Lecture 6: Skeletal System and Bone Tissue Overview

Long Bone

The "humerus" in the arm and the "femur" in the leg are typical long bones.

Flat Bone

A type of bone shape.

Short Bone

A type of bone shape.

Sesamoid Bone

A type of circular bone shape.

Irregular Bone

A type of bone shape.

Articular cartilage

Limits friction between articulating bones.

Proximal epiphysis

The end of a long bone closest to the body.

Epiphyseal line

Bone growth originates here.

Metaphysis

The area where the epiphyses and diaphysis join.

Red bone marrow

Responsible for the generation of blood cells (WBCs and RBCs).

Compact bone

Forms the diaphysis of long bones and the external layer of all bones.

Spongy bone

Lightweight bone that provides tissue support and forms much of the epiphysis.

Yellow marrow

Stores triglycerides.

Diaphysis

The shaft or body of a long bone.

Periosteum

A dense layer of vascular connective tissue enveloping the bones.

Functions of the Skeletal System

The skeletal system has 6 important functions: provide structural support, assist in body movements, protect internal organs, store and release salts of calcium and phosphorus, participate in blood cell production, and store triglycerides.

Thoracic Cavity

Contains the lungs and heart.

Cranial Cavity

Contains the brain.

Cranium

The skull that encases the brain.

Vertebral Cavity

Contains the spinal cord.

Cartilage

A poorly vascularized dense irregular connective tissue with a matrix composed of chondroitin sulfate and collagen.

Hyaline cartilage

Loose and soft due to minimal fibers, ideal for articulating regions.

Fibrocartilage

Very dense and strong, ideal for cushioning regions of heavy pressure.

Elastic cartilage

Contains a lot of elastin fibers.

Vertebral cartilage

Thick cushion layer of fibrocartilage that absorbs impact between vertebrae.

Epiphysial Plate

Associated with longitudinal (length) bone growth.

Periosteum

A tough sheath of dense, irregular connective tissue lining the outside of the bone, containing osteoblasts that help the bone grow in thickness only.

Medullary Cavity

A space within the diaphysis of long bones that contains fatty yellow bone marrow in adults.

Endosteum

A membrane that lines the medullary cavity, composed of osteoclasts, osteoblasts, and connective tissue.

Perichondrium

A dense irregular connective tissue lining that surrounds cartilage.

Chondrocytes

Cells that form cartilage.

Progenitor Bone Cell

A precursor to bone cells.

Osteoblast

Derived from osteogenic cells, their function is to form bones.

Osteocyte

Derived from osteoblasts, their function is to prevent unwanted breakdown of bone.

Osteogenic Cell

A bone stem cell formed from white blood cells derived from hematopoietic stem cells.

Osteoclast

Comes from the hematopoietic stem cell lineage, their function is to break down bone (remodeling).

Osteoblasts

Bone building cells that synthesize and secrete collagen fibers and other organic components.

Osteocytes

Mature osteoblasts responsible for maintenance of bone.

Osteoclasts

Large bone breakdown cells that migrate from the bone marrow to become fixed macrophages in the substance of the bone.

Red Marrow

Contains hematopoietic stem cells which give rise to different blood cells (WBCs and RBCs).

Yellow Marrow

Fills the medullary cavity, contains adipose tissue, stores fats, cushions the inner portion of the bone against impact trauma.

Bone Composition

Bone is 25% water, 25% proteins, and 50% mineral salts.

Collagen and Elastin

Fiber proteins that provide flexibility and tensile strength in bone.

Calcium Phosphate

An inorganic mineral salt represented by the formula (Ca3PO4)2.

Calcium Carbonate

An inorganic mineral salt represented by the formula CaCO3.

Epiphyseal Growth Plate

In adolescents, it contains hyaline cartilage and is actively dividing to elongate the bone.

Epiphyseal Line

In adults, the epiphyseal cartilage is replaced by calcified bone, marking the end of elongation.

Compact Bone

Contains units called osteons or Haversian systems formed from concentric lamellae.

Lacunae

Small spaces between the lamellae that house osteocytes.

Canaliculi

Small channels filled with extracellular fluid connecting the lacunae.

Central Canal

The center of the osteons where blood and lymphatic vessels are found.

Perforating Canals

Allow transit of blood and lymphatic vessels to the outer cortex of the bone.

Spongy Bone

Majority of the epiphyses of long bones is made up spongy bone. The use of spongy bone lessens overall bone weight.

Compact Bone

Makes up the superficial bone along the longitudinal length of the bone.

Ossification

The process of forming new bone.

Embryogenesis

Formation of bone in an embryo.

Adolescent Growth

Growth of bones until adulthood.

Bone Remodeling

Continually remodeling of bone.

Fracture Repair

Repair of fractures due to injury.

Intra-membranous Ossification

Produces spongy bone directly; spongy bone formed first.

Endochondral Ossification

A process whereby cartilage is replaced by bone; forms both compact and spongy bone.

Flat Bones

Used in forming the flat bones of the skull, mandible, and clavicle.

Calcification

Osteoblasts recruit Calcium and Phosphates to develop Bone.

Periosteum

Formed during intra-membranous ossification; some spongy bone becomes compact by secretion of more collagen fibers and recruitment of more Ca+ and PO3-.

Cartilage Model

Forms a common bone structure with distal and proximal epiphysis and diaphysis in the middle.

Chondrocytes

Replicate and secrete collagen and elastin fibers and sugar molecules and recruit Ca+ and PO3 for early calcification.

Primary Site of Ossification

Early development of spongy bone occurs along the diaphysis.

Medullary Cavity

Formed after the entire diaphysis region is converted to bone.

Secondary Ossification Centers

The distal and proximal epiphyses become activated and the cartilage in this region is converted to bone by calcification.

Articular Cartilage

Formed along the surface of the epiphyses.

Epiphyseal Growth Plate

Generated and responsible for longitudinal bone growth.

Bone Length Completion

Ossification from the epiphyseal growth plate is usually complete by 18-21 years of age.

Lateral Bone Growth

Refers to the thickening of bones.

Longitudinal Bone Growth

Refers to the lengthening of bones.

Human Growth Hormone (hGH)

Stimulates bone growth and muscle growth, loss of fat, and increased glucose output in the liver.

Human Growth Hormone (hGH)

A hormone that stimulates growth, cell reproduction, and regeneration in humans.

Side Effects of Excess hGH

Short term, it causes faster growth of bone and muscle, but long term, it makes bones more susceptible to fractures and muscles more susceptible to atrophy.

Bone Growth

The process by which bones increase in size and strength, influenced by hormones.

Sex Hormones

Hormones such as estrogen and testosterone that significantly affect bone growth.

Growth Spurt

A rapid increase in height that occurs during puberty, primarily influenced by sex hormones.

Estrogen

A sex hormone that promotes widening of the pelvis in females and is responsible for closing the epiphyseal plates at the end of puberty.

Testosterone

A sex hormone that contributes to male growth patterns and is responsible for the growth spurt during puberty.

Osteoclasts

Cells that break down bone tissue.

Osteoblasts

Cells that form new bone tissue.

Acromegaly

A condition resulting from excess growth hormone, leading to abnormally thick and heavy bones.

Osteoporosis

A condition characterized by excessive loss of calcium, leading to weakened bones.

Rickets

A bone disease in children caused by vitamin D deficiency, resulting in soft bones.

Osteomalacia

A bone disease in adults characterized by softening of the bones due to vitamin D deficiency.

Minerals for Bone Growth

Essential components including large amounts of calcium and phosphorus, and smaller amounts of magnesium, fluoride, and manganese.

Vitamin A

A vitamin that stimulates the activity of osteoblasts.

Vitamin C

A vitamin needed for the synthesis of collagen.

Vitamin D

A vitamin essential for healthy bones, promoting calcium absorption from food into the blood.

Vitamin K

A vitamin needed for the synthesis of bone proteins.

Vitamin B12

A vitamin needed for the synthesis of bone proteins.

Parathyroid Hormone (PTH)

A hormone critical for balancing calcium and phosphorus levels between blood and bone.

Calcium Homeostasis

The regulation of calcium levels in the body, involving hormones like PTH and calcitonin.

Calcitonin

A hormone that stimulates osteoblastic activity and lowers serum calcium levels.

Aging and Bone Tissue

A process where a decrease in bone mass occurs as sex hormone levels diminish, leading to brittleness and loss of tensile strength.

Osteoporosis Symptoms

Loss of bone mass and brittleness due to calcium depletion.