Specialised Cells and Tissues in Body Systems
Each body system contains specialised cells and tissues that are structurally suited to their functions.
Examples of specialised cells
Neurons
Structure: Neurons have long, branching extensions called dendrites and axons. Dendrites receive signals from other neurons, while the axon transmits these signals over long distances.
Function: Neurons are responsible for transmitting electrical impulses throughout the nervous system, facilitating communication between the brain, spinal cord, and other parts of the body.
Red blood cells
Structure: Red blood cells are disc-shaped and lack a nucleus, allowing them to have a flexible, biconcave shape. This shape increases their surface area for oxygen absorption and transport.
Function: To carry oxygen from the lungs and deliver it throughout the body.
Muscle cells
Structure: Muscle cells, or myocytes, are elongated and contain numerous mitochondria to provide the energy needed for contraction. They have a striated appearance due to the arrangement of actin and myosin filaments.
Function: Muscle cells contract and relax to facilitate movement and maintain posture. There are three types: skeletal (voluntary movement), cardiac (heart contractions), and smooth (involuntary movements in organs).
Epithelial cells
Structure: Epithelial cells are tightly packed in layers and form continuous sheets. They may have specialised structures such as cilia or microvilli depending on their location.
Function: They cover and protect surfaces and cavities of organs and structures, such as the skin, the lining of the gut and the respiratory tract. They also facilitate absorption, secretion and filtration.
Sperm cells
Structure: Sperm cells are small, with a streamlined shape and a flagellum (tail) for movement. They have a head containing the nucleus and an acrosome, which helps in penetrating the egg during fertilisation.
Function: The primary role of sperm cells is to deliver genetic material to the egg cell during fertilisation, contributing to the formation of a new organism.
Size and Shape (Surface Area to Volume Ratio)
The size and shape of cells and tissues are often adapted to maximise their surface area relative to their volume, a concept known as the surface area to volume ratio (SA:V). This adaptation is particularly important in systems where the exchange of substances is critical.
- Example in the Respiratory System: The alveoli in the lungs are tiny, thin-walled sacs with a large surface area relative to their volume. This design is essential for gas exchange, as it maximises the surface area available for oxygen and carbon dioxide to diffuse across the alveolar and capillary membranes. The increased SA:V ensures that oxygen can efficiently enter the bloodstream and carbon dioxide can be expelled from the body.
- Example in the Digestive System: The lining of the small intestine features finger-like projections called villi, which significantly increase the surface area for nutrient absorption. Each villus is further covered with microvilli, forming a brush border that maximises the absorption of nutrients into the bloodstream. The large surface area provided by the villi and microvilli enables efficient nutrient uptake, supporting the body’s energy and nutrient needs.
Organelle Composition
The specific composition of organelles within specialised cells is tailored to the functions these cells need to perform. Different organelles may be more abundant in different cell types, depending on their roles within the body system.
- Example in the Muscular System: Muscle cells, particularly those involved in sustained or intense physical activity, contain a high number of mitochondria. Mitochondria generate ATP (adenosine triphosphate) through cellular respiration. The abundant mitochondria in muscle cells provide the necessary energy for muscle contraction and endurance, enabling movement and physical activity.
- Example in the Digestive System: Pancreatic cells, especially those in the exocrine pancreas, are packed with rough endoplasmic reticulum (RER) and Golgi apparatus. The RER is involved in synthesising proteins, while the Golgi apparatus modifies, sorts and packages these proteins for secretion. These cells produce and secrete digestive enzymes that are crucial for breaking down food in the small intestine. The abundance of these organelles ensures that pancreatic cells can produce large quantities of enzymes efficiently, facilitating proper digestion and nutrient absorption.