nuts to meet your protein requirement.

      8.      Fasting regularly

                                                 It’s an absurd idea to compensate your feast with fast. When you eat larger portions than required, your body stores the extra calories in the form of fat and when you skip meals there is an urgent need of energy by the body and that is served by breaking muscle tissue because breaking down fat for energy is a long process and it doesn’t come into circulation that easily. Therefore all your effort goes waste.  

9.      Eggs are unhealthy

                                                When had for breakfast, eggs help limit your calorie intake all day. Eggs are a well-known rich source of protein along with several vitamins and minerals essential to your health like B2, B12, Vitamin A, E, iron, zinc and phosphorus. Boiling an egg is one of the healthiest ways you can consume it and is the perfect option for those watching their weight. You can include one egg in your daily diet without bothering about the cholesterol content as one egg will not do any harm. 

     10.  Fruits are the best breakfast option

                                              No doubt fruits are rich in many vitamins and minerals and carbohydrates. But cereal is a better option when it comes to refuelling your body after a long gap because it contains complex carbohydrate and protein and a fibre. Ideal breakfast should contain a serving of cereal, milk or milk product, and a fruit.

Indian dieting approach is surrounded by number of myths and gimmicks. Adopt an approach of eating a balanced diet, and keeping yourself active throughout the day for long term results.