Answer key

Link to histology questions:

Answer key to histology questions posted by Dr. Knight:

Tissue Types

1. The four tissue types are:

   • Epithelial tissue

   • Connective tissue

   • Muscle tissue

   • Nervous tissue

2. The six general features of epithelium are:

   • Cellular polarity (apical, basal surfaces)

   • Specialized cell contacts

   • Supported by connective tissue (basement membrane)

   • Avascular but innervated

   • Regenerative capacity

   • Forms continuous sheets

Connective Tissue, Bone & Cartilage

1. Examples of body structures:

   • (a) Loose connective tissue: blood

   • (b) Dense connective tissue: bone

2. Three specialized connective tissues:

   • Bone

   • Cartilage

   • Blood

3. Extracellular matrices:

   • (a) Tendon: Collagen fibers

   • (b) Bone: Mineralized matrix (hydroxyapatite)

   • (c) Blood: Plasma

   • (d) Cartilage: Proteoglycan-rich matrix

4. The connective tissue cell that gives rise to collagen in dense fibrous structures is the fibroblast.

5. The connective tissue cell that forms cartilage is the chondroblast.

6. The microscopic cavity within which chondrocytes live is the lacuna.

7. Three types of cartilage and their locations:

   • Hyaline cartilage: Trachea, articular surfaces of bones

   • Elastic cartilage: External ear, epiglottis

   • Fibrocartilage: Intervertebral discs, pubic symphysis

8. The connective tissue cell that forms bone by producing osteoid is the osteoblast.

9. The microscopic cavity within which osteocytes live is the lacuna.

10. The multinucleate cell that resorbs bone is the osteoclast.

11. Canaliculi are microscopic channels in bone that allow for communication and nutrient exchange between osteocytes.

12. Terms related to bone:

• Compact: Dense, outer layer of bone.

• Cortical: Synonymous with compact bone.

• Spongy (Trabecular, Cancellous): Lattice-like inner bone.

• Woven: Immature, rapidly formed bone.

• Mature: Organized lamellar bone.

13. Locations of woven bone:

• Normal: Near a healing fracture.

• Pathologic: In some bone tumors.

14. Regions of a long bone:

• Epiphysis: End of the bone.

• Physis: Growth plate.

• Metaphysis: Transitional zone between diaphysis and epiphysis.

• Diaphysis: Shaft of the bone.

15. Another term for a growth plate is the physis.

16. The fibrous outer covering of bone is the periosteum.

17. The material covering the articular surfaces of bones is hyaline cartilage.

Epithelium

1. Three glands:

   • Salivary glands

   • Sweat glands

   • Pancreatic glands like gall bladder

Two solid epithelial organs:

1. • Liver

   • Kidney

2. Exocrine glands secrete substances through ducts onto epithelial surfaces (e.g., sweat, saliva), while endocrine glands release hormones directly into the bloodstream (e.g., thyroid, adrenal glands).

3. Five main types of epithelial lining:

   • Simple squamous: Thin, allows diffusion (e.g., alveoli).

   • Simple cuboidal: Secretion and absorption (e.g., kidney tubules).

   • Simple columnar: Absorption and secretion (e.g., intestines).

   • Stratified squamous: Protection against abrasion (e.g., skin).

   • Pseudostratified columnar: Secretion and movement of mucus (e.g., respiratory tract).

4. Special name for the epithelium that lines the skin: Epidermis.

5. Special name for the epithelium that lines blood and lymphatic vessels: Endothelium.

6. Special name for the epithelium that lines the thoracic and abdominal cavities: Mesothelium.

7. The epithelial cell that secretes mucin is the goblet cell.

Integument

1. Three distinct layers of the skin:

   • Epidermis

   • Dermis

   • Hypodermis (subcutis)

2. The epidermis is made up of keratinized stratified squamous epithelium.

3. Epidermal thickness is maintained by a balance between the rate of keratinocyte production and the shedding (desquamation) of dead cells.

4. The dermis is composed of dense irregular connective tissue, including collagen and elastin fibers, with blood vessels, nerves, and glands.

5. The subcutis (hypodermis) consists of loose connective tissue and adipose tissue, which provides insulation and cushioning.

6. Around 90% of epidermal cells are keratinocytes.

7. The two other important cell types in the epidermis are:

   • Melanocytes: Contribute pigment (melanin).

   • Langerhans cells: Antigen-presenting cells.

8. Haired skin has two types of specialized glands:

   • Sebaceous glands: Secrete sebum, an oily substance that lubricates hair and skin.

   • Apocrine sweat glands: Secrete a thicker sweat, mainly in association with hair follicles, contributing to scent marking in animals.

9. Hair growth phases:

   • Anagen: Growth phase.

   • Telogen: Resting phase.

10. Anal sacs:

• Location: Near the anus of carnivores.

• Secretion: Produce a malodorous substance used for marking territory or defense.

Muscle and bone growth

1. Three different types of muscle and examples:

   • Skeletal muscle: Found in biceps brachii.

   • Cardiac muscle: Found in the heart.

   • Smooth muscle: Found in the walls of blood vessels and the intestines.

2. Growth plates (physes):

   • The surface with a pool of reserve chondrocytes faces the epiphysis.

   • The surface composed of mineralizing cartilage matrix faces the metaphysis/diaphysis.

Nervous System

1. Four glial cell types of the CNS and their functions:

   • Astrocytes: Support neurons, maintain the blood-brain barrier, and regulate nutrients.

   • Oligodendrocytes: Produce myelin in the CNS.

   • Microglia: Act as immune cells, clearing debris and damaged cells.

   • Ependymal cells: Line ventricles, producing and circulating cerebrospinal fluid (CSF).

2. The CNS glial cell crucial for the maintenance of the blood-brain barrier is the astrocyte.

3. The cell type that produces myelin in peripheral nerves is the Schwann cell.

4. Structures in the brain responsible for secreting cerebrospinal fluid (CSF) are the choroid plexuses.

5. Three meningeal layers of the CNS:

   • Dura mater (outermost).

   • Arachnoid mater (middle layer).

   • Pia mater (innermost).

6. CSF lies in the subarachnoid space, between the arachnoid mater and the pia mater.