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Developmental Aspects of Tissue

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Presentation on theme: "Developmental Aspects of Tissue"— Presentation transcript:

1 Developmental Aspects of Tissue
Primary germ layers: ectoderm, mesoderm, and endoderm Three layers of cells formed early in embryonic development Specialize to form the four primary tissues Nerve tissue arises from ectoderm

2 Developmental Aspects of Tissue
Muscle, connective tissue, endothelium, and mesothelium arise from mesoderm Most mucosae arise from endoderm Epithelial tissues arise from all three germ layers Figure 4.13

3 Skeletal Cartilage Contains no blood vessels or nerves
Surrounded by the perichondrium (dense irregular CT) that resists outward expansion Three types – hyaline, elastic, and fibrocartilage

4 BONES and SKELETAL TISSUE

5 Bones and Cartilages of the Human Body
Figure 6.1

6 Function of Bones Support – form the framework that supports the body and cradles soft organs Protection – provide a protective case for the brain, spinal cord, and vital organs Movement – provide levers for muscles Mineral storage – reservoir for minerals, especially calcium and phosphorus Blood cell formation – hematopoiesis occurs within the marrow cavities of bones

7 Reminder -Structure of Long Bone
Figure 6.3a, c

8 Reminder- Structure of Short, Irregular, and Flat Bones
Figure 6.4

9 Location of Hematopoietic Tissue (Red Marrow)
In infants Found in the medullary cavity and all areas of spongy bone In adults Found in the spongy bone of flat bones, and the head of the femur and humerus

10 Chemical Composition of Bone: Organic
Osteoblasts – bone-forming cells Osteocytes – mature bone cells Osteoclasts – large cells that resorb or break down bone matrix Osteoid – unmineralized bone matrix composed of proteoglycans, glycoproteins, and collagen

11 Chemical Composition of Bone: Inorganic
Hydroxyapatites, or mineral salts Sixty-five percent of bone by mass Mainly calcium phosphates Responsible for bone hardness and its resistance to compression

12 Bone Development Osteogenesis and ossification – the process of bone tissue formation, which leads to: The formation of the bony skeleton in embryos Bone growth until early adulthood Bone thickness, remodeling, and repair

13 Formation of the Bony Skeleton
Begins at week 8 of embryo development Intramembranous ossification – bone develops from a fibrous membrane Endochondral ossification – bone forms by replacing hyaline cartilage

14 Postnatal Bone Growth Growth in length of long bones
Cartilage on the side of the epiphyseal plate closest to the epiphysis is relatively inactive Cartilage abutting the shaft of the bone organizes into a pattern that allows fast, efficient growth

15 Long Bone Growth and Remodeling
Growth in length – cartilage continually grows and is replaced by bone as shown Remodeling – bone is resorbed and added by appositional growth as shown Figure 6.10

16 Hormonal Regulation of Bone Growth During Youth
During infancy and childhood, epiphyseal plate activity is stimulated by growth hormone During puberty, by testosterone and estrogens Initially promote adolescent growth spurts Cause masculinization and feminization of specific parts of the skeleton Later induce epiphyseal plate closure, ending longitudinal bone growth

17 Bone Remodeling Remodeling units – adjacent osteoblasts (deposit) and osteoclasts (resorb) bone at periosteal and endosteal surfaces

18 Bone Deposition Occurs where bone is injured or added strength is needed Requires a diet rich in protein, vitamins C, D, and A, calcium, phosphorus, magnesium, and manganese Alkaline phosphatase is essential for mineralization of bone Sites of new matrix deposition are revealed by: Osteoid seam – unmineralized band of bone matrix Calcification front – abrupt transition zone between the osteoid seam and the older mineralized bone

19 Bone Resorption Accomplished by osteoclasts
Resorption bays – grooves formed by osteoclasts as they break down bone matrix Resorption involves osteoclast secretion of: Lysosomal enzymes that digest organic matrix Acids that convert calcium salts into soluble forms Dissolved matrix is transcytosed across the osteoclast’s cell where it is secreted into the interstitial fluid and then into the blood

20 Importance of Ionic Calcium in the Body
Calcium is necessary for: Transmission of nerve impulses Muscle contraction Blood coagulation Secretion by glands and nerve cells Cell division

21 Control of Remodeling Two control loops regulate bone remodeling
Hormonal mechanism that maintains calcium homeostasis in the blood Mechanical and gravitational forces acting to the skeleton

22 Hormonal Mechanism Rising blood Ca2+ levels trigger the thyroid to release calcitonin Calcitonin stimulates calcium salt deposit in bone Figure 6.11

23 Hormonal Mechanism Falling blood Ca2+ levels signal the parathyroid glands to release PTH PTH signals osteoclasts to degrade bone matrix and release Ca2+ into the blood Figure 6.11

24 Response to Mechanical Stress
Wolff’s law – a bone grows or remodels in response to the forces or demands placed upon it Figure 6.12

25 Response to Mechanical Stress
Observations supporting Wolff’s law include: Long bones are thickest midway along the shaft (where bending stress is greatest) Curved bones are thickest where they are most likely to buckle Figure 6.12

26 Response to Mechanical Stress
Large, bony projections occur where heavy, active muscles attach Figure 6.12

27 Bone Fractures (Breaks)
Bone fractures are classified by: The position of the bone ends after fracture Completeness of the break The orientation of the bone to the long axis Whether or not the bones ends penetrate the skin

28 Types of Bone Fractures
Learn table with fracture types 6.2?

29 Stages in the Healing of a Bone Fracture
Hematoma formation Torn blood vessels hemorrhage A mass of clotted blood (hematoma) forms at the fracture site Site becomes swollen, painful, and inflamed Figure

30 Stages in the Healing of a Bone Fracture
Fibrocartilaginous callus forms Granulation tissue (soft callus) forms a few days after the fracture Capillaries grow into the tissue and phagocytic cells begin cleaning debris Figure

31 Stages in the Healing of a Bone Fracture
Bony callus formation New bone trabeculae appear in the fibrocartilaginous callus Fibrocartilaginous callus converts into a bony (hard) callus Bone callus begins 3-4 weeks after injury, and continues until firm union is formed 2-3 months later Figure

32 Stages in the Healing of a Bone Fracture
Bone remodeling Excess material on the bone shaft exterior and in the medullary canal is removed Compact bone is laid down to reconstruct shaft walls Figure

33 Homeostatic Imbalances
Osteomalacia Bones are inadequately mineralized causing softened, weakened bones Main symptom is pain when weight is put on the affected bone Caused by insufficient calcium in the diet, or by vitamin D deficiency

34 Homeostatic Imbalances
Rickets Bones of children are inadequately mineralized causing softened, weakened bones Bowed legs and deformities of the pelvis, skull, and rib cage are common Caused by insufficient calcium in the diet, or by vitamin D deficiency

35 Homeostatic Imbalances
Osteoporosis Group of diseases in which bone reabsorption outpaces bone deposit Spongy bone of the spine is most vulnerable Occurs most often in postmenopausal women Treatment Calcium and vitamin D supplements Increased weight bearing exercise Hormone (estrogen) replacement therapy (HRT) Prevented or delayed by sufficient calcium intake and weight-bearing exercise

36 Paget’s Disease Characterized by excessive bone formation and breakdown Pagetic bone with an excessively high ratio of woven to compact bone is formed Pagetic bone, along with reduced mineralization, causes spotty weakening of bone Osteoclast activity wanes, but osteoblast activity continues to work

37 Developmental Aspects of Bones
Mesoderm gives rise to embryonic mesenchymal cells, which produce membranes and cartilages that form the embryonic skeleton The embryonic skeleton ossifies in a predictable timetable that allows fetal age to be easily determined from sonograms At birth, most long bones are well ossified (except for their epiphyses)

38 Developmental Aspects of Bones
By age 25, nearly all bones are completely ossified In old age, bone resorption predominates A single gene that codes for vitamin D docking determines both the tendency to accumulate bone mass early in life, and the risk for osteoporosis later in life

39 Joints (Articulations)
Weakest parts of the skeleton Articulation – site where two or more bones meet Functions Give the skeleton mobility Hold the skeleton together

40 Classification of Joints: Structural
Structural classification focuses on the material binding bones together and whether or not a joint cavity is present The three structural classifications are: Fibrous Cartilaginous Synovial

41 Classification of Joints: Functional
Functional classification is based on the amount of movement allowed by the joint The three functional class of joints are: Synarthroses – immovable Amphiarthroses – slightly movable Diarthroses – freely movable

42 Example - Synovial Joints: Major Ligaments and Tendons (Anterior View)
Figure 8.11c

43 Inflammatory and Degenerative Conditions
Bursitis An inflammation of a bursa, usually caused by a blow or friction Symptoms are pain and swelling Treated with anti-inflammatory drugs; excessive fluid may be aspirated Tendonitis Inflammation of tendon sheaths typically caused by overuse Symptoms and treatment are similar to bursitis

44 Arthritis More than 100 different types of inflammatory or degenerative diseases that damage the joints Most widespread crippling disease in the U.S. Symptoms – pain, stiffness, and swelling of a joint Acute forms are caused by bacteria and are treated with antibiotics Chronic forms include osteoarthritis, rheumatoid arthritis, and gouty arthritis

45 Osteoarthritis (OA) Most common chronic arthritis; often called “wear-and-tear” arthritis Affects women more than men 85% of all Americans develop OA More prevalent in the aged, and is probably related to the normal aging process

46 Osteoarthritis: Treatments
OA is slow and irreversible Treatments include: Mild pain relievers, along with moderate activity Magnetic therapy Glucosamine sulfate decreases pain and inflammation SAM-e (s-adenosylmethionine) builds up cartilage matrix and regenerates tissue

47 Rheumatoid Arthritis (RA)
Chronic, inflammatory, autoimmune disease of unknown cause, with an insidious onset Usually arises between the ages of 40 to 50, but may occur at any age Signs and symptoms include joint tenderness, anemia, osteoporosis, muscle atrophy, and cardiovascular problems The course of RA is marked with exacerbations and remissions

48 Rheumatoid Arthritis: Course
RA begins with synovitis of the affected joint Inflammatory blood cells migrate to the joint, causing swelling Inflamed synovial membrane thickens into a pannus Pannus erodes cartilage, scar tissue forms, articulating bone ends connect The end result, ankylosis, produces bent, deformed fingers

49 Rheumatoid Arthritis: Treatment
Conservative therapy – aspirin, long-term use of antibiotics, and physical therapy Progressive treatment – anti-inflammatory drugs or immunosuppressants The drug Embrel, a biological response modifier, removes cells that promote inflammation

50 Gouty Arthritis Deposition of uric acid crystals in joints and soft tissues, followed by an inflammation response Typically, gouty arthritis affects the joint at the base of the great toe In untreated gouty arthritis, the bone ends fuse and immobilize the joint Treatment – colchicine, nonsteroidal anti-inflammatory drugs, and glucocorticoids

51 Developmental Aspects of Joints
By embryonic week 8, synovial joints resemble adult joints Few problems occur until late middle age Advancing years take their toll on joints including: Ligaments and tendons shorten and weaken Intervertebral discs become more likely to herniate OA is inevitable, and all people of 70 have some degree of OA Prudent exercise (especially swimming) that coaxes joints through their full range of motion is key to postponing joint problems

52 Sprains The ligaments (bone to bone) reinforcing a joint are stretched or torn Partially torn ligaments slowly repair themselves Completely torn ligaments require prompt surgical repair

53 Cartilage Injuries The snap and pop of overstressed cartilage
Common aerobics injury Repaired with arthroscopic surgery

54 Dislocations Occur when bones are forced out of alignment
Usually accompanied by sprains, inflammation, and joint immobilization Caused by serious falls and are common sports injuries Subluxation – partial dislocation of a joint


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