CHAPTER OUTLINE
- Cell Structure and Function
- Cell Division
- Gametogenesis
- Ovarian Cycle
- Development of Human Embryo
- Derivatives of the Germ Layers
- Development of Notochord
- Development of Neural Tube and its Derivatives
- Foldings of Embryo
- Development of Placenta
- Pharyngeal Apparatus
- Development of Heart
- Development of Face
- Development of Teeth
- Development of Tongue
- Development of Palate
- Development of Glands
- Development of Eye
- Development of Ear
- Development of Temporomandibular Joint
- Development of Skull
- Development of Vertebral Column
INTRODUCTION
The structural and functional unit of human body is a cell
- There are different types of cells:
- Epithelial cell
- Connective tissue cell
- Muscle cell
- Nerve cell.
- Human cell has 46 single chromosomes or diploid in nature.
STRUCTURE OF A CELL
- A living cell has the following components:
- Cell membrane: It forms the cell boundary. It is made up of three layers with glycosaminoglycans and phospholipids
- Protoplasm: The entire content within the cell membrane
- Cytoplasm: The protoplasm without nucleus. It has the liquid and solid components
- Cell organelles: The solid structures within the cytoplasm. They are:
- Mitochondria: It helps for production of energy for the activities of cell
- Golgi apparatus: Arranged in layers like stakes, produces and stores the secretion of the cell
- Endoplasmic reticulum: It helps for transport of chemicals within and outside the cell. They are of two types: (1) Smooth and (2) Rough endoplasmic reticulum
- Rough endoplasmic reticulum is studded with ribosomes
- Smooth endoplasmic reticulum does not have ribosomes on its surface. It is present in cells which are concerned with steroid production and fat metabolism.
- Centrosome: It has two centrioles. It produces the spindle fibers and helps for cell division
- Lysosome: Membrane bound vesicle containing peroxidase for destruction of foreign bodies
- Vacuole: Empty membrane bound vesicle
- Phagocyte: Vesicle that has engulfed an antigen
- Ribosome: For synthesis of proteins
- Nucleus: It is the functional unit of a living cell. It is bounded by nuclear membrane.
- Within the nuclear membrane, nucleoplasm and nucleolus are present
- Nucleoplasm consists of 46 single chromosomes in human cell
- The chromosomes are present as chromatin reticulum
- The nucleolus produces the ribosomes.
- The cells which do not have nucleus are:
- Red blood corpuscles
- Platelets.
- The cells which can move actively are:
- White blood corpuscles
- Sperms.
- Functions of nucleus:
- Synthesis of protein
- Cell division
- Inheritance of characters from one generation to another generation
- Active movements.
STRUCTURE OF A CHROMOSOME (FIG. 1.1)
- A single chromosome has a short or “p” arm and a long or “q” arm
- A secondary constriction is present
- At one end, a satellite is present
- Human cell has 46 single chromosomes. Out of them 44 are autosomes and 2 are allosomes or sex chromosomes.
- In male, the allosomes are XY
- In female, the allosomes are XX.
- The chromosomes are classified and numbered based on:
- The procedure to classify and map the chromosomes is karyotyping
- There are A, B, C, D, E, F and G groups.
- A group: 1, 2, 3
- B group: 4, 5
- C group: 6, 7, 8, 9, 10, 11, 12
- D group: 13, 14, 15
- E group: 16, 17, 18
- F group: 19, 20
- G group: 21, 22, 23.
FUNCTIONS OF CELLS
- Epithelial cells form a lining layer
- Glandular cells secrete either an enzyme or hormone
- Cells can absorb the nutrients or any chemical
- Cells excrete the waste products of metabolism
- Receptor cells perceive the stimuli
- Pigment cells give the color
- Connective tissue binds the different layers of an organ or different organs with one another. It gives mechanical support and protection
- Red blood corpuscles have hemoglobin for transport of oxygen to other cells
- White blood corpuscles help prevent invasion of pathogens
- Bones and cartilages form the framework of body, give attachment for muscles and ligaments and storage of minerals
- Muscle helps for movement by contraction
- Neurons either perceive or generate impulses and conduct them to produce a response.
POINTS TO PONDER
- Size and shape of the cell depends on its metabolic activity
- Mesenchymal cells are undifferentiated cells
- Lifespan of a cell depends on the kind and function of a cell
- Cell division helps for increasing the number of cells
- Self destruction of a cell occurs by apoptosis.