Histology is the study of tissues.
Tissues consist of collections of cells that serve a similar purpose or function.
Tissues can be made up of the same cell type or multiple cell types working together.
Multiple tissues form organs in the body.
Various estimates suggest the human body consists of approximately 50 trillion to 75 trillion cells.
There are roughly 200 different cell types in the human body.
Example: Bone has four different types of bone cells.
Blood has red blood cells and five different types of white blood cells, with additional developmental stages contributing to their formation.
Bone marrow produces cells that generate platelets.
All somatic (non-reproductive) cells in the body share the same genome composed of genes and their variations (alleles).
Exception includes gametes (sperm and egg), which are haploid and contain only half the number of chromosomes.
Despite sharing the same genome, cells can exhibit different appearances and functions.
This differentiation is largely due to gene expression, which determines which genes are turned on or off in different cell types.
Various stimuli, including signaling pathways, influence gene expression patterns.
Understanding tissues helps in identifying unknown organs or diagnosing diseases based on tissue appearance.
Recognizing features of healthy versus diseased tissues aids in diagnosing ailments.
Next lectures will explore specific primary tissue types with a focus on epithelial tissues.
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