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Sunday, September 8, 2013

Reproduction

Sunday, September 8, 2013 - 53 Comments

A cell does not go on growing indefinitely in size but at a certain optimum point divides into two daughter cells. Further, certain cells will undergo division to replace worn-out cells or those destroyed by disease. This kind of cell division is called mitosis or karyokinesis.

Activity begins in the nucleus. The nuclear membrane disappears and the chromatin changes character and becomes long filaments called chromosomes.

The centrosome divides and the two new centrosomes move away from each other to each end of the nucleus called the poles.

The chromosomes are then attracted to the poles and lie near the new centrosomes. The chromatin of which nucleus is formed now comes to rest and two new nuclei exist. Finally the protoplasm of the cell constricts and divides and the two new cells are complete.
Each new daughter cell resulting from mitosis contains forty six chromosomes, so that during mitosis each chromosome must duplicate itself. The process of chromosomal duplication is one of the least understood of the cell’s activities.

However, mitosis is not the only kind of cell division. In the sex organs, the ovary and testis, another kind of cell division occurs called meiosis. During the formation of the sex cells, or gametes, the number of chromosomes is halved, so that the spermatozoon contains only twenty-three chromosomes and the egg-cell or ovum, twenty three.

When fertilization occurs, that is when spermatozoon and ovum fuse to form the cell (zygote) which develops into a new individual the normal chromosomal complement of forty six is restored. By this means a mixing of the hereditary determinants or genes, from male and female is achieved.

Friday, August 23, 2013

Abou ben Adhem (Summary)

Friday, August 23, 2013 - 13 Comments


James Henry Leigh Hunt
This poem has been written by James Henry Leigh Hunt. In this poem the poet says that Abou ben Adhem was a pious man. He was the leader of his tribe. He was very kind and gentle to his people. One night he woke up from a sound sleep. As he woke up, he found straight light in his room. An angel was writing some thing in a golden book. Abou picked up courage and asked the angel what he was writing. The angel replied that he was writing the names of those persons who loved God. Abou asked him if his name was there. The angel replied in negative. Abou did not loose heart and asked the angel to write his name as a person who loved his fellow men. The angel did so and went away. Next night the angel came again and showed Abou the names of those person whom God had blessed. Abou was very much surprised and overjoyed to see his name at the top of the list.
Abou ben Adhem and the Angel

Lines from the Lay of the Last Minstrel (Summary)


Walter Scott
In this poem the poet Sir Walter Scott says that the man who has no love for his country is quite worthless. If he does not feel an excitement as he comes back from a foreign country, he is dull fellow. No body loves such a man and no singer sings in his honor though he has a lot of wealth and holds a high office. He is a selfish mean fellow, and always thinks about his interest only. He will be completely forgotten after his death and will be totally ignored in poetry and songs.
The Lay of the Last Minstrel

Wednesday, May 29, 2013

Nucleus (Short Note)

Wednesday, May 29, 2013 - 2 Comments

The nucleus consists of a more compact mass of protoplasm, separated from the cytoplasm by the nuclear membrane which is also selectively porous, allowing substances to escape from the nucleus into the cytoplasm or substances to pass into it. The nucleus controls the cell and all its activities. Without a nucleus the cell would die.

The nucleus contains many protein-rich threads lying in nuclear sap. In the ‘resting cell’ the threads are collectively spoken of as chromatin. These threads or chromosomes are vital to the everyday activities of the cell and are responsible for determining the hereditary characteristics of the human body. On the chromosomes in linear arrangement sit the genetic or hereditary determinants, the genes. The number of chromosomes in a body cell is constant for a particular species of organism. In man there are twenty three pairs of forty six chromosomes.

Cytoplasm (Short Note)

This contains the following essential requirements:
1. Mitochondria: Small, rod-like structure which are closely connected with the catabolic, or respiratory, processes of the cell body.
2. Golgi Apparatus: A canal like structure lying next to the nucleus and involved in the secretory activities of the cell.
3. Ground Cytoplasm: A highly complex colloidal material in which the other structures are embedded. It is highly concerned with the anabolic, or synthetic, activities of the cell.
4. Centrosome: A minute dense part of the cytoplasm, ling close to the nucleus. It plays an important part during cell division.

5. Cell Membrane: The cell boundary is no-static envelope. Many important functions are concerned with it, but in particular it acts as a selective sieve through which certain substances are allowed to pass into the cell, or which prevents other substances from gaining access to it. Thus it is moist important in maintaining the correct chemical composition of protoplasm.

Cell Structure (Short Note)

In considering the structure of the cell it is essential to relate its parts to its function.

The protoplasm of the cell is composed of a centrally placed body, the nucleus, and the cytoplasm or remainder of the protoplasm, which surrounds the nucleus.

Cytoplasm:
This contains the following essential requirements:
1. Mitochondria: Small, rod-like structure which are closely connected with the catabolic, or respiratory, processes of the cell body.
2. Golgi Apparatus: A canal like structure lying next to the nucleus and involved in the secretory activities of the cell.
3. Ground Cytoplasm: A highly complex colloidal material in which the other structures are embedded. It is highly concerned with the anabolic, or synthetic, activities of the cell.
4. Centrosome: A minute dense part of the cytoplasm, ling close to the nucleus. It plays an important part during cell division.
5. Cell Membrane: The cell boundary is no-static envelope. Many important functions are concerned with it, but in particular it acts as a selective sieve through which certain substances are allowed to pass into the cell, or which prevents other substances from gaining access to it. Thus it is moist important in maintaining the correct chemical composition of protoplasm.

Nucleus:
The nucleus consists of a more compact mass of protoplasm, separated from the cytoplasm by the nuclear membrane which is also selectively porous, allowing substances to escape from the nucleus into the cytoplasm or substances to pass into it. The nucleus controls the cell and all its activities. Without a nucleus the cell would die.
The nucleus contains many protein-rich threads lying in nuclear sap. In the ‘resting cell’ the threads are collectively spoken of as chromatin. These threads or chromosomes are vital to the everyday activities of the cell and are responsible for determining the hereditary characteristics of the human body. On the chromosomes in linear arrangement sit the genetic or hereditary determinants, the genes. The number of chromosomes in a body cell is constant for a particular species of organism. In man there are twenty three pairs of forty six chromosomes.

Monday, February 11, 2013

Body Planes in Anatomy

Monday, February 11, 2013 - 1 Comment


For the identification of specific areas, the body can be divided by imaginary flat surfaces or planes.

The midsagittal plane divides the left and right sides of the body lengthwise along the midline into externally symmetrical sections. If a longitudinal plane is placed off-centre and separates the body into asymmetrical left and right sections, it is called a sagittal plane. A frontal plane divides the body into asymmetrical anterior and posterior sections.


A transverse plane divides the body horizontally into upper (superior) and lower (inferior) sections. A transverse (or horizontal) plane is at right angles to the midsagittal, sagittal, and frontal planes. Transverse planes do not produce material halves.



The system of planes is also used with parts of body, including internal parts. If your laboratory manual or any other refers a book for drawing of a sagittal section, frontal section, or a transverse section, you should be aware of what is actually being shown and how it relates to corresponding plane. A cut which produces exposed surface of the head is called a midsagittal section. A cut along a frontal plane produces a frontal section.

Relative Directional Terms of the Body in Anatomical Terminology


Some of the directional terms of the body are defined as follows:
                                    Term               
Definition and Example
Superior (cranial)        


Inferior (caudal)


Anterior (ventral)


Posterior (dorsal)


Medial


Lateral


Proxima



Distal



Superficial


Deep


Peripheral
Toward the head.
e.g.: The leg is superior to the foot.

Toward the feet or tail region.
e.g.: The foot is inferior to the leg.

Toward the front of the body.
e.g.: The nose is anterior to the ears.

Toward the back of the body.
e.g.: The ears are posterior to the nose.

Toward the midline of the body.
e.g.: The nose is medial to the eyes.

Away from the midline of the body.
e.g.: The eyes are lateral to the nose.

Toward (nearer) the trunk of the body or the attached end of a limb.
e.g.: The shoulder is proximal to the wrist.

Away (farther) from the trunk of the body or the attached end of a limb.
e.g.: The wrist is distal to the forearm.

Nearer the surface of the body.
e.g.: The ribs are more superficial than the heart.

Farther from the surface of the body.
e.g.: The heart is deeper than the ribs.

Away from the central axis of the body.
e.g.: Peripheral nerves radiate away from the brain and spinal cord.

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