A&P: The Skeletal System

270, 206

A human is born with roughly ___ bones. As a person grows, this number decreases to approximately ___.

axial skeleton, appendicular skeleton

Anatomically, the skeletal system is divided into two major divisions: ________________ and ___________________. 

bones, cartilages, joints, ligaments

The **skeletal system**, or **skeleton**, is composed of:

20%

The skeleton accounts for ____ of body mass.

80, skull, vertebral column, thoracic cage

**Axial skeleton** consists of ___ bones divided into three major regions:

longitudinal axis, head, neck, trunk, brain, spinal cord, thoracic organs

Functions of axial skeleton:

* Form _________________ of body
* Support ______, ______, and ______
* Protect _____, _________, and ______________

upper and lower extremities, girdles, vertebral column

The **appendicular skeleton** comprises the bones of the _________________ and the associated ______that connect the extremities to the _______________.

pre-sacral vertebrae, 7 cervical, 12 thoracic, 5 lumbar vertebrae, sacrum, coccyx

**Twenty-four** of the bones in the **vertebral column** are called the _________________. These consist of ________, _____________, and ____________. The last two bones of the vertebral column are the _______ and ________.

active form

Bone is an _____________ of **connective tissue**.

support, movement, protection, mineral storage, hematopoeisis

Functions of the skeletal system:

body posture, rigid, upright, muscles

**Support:** Bones and cartilage support _________ because both structures are ___. They also allow a person to remain _______ and provide a framework to which soft tissues like _______ and organs can attach.

muscular system, ligaments

**Movement:** Bones of the skeletal system interact with the ____________ to help the body move. Bones themselves cannot move. But when connected to each other by ___________, along with the action of muscles, a human body can move.

external damage, skull, vertebral column, sternum, ribcage

**Protection:** The skeletal system protects vital organs from _____________. The _____ protects the brain, the __________ protects the spinal cord, and the ________ and _________ protect the lungs.

calcium, phosphorus, physiological functions

**Mineral storage:** Bone functions as a storage site for important minerals like _______ and __________. These minerals are used for a variety of _________________ in the body.

red blood cells, stem cells

**Hematopoiesis:** This is the process bones use to produce ______________ and ____________, which differentiate to a variety of different cell types in the body.

compact bones, spongy, cancellous bone

The overall structure of bone consists of an outer shell called ________________. It encloses another type of bone tissue that is loosely organized called _______ or _______________.

osteons, cylinders, mineral matrix, living bone cells

**Compact bone** is made of units called ________. These structures look like ________. They contain a _______ and _______________.

Haversian canal, blood vessels, nerve fibers

Each **osteon** also contains a ____________ that houses the bone’s __________ and _____________.

periosteum

Surrounding the compact bone is a fibrous membrane called the ___________.

blood vessels, nerve and lymphatic vessels

The periosteum consists of _________________________ that nourish the compact bone.

long, short, flat, irregular, sesamoid

There are five types of bones in the human body:

Elongated bones; longer than they are wide

Appearance of **long bones**:

Femur, tibia, clavicle, humerus and metacarpals

Examples of **long bones:**

Broad bones that are thin

Appearance of **flat bones:**

Scapula, hip bones (os oxo), sternum, nasal bone, and occipital/parietal/frontal bones of the skull

Example of **flat bones:**

Vertebrae

Example of **irregular bones:**

Small bones

Appearance of **sesamoid bones**:

Patella (kneecap)

Example of **sesamoid bones:**

About same width as length

Appearance of **short bones**:

Carpal and tarsal bones for the wrist and feet 

Example of **short bones:**

proximal epiphysis, diaphysis, and distal epiphysis.

The long bone consists of three major sections:

spongy bone, compact bone, bone growth

**Epiphysis:** This is found at each end of the long bone. It consists primarily of ____________ with a thin layer of ______________. _____________ occurs at the epiphysis.

Articular cartilage, frictions

**______________:** This covers the epiphysis. It decreases __________ at the joints.

compact bone

**Diaphysis:** This is the longest part of the long bone. It consists primarily of _______________.

Medullary cavity, red and yellow bone marrow, hematopoiesis, fat cells

**______________:** This is found inside the long bone. It is composed of ___________________. Red marrow is where __________ occurs. Yellow marrow consists primarily of __________.

Ossification, calcium and phosphorus

**_____________** is the process of bone formation that occurs first during embryonic development. This process transforms soft, flexible cartilage to hard bone. It does so by replacing the cartilage with mineral deposits, specifically _______________________.

center, end

 Ossification begins in the _____ of bones and spreads toward the ______ of the bones

growth plates

There are **____________** at the end of long bones. This region is also made of cartilage. As the child grows, this area of cartilage at the ____________ experiences ossification to elongate the bone, enabling a person to grow taller.

bone remodeling

Ossification also plays a role in ______________.

 bone resorption

Mature bone tissue is constantly being broken down through a process called _________________.

osteocytes, osteoblasts, osteoclasts

There are three types of bone cells:

collagen, extracellular matrix

**Osteocytes:** These are bone cells. They produce _________ and other substances that create the __________________ of bone.

bone-forming cells, on the surface

**Osteoblasts:** These are called _______________. They are found __________________ of bone and can be stimulated to differentiate into other type of bone cells called osteocytes.

bone-reabsorbing cells, dissolve

**Osteoclasts:** These are called ______________. They are found on the surface of bone. They _________ the bone.

deposition of new bone

Bone resorption frees calcium and other minerals from bone for use in the body and clears out older pieces of bone. In doing so, this process promotes the __________________.

ilium, ischium, pubis, hipbone

Half of the pelvic bone has three separate bones at birth: the ___, ____, and ___. By adulthood, these bones fuse into one bone called the _______.

pores

As the name implies, spongy bone is lighter and less dense than compact bone. It is spongy because it consists of open sections called ______. 

Osteon

1

Yellow bone marrow

2

Compact bone

3

Periosteum

4

Cartilage

5

Osteocyte

1

Nerve

2

Artery

3

Lymphatic vessel

4

Vein

5

Lamellae

6

Central canal

7

Osteoclast

8

Osteoblast

9

Osteogenic cell

Osteoblast

Osteocyte

\

Osteoclast

Proximal epiphysis

1

Diaphysis

2

Distal epiphysis

3

Articular cartilage

4

Spongy bone

5

Epiphyseal line

6

Periosteum

7

Compact bone

8

Medullary cavity (lined by endosteum)

9

skull

1

maxilla

2

mandible

3

humerus

4

sternum

5

ribs

6

clavicle

7

scapula

8

pectoral girdle

9

vertebral column

10

radius

11

ulna

12

acetabulum

13

carpals

14

metacarpals

15

phalanges

16

symphysis pubis

17

ilium

18

sacrum

19

coccyx

20

pubis

21

ischium

22

pelvic girdle

23

femur

24

patella

25

Tibia

26