Mature Connective Tissues Bone is a connective tissue

Mature Connective Tissues • Bone is a connective tissue with a calcified intracellular matrix. In the right circumstances, the chondrocytes of cartilage are capable of turning into the osteocytes that make up bone tissue. – We will study bone in detail in Chapter 6.

Mature Connective Tissues • Cartilage – Hyaline cartilage – Fibrocartilage – Elastic cartilage consists of chondrocytes located in a threadlike network of elastic fibers. • It makes up the malleable part of the external ear and the epiglottis.

Mature Connective Tissues • Blood and lymph are atypical liquid connective tissues that we will study in Chapters 19 and 22. As we have seen, blood has many cells. It also has fibers (such as fibrin that makes blood clot).

Summary of Mature Connective Tissues

Muscle and Nerve Tissues • Muscles and nerve tissues are the last of the 4 basic tissue types. Neurons and muscle fibers are considered excitable cells because they exhibit electrical excitability, the ability to respond to certain stimuli by producing electrical signals such as action potentials. – Action potentials can propagate (travel) along the plasma membrane of a neuron or muscle fiber due to the presence of specific voltage-gated ion channels. • Each will be studied in depth in upcoming chapters.

Muscle and Nerve Tissues

Epithelial Membranes • Combining two tissues creates an organ. However, most of the organs and all of the organs systems studied this year contain all 4 basic types of tissues. – Epithelial membranes are the simplest organs in the body, constructed of only epithelium and a little bit of connective tissue.

Epithelial Membranes • Epithelial membranes = epithelium + connective tissue – Mucous membranes – Serous membranes – Cutaneous membrane = skin • Skin is not a simple organ. We will study the integument as our first organ system in the next chapter.

Epithelial Membranes • Mucous membranes line “interior” body surfaces open to the outside: – Digestive tract – Respiratory tract – Reproductive tract • Serous membranes line some internal surfaces: – Parietal layer next to body wall – Serous fluid between layers – Visceral layer next to organ

Epithelial Membranes • Skin as a cutaneous membrane is studied in Chapter 5.

Synovial Membranes • Synovial membranes enclose certain joints and are made of connective tissue only.

Glands • Epithelial glands are another example of simple organs – Glands that secrete their contents directly into the blood are called endocrine glands. – Glands that secrete their contents into a lumen or duct are called exocrine glands. • We will look at some common types of exocrine glands (endocrine glands are studied in Chapter 18. )

Exocrine Glands • Exocrine glands secrete substances through ducts to the surface of the skin or into the lumen of a hollow organ. – Secretions of the exocrine gland include mucus, sweat, oil, earwax, saliva, and digestive enzymes. • Examples of exocrine glands are sudoriferous (sweat) glands.

Exocrine Glands • The two criteria for categorizing multicellular glands according to structure: – Whether the ducts are branched or unbranched… • In a simple gland the duct does not branch. • In a compound gland the duct branches. – … and the shape of the secretory portion of the gland • Tubular glands have tubular secretory parts. • Acinar glands have rounded secretory parts. • Tubuloacinar glands have features of both.

Exocrine Glands unbranched duct (simple) branched duct (compound)

Exocrine Glands tubular shape in secretory portion

Exocrine Glands acinar or alveolar (grape-like) shape in secretory portion

Exocrine Glands • The criteria for categorizing multicellular glands according to function is based on the manner in which the gland secretes its product from inside the cell to the outside environment. – Merocrine – Apocrine – Holocrine

Exocrine Glands • Merocrine secretion is the most common manner of secretion. – The gland releases its product by exocytosis and no part of the gland is lost or damaged.

Exocrine Glands • Apocrine glands “bud” their secretions off through the plasma membrane, producing membrane-bound vesicles in the lumen of the gland. – The end of the cell breaks off by “decapitation”, leaving a milky, viscous odorless fluid. – This type of sweat only develops a strong odor when it comes into contact with bacteria on the skin surface.

Exocrine Glands • Holocrine secretions are produced by rupture of the plasma membrane, releasing the entire cellular contents into the lumen and killing the cell (cells are replaced by rapid division of stem cells. ) – The sebaceous gland is an example of a holocrine gland, because its secretion (sebum) is released with remnants of dead cells.

Tissue Repair • A convenient way to refer to certain cells when discussing a tissue is Parenchyma or Stroma. – The parenchymal cells of an organ consist of that tissue which conducts the specific function of the organ. Cells of the stroma are everything else— connective tissue, blood vessels, nerves. • For example: The parenchyma of the heart is cardiac muscle cells. The nerves, intrinsic blood vessels, and connective tissue of the heart comprise the stroma.

Tissue Repair • Parenchyma is interesting. Because organspecific function usually centers on parenchymal cells (“how’s your heart working? ”), histological and physiological descriptions of the tissues of an organ often emphasize parenchyma. • Unfortunately, stroma is commonly ignored as just boring background tissue. No organ, however, can function without the mechanical and nutritional support provided by the stroma.

Tissue Repair • When tissue damage is extensive, return to homeostasis depends on active repair of both parenchymal cells and stroma. – Fibroblasts divide rapidly. – New collagen fibers are manufactured. – New blood capillaries supply materials for healing. • All of these processes create an actively growing connective tissue called granulation tissue.

Aging and Tissues • Tissue heals faster in young adults. • Surgery of a fetus normally leaves no scars. • Young tissues have a better nutritional state, blood supply, and higher metabolic rate. • Extracellular components also change with age. • Changes in the body’s use of glucose, collagen, and elastic fibers contribute to the aging process.

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