Introduction to cell
⇨Study of cell is Cytology.
⇨Study of tissue is histology.
⇨ROBERT HOOK coined the term Cell in 1665.
↬ Cell is the smallest structure and functional unit of our body and it formed the basic unit of tissue, later which form organ further system the body.
↬ Cell are not static as like we seeing in diagram in flate. they have three diamentional shape and these size can be varries from minimum 6µm(that of resting lymphocytes)- 80µm(That of mature ovum).
Structure of cell- A eukaryotic cells consist of the following structure.
Cell membrane or plasma membrane or unit membrane or three layered membrane.
↬impermeable for large molecules like protein permeable for small molecules like- Iron, metabolites, inside of the cells is-
Cytoplasm
Mitochondrion
nucleus
Nucleolus
Micro tubules
Smooth endoplasmic reticulum
Galgi apparatus
General Characteristics of Cell
Each cell in the body:
1. Each cells needs nutrition and oxygen.
2. Cells produces its own energy necessary for its growth,repair and other activities.
3. Cells eliminates carbon dioxide and other metabolic wastes.
4. Cells Maintains the medium, i.e. the environment for its survival.
5. Cells Shows immediate response to the entry of invaders such as bacteria or toxic substances into the body.
6. Reproduces by division. There are some exceptions such as neuron, which do not reproduce.
TISSUE
↬Tissue is defined as the group of cells having similar function. There are many types of tissues in the body. All the tissues are classified into four major types which are called the primary tissues. The primary tissues include:
1. Muscle tissue (skeletal muscle, smooth muscle and cardiac muscle).
2. Nervous tissue (neurons and supporting cells)
3. Epithelial tissue (squamous, columnar and cuboidal epithelial cells).
4. Connective tissue (connective tissue proper, cartilage, bone and blood).
ORGAN
↬An organ is defined as the structure that is formed by two or more primary types of tissues, which execute the functions of the organ. Some organs are composed of all the four types of primary tissues. The organs are of two types,
1. tubular or hollow organs
2. compact or parenchymal organs.
↬Some of the organs in the body are brain, heart, lungs, stomach, intestine, liver, gallbladder, pancreas, kidneys, endocrine glands, etc.
SYSTEM
↬The organ system is defined as group of organs that Work together to carry out specific functions of the body.
↬Each system performs a specific function.
Digestive system is concerned with digestion of food particles.
Excretory system eliminates unwanted substances.
Cardiovascular system is responsible for transport of substances between the organs. Respiratory system is concerned with the supply of oxygen and removal of carbon dioxide. Reproductive system is involved in the reproduction of species.
Endocrine system is concerned with growth of the body and regulation and maintenance of normal Iife.
Musculoskeletal system is responsible for stablity and movements of the body.
Nervous system Controls the locomotion and other activities including the intellectual functions
CELL MEMBRANE
↬Cell membrane is a protective sheath, enveloping the cell body.
↬It is also known as plasma membrane or plasmalemma.
↬This membrane separates the fluid out-side the cell called extracellular fluid (ECF) and the fluid inside the cell called intracellular fluid (ICF).
↬The cell membrane is a semipermeable membrane. S0, there Is free exchange of certain substances between ECF and ICF. Thickness of the cell membrane varies from 75 to 85O.
COMPOSITION OF CELL MEMBRANE
Cell membrane is composed of three types of substances:
1. Proteins (55%).
2. Lipids (40%).
3. Carbohydrates (5%).
STRUCTURE OF CELL MEMBRANE
⇨On the basis of structure, cell membrane is called a unit membrane or a three-layered membrane.
⇨ The electron microscopic study reveals three layers of cell membrane, namely, one central electron-lucent layer and two electron-dense layers.
⇨ The two electron- dense layers are placed one on either side of the central layer.
⇨The central layer is a lipid layer formed by lipid. substances. The other two layers are protein layers formed by proteins,
⇨ Cell membrane contains some carbohydrate molecules also.
FUNCTIONS OF CELL MEMBRANE
1. Protective function: Cell membrane protects the cytoplasm and the organelles present in the cyto-plasm
2. Selective permeability: Cell membrane acts as a semipermeable membrane, which allows only some substances to pass through it and acts as a barrier for other substances.
3. Absorptive function: Nutrients are absorbed into the cell through the cell membrane.
4. Excretory function: Metabolites and other waste products from the cell are excreted out through the cell membrane.
5. Exchange of gases: Oxygen enters the cell from the blood and carbon dioxide leaves the cell and enters the blood through the cell membrane.
6. Maintenance of shape and size of the cell: Cell membrane is responsible for the maintenance of shape and size of the cell.
Functions of Proteins in Cell Membrane
1. Integral proteins provide the structural integrity of the cell membrane.
2 Channel proteins help in the diffusion of water-soluble substances such as glucose and electrolytes.
3. Carrier or transport proteins help in the transport of substances across the cell membrane by means of active or passive transport.
4. Pump: Some carrier proteins act as pumps, by which ions are transported actively across the cell membrane for example Na+K+ ATPase pump, Ca++ATPase pump.
5. Receptor proteins serve as the receptor sites for hormones and neurotransmitters.
6. Enzymes: Some of the protein molecules form the enzymes and control chemical (metabolic) reactions within the cell membrane.
7. Antigens: Some proteins act as antigens and induce the process of antibody formation.
8. Cell adhesion molecules or the integral proteins responsible for attachment of cells to their neighbors or to basal lamina.
Functions of Lipid Layer in Cell Membrane
1. Lipid layer of the cell membrane is a semipermeable membrane and allows only the fat-soluble substances to pass through it.
2. Thus, the fat-soluble substances like oxygen, carbon dioxide and alcohol can pass through this
lipid layer.
3. The water-soluble substances like glucose. urea and electrolytes cannot pass through this layer.
Functions of Carbohydrates in Cell Membrane
1. Carbohydrate molecules are negatively charged and do not permit the negatively charged substances to move in and out of the cell.
2. Glycocalyx from the neighboring cells helps in the tight fixation of cells with one another.
3. Some carbohydrate molecules function as the receptors for some hormones.
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