1. Skeletal System
Biol Lecture 8
Chapter 5

2. Outline Overview of the skeletal system Function of bones
Bone structure
Bone cells
Cartilage
Tendons and Ligaments
Joints
Bone development
Hormonal regulation of bone growth
Homeostasis
Disorders of the skeletal system

3. Bones – rigid structure Cartilage – soft, cushions the joints
Skeletal System
The skeletal systems is composed of different types of connective tissues:
Bones – rigid structure
Cartilage – soft, cushions the joints
Ligaments – attach bone to bone
Tendons – attach muscle to bone.
Tendons link the skeletal and the muscular systems

4. Figure: 25-08
Title: Elements of the Skeletal System
Caption: Bones are the basic element of the skeletal system. Ligaments link one bone to another, and cartilage often serves as padding between bones. Tendons, while not part of the skeletal system, always link bone to muscle.

5. Supports and gives shape to the body. Protects soft body parts.
Functions of Bone
Supports and gives shape to the body.
Protects soft body parts.
Produce blood cells
Stores minerals (calcium and phosphate)
Stores fat.
Along with the muscles, permits flexible body movement.

6. Calcified tissue = osseous tissue Blood vessels Nerves
Bone
Bones have different types of tissue
Calcified tissue = osseous tissue
Blood vessels
Nerves
Contain collagen fibers that give flexibility
This combination of calcified tissue and collagen fibers make the bone strong but flexible

7. Compact bone – dense mineralized outer layer
Bone Structure
All bones have two layers of bone:
Compact bone – dense mineralized outer layer
Spongy bone – inner layer with open network filled with marrow

8. Typical Bone Structure
Epiphysis – rounded end of the typical long bone, composed mainly of red bone marrow where blood cells are made
Diaphysis – shaft of the typical long bone, has a cavity filled with yellow marrow where fat is stored.

9. Periosteum
Periosteum – fibrous outer covering of the bone, contains nerves, blood vessels, lymphatic vessels.
Functions in bone repair and growth

10. Typical Long Bone Structure
Spongy bone
(spaces contain
red bone
marrow)
Compact
bone on
surface
Yellow
bone
marrow
Blood
vessel
Periosteum
Central cavity
(contains
yellow bone
marrow)
(a) A long bone, such as the femur of the
leg, consists of a shaft and two heads,
or enlarged ends. Compact bone is
located on the outer surface of the bone.
Spongy bone is found in the heads.
Figure 5.1a

11. Spongy Bone
Figure 5.1e

12. Bone Is Living Tissue Figure 5.1b Osteon Periosteum Blood vessels
and nerve in
central canal
Bone-forming cells
(osteoblasts)
Spongy bone
Compact bone
(b)
The structural unit of compact bone is
an osteon. Mature, living bone cells
(osteocytes) are found in small spaces
within the hard matrix.
Figure 5.1b

13. Compact Bone Structure
Osteon – structural unit of the compact bone

14. Osteon Structure
Central Canal (Haversian) – contain blood vessels and nerves
Osteocytes – Mature bone cells. Maintain bone structure and density and minerals
Found in cavities called lacunae
Canaliculi are canals that connect the lacunae to the central canal

15. Figure 5.1c The structure of bone

16. Figure 5.1d The structure of bone

17. Bone cells
Osteoblasts
Osteocytes
Osteoclasts

18. Osteoblasts Osteoblasts = bone forming cells.
Immature cells that secrete material called “bone ground substance” = non-cellular matrix that surrounds the cells.
Osteoblasts mature into osteocytes after they have secreted enough material

19. Osteoclasts Osteoclasts – Bone absorbing cells.
These are bone cells on the outer edge of bones.
They release enzymes that eat away at the bone, releasing minerals

20. The arrow is pointing to:
Diaphysis
Epiphysis

21. Immature cells that secrete calcified material are:
Osteoclasts
Osteocytes
Osteoblasts

22. Osteocytes are found in cavities called
Central canals
Collagen
Lacunae
Vellus

23. Cartilage in bones
Two regions of cartilage remain at each end of the long bone
The cap that covers the surfaces that rub against other bones
A plate of cartilage called the epiphyseal plate, or growth plate

24. Bone development and growth
The skeleton begins to form at about 6 weeks.
Most bones grow through adolescence but some bones continue to grow through about age 25.
Ossification – formation of bones
10-5

25. Bone development and growth
The skeleton begins to form at about 6 weeks.
Most bones grow through adolescence but some bones continue to grow through about age 25.
Bone continue to change throughout life.
Osteoclasts are removing the bone matrix while Osteoblasts are building the matrix up.
Ossification – formation of bones
10-5

26. Figure 5.3 Steps of bone formation in long and short bones, from an embryo into childhood
Fetal Development
Cartilaginous
surface
Birth
Spongy
bone
formation
Spongy
bone
9 months
3 months
2 months
Calcified
cartilage
Cartilage
model
Cartilaginous
(epiphyseal)
growth plate
Blood
vessel
Bone
collar
Compact
bone
Deteriorating
cartilage
matrix
Step 1:
A cartilaginous
model of the
future bone
forms.
Step 2:
Osteoblasts form
a collar of bone
around the shaft
of the model.
Step 3: The shaft of the
cartilage model begins
to hollow out, and
spongy bone fills the
space. Blood vessels
continue to penetrate
the area, and the
region of bone
formation expands.
Step 4: Secondary
centers of bone
formation develop in
the ends of the bone.
Step 5: Cartilage
remains only on the
surfaces that rub against
other bones and in the
cartilage growth plates.

27. Bone Growth
Bone growth is stimulated by growth hormone during childhood
Thyroid hormones ensure that the skeleton grows with the proper proportions
At puberty, increasing levels of male or female sex hormones initially stimulate cartilage cells to divide, but eventually allow for the growth plates to fuse, and bone can no longer increase in length

28. Hormonal Regulation of Bone Growth
Growth hormone (GH) - directly stimulates growth of the epiphyseal plate and bone growth in general.
Vitamin D - converted to a hormone causing the intestines to absorb calcium.
Sex hormones - adolescents experience a growth spurt due to an increased level of hormones.
10-7

29. Hormonal regulation of Bone Calcium Levels
Parathyroid hormone (PTH) – produced by the parathyroid gland - accelerates bone recycling and increases blood calcium.
Calcitonin – produced by the thyroid gland - a hormone that decreases blood calcium levels, deposits calcium into the bone.
Homeostasis – maintaining a balance of calcium levels in blood and in bone.

30. Figure: 25-01
Title: Calcium Levels: An Example of Negative Feedback
Caption: Calcium levels in the bloodstream are regulated in part by the parathyroid glands. These glands can sense when calcium levels are too low (the stimulus in the drawing at left). In response, the parathyroids secrete a hormone that causes the bones to release calcium. This bring about high calcium levels, which the glands also can sense (the stimulus in the drawing at right). High calcium levels cause the parathyroids to halt their production of the calcium-liberating hormone.

31. Healing broken bones Broken bones and fractures are the same thing
Bone fractures are healed by fibroblasts and osteoblasts.
When a break occurs, there is bleeding followed by a clot.
Fibroblasts secrete collagen fibers that form a callus linking the two parts of the bone. This is later replaced by bone.

32. Bone Fractures are Healed by Fibroblasts and Osteoblasts
Formation of
blood clot
Formation of
cartilaginous callus
Cartilaginous
callus
Spongy
bone
struts
Blood
clot
(hematoma)
Step 1: Within hours
after the fracture, a
blood clot forms.
Step 2: A cartilaginous
callus is formed by
invading fibroblasts.
Figure 5.4 (1 of 2)

33. Bone Fractures are Healed by Fibroblasts and Osteoblasts
Formation of
bony callus
Bone remodeling
New
blood
vessels
Bony
callus
Healed
fracture
Step 3: Osteoblasts form
new bone, converting the
cartilaginous callus to
a bony callus.
Step 4: The fracture is
healed and bone is
remodeled, restoring
bone to original shape.
Figure 5.4 (2 of 2)

34. This hormones accelerates bone recycling and increases blood calcium
Growth hormone
Calcitonin
Parathyroid hormone

35. Calcitonin is produced by the ______ gland
Parathyroid
Thyroid
Anterior pituitary
Hypothalamus

36. Cartilage
Cartilage - flexible connective tissue not as strong as bone tissue.
Function: Cushion joints, flexiblilty
Found at the ends of long bones, nose, ends of ribs, larynx and trachea, disks between vertebrae and knee, ear flaps and epiglottis.
Cartilage cells are chondrocytes
Cartilage lacks blood vessels, so slow to heal

37. 10-4

38. Tendons and Ligaments
Ligaments – connective tissue that connects bone to bone
Tendons – connective tissue that connects muscle to bone

39. Synovial Joints Freely movable joints held together by ligaments.
Synovial membrane - produces synovial fluid, an excellent lubricant for the joints.
Bursae – fluid filled sacs, reduce friction
Menisci – cartilage between the bones, acts as a cushion
Cartilage is also found at the ends of the bones
10-18

40. Synovial Joints Femur Fat pad Tibia (a)
A bursa is a fluid-filled sac
that cushions certain joints
and reduces friction between
tendons and ligaments.
Femur
A layer of cartilage on the
articulating surfaces of the bones
reduces friction as the bones move.
The joint cavity is filled with
synovial fluid, which serves as a
shock absorber and lubricant.
Fat pad
The synovial membrane forms
the inner surface of the joint cavity
and secretes synovial fluid.
Tibia
(a)
Synovial joints, such as the knee shown here, permit a
great range of movement.
Figure 5.13a

41. Synovial Joints Quadriceps tendon Femur Posterior cruciate ligament
Lateral
collateral
ligament
Anterior cruciate
ligament
Medial collateral
ligament
Patellar ligament
Fibula
Patella
(kneecap)
Tibia
(b)
Ligaments hold bones together, support the joint,
and direct the movement of the bones.
Figure 5.13b

42. 10-19

43. Cartilage cells are
fibrocytes
osteocytes
chondrocytes

44. This type of connective tissue connects bone to bone
Ligaments
Tendons

45. fluid filled sacs are called:
Synovia
Menisci
Bursae

46. Disorders of the Skeletal System
Osteoarthritis - deterioration of cartilage at joints.
Rheumatoid Arthritis – chronic inflammatory disorder of the joints.
Sprains – When ligaments are torn or stretched
Bursitis – inflammation of bursa
Tendonitis – inflammation of tendon sheath
Fracture – broken bone
simple = bone breaks but does not penetrate the skin
compound = bone breaks and protrudes through the skin
10-22

47. Osteoporosis
When more bone is reabsorbed than is formed, this is when the homeostasis is not maintained and more calcium is taken out of the bones than is replaced.
Estrogen and Testosterone help maintain the bone density.
After menopause women produce less estrogen and this can lead to less bone density

48. Risk Factors Post menopausal Not enough exercise
Poor diet, not enough calcium in the diet
Smoking
Low vitamin D levels
Certain hormonal disorders

49. Treatment
Exercise
Increased Calcium in the diet, calcium supplements if needed, the type of calcium supplement is important
Estrogen replacement therapy
Prescription drugs

50. Ages Amount mg/day Birth - 6 months 210 6 months - 1 year 270 1-3 500
Recommended Calcium Intakes*
Ages
Amount mg/day
Birth - 6 months
210
6 months - 1 year
270
1-3
500
4-8
800
9-13
1300
14-18
19-30
1000
31-50
51-70
1200
70 or older

51. Food
Calcium (mg)
% DV*
Yogurt, plain, low fat, 8 oz.
415
42%
Yogurt, fruit, low fat, 8 oz.
25%-38%
Sardines, canned in oil, with bones, 3 oz.
324
32%
Cheddar cheese, 1 ½ oz shredded
306
31%
Milk, non-fat, 8 fl oz.
302
30%
Tofu, firm, ½ cup
204
20%
Mozzarella, part skim 1 ½ oz.
275
28%
Orange juice, calcium fortified, 6 fl oz.
20-26%
Turnip greens, boiled, ½ cup 99
10%
Kale, cooked, 1 cup 94 9%
Ready to eat cereal, calcium fortified, 1 cup
10%-100%
Cottage cheese, 1% milk fat, 1 cup unpacked
138
14%

52. Decreased Calcium Absorption
Oxalic acid – potent inhibitor of calcium absorption, and is found in high concentrations in spinach and rhubarb and in somewhat lower concentrations in sweet potato and dried beans.
Sodium – Increased sodium intake results in increased loss of calcium in the urine.
Protein – As dietary protein intake increases, the urinary excretion of calcium also increases.
Caffeine – Caffeine in large amounts increases urinary calcium content for a short time.

54. Fractured bones are the same thing as broken bones
True
False

55. Important Concepts Read Ch 7
What are the four components of the skeletal system, and their functions
What are the functions of bone
What are the two layers of bone
What is the periosteum and what is its function
What is the structure of the osteon, what are the features found in the osteon

56. Important Concepts
What are the three types of bone cells and their functions
What are the functions of cartilage, tendons, and ligaments.
What are the parts of synovial joints and their functions
What are the hormones involved in bone growth and homeostasis, what glands produce calcitonin and parathyroid hormones

57. Important Concepts What are the disorders of the skeletal system
How do bones heal
What is osteoporosis, what are the risk factors, what can you do to prevent it.

58. Definitions
Compact bone, osteon, central canal (haversian canal), Spongy bone, Epiphysis, Diaphysis, Periosteum, lacunae, callus, fibroblasts, Osteoblasts, Osteocytes, Osteoclasts, Chondrocytes, growth hormone, Parathyroid hormone (PTH), Calcitonin, Vitamin D, epiphyseal plate, growth plate