Tissues, Integumentary System, and Bone Structure and Function

Comprehensive practice flashcards covering Chapter 5 (Tissue Organization), Chapter 6 (Integumentary System), and Chapter 7 (Skeletal System: Bone Structure and Function).

What are the four primary tissue types found in the human body?

Epithelial, connective, muscle, and nervous tissue.

What are the core characteristics of epithelial tissue?

Epithelial tissue consists of one or more layers of closely packed cells with little or no extracellular matrix, lacks blood vessels (avascular), displays cellular polarity (apical, lateral, and basal surfaces), rests on a basement membrane, is extensively innervated, and exhibits high regeneration capacity.

How does epithelial tissue classification reflect both layer count and cell shape?

The first part of the name indicates the number of cell layers (simple for one layer, stratified for two or more layers, or pseudostratified), while the second part describes the shape of the cells at the apical surface (squamous, cuboidal, columnar, or transitional).

Where is nonkeratinized stratified squamous epithelium located, and what is its primary function?

It lines areas subjected to mechanical abrasion such as the oral cavity and esophagus, functioning to protect underlying tissues by withstanding abrasion from ingested materials.

What distinguishes endocrine glands from exocrine glands?

Endocrine glands lack ducts and secrete hormones directly into interstitial fluid and the bloodstream; exocrine glands maintain a connection to an epithelial surface through a duct that carries their secretions to the surface.

What three secretion mechanisms are depicted in (a), (b), and (c)?

(a) Merocrine gland secretion (vesicles release contents by exocytosis); (b) Apocrine gland secretion (the apical portion of the secretory cell pinches off); (c) Holocrine gland secretion (the whole cell disintegrates to release its product).

What are the three core structural components shared by all connective tissues?

Cells, protein fibers (collagen, reticular, and elastic fibers), and ground substance.

Which connective tissue resident cell type synthesizes protein fibers and ground substance?

Fibroblasts.

What nutritional deficiency causes scurvy, and how does it compromise connective tissue?

A deficiency in vitamin C causes scurvy because vitamin C is essential for the proper formation of healthy collagen fibers, leading to weakness, gum ulceration, hemorrhages, and abnormal bone growth.

What are the structural and functional differences among skeletal, cardiac, and smooth muscle tissue?

Skeletal muscle consists of long, cylindrical, multinucleated, striated fibers under voluntary somatic control; cardiac muscle contains short, branching, striated cells with one or two central nuclei connected by intercalated discs under involuntary control; smooth muscle consists of nonstriated, fusiform (tapered) cells with a single central nucleus under involuntary control.

What are the functional roles of neurons versus glial cells in nervous tissue?

Neurons receive, process, and transmit electrical nerve impulses; glial cells do not transmit impulses, but instead protect, support, and nourish neurons.

What two main layers compose the integument (skin), and what lies directly deep to them?

The superficial epidermis (keratinized stratified squamous epithelium) and the deeper dermis (composed of connective tissue proper); deep to the dermis is the subcutaneous layer (hypodermis), which is not considered part of the integument.

What are the five epidermal strata in thick skin, ordered from deep to superficial?

Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.

What three cell types reside in the stratum basale?

Keratinocytes (stem cells dividing to regenerate the epidermis), melanocytes (pigment-producing cells), and tactile cells (Merkel cells sensitive to touch).

What role do epidermal dendritic (Langerhans) cells play, and in which epidermal strata are they found?

They initiate an immune response against pathogens and are located within the stratum spinosum and stratum granulosum.

What key cellular events occur in the stratum granulosum during keratinization?

Keratinocytes fill with keratin protein while their nuclei and organelles disintegrate, resulting in the death of the cells across its $3\text{ to }5$ cell layers.

What structural differences distinguish thick skin from thin skin?

Thick skin is found on the palms and soles, possesses all five strata (including a stratum lucidum filled with eleidin), and contains sweat glands but lacks hair follicles and sebaceous glands; thin skin covers the rest of the body, lacks a stratum lucidum, and contains hair follicles, sebaceous glands, and sweat glands.

What four basic ridge patterns are formed by friction ridges on the epidermal surface?

Arch, whorl, loop, and combination.

How do the papillary and reticular layers of the dermis differ in connective tissue composition?

The superficial papillary layer consists of areolar connective tissue with dermal papillae; the deeper, major reticular layer consists of dense irregular connective tissue.

Why is the orientation of cleavage lines clinically important during surgical incisions?

Cleavage lines correspond to the parallel orientation of collagen and elastic fiber bundles; incisions made parallel to cleavage lines heal quickly without gaping, whereas incisions perpendicular to cleavage lines gape open due to cut elastic fibers, delaying healing and increasing scar formation.

Identify the labeled nail structures: the narrow band of epidermis at the proximal margin, the crescent white area, and the thickened stratum corneum under the free edge.

Eponychium (cuticle), lunula, and hyponychium.

What are the three zones along the length of a hair filament?

The hair bulb (swelling at the base originating in the dermis surrounding the hair papilla), the root (zone extending from the bulb to the skin surface), and the shaft (the portion extending beyond the skin surface).

How do merocrine sweat glands differ from apocrine sweat glands in location and secretion composition?

Merocrine sweat glands are coiled tubular glands that open directly to the skin surface, producing watery sweat ($99\%$ water) for thermoregulation; apocrine sweat glands empty into hair follicles in the axillae, pubic, anal, and nipple regions, releasing a cloudy, viscous secretion rich in lipids and proteins that creates body odor when broken down by bacteria.

What are the four sequential stages of wound healing in the integument?

(1) Cut blood vessels bleed into the wound; (2) A blood clot forms and leukocytes clean the wound; (3) Blood vessels regrow and granulation tissue forms; (4) The epithelium regenerates and connective tissue fibrosis occurs.

What distinguishes first-degree, second-degree, and third-degree burns?

First-degree burns affect only the epidermis (redness, pain); second-degree burns affect the epidermis and part of the dermis (blistering, pain, slight scarring); third-degree burns destroy the epidermis, dermis, and subcutaneous layer, leading to fluid loss, infection risk, severe scarring, and often requiring skin grafting.

How does Botox clinically reduce facial wrinkles?

Botox uses Clostridium botulinum toxin to block nerve impulses to specific facial expression muscles, temporarily preventing their contraction and decreasing facial crease lines.

What proportion of adult bone mass is composed of compact bone versus spongy bone?

Compact bone accounts for approximately $80\%$ of total bone mass, whereas spongy bone accounts for the remaining $20\%$.

What are the four structural classes of bones based on shape, and give an example of each?

Long bones (femur), short bones (tarsal bone), flat bones (frontal bone), and irregular bones (vertebra).

What are the primary anatomical regions of a typical long bone?

The diaphysis (shaft), epiphyses (proximal and distal expanded ends covered by articular cartilage), metaphysis (region between diaphysis and epiphysis containing the epiphyseal plate or line), and the central medullary cavity.

What are the two histological layers of the periosteum?

An outer fibrous layer of dense irregular connective tissue and an inner cellular layer containing osteoprogenitor cells, osteoblasts, and osteoclasts.

How does the distribution of red bone marrow differ between children and adults?

In children, red bone marrow is located in the spongy bone and medullary cavities of most bones; in adults, red bone marrow is restricted primarily to selected axial skeleton bones (skull, vertebrae, ribs, sternum, hip bones) and the proximal epiphyses of the humerus and femur.

What are the four bone cell types and their distinct functional roles?

Osteoprogenitor cells are stem cells that develop into osteoblasts; osteoblasts secrete osteoid to build matrix; osteocytes are mature cells housed in lacunae that maintain bone matrix and sense mechanical stress; osteoclasts are large, multinucleated cells derived from fused bone marrow cells that resorb bone matrix.

What are the chemical components and physical contributions of organic versus inorganic bone matrix?

The organic component (osteoid) consists of collagen fibers, proteoglycans, and glycoproteins, providing tensile strength and flexibility; the inorganic component consists of hydroxyapatite crystals ($\text{Ca}_{10}(\text{PO}_4)_6(\text{OH})_2$) with other mineral salts, providing compressional strength, hardness, and rigidity.

What are the microscopic components of an osteon in compact bone?

A central canal housing neurovascular structures, surrounded by concentric lamellae containing osteocytes residing inside lacunae, which communicate via cytoplasmic projections inside microscopic canaliculi.

How does interstitial growth of cartilage differ from appositional growth?

Interstitial growth occurs from within internal cartilage matrix (chondrocytes divide and produce new matrix internally, separating into individual lacunae); appositional growth occurs along the cartilage outer edge within the perichondrium (stem cells divide, differentiate into chondroblasts, and deposit new matrix along the periphery).

What is the primary difference between intramembranous ossification and endochondral ossification?

Intramembranous ossification produces flat bones of the skull and facial bones directly from thickened regions of mesenchyme; endochondral ossification forms long and most other bones by replacing a pre-existing hyaline cartilage model.

Name the five distinct zones of an epiphyseal plate in order from epiphyseal side to diaphyseal side.

Zone 1: Zone of resting cartilage; Zone 2: Zone of proliferating cartilage; Zone 3: Zone of hypertrophic cartilage; Zone 4: Zone of calcified cartilage; Zone 5: Zone of ossification.

What cellular mechanism drives appositional bone growth in bone diameter?

Osteoblasts in the inner cellular layer of the periosteum deposit circumferential bone lamellae onto the external bone surface, while osteoclasts resorb bone matrix along the inner medullary cavity boundary.

What are the three organ-level steps involved in the synthesis of active calcitriol?

(1) Ultraviolet light converts the precursor molecule 7-dehydrocholesterol into vitamin $\text{D}_3$ (cholecalciferol) in the skin; (2) The liver hydroxylates vitamin $\text{D}_3$ to form calcidiol; (3) The kidney adds another hydroxyl group to convert calcidiol into active calcitriol.

How do parathyroid hormone (PTH) and calcitriol act synergistically to raise depressed blood calcium levels?

PTH and calcitriol act on bone to increase osteoclast activity and release $\text{Ca}^{2+}$; they act on kidneys to decrease urinary excretion of $\text{Ca}^{2+}$; and calcitriol increases dietary absorption of $\text{Ca}^{2+}$ across the small intestine.

What is the source and physiological effect of calcitonin?

Calcitonin is secreted by the thyroid gland in response to high blood calcium levels; it inhibits osteoclast activity and promotes calcium excretion in urine to lower blood calcium concentration.

What defines osteoporosis, and what diagnostic tool is commonly used to measure bone mineral density?

Osteoporosis is a disease characterized by a severe reduction in bone mass sufficient to compromise normal physical function and dramatically elevate fracture risk; bone mineral density is assessed using a DEXA scan.