Chapter 4 & 5 (extra notes)

Bone Structure

• Bone Composition:

  • Bone appears structurally similar to a sponge, consisting of hard bony regions interspersed with open spaces.

  • Bone cells play a crucial role; they lay down collagen and subsequently secrete minerals to harden the collagen, making bone rigid.

Types of Bone

• Types:

  • There are two main types of bone: trabecular (spongy) and cortical (compact).

• Osteogenesis:

  • Osteoblasts are bone-forming cells that, once surrounded by bone material, transform into osteocytes, which serve to maintain bone tissue.

Hematopoiesis

• Blood Cell Formation:

  • The term "hematopoietic" refers to the formation of blood cells, primarily occurring in the bone marrow.

  • Hematopoietic stem cells give rise to erythrocytes (red blood cells) and leukocytes (white blood cells).

  • Leukocytes are immune cells important for defending the body against pathogens.

Connective Tissue Subcategories

• Types of Connective Tissue:

  • Four subcategories of connective tissue: hematopoietic stem tissue, proper connective tissue, bone, and cartilage.

  • Three of these types primarily consist of fibers embedded in a ground substance, produced by fibroblasts (connective tissue cells).

• Extracellular Matrix:

  • In connective tissues such as bone and cartilage, the component produced by cells is mainly the extracellular matrix, with cells occupying less volume.

Epithelial Membranes

• Epithelial Structures:

  • All epithelial tissues rest on a basal layer of connective tissue and serve various functions, including protection and secretion.

  • Stratified Squamous Epithelium:

    • The outer surface consists of thin, flattened cells, typical of epithelial membranes such as the skin.

  • Keratinization:

    • Keratin produced in keratinocytes forms the outermost layer, providing a protective barrier.

Mucous and Serous Membranes

• Mucous Membranes:

  • Line cavities open to the outside and exhibit varying epithelial types—simple squamous, simple columnar, or stratified columnar—depending on the location.

  • They remain moist for functionality, such as gas exchange in respiratory tissues.

• Serous Membranes:

  • Also known as serosa, these line body cavities not open to the outside, such as the peritoneum (abdominal) and pericardium (around the heart).

  • They secrete serous fluid that helps reduce friction between organs during movement.

Inflammation and Healing

• Response to Injury:

  • Inflammation is an innate immune response involving a series of events, such as pain, swelling, and increased blood flow.

  • Regeneration:

    • The process of repairing and renewing tissue, necessitating the presence of mitotically capable cells like stem cells.

• Fibrosis:

  • Refers to the formation of excess fibrous connective tissue, often replacing normal tissue in healing.

• Healing Process:

  • Begins with hemostasis (blood clot formation), followed by inflammatory response and granulation tissue formation.

  • Finally, epithelial tissue regenerates over the healed area with the help of macrophages.

Skin Structure and Function

• Skin as a Barrier:

  • The skin protects internal structures and assists in thermoregulation. It is analogous to a plasma membrane at the cellular level.

• Epidermal Layers:

  • The epidermis consists of multiple layers, with keratinocytes at different stages of development based on their proximity to the basal layer.

  • The deepest layer, the stratum basale, contains mitotically active keratinocytes, while the upper layers consist of increasingly keratinized (dead) cells that prevent dehydration and damage.

• Thick vs. Thin Skin:

  • Thick skin contains an additional layer compared to thin skin predominately found on the palms and soles.