A brief introduction to sickle cell disease (SCD)

Introduction

When I was 14 years old, I asked if I could go camping in the Jamaican countryside. My parents said that it was okay and before I knew it, I was in a cabin in the woods. I was with others my age and my cabin mates were all boys. While there, I met a boy who was not as active as the others were. At the time, I considered him my friend and wondered why he would not go out and play with us. So, I asked him just that. He explained that he had sickle cell disease (SCD) and got tired very easily. At the time, I did not quite understand what he was talking about, so I let him rest and went about my business. Years later, while taking a genetics course in college and subsequently co-authoring a research paper (unpublished as of this writing) on the topic, I am now a little familiar with the disease and complications that arise with it.

Sickle cell disease is a group of genetic blood disorders that arises from a single point mutation in the genetic code. The mutation occurs on the HBB gene where glutamic acid is replaced by valine at the 6th position (Glu6Val, βS).  The most common and severe form of sickle cell is the homozygous HbSS form with an inheritance of the βS trait from both parents. There are other forms of sickle cell that includes genetic variants such as: HbC, HbS, HbS with β-thalassaemia and HbS with other beta-globin variants such as HbSD or HbSOArab. All of these variations are different in the their range of symptoms. Though individuals with the sickle cell trait, HbAS are not considered to have the disease, they are still at risk of manifesting symptoms while performing high intensity exercise or when at high altitudes. Furthermore, people with HbAS are at higher risk of developing certain types of cancer.

Cause and Outcomes

The single change in the genetic code is the the root cause of the pathophysiology that arises.  This change leads to red blood cells (RBCs) sickling upon deoxygenation. RBCs are usually flexible, which is a characteristic that allows them to pass through the capillaries (the smallest blood vessels) of our bodies. In a person with SCD, these RBCs become rigid after it releases oxygen to the tissues. This rigidness causes vaso-occlusion and disrupts blood flow to an area of the body. This disruption causes babies who have SCD to lose their speen, an important organ in the immune system that helps fights against diseases such as influenza type b and streptococcus pneumonia. Without the speen, babies with SCD are usually placed on a broad spectrum anti-biotic and given vaccines to help build the immune system. This vaso-occlusion can also cause end organ damage to the heart, brain and kidneys. The most common form of death in adults with SCD is acute chest syndrome (ACS). In order to treat this, one gives oxygen, non steroidal anti inflammatory and opiods for the pain. Simple blood transfusions is also used to bring the RBC count back to baseline. People with SCD also have a higher risk of strokes and silent cranial infarcts. The vaso-occlusion in the brain also causes cognitive decline and with this cognitive decline, it can cause issues for a child with SCD to excel in an academic format.

SCD is by no means a death sentence like it was in yester-years. Childhood mortality has gone down significantly and there are continuing advances in the field. However, the problems outlined above still persists. There have been a few cases were people have been effectively cured with a bone-marrow transplant, however, that process is high risk and finding a suitable match can be difficult.

Figure 1: Shows how sickled cells could block blood flow due to their rigidity

Treatments

Currently, the most common treatment for SCD is hydroxyurea. Hydroxyurea increases fetal hemoglobin (HbF) in the blood and reduces the symptoms of the disease. I find it interesting that babies in the womb who have SCD do not manifest symptoms. This occurs because at that stage, the fetus mainly relays on HbF to transport blood. Symptoms do not arrive until a few months after birth, when the baby's body switches from fetal hemoglobin to adult hemoglobin. Other treatments include bone marrow transplants - which has shown to effectively cure an individual of the disease - and gene replacement therapy.

Why is this disease so prevalent?

So, growing up, I used to ask "why?" all of the time and expected a detail answer on whatever I was asking about. Many times I did not get a satisfactory answer and my older sisters used to tell me "you will know when you are older." Now that I am older, and went through four years of undergraduate study and now have a bachelor of science in Biology and Spanish Literature, I now know the answers to many of my childhood questions. The more I learn, the more I am able to recognize what I do not know.

Why is SCD and the sickle cell trait so predominant? On the surface, it seems like something so debilitating would have been selected against a long time ago while humans were evolving. It turns out that Malaria, a disease that is transmitted by mosquitoes, is prevalent where there is a high incidence of SCD and sickle cell trait. Malaria is a parasite that infects red blood cells. Upon infection, it generates a series of non-specific inflammatory response from the immune system. It seems that the carriers of sickle cell trait (HbAS) and people who have SCD have increased protection against Malaria. This could be due to the sickling nature of the red blood cells, making them harder to be infected.

The above is not meant to be an exhaustive piece on sickle cell. It is meant to give readers a taste in what goes on with an individual who has the disease.

Further reading:

Sickle Cell Ware RE

Genetic Determinants and Stroke in Children with SCD

How I treat and manage strokes in SCD

Where did the sun come from?

Looking up to the sky on a bright summer day - one could easily see the sun. That big ball of fire is the reason why we are all alive right now. But how did that ball of energy come about?

Stars like our sun was formed in space clouds called a nebula. A nebula is an enormous space cloud that is many light years across (a light year is the distance light travels within a year: which is nearly six trillion miles!).

These nebulae contains about 70% Hydrogen, 28% Helium and 2% of other elements.

In these nebulae, each particle of gas is so far a part that they don't even touch! But every now and then, a disturbance such as a supernova or irregularities in the nebula causes molecules to attract each other via gravity.

When this happens, the portion of the nebula that is disturbed starts collapsing unto itself bringing more and more molecules into close contact. As the size of the collapsing nebula decreases in size, it begins to rotate faster due to conservation of angular momentum. Angular momentum = mass x velocity x radius. Angular momentum has to stay the same and the mass does not change, therefore if the radius decreases, the velocity has to increase in order to keep angular momentum constant.

Now that the molecules are interacting more, the density, temperature, and pressure increases. The temperature increases because the kinetic energy of the molecules is converted to thermal energy. As the pressure increases, the pressure begins to counter the force of gravity.

When this happens, we get what is known as a protostar. The word "proto" just means precursor. A protostar is a start that did not start to fuse hydrogen at its core.

A protostar becomes a star when it starts fuse hydrogen at its core. Fusion of hydrogen into helium occurs when core temperature reaches 10 million degrees kelvin or approximately 18 million degrees Fahrenheit. A star is stabilized by the forces nuclear fusion exerts and the forces of gravity. These two forces are opposing forces, therefore they must balance each other for the sun to stay in stasis. This state is called hydrostatic equilibrium.

Planets are created in the same way as the sun. The main difference is that planets do not have enough gravitational force to initiate fusion and they contain different composition of elements. For comparative purposes: by weight, the earth is mostly oxygen and silicon, and the sun is mostly hydrogen and helium.

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References:

Composition of Elements on Earth
How is a star born
Star Birth
Life Cycle of Stars
How do Stars Form and Evolve?
The Outer Planets
A Star is Born

Why do cows chew their cud?

In my home country of Jamaica, cattle was prevalent. I would watch them from time to time and they would stand there lazily and chew - for what seems to be - forever. I have always wondered: "Why is that?" However, I never got a good answer. It seemed like no one could explain to me why an animal would chew its cud.

Many years later, I was in comparative anatomy class and the professor was discussing different types of digestive systems and fore gut fermenters was mentioned. Up until then, I was quit naive about the gastrointestinal (GI) tract of other animals that are not human. I mistakenly assumed that all GI tracts looked like the one of the human. although I was somewhat right, many animals in different niches have special modifications to their GI tracts so that they could properly digest and absorb their food of choice. The cattle is one such example. The bird and the horse also has specialized GI tracts and I may talk about that in detail in a later blog post.

Okay, let's get started. The cow's stomach is consisted of four parts: the rumen, reticulum, omasum and abomasum. Food (which mostly plant based) enters the mouth and travels through the esophagus to the rumen. The plant based food that a cattle consumes consists of a type of sugar called cellulose. Mammals lack the ability of  breaking down cellulose on their own, therefore, when the plant based food enters the rumen of a cattle, it is met by a team of microorganisms that aid in the digestion of cellulose.

These microorganisms are classified as protozoa and bacteria. They form a symbiotic relationship with the cattle. The microorganisms are capable of synthesizing cellulase, an enzyme that breaks down cellulose. When cellulose is fermented by the microorganisms, it is broken down into short organic acids, methane, and carbon dioxide. The saliva of the cattle is used as a buffer in which the microorganisms proliferate. The saliva also aids in detoxifying toxins such as alkaloids which may be in the food.

In order for cattle to get protein in their diet, the microorganisms in the rumen converts the simple nitrogenous compounds in the food into ammonia then the ammonia is used to make protein. Another way that the cattle gets its protein is through inhaled nitrogen in which the microorganisms convert to protein.

From time to time, the cattle would belch. In doing so, it releases some gas produced in the reticulorumen and also regurgitate some of its food. The food that is regurgitated is re-chewed or re-masticated by the cattle. This re-mastication is what we see when a cattle is chewing its cud! This cycle is repeated on numerous occasions until the physical substance is broken down enough to get past the reticulum, into the omasum and abomasum. The absomasum is where protein digestion normal protein digestion starts.

Hopefully, I didn't get too technical there. I was really trying not to. However, that is the process that happens inside the anterior region of a cattle's GI tract. The cattle has evolved a mechanism that effectively extracts most of the nutrients of the plant matter that it could. What about horses and rabbits? They don't chew their cuds and they consume plant matter ... Yes, they do not chew their cud, however in their GI tract, they have a cecum in the hind region. The cecum contains a team of bacteria that breaks down the cellulose. Rabbits have been observed eating their own feces in order to extract more nutrients from their food. These mammals are called hingut fermenters.

Hope that helped! Be sure to comment, share and subscribe to my Youtube channel Knosis, where I post science and technology videos!

Reference: Liem, Karl, et al., Functional Anatomy of the Vertebrates: An evolutionary perspective. 3rd ed. Belmont, CA: Emily Barosse . Print

The Purpose

Update (3/10/2019): It has been a number of years since I have updated this blog. I have had it on my to-do list for a while now, however, I have not prioritized it. I am starting medical school in 3 months and I plan on utilizing this space to write about the information that I find most interesting. It will be a great way for me to review my notes and to help out anyone who comes across this blog. I intend on dedicating at least 30 minutes a week to write about a topic that I find interesting from the previous week. Be sure to follow the blog to see what is to come!


As a young boy growing up, I had many questions for my older siblings and parents of why the world operates the way it does. Questions like "Why do cows chew their cud?" was one of the questions that I never got a complete answer for. Until I took comparative anatomy of chordates, in my third year of studying Biology. Okay, maybe if I really wanted the answer, I could of just Googled it eventually when I gained access to a computer, but the question faded away from my mind.

This blog is created to answer many of the common questions people ask as children but never got a complete answer for. Questions that will be covered will include, but not limited to: Why do we have fingernails?, Why are women and men so different? and are they really that different?, Why is the sky blue? How solar panels work? Why are some words bad and others that mean the same exact thing not bad?

These and other questions will be answered in future blog post. Enjoy your day Homo sapiens.