Question

(d) blood cells \(\quad\) (b) muscles (d) cartilages (d) ligaments.

Short answer

Blood cells, cartilages, and ligaments are types of connective tissue. Muscles are classified as muscle tissue.

Step-by-step solution

Identify the category for each item

First, determine what category each of the items listed falls under. In this case, we are categorizing them based on the type of tissue or structure they represent in the human body.

Matching items to their correct category

Blood cells are a type of cell found in the blood, muscles are a type of tissue that contracts to cause movement, cartilages are a type of connective tissue that provides flexible support in certain parts of the body, and ligaments are another type of connective tissue that connects bone to bone, providing stability to joints.

Categorize according to tissue types

Identify the correct type of tissue each item represents. Blood cells are considered 'connective tissue', as blood is classified as a specialized fluid connective tissue. Muscles fall under the category of 'muscle tissue'. Cartilages and ligaments are both 'connective tissues', with cartilage providing structural support and cushioning in joints, and ligaments supporting and strengthening joints.

Key concepts

Connective Tissue

In the human body, connective tissue plays a pivotal role, serving as the binder, supporter, and protector of organs. It comes in various forms, each with a unique function. Connective tissue includes various types like adipose tissue, blood, bone, tendons, cartilage, and ligaments.

One of the primary characteristics of connective tissues is the presence of extracellular matrix, which is a complex network of proteins and fibers that provide structural and biochemical support to the surrounding cells. This matrix allows connective tissues to bear weight, withstand tension, and endure abuse that other tissues cannot tolerate.

Blood, often overlooked as a connective tissue, is actually a specialized form owing to this matrix, being a fluid that transports nutrients, gases, and wastes. Similarly, cartilages provide flexible structural support in places like the ears, nose, and joints, while ligaments are tough, fibrous bands that connect bones at joints, ensuring stability and facilitating motion.

Muscle Tissue

Moving onto muscle tissue, this is the driver of motion and force in the body. It is characterized by its ability to contract in response to stimuli. The human body has three main types of muscle tissue: skeletal, smooth, and cardiac.

Skeletal Muscle Tissue

Skeletal muscles are connected to bones and are involved in voluntary movements—anything from lifting an object to running. These muscles are striated, which means they have a banded appearance, and they are also multinucleated, which helps them to sustain the vigorous activities of the body.

Smooth Muscle Tissue

Smooth muscle fibers are found in the walls of hollow organs like intestines and blood vessels. Unlike skeletal muscles, they operate involuntarily and have a non-striated appearance.

Cardiac Muscle Tissue

Cardiac muscle is exclusive to the heart and shares some characteristics with skeletal muscle, like striation, but it operates involuntarily and has a unique feature of intercalated discs that allow rapid transmission of electrical signals across cardiac cells for synchronized contractions.

Blood Cells

Blood cells serve critical functions in the body and are integral components of the circulatory system. There are three main types of blood cells: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).

Red Blood Cells

Red blood cells are responsible for transporting oxygen from the lungs to tissues and organs throughout the body. They contain hemoglobin, a protein that binds oxygen and imparts the characteristic red color.

White Blood Cells

White blood cells are the defenders of the body, playing an essential role in the immune system by fighting off infections and foreign invaders.

Platelets

Platelets, on the other hand, are involved in blood clotting which helps prevent excessive bleeding when injuries occur. Together, these cells work in harmony to maintain health and support body functions.

Cartilages and Ligaments

Cartilage and ligaments are distinct yet related types of connective tissue that contribute to the body’s stability and mobility. Cartilage is a semi-rigid yet flexible tissue that serves as a cushion between bones in joints like the knee or elbow. It's composed of chondrocytes embedded in a strong, rubbery matrix. Cartilage reduces friction, absorbs shock, and prevents the bones from rubbing against one another.

On the other hand, ligaments are dense bands of connective tissue that connect bones to other bones. Unlike cartilage, ligaments are highly elastic and very strong, designed to resist strain and provide a passive limitation to movement, preventing excessive or potentially injurious movements.

Both cartilage and ligaments are avascular, meaning they do not contain blood vessels, and therefore, they have a limited ability to repair themselves when damaged. This is why injuries to these tissues often take a long time to heal and may require medical intervention.