Cardiac Muscle and Connective Tissues

Cardiac Muscle

• Cardiac muscle is found in the heart and is responsible for the rhythmic contractions that pump blood throughout the body.
• Cardiac muscle cells are connected by intercalated discs, which allow for the rapid relay of nerve impulses between cells.
• Cardiac muscle fibers contain a sarcolemma, sarcoplasm, and a centrally located nucleus.
• Cardiac muscle fibers have numerous mitochondria and glycogen granules for energy production.
• Cardiac muscle is myogenic, meaning it can initiate its own contractions without stimulation from the nervous system.
• Cardiac muscle contractions are moderate in strength, rapid, and powerful, characterized by rhythmic contractions and relaxations.
• Cardiac muscle does not fatigue easily.

Connective Tissues

• Connective tissues are responsible for binding and supporting other tissues in the body.
• Connective tissues contain sparsely packed cells scattered throughout an extracellular matrix.
• There are three main types of connective tissues: compact bone, hyaline cartilage, and blood.

Compact Bone

• Compact bone is a strong and rigid type of connective tissue.
• The main components of compact bone are osteocytes, a hard calcium hydroxyapatite matrix, and collagen fibers.
• Compact bone is organized into Haversian systems (osteons), which are cylindrical structures with a Haversian canal at the center.
• Concentric circles called lamellae surround the Haversian canal, which contains an artery, vein, lymph vessels, and nerve fibers.
• Osteoblasts, bone-forming cells, are located in spaces between the lamellae known as lacunae.
• Fine channels called canaliculi connect the lacunae and contain cytoplasmic strands that allow for communication between osteocytes.
• Osteoblasts secrete matrix containing calcium phosphate, calcium carbonate, and protein.
• Once bone matures, osteoblasts become less active and are known as osteocytes.
• The combination of hard mineral and flexible collagen gives bone its strength and flexibility.
• Functionally, compact bone provides body shape, supports the skeleton, protects internal organs, provides surfaces for skeletal muscle attachment, acts as a reservoir for calcium and phosphorus, and is a site for blood cell production in the bone marrow.

Hyaline Cartilage

• Hyaline cartilage is a soft and elastic type of connective tissue.
• Hyaline cartilage is made up of chondrocytes embedded within a soft and elastic matrix called chondrin.
• Chondrin contains collagen fibers, which give cartilage its flexibility.
• Hyaline cartilage lacks blood vessels, nerves, and lymph vessels.
• Hyaline cartilage receives oxygen and nutrients from surrounding blood vessels by diffusion through the cartilage ground substance.
• Hyaline cartilage is found in the nose, ears, trachea, and on the ends of some bones.
• Perichondrium is a protective outer layer of hyaline cartilage that produces new chondroblasts.
• Chondroblasts are immature cartilage cells that later mature into chondrocytes.
• Chondrocytes are mature cartilage cells located in lacunae within the matrix.

Blood

• Blood is the only fluid type of connective tissue.
• Blood consists of blood cells suspended within plasma.
• Blood is composed of erythrocytes (red blood cells), leukocytes (white blood cells), platelets, plasma, and collagen fibers.
• Red blood cells make up approximately 45% of blood volume, while plasma makes up approximately 55%.