Tissues in Biological Systems

Tissues

• Tissues are groups of cells with a common function
• Four primary tissue types include epithelia, connective tissue, muscle, and nervous tissue

Epithelial Tissues

• Epithelial tissues cover body cavities and surfaces
• Examples include skin, the inner surface of lungs, and the digestive tract
• Functions include:
  • Protection of underlying tissues like skin
  • Reduction of friction, such as in blood vessels
  • Transportation and absorption of materials, such as in the intestine
  • Secretion of wastes, such as in the kidneys
• Glandular epithelia are epithelial cells adapted to form glands
  • Exocrine glands secrete into hollow organs and/or ducts to the exterior of the body
  • Endocrine glands secrete into the blood to carry chemical messages

Epithelial Tissues: Classification Based on Shape

• Squamous cells are flattened and line vessels, parts of lungs, and body surfaces
• Cuboidal cells are cube-shaped and form the lining of tubules and glandular tissue
• Columnar cells are column-shaped and line respiratory, digestive, and reproductive tracts

Epithelial Tissues: Classification Based on Number of Layers

• Simple/single layered epithelia are adapted for diffusion across cell barriers and line glands, respiratory, digestive, and reproductive systems
• Stratified/multiple layered epithelia provide protection, such as the skin surface

Epithelial Tissues: Attachments

• The basement membrane provides structural support and attaches the epithelial layer to underlying tissues
• Junctions hold epithelial cells together
  • Tight junctions: prevent passage of substances, like in the digestive tract
  • Adhesion junctions (spot desmosomes): allow some movement between cells, like in skin
  • Gap junctions: protein channels allowing movement of ions and water, like in the liver

Connective Tissue

• Functions of connective tissue:
  • Supports the softer organs
  • Connects body parts
  • Stores fat and produces blood cells
• Characteristics include few living cells with most of the structure composed of non-living extracellular material/matrix
• Matrix provides strength to connective tissue
• No cell-cell junctions
• Classification is diverse, but divisible into fibrous and specialized connective tissues

Fibrous Connective Tissue Types

• Loose connective tissue:
  • Primarily collagen and elastin fibers in no particular pattern
  • Flexible but only moderately strong
  • Surround internal organs, muscles, and blood vessels
• Dense connective tissue:
  • Mostly collagen in a parallel arrangement of fibers
  • Strong and found in tendons, ligaments, and the lower layers of skin
• Elastic connective tissue:
  • High proportion of elastin fibers
  • Stretches and recoils easily
  • Surrounds hollow organs that change shape or size
• Reticular (lymphoid):
  • Thin, interconnecting reticular fibers of collagen
  • Flexible internal framework in soft organs like the liver, spleen, tonsils, and lymph glands

Specialized Connective Tissue Types

• Cartilage:
  • Primarily collagen fibers in a ground substance containing a lot of water
  • Maintains shape and resists compression
  • Embryonic tissue that becomes bone and found in the nose, vertebral disks, and lining of joint cavities
• Bone:
  • Primarily hard mineral deposits of calcium and phosphate
  • Very strong and forms the skeleton
• Blood:
  • Blood cells, platelets, and plasma
  • Transports materials and assists in defense mechanisms within the cardiovascular system
• Adipose tissue:
  • Primarily adipocytes filled with fat deposits
  • Stores energy in the form of fat under the skin and around some internal organs

Muscle Tissue

• Muscle Tissue:
  • Shortens and contracts for movement
  • Composed of cells specialized to shorten or contract
  • Consists of tightly packed cells called muscle fibers, long, thin, and parallel to each other

Types of Muscle Tissue

• Skeletal muscles:
  • Moves body parts
  • Connected to tendons attached to bones
  • Voluntary muscles with multinucleated cells
  • Muscle fibers parallel to each other and shorten together
• Cardiac muscles:
  • Shorter than skeletal muscle fibers
  • One nucleus per cell, parallel to each other and involuntary
  • Gap junctions between ends of adjoining cells activate other cells down the line, allowing heart contraction in a coordinated fashion
• Smooth muscles:
  • Surrounds hollow structures
  • Involuntary
  • Single nucleus per cell arranged in circles with gap junctions

Nervous Tissue

• Nervous tissue transmits impulses and are located in the brain, spinal cord, and nerves
• The cells in the nervous tissue are neurons and glial cells
  • Neurons generate and transmit electrical impulses throughout the body
    • Structural components: cell body, dendrites, axon
  • Glial cells protect and support neurons

Organs and Organ Systems

• Organs are structures composed of two or more tissue types working together to perform specific functions
  • The heart is composed of cardiac muscle, smooth muscle in the blood vessels, nervous tissue, connective tissue & epithelial tissue

Organ Systems

• Organ systems are groups of organs that perform a common function
  • Digestive system includes the: mouth, throat, stomach, intestines, and liver
  • Lymphatic system includes: lymph nodes, tonsils, and spleen
  • (Other organ Systems):
    • Integumentary
    • Skeletal
    • Muscular
    • Nervous
    • Endocrine
    • Circulatory
    • Respiratory
    • Reproductive
    • Urinary

Body Cavities

• The thoracic cavity contains pericardial and pleural cavities and is separated from the abdominal cavity by the diaphragm

Tissue Membranes

• Tissue membranes line body cavities containing a layer of epithelial tissue and connective tissue that lines each body cavity
• Four major types of tissue membranes - Serous reduces friction between organs - Mucous lubricates surface, captures debris - Synovial lines movable joints - Cutaneous = skin

Skin: Integumentary System

• Function:
  • Prevent dehydration
  • Protect from injury
  • Serve as defense against microorganisms
  • Regulate body temperature
  • Synthesis of vitamin D
  • Provide sensation
• Structure includes the epidermis and dermis

Epidermis Structure

• The epidermis is the outer layer and is made of stratified squamous epithelial cells with no blood vessels
• Contains specialized keratinocytes (keratin) and melanocytes (melanin)

Dermis

• The dermis contains a deeper layer of primarily dense connective tissue that lies underneath the epidermis
• It lies underneath the epidermis and supports tissue
• Fibers like collagen and elastics provide strength and elasticity
• The cells in the dermis include fibroblasts (most abundant), mast cells, white blood cells, and fat cells
• Contains the following accessory structures
  • Hair shaft and follicle
  • Smooth muscle attached to the hair follicle for raising to upright position
  • Oil/sebaceous glands secrete substance to moistens and softens skin
  • Sweat glands secrete to help in temperature regulation
  • Supply blood vessels to give nutrients, remove waste, assists in temperature regulation
  • Sensory nerve endings that react to hot, cold, touch deep pressure vibration

Homeostasis

• The ability to maintain internal equilibrium through physiological process adjustments
• Mechanisms include:
  • Negative feedback
    • Deviations from normal are detected and counteracted
    • Components include:
      • A controlled variable
      • Sensor
      • Control center
      • Effector
  • Positive feedback
    • Amplifies original change
    • Rarely found in organisms

Explore tissue types and their primary characteristics. This includes epithelial tissues, cell junctions, and their roles. Understand tissue functions in biological systems.