Pathophysiology of Musculoskeletal System. Lecture notes by Dr Ammar

1. Introduction to
Muscloskeletal system
Dr.AMMAR JAWAD
MBChB, MPH

2. Musculoskeletal System
• The musculoskeletal system is the organ system
that gives us the ability to move (locomotion).
The primary functions of this system include:

3. Skeletal System
Functions:
1. Support
 The bones of the legs, pelvic, and vertebral column
support the weight of the erect body.
 The mandible (jawbone) supports the teeth.
 Other bones support various organs and tissues.
2. Protection
 The bones of the skull protect the brain.
 Ribs and sternum (breast bone) protect the lungs and
heart.
 Vertebrae protect the spinal cord.

4. Skeletal System
3. Movement
 Skeletal muscles use the bones as levers to move the
body.
4. Reservoir for minerals and adipose tissue
 99% of the body’s calcium is stored in bone.
 85% of the body’s phosphorous is stored in bone.
5. Hematopoiesis
 All blood cells are made in the marrow of certain bones.

5.  6. Triglyceride Storage
 Yellow bone marrow
 Triglycerides stored in adipose cells
 Serves as a potential chemical energy reserve
• 7. Heat generation

6. • The musculoskeletal system is comprised up of
the following tissues:
▫ Muscles
▫ Bones
▫ Cartilage, Ligaments, Tendons
▫ Joints

7. Muscles

8. Anatomy and Physiology
• Muscles
▫ Skeletal, smooth, and cardiac
• Joints
▫ The junction between two or more bones
• Tendons
▫ Cord-like structures that attach muscles to the
periosteum of the bone
▫ Attachments of the muscle
 Origin and insertion

9. Anatomy and Physiology
• Ligaments
▫ Fibrous tissue connecting two adjacent, freely
movable bones
• Cartilage
▫ Firm, dense type of connective tissue
• Bursae
▫ Small sac filled with synovial fluid
▫ Reduces friction between areas

10. Musculoskeletal System

11. •Ligaments connect
bone-to-bone or
reinforce joints--they
are made up of
tendinous tissue as
well
•E.g. knee ligaments
Ligaments

13. Tendons
• Tendons are calble-like fibrous tissues that connect
muscle-to-bone, functioning simply to transmit forces

14. Joints

15. Copyright 2010, John
Wiley & Sons, Inc.
Joints
• Points where bones meet
• Classifications
▫ Structurally: by their anatomy
 Fibrous, cartilaginous, or synovial
▫ Functionally: by the degree of movement they
permit
 Immovable, slightly movable, and freely movable

16. Structural Classification
• Based on what is between bones:
▫ Space (or not)
▫ Type of connective tissue present
• Types
▫ Fibrous joints - no cavity, just dense irregular
connective tissue
▫ Cartilaginous joints - no cavity, bones held
together by cartilage
▫ Synovial joints - have synovial cavity, dense
irregular tissue of articular capsule, and often
ligaments

17. Functional Classification
• Based on degree of movement they permit
• Types
▫ Synarthrosis: immovable
 Pelvis, sutures, teeth
▫ Amphiarthrosis: slightly movable
 Epiphyseal plate, tibia-fibula, vertebrae, pelvic
symphysis
▫ Diarthrosis: freely movable
 Most joints of the body
 All diarthrotic joints are synovial

18. Fibrous Joints
• Suture (synarthrosis)
▫ Joined by thin layer of dense fibrous connective
tissue
▫ Example: between bones of skull
• Syndesmosis
▫ Greater distance between bones and greater amount
of dense irregular connective tissue
▫ Examples
 Distal tibia to distal fibula (amphiarthrosis)
 Gomphosis (synarthrosis): tooth root in socket
(alveolar process) of mandible or maxilla

19. Fibrous Joints
• Interosseous membrane (amphiarthrosis)
▫ Has greater amount of dense irregular connective
tissue
▫ Examples: extensive membranes between shafts
of some long bones
 Radius-ulna
 Tibia-fibula

20. Fibrous Joints

21. Fibrous Joints

22. Fibrous Joints

23. Cartilaginous Joints
• Synchondrosis (synarthrosis)
▫ Cartilage connects two areas of bone
▫ Example
 Epiphyseal (growth) plate connecting epiphysis and
diaphysis of long bone (synarthrosis)
• Symphysis (amphiarthrosos)
▫ Cartilage connects two bones, but a broad disc of
fibrocartilage is present also
▫ Examples: pubic symphysis and intervertebral discs

24. Copyright 2010, John
Wiley & Sons, Inc.Cartilaginous Joints

25. Cartilaginous Joints

26. ▫ Synovial
 Most complex joints
 Allow a large degree of relative motion between
articulating bones
 Surrounded by a fibrous capsule (synovial capsule)
 Hip, knee, elbow, ankle, etc.

27. Musculoskeletal System
Synovial fluid:
The joint capsule secretes whitish fluid that
works like oil in a machine, lubricating the joint
surfaces to reduce friction to promote smooth
operation and extend joint life.

28. Synovial Joints: Structure
• Synovial cavity: space containing fluid
• Articular cartilage
▫ Covers ends of bones, absorbs shock
• Articular capsule
▫ Inner layer: synovial membrane that secretes
synovial fluid (reduces friction, supplies nutrients)
▫ Outer layer: dense, irregular connective tissue

29. Synovial Joints: Structure
• In some cases synovial joints include:
▫ Ligaments (either inside or outside of joint cavity)
▫ Menisci (cartilage discs)
▫ Articular fat pads
▫ Bursae
 Sacs made of synovial membranes containing fluid
 Located where friction can occur
 Examples: between skin-bone, tendons-bones,
muscles-bones, ligaments-bones

30. Copyright 2010, John
Wiley & Sons, Inc.Synovial Joints: Structure

31. Copyright 2010, John
Wiley & Sons, Inc.Knee Joint

32. Joints (Factors Affecting Contact and Range
for Motion at Synovial Joints)
• Range of motion (ROM)
▫ Refers to the range, measured in degrees of a circle,
through which the bones of a joint can be moved
• Factors contribute to keeping the articular
surfaces in contact and affect range of motion:
▫ Structure or shape of the articulating bones
 Shape of bones determines how closely they fit together
▫ Strength and tension of the joint ligaments
 Ligaments are tense when the joint is in certain positions
 Tense ligaments restrict the range of motion

33. Joints (Factors Affecting Contact and Range for
Motion at Synovial Joints)
▫ Arrangement and tension of the muscles
 Muscle tension reinforces the restraint placed on a joint by its
ligaments , and thus restricts movement
▫ Contact of soft parts
 The point at which one body surface contacts another may limit
mobility
 Movement be restricted by the presence of adipose tissue
▫ Hormones
 Flexibility may also be affected by hormones
 Relaxin increases the flexibility of the pubic symphysis and
loosens the ligaments between the sacrum and hip bone toward
the end of pregnancy
▫ Disuse
 Movement may be restricted if a joint has not been used for an
extended period

34. Bone and cartilage

35. Cartilage: Connective tissue
•Chondroblasts lay down the
matrix,
•become chondrocytes when
surrounded by extra cellular
matrix
•Chondrocytes do not mitose
•Poor healing
•On aging, cartilage becomes
calcified
•Less flexible
•Not bone

36. Elastic: More flexible, e.g., ear

37. • Hyaline
▫ usually in the joints

38. Fibrocartilage
Resists compression—IV Disk,
menisci

39. Types (shapes) of Bones
•Long
▫ Femur
•Short
▫ Carpal
•Sesamoid
▫ Patella
•Flat
▫ Scapula
•Irregular
▫ Vertebra

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Bone
• Bone classification
There are 206 bones in the human body.
• Skeleton system classified into two groups:
A. Axial skeleton
 Forms long axis of the body.
 Includes the bones of the skull, vertebral column, and rib
cage.
 These bones are involved in protection, support, and
carrying other body parts.

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Skeletal System
B. Appendicular skeleton
 Bones of upper & lower limbs and the girdles (shoulder
bones and hip bones) that attach them to the axial
skeleton.

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Skeletal System
• Basic Bone Structure
• Bones are organs composed of hard living tissue providing structural support to the
body.
• It is a hard matrix of calcium salts deposited around protein fibers. Minerals make
bone rigid and proteins (collagen) provide strength and elasticity.
Bones are organs. Thus, they’re composed of multiple tissue types. Bones are
composed of:
▫ Bone tissue (osseous tissue).
▫ Fibrous connective tissue.
▫ Cartilage.
▫ Vascular tissue.
▫ Lymphatic tissue.
▫ Adipose tissue.
▫ Nervous tissue.

43. Typical (Long) Bone Structure

44. Internal Organization of a Typical Bone
Osteon = Functional unit of bone

45. Types of Osseous Tissue
1. Compact Bone
1. Dense, found in the walls, or cortex
2. Spongy or Cancellous Bone
1. Network of struts and thin plates (trabeculae)
3. Marrow
1. Red and Yellow

46. 1. Compact Bone
• Osteon = functional unit of
bone
• The mineral matrix is
hydroxyapatite
• Osteoblasts lay down the
matrix in layers (lamellae)
▫ Become osteocytes when
surrounded by EC matrix
▫ Lacunae
• Osteoclasts break
down bone

47. 2. Spongy Bone
• No osteons
• Lacy network of
struts called
trabeculae reinforce
the bone
• Covered by
endosteum

48. 3. Marrow
• Red Marrow
▫ Active
▫ Blood Precursors
• Yellow Marrow
▫ Inactive
▫ Mostly fat

49. 49
Skeletal System
• Bone marrow is a general term for the soft tissue
occupying the medullary cavity of a long bone,
the spaces amid the trabeculae of spongy bone,
and the larger haversian canals.
 Red bone marrow looks like blood but with a thicker
consistency.
 It consists of a delicate mesh of reticular tissue saturated
with immature red blood cells and scattered adipocytes.

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Skeletal System
Bone Marrow

51. 51
Skeletal System
• In a child, the medullary cavity of nearly every
bone is filled with red bone marrow.
• In young to middle-aged adults, the long bones
are filled with fatty yellow bone marrow.
▫ Yellow marrow no longer produces blood, although in
the event of severe or chronic anemia, it can transform
back into red marrow
• In adults, red marrow is limited to the axial
skeleton, pelvic girdle, and proximal heads of the
humerus and the femur.

52. 52
Skeletal System
• Bone tissue is a type of connective tissue consist of
cells and a big amount of extra-cellular matrix.
• Bone cells:
• Osteogenic cells
▫ Undergo cell division; the resulting cells develop
into osteoblasts

53. Osteoblasts
Bone-building cells.
Synthesize and secrete collagen fibers and other organic components of
bone matrix.
Initiate the process of calcification.
Found in both the periosteum and the endosteum

54. 54
The blue arrows indicate the
osteoblasts. The yellow arrows indicate
the bone matrix they’ve just secreted.

55. 55
Skeletal System
Osteocytes
 Mature bone cells.
 Osteoblasts that have become trapped by the secretion of
matrix.
 No longer secrete matrix.
 Responsible for maintaining the bone tissue.

58. 58
Skeletal System
Osteoclasts
▫ Huge cells derived from the fusion of as many as 50
monocytes (a type of white blood cell).
▫ Cells that digest bone matrix – this process is called
bone resorption and is part of normal bone growth,
development, maintenance, and repair.
▫ Concentrated in the endosteum.

60. 60
Skeletal System
• Bone Matrix:
▫ Consists of organic and inorganic components.
▫ 1/3 organic and 2/3 inorganic by weight
▫ Organic component consists of several materials that
are secreted by the osteoblasts:

61. 61
Skeletal System
• Inorganic component of bone matrix
▫ Consists mainly of two components :
1. Calcium phosphate.
2. Calcium hydroxide.
▫ These 2 salts interact to form a compound called
hydroxyapatite.
▫ Bone also contains smaller amounts of magnesium,
▫ fluoride, and sodium.
▫ These minerals give bone its characteristic hardness and the
ability to resist compression.

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Skeletal System
• Long Bone Structure
• Shaft plus 2 expanded ends.
• Shaft is known as the diaphysis.
▫ Consists of a thick collar of compact bone surrounding a
central marrow cavity
• Expanded ends are epiphyses
▫ Thin layer of compact bone covering an interior of spongy
bone.
▫ Joint surface of each epiphysis is covered with a type of
hyaline cartilage known as articular cartilage.

63. 63

65. 65
Skeletal System
• The external surface of the entire bone except for the joint
surfaces of the epiphyses is covered by a double-layered
membrane known as the periosteum.
▫ Periosteum is richly supplied with nerve fibers, lymphatic vessels and
blood vessels.
 These enter the bone of the shaft via a nutrient foramen.
▫ Periosteum is connected to the bone matrix via strong strands of
collagen

66. 66
Skeletal System
• Internal bone surfaces are covered with a delicate
connective tissue membrane known as the
endosteum.
▫ Covers the spongy bone in the marrow cavities and
lines the canals that pass through compact bone.
▫ Contains both osteoblasts and osteoclasts.

68. Bone Development
• Osteogenesis (ossification): is the process of bone tissue formation.
• In embryos this leads to the formation of the bony skeleton.
• In children and young adults, ossification occurs as part of bone
growth.
• In adults, it occurs as part of bone re-modeling and bone repair.

71. Formation of the Bony Skeleton
• Before week 8, the human embryonic skeleton is made of
fibrous membranes and hyaline cartilage.
• After week 8, bone tissue begins to replace the fibrous
membranes and hyaline cartilage.
▫ The development of bone from a fibrous membrane is called intra-
membranous ossification.
▫ Plates of Bone e.g. skull
▫ The replacement of hyaline cartilage with bone is known as endo-
chondral ossification.
• Long Bones

72. Bone Circulation