Skeletal SystemMrs. Rago

BCTHS Anatomy & Physiology

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

cartilage

ligaments

Tendons

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

Long bone- femur

Irregular bone- patella

Flat bone- scapula

Short bones- wrist

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

Resistance

Fulcrom Force

Second-class Lever

Fulcrom

Force

Resistance

Third-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

periosteum

endosteumMedullary Canal

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