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Support & stabilize Protect vital organs Assists in movement Makes blood cells
◦ Hematopoiesis Storage area
Functions of Skeletal System
Cartilage◦ Connective tissue◦ Framework for bones in fetus
Ligaments◦ Tough connective tissue◦ Attachment point for other bones
Tendons◦ Attach muscle to bone
Associated Tissues
Long Bones◦ Long & thinner but with expanded ends◦ Ex: forearm & thigh bones
Short Bones◦ Cubelike: length & width roughly equal◦ Ex: wrists & ankles
Flat Bones◦ Platelike◦ Ex: ribs, scapulae, & some of skull bones
Irregular Bones◦ Variety of shapes & are usually connected to several
other bones
Bone Structure
Epiphysis◦ Articulates with another bone (joint)◦ Covered with articular cartilage
Layer of hyaline cartilage Diaphysis
◦ Shaft of bone
Parts of Long Bone
Long bones are very useful in lifting heavy loads◦ Act as a lever when lifting a weight
Theory behind long bones
Resistance force
fulcrom
First-class lever
Lever◦ Has 4 basic components
Rigid bar Pivot or fulcrum (what the bar turns on) Object that is moved against resistance Force that supplies energy for the movement of the
bar Only first-class & second-class lever
movements are found in the human body
Periosteum◦ Fibrovascular membrane that covers a bone
Endosteum◦ Line the medullary cavity
Medullary Cavity◦ Center of bone ◦ Contains bone marrow
Development of Bone
Osteoblasts◦ Precursors to osteocytes◦ Bone forming cells which deposit bony matrix
around themselves◦ Deposit bone in the endosteum (area of cells that line the
medullary cavity) Osteocytes
◦ Bone cells◦ Located in tiny chambers called lacunae
More bone Development
Osteoclasts◦ Responsible for reabsorption of bone◦ Remove bone and replace it during remodeling
Occurs especially when repairing a broken bone Also occurs when bone is reshaped (bow-legs) Osteocytes deposit new bone
Bone Development Again
Red bone marrow◦ Fills spaces within cancellous bone◦ Well supplied with blood◦ Produces blood cells = hematopoiesis
White & red blood cells◦ Found in adults, but only in select bones
Ribs, vertebrae, sternum, and pelvic bones◦ Found in humerus & femur but decreases with
age
Bone Marrow
Yellow Marrow◦ Connective tissue that consists largely of fat cells◦ Found predominantly in shafts of long bones in
medullary cavity◦ Can become red marrow in times of need (major
loss of blood) and produce blood cells if necessary
Bone Marrow
Intramembraneous Ossification◦ Dense connective tissue membranes are replaced
by deposits of inorganic calcium◦ Only bones of skull ◦ Does not occur until a few months after birth
Soft spot = fontanelle
Types of Ossification
Endochondral Ossification◦ Cartilage is formed first and then replaced by
mature bone cells Primary ossification center
◦ Found in center of a long bone◦ Bone develops from 1 ̊ ossification center toward the
ends of cartilaginous structure Secondary ossification center
◦ Appear later than 1 :ossicification centers◦ Are found in epiphyses◦ Spongy bone forms in all directions from 2 ̊
ossification center
Types of Ossification
Types of bone◦ Compact/dense bone
Dense & strong◦ Cancellous/spongy bone
Many open spaces
Histology of bone
Structure◦ Haversian Canal (osteon)
Allows for metabolism of surrounding mineral salts within compact bone
Looks similar to rings around central blood vessels Blood vessels found within haversian or central canal Concentric (circular) rings are called lamella
Lacunae Tiny cavities that contain the osteocytes Located between two lamella or rings of bone
Compact bone
Each lacunae are connected to all other lacunae through smaller canals= canaliculi◦ Canaliculi run horizontally between haversian
canals Also contain blood vessels Same as Volkmann’s or perforating canals
Canaliculi ◦ Allow osteocytes to get oxygen & nutrients and
dispose of waste products & CO2
Compact Bone
Also called spongy bone Located at ends of long bones and also
forms center of all other bones Trabeculae
◦ Network that forms the network of interconnecting sections of bone
◦ Creates sponelike appearance to bone◦ Gives bone strength without adding weight
Cancellous Bone
Red bone marrow◦ Fills spaces within cancellous bone◦ Well supplied with blood◦ Produces blood cells = hematopoiesis
White & red blood cells◦ Found in adults, but only in select bones
Ribs, vertebrae, sternum, and pelvic bones◦ Found in humerus & femur but decreases with
age
Bone Marrow
Yellow Marrow◦ Connective tissue that consists largely of fat cells◦ Found predominantly in shafts of long bones in
medullary cavity◦ Can become red marrow in times of need (major
loss of blood) and produce blood cells if necessary
Bone Marrow
Separates diaphysis & epiphysis in long bones
Area of new cell growth in growing bones Layers of cartilaginous cells
◦ Layer 1- resting cells (found closest to end of epiphysis)
◦ Layer 2- cells undergoing mitosis◦ Layer 3- older cells enlarging & becoming
calicified◦ Layer 4- dead cells & calcified intercellular
substance
Epiphyseal Plate
Resting cells
Cells under going mitosisII
III
Older cells enlarging and becoming calcified
Dead cells and calcified intercellular substance
III
IV
Healthy body◦ Balance between amount of calcium in blood and
calcium stored in bones Excess calcium secrete via kidneys Balance controlled by endocrine system
Parathyroid & calcitonin hormones
Maintaining bones
Growth hormone (GH)◦ Secreted by pituitary gland◦ Stimulates division of cartilage cells found within
epiphyseal plates◦ Absence of GH
Long bones fail to develop normally and individual fails to grow, leading to pituitary dwarfism
◦ Over production of GH (too much) Pituitary gigantism
Height over 8 ft tall Acromegaly
Hands, feet, & jaw enlarge
Hormones involved in Bones
Thyroid hormone◦ Stimulates replacement of cartilage in epiphyseal
plates◦ Halts bone growth by causing premature
ossification◦ Deficiency (not enough) thyroid hormone may
stunt growth◦ Secreted by thyroid gland
Parathyroid Hormone◦ Stimulates increase in number & activity of
osteoclasts
Hormones
Sex hormones◦ Estrogen & testosterone
Secreted from ovaries, testes, & adrenal glands Promotes formation of bone tissue Increase in abundance at puberty Also stop bone lengthening at a relatively early age
This effect is stronger in females, because estrogen is stronger than testosterone, so females stop growing sooner than males
Hormones
Physical stress◦ Stimulates bone growth◦ Lack of exercise leads to thinner & weaker bones (atrophy)
Vitamin D◦ Necessary for absorption of calcium in small intestine◦ In vitamin D poor diet, calcium is not absorbed properly
and deforms bones◦ Active form of Vit D requires exposure to ultraviolet light
Vitamin A & C◦ Vitamin A necessary for osteoblast & osteoclast activity
(lack may prevent normal bone development)◦ Vitamin C required for collagen synthesis (also may
prevent normal bone development)
Other factors affecting bone growth
Formation of blood cells Occurs in bone marrow Red marrow
◦ Produces red blood cells (erythrocytes), white blood cells (leukocytes), and blood platelets
◦ Called red marrow due to red, oxygen-carrying pigement (hemoglobin) that is found inside of the red blood cells
Hemopoiesis
Inorganic mineral salts account for 70 % of weight of bones
Inorganic salts are mostly tiny crystals of calcium phosphate (hydroxyapatite)
Low blood calcium results in parathyroid hormone stimulating osteoclasts to break down bone matrix releasing calcium into blood stream
High blood calcium results in calcitonin from the thyroid gland, which stimulates osteoblasts to form bone tissue
Inorganic salt storage