Anatomy & Physiology: Exam Review Study Notes

Skeletal System

Functions of the Skeletal System

The skeletal system provides the structural framework for the body and serves several essential functions.

• Support: The skeleton supports the body and maintains its shape.

• Protection: Bones protect vital organs, such as the brain (skull) and heart/lungs (rib cage).

• Movement: Bones act as levers for muscles to produce movement.

• Mineral Storage: Bones store minerals, especially calcium and phosphorus.

• Blood Cell Production: Hematopoiesis occurs in the red bone marrow.

Bone Cells and Their Functions

Bones are dynamic tissues maintained by specialized cells.

• Osteoclasts: Bone cells responsible for bone resorption (absorption and breakdown of bone tissue).

• Osteoblasts: Cells that build new bone matrix.

• Osteocytes: Mature bone cells that maintain bone tissue.

Hormonal Regulation of Bone

Hormones play a critical role in bone growth, maintenance, and remodeling.

• Estrogen: Deficiency in women is implicated in osteoporosis, as estrogen helps maintain bone density.

• Growth Hormone: Stimulates epiphyseal plate activity, promoting bone growth during childhood and adolescence.

• Calcitonin: Can temporarily decrease blood calcium levels if administered in large doses by inhibiting osteoclast activity.

• Parathyroid Hormone (PTH): Increases osteoclast activity, raising blood calcium levels.

Bone Structure

Bones are composed of different types of tissue and structures.

• Spongy Bone: Contains trabeculae, which are lattice-like structures providing strength and flexibility.

• Compact Bone: Dense and forms the outer layer of bones.

Prevention of Osteoporosis

Osteoporosis is a condition characterized by decreased bone density and increased fracture risk.

• Vitamin D: Essential for calcium absorption in the gut.

• Calcium: Necessary for bone mineralization and strength.

Blood and Hematology

Blood Components and Properties

Blood is a connective tissue composed of plasma and formed elements.

• Red Blood Cells (RBCs): Transport oxygen and carbon dioxide; lack a nucleus, which increases space for hemoglobin and gas transport.

• White Blood Cells (WBCs): Defend against infection; neutrophils are especially associated with bacterial infections.

• Platelets: Involved in blood clotting.

Blood Separation and Hematocrit

Blood can be separated into its components by centrifugation.

• Density Separation: RBCs sink to the bottom of a centrifuge tube due to their higher density compared to plasma.

• Hematocrit: The percentage of blood volume occupied by RBCs; increases if a person is administered erythropoietin (EPO), which stimulates RBC production.

Vitamin B12 and Intrinsic Factor

Vitamin B12 is essential for RBC production. Intrinsic factor, produced in the stomach, is required for B12 absorption.

• Pernicious Anemia: Caused by lack of intrinsic factor and subsequent deficiency in vitamin B12, leading to impaired RBC production.

Muscular System

Structure of Skeletal Muscle

Skeletal muscle is composed of muscle fibers (cells) organized into bundles.

• Endomysium: The connective tissue covering each individual muscle cell (fiber).

• Sarcoplasmic Reticulum: Specialized organelle in muscle cells that stores and releases calcium ions, essential for muscle contraction.

Properties of Skeletal Muscle

Skeletal muscle exhibits several key physiological properties.

• Contractility: The ability to shorten and generate force.

• Excitability: The ability to respond to stimuli.

• Extensibility: The ability to be stretched.

• Elasticity: The ability to return to original length after stretching.

Muscle Contraction and Rigor Mortis

Muscle contraction requires energy in the form of ATP.

• ATP: Required for muscle contraction and relaxation; absence of ATP leads to rigor mortis, a post-mortem stiffening of muscles.

Summary Table: Key Hormones and Their Effects

Hormone	Main Effect	Associated Condition
Estrogen	Maintains bone density	Osteoporosis (deficiency)
Growth Hormone	Stimulates bone growth at epiphyseal plates	Dwarfism/Gigantism (imbalance)
Calcitonin	Lowers blood calcium by inhibiting osteoclasts	Temporary hypocalcemia (large doses)
Parathyroid Hormone (PTH)	Increases blood calcium by stimulating osteoclasts	Hypercalcemia (excess)
Erythropoietin (EPO)	Stimulates RBC production	Increased hematocrit

Key Equations

• Hematocrit Calculation:

$\text{Hematocrit} = \frac{\text{Volume of RBCs}}{\text{Total Blood Volume}} \times 100$

• Muscle Contraction (Sliding Filament Theory):

$\text{Force} \propto \text{Number of Cross-Bridges Formed}$

Additional info:

• Parathyroid hormone (PTH) is the primary hormone that increases osteoclast activity, raising blood calcium levels.

• Vitamin D and calcium are both recommended for osteoporosis prevention due to their roles in bone health.

• Neutrophils are the most abundant type of white blood cell and are the first responders to bacterial infection.

• Pernicious anemia is specifically due to the lack of intrinsic factor, which impairs vitamin B12 absorption.