Tissues
Cellular task forces
Across biological kingdoms, tissues are the cell-based building materials of which complete plants or animal organs are made. The study of tissues is known as histology or, in the context of disease states, histopathology.
Animal tissues are categorized into several subtypes based on physiological form, function and location in the body:
Connective tissue is found throughout the body where it plays an essential role in defining the body's structure, maintaining the integrity and placement of organs, and providing cohesion and support among its internal components. All connective tissue consists of a cellular component together with an extracellular matrix, or ground substance, that surrounds the cells.
- Dense connective tissue consists of more fibrous material and less ground substance
- Loose connective tissue is richer in ground substance and more sparing in its fibrous components
- Special connective tissue includes tissue types more specific to location and function, such as bone, cartilage and adipose (fat) tissue
Cells found within connective tissue are grouped by their degree of mobility:
- Stationary cells are fixed in place (fibroblasts, adipose cells)
- Migrating cells may move freely through tissue (mast cells, macrophages
Cardiac tissue forms the wall of the heart, and is separated into three distinct layers with specialized functions:
- The innermost endocardium provides the smooth, non-adherent surface needed for consistent blood collection, unimpeded blood flow and effective pumping.
- The middle myocardium is composed of specialized cardiac muscle cells that respond to nervous stimulation and contract in a synchronized manner that keeps the heart beating.
- The outermost epicardium keeps the heart localized and protected from while providing an added layer of protection from trauma; also contains coronary blood vessels that nourish the heart.
Nervous tissue is found throughout the brain, spinal cord and nerves. Composed of electrochemically active neurons and mostly inactive glial cells, this tissue type provides a foundation for a wide range of body systems and functions, including:
- Gathering sensory information
- Creating environmental awareness
- Stimulating voluntary and involuntary muscle contraction
- Creating and storing memory
- Regulating emotion
- Driving processes of higher cognition and reasoning
Epithelial tissue makes up the epithelium that covers all body surfaces, from the outermost — the epidermal layer of our skin — to the inner linings of hollow organs at the body’s core. Many combinations of basic epithelial cell shape, cell arrangement and layer thickness make it possible for epithelial tissue to perform over a wide spectrum of biological functions, including:
- Secretion
- Absorption
- Filtration
- Excretion
- Protection
- Diffusion
- Sensory reception
Blood is often considered a type of "fluid connective tissue" as it features both a cellular component and a liquid ground substance called plasma.
The cellular component of blood includes red blood cells (RBCs), white blood cells (WBCs) and cell fragments with coagulative function known as platelets
Blood plasma, the extracellular matrix through which cellular components move, consists of water, dissolved proteins and hundreds of other biochemical factors necessary for the many functions blood performs, from oxygen and nutrient delivery to clearing of metabolic waste products.
