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CHAPTER 4: THE TISSUE LEVEL OF ORGANIZATION

DEFINITION OF TISSUE: A tissue is a group of similar cells that usually have similar embryological origin, and specialized for a particular function. The science that deals with the study of tissues is called histology. Pathologists are physicians, who specialize in laboratory studies of cells and tissues, aid other physicians in diagnosing; they also perform autopsies and biopsies.

TYPES OF TISSUES & THEIR ORIGIN: TYPES: Depending on their structure and function, tissues are classified into 4 types: • Epithelial tissue: covers the body surfaces; lines hollow

organs, body cavities, and ducts; forms glands. • Connective tissue: protects and supports the body and its

organs; binds organs together, stores energy reserve as fats, and provides immunity.

• Muscle tissue: responsible for movement and generation of heat (thermogenesis).

• Nervous tissue: initiates and transmits nerve impulses that help coordinate body activities.

ORIGIN: All tissues develop from one or more of the 3 primary germ layers – ectoderm, mesoderm, and endoderm. [Learn from Table 29.1, p 1112!]

CELL JUNCTIONS: Points of contact between adjacent plasma membranes; 3 types serve distinct functions: [Fig 4.1, p 109]

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• Tight Junctions: form fluid-filled seals between cells – common among epithelial cells that line the stomach, intestine, and urinary bladder.

• Anchoring Junctions: common in tissues subject to friction and stretching – epidermis, muscle of heart, lining of GI tract, etc. Examples: desmosomes, hemidesmosomes, and adherens junctions

Communicating Junctions: allow rapid action potentials from one cell to the next in some parts of the nervous system, and in the muscle of the heart and GI tract. Example: gap junctions

EPITHELIAL TISSUES: General Features: a. Closely packed cells with little extracellular material. b. Arranged in sheets – in either single or multiple layers. c. Apical surface (free surface) and a basal surface

attached to a basement membrane. d. Many cell junctions are present, providing secure

attachments among cells. e. Avascular; exchange of materials between epithelium

and adjacent connective tissue (CT) is by diffusion. f. Nerve supply g. High capacity for renewal (high mitotic rate)

Functions: Protection, filtration, lubrication, secretion, digestion, absorption, transportation, excretion, sensory reception, & reproduction Types: [Table 4.1, pp. 113-117) 1. On the basis of cell layers – (a) simple (one layer), (b)

stratified (several), and (c) pseudostratified (one layer that appears several)

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2. On the basis of cell shapes – (a) squamous (flat), (b) cuboidal (cube-like), (c) columnar (rectangular), and (d) transitional (variable)

[Arrangement of covering and lining epithelium reflects its location and function.] [Fig. 4.3, p 111] A. Simple Squamous Epithelium: single layer of flat,

scale-like cells: Location: parts of the body that are subject to little wear and tear, e.g., endothelium – lines the heart and blood vessels, mesothelium – lines the thoracic and abdominopelvic cavities and covers the organs within them. Functions: adapted for diffusion and filtration (lungs and kidneys); in serous membrane – osmosis and secretion.

B. Simple Cuboidal Epithelium: single layer of cube-shaped cells: Location: covering of ovaries; in kidneys and eyes; lining of some glandular ducts Functions: secretion (mucus, perspiration, enzymes, and hormones) and absorption (intake of fluids or other substances by cells)

C. Simple Columnar Nonciliated Epithelium: single layer of nonciliated rectangular or column-like cells: Location and Functions: lines most of the GI tract, where some specialized cells have microvilli (for absorption), some secrete enzymes, some mucus (e.g., goblet cells), and some hormones (e.g. enteroendocrine cells).

D. Simple Columnar Ciliated Epithelium: single layer of ciliated rectangular cells.

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Location: a few portions of the respiratory tract, uterine tubes (Fallopian tubes), uterus, some paranasal sinuses, and the central canal of the spinal cord. Function: moves fluid or particles along a passageway by ciliary action.

E. Pseudostratified Columnar Epithelium: only one layer, but gives the appearance of many. Location: part of male urethra and auditory tubes, ciliated variety in the most part of the upper respiratory tract. Functions: secretion and movement of mucus by ciliary action.

F. Stratified squamous Epithelium: several layers of cells in which the top layer is flat. Location: Keratinized variety: outer layer of skin (keratin, a

protein that makes skin waterproof and resistant to friction, and helps repel bacteria); some part of mucous membrane of tongue.

Nonkeratinized variety: lines the mouth, pharynx, esophagus, anal canal, and vagina.

Function: Protection G. Stratified Cuboidal Epithelium: several layers of

cells in which the top layer is cube-shaped. Location: ducts of adult sweat glands and parts of male urethra Function: Protection

H. Stratified Columnar Epithelium: several layers of cells in which the top layer is rectangular. Location: portions of male urethra and large excretory ducts of some glands Function: protection and secretion

I. Transitional Epithelium: Several layers of cells whose appearance is variable.

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Location: lines urinary bladder and portions of ureter and urethra. Function: capable of stretching and permits distension of an organ.

J. Glandular Epithelium: [Table 4.2, p 119] A gland may be a single cell or a mass of epithelial cells adapted for secretion. Endocrine glands (do not have any ducts) secrete hormones and they are carried by blood to their target cells. Exocrine (exo = outside; crine = secretion) glands (e.g., sweat, sebaceous, digestive glands) secrete their products into ducts that empty at the surface of covering and lining epithelium or onto a free surface. Structural Type: two types, unicellular and multicellular. Functional Type: based on whether the secretion is a product of a cell or consists of entire or partial glandular cells themselves: [Fig 4.5, p 121] (i) Holocrine (holo = total) glands: accumulate

secretory product in the cytosol; when the cell dies, it and its products are discharged as the glandular secretion (e.g., sebaceous gland).

(ii) Merocrine (mero = a part) glands: form the secretory products and discharge it by exocytosis (e.g., most exocrine glands, such as salivary glands).

(iii) Apocrine (apo = from) glands: accumulate their secretory product at the apical surface of the secreting cell; that portion then pinches off from the rest of the cell to form the secretion; the remaining part of the cell repairs itself and repeats the process (e.g., mammary glands).

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CONNECTIVE TISSUE: [Fig 4.6, p 122] Most abundant tissue in the body:

General Features: 1. It consists of 3 basic elements: cells, ground

substance, and fibers (the latter two combine to form the matrix.)

2. Matrix is abundant with relatively few cells. 3. Connective tissues do not occur on free surfaces. 4. Highly vascular (except cartilage) [unlike epithelium] 5. Nerve supply except for cartilage. 6. Matrix of CT may be fluid, semifluid, fibrous, or

calcified, usually secreted by CT cells and adjacent cells and determines the tissue quality.

Cells of Connective Tissue: Derived from Mesenchyme 1. Immature cells have names that end in –blast (e.g.,

fibroblast, chondroblast, osteoblast, etc) while mature cells have names that end in –cyte (e.g., fibrocyte, chondrocyte, and osteocyte).

2. Most mature cells have reduced capacity for mitosis and matrix formation and are mostly involved in maintaining the matrix.

TYPES OF CELLS FOUND IN VARIOUS CTs:

a. Fibroblasts (secrete fibers and matrix) b. Macrophages (or histiocytes – developing from

monocytes) c. Plasma cells (derived from B-lymphocytes – secrete

antibody) d. Mast cells – derived from basophils, secrete histamine e. Adipocytes (fat calls –store energy in the form of fat) f. White blood cells (leucoytes – neutrophils, eosiniphils,

basophils, lymphocytes, and monocytes).

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CONNECTIVE TISSUE MATRIX: EXTRACELLULAR SUBSTANCE OF CONNECTIVE TISSUE: Matrix: it contains protein fibers embedded in a fluid, gel, or solid ground substance. The latter includes a number of large molecules, adhesion proteins. Normally, most cells within a tissue remain in place, anchored to other cells, basement membranes, and connective tissues (exceptions are phagocytes and embryonic cells for differentiation and growth).

Ground Substance: The following substances are found: Hyaluronic acid, chondroitin sulfate, dermatan sulfate, keratan sulfate, and hydroxyapatite

Fibers: provide strength and support for tissues. • Collagen (colla = glue) fibers (composed of protein

collagen) – found in skin, blood vessels, tendons, ligaments, etc.

• Elastic fibers (consist of molecules of a protein called elastin surrounded by a glycoprotein called fibrillin, which is essential to the stability of an elastic fiber) – plentiful in skin, blood vessel walls, and lung tissue.

• Reticular (reticul = net) fibers (formed of collagen & glycoprotein) – form the basement membranes and framework (stroma) of many soft organs.

CLASSIFICATION OF CONNECTIVE TISSUES: [Table 4.3, p 124; Table 4.4, pp. 126-131] Because of diversity of cells, ground substance, and fibers and the differences of their relative proportions, it is difficult to classify connective tissues. The separation of connective tissues into categories is not always clear-cut. I. Embryonic Connective Tissue

A. Mesenchyme B. Mucous Connective Tissue

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II. Mature Connective Tissue A. Loose Connective Tissue

Areolar connective tissue Adipose tissue Reticular connective tissue

B. Dense Connective Tissue 1. Dense regular connective tissue 2. Dense irregular connective tissue 3. Elastic connective tissue

C. Cartilage 1. Hyaline cartilage 2. elastic cartilage 3. Fibrocartilage

D. Bone or Osseous Tissue E. Blood Tissue (Vascular Tissue) F. Lymph

I. EMBRYONIC CT: primarily present in the embryo or fetus. A. Mesenchyme: found exclusively in the embryo; tissue from which

other connective tissues arise eventually. B. Mucous CT (Wharton’s jelly): found in the umbilical cord of the

fetus, where it gives support. [Thomas Wharton, English anatomist (1614-1673)]

II. MATURE CT: exists in newborn, has cells differentiated from mesenchyme; does not change after birth. A. Loose CT: fibers loosely woven and there are many cells.

1. Areolar CT: 3 types of fibers, several types of cells, and a semifluid ground substance. Location: subcutaneous layer, mucus membrane, around blood vessels, nerves, and body organs. Function: lends strength, elasticity, & support.

2. Adipose Tissue: adipocytes, specialized for storage of triglycerides.

Location: subcutaneous layer, around organs, and in yellow bone marrow.

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Function: reduces heat loss through skin (insulates), serves as an energy reserve, supports, protects, and generates heat to help maintain proper body temperature in newborns (brown fat)

3. Reticular CT: fine interlacing reticular fibers and reticular cells.

Location: Liver, spleen, and lymph nodes. Function: It forms stroma of organ and binds together smooth muscle tissue cells.

B. DENSE CT: contains more numerous and thicker fibers but considerably fewer cells than loose CT.

1. Dense Regular CT: contains bundles of collagen fibers and fibroblasts.

Location: forms tendons (attach muscle to bone), most ligaments (attach bone to bone), and aponeurosis (sheet-like tendons – attach muscle to muscle or muscle to bone). Function: provides strong attachment between various

structures. 2. Dense Irregular CT: randomly arranged collagenous fibers

and a few fibroblasts. Location: fasciae, dermis of skin, periosteum, joint capsules around organs, heart valves. Function: provides strength.

3. Elastic CT: formed of elastic fibers and fibroblasts. Location: lungs, walls of arteries, trachea, true vocal cords, bronchial tubes, and some ligaments. Function: allows stretching of various organs.

C. CARTILAGE: jelly-like matrix (chondroitin sulfate) containing collagenous elastic fibers and chondrocytes in spaces in the matrix called lacunae; surrounded by perichondrium; no blood vessels or nerves (except in perichondrium); strength of cartilage is due to collagen fibers and its resilience is due to chondroitin sulfate.

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Hyaline Cartilage: most abundant type, fine collagen fibers embedded in gel-like matrix.

Location: embryonic skeleton, at the end of bone (articular cartilage), in the nose, and respiratory structures.

Function: flexible – allows movements at joints and provides support.

Fibrocartilage: bundles of collagen in its matrix, no perichondrium, strongest of three type of cartilage. Location: pubic symphysis, intervertebral discs, and menisci. Function: provides support.

Elastic Cartilage: thread-like network of elastic fibers within the matrix. Location: epiglottis, auditory tubes, and external ear. Function: supports and maintains shape.

D. BONE (OSSEOUS TISSUE): Matrix containing mineral salts, and collagenous fibers and cells (osteocyts in lacunae); surrounded by periosteum; calcium salts (hydroxyapatite) responsible for bones’ hardness and collagen fibers for its great strength.

Function: supports, protects, helps provide movement, stores minerals, and houses blood-forming tissue (hemopoietic tissue).

E. BLOOD (VASCULAR TISSUE): Liquid matrix (plasma) and formed elements (erythrocytes, leukocytes, and thrombocytes). Function: transport, phagocytosis, allergic reactions, immunity, and clotting.

MEMBRANES: The combination of an epithelial layer and an underlying connective tissue layer constitutes an epithelial membrane. There are 4 kinds: mucous, serous, cutaneous, and synovial membranes. [Fig. 4.7, p 133]

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1. Mucous Membranes: line cavities that open to the exterior, e.g., GI tract: a. Epithelial layer of mucous membrane acts as barrier to

pathogens and trapping surface for particles. b. Lamina propria – connective tissue layer.

2. Serous Membrane or Serosa (e.g., pleura, pericardium, and peritoneum): lines body cavity that does not open directly to the exterior, and covers the organs that lie within the cavity.

a. Consists of parietal and visceral portions. b. Epithelial layer secretes a lubricating serous fluid

that reduces friction between organs and the walls of cavities in which they are located.

3 Cutaneous Membrane: the skin 4 Synovial Membranes: line joint cavities, bursae, and

tendon sheaths and do not contain epithelium; secrete a lubricationg synovial fluid.

EXTRACELLULAR FLUID (ECF): It is fluid that is external to all body cells; it provides a medium for dissolving and mixing solutes, transporting substances, and carrying out chemical reactions. Interstitial (Intercellular) Fluid: a subdivision of ECF, filling the interstitial spaces between cells in tissue. Plasma: a subdivision of ECF – the liquid portion of blood in blood vessels. Lymph: a subdivision of ECF in the lymphatic capillaries, vessels, and ducts.

MUSCLE TISSUE (Table 4.5, pp. 135-136]

Consists of fibers (cells) that are modified for contraction, and thus provide motion, maintenance of posture, and heat production.

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3 Types:

1. Skeletal muscle tissue: attached to bones, striated, and voluntary.

2. Cardiac muscle tissue: most of the heart wall, striated, autorhythmic, and involuntary; pumps blood to all parts of the body.

3. Smooth (visceral) muscle tissue: involuntary, non-striated, found in the walls of hollow internal structures; provides motion (propulsion of food, contraction of gall bladder, and urinary bladder, etc.).

NERVOUS TISSUE: [Table 4.6, p 137]

Composed of two principal kinds of cells: neurons (nerve cells), constituting about 10% of neural tissue and neuroglia (protective and supporting cells) constituting about 90% of neural tissue.

Neurons: Consist of cell body and two types of processes – axons and dendrites; sensitive to stimuli, convert stimuli into nerve impulses and conduct them to other neurons, muscle fibers, or glands. Neuroglia: Protect and support neurons; often sites of tumor (glioma). TISSUE REPAIR: RESTORING HOMEOSTASIS

BASIC CONCEPTS: 1. Tissue repair means replacement of damaged or destroyed

cells by healthy ones. 2. Parenchyma cells form the organ’s functioning part. 3. Stroma is the supporting connective tissue that makes the

framework of the organ; new cells originate from the stroma by cell division.

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4. Restoration of an injured organ or tissue to normal depends upon whether parenchymal or stromal cells are active in the repair:

a. Parenchymal repair results in return to a greater degree of structural and functional normality – tissue regeneration.

b. Stromal repair (by fibroblasts of stroma) replaces parenchyma with scar tissue.

5. Adhesions, sometimes, result from scar tissue formation called fibrosis, cause abnormal joining of adjacent tissues (especially in the abdomen and sites of previous surgery).

6. The cardinal factor in tissue repair is the capacity of parenchymal tissue to regenerate – it depends on the ability of parenchymal cells to replicate quickly:

a. During embryonic development muscle and nerve tissues become highly differentiated and lose their capacity for mitosis.

b. Epithelial and connective tissues generally have a continuous capacity for renewal.

REPAIR PROCESS: • If injury is superficial, tissue repair involves pus removal (if

present), scab formation, and parenchymal regeneration. • If damage is extensive, granulation tissue (growing

connective tissue) is involved. CONDITIONS AFFECTING REPAIR: • Nutrition: important to tissue repair; various vitamins (A,

some B, C, D, E, and K) and a protein-rich diet are needed. • Proper blood circulation is essential. • Tissues of young people repair more rapidly and efficiently;

the process slows down with aging. CERTAIN TERMS THAT ARE IMPORTANT:

SOMATIC DEATH: Death of the body as a whole. NECROSIS: Cellular or tissue death within the body.

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GANGRENE: Massive necrosis of tissues accompanied by an invasion of microorganisms that live on decaying tissue. BIOPSY: Removal of a section of living tissue for examination TISSUE TRANSPLANTATION:

Autotransplants: from one place on a person’s body and moved to another place (in bypass surgery); it is very successful. Isotransplants: between individuals who are closely related; identical twins have the best acceptance. Homotransplants: between individuals of the same species. Heterotransplants: between two different species (e.g., between baboon and human); low acceptance percentages because of a tissue-rejection reaction.

CHAPTER 6: THE SKELETAL SYSTEM: BONE TISSE OVERVIEW: FUNCTIONS HOMEOSTASIS HISTOLOGY

BONE

TISSUE FRACTURES OSSIFICATION I. INTRODUCTION:

Bone (osseous tissue) forms most of the skeleton, the framework that supports and protects our organs and allows us to move.

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II. PHYSIOLOGY: Bone tissue and skeletal system perform many functions: 1. Provide support of soft tissue and attachment sites for

muscles, creating a framework for our body. 2. Protection from injury. 3. Movement: bones provide leverage for muscle

contraction. 4. Mineral homeostasis: minerals are stored in bones and can

be mobilized when needed elsewhere in the body. 5. Hemopoiesis: occurs in red bone marrow. 6. Storage of energy: lipids in yellow bone marrow.

III. ANATOMY: [Structure of bone: to be discussed in the lab & lecture]

IV. HISTOLOGY: A. Widely separated cells surrounded by large amount of

matrix. B. Four principal types of cells in bone tissue:

osteoprogenitor (osteogenic) cells, osteoblasts, osteocytes, and osteoclasts. [Fig 6.2, p 174]

C. Matrix: contains 25% water, 25% protein fibers, and 50% crystallized mineral salts – primarily hydroxyapatite and some calcium carbonate. The mineral salts are deposited in a framework (osteoid) of collagen fibers by a process called mineralization or calcification. Mineral salts confer hardness on bone while collagen fibers give bone its great tensile strength.

D. Depending on the size and distribution of the spaces between hard components of bone, the regions of a bone may be characterized as compact or spongy. [To be discussed in the lab and lecture; Fig. 6.3, p 176] 1. Compact Bone: consists of osteons (Haversian

Systems); osteons contain blood vessels, lymphatic vessels, nerves, and osteocytes along with the calcified matrix.

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2. Spongy (Cancellous) Bone: does not contain osteons; forms most of the structure of short, flat, and irregular bones’ and the epiphyses of long bones; it is light and supports and protects the red bone marrow.

3. Blood and Nerve Supply: Vessels are needed to supply the bone tissues with both nutrients and waste disposal through a number of interconnecting channels in the bone matrix. [Fig 6.4, p 177] (i) Nutritional artery passes through a nutrient

canal and sends branches in to the central (Haversian) canals to provide for osteocytes.

(ii) Artery continues into medullary cavity to supply blood for marrow and cells via epiphyseal artery.

(iii) Periosteal arteries pass through Volksmann’s canal to a multitude of vessels that supply the outer compact bone region.

Nerves follow vessels into bone tissue and periosteum where they sense damage and transmit pain messages.

V. BONE FORMATION: OSSIFICATION (OSTETEOGENESIS): A. Ossification begins when messenchymal cells become

transformed into osteoprogenitor (osteogenic) cells, which then undergo cell division giving rise to cells that differentiate into osteoblasts. Osteoblasts do not undergo mitosis but later change into osteocytes. Osteoclsts are also formed (from the fusion of as many as 50 monocytes).

B. The process begins during the 6th or 7th week of embryonic life and continues throughout adulthood. There are two types of ossification that do not lead to the differences in the structure of mature bones, they are simply different methods: (1) intramembranous

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ossification (gives rise to flat bones) and (2) endochondral ossification (gives rise to the rest of bones). 1. Intramembranous Ossification: occurs within fibrous

membranes of the embryo and the adult: [See Fig. 6.5, p 179] a. An ossification center forms from messenchymal

cells as they convert to osteoblasts and lay down osteoid matrix.

b. The matrix surrounds the cell and then calcifies, as the osteoblast becomes an osteocyte.

c. The calcifying matrix centers join to form bridges of trabeculae that constitute spongy bone with red bone marrow between.

d. The periosteum first forms a collar of spongy bone that is replaced by compact bone.

2. Endochondral (intracartilaginous) Ossification: refers to the formation of bone within a hyaline cartilage model: [See Fig. 6.6, p 180]: a. Mesenchymal cells differentiate into chondroblasts

that form the hyaline cartilage model. b. The cartilage model is enclosed by a connective

tissue called the perichondrium. c. A blood vessel enters the inner layer of the

perichondrium and stimulates certain cells (osteogenic cells) to enlarge and become osteoblasts.

d. These osteoblasts begin to make bone around the diaphysis of the cartilage model.

e. The perichondrium is now called the periosteum. f. Within the diaphysis, i.e., primary ossification

center, the chondrocytes get larger and eventually burst. This bursting of chondrocytes release materials that change the pH of the surrounding matrix and cause the matrix to calcify.

g. Cavitation of the hyaline cartilage within the cartilage model: it grows by interstitial and

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appositional growth. Chondrocytes in the mid-region calcify the matrix’ vacated lacunae form small cavities; osteoblasts in the perichondrium produce periosteal bone collar.

h. Once calcification occurs, nutrients cannot easily reach the remaining cells and they die. The dying of these cells cause the cartilage to degenerate, thereby, leaves spaces within the matrix. Blood vessels now invade these spaces and enlarge them. These spaces form the marrow cavity.

i. Blood vessels now enter the epiphyses that are now called secondary ossification centers.

j. The diaphysis and epiphyses continue to ossify toward one another, leaving a cartilage between them called epiphyseal plate, which remains as cartilage as long as bone growth in length is occurring.

k. When lengthening of bone is complete, the epiphyseal plate ossifies and becomes epiphyseal line.

l. The hyaline cartilage covering the articulating end of the bone remains unossified and is called articular cartilage.

[Appositional Growth: Growth due to surface deposition of material, as in the growth in diameter of a cartilage and bone (also called exogenous growth). Interstitial Growth: Growth from within, as in the growth of cartilage and bone (also called endogenous growth).]

VI. BONE GROWTH: A. Growth in Length: [See Fig. 6.7, p 182]

1. To understand how a bone grows in length, knowledge of the structure of epiphyseal plate is important.

2. The epiphyseal plate has 4 zones: (a) the zone of resting cartilage, (b) the zone of proliferating

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cartilage, (c) the zone of hypertrophic cartilage, and (d) the zone of calcified cartilage.

3. Because of the activity of the epiphyseal plate, the diaphysis of a bone increases in length by interstitial growth.

B. Growth in Thickness (and Diameter): [See Fig. 6.8, p 183]

Bone grows in diameter only by appositional addition of new bone tissue by osteoblasts around the outer surface of the bone and to a lesser extent internal bone dissolution by osteoclasts in the bone cavity.

B. Hormonal Regulation of Bone Growth: 1. Prior to puberty human growth hormone (hGH)

and insulin-like growth factor (IGF) stimulate bone deposition and changes during growth. Other hormones that are necessary for bone growth are thyroid hormones, T3, T4, calcitonin, and parathyroid hormone. Variation from normal levels of these hormones can lead to either gigantism or dwarfism.

2. At puberty the sex hormones, estrogen and testosterone, stimulate sudden growth and modification of the skeleton to create the female and male forms respectively.

VII. BONE HOMEOSTASIS: A. Remodeling:

1. Remodeling is the ongoing replacement of old bone tissue by new one.

2. Old bone is constantly destroyed by osteoclasts, whereas new bone is constructed by osteoblasts.

B. Fracture and Repair of Bone: [See Fig. 6.10, p 187] 1. A fracture is any break in bone.

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2. Fracture repair involves: (a) formation of a clot called a fracture hematoma, (b) organization of the fracture hematoma into granulation tissue called a procallus (subsequently transformed into a fibrocartilaginous soft callus), (c) conversion of the fibrocartilaginous callus into the spongy bony (hard) callus, and finally (d) remodeling of the hard callus to nearly original form.

3. The types of fractures include partial, complete,

closed (simple), open (compound), comminuted, greenstick, spiral, impacted, displaced, nondisplaced, stress, Pott’s, and Colle’s. [See Fig. 6.9, p 185] [Learn the different types of fracture!]

C. Bone’s Role in Calcium Homeostasis: [See Fig. 6.11, p 188] 1. Bone is a major reservoir of calcium ions in the

body. The blood level of calcium ions is closely regulated due to calcium’s importance in cardiac, muscle, nerve, enzyme, and blood physiology.

2. An important hormone regulating calcium ion exchange between blood and bone is PTH (parathyroid hormone) from parathyroid glands – it increases the blood calcium level.

3. Calcitonin (CT) is another hormone (secreted from thyroid gland) that contributes to the blood calcium – it decreases the blood calcium level.

VIII. EXERCISE AND BONE: A. Within limits, bone has the ability to alter its strength in

response to mechanical stress by increasing deposition of mineral salts and production of collagen fibers.

B. Removal of mechanical stress weakens bone through demineralization and collagen reduction.

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C. Weight-bearing activities, such as walking or moderate weightlifting, help build and retain bone mass.

IX. AGING AND BONE TISSUE: A. Of 2 principal effects of aging on bone, the first is

the loss of calcium and other minerals from bone matrix, which may result in osteoporosis.

B. The second principal effect on the skeletal system is a decreased rate of protein synthesis, resulting in decreased production of matrix components (mostly collagen) and making bones more susceptible to fracture.

IX. DISORDERS: HOMEOSTATIC IMBALANCES A. Osteoporosis is a decrease in the amount and

strength of bone tissue owing to decrease in hormone output. In osteoporosis, bone resorption outpaces bone formation. [Fig 6.12, p 189]

B. Massive osteoclastic resorption and extensive bone formation due to osteoblastic activities characterize Paget’s disease. As a result there is an irregular thickening and softening of the bones and greatly increased vascularity, especially in bones of skull, pelvis, and limbs.

XII. MEDICAL TERMINOLOGY: [Osteoarthritis, Osteogenic sarcoma, Osteomyelitis, and Osteopenia] [Learn from p 190] Human body contains 1,200-1,400 g of calcium, over 99% of, which is present as bone minerals. Less than 1.5 g is present in the blood and blood calcium levels are maintained within 9-11 mg/100 ml of blood by the hormonal loop. Calcium is absorbed from the intestine under the control of Vitamin D metabolites. The daily requirement of calcium is 1200 mg during the time when bones are still growing and increasing in mass.

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CHAPTER 9: JOINTS (ARTICULATIONS)

DEFINITION: An articulation (joint) is a point of contact between two or more bones, between cartilage and bones, and between teeth and bones.

ARTHROLOGY: Scientific study of joints.

KINESIOLOGY: Study of motion of the human body.

The joint’s structure determines how it functions, allowing no movement, slight movement, or considerable movement. Support is lent to joints by ligaments and joint capsules, and by action of surrounding muscles. CLASSIFICATION OF JOINTS:

A. Structural: based on the presence or absence of joint cavity (sinovial cavity) and type of connective tissue. a. Fibrous joints b. Cartilaginous joints c. Sinovial joints

B. Functional: based on the degree of movement permitted. a. Synarthroses (immovable) b. Amphiarthroses (partially/slightly movable) c. Diarthroses (freely movable)

SYNARTHROSES: [See Fig. 9.1 - 9.2, pp. 260-261] • Suture: a fibrous joint composed of a thin layer of dense

fibrous connective tissue that unites skull bones, e.g., coronal suture.

• Gomphosis: a fibrous joint, in which a cone-shaped peg fits into a socket, e.g., root of a tooth in its socket attached by periodontal ligaments.

• Synchondrosis: a cartilaginous joint in which the connecting material is hyaline cartlage, e.g., epiphyseal plate.

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AMPHIARTHROSES: [See Fig. 9.1- 9.2] • Syndesmosis: a fibrous joint in which there is more

fibrous CT than in a suture, e.g., distal articulation between tibia and fibula.

• Symphysis: a cartilaginous joint in which the connecting material is a fibrocartilage, e.g., intervertebral disc and pubic symphysis.

[Hormones may affect joint flexibility (e.g., relaxin relaxes the pubic symphysis during childbirth).]

DIARTHROSES: [See Fig. 9.3, p 261]

A. STRUCTURE: • All diarthroses are synovial joints (because they all have

joint cavities). • Presence of articular cartilage and an articular capsule.

• Articular capsule surrounds a diarthrosis, enclosing the synovial cavity and uniting the articulating bones.

• Articular capsule is composed of two layers – outer fibrous capsule (may contain ligaments) and inner synovial membrane (secreting a lubricating and joint-nourishing synovial fluid, SF).

• Many diarthroses contain accessory ligaments (extracapsular and intracapsular), articular discs (menisci), and bursae.

• Torn cartilage (occurring frequently in the knees of athletes) is damage to articular discs. Removal of torn cartilage to prevent erosion and arthritis is usually accomplished by arthroscopy.

B. FACTORS AFFECTING MOVEMENT AT DIARTHROSES: • Structure or shape of the articulating bones. • Strength and tension of ligaments. • Arrangement and tension of muscles and tendons.

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• Apposition of soft parts. C. TYPES OF DIARTHROSES: [See Fig. 9.10, pp 269-270]

• Gliding (planar) joints: Articulating surfaces are flat and movement is either back-and-forth or side-to-side, e.g., joints between tarsals, and between carpals.

• Hinge joints: Convex surface of one bone fits into the concave surface of the other. Movement is primarily flexion or extension in a single plane (monoaxial or uniaxial), e.g., elbow joint, knee joint, etc.

• Pivot (trochoid) joint: A round or pointed surface of one bone fits into a ring formed by another bone and a ligament. Movement is rotational and monoaxial, e.g., when atlas rotates around the axis.

• Ellipsoidal (condyloid) joint: An oval-shaped condyle of one bone fits into an elliptical cavity of another bone. Movements are flexion-extension, abduction-adduction (biaxial) and circumduction, e.g., joint between the carpals and the radius.

• Saddle (sellaris) joint: contains one bone, the articular surface of which is saddle-shaped and another bone, the articular surface of which is shaped like a rider sitting on the saddle. Movements are flexion-extension and circumduction, e.g., joint between trapezium and metacarpal of the thumb.

• Ball-and-socket (spheroid) joint: Ball-shaped surface of one bone fits into the cup-like depression (socket) of another. Movements are flexion-extension, abduction-adduction, rotation, and circumduction, e.g., hip and shoulder joints

[LEARN TABLE 9.2, P 271: SUMMARY OF STRUCTURAL CATEGORIES AND FUNCTIONAL CHARACTERISTICS OF JOINTS]

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D. COMMON TYPES OF MOVEMENTS AT DIARTHROSES: [See Table 9.1, p 268; Fig. 9.4 - 9.8, pp. 263, 265-267] • Flexion: decreases the angle between articulating

bones. • Extension: increases the angle between articulating

bones. • Hyperextension: continuation of extension beyond

anatomical position. • Rotation: a bone moves in a single plane around a

longitudinal axis. • Circumduction: the distal end of a part of the body

moves in a circle. • Abduction: movement of a bone away from the midline

of the body. • Adduction: movement of a bone toward the midline of

the body.

E. SPECIAL MOVEMENTS AT DIARTHROSES: [See Fig. 9.9, p 267] Special movements occur at particular joints: • Elevation: Upward movement of a part of the body. • Depression: Downward movement of a part of the

body. • Protraction: Forward movement of the mandible or

shoulder girdle on a plane parallel to the ground. • Retraction: Movement of the protracted part of the

body backward on a plane parallel to the ground. • Inversion: Movement of the soles inward (medially) so

they face each other. • Eversion: Movement of the soles outward (laterally) so

that they face away from each other. • Dorsiflexion: Bending of the foot in the direction of the

dorsum (upper surface).

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• Plantar flexion: Bending of the foot in the direction of the plantar surface (sole).

• Supination: Movement of the forearm that turns the palm anteriorly or superiorly.

• Pronation: Movement of the forearm that turns the palm posteriorly or inferiorly.

[See Table 9.2, p 256: Summary of Movements at Synovial Joints]

F. SHOULDER AND KNEE JOINTS: [Fig 9.12, pp. 276-277; 9.15, p 283] 1. Shoulder (Glenohumeral) Joint: It is the juncture

between the head of the humerus and the scapular glenoid fossa. It is a ball-and-socket joint. It consists of: • Articular capsule • Coracohumeral ligament • Glenohumeral ligaments – 3 • Transverse humeral ligament • Glenoid labrum • Bursae – 4 (subscapular, subdeltoid, subacromial,

and subcoracoid) The shoulder joint has more freedom of movement than any other joint in the body. The movements permitted at this joint are flexion (humerus down forward), extension (humerus down backward), abduction (humerus drawn away from the midline), adduction (humerus drawn toward the midline), medial rotation, lateral rotation, and cicumduction.

2. Knee (Tibiofemoral) Joint: This joint is formed by the patella and femur and by the tibia and femur. It is the largest joint of the body. There are three joints – (a) an intermediate patellofemoral joint, (b) a lateral tibiofemoral joint, and (c) a medial tibiofemoral joint.

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The patellofemoral is a gliding joint, while the lateral and medial tibiofemoral are modified hinge joints. Anatomical Components of the Knee Joint: • Articular capsule • Medial and lateral patellar retinacula • Patellar ligament • Infrapatellar fat pad • Oblique popliteal ligament • Arcuate popliteal ligament • Medial (tibial) collateral ligament • Lateral (fibular) collateral ligament • Intracapsular ligaments

• Anterior cruciate ligament (ACL) • Posterior cruciate ligament (PCL)

• Articular discs (menisci) • Medial meniscus • Lateral meniscus

• Bursae (prepatellar, infrapatellar, suprapatellar) DISORDERS: HOMEOSTATIC IMBALANCES [pp. 285-286] A. Rheumatism: refers to any painful state of the supporting

structures of the body, such as, bones, ligaments, tendons, joints, and muscles.

B. Arthritis: refers to many different diseases – characterized by inflammation of joints and often accompanied by stiffness of adjacent structures: Rheumatoid arthritis: an autoimmune disease –

inflammation of the synovial membrane, causing swelling, pain, and loss of function.

Osteoarthritis: a degenerative joint disease, commonly called “wear-and-tear” arthritis – characterized by deterioration of articular cartilage and bone spur formation. It is noniflammatory and primarily affects weight-bearing joints.

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Gouty arthritis: also called chemical arthritis; sodium urate crystals are deposited in soft tissues of joints, causing inflammation, swelling, and pain. If untreated, bones at affected joints will eventually fuse, rendering the joints immobile.

C. Lyme disease: caused by a bacterium (Borrelia burgdorferi) transmitted to humans by deer ticks (Ixodes dammini). Symptoms may include a rash followed by flu-like illness. This may be followed by cardiac or neurologic problems. The principal complication is arthritis.

D. Bursitis: inflammation of bursae caused by trauma, infection, or by rheumatoid arthritis.

E. Ankylosing spondylitis: inflammatory disease that affects joints between vertebrae and between the sacrum and hipbone (sacroiliac joint).

F. Sprain and strain: A sprain is a forcible wrenching or twisting of a joint with partial rupture to its attachment without dislocation. A strain is the overstretching of a muscle.

CHAPTER 10: MUSCLE TISSUE

Motion results from alternating contraction (shortening) and relaxation of muscles. The skeletal system provides leverage and a supportive framework for the movement. Myology: Scientific study of muscles. Types of Muscle Tissue: 1. Skeletal muscle tissue: primarily attached to bones; it is

striated and voluntary. 2. Cardiac muscle tissue: forms the wall of the heart; it is

striated and involuntary – autorhythmic. 3. Smooth (visceral) muscle tissue: located in the viscera; it is

nonstriated (smooth) and involuntary. Functions of Muscle Tissue: 1. Producing body movements

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2. Moving substances in the body 3. Stabilizing body positions 4. Regulating organ volume 5. Producing heat (thermogenesis)

Characteristics of Muscle Tissue: 1. Excitability (irritability): ability to respond to certain

stimuli by producing electrical signal called action potentials.

2. Contractility: ability to shorten and thicken (contract), generating force to do work.

3. Conductivity: ability to propagate or conduct action potential along the plasma membrane.

4. Extensibility: ability to be extended (stretched) without damaging the tissue.

5. Elasticity: ability to return to original shape after contraction or extension.

Anatomy & Innervation of Skeletal Muscle Tissue:

A. Connective Tissue Components: (Fig. 10.1, p 293) 1. Superficial fascia: sheet or broad band of fibrous CT

under the skin. 2. Deep fascia: sheet or broad band of fibrous CT around

muscles and organs of the body. 3. Epimysium: CT covering the entire muscle. 4. Perimysium: CT covering fascicle. 5. Endomysium: CT covering individual fiber.

All (epimysium, perimysium, and endomysium) are extensions of deep fascia.

6. Tendons and aponeurosis: extensions of CT beyond muscle cells that attach the muscle to bone or other muscle. (e.g., epicranial aponeurosis, Fig. 11.3, p 334) a. Tendon sheaths enclose certain tendons and allow

them to slide back and forth more easily.

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b. Tenosynovitis: inflammation of the tendon sheaths and synovial membranes of certain joints (e.g., wrists, ankles, shoulders, etc.).

B. Nerve and Blood Supply: 1. Motor neurons convey impulses for muscular

contraction. 2. Blood provides nutrients and oxygen for contraction.

C. Motor Unit: [Fig 10.13, p 309] 1. A motor neuron and all the muscle fibers it stimulates

are collectively called a motor unit. 2. A single motor unit may innervate as few as 2-3 (as

muscles of the larynx) or 10-20 (as muscles controlling eye movement) or as many as 2000 (powerful gross muscles, e.g., gastrocnemius, biceps brachii, etc.) fibers, with an average of 150 fibers/motor unit.

D. Neuromuscular Junction (NMJ) or Myoneural Junction

[Fig. 10.10, pp 303-304] 1. A motor neuron transmits a nerve impulse (action potential)

to a skeletal muscle where the nerve impulse serves as a stimulus for contraction.

2. Neurons and muscle fibers (excitable cells) make contact and communicate at specialized regions called synapses.

3. A neuromuscular junction refers to an axon terminal of a motor neuron and the portion of the muscle fiber sarcolemma called motor end plate (contains 30-40 million ACh receptors).

4. Acetylcholine (ACh) is a neurotransmitter released by synaptic vesicles of a motor neuron, which triggers a muscle action potential.

5. Synaptic cleft: a small gap, which separates the two cells that form neuromuscular junction.

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E. Microscopic Anatomy: (Fig. 10.2, p 295) • Skeletal muscle consists of fibers (cells) covered by

sarcolemma (plasma membrane); a fiber contains sarcoplasm (cytoplasm), nuclei, sarcoplsmic reticulum (SR, which is the endoplasmic reticulum), and transverse tubules.

• Myofibrils constitute each fiber. Each myofibril is 1-2 µm in diameter and consists of thick filaments (16 nm in diameter) and thin filaments (8 nm in diameter), and elastic filaments (< 1nm in diameter). [There are hundreds to thousands of myofibrils in a single muscle fiber depending on its size, and, they account for about 80% of cellular volume.]

• Thick filaments consist mostly of myosin (each thick filament has approximately 200 myosin molecules). Each myosin molecule is shaped like two golf clubs twisted together; the golf club heads are called myosin heads or crossbridges that contain actin and ATP binding sites. [Fig 10.5, p 298]

• Thin filaments consist of actin, tropomyosin, and troponin.

• Actin and myosin are two contractile proteins in muscles.

• Tropomyosin and troponin are muscles’ regulatory proteins.

• Elastic filaments help stabilize the position of the thick filaments.

• The filaments are compartmentalized into sarcomeres – structural and functional units of contraction of skeletal muscle (from one Z disc to the next Z disc).

• A sarcomere shows distinct dark (A band) and light (I band) areas. (Figs. 10.3, 10.4, pp 296-297)

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• The darker middle portion is A (anisotropic) band, consisting primarily of the thick filaments with some thin filaments overlapping the thick ones.

• The lighter sides are I (isotropic) bands, which consist of thin filaments only.

• A Z disc passes through the center of I band. • A narrow H zone in the center of A band contains

thick but no thin filaments. • Supporting proteins that hold the thick filaments

together at the center of the H zone form the M line so named because it is at the middle of the sarcomere.

E. Muscle Proteins: a. Contractile proteins generate force during contraction.

• Myosin functions as a motor protein. Motor proteins push or pull their cargo to achieve movement by converting energy from ATP into mechanical energy of motion.

• Actin connects to the myosin for the sliding together of the filaments.

b. Regulatory proteins help switch the contractions on and off. • Troponin and tropomyosin are a part of thin filament. • In relaxed muscle, tropomyosin, which is held in place by

troponin, blocks the myosin binding sites on actin, preventing myosin from binding to actin.

c. Structural proteins keep the thick and thin filaments in proper alignment, give the myofibril elasticity and extensibility, and link the myofibrils to the sarcolemma and extracellular matrix. • Titin helps a sarcomere return to its resting length after a

muscle has contracted or been stretched. • Mymesin forms the M line. • Nebulin helps maintain alignment of the thin filaments in

the sarcomere. • Dystrophin reinforces the sarcolemma and helps transmit

the tension generated by the sarcomeres to the tendons.

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Contraction of Muscles: A. Sliding Filament Mechanism: [Fig. 10.6, p 299; Fig. 10.7, p 300; Fig. 10.8, p 301]

• Myosin crossbridges pull on thin filaments during muscle contraction, causing them to slide inward toward the H zone. • Z discs come toward each other and the sarcomere

shortens but the thick and thin filaments do not change in length.

• A band does not change in length. • I band shortens. • H zone shortens. • The sliding of filaments and shortening of sarcomeres

cause the shortening of the whole muscle fiber and ultimately the entire muscle.

• When a nerve impulse (nerve action potential) reaches an axon terminal, the synaptic vesicles release ACh (acetylcholine) in the synaptic cleft, which ultimately initiates a muscle action potential in the sarcolemma (motor end plate) of the muscle fiber that then travels into the T-tubules and causes some of its stored Ca2+ to be released into sarcoplasm.

• The muscle action potential releases Ca2+ that combine with troponin, causing it to pull on tropomyosin to change its orientation, thus exposing myosin binding sites on actin.

• The immediate, direct source of energy is ATP. ATP-ase splits ATP into ADP and Pi (inorganic phosphate) and the released energy activates myosin crossbridges.

• Activated crossbridges attach to actin and a change in the orientation of the crossbridges occurs – power stroke; their movement results in the sliding of thin filaments.

• Once the power stroke is complete, ATP again combines with the ATP-binding site on the myosin crossbridges; as ATP binds, the myosin heads detach from actin and the cycle may be reinitiated repeatedly.

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• Relaxation is brought about when ACh is broken down by the enzyme AChE (acetylcholinesterase) and Ca2+ are moved from sarcoplasm back into SR (sarcoplsmic reticulum); Ca2+ removal is done by active transport pumps and a calcium-binding protein called calsequestrin.

• Summary of events associated with contraction and relaxation is given in Fig.10.11, p 305.

• Rigor mortis is a state of muscular rigidity following death, results from a lack of ATP to split actin-myosin crossbridges.

Homeostasis of Body Temperature: (Fig. 25.19, p 978) • During contraction of skeletal muscle, most of the energy

produced is heat (thermogenesis). • If the body temperature decreases, shivering can help elevate

it to normal. Control of Muscle Tension: [When considering the contraction of a whole muscle, the tension it can generate depends on the number of fibers that are contracting in unison.] A. According to all-or-none principle, individual muscle fibers

contract to their fullest extent; they do not partially contract; a muscle can have graded contractions to perform different tasks.

B. Twitch Contraction (Fig. 10.14, p 309; Fig 10.15a, p 310): It is a brief contraction of all the muscle fibers in a motor unit in response to a single action potential. 1. Myogram: Recording of a muscle contraction – it includes

three periods: l atent, contraction, and relaxation. 2. Refractory period: Time, when a muscle has temporarily

lost excitability; skeletal muscles have a short refractory period and cardiac muscle has a long refractory period.

C. Wave (Temporal) Summation (Fig. 10.15b, p 310): The increased strength of contraction resulting from the application of a second stimulus before the muscle has completely relaxed after a previous stimulus

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D. Treppe (Staircase effect): Each of the first few contractions is a little stronger than the last

E. Incomplete (Unfused) Tetanus: A sustained muscle contraction that permits partial relaxation between stimuli (Fig. 10.15c).

F. Complete (Fused) Tetanus: A sustained contraction that lacks partial relaxation between stimuli (Fig. 10.15d).

G. A muscle fiber develops its greatest tension when there is an optimal zone of overlap between thick and thin filaments. (Fig. 10.9, p 302)

H. Muscle Tone: (Active and passive tension) 1. A sustained partial contraction of portions of a relaxed

skeletal muscle results in firmness known as muscle tone. 2. At any given moment, a few muscle fibers within a muscle

are in contracted while most are relaxed. The small amount of contraction is essential for maintaining posture.

3. Hypotonia refers to decreased or lost muscle tone; such muscles are said to be flaccid.

4. Hypertonia refers to increased muscle tone and may be expressed as either spasticity (stiffness) or rigidity.

5. Tension generated by contractile elements (thick & thin filaments) is called active tension; tension generated by elastic elements is called passive tension and is not related to muscular contraction.

F. Isotonic contractions occur when a constant load is moved through the range of motions possible at a joint and include concentric contraction (muscle shortens) {Fig.10.16a, p 311} and eccentric contraction (muscle lengthens) {Fig.10.16b, p 311}.

G. In isometric contraction, the muscle does not shorten but tension increases; an example would be holding a book steady using an outstretched arm (Fig.10.16c, p 311).

H. Muscular atrophy refers to wasting away of muscle, which may be caused by disuse or severing of the nerve supply.

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I. Muscular hypertrophy refers to an increase in diameter of the muscle fibers resulting from very forceful and repetitive muscular activity.

Muscle Metabolism: (Fig. 10.12, 307) A. On demand, skeletal muscle fibers can step up ATP production. B. Creatine phosphate (phophocreatine) and ATP constitute the

phosphagen system. This energy system can power maximal muscle contraction for approximately 15 seconds and is used for maximal short bursts of energy (e.g., 100-meter dash).

C. Glycogen-lactic acid system or glycolytic system, which is anaerobic and involves partial catabolism of glucose to generate ATP; this system can provide enough energy for about 30-40 seconds of maximal muscle activity (e.g., 400-meter race).

D. Aerobic system is involved in muscular activity lasting more than 30 seconds – reactions require oxygen; this system of ATP production involves complete oxidation via cellular respiration (biological oxidation): 1. Muscle tissue has two sources of oxygen:

a. Oxygen can diffuse into muscle fibers from blood. b. Oxygen is also released by myoglobin inside muscle fibers.

2. The aerobic system will provide enough ATP for prolonged activity so long as sufficient oxygen is available.

E. Elevated oxygen use after exercise is called recovery oxygen consumption (formerly termed oxygen debt).

F. Muscle fatigue: Inability of a muscle to maintain its strength of contraction or tension; it occurs when a muscle cannot produce enough ATP to meet its needs.

G. Microscopic muscle damage is a major contributing factor to muscle soreness that follows bouts of strenuous exercise.

Types of Skeletal Muscle Fibers: [Table 10.1, p 313] A. All skeletal muscle fibers are not identical in structure and

function. 1. Color varies according to the content of myoglobin, an oxygen-

storing reddish pigment. Red muscle fibers have high

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myoglobin content while the myoglobin content of white muscle fibers is low.

2. Fiber diameter varies as do cell’s allocations of mitochondria, blood capillaries, and SR.

3. Contraction velocity and resistance fatigues also differ between fibers.

B. On the basis of structure and function, skeletal muscle fibers are classified as

1. Slow oxidative (Type I) fibers (also called slow-twitch or fatigue-resistant fibers)

2. Fast oxidative-glycolytic (Type IIA) fibers (also called fast-twitch A fibers)

3. Fast glycolytic (Type IIB) fibers (also called fast-twitch B or fatigable fibers)

C. Most skeletal muscles contain a mixture of all three fiber-types, their proportions varying with the usual action of the muscle. All fibers of any one motor unit are the same.

D. Although the number of different skeletal muscle fibers does not change, various types of exercise can alter the characteristics of those that are present.

E. Use of anabolic steroids by athletes to increase muscle size, strength, and endurance can have very serious side effects, some of which are life threatening.

DISORDERS: HOMEOSTATIC IMBALANCES: [Learn from p 319!] MEDICAL TERMINOLOGY: [Learn from p 320!]

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