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

Comprehensive review flashcards covering Chapter 4 (Tissues), Chapter 5 (The Integumentary System), and Chapter 6 (Bones and Cartilage).

How is a tissue defined in human anatomy and physiology?

A group of cells similar in structure that perform a common or related function.

What is histology?

The scientific study of tissues.

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

Epithelial, connective, muscle, and nervous tissue.

What are the two main functional forms of epithelial tissue?

Covering and lining epithelia (found on external and internal body surfaces) and glandular epithelia (secretory tissue in glands).

What are the six major functions of epithelial tissue?

Protection, absorption, filtration, excretion, secretion, and sensory reception.

How is a gland defined in histology?

One or more cells that make and secrete an aqueous fluid called a secretion.

How are glands classified based on their site of product release?

Endocrine glands (internally secreting hormones into interstitial fluid) and exocrine glands (externally secreting products onto body surfaces or into body cavities).

Why are endocrine glands described as ductless glands?

Because their secretions are not released into a duct, but rather released into the surrounding interstitial fluid where they are picked up by the circulatory system.

What chemical messengers are produced and secreted by endocrine glands?

Hormones, which travel through lymph or blood to reach specific target organs.

Where do multicellular exocrine glands release their secretions?

Into ducts that transport the secretions onto body surfaces (such as skin) or into body cavities.

Which mode of exocrine secretion is illustrated in diagram (b), where the entire secretory cell ruptures to release its contents?

Holocrine secretion.

How do merocrine exocrine glands discharge their secretions?

By exocytosis as secretions are produced, without damaging or rupturing the secretory cells.

How do holocrine exocrine glands release their secretions?

Secretory cells accumulate their products internally until they rupture, releasing their secretions along with dead cell fragments.

What are the four main classes of connective tissue?

Connective tissue proper, cartilage, bone, and blood.

What are the major physiological functions of connective tissue?

Binding and support, protecting, insulating, storing reserve fuel, and transporting substances (via blood).

What is the primary role of undifferentiated 'blast' cells in connective tissue?

They are immature, actively dividing cells that secrete the ground substance and extracellular matrix (ECM) fibers.

What specific 'blast' cells synthesize the matrix in connective tissue proper, cartilage, and bone?

Fibroblasts in connective tissue proper, chondroblasts in cartilage, and osteoblasts in bone.

What is the role of mature 'cyte' cells in connective tissue?

They are less active cells that maintain the health and structural integrity of the extracellular matrix.

What are the three structural elements that compose connective tissue?

Fibers, ground substance, and cells.

What contractile proteins make up the myofilaments of muscle tissue?

Actin and myosin.

What are the three distinct types of muscle tissue in the human body?

Skeletal muscle, cardiac muscle, and smooth muscle.

What two functional cell types comprise nervous tissue?

Neurons (specialized nerve cells that generate and conduct electrical impulses) and supporting cells (which support, insulate, and protect neurons).

What is the difference between regeneration and fibrosis during tissue repair?

In regeneration, destroyed tissue is replaced by the same kind of tissue, fully restoring original function; in fibrosis, destroyed tissue is replaced by dense connective tissue (scar tissue), causing original function to be lost.

What physiological changes take place during Step 1 (Inflammation sets stage) of tissue repair?

Inflammatory chemicals are released, causing dilation of local blood vessels, an increase in blood vessel permeability, and blood clotting.

What key events occur during Step 2 (Organization restores blood supply) of tissue repair?

The blood clot is replaced with granulation tissue, surface epithelium begins regenerating, fibroblasts produce collagen fibers to bridge the wound, and macrophages phagocytize debris.

What events finalize tissue repair during Step 3 (Regeneration and fibrosis effect permanent repair)?

The scab detaches, fibrous scar tissue matures and contracts, and the epithelium thickens until it resembles the adjacent normal tissue.

What tissue type forms the epidermis, and what is its vascular status?

Keratinized stratified squamous epithelium; it is avascular.

What primary tissue type comprises the dermis, and what is its vascular status?

Mostly fibrous connective tissue; it is vascular.

What is the hypodermis (superficial fascia) and what are its functions?

A subcutaneous layer deep to the skin (not technically part of the skin) consisting mostly of adipose tissue that absorbs shock, provides thermal insulation, and anchors the skin to underlying structures (mainly muscles).

What is the primary function of keratinocytes in the epidermis?

To produce fibrous keratin (a protective protein) and maintain a tightly connected epidermal barrier via desmosomes.

What is the role of melanocytes and melanosomes in the epidermis?

Melanocytes synthesize the pigment melanin and package it into melanosomes, which are transferred to keratinocytes to form a protective shield over the nucleus against UV radiation damage.

What is the primary role of dendritic cells in the skin?

They are star-shaped cells in the deep epidermis that patrol for foreign invaders and act as key activators of the immune system.

What is the function of tactile (Merkel) cells in the epidermis?

They associate with sensory nerve endings to function as sensory touch receptors.

What is the correct anatomical order of epidermal strata from deepest to most superficial in thick skin?

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

Why is the stratum basale also called the stratum germinativum?

Because it contains a single row of stem cells undergoing continuous, rapid mitosis to generate new keratinocytes.

How long does it take for a daughter cell produced in the stratum basale to journey to the epidermal surface?

$25\text{--}45\text{ days}$.

What percentage of the stratum basale is composed of melanocytes?

$10\%\text{--}25\%$.

Why are the keratinocytes in the stratum spinosum referred to as 'prickle cells'?

Because the cells shrink during histological preparation while their desmosomes remain attached, causing them to appear spiky.

What morphological and biochemical changes occur in keratinocytes within the stratum granulosum?

Cells flatten, nuclei and organelles disintegrate, and cells accumulate keratohyaline granules (for keratin assembly) and lamellar granules containing water-resistant glycolipids.

Where is the stratum lucidum located, and what is its histological appearance?

Found only in thick skin (palms and soles), consisting of a thin, translucent band of $2\text{--}3\text{ rows}$ of clear, flat, dead keratinocytes.

What are the structural characteristics of the stratum corneum?

It consists of $20\text{--}30\text{ rows}$ of flat, anucleated, keratinized dead cells, accounting for three-quarters ($75\%$) of total epidermal thickness.

Approximately how many dead epidermal cells do humans slough off every minute via apoptosis?

Approximately $50{,}000\text{ cells per minute}$.

What are the two distinct layers of the dermis, and what tissue constitutes each?

The papillary layer (areolar connective tissue) and the reticular layer (dense irregular connective tissue).

What structures are housed within the dermal papillae of the papillary dermis?

Capillary loops, free nerve endings (pain receptors), and tactile corpuscles (Meissner's corpuscles).

What are friction ridges and what are their physiological roles?

Epidermal ridges supported by dermal ridges on fingertips, palms, and soles that enhance gripping ability, amplify touch sensations, and leave fingerprint patterns from sweat pores.

What proportion of total dermal thickness is comprised by the reticular layer?

Approximately $80\%$.

What are cleavage (tension) lines, and why are they clinically critical for surgeons?

Separations between underlying collagen fiber bundles running parallel to the skin surface; surgical incisions made parallel to cleavage lines gape less and heal more readily.

What are flexure lines in the reticular dermis?

Dermal folds that occur at or near joints where the dermis is tightly anchored to deeper structures (visible on wrists, palms, fingers, soles, and toes).

What causes striae (commonly known as stretch marks)?

Extreme stretching of the skin that tears collagen fibers within the dermis, leaving silvery-white scars.

How does a blister form in response to acute, short-term trauma?

Fluid accumulates in a pocket that physically separates the epidermis from the dermis.

What three pigments contribute to natural human skin color?

Melanin (the only pigment synthesized in skin), carotene (yellow-to-orange pigment), and hemoglobin (pink hue of red blood cells).

What underlying physiological issue causes cyanosis (blue skin coloration)?

Low oxygen saturation of hemoglobin.

What clinical conditions or emotional states can trigger pallor (blanching of skin)?

Anemia, low blood pressure, fear, or anger.

What underlying organ dysfunction is signaled by jaundice (yellow cast)?

Liver disorders.

What is the hair matrix, and where is it located?

The actively dividing germinal cell layer located within the hair bulb that produces new hair cells.

What is the function of the arrector pili muscle?

A bundle of smooth muscle attached to the hair follicle that contracts to pull the hair upright, producing 'goose bumps.'

Identify the white, crescent-shaped region at the proximal end of the nail bed indicated in this figure.

The lunule.

How do vellus hair and terminal hair differ in morphology and distribution?

Vellus hair is pale, fine body hair found on children and adult females; terminal hair is coarse, longer hair found on the scalp, eyebrows, and after puberty in the axillary and pubic regions (and male face/neck).

What is the average weekly growth rate of human hair and the normal daily loss of scalp hairs?

Hair grows an average of $2.25\,mm\text{ per week}$, and about $90\text{ scalp hairs}$ are lost daily.

What metabolite is responsible for triggering male pattern baldness?

DHT (dihydrotestosterone).

What is telogen effluvium (TE)?

Abrupt hair thinning that occurs when systemic stress (hormonal shifts, surgery, severe trauma, crash dieting) causes many hair follicles to enter the resting (telogen) phase simultaneously.

How do eccrine sweat glands differ functionally and distribution-wise from apocrine sweat glands?

Eccrine glands are widely distributed (especially palms, soles, forehead) and secrete hypotonic watery sweat for thermoregulation; apocrine glands are confined to axillary and anogenital regions and secrete a viscous, lipid- and protein-rich sweat that produces body odor upon bacterial decomposition.

What are two specialized anatomical variants of apocrine sweat glands?

Ceruminous glands (which secrete cerumen or earwax in the ear canal) and mammary glands (which secrete milk).

What substance is secreted by sebaceous glands and what are its physiological roles?

Sebum, an oily holocrine secretion that softens skin and hair, slows water loss, and has bactericidal properties.

What infant clinical condition is depicted here, caused by overactive sebaceous glands shortly after birth?

Cradle cap (seborrhea).

How do insensible perspiration and sensible perspiration differ in daily volume?

Insensible perspiration is unnoticeable basal sweat of about $500\,mL/\text{day}$; sensible perspiration is visible sweating that can reach up to $12\,L$ ($3\text{ gallons}$) per day to cool the body.

What are the chemical stages of vitamin D synthesis initiated in the skin?

UVB sunlight converts cholesterol precursors into cholecalciferol (inactive $D_3$), which is converted to calcidiol in the liver, and finally into calcitriol (the active hormone) in the kidneys.

Identify the type of skin cancer shown in this image, which arises from proliferation of stratum basale cells and is the least malignant form.

Basal cell carcinoma.

Identify the type of skin cancer shown in this image, which arises from keratinocytes of the stratum spinosum.

Squamous cell carcinoma.

What criteria comprise the ABCD rule for the early clinical detection of melanoma?

A: Asymmetry (halves do not match), B: Border irregularity (indentations), C: Color (multiple shades), and D: Diameter (greater than $6\,mm$, the size of a pencil eraser).

What are the immediate systemic threats to life following severe extensive burns?

Catastrophic loss of fluids and electrolytes, leading to dehydration, electrolyte imbalance, renal shutdown, and circulatory shock.

According to the Rule of Nines shown here, what percentage of total body surface area is allocated to the entire trunk (anterior and posterior)?

$36\%$ ($18\%$ anterior trunk plus $18\%$ posterior trunk).

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

First-degree affects only the epidermis; second-degree injures the epidermis and upper dermis (causing blisters); third-degree destroys the entire thickness of the skin (full-thickness burn).

Under what specific clinical parameters are burns considered critical?

When $>25\%$ of the body has second-degree burns, $>10\%$ of the body has third-degree burns, or third-degree burns involve the face, hands, or feet.

What is skeletal cartilage primarily composed of, and does it contain blood vessels or nerves?

Highly resilient cartilage tissue consisting primarily of water; it is avascular and contains no nerves.

What is the perichondrium and what are its key functions?

A layer of dense connective tissue surrounding cartilage like a girdle that resists outward expansion and contains blood vessels providing nutrient diffusion.

What are the characteristics and body locations of hyaline cartilage?

The most abundant cartilage type, containing only collagen fibers to provide support, flexibility, and resilience; located at articular joints, costal ribs, respiratory larynx, and the nasal tip.

Where is elastic cartilage located in the human body?

In the external ear and the epiglottis.

What structural fiber gives fibrocartilage its high tensile strength, and where is it found?

Thick collagen fibers; located in the menisci of the knee and the intervertebral discs.

How does appositional growth of cartilage differ from interstitial growth?

Appositional growth ('outside to in') occurs when new matrix is secreted onto the external surface of cartilage; interstitial growth ('inside to out') occurs when chondrocytes within lacunae divide and secrete new matrix from within.

How many named bones are in the adult human skeleton, and what are its two main divisions?

$206\text{ named bones}$, divided into the axial skeleton (long axis) and the appendicular skeleton (limbs and girdles).

Based on shape, classify each of the four bones labeled (a), (b), (c), and (d) in this diagram.

(a) Humerus: Long bone; (b) Vertebra: Irregular bone; (c) Sternum: Flat bone; (d) Talus: Short bone.

What is a sesamoid bone and what is the primary human example?

A special type of short bone that forms within a tendon, such as the patella (kneecap).

What are the seven primary physiological functions of bones?

Support, protection, movement, mineral and growth factor storage, blood cell formation (hematopoiesis), triglyceride (fat) storage, and hormone production.

What hormone is secreted by bone tissue to regulate insulin secretion and energy metabolism?

Osteocalcin.

What structural term designates the spongy bone layer sandwiched between compact bone plates in flat bones?

Diploë.

What is the diaphysis of a long bone, and what does it contain in adults?

The tubular shaft along the long axis of the bone, composed of compact bone enclosing a central medullary cavity filled with yellow bone marrow.

What is the epiphyseal line in an adult long bone?

A bony remnant of the childhood hyaline cartilage epiphyseal plate where lengthwise bone growth occurred.

What are Sharpey's fibers (perforating fibers)?

Collagen fibers extending from the outer fibrous layer of the periosteum deep into the bone matrix to anchor the periosteum securely.

Where is the endosteum located, and what cells does it contain?

A delicate connective tissue membrane covering internal bone surfaces (trabeculae and canals), containing osteogenic cells.

Where are the primary active sites of hematopoiesis located in an adult human?

In the diploë of flat bones (such as the sternum) and irregular bones (such as the hip bone), as well as the heads of the femur and humerus.

In bone markings, what is a trochanter, and on which bone is it exclusively found?

A very large, blunt, irregularly shaped projection found exclusively on the femur.

In bone markings, what is a condyle?

A rounded articular projection that typically articulates with a corresponding fossa to form a joint.

How does a bone foramen differ anatomically from a meatus?

A foramen is a round or oval opening through a bone for blood vessels and nerves; a meatus is a canal-like passageway.

What are osteogenic (osteoprogenitor) cells?

Mitotically active stem cells located in the periosteum and endosteum that differentiate into osteoblasts or bone-lining cells.

What is osteoid, and what cell type synthesizes it?

The unmineralized organic bone matrix secreted by osteoblasts, composed of ground substance and collagen ($90\%$ of bone protein).

Why do collagen fibers run in alternating directions in adjacent lamellae of an osteon as shown here?

To withstand multidirectional mechanical stress and resist torsional (twisting) forces.

What are osteocytes, where are they housed, and what is their primary function?

Mature, non-dividing bone cells housed in lacunae that monitor and maintain the bone matrix and act as mechanical strain sensors.

What cell lineage gives rise to osteoclasts, and what is their functional role?

Hematopoietic stem cells (the same lineage that produces macrophages); they are giant multinucleated cells that resorb (break down) bone matrix.

What constitutes the inorganic chemical component of bone matrix, and what percentage of total bone mass does it represent?

Hydroxyapatites (mineral salts), consisting mainly of tiny calcium phosphate crystals in and around collagen fibers, accounting for $65\%$ of bone mass.