Human Anatomy Quiz: Bone Development

Anatomy Lecture 2: Tissues and Structures of the Body

• The lecture discusses tissues and structures of the lower limbs, radiology, and a summary for the following week.
• The body's components are organized from chemicals to "cell bits" (organelles) to cells, tissues, organs, organ systems, and finally, a whole body.
• Structures in the body can be made of one or many tissue types. For example, bone is primarily connective tissue, but the heart has epithelial, muscle, and connective tissues, along with nerves.
• Four main tissue types are:
  • Epithelial: A covering material
  • Connective: Connects and provides support
  • Muscle: Contracts for movement
  • Nervous: Communicates between body parts via electrical impulses
• Bone is a living, constantly changing structure that remodels in response to stress (Wolff's Law).
  • Functions of bone include protection, framework for other structures, acting as levers for movement, calcium and fat storage, and blood cell formation.
  • Bone structure includes osteocytes laying down new bone and osteoclasts breaking down old bone.
  • The matrix of bone is dense, tough connective tissue with calcium phosphate, resilient, and slightly elastic, resisting compression.
  • Bone is supplied by vascular structures and nerves.
  • Periosteum surrounds bone; two layers: outer fibrous; inner highly vascular (cambium) layer with progenitor cells.
• Bone classifications:
  • Compact (cortical): Strong, dense, forms tubular bodies, filled with marrow.
  • Cancellous (spongy): Lattice-like bony spicules (trabeculae), helps redistribute stress and absorb shock.
  • Long bones (e.g., femur, tibia, metatarsals): Compact shaft, cancellous ends, hyaline cartilage at joints.
  • Short bones (e.g., calcaneus, talus): Mostly cancellous, surrounded by a compact shell, cube-shaped, hyaline cartilage at joints.
  • Flat bones (e.g., skull, scapula): Thin layers of cortical bone separated by cancellous bone.
  • Irregular bones (e.g., vertebrae): Thin shell of compact bone surrounding cancellous bone; irregular shape.
  • Sesamoid bones (e.g., patella, sesamoids in the foot): Small, round bones within tendons, where tendons would otherwise rub over bony parts.
• Bone marrow occupies cavities in long and short bones, and gaps between trabeculae in other cancellous bones.
  • In children, it's all red (hematopoietic) marrow, producing red and white blood cells, platelets.
  • Gradually replaced by yellow marrow (fatty) after age 7.
  • In adulthood, about 50% of marrow is red, 50% yellow.
• Bone development has two methods:
  • Membranous: Bone develops directly from connective tissue membrane (less common).
  • Endochondral: Cartilage model laid down, gradually replaced by bone formation (how most limbs form).
• The process takes 20+ years, and different bones ossify at varying rates.
• Ossification rates differ depending on the bone.
• Radiographic views of adult and child knees were shown.
• Bones of the pelvis (ilium, sacrum, pubis, ischium) and features of the joint were presented.
• The knee joint structure with ligaments (cruciate, collateral, menisci) was shown.
• The rear foot and ankle joint structure with ligaments and tarsal bones (talus, calcaneus, cuboid, navicular, cuneiforms) was shown in a diagram.
• Cartilage: A type of connective tissue with collagen fibers in a gel-like matrix.
  • Hyaline cartilage: Crucial for bone formation, covers bone ends, provides protection, and lubrication.
  • Fibrocartilage: Lots of fibers, tough, found in many joint types.
  • Elastic cartilage: Elastic fibers, springy, located in the external ear (pinna).
  • Cartilage is aneural and avascular, and cannot repair itself very well.
  • Can calcify and turn to bone over time.
• Ligaments: Bands/cords of connective tissue linking two or more structures, often bones in a joint.
  • Inelastic (e.g., ankle, knee) vs. Elastic (e.g., plantar calcaneonavicular 'spring' ligament in the foot).Ligaments within the joint capsule are intracapsular; those outside are extracapsular.
• Synovial membranes/sheathes are sacs filled with fluid.
  • Synovial membranes form the inner lining of movable joint capsules, secreting fluid to lubricate the joint.
  • Synovial sheaths surround tendons, reduce friction, and protect them (e.g., around tendons moving over bends, passing under structures).
• Bursae are fluid-filled sacks under tendons to separate them from bone, preventing friction and irritation (e.g., retrocalcaneal bursa).
• Muscles: Structures for body movement.
  • Three types: cardiac (heart), smooth (internal organs), skeletal (most studied).
  • Skeletal muscle is under conscious brain control, has striated (striped) fibers, works by contracting.
  • Has a point of origin (typically bony attachment) and insertion (via tendon or aponeurosis, usually bony).
• Muscle Structure: Muscle cells (fibers), Perimysium (surrounding bundle), Endomysium (surrounding single cell), Fascicle.
• Muscle types: slow twitch (red), fast twitch (white), intermediate.
• Muscle Shapes: Rhomboid, Quadrilateral, Strap, Strap with tendinous intersections, Fusiform, two bellies, two headed, Triangular, Unipennate, Bipennate, Multipennate.
• Muscle Contractions: Dynamic (concentric, eccentric) vs. Static (isometric).
• Muscle jobs: Prime mover (agonist), Antagonist, Fixator (stabilizer), Synergist.
• Nervous System: Brain & spinal cord.
• Peripheral Nervous System (PNS): Nerves throughout the body.
• Spinal nerves exit spinal cord, predictable locations for different body parts (Lumbar, Sacral Plexuses).
• Main nerves in the lower limbs (Femoral, Obturator, Sciatic).
• Skin: Largest organ, protecting underlying structures, maintaining temperature, synthesizing vitamin D, and housing sensory receptors.
• Layers of skin: epidermis, dermis, subcutaneous tissue.
• Cardiovascular System: Heart and blood vessels in pulmonary / systemic circuits.
• Other vascular structures: Arteries, Arterioles, Metarterioles, Pre-capillary sphincters, Capillaries, Venules, Veins, Lymphatics.
• Functions of the cardiovascular system: Gas exchange, nutrient delivery, hormone delivery, waste removal, protection (clotting), temperature regulation, homeostasis.
• Classifications of joints: Fibrous, Cartilaginous, Synovial
• Types of synovial joint shapes: Hinge, Ball & socket, Plane, Saddle, Ellipsoid, condyloid, Pivot.

Summary

• The lecture covers anatomy of the body.
• Discusses the different tissues & their structure, location.
• Details of bone development, classifications, features, bones of the lower limb, and their function, muscles, and associated structures.
• Explains the various classifications of joints, including synovial joints.
• It also introduces the structure and function of the nervous, cardiovascular, and lymphatic systems.

Next Week

• Students should review notes and relevant anatomy text book.
• Understand surface anatomy for the lower limb.
• Study osteology of the lower limb, focusing on the anterior compartment of the thigh.
• Prepare for classes; time and location.