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Mysteries of The Human Body, Addis Ababa (2025)

04/11/2018

Parts Of A Typical Human Cell

20/10/2018

From A Single Pluripotent Cell To 100 Trillion Specialized Cells. How?

Life begins at the time of conception when a s***m cell fertilizes an o**m. This takes place in the widest part of the Fallopian tube (the ampulla) and involves the fusion of the s***m cell and the o**m. By fusion we mean the o**m and the s***m cell,two cells, become a single cell called zygote. It is this single cell that has the potential to divide and become any other type of cell in our body.

cells of our body can be broadly classified as somatic cell and germ cell. Somatic cells are found all over our body whereas germ cells are confined to the primary reproductive organs,ovaries in female and te**is in male.

Somatic cells divide themselves to replace worn out cells and their division produces two identical daughter cells that are genetically the same as the parent cells. This kind of cell division is called mitosis (refer the figure in the first comment). Examples of somatic cells include skin cells (called keratinocytes), muscle cells ( called myocytes), liver cells (called hepatocytes), nerve cells (called neurons) and others, to list a few. Somatic cells are already differentiated at birth. This means,for example, a liver cell divides only to give rise to two identical liver cells (it cannot give rise to muscle cell, skin cell or nerve cell). In the same manner, a muscle cell divides to give rise to two identical muscle cells (it cannot give rise to a liver cell,skin cell or nerve cell). This principle works for the rest of somatic cells

Germ cells are different in that they are found only in the go**ds (the te**is and ovaries) and have the potential to become any other type of cell (such as liver cell,skin cell,nerve cell etc) but only after fertilization. This requires, however, a process called gametogenesis (formation of the male and female gamete, the s***matozoa and the ova respectively). Gametogenesis involves a special type of cell division that takes place only in germ cells called meiosis. Meiosis is divided into two series of cell divisions,meiosis I and meiosis II. In these two series of cell division the germ cell of the male (called s***matocytes) and that of female (called oocytes) divide and reduce their chromosome number from 46 to 23 so that the 46 number of chromosome is restored after fertilization (23 from the s***matozoa and another 23 from the ova). The difference between gametes and germ cells is that germ cells are the parent cells of the gametes and the gametes are the daughter cells of germ cells (refer the figure in the second comment)

After fertilization and formation of the zygote further cell division occurs by mitosis. as it is illustrated in the figure below the zygote divides and passes through 2 cell, 4 cell, 8 cell and 16 cell stage and above (called morulla). as the zygote divides the daughter cells get smaller an smaller and they are called blastomeres. As the morulla enters into the uterus, fluid forms between the blastomeres and this stage is called blastocyst. the inner cell mass of the blastocyst divides and differentiated to become the cells of the fetus whereas the outer cell mass become the placenta.

16/10/2018

How Do You Become Male Or Female In Utero

We all have 23 pairs of chromosomes with the 22 pairs called autosomal chromosome and the remaining one pair is called s*x chromosome. In male this s*x chromosome is XY, whereas in female it is XX. Our s*x is established right after fertilization (the fusion of the s***m and the egg). Since all oocytes (eggs) in female contains X chromosome, it is the s***m cell that determines our genetic s*x. i.e if the s***m carries Y chromosome, the genetic s*x becomes male. On the other hand, if the s***m carries the X chromosome, the genetic s*x becomes female.
the difference between male and female is not just at chromosome level. there are differences in the internal and external ge***alia as well as the go**ds (the te**is or the o***y). To illustrate further, while males have te**is, females have ovaries instead. This is also true for that while females have l***a majora and cl****is, males have sc***um and p***s instead. To compare their internal s*x organ,females have Fallopian tube, uterus, and va**na, whereas males have epididymis,vas deferens and seminal vesicle. (refer the first and second figure below)
With the above concepts in mind, how does nature works to bring about these s*xual differences in utero? As mentioned earlier the s*xual difference begins starting from fertilization as either XX or XY genetic s*x. It is the Y chromosome that determines the other s*xual differences. Specifically, there is a region on Y chromosome that is called SRY gene (for s*x determining region on Y chromosome) which encodes for a protein called Te**is Determining Factor. In the presence of this factor the ge***al ridge (i.e the common precursor of both o***y and te**is) becomes te**is. Otherwise the o***y develops.
Both in male and female embryo there are two tubes or ducts, the mesonephric or wolffian duct, and the paramesonephric or mullerian duct. From these two ducts only one should remain and develop into either s*x. In male the already differentiated te**is produce two hormones, the antimullerian hormone (AMH) and testosterone. As the name suggests the the antimullerian hormone inhibit the development of the paramesonephric or the mullerian duct while at the same time the mesonephric or the wolffian duct develops into male internal s*x organs, that are mentioned above, only in the presence of testosterone. In females, since there is no te**is (there is o***y instead) the above two hormones cannot be produced. That means, there is no AMH to inhibit the development of the mullerian duct. At the same time there is no testosterone to stimulate the development of the wolffian duct into male s*x organs. This leads to the degeneration of wolffian duct and the development of the mullerian duct into female internal s*x organ mentioned above. (refer the figure in the second and third comment for this post)
The external ge***alia (or s*x organ) of both male and female develop from the same precursors, the ge***al tubercle, the urethral fold and the ge***al swelling. In male under the influence of testosterone,from the already developed te**is, the above precursors develop into p***s,penile urethra and sc***um,in their order. On the other hand, in female in the absence of testosterone and under the influence of estrogen (from the already developed ovaries) these same precursors become cl****is,l***a minora and l***a majora, in their order. (refer
the third figure below and the one in the first comment)

In humans the default s*x is female (meaning,in the absence of Y chromosome what would develop is female s*x organ)

12/10/2018

Palpating the Pulse of an Artery
(to palpate means to examine part of the body by touching it)

The cardiovascular system consistes of the heart,the blood and the blood vessels. There are three types of blood vessels that are connected to one another in series. These are arteries,veins and capillaries. The heart pumps blood into the arterial system which then distributes oxygen and nutrient rich blood to different parts of the body (an exception here is the pulmonary artery which carries deoxygenated blood from the right part of the heart to the lungs). On the other hand, the venous system returns deoxygenated blood, that contains CO2 and other cellular wastes, to the heart (an exception here is pulmonary vein which returns oxygenated blood from the lungs to the left part of the heart). While the capillary system is sites of exchange of nutrients and metabolic wastes between the blood and the tissue (refer the figure given as a comment for this post). Due to the fact that arteries (not veins or capillaries) carry blood that is pumped by the heart, they have their own rhythm or pulsation that is synchronus to the heart beat. However, since most arteries are found deep into our body covered by muscles and organs, thier rhythm or pulsation cannot be felt with our hand. Neverthless, there are a few sites of the body where we can feel the pulsation of an artery (these sites are listed as well as are depicted in the figure below). Palpating an artery is important to measure blood pressur and detect abnormalities in the activity of the heart. By palpating an artery we can count the number of pulses/beats per minute (BPM), characterize the rhythm (as regular or irregular) and the volume of the pulse (graded as absent, barely palpable, easily palpable,full and bounding). Normal pulse has a rate of 60-100BPM that is regular in rhythm and full in volume. Among the superficialy palpable arterires listed below,the radial artery is commonly used in clinical practice (see the figure in the comment).
The following are among the few palpable arteries:-
Radial artery
Brachial artery
Common carotid artery
Temporal artery
Facial artery
Femoral artery
Popliteal artery
Dorsalis pedis artery
Posterior tibial artery
You can feel the pulses of the above arteries on your own body. (Refer the figure below to exactly locate the respective arteries))

09/10/2018

We Are 50-60% Water.

An average 70kg adult man is composed of 42 liters of water that contributes to 60% of his body weight. This water contains a number of solutes (such as glucose,amino acid,NaCl,CO2..) and is termed as body fluid. The total body fluid (TBF) or the total body water (TBW) is compartmentalized into intracellular and extracellular fluid. The intracellular fluid represents the fluid inside the 100 trillion cells and it accounts for 28 liters of the total body fluid/water. The rest 14 liters is from the extracellular fluid(ECF) on which the 100 trillion cells are suspended. The ECF is further divided into interstitial fluid/IF/ (about 11 liters) and plasma (about 3 litres). The IF is the fluid outside the cell and that is not not in the blood. While,the plasma is the fluid component of the blood.

The above numbers vary based on age, s*x, percentage of body fat. For example,in women the TBF/TBW is less than that of men and it contributes to 50% of their body weight. Whereas, in the newborn the TBF/TBW contributes for 70-75% of the body weight. It is also true that as a person grows older, the percentage of total body weight that is fluid gradually decreases. One implication here is a persone who aquires Cholera can lose upto 20 liters of this body fluid per day which is fatal.

09/10/2018

THE INTERNAL ENVIRONMENT OF THE BODY
The 100 trillion cells that make up a human being are suspended in, what I call it,a microscopic lake called the interstitial fluid. This fluid is continuously exchanged with the blood through small blood vessels called capillaries.. Both the interstitial fluid and the fluid part of the blood (i.e the plasma) constitutes what is called the internal environment of the body.This is in contrast with the external environment of the body which is outside of the whole body.(illustrated in the figur below)

05/10/2018

The human skeleton is the bony framework of the body. In adults it is made up of 206 bones that are broadly classified into two,the axial and the appendicular skeleton(refer the figure below). In the following list,for example, 'head-29 bones' means the head is made up of 29 bones. This works for the rest of the list.
1. The Axial Skeleton(bones of the head, neck, back, ribs and sternum)
Head-29 bons
Neck-7 bones
Back-19 bones
Ribs and sternum-25 bones
2. The Appendicular Skeleton:
classifed further as upper limb and lower limb skeleton (for convenienc of this study) and it is made up of a pair of the following number of bones
2.1 Upper limb skeleton (bones of the hand, forearm,arm, sholder)
Fingures-14 bones (called phalanges)
Palm-5 bones (called metacarpals)
Wrist-8 bones (called carpals)
Forearme-2 bones (radius & ulna)
Arm-1 bone (called humerus)
Shoulder-2 bones (scapula & clavicle)

2.2 Lower limb skeleton (bones of the foot, leg, kneecap, thigh, hip)
Toes-14 bones(collectively called phalanges)
The rest of the foot-12 bones
Leg-2 bones (tibia & fibula)
Thigh-1 bone (called femur)
Kneecap-1 bone (called patella)
Hip-1 bone (fused bone of ischium, ilium, p***s)

Now, let's add the above figures.

Total number of bones (TNB) = No. of axial bones (80) + 2 times No. of appendicular bones (63)
(We multiply the No. of appendicular bones by 2 since we have a pair of them. I.e we have a pair of foot,a pair of leg, a pair of thigh, a pair of arm, a pair of forearm,a pair of shoulder etc.)
Therfore TNB = 80 +2*63 = 206

05/10/2018

AS AN ADULT YOU ARE MADE UP OF 206 BONES.WHAT SEEMS SURPRISING HOWEVER IS THAT A NEWBORN IS MADE UP OF 270 BONES.THIS IS BECAUSE IN ADULTS SOME BONES FUSE TOGETHER TO FORM A SINGLE BONE.(if you are interested to know the details read the next post)

04/10/2018

With the above two concepts in the previous post we will begin discovering the human body further.as a multi-cellular organism a human being is made up of 100 trillion cells that are surprisingly organized into the following just four groups (a group of cells is technically called tissues).
1. Epithelial tissue
2. Connective tissue
3. Muscle tissue and
4. Nervous tissue.
The four types of tissues, listed above, are organized in different proportion to form an organ such as heart, lung, eye, stomach, liver, kidney etc. Organs in turn works in coordination to form an organ system with specific function. Multiple of these systems constitute and maintain the human being alive as an organism. The human body is made up of the following ten organ systems and in bracket are the organs that make up the system
1. The nervous system (brain, spinal cord, nerves, sense organs)
2. The endocrine system (8 glands namely, hypothalamus, pineal, pituitary, thyroid, parathyroid, adrenal gland, pancreas and go**ds)
3. The cardiovascular system (heart, blood and blood vessels)
4. The respiratory system (nasal cavity, pharynx, larynx, trachea, bronchi, the lungs)
5. The digestive system (oral cavity, salivary glands, pharynx, esophagus, stomach, intestine, pancreas, gallbladder, liver)
6. The excretory system (urine-the kidneys, ureters, bladder, urethra; f***s- liver, the re**um, a**s)
7. The immune system (lymph nodes, thymus, spleen, tonsils, WBC)
8. The integumentary system (skin, nail, hair, hypodermis, sweat & sebaceous glands)
9. The musculoskeletal system (bones, cartilages, joints, ligaments,tendons,deep fascia, muscles)
10. The reproductive system (in male-te**is, epididymis, vas deferens, prostate, seminal vesicles, bulbourethral gland, p***s; in female-ovaries, Fallopian tube, uterus, cervix, va**na, cl****is, v***a, Bartholin’s gland and breast)
Till now we have studied the organization of the human body from trillions of cells to the aforementioned ten organ systems. Let me give you one example and conclude our study of the human body. The cardiovascular system, for instance, is made up of the organs heart, blood and blood vessels. Let’s pick the heart as an organ it is made of muscle tissue, to a large proportion, and connective tissue. As an example, this muscle tissue is made up of group of cells called cardiomyocytes. From the previous two posts we have studied the organization of the human body.By now you should be able to understand the upcoming posts.

Mysteries of The Human Body

04/11/2018

20/10/2018

16/10/2018

12/10/2018

09/10/2018

09/10/2018

05/10/2018

05/10/2018

04/10/2018

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