Cell Structure and Histology

Study Notes

Define the cell and its main components
Identify the histological structure of different components of the cell
Recognize the correlation between the structure of different cell components and their functional significance

Definition: regulates the passage of materials between the cell and its environment
Thickness: 9-10 nm, appears as three layers (trilamellar) under electron microscope
Chemical structure: formed of lipid, protein, and carbohydrates arranged in a specific manner

Components:
- Cell organelles
- Cell inclusions
- Cell matrix
Cell organelles:
- Membranous organelles (mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes)
- Non-membranous organelles (cytoplasmic filaments, microtubules, centrioles, cilia, flagella)
Cell inclusions:
- Non-living materials in the cytoplasm
- Types: carbohydrates (glycogen granules), lipids (lipid droplets or globules), pigments (exogenous and endogenous)

Definition: the power house of the cell, provides ATP
Number: varies in different cells according to energy requirement
Structure:
- Double membranous vesicles
- Outer membrane: smooth
- Inner membrane: reveals a number of folds (cristae) which usually project like shelves in the matrix
- Matrix: contains enzymes of Kreb's cycle, mitochondrial DNA and RNA

Definition: membranous cell organelle formed of a reticulum of anastomosing and inter-communicating narrow tubules and vesicles
Types:
- Smooth ER (sER): outer surface smooth, functions in lipid synthesis and muscle contraction
- Rough ER (rER): outer surface rough, functions in segregation of proteins inside the lumen, initial glycosylation of proteins

Definition: membranous cell organelle which plays an important role in the secretory functions of the cell
Structure:
- Golgi saccules: 4-10 flattened membranous interconnected saccules piled one above the other forming a stack
- Micro-vesicles (transfer vesicles): tiny vesicles present at the immature face originating by budding from the rER
- Macro-vesicles (secretory vesicles): large vesicles present at the mature face containing modified protein which can be excreted as secretory product or remain in the cell as lysosomes

Definition: network of microfilaments and microtubules that bind together by proteins to maintain the shape of cells and support them
Types:
- Microfilaments
- Microtubules
- Intermediate filaments

Definition: non-membranous organelles, thread-like structures
Types:
- Thin filaments: contractile, found in muscle, microvilli, and cleavage furrow
- Intermediate filaments: non-contractile, found in muscle, nerves, and epithelial cells
- Thick filaments: contractile, found in muscles, forming myofibrils with actin filaments

Definition: pipe-like hollow structure of uniform diameter, but of variable length
Function:
- Cytoskeleton
- Guiding tracks for transporting material and organelles
- Main structural component of centriole, cilia, and flagella

Definition: non-membranous organelles important for cell division and act as basal bodies of cilia
Structure:
- 2 short cylinders lying at right angle with each other, composed of 27 microtubules arranged in 9 bundles by T.S.
- Each bundle consists of three micro-tubules (triplets)

Definition: hair-like striations seen on the surface of the cell facing the lumen or cavity
Structure:
- Shaft: contains 9 peripheral doublets of microtubules and 2 central singlets microtubules by T.S.
- Basal body: identical appearance to a centriole
- Rootlets: striated fibers, anchoring the basal body to the surrounding cytoplasm

Definition: cell control center for all cellular metabolic activities and plays an important role in cell division and heredity
Site: present in all cells except mature RBCs
Number: mononucleated, binucleated, or multinucleated
Structure:
- Nuclear membrane (2 thin membranes separated by a perinuclear space)
- Chromatin (DNA conjugated with histone protein)