Connective Tissues (physiology)

What are the functions of tendons?

Resist tensile loads parallel to fiber orientation

facilitate muscle contraction by providing rigid structure for high tensile F

What is the composition and organization of tendons?

dense regular CT

composed primarily of type I collagen

75–85% of solid content and 65–75% water

tropocollagen → collagen fibrils → fibers → fascicles → tendon

How do tendons adapt to stress?

Crimped collagen fibrils inc. extensibility in response to tensile F

collagen fibers adapt to mechanical demands

What are the functions of ligaments and joint capsules?

attach to bone

resist tensile F in diff. directions

restrict excessive joint motion

What is the composition of ligaments?

55–65% water

primarily type I collagen (~75% of dry content)

How do ligaments adapt to stress?

Collagen fibers organized along stress line resistance

tension stims. CT adaptation

What are the functions of fascia?

create compartments for muscle

contain/separates tissues

provides sites for muscle attachment

What is the composition of fascia?

Superficial fascia: loose irregular CT

deep fascia: dense regular + irregular CT

How does fascia adapt to stress?

variable

interwoven collagen fibers allow to accommodate stress from diff. directions

What is the function of a bursa?

bursa reduces friction btw moving structures

between tendons, ligaments, + bone

What is the composition of a bursa?

fluid-filled sac lined w/ synovial membrane

contains viscous synovial fluid

What are the functions of bone?

support

resists mechanical loads

produces RBCs

remodels in response to stress

What is the composition of bone?

<10% water

organic components (type I collagen + proteoglycans)

high mineral content (hydroxyapatite crystals)

How does bone adapt to stress?

Wolff’s Law

bone remodels internal struct. in response to external stress + mechanical demand

How do cortical and trabecular bone differ in stress adaptation?

Cortical: resist bending + torsional loads

trabecular: resist compressive F + aligns according to loading direction

What are the functions of articular hyaline cartilage?

distributes + transmits loads

protects underlying bone

allows ~ frictionless joint movement

What is the composition of articular hyaline cartilage?

65–80% water

distributed chondrocytes

densely organized type II collagen fibers

How do the zones of hyaline cartilage adapt to stress?

superficial zone: resists shear

transitional zone: resists F from multiple directions

radial zone: resists tensile + compressive F (anchoring cartilage to bone)

What are the functions of fibrocartilage?

inc. joint congruity

absorbs shock

joint lubrication

resists compressive F

What is the composition of fibrocartilage?

70–78% water

chondrocytes

bundles of type I collagen.

How is fibrocartilage adapted to stress?

abundant type I collagen bundles resists compressive F + joint loading

What is the function of scar tissue?

body's glue for tissue damage

What is the composition of scar tissue?

type I collagen

inelastic but highly adaptable

How does scar tissue adapt to stress?

collagen turnover allows randomly deposited collagen fibers to be reorganized when Fs are applied

How does collagen contribute to connective tissue adaptation?

more collagen content improves resistance to tensile F + provide stronger structural framework

How do proteoglycans help connective tissues adapt to stress?

attract water → increasing buoyancy

resistance to compression

allow collagen fibers to move relative to another

What is the Stretch-Hypertrophy Rule?

Intermittent tension stims cells to prod collagen + promote arrangement of new fiber

What is the General Theory of Functional Adaptation?

Compression stims: bone adaptation

tension stims: CT adaptation

shear stims: cartilage adaptation

What effect does immobilization have on tendons?

decreases normal cross-links

weakens structure

collagen degradation to exceed synthesis

What effect does immobilization have on ligaments and capsules?

capsular contracture

reduced GS

increased immature cross-links

decreased energy absorption

lower failure loads

glycosaminoglycan degradation

What effect does immobilization have on articular cartilage?

diminished cartilage thickness

proteoglycans loss

less proteoglycan aggregates

What effect does immobilization have on bone?

Bone stiffness: decrease up to 69% after 8 wks

bone atrophy esp. evident in trabecular

What effect does immobilization have on muscle connective tissue?

decreased myofibrils + sarcomeres

myofibril disorganization

reduced protein synthesis

muscle atrophy

What effect does immobilization have on nerves?

mechanoreceptor atrophy

CT adhesions around nerves

What are the effects of immobilization on periarticular tissues?

Decreased collagen mass

fibrofatty tissue proliferation

weakened ligament insertions

osteoporosis

cartilage erosion

adhesions

contractures

reduced ROM

possible ankylosis

What is mobilization?

attempt to restore efficient motion to body segments + return to normal function/ movement

What are the effects of mobilization on connective tissues?

counteract effects of immobilization

reverse tissue degradation

enhance tissue properties (when not performed too aggressively)

What methods can be used for mobilization?

Stretching

massage

joint mobilization

manual mobilization

functional activity

exercise

How does aging affect ligaments?

Ligament cells → less active

collagen content incr

abnormal collagen cross-links incr

water content decr

elasticity decr

ligament-bone interface weakens

How does aging affect tendons?

Crimp → less extensible

elasticity decr

capillary blood supply decr

tendon-bone interface weakens

How does aging affect hyaline articular cartilage?

thickness decr

abnormal collagen cross-links incr (greater stiffness)

How does aging affect bone?

Osteoclastic activity incr

bone porosity incr

osteoblastic activity decr

skeletal weight decr

# bone cells decr