Bio 211 Exam 2 Study Guide: Histology, Integumentary System, and Skeletal System

Histology

Types of Tissues

Histology is the study of tissues. The human body is composed of four primary tissue types:

• Epithelial Tissue: Covers body surfaces and lines cavities.

• Connective Tissue: Supports, protects, and binds other tissues.

• Muscle Tissue: Responsible for movement.

• Nervous Tissue: Initiates and transmits electrical impulses.

Epithelial Tissue

Epithelial tissue forms the linings of internal and external surfaces. It serves several functions:

• Protection: Shields underlying tissues from injury and infection.

• Absorption: Takes in nutrients and substances (e.g., intestines).

• Secretion: Produces sweat, mucus, enzymes, etc.

• Filtration: Filters substances (e.g., kidney tubules).

Epithelia are found on skin, lining of digestive tract, blood vessels, and glands.

Naming Epithelium

• Based on number of layers and cell shape:

• Simple: One layer

• Stratified: Multiple layers

• Squamous: Flat cells

• Cuboidal: Cube-shaped cells

• Columnar: Tall, column-like cells

• Example: Simple columnar epithelium (one layer, tall cells)

Endothelium and Mesothelium

• Endothelium: Simple squamous epithelium lining blood vessels and heart.

• Mesothelium: Simple squamous epithelium lining body cavities (e.g., peritoneum, pleura).

Specialized Epithelia

• Simple columnar epithelium: Found in digestive tract; contains microvilli (brush border) for absorption.

• Transitional epithelium: Found in urinary bladder; stretches to accommodate volume changes.

• Stratified epithelium: Major role is protection (e.g., skin).

Glands

• Exocrine glands: Secrete products into ducts (e.g., sweat, salivary glands).

• Endocrine glands: Secrete hormones directly into bloodstream.

• Unicellular glands: Goblet cells (produce mucin, found in intestines and respiratory tract).

• Multicellular glands: Classified as merocrine (secrete by exocytosis) or holocrine (cells rupture to release product).

Mucin: Glycoprotein secreted by goblet cells; forms mucus when hydrated.

Connective Tissue (CT)

Connective tissue supports and connects other tissues. It is classified by function and structure:

• Functions: Support, protection, insulation, transport.

• Categories: Loose CT, Dense CT, Cartilage, Bone, Blood.

Components: Cells (fibroblasts, adipocytes, chondrocytes, osteocytes), fibers (collagen, elastic, reticular), ground substance.

Vascularity: Varies; cartilage is avascular, bone is highly vascular.

Adipose Tissue

• Cell type: Adipocytes

• Vascularity: Highly vascular

• White fat: Stores energy

• Brown fat: Generates heat

Other Connective Tissues

• Reticular CT: Found in lymph nodes, spleen.

• Dense Regular CT: Tendons, ligaments; fibroblasts, parallel collagen fibers, poor vascularity, few cells.

• Dense Irregular CT: Dermis of skin; randomly arranged fibers.

• Elastic CT: Walls of large arteries.

• Cartilage: Three types—hyaline (joints), elastic (ear), fibrocartilage (intervertebral discs).

• Blood: Contains red and white blood cells, platelets.

Membranes

• Cutaneous: Skin

• Mucosal: Lines body cavities open to exterior

• Serous: Lines closed body cavities

Integumentary System

Definition and Structure

The integumentary system includes the skin and its derivatives (hair, nails, glands). It protects the body and regulates temperature.

• Skin: Composed of stratified squamous epithelium (epidermis) and connective tissue (dermis).

• Keratinocytes: Produce keratin, a protective protein.

• Melanocytes: Produce melanin, pigment for skin color.

Layers of the Epidermis

• Stratum basale: Deepest layer; contains stem cells, melanocytes.

• Stratum granulosum: Cells flatten; above this layer, cells are dead.

• Stratum lucidum: Present only in thick skin (palms, soles).

• Dander: Flakes of dead skin cells.

Dermis

• Layers: Papillary (loose CT), reticular (dense irregular CT).

• Dermal papillae: Projections that increase surface area.

• Cleavage lines: Natural lines in skin; important for surgery.

• Flexure lines: Folds at joints.

• Striae: Stretch marks.

• Melanin: Brown-black pigment.

• Carotene: Yellow-orange pigment.

Alterations in Skin Color

Condition	Appearance	Associated Cause
Cyanosis	Blue	Low oxygen
Pallor	Pale	Shock, anemia
Jaundice	Yellow	Liver dysfunction
Bronzing	Bronze	Addison's disease
Bruising	Black/blue	Blood vessel damage

Other Features

• Arrector pili muscle: Causes hair to stand up (goosebumps).

• Hirsutism: Excessive hair growth.

• Baldness, alopecia: Hair loss.

Sweat Glands

• Major components of sweat: Water, salts, urea.

• Eccrine glands: Found all over body; produce watery sweat.

• Apocrine glands: Found in axilla, groin; produce thicker, odoriferous sweat.

• Ceruminous glands: Found in ear canal; produce earwax (cerumen).

Skin Cancer

Type	Origin	Metastasis Risk
Basal cell carcinoma	Stratum basale	Low
Squamous cell carcinoma	Stratum spinosum	Moderate
Melanoma	Melanocytes	High

Most likely to metastasize: Melanoma

Tissue type where most cancers originate: Epithelial tissue

Burns

• Degrees: First (epidermis), second (epidermis + dermis), third (full thickness).

• Treatments: Fluid replacement, infection prevention.

• Immediate threat: Loss of fluids, infection.

Skeletal System

Cartilage

• Perichondrium: Dense CT covering cartilage; provides nutrients.

• Types: Hyaline, elastic, fibrocartilage.

• Growth: Appositional (surface), interstitial (within).

Bone Functions

• Support

• Protection

• Movement

• Mineral storage

• Blood cell formation (hematopoiesis)

Bone Classification

• Axial skeleton: Skull, vertebral column, rib cage.

• Appendicular skeleton: Limbs, girdles.

• Shape: Long, short, flat, irregular bones.

Bone Structure

• Compact bone: Dense, found on outer surfaces.

• Spongy bone: Porous, found inside bones.

• Long bones: Diaphysis (shaft), epiphyses (ends).

• Periosteum: CT covering bone; contains osteogenic layer (stem cells).

• Sharpey’s fibers: Collagen fibers anchoring periosteum to bone.

• Endosteum: Lines internal bone surfaces.

Hematopoiesis

• Occurs in red marrow (found in flat bones, ends of long bones).

Bone Cells

• Osteoblasts: Build bone.

• Osteocytes: Mature bone cells.

• Osteoclasts: Break down bone.

Microscopic Structure

• Osteon: Structural unit of compact bone.

• Haversian canals: Central canals for blood vessels.

• Volkmann’s canals: Perpendicular canals connecting osteons.

Bone Homeostasis

• Growth hormone: Stimulates bone growth.

• Parathyroid hormone (PTH): Increases blood calcium by stimulating osteoclasts.

• Calcium homeostasis: Maintained by feedback system involving PTH and calcitonin.

Calcium Homeostasis Equation:

$\text{Blood Ca}^{2+} \uparrow \Rightarrow \text{Calcitonin released} \rightarrow \text{Bone deposition}$

$\text{Blood Ca}^{2+} \downarrow \Rightarrow \text{PTH released} \rightarrow \text{Bone resorption}$

Case Studies

• Apply knowledge of bone and skin disorders to clinical scenarios.

Additional info: Expanded explanations and context were added for clarity and completeness, including definitions, examples, and tables for skin color alterations and skin cancer types.