A&P 1 Unit 2 (5,6,7,9)

Tissues

Groups of cells similar in structure that perform common or related function

Epithelial tissue (epithelium)

is a sheet of cells that covers body surfaces or cavities

•Two main forms:

•Covering and lining epithelia- On external and internal surfaces (example: skin)

•Glandular epithelia- Secretory tissue in glands (example: salivary glands)

Main functions: protection, absorption, filtration, excretion, secretion, and sensory reception

Simple epithelia

Involved in absorption, secretion, or filtration processes

Simple squamous epithelium

•Cells are flattened laterally, and cytoplasm is sparse

•Function where rapid diffusion is priority

-Example: kidney, lungs

•Two special simple squamous epithelia are based on locations

-Endothelium: lining of lymphatic vessels, blood vessels, and heart

-Mesothelium: serous membranes in the ventral body cavity

Simple cuboidal epithelium

•Single layer of cells

•Involved in secretion and absorption

•Forms walls of smallest ducts of glands and many kidney tubules

Simple columnar epithelium​

• Single layer of tall, closely packed cells​

  • Some cells have microvilli, and some have cilia​

  • Some layers contain mucus-secreting goblet cells​

• Involved in absorption and secretion of mucus, enzymes, and other substances​

  • Ciliated cells move mucus​

• Found in digestive tract, gallbladder, ducts of some glands, bronchi, and uterine tubes​

Pseudostratified columnar epithelium

• Cells vary in height and appear to be multi-layered and stratified, but tissue is in fact single-layered simple epithelium​

  • “Pseudo” means false​

  • Many cells are ciliated​

• Involved in secretion, particularly of mucus, and also in movement of mucus via ciliary sweeping action​

• Located mostly in upper respiratory tract, ducts of large glands, and tubules in testes​

Stratified epithelial tissues

• Involve two or more layers of cells​

• New cells regenerate from below​

  • Basal cells divide and migrate toward surface​

• More durable than simple epithelia because protection is the major role​

Stratified squamous epithelium​

• Most widespread of stratified epithelia​

• Free surface is squamous, with deeper cuboidal or columnar layers​

• Located in areas of high wear and tear (example: skin)​

• Keratinized cells found in skin; nonkeratinized cells are found in moist linings​

Stratified cuboidal epithelium ​

• Quite rare​

• Found in some sweat and mammary glands​

• Typically, only two cell layers thick​

Stratified columnar epithelium

• Very limited distribution in body​

• Small amounts found in pharynx, in male urethra, and lining some glandular ducts​

• Usually occurs at transition areas between two other types of epithelia​

• Only apical layer is columnar​

Transitional epithelium​

• Forms lining of hollow urinary organs ​

  • Found in bladder, ureters, and urethra​

• Basal layer cells are cuboidal or columnar​

• Ability of cells to change shape when stretched allows for increased flow of urine and, in the case of bladder, more storage space​

Gland

• One or more cells that makes and secretes an aqueous fluid called a secretion​

• Classified by:​

  • Site of product release:​

    • Endocrine: internally secreting (example: hormones)​

    • Exocrine: externally secreting (example: sweat)​

• Relative number of cells forming the gland​

  • Unicellular (example: goblet cells) or multicellular (example: salivary)​

Endocrine glands

• Ductless glands​

  • Secretions are not released into a duct; are released into surrounding interstitial fluid, which is picked up by circulatory system​

• Secrete (by exocytosis) hormones, messenger chemicals that travel through lymph or blood to their specific target organs​

• Target organs respond in some characteristic way​

Exocrine glands​

• Secretions are released onto body surfaces, such as skin, or into body cavities​

• More numerous than endocrine glands​

• Secrete products into ducts​

• Examples include mucous, sweat, oil, and salivary glands​

• Can be:​

  • Unicellular​

  • Multicellular​

Unicellular exocrine glands​

• The only important unicellular glands are mucous cells and goblet cells​

• Found in epithelial linings of intestinal and respiratory tracts​

• All produce mucin, a sugar-protein that can dissolve in water to form mucus, a slimy protective, lubricating coating​

Multicellular exocrine glands

• Mode of secretion​

  • Merocrine​

  • Holocrine​

  • Apocrine

Merocrine

most secrete products by exocytosis as secretions are produced (sweat, pancreas)

Holocrine

accumulate products within, then rupture (sebaceous oil glands)​

Apocrine

accumulate products within, but only apex ruptures; whether this type exists in humans is controversial (maybe mammary cells?)​

Connective Tissue​

is the most abundant and widely distributed of primary tissues​

• Major functions: binding and support, protecting, insulating, storing reserve fuel, and transporting substances (blood)​

• Four main classes​

  • Connective tissue proper​

  • Cartilage​

  • Bone ​

  • Blood​

All connective tissues have three main elements​:

• Ground substance​

• Fibers​

• Cells​

  • The first two elements (ground substance and fibers) together make up the extracellular matrix​

Ground substance

• Unstructured gel-like material that fills space between cells​

  • Medium through which solutes diffuse between blood capillaries and cells​

• Components​

  • Interstitial fluid​

  • Cell adhesion proteins (“glue” for attachment) ​

  • Proteoglycans (sugar proteins), made up of protein core + large polysaccharides ​

    • Example: chrondroitin sulfate and hyaluronic acid​

  • Water also is trapped in varying amounts, affecting viscosity of ground substance​

Collagen​ (connective tissue fibers)

• Strongest and most abundant type​

• Tough; provides high tensile strength​

Elastic fibers (connective tissue fibers)​

Networks of long, thin, elastin fibers that allow for stretch and recoil​

Reticular (connective tissue fibers)

• Short, fine, highly branch ​

• Branching forms networks that offer more “give” ​

“Blast” cells​

• Immature form of cell that actively secretes ground substance and ECM fibers ​

• Hematopoietic stem cells in bone marrow​

Fibroblasts

found in connective tissue proper

Chondroblasts

found in cartilage

Osteoblasts

found in bone

“Cyte” cells​

Mature, less active form of “blast” cell that now becomes part of and helps maintain health of matrix​

Fat cells​

store nutrients

White Blood Cells

• Neutrophils, lymphocytes​

• Tissue response to injury​

Mast cells

Initiate local inflammatory response against foreign microorganisms they detect​

Macrophages

Phagocytic cells that “eat” dead cells, microorganisms; function in immune system​

Connective tissue proper​

• Consists of all connective tissues except bone, cartilage, and blood​

CT proper: loose connective tissues​

• Areolar​

• Adipose​

• Reticular​

CT proper: dense connective tissues​

• Dense regular​

• Dense irregular​

• Elastic​

Areolar connective tissue​

• Most widely distributed CT​

• Supports and binds other tissues​

• Universal packing material between other tissues​

• Contains fibroblasts that secrete loose arrangement of mostly collagen fibers​

• Loose fibers allow for increased ground substance, which can act as water reservoir by holding more interstitial fluid​

• Macrophages and fat cells are contained in spaces​

Adipose tissue

• White fat ​

  • Similar to areolar tissue but greater nutrient storage​

  • Cells are called adipocytes​

  • Scanty matrix​

  • Richly vascularized​

  • Functions in shock absorption, insulation, and energy storage​

• Brown fat​

  • Use lipid fuels to heat bloodstream rather than to produce ATP, as does white fat​

Reticular connective tissue​

• Resembles areolar tissue, but fibers are thinner reticular fibers​

• Fibroblast cells are called reticular cells​

  • Secrete reticular fibers made up of thin collagen​

• Reticular fibers form a mesh-like stroma that acts as a support for blood cells in lymph nodes, spleen, and bone marrow​

Dense regular connective tissue

• Very high tensile strength; can withstand high tension and stretching​

• Closely packed bundles of thick collagen fibers run parallel to direction of pull​

  • Fibers appear as white structures​

    • Great resistance to pulling​

  • Fibers slightly wavy, so stretch a little​

• Fibroblasts manufacture collagen fibers and ground substance​

• Very few cells and ground substance, mostly fibers​

• Poorly vascularized​

• Example: tendons and ligaments​

Dense irregular connective tissue​

• Same elements as dense regular, but bundles of collagen are thicker and irregularly arranged​

• Forms sheets rather than bundles​

• Resists tension from many directions​

• Found in:​

  • Dermis​

  • Fibrous joint capsules​

  • Fibrous coverings of some organs​

Elastic connective tissue​

• Some ligaments are very elastic​

  • Example: ligaments connecting adjacent vertebrae must be very elastic​

• Also found in walls of many large arteries​

  • Arteries need to stretch when blood enters and recoil to push blood out​

Cartilage

• Matrix secreted from chondroblasts (during growth) and chondrocytes (adults)​

  • Chondrocytes found in cavities called lacunae​

  • 80% water, with packed collagen fibers and sugar proteins (chondroitin and hyaluronic acid)​

• Tough yet flexible material that lacks nerve fibers​

• Avascular: receives nutrients from membrane surrounding it (perichondrium)​

  • Periochondrium gives rise to chondroblasts and chondrocytes​

Hyaline cartilage

• Most abundant; “gristle”​

• Appears as shiny bluish glass​

• Found at tips of long bones, nose, trachea, larynx, and cartilage of the ribs​

Elastic cartilage

• Similar to hyaline but with more elastic fibers​

• Found in ears and epiglottis​

Fibrocartilage​

• Properties between hyaline and dense regular tissue​

• Strong, so found in areas such as intervertebral discs and knee

Muscle Tissue​

• Highly vascularized​

• Responsible for most types of movement​

  • Muscle cells possess myofilaments made up of actin and myosin proteins that bring about contraction​

• Three types of muscle tissues:​

  • Skeletal muscle​

  • Cardiac muscle​

  • Smooth muscle​

Skeletal muscle tissue​

• Attached to and causes movement of bones​

• Also called voluntary muscle​

  • Skeletal muscles can be consciously controlled​

• Cells are called muscle fibers​

  • Contain multiple nuclei​

  • Appear striated or banded​

Cardiac muscle tissue

• Found only in walls of heart​

• Involuntary muscle​

• Like skeletal muscle, contains striations; but cells have only one nucleus​

• Cells can have many branches that join branches of other cardiac cells​

  • Intercalated discs are special joints where cardiac cells are joined​

Smooth muscle tissue​

• Found mainly in walls of hollow organs (other than heart)​

• Involuntary muscle​

• Has no visible striations​

• Spindle-shaped cells with one nucleus​

Integument

skin

Cutaneous membrane

covers the entire outermost surface of the body

Epidermis

• top layer of skin

• Stratified squamous epithelium​

Dermis

• Deeper layer​

• Primarily dense irregular connective tissue​

Subcutaneous layer (hypodermis)​

• Deep to dermis​

• Layer of alveolar and CT​

• Not part of integumentary system​

Layers (strata) from deep to superficial

1. Stratum corneum​

2. Stratum lucidum​

3. Stratum granulosum​

4. Stratum spinosum​

5. Stratum basale​

First three layers composed of living keratinocytes

Stratum Corneum

• Superficial stratum composed of 20 to 30 layers of dead, interlocking, anucleate (lacking a nucleus), keratinized cells​

• Dry, thickened surface is protective against abrasion and infection​

Stratum Lucidum

• Translucent layer, 2 to 3 cell layers thick ​

• Found only on thick skin on palms and soles​

Stratum granulosum​

• 3 to 5 layers of keratinocytes​

• Keratinocytes begin keratinization​

• Keratinocytes fill with keratin​

• Nucleus and organelles to disintegrate, cells are dead​

Stratum Spinosum​

• New cells from stratum basale pushed into this layer​

• Nondividing keratinocytes attached by desmosomes​

Epidermal dendritic cells (Langerhans cells)

• found in stratum spinosum and granulosum​

• Initiate immune response​

Stratum Basale​

• Deepest epidermal layer​

• Single layer of cuboidal to low columnar cells​

• Three cell types:​

1. Keratinocytes​

2. Melanocytes​

3. Tactile cells​

Keratinocytes​

• Found in all layers​

• Those in stratum basale are large stem cells ​

• Divide to regenerate new cells​

• Synthesize keratin​

  • Protein that strengthens epidermis​

Melanocytes​

• Scattered among keratinocytes in stratum basale​

• Produce and store pigment (melanin) in response to ultraviolet light​

• Transfer pigment granules (melanosomes) into keratinocytes​

  • Shield nuclear DNA from UV radiation​

Tactile cells

• Merkel cells​

• Few in number​

• Sensitive to touch​

  • When compressed, release chemicals, stimulate sensory nerve endings​

Thick skin​

• Palms of hands, soles of feet​

• Contains all five layers of epidermal strata​

• Sweat glands but no hair follicles or sebaceous glands​

Thin skin

• Covers most of body​

• Lacks a stratum lucidum​

• Sweat glands, hair follicles, and sebaceous glands​

Hemoglobin​

• Oxygen-binding protein in red blood cells​

• Bright red color upon binding oxygen

Melanin​

• Dark pigment produced in melanocytes, transferred to keratinocytes​

• Eumelanin – brown, black shades; pheomelanin – lighter shades: tan, yellow, red​

• Amount in skin varies (heredity, UV exposure)​

  • Albinism: Melanocytes unable to produce melanin​

Carotene​

Yellow-orange pigment acquired from some vegetable​

Friction ridges​

• Large folds and valleys of dermis and epidermis​

• Fingerprints​

Dermis

• Deep to epidermis​

• Composed of CT proper​

  • Other structures present: Blood vessels, sweat glands, sebaceous glands, hair follicles, nail roots, sensory nerve endings, arrector pili, motile dendritic cells​

• Papillary and reticular layers​

Papillary layer of dermis

• Superficial region of dermis, deep to epidermis​

• Areolar connective tissue​

• Named for projections of dermis, dermal papillae​

  • Interlock with epidermal ridges to increase area of contact between layers​

Reticular layer of dermis

• Deeper, major portion of dermis​

• Dense irregular connective tissue​

lines of cleavage (tension lines)​

• Incisions parallel to cleavage lines more likely to heal quickly​

• Incisions perpendicular to cleavage lines are more likely to open due to cut elastic fibers​

Subcutaneous Layer - Hypodermis​

• Not part of integument​

• Areolar and adipose CT​

• Functions: Protection, energy storage, and insulation​

• Common drug injection site​

  • Extensive vascular network promotes rapid absorption​

• Thickness/distribution influenced by sex hormones​

Functions of Epidermis​

• Protection from the external environment​

  • Protects body from injury, harmful substances, microbes, extreme temperatures, and UV radiation​

• Prevention of water loss/gain​

  • Epidermis is water resistant, not waterproof​

  • Water lost by sweat and transpiration​

• Vitamin D synthesis​

  • Formation of vitamin D3, a precursor to calcitriol​

    • Calcitriol increases absorption of calcium and phosphate from diet; regulates blood calcium levels​

• Secretion​

  • Waste products secreted onto skin surface during sweating​

• Absorption​

  • Skin absorbs some chemicals/drugs but blocks others​

• Selectively permeable​

  • Suitable for transdermal administration of some drugs​

• Immune function​

  • Dendritic cells in epidermis and dermis capable of initiating immune response​

• Temperature regulation​

  • Dermal blood vessels capable of vasoconstriction to conserve heat or vasodilation to release heat​

• Sensory reception​

  • Receptors detect stimuli (e.g., touch, pressure)​

Three types of hair

• Lanugo

• Vellus

• Terminal hair

Lanugo

• fine, unpigmented, downy hair​

• Appears in last trimester​

Vellus

• fine hair​

• Primary human hair​

• Found on upper and lower limbs​

Terminal hair

• coarser, pigmented, longer​

• On scalp, eyebrows, and eyelashes, men’s beards​

• During puberty, replaces vellus hair in axillary and pubic regions​

Hair matrix​

• Structure at base of the hair bulb​

• Epithelial cells divide here​

• Produce new cells, gradually pushed toward surface​

Medulla​

• Remnant of matrix​

• Flexible, soft keratin​

Cortex​

• Flattened cells closer to outer hair surface​

• Relatively hard

Cuticle​

Single cell layer around cortex​

Hair follicle

• Oblique tube surrounding hair root​

• Extends into dermis and sometimes subcutaneous layer​

• Outer connective tissue root sheath originating in dermis​

• Inner epithelial tissue root sheath originating from epidermis​

Arrector pili​

• Thin ribbons of smooth muscle​

• Extend from hair follicle to dermal papillae​

• Elevates hair with contraction, “goosebumps”​

Hair Functions​

• Protection​

  • On head, from sunburn and injury​

  • Respiratory system and ears – hair traps particles, debris​

• Heat retention​

• Sensory reception​

  • Root hair plexuses detect light touch​

• Visual identification

Hair Color​

• Synthesis of melanin in matrix produces hair color​

• Lightens with age as pigment production decreases​

• Gray hair results from gradual reduction in melanin​

• White hair occurs due to complete stoppage of melanin production​

• An Abundance of eumelanin results in brown or black hair​

• An abundance of pheomelanin results in red hair

Sweat glands and sebaceous glands​

• Sweat glands include two types​

• Merocrine​

• Apocrine​

• Both types have a coiled, secretory portion with myoepithelial cells that aid in secretion process​

• Both types contain a sweat gland duct​

• Sweat gland duct opens to sweat pore​

Merocrine (eccrine) sweat glands​

• Most numerous and widely distributed​

• Simple, coiled tubular glands​

• Discharge secretions onto skin surface​

• Produce secretion by exocytosis​

• Secrete sweat​

  • Composed of 99% water and 1% other chemicals​

  • Includes: electrolytes, metabolites, and waste products​

• Major role in thermoregulation​

Apocrine sweat glands​

• Coiled, tubular glands​

• Discharge secretions into hair follicles located axillae, around nipples, in pubic and anal region​

• Produce secretion by exocytosis​

• Produce viscous cloudy secretions​

  • Contain proteins and lipids​

  • Produce odor when acted on by bacteria​

• Start producing secretions during puberty​

Sebaceous glands​

• Holocrine glands​

• Produce oily secretion, sebum​

  • Lubricant for skin and hair​

  • Bacterial ​

  • Discharges into a hair follicle​

• Secretion stimulated by hormones, especially male sex hormones​

• Activated during puberty​

Ceruminous glands​

• Modified apocrine sweat glands​

• Located only in external ear canal​

• Secretions of waterproof earwax, cerumen​

  • Traps foreign material​

  • Lubricates acoustic meatus and eardrum

Mammary glands​

• Modified apocrine sweat glands of breast​

• Only function in pregnant and lactating females​

• Produce breast milk​

Three major types of skin cancer​

• Basal cell carcinoma​

• Squamous cell carcinoma​

• Melanoma​

Basal cell carcinoma

• Least malignant and most common​

• Stratum basale cells proliferate and slowly invade dermis and hypodermis​

• Cured by surgical excision in 99% of cases​

Squamous cell carcinoma

• Second most common type; can metastasize​

• Involves keratinocytes of stratum spinosum​

• Usually is a scaly reddened papule on scalp, ears, lower lip, or hands​

• Good prognosis if treated by radiation therapy or removed surgically​