Genetics, Cellular Functions, Histology, and Osseous Tissue

Vocabulary flashcards covering transcription and translation, histological gland secretion mechanisms, membranes, the integumentary system layers and cell types, and osseous bone anatomy.

Transcription

The process by which DNA code is transferred into RNA inside the nucleus using enzymes and proteins to unzip DNA and create a complementary RNA strand.

mRNA (messenger RNA)

A form of RNA produced in the nucleus that undergoes modification, exits the nucleus, and serves as the template to create a protein.

rRNA (ribosomal RNA)

The structural and functional type of RNA that makes up the ribosome.

tRNA (transfer RNA)

RNA that picks up amino acids from the cytosol and carries them to the ribosome to assemble the polypeptide sequence.

DNA helicase

An enzyme that unzips the double-stranded DNA molecule to expose its base pairs.

Exons

The segments of pre-mRNA that stay in the sequence and code for mRNA and proteins.

Introns

Non-coding portions of pre-mRNA that are spliced out during RNA processing.

Translation

The synthesis of a protein from mRNA occurring in the cytoplasm at a ribosome using tRNA.

Triplet codon

A three-nucleotide base sequence on mRNA that is converted into a specific amino acid during translation.

Eccrine secretion (merocrine secretion)

A glandular secretion mechanism where products are released by exocytosis without loss of cytoplasm (e.g., tear glands and salivary glands).

Apocrine secretion

A secretion mechanism where the product is synthesized in vesicles and released along with part of the cell membrane.

Holocrine secretion

A secretion mechanism in which entire gland cells die and disintegrate, forming a thick, oily secretion consisting of the product and dead cellular debris (e.g., sebum).

Serous membrane

A membrane lining closed internal body cavities and covering organs in motion (such as the pleurae, pericardium, and peritoneum), consisting of mesothelium, thin serous fluid, and connective tissue.

Mesothelium

The simple epithelial layer of a serous membrane that secretes a lubricating fluid similar in composition to blood.

Cutaneous membrane

An external membrane (the skin) consisting of keratinized stratified squamous epithelium resting on a layer of dense irregular connective tissue (dermis) that resists dehydration.

Keratinocytes

The most abundant cells of the epidermis that synthesize keratin.

Epidermal stem cells

Undifferentiated cells confined to the stratum basale that divide and differentiate into keratinocytes.

Melanocytes

Cells located only in the stratum basale that synthesize melanin and have branching processes that transfer pigment to keratinocytes.

Tactile cells (Merkel cells)

Touch receptors found in the basal layer of the epidermis that associate with underlying dermal nerve fibers.

Dendritic cells

Immune cells originating in bone marrow that reside in the stratum spinosum and stratum granulosum to guard against toxins and microbes.

Stratum basale

The deepest epidermal layer consisting of a single layer of cuboidal keratinocytes on the basement membrane; the primary site of mitosis.

Stratum spinosum

The thickest stratum of the epidermis; its deepest cells continue dividing, upper cells flatten, and cells are anchored tightly by desmosomes.

Stratum granulosum

An epidermal layer consisting of $3\text{--}5$ layers of coarse, dark-staining keratinocytes containing lipid-filled lamellar granules.

Stratum lucidum

A clear, translucent layer packed with clear protein and keratinocytes, found only in thick skin.

Stratum corneum

The durable, protective surface layer of the epidermis composed of up to $30$ layers of dead, keratinized, anucleate cells that flake off as dander.

Papillary region

The superficial, thin zone of the dermis composed of areolar connective tissue; rich in small blood vessels and allows the mobility of defensive leukocytes.

Reticular region

The deeper, thicker portion of the dermis consisting of dense irregular connective tissue; more fibrous and cellular, providing toughness.

Apocrine sweat glands

Scent glands located in the groin, axilla, and areola that produce a thicker, milky sweat containing fatty acids via exocytosis; they become active at puberty.

Eccrine sweat glands

Thermoregulatory sweat glands distributed over most of the body (most abundant in palms, soles, and forehead) that secrete water and salts via exocytosis using contracting myoepithelial cells.

Sebaceous glands

Flask-shaped holocrine glands with short ducts opening into hair follicles that secrete sebum.

Diaphysis

The elongated, cylindrical shaft of a long bone.

Epiphysis

The expanded head located at each end of a long bone, containing spongy bone.

Periosteum

A dense irregular connective tissue outer sheath covering the compact cortical bone.

Endosteum

The thin internal tissue layer that lines the medullary cavity of a bone.

Medullary canal

The hollow internal space running through the diaphysis of a long bone that contains bone marrow.

Osteon

The basic structural unit of compact (cortical) bone, composed of concentric lamellae surrounding a central Haversian canal.

Canaliculi

Tiny microscopic canals in compact bone that connect concentric lamellar layers to the central Haversian canal.

Spongy bone

Porous osseous tissue found at the ends of long bones; also known as cancellous or trabecular bone.