CELLS

First of all, we should understand what is Human body. Our body is made up of trillions of cells. A Cell is the smallest unit of our body. The cell is the basic structural, functional, and biological unit of our body. A cell can replicate independently and are often called the “building blocks of life”. The study of cells is called cytology. The cell was discovered by Robert Hooke in 1665. The cells provide structure to our body, they take in nutrients from food, convert those nutrients into energy, and carry out specialized functions.

A cell is covered by cell membrane and it contains the following organelles:

Nucleous is the most conspicuous organelle found in a cell. It houses the chromosomes, and is the place where almost all DNA replication and RNA synthesis (transcription) occur. The nucleus is spherical and separated from the cytoplasm by a double membrane called the Nuclear envelope which protects cell’s DNA from various molecules that could accidentally damage its structure or interfere with its processing. During processing, the DNA is transcribed or, copied into a special RNA, called messange RNA (mRNA).

Ribosomes are a cell structure that makes protein. Protein is needed for many cell functions such as repairing damage or directing chemical processes. They can be found floating within the cytoplasm or attached to the Endoplasmic Reticulum (ER).

Endoplasmic Reticulum (ER) is a transport network for molecules. The ER has two forms-the rough ER, which has ribosomes on its surface that secrete proteins into the ER, and the smooth ER, which lacks ribosomes. The smooth ER plays a role in calcium sequestration and release.

Mitochondria (also called Power house of cell) generate energy for the cell. The Mitochondria are self-replicating organelles that occur in various numbers, shapes, and sizes in the cytoplasm. The Respiration occurs in the cell mitochondria, which generate the cell’s energy by oxidative phosphorylation, using Oxygen to release energy stored in cellular nutrients (typically pertaining to glucose) to convert ADP (Adenosine Di Phosphate) into ATP (Adenosine Tri Phosphate).

Golgi apparatus is also called Golgi Body and it’s primary function is to process and package the macromolecules such as proteins and lipids that are synthesized by the cell.

Lysosomes and Peroxisomes are spherical vesicles which contain Hydrolytic enzymes that can break down virtually all kinds of biomolecules. They digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria. Peroxisomes have enzymes that rid the cell of toxic peroxides. The cell could not house these destructive enzymes if they were not contained in a membrane-bound system. The Lysosome is also involved in various cell processes, including secretion, repair of Plasma membrane, cell signalling & energy metabolism.

The lysosomes also act as the waste disposal system of the cell by digesting unwanted materials in the cytoplasm both from outside of the cell and obsolete components inside the cell.

Lysosomes are known to contain more than 50 different enzymes. Enzymes of the lysosomes are synthesised in the rough ER.

Centrosome produces the microtubules of a cell. It directs the transport through the ER and the Golgi Body. Centrosomes are composed of two centrioles, which separate during cell division and help in the formation of the mitotic spindle.

Vacuoles removes cell’s waste products. They are often described as liquid filled space and are surrounded by a membrane.

Cell growth and Metabolism are two processes which occur regularly in body. Between successive cell divisions, cells grow (cell division) through the functioning of cellular metabolism. Cell metabolism is the process by which individual cells process nutrient molecules. Metabolism has two distinct divisions: catabolism, in which the cell breaks down complex molecules to produce energy and anabolism, in which the cell uses energy to construct complex molecules and perform other biological functions. The cell division involves a single cell (called a mother cell) dividing into two daughter cells. This leads to cells usually undergo a process of nuclear division, called mitosis, followed by division of the cell which may also undergo meiosis to produce haploid cells, usually four.

              TISSUES

The cells of similar shape and size are combined to form Tissue and billions of different kind of tissues. Tthe study of Tissue is called Histology.

Human body is composed of billions of tissues and specific tissues are group of many cells with a similar structure working together for a specific function. There are 4 main types of tissues in our body viz: Muscle tissue, Connective tissue, Epithelial tissue and Nervous tissue.

Muscle Tissue are of two types in our body; one is called Skeletal or, Striated muscle, used for Voluntary actions like moving hands, neck, leg etc. The second is called Smooth or, non-striated muscle, used for involuntary actions like in stomach, intestine, rectum etc. The heart muscle are exceptional because, here the muscles are striated but, used for involuntary actions.

Epithelial tissues can be flat, cuboidal or, columnar. They are joined tightly together, making a single or stacked continuous sheet. Like a quilt that is tightly stitched, epithelium makes an excellent protective cover for the body, in the form of skin. Epithelial tissue can also be found lining some internal cavities and organs.

Connective tissues make a connective web inside our body and hold the body parts together and provide support. The Connective tissue fills the spaces inside our body with a matrix made of fibers within a liquid, solid, or jelly-like substance as we find fruits, suspended in salad.

Nervous tissue is found within the nervous system and is made up of unique specialized cells, called Neurons. Each Neuron contains a nucleous, Axon & Dendrite and it works like electrical circuits. The nervous system transmits signals from nerves to the spinal cord and brain and vice versa. The Neurons conduct impulses, making it possible for us to use our senses through Sensory nerves and Motor nerves.

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