Whole bone? Name the shape first
Check proportions: shaft with two ends = long; cube = short; plate = flat; odd processes = irregular; seed in a tendon = sesamoid.Your course describes Lab Exam 1 as bone identification: you will look at whole bones, sectioned bone models, and diagrams of compact bone, then name the shape class, the region, or the microscopic structure being pointed to. This review walks through the long bone from the outside in, then zooms down to the osteon. If your Lab Exam 1 also covers Labs 1 to 3, work through those reviews as well.
Your lab manual wins. Lab sections vary in which models, slides, and terms they use. If anything here differs from your lab handout or what your instructor emphasized, go with your lab material and tell your tutor so this review can be updated.
Bone Shapes
Shape is about proportions. A long bone is longer than it is wide and has a shaft, so the finger bones count even though they are small. A short bone is cube-like. A flat bone is a thin plate. An irregular bone fits none of these. A sesamoid bone forms inside a tendon; the patella is the one you must know.
| Shape | What it looks like | Examples to know | Tip |
|---|---|---|---|
| Long | Longer than wide; a shaft with two expanded ends | Humerus, radius, ulna, femur, tibia, fibula, metacarpals, metatarsals, phalanges | Size does not matter: the tiny finger phalanges are long bones |
| Short | Roughly cube-shaped, about as long as wide | Carpals (wrist), tarsals (ankle) | Mostly spongy bone inside a thin compact shell |
| Flat | Thin, flattened, often curved plates | Frontal and parietal bones, sternum, ribs, scapula | Spongy layer (diploë) sandwiched between two compact plates |
| Irregular | Complex shapes that fit no other group | Vertebrae, sacrum, many facial bones (e.g., sphenoid, ethmoid), hip bone in some texts | If it has odd processes in many directions, think irregular |
| Sesamoid | Small, seed-shaped, formed inside a tendon | Patella (kneecap); small ones in the hands and feet | Some courses list only four shapes and treat sesamoid as a special case |
Naming varies by course. Your week 7 study guide lists four main shapes (long, short, flat, irregular). Many lab manuals add sesamoid as a fifth, and a few add sutural (Wormian) bones, the small extra bones in skull sutures. If you are asked for the shape of the patella, "sesamoid" is the expected answer; "short" is accepted only in courses that use four classes.
Long Bone Anatomy
Read the model top to bottom, then outside to inside. Ends = epiphyses; shaft = diaphysis; the flared zone between = metaphysis. Outside: articular cartilage on the joint surfaces and periosteum everywhere else. Wall: compact bone. Inside the ends: spongy bone with red marrow. Inside the shaft: the medullary cavity with yellow marrow, lined by endosteum.
| Structure | Where | Job / identifying feature |
|---|---|---|
| Diaphysis | The shaft | Thick compact bone around the medullary cavity; resists bending |
| Epiphysis (proximal, distal) | Each expanded end | Spongy bone with red marrow inside a thin compact shell; forms the joint |
| Metaphysis | Where the diaphysis widens into the epiphysis | Contains the epiphyseal plate or line |
| Epiphyseal plate | Hyaline cartilage disc between epiphysis and diaphysis (child) | Lengthwise growth happens here |
| Epiphyseal line | Bony remnant of the plate (adult) | Means growth in length has stopped |
| Articular cartilage | Hyaline cartilage on the joint surfaces of the epiphyses | Smooth, low-friction surface; no periosteum here |
| Periosteum | Dense irregular CT membrane covering the outside (except joint surfaces) | Anchors tendons and ligaments via perforating (Sharpey's) fibers; contains osteoblasts for growth in width and repair |
| Endosteum | Thin membrane lining the medullary cavity and covering trabeculae | Contains osteogenic cells, osteoblasts, osteoclasts; remodels from inside |
| Medullary (marrow) cavity | Hollow center of the diaphysis | Holds yellow marrow (fat) in adults |
| Red marrow | In the spaces of spongy bone | Makes blood cells (hematopoiesis); in adults mainly in flat bones, vertebrae, and the proximal epiphyses of the femur and humerus |
| Compact bone | Dense outer layer, thickest in the diaphysis | Built from osteons; strength |
| Spongy bone | Lattice of trabeculae, mostly in the epiphyses | Light but strong; houses red marrow |
| Nutrient foramen | Small hole through the diaphysis wall | Passage for the nutrient artery and vein into the medullary cavity |
On a plastic model: the medullary cavity is usually painted yellow, red marrow areas red, articular cartilage blue or white, and the periosteum may be a peeled-back flap. Colors differ between models, so identify by position, not color.
Label It · Long Bone
Pins on the gray brackets ask for the region the bracket spans. The other pins point to a structure at the end of the leader line. Choose an answer for each, then press Check answers.
Microscopic Anatomy
Compact bone is a bundle of osteons. Each osteon is a set of concentric lamellae (rings) around a central canal. Osteocytes sit in lacunae between the rings and reach each other through canaliculi. Perforating canals cross at right angles to link central canals. Between osteons are interstitial lamellae; around the whole shaft are circumferential lamellae. Spongy bone has no osteons: it is a lattice of trabeculae with red marrow in the gaps.
| Structure | How to find it | Function |
|---|---|---|
| Osteon (Haversian system) | Cylinder of concentric rings around a central canal | Structural unit of compact bone; runs parallel to the long axis |
| Central (Haversian) canal | Hole in the center of each osteon | Blood vessels and nerves run lengthwise |
| Perforating (Volkmann) canal | Channel running across, perpendicular to the central canals | Connects central canals to each other, the periosteum, and the marrow cavity |
| Concentric lamellae | The rings of an osteon | Layers of matrix; collagen fibers alternate direction ring to ring |
| Lacunae | Small spaces between lamellae | Each holds one osteocyte |
| Osteocyte | The cell inside a lacuna | Mature bone cell; maintains matrix, senses stress |
| Canaliculi | Hair-thin channels radiating from lacunae | Connect osteocytes to each other and to the central canal; nutrient and waste exchange |
| Interstitial lamellae | Incomplete ring fragments between osteons | Leftovers of old osteons broken down during remodeling |
| Circumferential lamellae | Rings that run all the way around the bone, just under the periosteum (outer) and next to the endosteum (inner) | Resist twisting of the whole shaft |
| Trabeculae | Struts and plates of spongy bone | No osteons; aligned along stress lines; red marrow fills the spaces between them |
Central vs. perforating canal, the fast way: in a cross section, central canals look like round holes in the middle of ring systems. Perforating canals look like channels that cut sideways across the rings, joining one central canal to another or to the surface. Central = lengthwise; perforating = crosswise.
Label It · Osteon
Click a numbered pin (or its row), choose the structure it points to, then press Check answers. Wrong answers show the correction in green.
Bone Cells
| Cell | Where | Job | How to recognize it |
|---|---|---|---|
| Osteogenic (osteoprogenitor) cell | Periosteum and endosteum, on bone surfaces | Stem cell; divides and becomes osteoblasts | Flat cell lying on the surface |
| Osteoblast | Growing or repairing bone surfaces | Secretes osteoid (unmineralized matrix) and starts mineralization | Cuboidal cells in a row; "b" for build |
| Osteocyte | Inside lacunae | Maintains the matrix; senses mechanical stress | An osteoblast that walled itself in |
| Osteoclast | In pits on bone surfaces | Dissolves matrix with acid and enzymes, releasing calcium (activated by PTH) | Huge, multinucleated, ruffled border; "c" for chew/clear |
Remodeling in one sentence: osteoclasts remove old bone and osteoblasts replace it; when breakdown outpaces building for years, bone becomes porous (osteoporosis). Low blood calcium → PTH → more osteoclast activity.
Exam Strategy
| Look-alikes | How to tell them apart |
|---|---|
| Epiphyseal plate vs. line | Plate = cartilage band in a child (still growing). Line = thin bony line in an adult (done growing). |
| Periosteum vs. endosteum | Peri- = around (outer surface). Endo- = within (lines the marrow cavity and trabeculae). |
| Central vs. perforating canal | Central runs lengthwise in the middle of an osteon; perforating runs crosswise and connects central canals. |
| Lacuna vs. osteocyte | Lacuna = the space. Osteocyte = the cell living in it. On an empty ground-bone slide you see lacunae; the cells are gone. |
| Concentric vs. interstitial vs. circumferential lamellae | Concentric = complete rings of one osteon. Interstitial = broken fragments between osteons. Circumferential = run around the entire bone. |
| Compact vs. spongy bone | Compact = solid, with osteons; spongy = open lattice of trabeculae, no osteons, red marrow in the spaces. |
| Red vs. yellow marrow | Red = blood-forming, in spongy bone. Yellow = mostly fat, in the adult medullary cavity. |
Check Yourself
Two tries per question; the explanation appears after you answer.
Rapid Recall
Say the answer out loud, then tap the card to check. Shuffle and go again until every card is automatic.
Practical Simulation
This runs like a real bone ID practical: one pinned structure, whole bone, or question per station, a timer, and you type the answer with no word bank. Spell it fully. 20 stations are drawn at random from a larger pool each attempt.
20 stations · 45 seconds each · stations come in random order every attempt.
| # | Station | Your answer | Correct |
|---|
Watch Out
| The mistake | The fix |
|---|---|
| Calling a small bone "short." | Shape is proportions. Phalanges, metacarpals, and metatarsals are long bones. |
| Writing "epiphyseal plate" on an adult bone. | Adults have an epiphyseal line. The plate (cartilage) exists only while the bone is still growing. |
| Swapping periosteum and endosteum. | Peri- = around the outside. Endo- = inside, lining the cavity. |
| Calling the medullary cavity "spongy bone." | The cavity is the hollow center of the shaft (yellow marrow). Spongy bone is the lattice in the ends. |
| Mixing up central and perforating canals. | Central = lengthwise, center of an osteon. Perforating = crosswise connector. |
| Naming the cell when the pin is on the space. | Pin on the hollow space = lacuna. Pin on the cell or its nucleus = osteocyte. |
| Forgetting interstitial lamellae. | If the pin is on broken ring fragments between osteons, it is interstitial, not concentric. |
| Spelling slips: "Haversion," "canaliculus" for many, "lacunas." | Haversian canal; canaliculi (plural); lacuna (one) / lacunae (many); lamella / lamellae. |
Cheat Sheet
Print it or screenshot it for a last look before the lab.
| Topic | Know this |
|---|---|
| Bone shapes | Long (shaft, e.g., femur, phalanges); short (cube, carpals/tarsals); flat (sternum, ribs, cranial); irregular (vertebrae); sesamoid (patella) |
| Long bone regions | Proximal epiphysis, metaphysis, diaphysis, metaphysis, distal epiphysis |
| Growth | Epiphyseal plate (cartilage, child) → epiphyseal line (bone, adult) |
| Coverings | Articular cartilage (hyaline) on joint surfaces; periosteum everywhere else outside; endosteum inside |
| Bone tissue types | Compact (dense wall, osteons) vs. spongy (trabeculae, red marrow) |
| Marrow | Red = blood-forming, in spongy bone. Yellow = fat, in adult medullary cavity |
| Nutrient foramen | Hole in the diaphysis for the nutrient artery |
| Osteon | Central canal + concentric lamellae + lacunae + osteocytes + canaliculi |
| Canals | Central (Haversian) = lengthwise; perforating (Volkmann) = crosswise |
| Other lamellae | Interstitial = between osteons; circumferential = around the whole bone |
| Bone cells | Osteogenic (stem), osteoblast (builds), osteocyte (maintains, in lacuna), osteoclast (breaks down) |
| Bone functions | Support, protection, movement, mineral storage, blood cell production |
| Calcium control | Low blood Ca2+ → PTH → osteoclasts release Ca2+ (negative feedback) |
Debrief
You can now classify any bone by shape, label a sectioned long bone, and walk an osteon from the central canal out. Next up: the Lab Exam 2 review, where you will identify the individual bones of the skeleton and the joint movements.
💭 Before the real thing: run the practical simulation until you score 90% or better twice in a row. Then do it once with the timer on.