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Gross Anatomy of Bone

Author: Sophia

what's covered

In this lesson, you will learn the gross anatomical features of bone. Specifically, this lesson will cover:

1. Gross Anatomy of Bone
2. Bony Landmarks
3. Blood and Nerve Supply

before you start

Bone (osseous tissue) differs greatly from other tissues in the body. Bone is hard and many of its functions depend on that characteristic. Future lessons will show that bone is also dynamic in that its shape adjusts to accommodate stresses. This lesson will focus on exploring the gross anatomy of bone.

1. Gross Anatomy of Bone

The structure of a long bone (as opposed to the other four categories based on shape) allows for the best visualization of all of the parts of a bone. As a whole, a long bone can be divided into two parts: the diaphysis and the epiphysis. The diaphysis is the tubular shaft that runs between the proximal and distal ends of the bone. The hollow central region in the diaphysis is called the medullary cavity, which is filled with yellow marrow. The walls of the diaphysis are predominantly composed of compact bone, a dense osseous tissue able to sustain compressive forces.

This illustration depicts an anterior view of the right femur, or thigh bone. The inferior end that connects to the knee is at the bottom of the diagram and the superior end that connects to the hip is at the top of the diagram. The bottom end of the bone contains a smaller lateral bulge and a larger medial bulge. A blue articular cartilage covers the inner half of each bulge as well as the small trench that runs between the bulges. This area of the inferior end of the bone is labeled the distal epiphysis. Above the distal epiphysis is the metaphysis, where the bone tapers from the wide epiphysis into the relatively thin shaft. The entire length of the shaft is the diaphysis. The superior half of the femur is cut away to show its internal contents. The bone is covered with an outer translucent sheet called the periosteum. At the midpoint of the diaphysis, a nutrient artery travels through the periosteum and into the inner layers of the bone. The periosteum surrounds a white cylinder of solid bone labeled compact bone. The cavity at the center of the compact bone is called the medullary cavity. The inner layer of the compact bone that lines the medullary cavity is called the endosteum. Within the diaphysis, the medullary cavity contains a cylinder of yellow bone marrow that is penetrated by the nutrient artery. The superior end of the femur is also connected to the diaphysis by a metaphysis. In this upper metaphysis, the bone gradually widens between the diaphysis and the proximal epiphysis. The proximal epiphysis of the femur is roughly hexagonal in shape. However, the upper right side of the hexagon has a large, protruding knob. The femur connects and rotates within the hip socket at this knob. The knob is covered with a blue-colored articular cartilage. The internal anatomy of the upper metaphysis and proximal epiphysis are revealed. The medullary cavity in these regions is filled with mesh-like spongy bone. Red bone marrow occupies the many cavities within the spongy bone. There is a clear, white line separating the spongy bone of the upper metaphysis with that of the proximal epiphysis. This line is labeled the epiphyseal line. — Anatomy of a Long Bone - A typical long bone shows the gross anatomical characteristics of bone.

The wider section at each end of the bone is called the epiphysis (plural, epiphyses), which is predominantly filled with spongy bone, a porous osseous tissue which provides strength along with storage of red bone marrow. In a growing bone, where each epiphysis meets the diaphysis, there is an epiphyseal plate (growth plate), a layer of hyaline cartilage in a growing bone. When the bone stops growing in early adulthood (approximately 18–21 years), the cartilage is replaced by osseous tissue and the epiphyseal plate becomes an epiphyseal line.

The medullary cavity has a thin connective tissue lining called the endosteum (endo, inside; osteo, bone), where bone growth, repair, and remodeling occur. The outer surface of the bone is covered with a fibrous membrane called the periosteum (peri, around or surrounding). The periosteum contains blood vessels, nerves, and lymphatic vessels that nourish compact bone. Tendons and ligaments also are connected to bones by attaching to the periosteum. The periosteum covers the entire outer surface except where the epiphyses meet other bones to form joints. In this region, the epiphyses are covered with articular cartilage, a thin layer of cartilage that reduces friction and acts as a shock absorber.

The top of this illustration shows an anterior view of the proximal end of the femur. The top image has two zoom-in boxes. The left box is situated on the border between the diaphysis and the metaphysis. Its callout magnifies the periosteum on the right side of the femur. The view shows that the periosteum contains an outer fibrous layer composed of yellow fibers. The inner layer of the periosteum is called the cellular layer, which is composed of irregularly shaped cells. The cellular layer gradually shrinks in width as it transitions from the metaphysis to the diaphysis. A small blood vessel runs through both layers and enters the bone. The right zoom-in box magnifies the endosteum on the left side of the bone. The box is situated just inferior to the border between the diaphysis and the metaphysic. It calls out the inner edge of the compact bone layer. The magnified view shows concentric circles of dark-colored bone matrix. Between the circles are small cavities containing orange, diamond-shaped cells labeled osteocytes. The left edge of the bone matrix is lined with a single layer of flattened cells called the endosteum. There is a large cell, labeled an osteoclast, between two of the endosteum cells. The osteoclast is cutting a depression into the bony matrix under the endosteum. At another part of the endosteum, three smaller osteoblasts are secreting a blue substance that builds up the outermost layer of the bony matrix. — Periosteum and Endosteum - The periosteum forms the outer surface of bone, and the endosteum lines the medullary cavity.

Flat bones, like those of the cranium shown in the image below, consist of a layer of diploë (spongy bone), lined on either side by a layer of compact bone. The two layers of compact bone and the interior spongy bone work together to protect the internal organs. If the outer layer of a cranial bone fractures, the brain is still protected by the intact inner layer.

This illustration shows a cross section of a cranial bone, constructed somewhat like a sandwich. The topmost and bottommost layers are the thin, translucent, periosteum. The upper and lower periosteum cover an upper and lower layer of compact bone, respectively. The compact bone is solid, with each layer occupying about one-tenth of the thickness of the cranial bone. The majority of the cross section is occupied by the spongy bone, or diploe, sandwiched between the upper and lower compact bone. The spongy bone contains many crisscrossing threads of bone. Dark air spaces occur between the threads, giving the bone a porous appearance, much like that of a sponge or Swiss cheese. — Anatomy of a Flat Bone - This cross-section of a flat bone shows the spongy bone (diploë) lined on either side by a layer of compact bone.

terms to know

Diaphysis

The tubular shaft that runs between the proximal and distal ends of a long bone.

Medullary Cavity

The hollow central region in the diaphysis.

Compact Bone

A dense osseous tissue able to sustain compressive forces.

Epiphysis

The wider section at the proximal and distal ends of a long bone (plural, epiphyses).

Spongy Bone

A porous osseous tissue that provides strength and red bone marrow storage.

Epiphyseal Plate

A layer of hyaline cartilage in a growing long bone where the diaphysis meets the epiphysis.

Epiphyseal Line

The ossified epiphyseal plate in a long bone that has completed its growth.

Endosteum

A thin connective tissue lining the medullary cavity.

Periosteum

A fibrous membrane that covers the superficial surface of a bone except for regions participating in a joint.

Diploë

The central region of a flat bone composed of spongy bone.

2. Bony Landmarks

key concept

The surface features of bones vary considerably, depending on the function and location in the body. There are two general classes of bony landmarks (also referred to as markings), projections and depressions.

As the name implies, a projection is an area of a bone that projects above the surface of the bone. These are the attachment points for tendons and ligaments. In general, their size and shape are an indication of the forces exerted through the attachment to the bone. Also implied by the name, a depression (bone) is an area of a bone that sinks below the surface of the bone. These are an opening or groove in the bone that allows other structures (i.e., tendons, ligaments, blood vessels, nerves) to enter the bone. As with the other landmarks, their size and shape reflect the size of the structures that penetrate the bone at these points. Additionally, certain projections and depressions also function together as an articulation, which is where two bone surfaces come together to form a joint (articulus, joint).

The table below provides an abridged version of the general bony landmarks that you will find on many bones. You will learn many specific bone landmarks in future lessons.

learn more

To review a full list of the general bony landmark terms, reference the supplemental Bone Landmark Terms.pdf.

Bony Landmarks - Projections

Projection	Description	Example
Trochanter	Large, rough projection	Trochanter of femur
Tubercle	Small, rounded projection	Tubercle of humerus
Spine	Sharp projection	Ischial spine

Bony Landmarks - Depressions

Depression	Description	Example
Fossa	Shallow depression	Mandibular fossa
Sulcus	Groove	Sigmoid sulcus of the temporal bones
Fissure	Slit through bone	Auricular fissure
Foramen	Hole through bone	Foramen magnum in the occipital bone
Sinus	Air-filled space in bone	Nasal sinus

Bony Landmarks - Articulations

Articulation Markings	Description	Example
Head	Prominent rounded surface	Head of femur
Facet	Flat surface	Vertebrae
Condyle	Rounded surface	Occipital condyles

terms to know

Projection

An area of a bone that projects above the surface of the bone.

Depression (bone)

An area of a bone that projects below the surface of the bone.

Articulation

Where two bones come together to form a joint.

3. Blood and Nerve Supply

Bone tissue receives nourishment from arteries that pass through the bone matrix. The arteries enter through the nutrient foramen (plural, foramina), small openings in the bone. Nutrients diffuse through bone marrow or canals in the bone matrix to reach bone cells. As wastes are generated, they are collected by veins which then pass out of the bone through the same foramina. The epiphysis contains its own series of blood vessels which enter through a separate foramen. In adults, these blood vessel networks merge to share supply between all portions of the bone.

In addition to the blood vessels, nerves follow the same paths into the bone where they tend to concentrate in the more metabolically active regions of the bone. The nerves sense pain, and it appears the nerves also play roles in regulating blood supplies and in bone growth, hence their concentrations in metabolically active sites of the bone.

This illustration shows an anterior view of the right femur. The femur is split in half lengthwise to show its internal anatomy. The outer covering of the femur is labeled the periosteum. Within it is a thin layer of compact bone that surrounds a central cavity called the medullary or marrow cavity. This cavity is filled with spongy bone at both epiphyses. A nutrient artery and vein travel through the periosteum and compact bone at the center of the diaphysis. After entering the bone, the nutrient arteries and veins spread throughout the marrow cavity in both directions. Some of the arteries and veins in the marrow cavity also spread into the spongy bone within the distal and proximal epiphyses. However, additional blood vessels called the metaphyseal arteries and the metaphyseal veins enter into the metaphysis from outside of the bone. — Diagram of Blood and Nerve Supply to Bone - Blood vessels and nerves enter the bone through the nutrient foramen.

term to know

Nutrient Foramen

Small openings in the bone where blood vessels enter and exit.

summary

In this lesson, you learned to identify the gross anatomical features of a bone. You learned the major structures found in long and flat bones, how to categorize bony landmarks, and where bones obtain their blood and nerve supply.

Source: THIS CONTENT HAS BEEN ADAPTED FROM OPENSTAX "ANATOMY AND PHYSIOLOGY 2E" AT openstax.org/details/books/anatomy-and-physiology-2e

Terms to Know

Articulation: Where two bones come together to form a joint.
Compact Bone: A dense osseous tissue able to sustain compressive forces.
Depression (bone): An area of a bone that projects below the surface of the bone.
Diaphysis: The tubular shaft that runs between the proximal and distal ends of a long bone.
Diploë: The central region of a flat bone composed of spongy bone.
Endosteum: A thin connective tissue lining the medullary cavity.
Epiphyseal Line: The ossified epiphyseal plate in a long bone that has completed its growth.
Epiphyseal Plate: A layer of hyaline cartilage in a growing long bone where the diaphysis meets the epiphysis.
Epiphysis: The wider section at the proximal and distal ends of a long bone (plural, epiphyses).
Medullary Cavity: The hollow central region in the diaphysis.
Nutrient Foramen: Small openings in the bone where blood vessels enter and exit.
Periosteum: A fibrous membrane that covers the superficial surface of a bone except for regions participating in a joint.
Projection: An area of a bone that projects above the surface of the bone.
Spongy Bone: A porous osseous tissue that provides strength and red bone marrow storage.

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Gross Anatomy of Bone

Table of Contents

1. Gross Anatomy of Bone

2. Bony Landmarks

3. Blood and Nerve Supply