Block 9 Histology Flashcards
What are the three layers of the skin, from superficial to deep? How do they stain on H&E?
- Epidermis - purple/blue
- Dermis - pink (mostly collagen)
- Subcutis - clear (mostly adipose)
Describe the composition of the epidermis.
Multiple layers of keratinocytes (keratin-containing epithelial cells) + melanocytes, Merkel cells, and Langerhans cells dispersed throughout
What are the 3 major functions of the epidermis?
- Maintenance of fluid and electrolyte balance
- Protection from UV light
- Sensory and immune function
What are the 5 layers of the epidermis, from superfical to deep?
- Stratum corneum
- Stratum lucidum
- Stratum granulosum
- Stratum spinosum
- Stratum basale
Cancel Lab Get Some Beer
Compare the appearance of the stratum corneum in thin vs. thick skin.
Thin - basket-weave
Thick - compact, thicker
Which layer of the epidermis does squamous cell carcinoma typically arise from?
Stratum spinosum
What is the most common cutaneous skin cancer in humans and which layer of the epidermis does it arise from?
Basal cell carcinoma; stratum basale
What is a Rete ridge?
Finger-like projection of the epidermis down into the dermis (adhesion)
Compare the locations of thin and thick skin?
Thin: entire body except thick skin areas
Thick: palmas of hands and soles of feet
What is acral skin?
The palms of the hands and soles of the feet, which are covered by thick skin
Which layer of the epidermis is not found in thin skin?
Stratum lucidum
Compare the presence of hair follicles and other structures in thin and thick skin.
Thin skin: hair follicles except lips, labia minora, and glans penis
Thick skin: no hair follicles, more sensory receptors, increased eccrine glands, fewer sebaceous glands
Discuss the process of desquamatization.
The layers of the epidermis represent vertical maturation from undifferentiated basal cells to fully differentiated cornified cells. This process takes about 25 days.
Shorter epidermal maturation periods are seen in what types of conditions?
Inflammatory, such as psoriasis
How do cells adhere to one another in the epidermis?
Desmosomes connect keratinocytes at the macula adherens; hemidesmosomes connect keratinocytes to the basement membrane.
What process is prevented by cell-cell adherence in the epidermis?
Acantholysis
What are melanocytes and where are they found?
Clearish cells in the basal layer with dark nuclei (1:10 ratio - melanocyte: keratinocyte) that produce melanin (which is distributed to nearby keratinocytes)
Where are Langerhans cells found in the epidermis and what do they do?
Mid-spinous layer; dendritic cells
Where are Merkel cells found in the epidermis and what do they do?
Stratum basale; receptor cells that establish synaptic contacts with sensory nerves
Benign proliferations of melanocytes are called ___ and ___; malignant transformation results in ___.
Lentigos; nevi; melanoma
Keratinocytes wear melanin pigment like a ___.
Cap on top of their nuclei
What connects the epidermis and dermis?
Dermal-epidermal junction (DEJ)
What are the components of the DEJ?
- Hemidesmosome (connects basal keratinocytes to the BM)
- BM
- Anchoring fibrils attach the BM to the dermis (hooks onto 7 and 1)
What are the two components of the basement membrane and what types of collagen are contained in each?
- Lamina lucida (17, 13, laminin 5 and 6)
2. Lamina densa (7)
What is the the dermis?
Everything below the DEJ/basement membrane - connective tissue layer containing blood vessels, nerves, sensory receptors, adnexal structures
The dermis is composed mostly of type ___ collagen.
1
What are the two layers of the dermis?
- Papillary dermis - includes the dermal papilla which project into the epidermis, as well as capillaries, free nerve endings, and Meissner’s corpuscles
- Reticular dermis - between papillary dermis and subcutis
What is the function of dermal papilla?
Increased contact area, prevents epidermal detachment; leads to fingerprints
What are the two major types of fibers composing the dermis?
- Type I collagen
2. Elastic fibers
What are the adnexal structures of the reticular dermis?
- Sebaceous glands
- Hair follicles
- Eccrine glands
- Apocrine glands
- Erector pili (smooth muscle)
How do the sebaceous glands appear on H&E stain?
Clear, bubbly cells
Sebaceous glands utilize holocrine secretion - what is this?
The entire cell disintegrates and collapses to form the secretion
Sebaceous glands are usually associated with ___.
Hair follicles
What are the layers of the hair follicle, from superficial to deep?
- Infundibulum
- Isthmus
- Stem
- Bulb (contains papilla)
What are the layers of the hair follicle in cross section, from inner to outer?
- Medulla
- Cortex
- Cuticle
- Inner root sheath
- Outer root sheath
- Connective tissue sheath
What are eccrine glands?
Merocrine sweat glands that adjust body temperature
What are the three types of cells found in eccrine glands?
- Dark cells (pyramid shaped with secretory granules lining the lumen of the tube)
- Clear cells (near BM)
- Myoepithelial cells spindle shaped contractile cells)
What are apocrine glands?
Glands with larger lumens and ducts that empty onto superficial regions of hair follicles
What is apocrine snouting?
The release of product from apocrine glands via shedding of part of cytoplasm
What are apocrine glands found and what influences them?
Axilla, areola, perianal, genital area; hormones
What is the subcutis?
Area deep to the dermis (includes the hypodermis); loose connective tissue containing adipose tissue, nerves, sensory receptors (Pacinian corpuscles), arteries, and veins; provides a flexible attachment to the underlying muscle and fascia
Which sensory receptor appears like an onion skin? What sensory information does it convey?
Pacinian corpuscle; deep touch and vibration
What are the main functions of bone?
- Support
- Protection (of internal organs)
- Movement (leverage system for muscles, tendons, ligaments, joints)
- Mineral homeostasis (reserve)
- Hematopoiesis
- Storage of adipose tissue (yellow marrow)
What is the long shaft of bone?
Diaphysis (composed of compact bone)
What are the ends of bones?
Epiphysis (composed of spongy bone)
What is the growth plate of bone?
Epiphyseal plate (made of hyaline cartilage)
What is the area between the epiphysis and diaphysis?
Metaphysis
What covers the epiphysis?
Articular cartilage
What covers bone?
Periosteum
What attaches the periosteum to the underlying bone?
Sharpey’s fibers
What is the hollow chamber in bone?
Medullary cavity
What does the red marrow produce?
Blood cells
What is the yellow marrow?
Adipose tissue
What is the thin layer lining the medullary cavity?
Endosteum
What supplies blood to the bone?
- Periosteal arteries
2. Epiphyseal veins
What is the difference between compact and spongy bone?
Compact - dense outer layer of long bone, no trabeculae
Spongy - honeycomb of trabeculae, filled with red and yellow bone marrow
Compact bone is also known as ___ bone, and it makes up the majority of all ___ bones. What is its primary function?
Lamellar; long; protection and strength
Blood vessels and nerves penetrate the periosteum of compact bone through horizontal openings called ___.
Perforating (Volkmann’s) canals
What is an osteon?
Canal surrounded by concentric lamelli
What are central (Haversian) canals?
Canals running longitudinally through compact bone
Describe the osteon system.
Concentric lamella surround central canals.
Osteocytes occupy lacunae, which are between the lamella.
Canaliculi are channels that radiate from the lacunae.
Describe the hard matrix of the bone.
25% water
25% protein
50% mineral salts
Organic (non-calcified components): type I collagen and non-mineralized ground substance, found in “new bone” or osteoid
Inorganic (calcified) - hydroxyapatite, mineralized calcified osteoid
What are the 4 cell types that make up osseous tissue?
- Osteoprogenitor cells
- Osteoblasts
- Osteocytes
- Osteoclasts
What are osteoprogenitor cells?
Unspecialized stem cells that undergo mitosis and develop into osteoblasts; found on inner surface of the periosteum and endosteum
What are osteoblasts?
Bone forming cells, also secrete collagen; found on the surface of bone
What are osteocytes?
Mature bone cells derived from osteoblasts; do not secrete material; exchange nutrients and waste with blood
What are osteoclasts?
Bone resorbing cells found on the surface of the bone; function in growth, maintenance, and repair
How do osteoclasts appear on H&E?
Large, multinucleated
What are chondrocytes?
Cartilage producing cells
What are lacunae?
Small cavities where the chondrocytes are encased
What is the ECM of the cartilage?
Jellylike ground substance
What is the perichondrium?
Layer of dense irregular connective tissue that surrounds the cartilage
Does the cartilage have blood vessels or nerves?
No
List the three types of cartilage.
- Hyaline (glassy)
- Elastic
- Fibrocartilage
What is the most abundant type of cartilage?
Hyaline
What is the role of hyaline cartilage and where is it found?
Support through flexibility; articular cartilages and costal cartilage, larynx, trachea, nose
What is the role of elastic cartilage and where is it found?
Tolerates repeated bending; ear and epiglottis
What is the role of fibrocartilage and where is it found?
Resists strong compression and strong tension (intermediate between the other two); intervertebral discs and pubic symphasis
What is the process of bone formation?
Ossification
What are the 4 situations in which ossification occurs?
- Formation of bone in an embryo
- Growth of bones until adulthood
- Remodeling
- Repair of fractures
Cartilage formation and ossification occurs during the ___ week of embryonic development.
Sixth
Describe the process of intramembranous ossification.
- An ossification center appears in the fibrous connective tissue membrane.
- Osteoblasts secrete bone matrix within the fibrous membrane
- Osteoblasts mature into osteocytes
List the steps of endochondral ossification.
- Cartilage model
- Developing cartilage model
- Formation of bone collar
- Formation of primary ossification center
- Formation of bony trabeculae
- Formation of the secondary ossification center
- Continuous primary and secondary ossification
List the five zones of bone growth seen at the epiphyseal plate.
- Reserve (inactive chondrocytes)
- Proliferation (chondrocytes undergo mitosis and arrange in columns)
- Hypertrophy (mature chondrocytes with increased size)
- Calcification zone (cartilage matrix becomes calcified)
- Ossification zone (blood vessels and primary marrow, bone deposition)
What is growth of a bone by addition of bone tissue to its surface that allows for bones to widen as they lengthen?
Appositional bone growth
How does appositional bone growth occur?
Bone is resorbed at the endosteal surface and added at the periosteal surface (osteoclasts remove bone form the internal surface of the diaphysis, osteoblasts add it to the external surface)
Which type of bone is replaced more frequently (spongy vs. compact)?
Spongy (every 3-4 years, vs. every 10 years)
