Difference Between Lacunae and Osteocytes

The key difference between lacunae and osteocytes is that lacunae are small spaces in the lamellae that provide an area for osteocytes, while osteocytes are a type of bone cells that maintain the bone mass.

Bone is a living and growing tissue that makes the skeleton of humans and other vertebrates. It consists of different cell types, such as osteoblasts, osteocytes, osteoclasts and bone lining cells. These cells fulfil different functions within the bone. Among the four types of cells, osteocytes are responsible for the maintenance of the bone mass. Moreover, the compact bone forms the outer layer of most bones and provides protection and support. Osteon is the main functional unit of compact bone, and it has four different components. They are Haversian canal, lamellae, lacunae and canaliculi. The lacunae are small spaces in the lamellae which provide an area for the bone cells or osteocytes.

CONTENTS

1. Overview and Key Difference
2. What are Lacunae 
3. What are Osteocytes
4. Similarities Between Lacunae and Osteocytes
5. Side by Side Comparison – Lacunae and Osteocytes in Tabular Form
6. Summary

What are Lacunae?

Lacunae are small oblong spaces which house the osteocytes. In other words, lacunae surround osteocytes in the osteons. Most importantly, one lacuna houses only one osteocyte. Therefore, a lacuna cannot contain more than one osteocyte inside it. There are numerous lacunae in an osteon located between lamellae. Under the microscope, they appear as fusiform opaque spots.

Small canals called canaliculi connect lacunae with each other. These canaliculi facilitate the transfer of substances, including nutrients and waste products from osteocytes to the exterior via diffusion.

What are Osteocytes?

Osteocytes are a type of bone cells present inside the mature bones. Structurally, they are star-shaped cells with projections. The size of a cell body of an osteocyte may vary from 5-20 micrometres in diameter. Generally, a mature osteocyte contains only one nucleus. In addition to these, it consists of a reduced endoplasmic reticulum, mitochondria and Golgi apparatus and also cell processes which radiate towards the matrix. There are about 42 billion osteocytes in an average human body. These cells contain an average half-life of 25 years.

Osteocytes inhabit spaces called lacunae. They originate from osteoblasts. Once the osteoblasts get trapped inside the matrix which they secrete themselves, they develop and mature into osteocytes. Osteocytes occur interconnected and networked to each other through long cytoplasmic extensions.

Osteocytes carry out several functions including molecular synthesis, modification and distant signal transmission. Thus, their functions are similar to the nervous system. Mature osteocytes carry out the majority of the important receptor activities in bone function. Furthermore, osteocytes act as a major regulator of bone mass and as an endocrine regulator in phosphate metabolism. There are several factors affecting the death of osteocytes. They are necrosis, senescence, apoptosis or engulfment of osteoclasts. Osteocyte destruction may, therefore, cause the disease called osteoporosis.

What are the Similarities Between Lacunae and Osteocytes?

• Lacunae surround osteocytes or bone cells.
• They are seen in bones.
• They are situated between lamellae.
• There are numerous lacunae and osteocytes in bones.
• In one lacuna, there is only one osteocyte.

What is the Difference Between Lacunae and Osteocytes?

The key difference between lacunae and osteocytes is that lacunae are spaces while osteocytes are nucleated living bone cells. The main function of lacunae is to provide spaces for osteocytes while the main function of osteocytes is the maintenance of the bone structure. So, this is the functional difference between lacunae and osteocytes.

Below infographic shows more details on the difference between lacunae and osteocytes.

Summary – Lacunae vs Osteocytes

Osteon is a unit of a compact bone. It consists of different components, including lacunae and osteocytes. Lacunae are small oblong spaces that house osteocytes. Osteocytes are one of the four types of bone cells that are star-shaped. These cells are responsible for the maintenance of bone mass and structure mainly. Thus, this summarizes the difference between lacunae and osteocytes.

Reference:

1.“Lacuna (Histology).” Wikipedia, Wikimedia Foundation, 18 June 2018, Available here.
2. “Structure of Bones.” Biology for Majors II.” Lumen, Available here.

Image Courtesy:

1. “Gray74” By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body (See “Book” section below)Bartleby.com: Gray’s Anatomy, Plate 74 (Public Domain) via Commons Wikimedia
2. “604 Bone cells” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013 (CC BY 3.0) via Commons Wikimedia