Histology: Tissues, Cells and Body Organization

Histology

• Histology involves the study of body tissues and their arrangement to form organs

Importance of Histology

• Histology helps diagnose diseases, including malignant conditions
• Histology monitors treatment by observing cell and tissue structures
• Histology is useful for forensic and autopsy procedures

Histopathology

• Histopathology is the study of tissue diseases

Structural Organization of the Body

• Chemical Level
• Cellular Level
• Tissue Level
• Organ Level
• Organ System Level
• Organismal Level

Cell Definition

• Cells constitutes the basic structural, functional, and biological unit of organisms
• Human body comprises trillions of cells with specialized functions
• Cells consist of organelles that carry out its function

Cell Types

• Eukaryotic
• Prokaryotic

Cell Functions

• Structure and support growth
• Energy production metabolic process
• Reproduction transport

Biochemistry of the Cell

• 60-90% Water
• Ions include Na, K, Ca, and Cl
• 3% Carbohydrates
• 40% Lipids serve as structural components and facilitate cell communication, also aids in energy storage
• 50-60% Proteins
• Nucleic acids are a component of the cell

Cell Membrane Functions

• Acts as a physical barrier
• Regulates material movement
• Maintains electrical charge difference
• Participates in cell communication Forms selectively permeable boundary via a phospholipid bilayer containing cholesterol, proteins, and some carbohydrates

Nucleus

• Houses DNA for protein synthesis
• Contains chromatin, nucleolus, and nucleoplasm within a double membrane structure

Nuclear Envelope

• Separates nucleus and cytoplasm
• It forms a double membrane boundary

Nuclear Pores

• Facilitate passage of materials, including RNA, protein, ions, and water-soluble molecules
• They form openings through the nuclear envelope

Nucleolus

• Functions in ribosome synthesis
• It is a prominent large structure within the nucleus

Cytoplasm

• Contains cellular contents between the plasma membrane and the nuclear envelope
• Responsible for many processes

Cytosol

• Supports organelles
• Acts as a viscous fluid medium for diffusion

Organelles

• Carry out specific metabolism activities

Endoplasmic Reticulum (ER)

• Includes Rough ER with ribosomes modifies, transports, and stores proteins
• Includes Smooth ER lacks ribosomes and detoxifies drugs, alcohol, and poisons

Golgi Apparatus

• Modifies, packages, and sorts materials from the ER in transport vesicles

Lysosomes

• Digest microbes or materials, including cellular components

Mitochondria

• Synthesize ATP through aerobic cellular respiration by digesting fuel molecules

Ribosomes

• Composed of protein & rRNA in large & small subunits
• Engage in protein synthesis
• Bound ribosomes produce secreted proteins; free ribosomes produce proteins used internally
• Includes: Bound & Free Ribosomes

Cytoskeleton Functions

• Structural support
• Stabilizes junctions between cells
• Assists with cytosol streaming/motility
• Moves organelles
• Helps move chromosomes during cell division

Filaments

• Microfilaments maintain cell shape & support microvilli Separates cells during cytokinesis & facilitates change in shape Composed of actin monomers into actin filaments
• Intermediate Filaments provide structural support & stabilize junctions Includes various protein components
• Microtubules maintain cell shape & rigidity Organize/move organelles & support cilia/flagella Participate in vesicular transport Separate chromosomes during division composed of tubulin protein

Cell Reproduction

• Cell division is reproduction
• Nuclear & cytoplasmic division are the two types

Cell Division Purpose

• Cell division is vital for growth & tissue repair
• A parent cell produces two daughter cells with same DNA content
• Daughter cells differentiate to have different functions
• Mitosis and Cytokinesis are two main events in cell division

Somatic Cell Division

• Parent cell divides into two identical daughter cells with the same chromosomes
• Somatic cells contain 23 pairs of chromosomes
• Diploid cells have two homologous copies of each chromosome

Chromosome Numbers

• Haploid cells have half the chromosome as diploid or somatic
• During meiosis, a diploid cell replicates chromosomes to form four sets, then divides into four cells with a single set
• Diploid cells have 46 chromosomes; haploid cells have 23 in humans

Cell Cycle Phases

• The cell cycle controls cell growth/division
• Encompasses changes from formation to division
• Divided into interphase and cell division (mitosis and cytokinesis)
• The Interphase has subphases G1 (metabolic activities), S (DNA replication), and G2 (prepares for division)
• Following mitosis, two cells form through cytokinesis, starting new cell cycles: Many cells enter the G0 phase until stimulated to divide

Nuclear Division (Mitosis)

• Distributes two sets of chromosomes

Prophase

• Centrosomes move to poles
• Nuclear envelope disappears
• Chromosomes condense and become visible
• Chromosomes comprise two chromatids linked by kinetochore protein complexes

Metaphase

• Chromosomes align at the equatorial plate as a result of their attachments to:
• The dynamic microtubules of the mitotic spindle
• The spindle is made of kinetochore microtubules, polar microtubules, and shorter astral microtubules

Anaphase:

• Kinetochores separate, chromatids pulled to centrosomes by tubules

Telophase:

• Cell pinches in two, chromosomes decondense, nucleoli reappear, nuclear envelope reassembles

Reproductive Cell Division

• Meiosis produces gametes (in ovaries/testes) which halves chromosome number

Meiosis Features

• Homologous chromosomes pair (synapsis)
• DNA breaks/repairs, crossovers between chromosomes
• Cells produced are haploid, having one chromosome from each pair