The 4 Types of Tissues: Connective

Home , Elastic fiber, Ground substance, Loose connective tissue, Mesenchyme, Reticular fiber, Stroma (tissue)

The 4 Types of Tissues: connective

Connective Tissue

General structure of CT

 cells are dispersed in a matrix

 matrix = a large amount of extracellular

material produced by the CT cells and plays a

major role in the functioning

 matrix component = ground substance often

crisscrossed by protein fibers

 ground substance usually fluid, but it can also

be mineralized and solid (bones)

 CTs = vast variety of forms, but typically 3

characteristic components: cells, large

amounts of amorphous ground substance,

and protein fibers. Connective Tissue

GROUND SUBSTANCE

In connective tissue, the ground substance is an amorphous gel-like substance surrounding the cells. In a tissue, cells are surrounded and supported by an extracellular matrix. Ground substance traditionally does not include fibers (collagen and elastic fibers), but does include all the other components of the extracellular matrix . The components of the ground substance vary depending on the tissue. Ground substance is primarily composed of water, glycosaminoglycans (most notably hyaluronan ), proteoglycans, and glycoproteins. Usually it is not visible on slides, because it is lost during the preparation process. Connective Tissue

Functions of Connective Tissues  Support and connect other tissues  Protection (fibrous capsules and bones that protect delicate organs and, of course, the skeletal system).  Transport of fluid, nutrients, waste, and chemical messengers is ensured by specialized fluid connective tissues, such as blood and lymph.  Adipose cells store surplus energy in the form of fat and contribute to the thermal insulation of the body.

Embryonic Connective Tissue All connective tissues derive from the mesodermal layer of the embryo . The first connective tissue to develop in the embryo is mesenchyme , the stem cell line from which all connective tissues are later derived. Clusters of mesenchymal cells are scattered throughout adult tissue and supply the cells needed for replacement and repair after a connective tissue injury. A second type of embryonic connective tissue forms in the umbilical cord, called mucous connective tissue or Wharton’s jelly. This tissue is no longer present after birth, leaving only scattered mesenchymal cells throughout the body. Connective Tissue

Classification of CTs 3 broad categories of CT are classified according to the characteristics of their ground substance and the types of fibers found within the matrix

Connective Tissue

Connective Tissue Proper CELLS . Fibroblasts present in all CT proper . Fibrocytes, adipocytes, and mesenchymal cells are fixed cells (remain within the connective tissue). . Other cells move in and out in response to chemical signals: macrophages, mast cells, lymphocytes, plasma cells, and phagocytic cells (actually part of the immune system)

Connective Tissue

Connective Tissue Proper

Connective Tissue Fibers and Ground Substance (all secreted by fibroblasts) 3 main types :

• Collagen fiber = made from fibrous protein subunits linked together to form a

long and straight fiber, while flexible, have great tensile strength, resist stretching, and give ligaments and tendons their characteristic resilience and strength. • Elastic fiber = protein elastin (that after being stretched or compressed, it will return to its original shape) along with lesser amounts of other proteins and glycoproteins. • Reticular fiber = also formed from the same protein subunits as collagen fibers, but arrayed in a branching network.

• All of these fibers embedded in ground substance = made of polysaccharides,

specifically hyaluronic acid, and proteins (combined to form a proteoglycan with a protein core and polysaccharide branches) . The proteoglycan attracts and traps available moisture forming a clear, viscous, colorless matrix. Connective Tissue

Connective Tissue Proper

Loose Connective Tissue found between many organs where it acts both to absorb shock and bind tissues togethe + allows water, salts, and various nutrients to diffuse through to adjacent or imbedded cells and tissues. 1. Adipose tissue = mostly of fat storage cells, with little extracellular matrix. White fat contributes mostly to lipid storage and can serve as insulation from cold temperatures and mechanical injuries. Brown adipose tissue is more common in infants (“baby fat”) and is thermogenic

Connective Tissue

Connective Tissue Proper

Loose Connective Tissue 2. Areolar tissue shows little specialization and fills the spaces between muscle fibers, surrounds blood and lymph vessels, and supports organs in the abdominal cavity. Areolar tissue underlies most epithelia and represents the connective tissue component of epithelial membranes. 3. Reticular tissue = mesh-like, supportive framework for soft organs such as lymphatic tissue, spleen, and liver.

Connective Tissue Supportive

Connective Tissues allow the body to maintain its posture and protect internal organs + 2 major forms:

1. Cartilage The distinctive appearance of cartilage is due to polysaccharides called chondroitin sulfates, which bind with ground substance proteins to form proteoglycans. Embedded within the cartilage matrix are chondrocytes and the space they occupy are called lacunae (singular = lacuna). A layer of dense irregular connective tissue, the perichondrium, encapsulates the cartilage. avascular very slow healing. 3 main types: 2. Bone the hardest CT with rigid extracellular matrix contains mostly collagen fibers embedded in a mineralized ground substance containing hydroxyapatite. Osteocytes are located within lacunae. highly vascularized tissue. Connective Tissue

Fluid Connective Tissue = blood and lymph where cells circulate in a liquid extracellular matrix Connective Tissue

The following types of connective tissue are covered in this activity:

1. Loose (areolar) connective tissue (delicate thin layers between tissues; present in all mucous membranes) 2. Adipose tissue (fat) 3. Dense connective tissue (tendons/ligaments) 4. Hyaline cartilage (nose/ends of long bones/ribs) 5. Elastic cartilage (outer ear/epiglottis) 6. Fibrocartilage (between vertebrae/knee joints/pubic joint) 7. Bone (skeletal system) 8 Blood (bloodstream)

Connective Tissue

Table 4.1 Comparison of Classes of Connective Tissues (1 of 2)

Connective Tissue

Table 4.1 Comparison of Classes of Connective Tissues (2 of 2) Figure 4.8a Connective tissues.

(a) Connective tissue proper: loose connective tissue, areolar

Description: Gel-like matrix with all three fiber types; cells: fibroblasts, macrophages, mast cells, and some Elastic white blood cells. fibers

Function: Wraps and cushions organs; its macrophages phagocytize bacteria; plays important role in Collagen inflammation; holds and conveys fibers tissue fluid.

Location: Widely distributed under epithelia of body, e.g., forms lamina propria of mucous membranes; Fibroblast packages organs; surrounds nuclei capillaries.

Epithelium

Photomicrograph: Areolar connective tissue, a Lamina soft packaging tissue of the body (300x). propria

Copyright © 2010 Pearson Education, Inc. Figure 4.7 Areolar connective tissue: A prototype (model) connective tissue. Cell types Extracellular matrix Ground substance Macrophage Fibers • Collagen fiber • Elastic fiber • Reticular fiber

Fibroblast Lymphocyte

Fat cell Capillary Mast cell

Neutrophil

(b) Connective tissue proper: loose connective tissue, adipose

Description: Matrix as in areolar, but very sparse; closely packed adipocytes, or fat cells, have nucleus pushed to the side by large fat droplet.

Function: Provides reserve food Nucleus of fuel; insulates against heat loss; fat cell supports and protects organs.

Location: Under skin in the hypodermis; around kidneys and eyeballs; within abdomen; in breasts.

Adipose Vacuole tissue containing fat droplet

Photomicrograph: Adipose tissue from the Mammary subcutaneous layer under the skin (350x). glands

Description: Network of reticular fibers in a typical loose ground substance; reticular cells lie on the network.

Function: Fibers form a soft internal skeleton (stroma) that supports other cell types including white blood cells, mast cells, and macrophages. White blood cell Location: Lymphoid organs (lymph (lymphocyte) nodes, bone marrow, and spleen).

Reticular fibers

Spleen

Photomicrograph: Dark-staining network of reticular connective tissue fibers forming the internal skeleton of the spleen (350x).

(d) Connective tissue proper: dense connective tissue, dense regular

Description: Primarily parallel collagen fibers; a few elastic fibers; major cell type is the fibroblast.

Collagen Function: Attaches muscles to fibers bones or to muscles; attaches bones to bones; withstands great tensile stress when pulling force is applied in one direction.

Location: Tendons, most ligaments, aponeuroses.

Nuclei of fibroblasts Shoulder joint

Ligament Photomicrograph: Dense regular connective tissue from a tendon (500x). Tendon

(e) Connective tissue proper: dense connective tissue, dense irregular Description: Primarily irregularly arranged collagen fibers; some elastic fibers; major cell type is the fibroblast. Nuclei of Function: Able to withstand fibroblasts tension exerted in many directions; provides structural strength. Location: Fibrous capsules of organs and of joints; dermis of the skin; submucosa of Collagen digestive tract. fibers

Fibrous joint capsule Photomicrograph: Dense irregular connective tissue from the dermis of the skin (400x).

(f) Connective tissue proper: dense connective tissue, elastic

Description: Dense regular connective tissue containing a high proportion of elastic fibers.

Function: Allows recoil of tissue following stretching; maintains pulsatile flow of blood through arteries; aids passive recoil of lungs following inspiration. Elastic fibers Location: Walls of large arteries; within certain ligaments associated with the vertebral column; within the walls of the bronchial tubes.

Aorta

Photomicrograph: Elastic connective tissue in Heart the wall of the aorta (250x).

(g) Cartilage: hyaline

Description: Amorphous but firm matrix; collagen fibers form an imperceptible network; chondroblasts produce the matrix and when mature (chondrocytes) lie in lacunae. Function: Supports and reinforces; has resilient cushioning properties; resists compressive stress.

Location: Forms most of the embryonic skeleton; covers the ends Chondrocyte of long bones in joint cavities; forms in lacuna costal cartilages of the ribs; cartilages of the nose, trachea, and larynx.

Matrix

Costal Photomicrograph: Hyaline cartilage from the cartilages trachea (750x).

(h) Cartilage: elastic Description: Similar to hyaline cartilage, but more elastic fibers in matrix.

Function: Maintains the shape of a structure while allowing Chondrocyte great flexibility. in lacuna

Location: Supports the external Matrix ear (pinna); epiglottis.

Photomicrograph: Elastic cartilage from the human ear pinna; forms the flexible skeleton of the ear (800x).

(i) Cartilage: fibrocartilage

Description: Matrix similar to but less firm than that in hyaline cartilage; thick collagen fibers predominate.

Function: Tensile strength with the ability to absorb compressive shock.

Location: Intervertebral discs; pubic symphysis; discs of knee joint. Chondrocytes in lacunae Intervertebral discs Collagen fiber

Photomicrograph: Fibrocartilage of an intervertebral disc (125x). Special staining produced the blue color seen.

(j) Others: bone (osseous tissue)

Description: Hard, calcified matrix containing many collagen fibers; osteocytes lie in lacunae. Very well vascularized. Central Bone supports and Function: canal protects (by enclosing); provides levers for the muscles Lacunae to act on; stores calcium and other minerals and fat; marrow inside bones is the site for blood cell formation (hematopoiesis). Lamella Location: Bones

Photomicrograph: Cross-sectional view of bone (125x).

(k) Others: blood Description: Red and white blood cells in a fluid matrix (plasma). Plasma

Function: Transport of respiratory gases, nutrients, Neutrophil wastes, and other substances.

Location: Contained within blood vessels. Red blood cells

Lymphocyte

Photomicrograph: Smear of human blood (1860x); two white blood cells (neutrophil in upper left and lymphocyte in lower right) are seen surrounded by red blood cells.

EXAMPLES

Can you name? First, the tissue type Second, where in the body the tissue is found

Connective Tissue

What kind of tissue does this represent? Loose (areolar) connective tissue

Where in the body can you find this tissue? delicate thin layers between tissues; present in all mucous membranes Connective Tissue

What kind of tissue does this represent? Adipose tissue

Where in the body can you find this tissue? fat Connective Tissue

What kind of tissue does this represent? Dense connective tissue

Where in the body can you find this tissue? tendons; ligaments Connective Tissue

What kind of tissue does this represent? Hyaline cartilage

Where in the body can you find this tissue? nose; ends of long bones; ribs Connective Tissue

What kind of tissue does this represent? Elastic cartilage

Where in the body can you find this tissue? outer ear; epiglottis Connective Tissue

What kind of tissue does this represent? Fibrocartilage

Where in the body can you find this tissue? between vertebrae; knee joints; pubic joint Connective Tissue

What kind of tissue does this represent? Bone

Where in the body can you find this tissue? skeletal system Connective Tissue

What kind of tissue does this represent? Blood

Where in the body can you find this tissue? bloodstream Muscle Tissue

• characterized by properties that allow movement.

• muscle cells are excitable (=respond to a stimulus) + contractile (=can shorten and generate a pulling force) • some muscle movement is voluntary (=under conscious control) other involuntary (ie contraction of your pupil) • classified into 3 types according to structure and function Muscle Tissue

• Skeletal muscle makes possible

locomotion, facial expressions, posture, and other voluntary movements (40% body mass), participate in thermal homeostasis: myocyte (from myoblasts, mesoderm) and their numbers remain relatively constant throughout life. Arranged in bundles surrounded by connective tissue. striated (due to the regular alternation of the contractile proteins actin and myosin), with many nuclei squeezed along the membranes (as a result of the fusion of the many myoblasts to form each long muscle fiber). Muscle Tissue

Skeletal muscle cells (fibers), with cross- striations and peripheral nuclei. Muscle Tissue

Higher power of skeletal muscle for details of cross-striations. Notice thin Z discs and heavy A bands. From one Z disc to the next is a sarcomere, the unit of muscle contraction. In the upper muscle cell notice shadowy myofibrils running longitudinally. Muscle Tissue

EM of several myofibrils running longitudinally through skeletal muscle cell. Between individual myofibrils lie the mitochondria (M) and glycogen (G) of the cytoplasm. Within each myofibril are the typical striations: A= A band; I= I band; Z= Z line; and H= H band. The banding is formed by the arrangement of myosin and actin filaments. Muscle Tissue

• Smooth muscle responsible for involuntary movements in the internal organs. It forms the contractile component of the digestive, urinary, and reproductive systems as well as the airways and arteries. Each cell is spindle shaped with a single nucleus and no visible striations Muscle Tissue

Smooth muscle - long, slender central nuclei, lying within narrow, fusiform cells that lie parallel to each other in a smooth arrangement. (Muscle cells are often referred to as muscle fibers because of their narrowness and length.) Muscle Tissue

Smooth muscle - with cells more separated so as to see their extent and shape better, and the central position of their nuclei. A loose, irregular connective tissue (endomysium) lies between the cells. Nuclei seen in this c.t. belong to fibroblasts mainly. Muscle Tissue

Smooth muscle with wrinkled nuclei due to contraction of cells. Muscle Tissue

EM of smooth muscle showing typical "hairy" look of primarily filaments in the cytoplasm. Part of the cytoplasm is clear of filaments and shows mitochondria and polyribosomes. The cell membrane is at the lower right of the field and shows a few pinocytotic vesicles toward the extreme right. The left-hand extent of that same membrane seems darker and denser: probably a plaque, where filaments attach. The fuzzy density just outside the cell membrane is the basal lamina. Muscle Tissue

• Cardiac muscle (contractile walls of the

heart), cardiomyocytes, also striated single cells typically with a single centrally located nucleus, contract on their own intrinsic rhythms without any external stimulation and attach to one another with specialized cell junctions = intercalated discs (both anchoring junctions and gap junctions)  long, branching cardiac muscle fibers that are, essentially, a mechanical and electrochemical syncytium with synchronized actions that pumps blood under involuntary control. Muscle Tissue

Cardiac muscle with cross-striations, dark intercalated discs, and centrally located nuclei. Notice too that the nuclei are stubby in appearance, and that they lie in a rather granular cytoplasm. Some of the intercalated discs form a straight line across muscle fibers; others make a step-like arrangement. Muscle Tissue

EM of intercalated disc between the ends of two cardiac muscle cells. Both desmosomes (1) and fasciae adheretes (2) are identified. Notice mitochondria and glycogen particles lying between myofibrils. Muscle Tissue

Another view of cardiac muscle showing wavy connective tissue (endomysium) between muscle cells. Also, notice capillaries with r.b.c.'s; muscle is a highly vascularized tissue. Some yellow granular cytoplasm can be seen inside the lower muscle cells, where myofibrils are parted. This picture also gives some indication of the branching of cardiac fibers. The 4 Types of Tissues: muscle

The 4 Types of Tissues: nervous

Nervous Tissue

• excitable and capable of sending and receiving electrochemical signals that provide the body with information. • 2 main classes of cells: neuron (propagate information via electrochemical impulses, called action potentials, which are biochemically linked to the release of chemical signals) and neuroglia (play an essential role in supporting neurons and modulating their information propagation) Nervous Tissue

Neurons = distinctive morphology  role as conducting cells, with 3 parts. The cell body includes most of the cytoplasm, the organelles, and the nucleus. Dendrites branch off the cell body and appear as thin extensions. A long “tail,” the axon, extends from the neuron body and can be wrapped in an insulating layer known as myelin, which is formed by accessory cells. The synapse is the gap between nerve cells, or between a nerve cell and its target, for example, a muscle or a gland, across which the impulse is transmitted by chemical compounds known as neurotransmitters. Neurons categorized: multipolar, bipolar and unipolar. When a neuron is sufficiently stimulated, it generates an action potential that propagates down the axon towards the synapse. If enough neurotransmitters are released at the synapse to stimulate the next neuron or target, a response is generated. Nervous Tissue

The second class of neural cells: neuroglia or glial cells, (from the Greek word for glue).

Astrocyte cells, (star shape) abundant in the CNS, have many functions: regulation of ion concentration in the intercellular space, uptake and/or breakdown of some neurotransmitters, and formation of the blood-brain barrier. Microglia protect the nervous system against infection (related to macrophages). Oligodendrocytes produce myelin in the CSN (brain and spinal cord) while the Schwann cell produces myelin in the peripheral nervous system [email protected] [email protected]