What are the characteristics of the four basic tissues of the human body in structure and distribution?

Cell is the basic structure and functional unit of human body, and there is intercellular substance between cells. Interstitial is a substance produced by cells without cell morphology and structure. It includes fiber, matrix and fluid substances (interstitial fluid, lymph, plasma, etc.). ), which supports, protects, connects and nourishes cells and participates in the formation of the microenvironment for cell survival. Many cells with similar morphology and function are composed of interstitial cells, which are called tissues. There are many types of human tissues, which are traditionally divided into four basic tissues, namely epithelial tissue, connective tissue, muscle tissue and nerve tissue. With one organization as the main body, several organizations are organically combined to form organs with certain morphological, structural and functional characteristics. A series of organs that perform the same function are organically linked to form a system with specific functions. The system that constitutes the human body includes the movement system, including bones, joints and muscles, which is the structural basis for people to carry out various activities such as labor, displacement and posture maintenance. The organs of internal organs respectively constitute the digestive system-responsible for the digestion, absorption and residue discharge of ingested food; Respiratory system-gas exchange; Urinary system-the final product produced by excreted tissues and cells; Reproductive system-producing germ cells and forming new individuals to continue the race; And a circulation system which is connected with the system for performing metabolism, provides nutrition for the system and transports metabolites; The nervous system includes the brain and spinal cord in the central part, peripheral nerves all over the body, and sensory organs as special sensory devices, which feel various stimuli from the internal and external environment of the human body and produce appropriate responses; In addition, endocrine glands with different functions are scattered in the body. Each system of the human body not only has its own unique shape, structure and function, but also relates, restricts and coordinates with each other under the unified control of the nervous system and the regulation of neurohumors. * * * With the completion of unified overall activities and advanced consciousness activities, it can achieve a high degree of unity with the rapidly changing internal and external environment.

In order to have a deeper understanding of the observed structure in anatomical practice, the following will briefly introduce the basic tissues of the human body.

epithelium

Epithelial tissue is composed of dense epithelial cells with little intercellular substance. Has the functions of protection, absorption, secretion and excretion. There are no blood vessels in epithelial tissue. Generally speaking, it can be divided into covering epithelium and glandular epithelium. The former covers the body surface or lines the cavity surface of body cavity or lumen, and the latter is the main tissue that constitutes glandular organs (such as liver and pancreas).

The covering epithelium is divided into monolayer epithelium and stratified epithelium according to the level of its constituent cells, and the latter is composed of multilayer cells; According to the morphology of the cells, they can also be divided into flat epithelium, cubic epithelium and columnar epithelium. The classification and distribution of covering epithelium are as follows:

Classification and distribution of epidermal epithelium

classify

Be distributed

single layer

Single-layer flat epithelium (figure 1-2)

The cavity surface of the heart, blood vessels and lymphatic vessels

The surface of pleura, peritoneum, pericardium and joint cavity.

Alveolar wall, renal capsule wall, etc.

Monolayer cubic epithelium

Renal tubular wall

simple columnar epithelium

Mucosal epithelium of gastrointestinal tract, uterine cavity surface and so on.

Pseudostratified columnar ciliated epithelium

The cavity surface of the breathing tube, etc.

Multilayer coating

stratified epithelium

The epidermis of the skin (including keratinized layer, nails and hair)

Oral cavity, esophagus, vagina and other cavity surfaces

Multilayer columnar epithelium

Eyelid conjunctiva, male urethral cavity, etc.

Transitional epithelium

Cavity surface of renal calyx, renal pelvis, ureter and bladder

2. Connective tissue

Connective tissue consists of a large number of interstitial cells and scattered cells. Interstitial cells contain matrix, fibers and interstitial fluid. Connective tissue is widely distributed in human body and almost all organs. Among them, in addition to its own soft connection connective tissue,

Blood tissue, bone and cartilage of human body belong to connective tissue. Connective tissue proper can be divided into loose connective tissue and dense connective tissue according to its structure and function.

(1) Loose connective tissue is widely distributed among organs, tissues and cells. Its structure is characterized by a large number of interstitial cells, more matrix and less fiber. There are mainly coarse collagen fibers and fine elastic fibers, with few cells but many types, mainly fibroblasts, adipocytes, macrophages, plasma cells and swimming mast cells. Because of its loose structure and honeycomb shape, it is also called honeycomb structure. It is distributed in subcutaneous tissue (superficial fascia), fascia space, between organs and around vascular nerve bundles. It has the functions of connection, support, defense, nutrition and wound repair.

In loose connective tissue, such as a large number of fat cells, fat cell clusters are formed and separated into lobules by loose connective tissue, which is called fat tissue. Adipose tissue is distributed in subcutaneous tissue, yellow bone marrow, omentum, peritoneum and renal capsule, accounting for about 10% of adult body weight. It has the functions of storing and maintaining body temperature, buffering shock and participating in fat metabolism to generate heat energy.

(2) Dense connective tissue is characterized by thick fibers and dense arrangement in the stroma, but there are few basal substances and few cell components. Tendons and aponeurosis of human body are composed of dense connective tissue. The structural feature of tendon is that thick collagen fiber bundles are arranged along the stress direction, dense and parallel to each other, with specialized fibroblasts-tendon cells arranged in rows in the middle. The fibrous layer of dermis, deep fascia, organ capsule, periosteum, joint capsule, ligament and fibrous pericardium are another kind of dense connective tissue, which is characterized by thick collagen fibers interwoven into a dense lamellar structure with only a small amount of matrix and fibroblasts scattered in it. It mainly plays the role of support, protection and connection. In addition, there are elastic connective tissues with elastic fibers as the main body, such as the ligamentum flavum between the nuchal ligament and the vertebral arch, which are mainly composed of thick elastic fibers arranged in parallel bundles to meet the needs of spinal movement for elasticity and flexibility.

3. Muscle tissue

Muscle tissue consists of muscle cells or muscle fibers. According to its position, structure and function, it can be divided into skeletal muscle, smooth muscle and myocardium.

(1) Skeletal muscles are voluntary muscles distributed in the trunk and limbs. Muscle fiber is slender and cylindrical (length1-30mm, diameter10-300mm, diameter10-0/00μ m), and several to hundreds of nuclei are located at the periphery of the fiber. The outer side of the muscle is an adventitia composed of connective tissue, which contains blood vessels and nerves, and extends into the muscle to divide the muscle into several muscle bundles. The adventitia itself forms a perimuscular membrane covering the muscle bundles, and then extends around each muscle fiber to form an endocardium rich in capillaries and nerve fibers. These connective tissues can not only support, protect and nourish muscle tissue, but also regulate the activities of individual muscle fibers and muscle bundles. The sarcoplasm of muscle fibers contains many myofibrils arranged parallel to the long axis of cells. Each myofibril consists of bright bands and dark bands alternately, and the bright bands and dark bands of each myofibril are arranged at the same level. Therefore, muscle fibers are striped with alternating light and dark, so they are also called striated muscles. When muscle fibers contract, the length of myofibril dark zone remains unchanged, and the adjacent bright zones at both ends of dark zone become shorter. Skeletal muscle is controlled by somatic nerves and consciousness and belongs to voluntary muscle. Contraction is rapid and powerful, but it is easy to get tired.

(2) Smooth muscle is mainly distributed on the walls of viscera and blood vessels, so it is also called visceral muscle. Smooth muscle fibers are spindle-shaped without transverse stripes, and the nucleus is located in the center of muscle fibers. The length of fibers varies from 200μm to 20μm, the former is found in the muscular layer of intestinal wall, and the latter is found in the wall of small blood vessels. In some organs with large physiological expansion, such as pregnant uterus, muscle fibers can be as long as 600 μ m, and smooth muscle is controlled by visceral nerves and is not controlled by consciousness, which belongs to involuntary muscle. Visceral smooth muscle is characterized by automaticity, that is, muscle fibers can automatically generate excitement and contraction when they are out of innervation or cultured in vitro.

(3) Myocardium is mainly distributed in the heart wall, and also exists near the heart end of great blood vessels. The myocardial fibers are short columnar and branched, which coincide with each other to form a network. The nucleus is oval, located in the center of muscle fibers, with two nuclei and occasionally multiple nuclei. Myofibrils also have bright bands and dark bands, so they also have horizontal stripes. However, the myocardium is dominated by visceral nerves and belongs to involuntary muscles. Myocardial contraction is slow, rhythmic and lasting, and it is not easy to get tired.

4 nerve tissue

Mainly composed of nerve cells and glial cells. Nerve cells, also known as neurons, are the main components of nerve tissue, have the ability to feel stimuli and conduct nerve impulses, and are the basic units of the structure and function of the nervous system. Glial cells play a role in supporting, nourishing and protecting neurons.