Overview
This lecture covers the types and functions of tissues in the human body, focusing on epithelial and connective tissues, their structures, characteristics, and examples.
Introduction to Tissues
- Tissues are groups of cells organized for a specific function.
- Major tissue types: epithelial, connective, muscle, and neural tissue.
- Histology is the study of tissues, usually with a microscope.
Epithelial Tissue
- Epithelial tissue (epithelium) covers external and internal body surfaces.
- Always anchored to a non-cellular basement membrane (basal lamina).
- Epithelial tissue is avascular (no direct blood supply; nutrients by diffusion/osmosis).
- Constantly regenerates via stem cells, especially in high-friction areas.
- Main functions: secretion, absorption, protection.
- Cell arrangement classified as simple (one layer) or stratified (multiple layers).
- Shapes include squamous (flat/plate-like), cuboidal (cube-shaped), and columnar (tall/column-shaped).
Types of Epithelium and Examples
- Simple squamous: one layer, plate-shaped; ideal for diffusion (e.g., alveoli, capillaries).
- Stratified squamous: multiple layers, plate-shaped; protection against friction (e.g., skin epidermis, esophagus).
- Simple columnar: one layer, column-shaped; absorption and secretion (e.g., intestines).
- Stratified columnar: multiple layers, column-shaped; protection (e.g., epiglottis, anus, urethra).
- Pseudostratified columnar: appears layered but is one layer; nuclei at different levels, often with cilia (e.g., trachea, bronchi).
- Simple cuboidal: one layer, cube-shaped; secretion and absorption (e.g., kidney tubules, thyroid).
- Stratified cuboidal: multiple layers, cube-shaped; protection, secretion (e.g., sweat glands).
- Transitional epithelium: stretches and recoils (e.g., bladder, uterus).
- Glandular epithelium: produces/releases secretions; types include merocrine (saliva), apocrine (milk), holocrine (oil/sebum).
Connective Tissue
- Most abundant tissue type; connects and stabilizes body parts.
- Made of protein fibers (collagen, elastic, reticular) and cells.
- Collagen fibers: strong, flexible, usually in one direction (e.g., tendons, ligaments).
- Elastic fibers: flexible, found in structures needing stretch (e.g., intervertebral discs).
- Reticular fibers: net-like, structural support (e.g., liver).
- Major cell types: fibroblasts (produce fibers), macrophages (engulf foreign bodies), mast cells (release histamine and heparin), lymphocytes (produce antibodies), adipocytes (store fat), melanocytes (produce melanin).
- Examples: adipose tissue (fat storage), tendons/ligaments, blood, cartilage, bone, muscle.
Key Terms & Definitions
- Epithelium — tissue covering body surfaces, lining cavities, and forming glands.
- Basement Membrane/Basal Lamina — protein layer anchoring epithelium to underlying tissue.
- Avascular — lacking blood vessels.
- Diffusion/Osmosis — passive transport of substances across cell membranes.
- Lumen — inner open space of a tubular organ.
- Simple/Stratified — one layer/multiple layers of cells in tissue.
- Microvilli/Cilia — surface structures for absorption (microvilli) or movement (cilia).
- Glandular Epithelium — epithelial tissue forming glands and secreting products.
- Collagen/Elastic/Reticular fibers — main protein fibers in connective tissue.
- Fibroblast — cell that produces connective tissue fibers.
- Macrophage — immune cell that engulfs pathogens.
- Adipocyte — fat-storing cell.
- Mast cell — releases histamine (inflammation) and heparin (anticoagulant).
- Lymphocyte/Plasma cell — immune cells producing antibodies.
- Melanocyte — pigment-producing cell.
Action Items / Next Steps
- Review histology slides of different epithelial tissues.
- Study examples of connective tissue and relate structure to function.
- Prepare for quiz on epithelial and connective tissue types and functions.