Overview
This lecture covers the structure, function, and types of tissues in the human body, focusing on epithelial and connective tissues, their subtypes, cellular features, and functions.
Introduction to Tissues
- Tissues are groups of cells organized for specific functions within the body.
- Four primary tissue types: epithelial, connective, muscle, and neural tissues.
- Histology is the study of tissues using microscopic techniques.
Epithelial Tissue
- Epithelial tissue covers external and internal body surfaces and lines organs.
- Always attached to a basement membrane (basil lamina), a non-cellular protein layer.
- Epithelial tissue is avascular (no blood vessels); nutrients reach via diffusion/osmosis.
- High regeneration rate due to frequent damage, aided by stem cells.
Types of Epithelial Tissue
- Simple Squamous Epithelium: One layer of flat cells; allows rapid diffusion (e.g., alveoli, capillaries).
- Stratified Squamous Epithelium: Multiple layers of flat cells; protection in high friction areas (e.g., skin, esophagus).
- Simple Columnar Epithelium: One layer of tall, column-shaped cells; absorption/secretion (e.g., stomach, intestines).
- Stratified Columnar Epithelium: Multiple layers of column-shaped cells for protection (e.g., epiglottis, anus).
- Pseudostratified Columnar Epithelium: Appears multi-layered but is one layer; often with cilia for moving mucus (e.g., trachea).
- Simple Cuboidal Epithelium: One layer of cube-shaped cells; secretion/absorption (e.g., kidney tubules, thyroid gland).
- Stratified Cuboidal Epithelium: Multiple layers of cube-shaped cells; protection (e.g., sweat gland ducts).
- Transitional Epithelium: Stretches and recoils (e.g., bladder, uterus).
- Glandular Epithelium: Specialized for secretion; classified as merocrine (saliva), apocrine (milk), or holocrine (oil).
Connective Tissue
- Most abundant tissue; connects, binds, and supports body structures.
- Made of protein fibers (collagen, elastic, reticular) and various cells.
Connective Tissue Fibers
- Collagen fibers: Strong, flexible, arranged in one direction (e.g., tendons, ligaments).
- Elastic fibers: Stretchy, less strong than collagen (e.g., intervertebral discs).
- Reticular fibers: Net-like, offers structural support (e.g., liver).
Connective Tissue Cells
- Fibroblasts: Produce fibers and aid in tissue repair.
- Macrophages: Engulf and digest pathogens and debris.
- Mast cells: Secrete histamine (inflammation) and heparin (anticoagulant).
- Lymphocytes: Produce antibodies; key in immune response.
- Adipocytes: Store fat.
- Melanocytes: Produce melanin pigment.
Examples of Connective Tissue Types
- Adipose tissue: Fat storage (e.g., hypodermis).
- Tendons/ligaments: Connect muscles and bones.
- Blood: Fluid connective tissue with various cell types.
- Cartilage and bone: Provide structure and support.
Key Terms & Definitions
- Epithelium — Tissue lining surfaces and cavities, forming boundaries.
- Basement membrane (basil lamina) — Protein layer anchoring epithelial cells.
- Avascular — Lacking blood vessels.
- Lumen — Central cavity within an organ or vessel.
- Histology — Study of tissues at the microscopic level.
- Collagen — Main structural protein in connective tissue.
- Macrophage — Large immune cell that digests foreign particles.
- Mast cell — Cell releasing histamine and heparin.
- Adipocyte — Fat-storing cell.
- Melanocyte — Pigment-producing cell.
Action Items / Next Steps
- Review histology slides for identification of epithelial and connective tissues.
- Complete assigned textbook reading on tissue types and histology basics.
- Prepare for lab identification of tissue samples.