Connective Tissue Types

Connective Tissue

• Ground substance: gelatinous, rubbery consistency, helps absorb compressive forces and protect cells
• Areolar tissue: loose arrangement of collagenous and elastic fibers, scattered cells, significant space between cells, lots of ground substance and blood vessels, found underlying epithelial tissue and surrounding blood vessels and nerves
  • Functions: loosely binds epithelial tissue to its surface, provides blood and nutrients for epithelial tissue
• Reticular tissue: loose arrangement of reticular fibers, numerous lymphocytes and other blood cells, found in lymph nodes, spleen, and bone marrow
  • Functions: supportive sponge-like network for lymphatic system, filters lymphatic fluid
• Dense Regular tissue: few cells, numerous collagen and elastic fibers, fibers occupy more space than cells or ground matrix, organized wavy pattern
  • Functions: resists stress in one direction, found in ligaments and tendons
• Dense Irregular tissue: few cells, lots of collagen fibers, but fibers are not organized, found in dermis of the skin
  • Functions: resists stress in multiple directions

Adipose Connective Tissue

• Consists primarily of closely packed adipocytes (fat cells) that store triglycerides
  • Functions: provides energy, thermal insulation, and protective cushioning
• Found: at the base of the skin, in tissues of the breasts, and around some internal organs

Cartilage Connective Tissue

• Has a stiff, rubbery matrix, avascular, consists of chondrocytes (cartilage cells) in a rubbery matrix
• Three forms: Hyaline, Elastic, and Fibrocartilage
  • Hyaline cartilage: fine collagen fibers, used at the end of bones to reduce friction, part of the trachea and larynx, makes up most of the fetal skeleton
  • Elastic cartilage: has both elastin and collagen fibers, used in the external ear and the epiglottis in the throat
  • Fibrocartilage: has coarse collagen fibers, used in areas that need more long-term durability due to stress

Bone Connective Tissue

• Contains osteocytes (bone cells) surrounded by a matrix that is strong and flexible
• Functions: supports softer tissues, provides leverage for muscles, protects some internal organs, stores minerals
• Makes up the bones (organs) of the skeleton

Blood Connective Tissue

• Has a liquid matrix that surrounds cells and cell-like structures (formed elements)
• Includes: WBC, RBC, and platelets
• Functions: transports substances, aids in protection from infection, found in the chambers of the heart and in the hollow lumens of the blood vessels

Nerve Tissue

• Used to transmit electrical signals within the body for communication
• Contains neurons and neuroglial cells
  • Neurons: highly excitable cells that transmit signals
  • Neuroglia: cells that support the neurons
• Found in the brain, spinal cord, and nerves

Muscle Tissue

• Used to cause movement
• Myocytes (muscle cells) are elongated and highly excitable
  • Can contract (shorten) when excited, leading to movements of the body and/or movement of substances within the body
• Three types: Skeletal, Cardiac, and Smooth

Glands

• Cell or organs that secrete substances for use elsewhere in the body
• Types: Exocrine and Endocrine
  • Exocrine glands: use tube-like structures called ducts to secrete or excrete their products to a nearby surface
  • Endocrine glands: secrete their products into the bloodstream for transport to another cell

Membrane

• Flat sheet or layer made up of several tissues working closely together
• Types: Mucous, Serous, Synovial, Endothelium, and Cutaneous
  • Mucous membrane: lines passages that open to the exterior of the body, functions: absorption, secretion, and protection
  • Serous membrane: produces serous fluid, found on organs and lines/surrounds cavities, functions: reduces friction as organs move
  • Synovial membrane: associated with joints, secretes synovial fluid, functions: protects and lubricates joints
  • Endothelium: lines the vessels of the circulatory system, functions: allows for exchange of nutrients and gases
  • Cutaneous membrane: commonly known as skin, consists of 2 layers: dermis and epidermis, functions: resistance to trauma and infection, barrier functions, vitamin D synthesis, sensation, thermoregulation, and nonverbal communication

Integumentary System

• Skin is the largest and heaviest organ, making up 15% of the body weight
• Functions: resistance to trauma and infection, barrier functions, vitamin D synthesis, sensation, thermoregulation, and nonverbal communication
• Structure: Epidermis, Dermis, and Hypodermis
  • Epidermis: made up of stratified squamous epithelium, functions: physical and chemical protection, barrier against UV rays and chemicals
  • Dermis: made up of connective tissue, functions: supports the epidermis, provides blood vessels and nerve endings
  • Hypodermis: made up of connective tissue, functions: attaches the skin to underlying structures### Epidermis
• The epidermis is the outermost layer of the skin, consisting of 5 layers: Stratum basale, Stratum spinosum, Stratum granulosum, Stratum lucidum, and Stratum corneum.
• Keratinocytes, melanocytes, and tactile cells are found in the Stratum basale.
• The Stratum corneum is the most superficial layer, containing dead keratinocytes and keratin.
• It takes about 30-40 days for a keratinocyte to reach the surface and be sloughed off.
• The epidermis is avascular, with very few nerve supply through the tactile cells.
• It is highly mitotic, with the fastest reproducing cells in the body.

Dermis

• The dermis provides support for the epidermis and is much thicker than the epidermis.
• It is divided into two layers: papillary and reticular.
• The papillary layer is a thin layer near the dermal papillae, consisting of areolar loose connective tissue and abundant blood vessels.
• The reticular layer is a thick layer below the papillary layer, consisting of dense irregular connective tissue.
• The dermis contains associated structures such as glands, hair, and follicles.

Subcutaneous Membrane (Hypodermis)

• The subcutaneous membrane is a layer beneath the skin, binding skin to underlying tissue and structures.
• It is not as well defined as the boundary between the dermis and epidermis.
• It has more areolar and adipose tissue than the dermis.
• It is highly vascular and functions in padding the body, providing cushion and thermoregulation, and binding the skin to underlying tissue.

Accessory Organs

Hair (Pilus)

• Hair is found almost everywhere except for palms, soles, certain areas of fingers and toes, nipples, and parts of the genitals.
• It consists of the follicle, bulb, root, and shaft.
• The piloreceptor is the arrector pili, a small muscle attached to hair follicles in mammals.
• Hair functions as a warning system, for heat retention, identification, and vestigially.

Nail

• The nail is an extension of the stratum corneum, consisting of dead keratinocytes densely packed with parallel hard keratin fibers.
• It is a distinguishing characteristic of primates.
• It allows for more sensitive and tactile finger tips.
• It functions as a tool for picking and manipulating objects.

Glands

• There are two types of glands: endocrine and exocrine.
• Exocrine glands use ducts to transport their products.
• Examples of exocrine glands include:
  • Merocrine glands: produce water perspiration for temperature regulation and waste removal.
  • Apocrine sweat glands: produce pheromones and are stimulated in response to stress and sexual stimulation.
  • Sebaceous glands: produce sebum, which keeps the skin from becoming dry and brittle and makes hair shiny.
  • Ceruminous glands: produce secretions that combine with sebum to form ear wax.
  • Mammary glands: produce milk.

Tissues

• Tissues are a collection of specialized cells that function together.
• Matrix is non-living, extracellular material that surrounds the cells.
• There are four categories of tissues: epithelial, nervous, connective, and muscle.

Epithelial Tissues

• General characteristics:
  • Line surfaces and cover surfaces.
  • Avascular: no blood supply.
  • Tightly packed cells with little to no space between cells.
  • Highly mitotic: reproduce rapidly.
  • Have a basement membrane at their deepest point.
• Functions:
  • Protection.
  • Secretion.
  • Excretion.
  • Absorption.
  • Filtration.
  • Sensation.

Connective Tissue

• Consists of mostly non-living matrix with widely spaced cells.
• It is vascular: has a blood supply.
• Functions:
  • Binding of organs or enclosing of organs.
  • Support of the body.
  • Physical protection of vital organs.
  • Immune protection.
  • Movement.
  • Energy storage.
  • Heat production and temperature regulation.
  • Transportation of nutrients and gases via blood.

Fibrous Connective Tissue

• Matrix contains significant amounts of protein fibers.

• Cell types:

  • Fibroblast: produce the fibers and ground substance.
  • Mast cells: secrete hormones that regulate blood flow and clotting.
  • Macrophages: ingest and help get rid of particles and infections microorganisms.
  • Leukocytes: WBC that play various protective roles.
  • Plasma cells: specialized WBC that help with immunity.
  • Adipocytes: fat-storing cells.

• Matrix: non-living material around the cells (has fibers and ground substance).

• Fibers are found in three forms:

  • Collagenous: made out of protein collagen.
  • Reticular: have thin collagen fibers.
  • Elastic: made out of protein elastin.