Human Anatomy and Physiology: Tissues, Integumentary System, and Bone Biology

Comprehensive practice flashcards covering basic histology, epithelial and connective tissue repair, structural anatomy of the integumentary system, cutaneous glands, burns, skin cancers, and bone histology and architecture.

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

The four basic tissue types are epithelial tissue, connective tissue, muscle tissue, and nervous tissue.

How do endocrine and exocrine glands differ in their duct structure and route of secretion?

Endocrine glands are ductless glands that secrete hormones directly into the surrounding interstitial fluid to enter the blood or lymph. Exocrine glands retain ducts and secrete their products onto body surfaces (such as skin) or into body cavities.

How do merocrine and holocrine glands differ in their cellular mode of secretion?

Merocrine glands secrete products by exocytosis without cellular damage as secretions are produced (e.g., pancreas, eccrine sweat glands). Holocrine glands accumulate their products within the cells until the entire secretory cell ruptures, releasing secretions and dead cell fragments (e.g., sebaceous glands).

What three basic structural elements compose all connective tissues?

Connective tissue is composed of ground substance, fibers (collagen, elastic, and reticular), and cells.

In connective tissues, what functional distinction separates "-blast" cells from "-cyte" cells?

"-Blast" cells are undifferentiated, actively mitotic cells that secrete ground substance and extracellular matrix fibers (such as fibroblasts, chondroblasts, and osteoblasts). "-Cyte" cells are the mature, less active forms that reside in and maintain the health of the matrix.

What are the three successive steps involved in tissue repair following an injury?

Step $1$: Inflammation sets the stage (vessel dilation, increased permeability, and blood clotting). Step $2$: Organization restores blood supply (blood clot is replaced by granulation tissue, fibroblasts produce collagen, and debris is phagocytized). Step $3$: Regeneration and fibrosis effect permanent repair (the scab detaches, fibrous tissue matures and contracts, and epithelium thickens).

How does tissue regeneration differ from fibrosis during wound repair?

Regeneration replaces destroyed tissue with the exact same kind of tissue, fully restoring original function. Fibrosis replaces destroyed tissue with dense fibrous connective tissue (scar tissue), causing the loss of original tissue function.

What two distinct skin regions form the integument, and what layer lies directly deep to them?

The skin consists of the superficial epidermis (an avascular keratinized stratified squamous epithelium) and the underlying dermis (a vascular fibrous connective tissue). Deep to the dermis lies the hypodermis (superficial fascia), which is primarily adipose tissue that anchors the skin to muscle.

What are the four cell types found within the epidermis, and what is each cell's primary role?

1. Keratinocytes: Produce tough fibrous keratin and desmosomes to protect skin.
2. Melanocytes: Synthesize melanin pigment in melanosomes to shield keratinocyte nuclei from UV damage.
3. Dendritic cells: Star-shaped immune cells that patrol deep layers and activate the immune system.
4. Tactile (Merkel) cells: Sensory touch receptors located at the epidermal-dermal junction.

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

1. Stratum basale (stratum germinativum)
2. Stratum spinosum
3. Stratum granulosum
4. Stratum lucidum (found only in thick skin)
5. Stratum corneum

What distinct histological features characterize the stratum corneum?

It consists of $20\text{--}30$ rows of flat, anucleated, keratinized dead cells surrounded by glycolipids. It accounts for approximately three-quarters of total epidermal thickness and protects against water loss, abrasion, and biological or chemical assaults.

What two layers make up the dermis, and what tissue types compose each?

The superficial papillary layer consists of loose areolar connective tissue containing dermal papillae, capillary loops, and tactile (Meissner's) corpuscles. The deeper reticular layer accounts for approximately $80\%$ of dermal thickness and consists of coarse, dense irregular connective tissue.

What are cleavage (tension) lines in the reticular dermis, and why are they clinically significant?

Cleavage lines represent separations between underlying bundles of collagen fibers that run parallel to the skin surface. Surgical incisions made parallel to cleavage lines heal faster and gap less than incisions made across them.

What anatomical structural events produce striae and blisters?

Striae ("stretch marks") are silvery-white scars caused by extreme stretching that tears collagen fibers in the dermis. A blister is a fluid-filled pocket caused by acute, short-term trauma that physically separates the epidermal and dermal layers.

What three pigments determine human skin color?

1. Melanin: Made by melanocytes in two forms (reddish-yellow to brownish-black); absorbs UV radiation.
2. Carotene: Yellow-to-orange pigment that can accumulate in stratum corneum and convert to vitamin A.
3. Hemoglobin: Oxygenated red pigment in dermal capillaries that produces the pinkish hue of fair skin.

What clinical conditions are indicated by cyanosis, erythema, and jaundice?

Cyanosis (blue hue) indicates low oxygenation of hemoglobin. Erythema (redness) indicates fever, hypertension, inflammation, or allergy. Jaundice (yellow cast) indicates a liver disorder causing bilirubin accumulation.

How do eccrine and apocrine sweat glands differ in location and secretion content?

Eccrine sweat glands are widely distributed (especially palms, soles, and forehead) and secrete a hypotonic filtrate consisting of $99\%$ water, salts, vitamin C, antibodies, and dermcidin for thermoregulation. Apocrine sweat glands are restricted to axillary and anogenital areas, empty into hair follicles, and produce a viscous milky/yellowish secretion enriched with fatty substances and proteins that causes body odor when metabolized by bacteria.

What do sebaceous glands produce, and what stimulates their secretory activity?

Sebaceous glands produce sebum, an oily holocrine secretion with bactericidal properties that softens hair and skin and retards water loss. They are largely inactive until puberty, when they are stimulated by hormones, particularly androgens.

What enzymatic and metabolic sequence converts skin precursors to active vitamin D ($\text{calcitriol}$)?

UVB sunlight converts cholesterol precursors in the skin to cholecalciferol (inactive vitamin $D_3$). Cholecalciferol travels to the liver, where it is converted to calcidiol, and subsequently to the kidneys, where it is transformed into calcitriol, the active hormone that enables intestinal calcium absorption.

What are the three major forms of skin cancer, and which stratum does each arise from?

1. Basal cell carcinoma: Arises from stratum basale cells; least malignant and most common.
2. Squamous cell carcinoma: Arises from keratinocytes of the stratum spinosum; second most common.
3. Melanoma: Arises from melanocytes; most dangerous and highly metastatic.

What are the criteria of the ABCD rule for recognizing melanoma?

A = Asymmetry (the two halves of the pigmented spot do not match) B = Border irregularity (exhibits indentations or scalloping) C = Color (contains multiple colors: brown, black, tan, red, or blue) D = Diameter (larger than $6\,\text{mm}$, approximately the size of a pencil eraser)

Using the Rule of Nines, what percentage of the total body surface area is assigned to the anterior and posterior trunk?

The anterior trunk accounts for $18\%$ and the posterior trunk accounts for $18\%$, totaling $36\%$ of the total body surface area.

How are first-, second-, and third-degree burns classified based on depth of damage and pain?

First-degree burns involve only the epidermis, presenting with localized redness, edema, and pain. Second-degree burns damage the epidermis and upper dermis, resulting in blisters and pain (first- and second-degree burns are partial-thickness burns). Third-degree (full-thickness) burns destroy the entire skin thickness, appearing gray-white, cherry-red, or blackened, and are initially non-painful because nerve endings have been destroyed.

Under what three conditions are burn injuries clinically classified as critical?

Burns are considered critical if:

1. Over $25\%$ of the body has second-degree burns.
2. Over $10\%$ of the body has third-degree burns.
3. Third-degree burns are located on the face, hands, or feet.

What three types of cartilage occur in the human skeletal system, and where is each found?

1. Hyaline cartilage: Most abundant; contains collagen fibers only; found on articular ends of bones, costal cartilage of ribs, respiratory structures (larynx), and nasal cartilage.
2. Elastic cartilage: Contains elastic fibers; found in the external ear and epiglottis.
3. Fibrocartilage: Thick collagen fibers with high tensile strength; found in knee menisci and intervertebral discs.

What is the structural difference between appositional and interstitial growth of cartilage?

Appositional growth occurs from the outside in, as new matrix is deposited onto the external surface of existing cartilage by cells in the perichondrium. Interstitial growth occurs from the inside out, as chondrocytes within lacunae divide and secrete new matrix internally.

What four shape categories are used to classify human bones?

1. Long bones: Longer than wide (e.g., humerus, femur, limb bones).
2. Short bones: Cube-shaped bones (e.g., carpals, tarsals) and sesamoid bones (e.g., patella).
3. Flat bones: Thin, flattened, slightly curved plates (e.g., sternum, scapulae, ribs, most skull bones).
4. Irregular bones: Complicated shapes that fit no other class (e.g., vertebrae, hip bones).

What are the seven primary physiological and mechanical functions of bones?

1. Support (framework for body and soft organs)
2. Protection (skull protects brain, vertebrae protect spinal cord, rib cage protects thoracic organs)
3. Movement (levers for muscles)
4. Mineral and growth factor storage (calcium and phosphate reservoir)
5. Blood cell formation (hematopoiesis in red marrow)
6. Triglyceride storage (yellow marrow in bone cavities)
7. Hormone production (osteocalcin regulates insulin secretion, glucose levels, and metabolism)

What are the anatomical regions and interior cavities of a typical long bone?

A long bone consists of a tubular shaft called the diaphysis, which surrounds a central medullary cavity filled with yellow bone marrow in adults, and expanded bone ends called epiphyses, which contain spongy bone internally and compact bone externally. The epiphyseal line lies between the diaphysis and epiphysis as a remnant of the childhood epiphyseal plate.

What are the two layers of the periosteum, and what structures secure it to the bone matrix?

The periosteum has an outer fibrous layer composed of dense irregular connective tissue and an inner osteogenic layer containing primitive osteogenic stem cells. Perforating (Sharpey's) fibers are collagen bundles that extend from the fibrous layer deep into the bone matrix to anchor the membrane.

Where is active hematopoietic red marrow located in adult bones versus newborns?

In newborns, medullary cavities of long bones and all areas of spongy bone contain red marrow. In adults, red marrow is restricted to the heads of the femur and humerus, and active hematopoiesis occurs predominantly in the diploë of flat bones (such as the sternum) and irregular bones (such as the hip bone).

What are the distinct physiological roles of osteoblasts, osteocytes, and osteoclasts?

Osteoblasts are bone-forming mitotic cells that secrete osteoid (unmineralized collagenous matrix). Osteocytes are non-dividing mature bone cells trapped in lacunae that monitor the matrix and act as mechanical strain sensors. Osteoclasts are multinucleated cells derived from hematopoietic stem cells that resorb (break down) mineralized bone matrix inside resorption bays.

How is an osteon arranged, and how do adjacent lamellae resist torsional and twisting forces?

An osteon (Haversian system) consists of concentric cylindrical rings of bone matrix called lamellae surrounding a central canal. Collagen fibers run in opposite directions in adjacent lamellae, which reinforces the bone and allows it to withstand significant twisting stress.

What are canaliculi, and how do they facilitate nutrient and waste transfer in compact bone?

Canaliculi are tiny hairlike canals connecting adjacent lacunae to each other and to the central Haversian canal. Osteocytes maintain cell projections through these canals that connect via gap junctions, allowing nutrients, hormones, and metabolic wastes to relay directly between cells.

What components make up the organic and inorganic fractions of bone matrix, and what mechanical property does each provide?

The organic components comprise bone cells and osteoid (ground substance and collagen fibers), making up approximately $\frac{1}{3}$ of the matrix; they provide tensile strength, flexibility, and resistance to stretch via sacrificial bonds. The inorganic components are hydroxyapatites (mineral salts, primarily calcium phosphate crystals), making up $65\%$ of bone mass; they provide hardness and resistance to compression.