Types and causes of moles- Biology Bug

What are moles?

Moles are the growth on the skin which are brown, black or red colored lesions which can appear alone or exist in groups. They can appear anywhere on your body including the eyes, nose, hands, legs, chest, back or even the genitals. The medical term for the moles is melanocytic nevus (visible chronic lesions on skin). Some people describe them as imperfection on the body while most of the beauty experts consider them as beauty mark. Most of the times moles appear in early childhood and during first 25 years. But have you ever thought what the factors which cause mole are? Let’s discuss some of them.

What causes mole?

  • Exposure to sun
  • Genetic factors
  • Hormonal imbalance

Exposure to sun

Every individual gets a distinct skin color because of different melanin levels. Melanin is a pigment which is produced by specialized skin cells called as melanocytes. These melanocytes produces more melanin when exposed to sun in order to protect the skin from harmful radiation. This is one of the reason why we get tan when exposed to the sun. Moles are concentrated clumps of melanocytes, which is why they look darker. A normal individual can have 15-30 moles. However the people with more number of moles have higher risk of melanoma. Melanoma is a type of cancer that develops from melanocytes. But most of the moles are non-carcinogenic in nature.

Role of genetics

The role of genetics is not well understood for mole development. However the study for melanoma has been widely published and hence we can relate it to development of benign moles. DNA present in the skin cells contains several genes. There can be mutation, hereditary factors or exposure to harmful radiation can result into variation of certain genes which includes FGFR3, PIK3CA, HRAS, and BRAF. Variation in these genes can lead to benign moles. For example, mutation in BRAF gene leads to production of an altered protein that causes melanocytes to aggregate into moles. 

Hormonal imbalance

Hormones can be imbalanced because of several reasons including pregnancy, menopause, puberty or medications. During pregnancy the level of progesterone and estrogen vary each month. Also there is small variation in amount of MSH i.e. melanocyte stimulating hormone which is produced by pituitary gland. MSH hormones stimulate the melanin production in melanocytes. Hence you can see dark or tan patches on the skin in case of pregnant ladies. It frequently occurs during the menopause since the hormonal level is fluctuating continuously and results into increase in either the size of mole or number of moles.

Types of moles

There are basically three types of moles that are symmetrical, irregular and regular. But in medicine it is divided into several types according to their location, shape and time of appearance.

Common moles

It is about 5mm large with distincy edges and dome like surface with brown pigmentation. They are found on the skin when exposed to the sun.


This type of mole shows irregular symptoms. They have blurry borders and can vary in color. They are comparatively larger than the common moles. Also they can be flat or raised lesions. If a person is having too many atypical moles then the risk of skin cannot be neglected. The person should go for regular examination.

Congenital moles

They are also known as congenital nevi. They appear at the time of birth or within first year of baby’s life. These moles can be caused by melanocyte cells in middle layer of skin, outer layer of skin or both. They can be referred as birthmarks.

Acquired moles

Acquired moles are moles that appear during childhood and adulthood. Most of these moles are benign and pose no risk, although sometimes they can turn into cancerous moles with age. This type of mole is the most common, and repeated sun exposure usually causes it. These moles appear during early childhood or sometimes in adulthood. This type of mole generally do not pose any risk in future. They are one of the commonly seen moles.

Junctional melanocytic moles

They occur due to accumulation of melanocytes where the dermis and epidermis meet. They are slightly raised with regular borders and dark pigmentation (range from tan to dark brown). As the age increases these moles can migrate down to deeper layers of skin.

Intradermal moles

They are skin colored moles and their pigmentation is not as dark as junctional ones because they are located in the middle layer of your skin. They usually develop during late childhood or throughout the adulthood.

 Now remembering all the types of moles with their unique qualities can be little difficult. Hence doctors have introduced ABCDE method.

A: Asymmetrical

B: Irregular border

C: Multiple color

D: Bigger diameter

E:  Evolving, new or changing

External Links:

  • https://www.webmd.com/skin-problems-and-treatments/guide/moles-freckles-skin-tags
  • https://www.healthline.com/health/new-mole#types
  • https://www.medicinenet.com/moles/article.htm#what_are_moles
  • https://ghr.nlm.nih.gov/primer/traits/moles
  • https://www.skinvision.com/articles/types-of-skin-moles-and-how-to-know-if-they-re-safe

Thanks for reading. Tell me which type of mole you’ve seen? Comment down below.

Nail growth |process|why nails keep growing – Biology Bug

Do you ever realize that your nails never stop growing. But how do they grow even after cutting? Let me tell you that they are growing before you were born. Nails are hardened structure made of dead cells. They grow by the process of keratinization. Keratin is a protein which is responsible for our hair and nail growth. The article discuss about why there is continuous growth of nails and what are the factors associated with it.

Key points: nail growth, structure of nail, process of growth, role of keratin

Keratin is a protein made by our skin cells. As the cells push upwards to the skin they die and becomes harden. This process is known as keratinization. However there are several other factors which contribute to the growth of nails. Amino acids are required to synthesize any protein in your body. Similarly the amino acids which are required for synthesizing keratin are dependent on amount of Sulfur present in your body. Vitamin A is essential for absorbing this protein. Vitamin C works with zinc to create a protein called collagen. This protein develop healthy connective tissue in your finger and rest of the body. Collagen is also known to be skin tightening and glowing agent. Before we discuss the process in details, let us understand some of facts regarding the nail growth.

1) Growth of the nails depends upon the season. They grow faster in summer than any other season. 2) Fingernails grow faster than toenails. 3) Men show higher rate of growth than women.

Note: Technically nails aren’t growing tissue, hence they do not grow. They are results of those cells which stopped growing due to their genetic mechanism.

Structure of Nail:

The structure includes these important parts,

  1. Matrix
  2. Cuticle
  3. Lunula
  4. Nail bed
  5. Nail plate
  6. Hyponichium
  7. Nail grooves

Matrix: This is the root of the nail. Its function is to make new cells. These new cells pushed up by the old one through the skin. This part contains lots of nerves and blood vessels which are essential for cell reproduction. Technically it is the only living part of the nails at initial stage but ultimately results into dead cells which forms nail.

Cuticle: This is a small sliver of skin where the nail grows out of the finger. It basically protects the matrix from any germs or infections

Lunula: it is a small whitish curved like structure that sometime you see at the bottom of the nails. It can be said as a part of the matrix. Most of the time it is under the skin. Therefore not every individual can see the lunula.

Nail bed: This area lies under nail plate. Nail plate is the visible part of nails which is the result of keratinization.

Hyponichium: this is the line where nail plate separates from nail bed.

Nail grooves: These are the grooves at the side of your free edge which gives direction for nail growth.

Process of Growth

  • The process starts with the DNA and the gene which codes for keratin. Especially in the case of nails there is one gene called as CRATIN which is actively present in our nail cells.
  • This gene will code for the protein i.e. keratin which will be more produced near the nail area.
  • Now the matrix is continuously producing cells because it is rich in blood vessels. The keratin is present in every cell until the cell undergoes a death cycle.
  • As more new cells are produced, the older ones get pushed up by the new cells. This is a sensitive phase where a mineral balance (zinc, iron, cobalt) and hormonal balance is required (minerelocorticoids, thyroxine etc.)
  • The keratin protein in the cells grows harder and beyond a certain point there are no longer living cells with nuclei.
  • The growing hard structure continues to from a nail plate. Most of the growth takes place underside the nail plate and that area is called as germinal matrix. The outer layer of germinal matrix is a half-moon shaped structure that is lunula.
  • The nail plate is loosely attached to the germinal matrix. It also held by some skin at the bottom and at its sides. As it grows the nail will acquire a concave shape.

 Why do we have nails?

The nails are flattened version of claws. It is one of the important features of primates. If you observe the arboreal animals like apes, monkeys, lemurs etc. possess the same feature. Humans are primates and nails are our distinguished character. They are nothing but dead cells and hence not really useful as claws.

Do nails grow after death?

No. it is clearly a myth. Fingernails might appear long after death. It is not because they are still growing but the skin around that area is retracted. If you have carefully observed that the skin and other soft tissues starts shrinking after death. It is an optical illusion which makes the nails look bigger than the ordinary size.

Can they stop growing in certain cases?

This depends on various factors. One of the common reason which we usually see around us is the habit of biting nails. This in certain cases can damage the nail bed or matrix or lunula. If any sensitive area of the nail is damaged because of biting, injury, accident or by using sharpened objects then there is a possibility that the nail might stop growing.

External links:

  1. https://www.livestrong.com/article/181963-what-makes-your-hair-nails-grow/
  2. https://www.aad.org/public/kids/nails/how-nails-grow
  3. https://www.nytimes.com/2015/08/25/science/the-inexorable-forces-of-nail-growth.html
  4. https://classroom.synonym.com/the-process-of-nail-growth-12079176.html
  5. https://nailbees.com/nail-structure

Thank you for reading. Did you find this article helpful? Mention in the comments.

Structure of nephron and Formation of Urine|Process of excretion

Key points: kidneys, nephron, structure of nephron, process of urine formation.

Kidneys play an essential role in excretion. They are bean shaped, reddish brown organs which are covered by renal capsule. There is a con caved side of a kidney that has a depression where a renal artery enters and a renal vein exits towards uterus. The kidneys are located at the rear wall of abdominal cavity.

Internal structure of kidney

Kidney has an outer dark cortical region, an inner medullary region and a funnel shaped renal pelvis region.

  • Renal cortex: This region contains glomeruli of nephrons. It appears to be dark and dotted due to the presence of malpighian bodies.
  • Renal medulla: It is a region just inner to renal cortex. It contains renal tubules, collecting ducts and blood vessels present in the form of pyramids. The conical shape of pyramid projects into pelvis.
  • Renal pelvis: It is large funnel shaped space behind the medulla region. Urine is collected in renal pelvis and passed down to uterus.
Internal structure of kidney

NOTE: Each kidney consists of large number of filtering units called as ‘nephrons’. It has approximately 1.3 million nephrons.

Each nephron originates in the cortex region and extends into medulla region.

Structure of Nephron

A nephron is also called as uriniferous tubule which is a functional unit of kidney. Each nephron filters a part of blood and produces a small amount of urine. It consists of two parts,

  1. Malpighian body
  2. Long coiled tubule

Malpighian body

Malpighian body is also divided into two main parts:  a) Glomerulus b) Arterioles   c) Bowman’s capsule

a) Glomerulus

It is like a capillary network that receives its blood from afferent arteriole from renal circulation. The glomerular blood pressure provides the driving force for fluid and solutes to be filtered out and into the space made by Bowman’s capsule. The remainder of the blood which is not filtered

into glomerulus passes into the narrower efferent arteriole. It then moves to vasa recta which are collecting capillaries.  

b) Afferent and efferent arteriole

Afferent arteriole supplies blood to the glomerulus. A group of specialized cells known as juxtaglomerular cells are located around the afferent arteriole, where it enters the renal corpuscle. The efferent arteriole drains the glomerulus. Specialized cells lies between two arterioles and those are called macula densa. The juxtaglomerular cells and macula densa together forms a juxtaglomerular apparatus.

Bowman’s capsule

Bowman’s capsule surrounds the glomerulus and is composed of visceral and parietal layers. The visceral layer lies beneath the thickened glomerular basement membrane and it is made of podocytes. The parietal layer is lined by single layer of squamous epithelium. Between the visceral and parietal layer is Bowman’s space, into which the filtrate enters after passing through podocytes. Any small molecules such as water, glucose, salts and urea pass freely into Bowman’s space but cells, platelets and large proteins cannot pass through it. As a result the filtrate leaving the Bowman’s capsule is very similar to blood plasma in composition.

c) Long coiled tubule

It consists of three important parts as follows;

  • Proximal convoluted tubule
  • Loop of Henle
  • Distal convoluted tubule

Its various parts are modified for absorption of salts and water from the blood. It opens into collecting duct. The capillaries that take blood out from glomerulus, form a network all over the long tubule and finally unite to form a renal vein.

Formation of Urine

Urine formation in nephron involves three basic steps


Selective reabsorption

Tubular secretion

Single nephron: mechanism of urine formation


Blood enters the afferent arteriole and flows into glomerulus. Blood in the glomerulus has both filterable and non-filterable blood components. The blood flows under pressure in the renal artery. Also in the glomerulus the efferent arteriole leaving the glomerulus is narrower than afferent arterioles. Therefore this pressure helps the fluid to filter out through thin capillary walls of glomerulus. The filterable components include water and dissolved molecules while non filterable components are blood cells and proteins. The glomerular filtrate is not the same consistency as urine. Ultrafiltration is purely a physical process and energy for filtration is derived from the hydrostatic pressure of blood.


Sodium chloride reabsorbed into the system increases the osmolarity of blood in comparison to the glomerular filtrate. This reabsorption process allows water to pass from the glomerular filtrate back into the circulatory system. Glucose and amino acids are reabsorbed into circulatory system. If too much glucose appears in the glomerular filtrate it increases the osmolarity of filtrate, causing water to be released into the urine rather than reabsorbed by the circulatory system. Frequent urination and unexplained thirst are warning signs of diabetes, due to water not being reabsorbed. Glomerular filtrate has now been separated into two forms reabsorbed filtrate and non-reabsorbed filtrate. Non reabsorbed filtrate is now known as tubular fluid as it passes through the collecting duct to be processed into urine. Simultaneously any excretory wastes that were not filtered out at the glomerulus are put back into the tubule by the capillaries.


Finally at the end of the tubule, as a result of all the mechanisms that are ultrafiltration, selective reabsorption, tubular secretion the filtrate contains urea, other wastes, excess salts and small amount of water. This fluid is now called as urine. It is drained into the collecting duct. A collecting duct collects urine from several nephrons. Finally all collecting ducts drain urine into a space called renal pelvis in the kidney, from where it passes out into the ureter, and then to urinary bladder where it is stored till excreted out of the body.


Micturition is the process by which the urinary bladder empties when it becomes filled. This process involves two main steps: First, the bladder fills progressively until the tension on its wall rises above a threshold level. This elicits the second step, which is a nervous reflex called the micturition reflex that empties the bladder or if this fails, at least causes a conscious desire to urinate.


In ultra filtration process blood pressure forces the fluid and small molecules like glucose, salts and amino acids are filtered. Selective re-absorption there is active re-absorption of useful molecules such as water, glucose and salts. In case of tubular secretion the filtrate contains all the excretory waste and small amount of water.

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Pancreas: Exocrine or endocrine gland?

key points: pancreas, exocrine gland, endocrine gland, pancreatic enzymes, islets of Langerhans, glucose, glucagon etc.

Do you remember studying different types of glands? Some of them were endocrine while some of them were exocrine. Before we go to Pancreas, let us first understand what are endocrine and exocrine glands?

What are endocrine glands?

Our nervous system controls and co ordinates with different organs as well as try to responds with the external environment. But human body carries several activities in various organ systems at the same time, Therefore nervous system has to maintain a balance and regulates each activity at certain time. Endocrine system brings all the co ordination and balance the activities with the help of chemical messengers called as ‘hormones’. But what does the endocrine system do? (Endo- inside and crine- separate) The system literally means secrete internally. The endocrine system consists of certain endocrine glands which perform the function of secreting hormones. They are also known as ductless glands since they release the hormones into bloodstream and not via any specialized ducts. For example, Pituitary gland- oxytocin, ADH and thyroid gland- thyroxine etc.

What are exocrine glands?

Exocrine glands require the ducts to transport the secreted substance at target site. They can not release the substance directly into bloodstream and also the substance which are produced by them shows the action at nearby areas. There are several exocrine glands such as lacrimal glands which produce tears or sweat gland for production of sweat or salivary gland for producing saliva. If you notice their function of these glands their action is restricted to certain area and shows effect around the area where they are located.

Pancreas as endocrine and exocrine glands

Liver and pancreas are the only glands in human body which act as both endocrine and exocrine glands. Let us first understand the endocrine function of pancreas.

Pancreas are located in the abdominal cavity close to duodenum and behind the stomach. They are mainly responsible for two functions are as follows:

  1. Secreting of hormones for controlling glucose (Insulin and Glucagon).
  2. Secreting digestive enzymes.

Pancreas as an endocrine gland:

Pancreas has a region called as “Islets of Langerhans” which typically consists of four cells

  1. Alpha cells
  2. Beta cells
  3. Delta cells
  4. F cells

Beta cells are responsible for producing insulin whereas alpha cells produce glucagon. Both the hormones carry the function of maintaining glucose balance inside the blood stream. The delta cells produce a hormone known as somatostatin which restrains the secretion of insulin and glucagon.

Brief mechanism of insulin and glucagon

Case I: Consider that a person had carbohydrate diet which means he is now having a lots of sugar inside the body. This is sensed by pancreas and it stimulates the beta cells to produce glucose controlling hormone called as “Insulin”.  This insulin gets released into the blood stream and bind to the glucose. This glucose is stored in the liver in the form of glycogen.

Case II: Now consider that the same person is starving and has no food to eat. In this case the pancreas stimulate alpha cells to produce “Glucagon”. Many times people get confused between glycogen and glucagon. Let’s fix this mind, glycogen is a complex form of sugar while glucagon is a hormone to break that sugar into glucose i.e. simple sugar. Hence the stored glycogen is now broken by glucagon and free glucose is released into the blood stream.

Pancreas as exocrine gland

As a duct gland it secrets digestive juices which break down the nutrients. These juices are then poured to the duodenum which is the beginning of small intestine. These enzymes travel through series of ducts and meets the pancreatic duct. The pancreatic duct meets the common bile duct and it carries bile to duodenum.


Pancreas secrete several enzymes which helps in the digestion. The enzymes are transported via certain ducts. Therefore Pancreas are said to have an exocrine function. Also to maintain blood sugar level it secretes hormones (insulin and glucagon) which defines its endocrine function. Hence pancreas act as both endocrine and exocrine system.

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