Learning Outcomes
- Discuss the different types of connective tissues in animals
Connective tissues are made up of a matrix consisting of living cells and a non-living substance, called the ground substance. The ground substance is made of an organic substance (usually a protein) and an inorganic substance (usually a mineral or water). The principal cell of connective tissues is the fibroblast. This cell makes the fibers found in nearly all of the connective tissues. Fibroblasts are motile, able to carry out mitosis, and can synthesize whichever connective tissue is needed. Macrophages, lymphocytes, and, occasionally, leukocytes can be found in some of the tissues. Some tissues have specialized cells that are not found in the others. The matrix in connective tissues gives the tissue its density. When a connective tissue has a high concentration of cells or fibers, it has proportionally a less dense matrix.
The organic portion or protein fibers found in connective tissues are either collagen, elastic, or reticular fibers. Collagen fibers provide strength to the tissue, preventing it from being torn or separated from the surrounding tissues. Elastic fibers are made of the protein elastin; this fiber can stretch to one and one half of its length and return to its original size and shape. Elastic fibers provide flexibility to the tissues. Reticular fibers are the third type of protein fiber found in connective tissues. This fiber consists of thin strands of collagen that form a network of fibers to support the tissue and other organs to which it is connected. The various types of connective tissues, the types of cells and fibers they are made of, and sample locations of the tissues is summarized in Table 1.
| Table 1. Connective Tissues | |||
|---|---|---|---|
| Tissue | Cells | Fibers | Location |
| loose/areolar | fibroblasts, macrophages, some lymphocytes, some neutrophils | few: collagen, elastic, reticular | around blood vessels; anchors epithelia |
| dense, fibrous connective tissue | fibroblasts, macrophages, | mostly collagen | irregular: skin regular: tendons, ligaments |
| cartilage | chondrocytes, chondroblasts | hyaline: few collagen fibrocartilage: large amount of collagen | shark skeleton, fetal bones, human ears, intervertebral discs |
| bone | osteoblasts, osteocytes, osteoclasts | some: collagen, elastic | vertebrate skeletons |
| adipose | adipocytes | few | adipose (fat) |
| blood | red blood cells, white blood cells | none | blood |
Loose/Areolar Connective Tissue
Figure 1.Loose connective tissue is composed of loosely woven collagen and elastic fibers. The fibers and other components of the connective tissue matrix are secreted by fibroblasts.
Loose connective tissue, also called areolar connective tissue, has a sampling of all of the components of a connective tissue. As illustrated in Figure 1, loose connective tissue has some fibroblasts; macrophages are present as well. Collagen fibers are relatively wide and stain a light pink, while elastic fibers are thin and stain dark blue to black. The space between the formed elements of the tissue is filled with the matrix. The material in the connective tissue gives it a loose consistency similar to a cotton ball that has been pulled apart. Loose connective tissue is found around every blood vessel and helps to keep the vessel in place. The tissue is also found around and between most body organs. In summary, areolar tissue is tough, yet flexible, and comprises membranes.
Fibrous Connective Tissue
Fibrous connective tissues contain large amounts of collagen fibers and few cells or matrix material. The fibers can be arranged irregularly or regularly with the strands lined up in parallel. Irregularly arranged fibrous connective tissues are found in areas of the body where stress occurs from all directions, such as the dermis of the skin. Regular fibrous connective tissue, shown in Figure 2, is found in tendons (which connect muscles to bones) and ligaments (which connect bones to bones).
Figure 2.Fibrous connective tissue from the tendon has strands of collagen fibers lined up in parallel.
Cartilage
Cartilage is a connective tissue with a large amount of the matrix and variable amounts of fibers. The cells, called chondrocytes, make the matrix and fibers of the tissue. Chondrocytes are found in spaces within the tissue called lacunae.
Figure 3.Hyaline cartilage consists of a matrix with cells called chondrocytes embedded in it. The chondrocytes exist in cavities in the matrix called lacunae.
A cartilage with few collagen and elastic fibers is hyaline cartilage, illustrated in Figure 3. The lacunae are randomly scattered throughout the tissue and the matrix takes on a milky or scrubbed appearance with routine histological stains. Sharks have cartilaginous skeletons, as does nearly the entire human skeleton during a specific pre-birth developmental stage. A remnant of this cartilage persists in the outer portion of the human nose. Hyaline cartilage is also found at the ends of long bones, reducing friction and cushioning the articulations of these bones.
Elastic cartilage has a large amount of elastic fibers, giving it tremendous flexibility. The ears of most vertebrate animals contain this cartilage as do portions of the larynx, or voice box. Fibrocartilage contains a large amount of collagen fibers, giving the tissue tremendous strength. Fibrocartilage comprises the intervertebral discs in vertebrate animals. Hyaline cartilage found in movable joints such as the knee and shoulder becomes damaged as a result of age or trauma. Damaged hyaline cartilage is replaced by fibrocartilage and results in the joints becoming “stiff.”
Bone
Bone, or osseous tissue, is a connective tissue that has a large amount of two different types of matrix material. The organic matrix is similar to the matrix material found in other connective tissues, including some amount of collagen and elastic fibers. This gives strength and flexibility to the tissue. The inorganic matrix consists of mineral salts—mostly calcium salts—that give the tissue hardness. Without adequate organic material in the matrix, the tissue breaks; without adequate inorganic material in the matrix, the tissue bends.
There are three types of cells in bone: osteoblasts, osteocytes, and osteoclasts. Osteoblasts are active in making bone for growth and remodeling. Osteoblasts deposit bone material into the matrix and, after the matrix surrounds them, they continue to live, but in a reduced metabolic state as osteocytes. Osteocytes are found in lacunae of the bone. Osteoclasts are active in breaking down bone for bone remodeling, and they provide access to calcium stored in tissues. Osteoclasts are usually found on the surface of the tissue.
Bone can be divided into two types: compact and spongy. Compact bone is found in the shaft (or diaphysis) of a long bone and the surface of the flat bones, while spongy bone is found in the end (or epiphysis) of a long bone. Compact bone is organized into subunits called osteons, as illustrated in Figure 4. A blood vessel and a nerve are found in the center of the structure within the Haversian canal, with radiating circles of lacunae around it known as lamellae. The wavy lines seen between the lacunae are microchannels called canaliculi; they connect the lacunae to aid diffusion between the cells. Spongy bone is made of tiny plates called trabeculae these plates serve as struts to give the spongy bone strength. Over time, these plates can break causing the bone to become less resilient. Bone tissue forms the internal skeleton of vertebrate animals, providing structure to the animal and points of attachment for tendons.
Figure 4.(a) Compact bone is a dense matrix on the outer surface of bone. Spongy bone, inside the compact bone, is porous with web-like trabeculae. (b) Compact bone is organized into rings called osteons. Blood vessels, nerves, and lymphatic vessels are found in the central Haversian canal. Rings of lamellae surround the Haversian canal. Between the lamellae are cavities called lacunae. Canaliculi are microchannels connecting the lacunae together. (c) Osteoblasts surround the exterior of the bone. Osteoclasts bore tunnels into the bone and osteocytes are found in the lacunae.
Adipose Tissue
Figure 5.Adipose is a connective tissue is made up of cells called adipocytes. Adipocytes have small nuclei localized at the cell edge.
Adipose tissue, or fat tissue, is considered a connective tissue even though it does not have fibroblasts or a real matrix and only has a few fibers. Adipose tissue is made up of cells called adipocytes that collect and store fat in the form of triglycerides, for energy metabolism. Adipose tissues additionally serve as insulation to help maintain body temperatures, allowing animals to be endothermic, and they function as cushioning against damage to body organs. Under a microscope, adipose tissue cells appear empty due to the extraction of fat during the processing of the material for viewing, as seen in Figure 5. The thin lines in the image are the cell membranes, and the nuclei are the small, black dots at the edges of the cells.
Blood
Blood is considered a connective tissue because it has a matrix, as shown in Figure 6. The living cell types are red blood cells (RBC), also called erythrocytes, and white blood cells (WBC), also called leukocytes. The fluid portion of whole blood, its matrix, is commonly called plasma.
Figure 6.Blood is a connective tissue that has a fluid matrix, called plasma, and no fibers. Erythrocytes (red blood cells), the predominant cell type, are involved in the transport of oxygen and carbon dioxide. Also present are various leukocytes (white blood cells) involved in immune response.
The cell found in greatest abundance in blood is the erythrocyte. Erythrocytes are counted in millions in a blood sample: the average number of red blood cells in primates is 4.7 to 5.5 million cells per microliter. Erythrocytes are consistently the same size in a species, but vary in size between species. For example, the average diameter of a primate red blood cell is 7.5 µl, a dog is close at 7.0 µl, but a cat’s RBC diameter is 5.9 µl. Sheep erythrocytes are even smaller at 4.6 µl. Mammalian erythrocytes lose their nuclei and mitochondria when they are released from the bone marrow where they are made. Fish, amphibian, and avian red blood cells maintain their nuclei and mitochondria throughout the cell’s life. The principal job of an erythrocyte is to carry and deliver oxygen to the tissues.
Leukocytes are the predominant white blood cells found in the peripheral blood. Leukocytes are counted in the thousands in the blood with measurements expressed as ranges: primate counts range from 4,800 to 10,800 cells per µl, dogs from 5,600 to 19,200 cells per µl, cats from 8,000 to 25,000 cells per µl, cattle from 4,000 to 12,000 cells per µl, and pigs from 11,000 to 22,000 cells per µl.
Lymphocytes function primarily in the immune response to foreign antigens or material. Different types of lymphocytes make antibodies tailored to the foreign antigens and control the production of those antibodies. Neutrophils are phagocytic cells and they participate in one of the early lines of defense against microbial invaders, aiding in the removal of bacteria that has entered the body. Another leukocyte that is found in the peripheral blood is the monocyte. Monocytes give rise to phagocytic macrophages that clean up dead and damaged cells in the body, whether they are foreign or from the host animal. Two additional leukocytes in the blood are eosinophils and basophils—both help to facilitate the inflammatory response.
The slightly granular material among the cells is a cytoplasmic fragment of a cell in the bone marrow. This is called a platelet or thrombocyte. Platelets participate in the stages leading up to coagulation of the blood to stop bleeding through damaged blood vessels. Blood has a number of functions, but primarily it transports material through the body to bring nutrients to cells and remove waste material from them.
Pathologist
A pathologist is a medical doctor or veterinarian who has specialized in the laboratory detection of disease in animals, including humans. These professionals complete medical school education and follow it with an extensive post-graduate residency at a medical center. A pathologist may oversee clinical laboratories for the evaluation of body tissue and blood samples for the detection of disease or infection. They examine tissue specimens through a microscope to identify cancers and other diseases. Some pathologists perform autopsies to determine the cause of death and the progression of disease.
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FAQs
What are the 2 main types of connective tissues and what do they do? ›
Connective tissue proper is further subdivided into loose and dense connective tissues. Specialized connective tissues are diverse as they are composed of varying specialized cells and ground substance. Specialized connective tissues include adipose, cartilage, bone, blood, and reticular tissues.
What are the 2 parts of connective tissue? ›All forms of connective tissue are composed of (1) extracellular fibres, (2) an amorphous matrix called ground substance, and (3) stationary and migrating cells.
What are the 4 types of connective tissue? ›Classification of connective tissues:
There are four classes of connective tissues: BLOOD, BONES, CARTILAGE and CONNECTIVE TISSUE PROPER.
The types of connective tissue include loose connective tissue, adipose tissue, dense fibrous connective tissue, elastic connective tissue, cartilage, osseous tissue (bone), and blood.
What are 3 types of connective tissue? ›- Collagen fibers - most are type I collagen (most abundant protein in the body)
- Elastic fibers - contain elastin and fibrillin.
- Reticular fibers - contain type III collagen.
Connective tissue is found in between other tissues everywhere in the body, including the nervous system. The three meninges, membranes that envelop the brain and spinal cord, are composed of connective tissue.
What are 2 types of connective tissues that attach muscle to bone? ›Ligaments connect bones together. Tendons. Tendons (another type of tough connective tissue) on each side of a joint attach to muscles that control movement of the joint. Tendons connect muscles to bones.
What 2 types of connective tissues are found in the dermis? ›The dermis is a connective tissue layer of mesenchymal origin located deep to the epidermis and superficial to the subcutaneous fat layer. [1] The composition of the dermis is mainly fibrous, consisting of both collagen and elastic fibers.
What are the 2 types of connective tissue and how they attach muscle to bone and bone to bone? ›A tendon serves to move the bone or structure. A ligament is a fibrous connective tissue that attaches bone to bone, and usually serves to hold structures together and keep them stable.
What are the 5 types of connective tissue cells? ›The common cell types in connective tissue include: fibroblasts, mast cells, plasma cells, macrophages, adipocytes, and leukocytes.
Which is not a connective tissue? ›
Heart muscle is a type of muscular tissue and not connective tissue.
What are the 4 types of tissue and their functions? ›Overview. There are 4 basic types of tissue: connective tissue, epithelial tissue, muscle tissue, and nervous tissue. Connective tissue supports other tissues and binds them together (bone, blood, and lymph tissues). Epithelial tissue provides a covering (skin, the linings of the various passages inside the body).
How many connective tissues are in the body? ›There are seven types of connective tissues found in the body of people.
Is The skin A connective tissue? ›Skin is made up of connective tissue that consists of cellular components and an extracellular matrix. The extracellular matrix contains two main types of macromolecules: polysaccharide glycosaminoglycans and collagens.
What are 3 characteristics of all connective tissue? ›Connective tissues come in a vast variety of forms, yet they typically have in common three characteristic components: cells, large amounts of amorphous ground substance, and protein fibers.
What type of tissue is bone? ›Bone is made up of compact tissue (the hard, outer layer) and cancellous tissue (the spongy, inner layer that contains red marrow).
What is connective tissue made of? ›Connective tissue is made up of cells, fibers, and a gel-like substance. Types of connective tissue include bone, cartilage, fat, blood, and lymphatic tissue.
Why is connective tissue important? ›Connective tissues perform many functions in the body, but most importantly, they support and connect other tissues; from the connective tissue sheath that surrounds muscle cells, to the tendons that attach muscles to bones, and to the skeleton that supports the positions of the body.
Are muscles a connective tissue? ›Each muscle is made up of groups of muscle fibers called fascicles surrounded by a connective tissue layer called perimysium. Multiple units of individual muscle fibers within each fascicle are surrounded by endomysium, a connective tissue sheath.
What connects muscle to muscle? ›Because tendons connect every muscle in your body, a wide range of injuries and disorders can cause tendon problems. Tendon issues are more common with age.
What connects muscle to bone? ›
Listen to pronunciation. (TEN-dun) Tough, fibrous, cord-like tissue that connects muscle to bone or another structure, such as an eyeball. Tendons help the bone or structure to move.
What connects muscles to bone? ›Tendons — these are made of strong fibrous connective tissue and they connect muscles to bone. They appear as the long thin ends of the muscles. The Achilles tendon is the largest tendon in the body — it joins the calf muscle to the heel bone.
Is blood is a connective tissue? ›Blood is one of the connective tissues. As a connective tissue, it consists of cells and cell fragments (formed elements) suspended in an intercellular matrix (plasma).
Which connective tissue is present in skin? ›Elastic tissues such as the skin require a strong and resilient structural framework. This framework is called the extracellular matrix, or connective tissue.
What glands respond to rising androgen levels? ›Glands that respond to rising androgen levels are the sebaceous (oil) glands.
What are the 2 types of proteins embedded within the matrix of connective tissues? ›Collagen fibers provide strength to the tissue, preventing it from being torn or separated from the surrounding tissues. Elastic fibers are made of the protein elastin; this fiber can stretch to one and one half of its length and return to its original size and shape. Elastic fibers provide flexibility to the tissues.
What are 2 ways skeletal muscles attach? ›A skeletal muscle attaches to bone (or sometimes other muscles or tissues) at two or more places. If the place is a bone that remains immobile for an action, the attachment is called an origin. If the place is on the bone that moves during the action, the attachment is called an insertion.
Is skeletal muscle a connective tissue? ›Muscle: Skeletal Muscle Connective Tissue
Skeletal muscle has three different connective tissue layers: The whole muscle is enclosed by a dense connective tissue sheath called the epimysium. (Epi - greek for upon, mys - greek for muscle). The muscle fibres are divided up into bundles of fibres called 'fascicles'.
The tough, thin outer membrane covering the bones is called the periosteum.
Is a bone a connective tissue? ›Bone is a connective tissue containing cells, fibers and ground substance. There are many functions in the body in which the bone participates, such as storing minerals, providing internal support, protecting vital organs, enabling movement, and providing attachment sites for muscles and tendons.
What is the skeletal connective tissue? ›
The skeletal tissue is a connective tissue that possesses a solid matrix and the living cells in the fluid-filled spaces called lacunae. Generally, the skeletal tissues provide support and protection, thereby forming an endoskeleton. There are two types of skeletal tissues, namely, Bones and Cartilages.
Which tissue lacks blood supply? ›Cartilage, once synthesized, lacks lymphatic or blood supply and the movement of waste and nutrition is chiefly via diffusion to and from adjacent tissues.
Why is blood a connective tissue? ›Blood is considered a connective tissue because it has a matrix. The living cell types are red blood cells, also called erythrocytes, and white blood cells, also called leukocytes. The fluid portion of whole blood, its matrix, is commonly called plasma.
Is cartilage a bone? ›Cartilage is a flexible connective tissue that differs from bone in several ways; it is avascular and its microarchitecture is less organized than bone. The cells (chondrocytes) are scattered and lie firmly fixed in matrix supported by collagen and elastic fibres.
What are the 12 tissues? ›- Epithelial tissue. Cell surfaces. Tissue structure. Specialized epithelial tissue.
- Connective tissue. Connective tissue cells. Connective tissue fibers. Connective tissue classification.
- Muscle tissue. Skeletal muscle. Cardiac muscle. Smooth muscle.
- Nervous tissue. Neurons.
- Highlights. Tissue. Epithelial tissue. ...
- Sources.
Human tissue is described as an organ or part of a human body or any substance extracted from a human body. The Human Tissue Act 1983 sets out the law for the use of human tissue in NSW. For more information, see frequently asked questions on: Anatomy and body donation.
What is body tissue? ›Tissue is a group of cells that have similar structure and that function together as a unit. A nonliving material, called the intercellular matrix, fills the spaces between the cells. This may be abundant in some tissues and minimal in others.
How do you remember connective tissues? ›Examples of Connective Tissue "Aditi Argued with Carl and BoB" is the mnemonic that will help to remember examples of connective tissue.
Is a nerve connective tissue? ›The connective tissue inside nerves functions to support and protect nerves blood and lymphatic vessels (see Figure 1 and 2). The connective tissue of peripheral nerves takes different names according to its location. On the outside of each peripheral nerve, there is collagenous tissue: epineurium.
Is connective tissue in all organs? ›Connective tissue is the tough, often fibrous tissue that binds the body's structures together and provides support and elasticity. It is present in almost every organ, forming a large part of skin, tendons, joints, ligaments, blood vessels, and muscles.
Is connective tissue fat or protein? ›
Connective tissue composed primarily of fat cells is called adipose tissue. The fibers found in connective tissue include flexible collagen fibers with high tensile strength, delicate reticular fibers, and elastic fibers, which can undergo extensive stretching.
Is collagen a connective tissue? ›Collagen is the most abundant protein in the body. Its fiber-like structure is used to make connective tissue. Like the name implies, this type of tissue connects other tissues and is a major component of bone, skin, muscles, tendons, and cartilage.
How do the 2 types of connective tissue structures differ from one another? ›Dense connective tissue is stronger than loose connective tissue and can be further divided into two subcategories: dense regular connective tissue, which has parallel bundles of proteins, and dense irregular connective tissue, with less orderly collagen fibers.
What are 2 common characteristics of connective tissue? ›- They are highly vascularised.
- The cells are dispersed in a matrix.
- The matrix is composed of ground substance criss-crossed by protein fibers (The ground substance is mostly formed of fluid but may also be composed of minerals e.g: in bones).
Dense connective tissue supports, protects, and holds bones, muscles, and other tissues and organs in place. Ligaments, tendons, the inner layer of the skin, and the sclera (the white outer layer of the eye) are all types of dense connective tissue. Also called fibrous connective tissue.
What are the two types of connective tissue in a muscle quizlet? ›What are the two principal types of connective tissue in a muscle? collagen-white fibers that provide structure and support, elastin-yellow fibers that are elastic and flexible.
What are the two types of loose connective tissue? ›The three types of loose connective tissue include adipose, areolar and basement membrane. There are two types of adipose; brown and white, and they function to keep the body warm and provide energy. Areolar is the most abundant of the types of loose connective tissue.
What are 2 facts about connective tissue? ›Connective tissue also stores fat, helps move nutrients and other substances between tissues and organs, and helps repair damaged tissue. Connective tissue is made up of cells, fibers, and a gel-like substance.
What are 2 characteristics that connective tissue provide to the skin? ›Dense connective tissue is reinforced by bundles of fibers that provide tensile strength, elasticity, and protection.
How does connective tissue differ from the other three major tissue types? ›Connective tissue is composed of cells embedded in a ground substance. That ground substance is composed of a matrix and fibers. All other tissue types are composed solely of cells and no ground susbtance.
What is the difference between loose and dense connective tissue? ›
Both tissues have a variety of cell types and protein fibers suspended in a viscous ground substance. Dense connective tissue is reinforced by bundles of fibers that provide tensile strength, elasticity, and protection. In loose connective tissue, the fibers are loosely organized, leaving large spaces in between.
Which type of connective tissue is strong and dense? ›Dense irregular connective tissue
Collagen fibers have good tensile strength meaning that they are resistant to breaking under tension. This therefore makes collagen important in the supportive functions of this tissue. They are also surrounded by small amounts of ground substance.
A type of tissue that is mostly made up of tough protein fibers called collagen and cells called fibroblasts.
Which connective tissue is composed of muscle cells? ›Each muscle is made up of groups of muscle fibers called fascicles surrounded by a connective tissue layer called perimysium. Multiple units of individual muscle fibers within each fascicle are surrounded by endomysium, a connective tissue sheath.
What types of connective tissue are in skeletal muscle? ›There are three layers of connective tissue: epimysium, perimysium, and endomysium. Skeletal muscle fibers are organized into groups called fascicles. Blood vessels and nerves enter the connective tissue and branch in the cell.