Core of actin filaments for stiffening Nucleus: Genetic library with blueprints for nearly all cellular proteins. Responds to signals and dictates kinds and amounts of proteins to be synthesized. Most cells are uninucleate. Red blood cells are anucleate. Skeletal muscle cells, bone destruction cells, and some liver cells are multinucleateCell Cycle: Defines changes from formation of the cell until it reproduces. Includes: Interphase and Cell division (mitotic phase)Interphase: Period from cell formation to cell division10
Nuclear material called chromatin. Four subphases: G1(gap 1)—vigorous growth and metabolism. G0—gap phase in cells that permanently cease dividing. S (synthetic)—DNA replication. G2(gap 2)—preparation for divisionChapter 5Skin (Integument): Consists of three major regions- Epidermis-superficial region. Dermis—middle region. Hypodermis (superficial fascia)—deepest region. Subcutaneous layer deep to skin (not technically part of skin). Mostly adipose tissueEpidermis: Keratinized stratified squamous epithelium Cells of epidermis:oKeratinocytes- produce fibrous protein keraoMelanocytes- 10–25% of cells in lower epidermis. Produce pigment melaninoEpidermal dendritic (Langerhans) cells- macrophages that help activate immune systemoTactile (Merkel) cells- touch receptorsStratum corneum: 20–30 rows of dead, flat, keratinized membranous sacs. Three-quarters of the epidermal thickness. Functions: Protects from abrasion and penetration, Waterproofs, and Barrier against biological, chemical, and physical assaultsDermis: Strong, flexible connective tissue. Cells include fibroblasts, macrophages, and occasionally mast cells and white blood cells. Two layers: Papillary and ReticularPapillary layer: Areolar connective tissue with collagen and elastic fibers and blood vessels. Dermal papillae contain: Capillary loops, Meissner’s corpuscles, and Free nerve endings Reticular layer: ~80% of the thickness of dermis. Collagen fibers provide strength and resiliency. Elastic fibers provide stretch-recoil propertiesSkin Color: Three pigments contribute to skin color: melanin, carotene, and hemoglobin Melanin: Yellow to reddish-brown to black, responsible for dark skin colors. Produced in melanocytes; migrates to keratinocytes where it forms “pigment shields” for nuclei. Freckles and pigmented moles are local accumulations of melaninCarotene: Yellow to orange, most obvious in the palms and soles Hemoglobin: Responsible for the pinkish hue of skinSweat Glands: Two main types of sweat (sudoriferous) glands: eccrine sweat glands and apocrine sweat glands11
Eccrine (merocrine) sweat glands—abundant on palms, soles, and forehead. Sweat: 99% water, NaCl, vitamin C, antibodies, dermcidin, metabolic wastes. Ducts connect to pores. Function in thermoregulationApocrine sweat glands—confined to axillary and anogenital areas. Sebum: sweat + fatty substances and proteins. Ducts connect to hair follicles. Functional from puberty onward(as sexual scent glands?)Specialized apocrine glands: Ceruminous glands (in external ear canal; secrete cerumen)
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