The document discusses the structure and function of long bones. It describes the key parts of long bones including the diaphysis, epiphyses, articular cartilage, periosteum, medullary cavity, compact and spongy bone. It also discusses bone formation through intramembranous and endochondral ossification as well as homeostasis and functions of bone such as support, protection, movement, blood cell formation, and storage of inorganic salts.

1. Bone Function and Formation Chapter 7 (Part 1)

2. Parts of a Long Bone Long bones are defined as any bone that is longer than it is wide.

3. Parts of a Long Bone The expanded bulge at each end of a long bone is called the epiphysis The epiphysis articulates with other bones Each long bone has a proximal epiphysis and a distal epiphysis The epiphyseal surface that articulates with other bones is covered in articular cartilage

4. Parts of a Long Bone

5. Parts of a Long Bone The long shaft of the bone is called the diaphysis

6. Parts of a Long Bone Bones are covered in a thin, tough layer called the periosteum . The periosteum covers the entire bone, except where there is articular cartilage It is firmly attached to the bone and is continuous with ligaments and tendons connecting to the bone.

7. Parts of a Long Bone Periostium

8. Parts of a Long Bone

9. Parts of a Long Bone The wall of the diaphysis is composed mostly of compact bone Very tightly packed bone cells No spaces in the extracellular matrix.

10. Parts of a Long Bone The wall of the diaphysis is composed mostly of compact bone Very tightly packed bone cells No spaces in the extracellular matrix.

11. Parts of a Long Bone In the center of the diaphysis, is a tube called the medullary cavity . Special layer of cells called the endosteum produce marrow inside the cavity.

12. Marrow Bone marrow comes in two different types Red marrow produces red blood cells, white blood cells, and platelets Yellow marrow stores fat inside the bone As we age, red marrow is replaced with yellow marrow The two can be converted from one to the other, as needed.

13. Parts of a Long Bone The epiphysis is composed mostly of spongy bone . Lots of space between bone cells Only a very thin layer of compact bone covers the epiphysis Helps to reduce the bone’s weight

14. Microscopic Anatomy Bone is composed of cells called osteocytes (os- = bone ) Found in small chambers called lacunae Surround osteocytes Made of hard extracellular material (bone matrix) Calcium carbonate Calcium phosphate

15. Microscopic Anatomy Bone matrix is deposited in concentric circles called lamellae (singular: lamella)

16. Microscopic Anatomy The lamellae surround a central canal Every central canal contains a blood vessel that supplies nutrients to the osteocytes in the surrounding lamellae

17. Microscopic Anatomy Osteocytes have cytoplasmic extensions called canaliculi Used to help osteocytes obtain nutrients & communicate with surrounding osteocytes

18. Bone Formation During development, tissue that will become bone starts off as cartilage There are two basic ways bone can form: Intramembranous Bone Endochondral Bone

19. Intramembranous Bone These bones develop into thin, sheet-like bones like those found in the cranium Originates between two sheet-like layers of connective tissue Bone forming cells called osteoblasts lay down spongy bone near the center between the membranes Cells of the membrane form the periosteum Cells of the periosteum produce osteoblasts that form compact bone to surround the spongy bone.

20. Intramembranous Bone

21. Intramembranous Bone

22. Endochondral Bone Most of the bones are endochondral 1. Blob of cartilage, shaped somewhat like the bone they will become, is what we start with

23. Endochondral Bone 2. Near the middle of the long bone (diaphysis), the cartilage breaks down. 3. Osteoblasts invade the space left by cartilage breaking down, forming spongy bone This is called the primary ossification center 4. Osteoblasts lay down a periosteum to surround the diaphysis

24. Endochondral Bone 5. After a time of growth and ossification in the diaphysis, the cartilage in the epiphyses begins to break down 6. Osteoblasts invade the areas in the epiphyses Create a secondary ossificaiton center

25. Endochondral Bone

26. Endochondral Bone As the primary and secondary ossification centers grow toward each other, they form an epiphyseal plate AKA: Growth Plate

27. Endochondral Bone As toddlers and teenagers grow, bones lengthen by laying down new bone matrix from the epiphyseal plate Damage = bad!

28. Homeostasis of Bones Throughout life, old bone tissue is broken down and “digested” by osteoclasts New bone tissue is formed by osteoblasts .

29. Bone Function Support the body Protect internal organs Allow for attachment of muscles that help up move Produce blood cells Store inorganic salts

30. Protection The skull protects the brain, eyes, nasal & oral passages The ribs protect the heart, lungs, windpipe, and esophagus Pelvis (hips) protect internal reproductive organs (female) and the urinary bladder.

31. Movement Bones (and their associated muscles) act as levers in the body Levers have three parts: A long, rigid rod or bar (the bone) A pivot point (a joint) Something that supplies a force to move the rod (muscle)

32. Blood Cell Formation Blood cells form in the spleen and liver during prenatal development Later, they form in the red marrow found in the medullary cavities of long bones. Hematopoiesis

33. Storage of Inorganic Salts This is another homeostatic mechanism You know how much I love to test you on these The bones store a reserve of calcium salts, which are vital to metabolic processes and muscle contraction The glands involved in this HM are the thyroid and parathyroid

34. Storage of Inorganic Salts If blood calcium levels get too low: Parathyroid (receptor) releases parathyroid hormone to stimulate osteoclast activity. Osteoclasts (effectors) break down bone tissue, releasing calcium salts If blood calcium levels get too high: Thyroid gland releases calcitonin , which activates osteoblasts Osteoblasts store calcium by forming new bone tissue. Check page 132

35. Storage of Inorganic Salts

36. Osteoperosis Caused by increased osteoclast and decreased osteoblast activity. Bone tissue is broken down and replaced with fatty tissue Bones break easily Most common in fair-skinned females after menopause Some research suggests it is due to a decline in Vitamin D

37. Osteoperosis

38. Osteoperosis

39. Osteoperosis Preventing the disease: Avoid smoking and excess alcohol Exercise (especially early in life) Bone mass usually begins to dwindle in the mid-30s. As you near this age, begin to take in extra calcium (milk or supplements) Be sure to get plenty of Vitamin D Take supplements Spend 10-15 minutes in direct sunlight everyday. Your skin makes Vitamin D using UV light.