Types of Cells and Tissues in the Human Body

Posted on May 12, 2024 in Biology

Type of Cells

Cells are classified according to their embryological origin and their morphological and functional characteristics. The four fundamental types are:

  • Epithelial cells
  • Muscle cells (Myocytes or muscle fibers)
  • Nerve cells (Neurons)
  • Connective tissue cells

Tissues

Cells with a similar structure and function group together to form tissues. A tissue consists of a set of cells, similar in structure and function, and the substance that surrounds them (intercellular substance).

Tissue Types

There are four basic types of tissue: connective, epithelial, muscular, and nervous.

  • Epithelial tissue: As its name suggests, epithelial tissue covers the outer surface of the body and lines the internal organs and cavities.
  • Connective tissue: Cells such as bone cells, together with the intercellular substance, form bone tissue, a type of connective tissue.
  • Nervous tissue: Nerve cells structured together lead to nerve tissue.
  • Muscle tissue: Muscle tissue can be of different types:
    • Smooth muscle
    • Striated muscle: skeletal and cardiac

1. Smooth Muscle Tissue

Smooth muscle is found in internal organs (digestive tract, blood vessels). Smooth muscle contractions are rather slow and incremental and do not depend on the individual’s conscious will.

2. Striated Muscle Tissue

There are two different classes of striated muscle: skeletal striated muscle and cardiac muscle.

Systems and Apparatuses

Nervous System. Endocrine System. Respiratory System. Digestive System. Excretory System. Circulatory System. Reproductive System. Locomotor Apparatus.

The Nervous System

It is divided into two parts: the central nervous system (receives stimuli and causes voluntary actions) and the peripheral nervous system. The peripheral nervous system is part of the autonomic nervous system, which regulates the activities of vegetative life (outside of voluntary control).

The Endocrine System

The endocrine system secretes chemicals: hormones.

Locomotor System

Besides structural support and protection, the locomotor system provides functions such as locomotion. The components of this system are the bones with their joints, and the skeletal muscles that provide mobility.

Blood

  • Red blood cells (erythrocytes)
  • Hematocrit, which is the percentage of blood volume occupied by red blood cells.
  • White blood cells (leukocytes): Their main function is defense against infectious or toxic agents. They are formed in the bone marrow and lymph nodes.
  • Platelets: Platelets are responsible for blood coagulation, such as occurs when there is a wound.
  • Plasma: Plasma is the liquid part of blood. It has a yellowish color and is made up of water and many dissolved substances.

Heart

The heart is a hollow muscular organ divided into four cavities: two atria (upper) and two ventricles (lower). The heart is surrounded by three layers: the endocardium, myocardium, and pericardium. The endocardium is the inner layer that lines the cavities and forms the valves. The middle layer or myocardium consists of cardiac muscle cells. The pericardium is the outer layer and surrounds the heart and great vessels.

3 Cardiac Rhythm or Cycle

The cardiac cycle is the cyclical alternation of contraction and relaxation that allows the heart to function as a pump. The rhythm of the heart is characterized by a phase of contraction, systole, and a phase of relaxation, diastole. A systole and diastole of the atria and the ventricles constitute the heart cycle. The frequency at which the cardiac cycle occurs is called the heart rate.

Blood Vessels and Circulation

The vascular system is the set of vessels through which blood circulates. It is divided into pulmonary circulation and systemic circulation, which are interconnected.

Nervous Regulation of Breathing

The respiratory rate can increase (tachypnea), decrease (bradypnea), or stop (apnea).

Difference Between Food and Nutrition

Metabolism, responsible for regulating nutrition, is the set of biochemical reactions that take place inside the cell and lead to the transformation of different compounds. We voluntarily ingest food to supply our bodies. Nutrition is the involuntary process of absorbing nutrients into the body.

1 Catabolism

Catabolism consists of the transformation of complex organic substances into simpler molecules, generating energy in the form of ATP. This ATP is used for tissue construction (anabolism) or as energy to maintain vital functions and physical activity.

a) Bone Classification

Bones can be classified into:

  • Long bones: Their length is greater than their thickness and width. Their central part is called the diaphysis, while their ends are called epiphyses (the proximal epiphysis is closer to the center of the body, and the distal epiphysis is farther away). Examples of long bones are the femur, tibia, and humerus.
  • Flat bones: Their width and length are similar and always greater than their thickness. Flat bones limit cavities that contain and protect organs. An example of flat bones are the bones of the skull.
  • Short bones: Their three dimensions, length, width, and thickness, are similar. Examples of short bones are the bones of the hand and the vertebrae of the spine.

The surfaces of bones can be completely smooth or present irregularities, which are called apophyses, spines, tuberosities, lines, ridges, or eminences.

b) Components of Bone

The three main components of bone are:

  • The periosteum: A membrane rich in blood vessels, lymph vessels, and nerve pathways that covers the outer surface of bones. Its outer layer has a protective function, and the inner layer contains vessels and nerve fibers. The inner layer contains bone cells (osteoblasts) that are responsible for bone growth and repair. If a bone breaks (fracture), new bone can form. Thus, the periosteum not only protects the bone but also nourishes it, makes it grow, and repairs it in case of injury.
  • Bone tissue: This is where bone cells are surrounded by a calcified material (the bone matrix) that gives bones their characteristic hardness. The bone matrix consists of proteins like collagen and minerals such as calcium phosphate salts. Bone tissue seen under the microscope presents two types of structure:
    • Compact bone: Bone formed by lamellae arranged concentrically around a channel called the Haversian canal, through which blood vessels that nourish the bone pass. Compact bone is found in the diaphysis of long bones and the outer part of flat and short bones.
    • Spongy bone: Spongy bone is organized in columns arranged in a tissue called trabeculae, similar to the supporting pillars of a building with bricks. The trabeculae allow bones to withstand the different loads of pressure or tension generated by their own weight or by movement. This demonstrates that the trabecular structure adapts to the principles and dynamics of statics. Spongy bone is found in the inner part of short and flat bones and the epiphyses of long bones.
  • Bone marrow: This refers to the internal cavities of bones and can be red or yellow.
    • Red bone marrow: Red bone marrow is found in the cavities of the spongy trabecular bone. It is responsible for producing blood cells that pass into the bloodstream. In the fetus, newborn, and infant, all bone marrow is red. These are periods of maximum growth. Subsequently, in adults, red marrow only remains in some bones of the trunk and skull.
    • Yellow bone marrow: Yellow marrow is the result of the transformation of red marrow as our body grows. It consists mainly of fat and does not produce blood cells. It is found in the diaphysis of long bones.

c) Formation of Bone Tissue

Bone tissue is formed through two pathways:


– Direct ossification: from the tissue forming the membranous coating or as
the clavicle and the skull or bones of the face.
– Indirect ossification: from cartilage, bone cartilaginous forms a first phase that was
being replaced by bone tissue.
The points are the core lossificació begins dossificació. In the long bone between the diaphysis and lepífisi
There is a layer of cartilage: cartilage growth.

– Fixed Joints (sinartrosi)
Mobile joints (diartrosi)
Dune diartrosi components are:
– The joint surfaces
– The synovial membrane and synovial fluid
– Ligaments
– The joint capsule

b) Movements articular

The diartrosi joints that are three possible types of movement: sliding, rotation and
angular movement. Each time the articular surfaces glide over laltra luna, without losing
its parallel, we have a sliding movement. The movement of rotation occurs when a segment
bone rotates on its vertical axis to keep in contact with the articular surface of segment laltre
bone with which sarticula. The movements can be rotation in two ways:
– Internal rotation: when the direction of rotation of the bony segment is towards the center of the body.
– External rotation: when the direction of rotation of the bony segment is lexterior toward the center of the body.
The angular movement takes as reference the different planes of the human body.
On the front can be given movements [WRC Fig. 70 pp. 85]:
– Abduction: every time a bear sallunya vertical centering of the body.
– Adducció each time a bear sapropa centering vertically in the body.
In the sagittal plane there are two types of movement:
– Deflection: the moves that makes an angle with them what sarticula.
– Extension: Those who move comes on the same plan with them which sarticula.
Besides the three known movements is also possible that the movement is not circumdicció
than the combination of various angular movements.