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

Histology

Types of Tissues

Histology is the study of tissues, which are groups of cells with similar structure and function. The human body contains four primary tissue types:

• Epithelial Tissue: Covers surfaces, lines cavities, forms glands.

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

• Muscle Tissue: Responsible for movement.

• Nervous Tissue: Conducts electrical impulses, communication.

Epithelial Tissue

Epithelial tissue functions as a protective barrier, controls permeability, and forms glands. It is found lining the skin, digestive tract, respiratory system, and blood vessels.

• Functions: Protection, absorption, filtration, excretion, secretion, sensory reception.

• Locations: Skin (epidermis), lining of GI tract, respiratory passages, blood vessels (endothelium).

Naming Epithelium

Epithelium is named based on cell layers and cell shape:

• Layers: Simple (one layer), Stratified (multiple layers).

• Shapes: Squamous (flat), Cuboidal (cube-shaped), Columnar (tall).

• Example: Simple squamous epithelium (one layer of flat cells).

Endothelium and Mesothelium

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

• Mesothelium: Simple squamous epithelium lining serous membranes (pleura, pericardium, peritoneum).

Specialized Epithelia

• Simple Columnar Epithelium: Found in digestive tract; contains microvilli (brush border) for increased absorption.

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

• Stratified Epithelium: Major role is protection; found in skin, mouth, esophagus.

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 respiratory and digestive tracts.

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

Mucin

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

Connective Tissue (CT)

Connective tissue supports, protects, and binds other tissues. It is classified based on structure and function.

• 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; bone is highly vascular, cartilage is avascular.

Adipose Tissue

• Cell Type: Adipocytes.

• Vascularity: Highly vascular.

• White Fat: Stores energy, insulates.

• Brown Fat: Generates heat (thermogenesis).

Other Connective Tissues

• Reticular CT: Found in lymph nodes, spleen, bone marrow.

• Dense Regular CT: Cell type: fibroblasts; fibers: parallel collagen; low vascularity; few cells; found in tendons, ligaments.

• Dense Irregular CT: Found in dermis; fibers arranged irregularly.

• Elastic CT: Found in large arteries, some ligaments.

Cartilage

• Hyaline Cartilage: Found in nose, trachea, ends of long bones.

• Elastic Cartilage: Found in ear, epiglottis.

• Fibrocartilage: Found in intervertebral discs, pubic symphysis.

Blood

• Cells: Erythrocytes (RBCs), leukocytes (WBCs), platelets.

Membranes

• Cutaneous Membrane: Skin.

• Mucosal Membrane: Lines body cavities open to exterior (digestive, respiratory).

• Serous Membrane: Lines closed cavities (pleura, pericardium, peritoneum).

Integumentary System

Definition and Structure

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

• Skin: Composed of stratified squamous epithelium; main cell types are keratinocytes (produce keratin) and melanocytes (produce melanin).

Layers of the Epidermis

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

• Stratum Spinosum: Several layers; keratinocytes, dendritic cells.

• Stratum Granulosum: Flattened cells; above this layer, cells are dead.

• Stratum Lucidum: Only in thick skin (palms, soles).

• Stratum Corneum: Outermost; dead, keratinized cells.

Other Features

• Dander: Flakes of dead skin cells.

• Dermis: Two layers: papillary (loose CT, dermal papillae) and reticular (dense irregular CT).

• Dermal Papillae: Projections that increase surface area; form fingerprints.

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

• Flexure Lines: Where skin folds at joints.

• Striae: Stretch marks.

• Melanin: Pigment produced by melanocytes; determines skin color.

• Carotene: Yellow-orange pigment from diet.

Alterations in Skin Color

Condition	Description	Associated Causes
Cyanosis	Blue skin	Low oxygen
Pallor	Pale skin	Anemia, shock
Jaundice	Yellow skin	Liver dysfunction
Bronzing	Bronze skin	Addison's disease
Bruising	Black/blue marks	Blood vessel damage

Other Structures

• Arrector Pili Muscle: Smooth muscle; causes hair to stand up (goosebumps).

• Hirsutism: Excessive hair growth.

• Baldness: Loss of hair.

• Alopecia: General term for hair loss.

Sweat Glands

• Major Components of Sweat: Water, salts, urea, ammonia.

• Eccrine Glands: Found all over body; produce watery sweat for cooling.

• Apocrine Glands: Found in axilla, groin; produce thicker sweat, odor.

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

Skin Cancer

Type	Description	Metastasis Risk
Basal Cell Carcinoma	Most common, least dangerous	Low
Squamous Cell Carcinoma	Second most common	Moderate
Melanoma	Arises from melanocytes	High (most likely to metastasize)

• Tissue Type: Most cancers originate in 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 and Bone Structure

• Perichondrium: Dense CT covering cartilage; provides nutrients.

• Cartilage Types: Hyaline, elastic, fibrocartilage.

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

Functions of Bone

• Support

• Protection

• Movement

• Mineral storage (Ca2+, phosphate)

• Blood cell formation (hematopoiesis)

• Triglyceride storage

Classification and Structure

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

• Appendicular Skeleton: Limbs, girdles.

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

• Compact Bone: Dense, found in outer layer.

• Spongy Bone: Porous, found in ends of long bones, inside flat bones.

Structure of Long Bones

• Diaphysis: Shaft.

• Epiphysis: Ends.

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

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

• Endosteum: Lines internal bone surfaces.

Hematopoiesis

• Location: Red bone marrow (in spongy bone).

• Function: Formation of blood cells.

Bone Cells

• Osteoblasts: Build bone.

• Osteocytes: Mature bone cells; maintain bone.

• 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 negative feedback system.

Calcium Homeostasis Equation:

$\text{If blood Ca}^{2+} \text{ is low:} \rightarrow \text{PTH released} \rightarrow \text{osteoclasts break down bone} \rightarrow \text{Ca}^{2+} \text{ released to blood}$

$\text{If blood Ca}^{2+} \text{ is high:} \rightarrow \text{calcitonin released} \rightarrow \text{osteoblasts build bone} \rightarrow \text{Ca}^{2+} \text{ stored in bone}$

Additional info: Case studies may involve clinical scenarios related to bone fractures, calcium disorders, or skin pathologies. Review feedback mechanisms and clinical applications for exam preparation.