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[Visitor (112.0.*.*)]answers [Chinese ]Time :2022-05-28

It can be divided into three parts: cell membrane, cytoplasm and nucleus. Cell membranes are mainly composed of proteins, lipids and sugars, which protect cells, maintain stability inside cells, and control the exchange of substances inside and outside cells. Cytoplasm is the center of cell metabolism, mainly composed of water, proteins, ribonucleic acid, enzymes, electrolytes and so on. Various organelles are also suspended in the cytoplasm. The main organelles are mitochondria, endoplasmic reticulum, lysosomals, centrosomes, etc. The nucleus is surrounded by a nuclear membrane with kernels and chromatin inside. Chromatin contains nucleic acids and proteins. Nucleic acids are substances that control biological inheritance.

Four major organizations
Epithelial tissue is the basic tissue of an animal consisting of densely arranged epithelial cells and a very small amount of cell interstitium. Generally, they are connected to each other in a diaphragm, which is covered on the surface of the body, or lined with the cavity surface of hollow organs in the body, as well as the cavity surface of the body cavity. According to the characteristics of function and structure, epithelial tissue can be divided into three categories: covered epithelium, glandular epithelium, and sensory epithelium. Among them, the coated epithelium is generally referred to as epithelial tissue, which is the most widely distributed.
Neural tissue is made up of neurons and glial cells and is highly inductive and conductive. Neurons are made up of cell bodies, dendrites, and axons. Dendrites are short, branching like branches, and their function is to transmit impulses to the cell body; The axons are long, with nerve endings, and their function is to transmit impulses outward from the cell body

Muscle tissue is made up of muscle cells. Muscle cells have the function of contraction. Muscle tissue can be divided into three categories according to form and function: skeletal muscle, smooth muscle and myocardium
Connective tissue is made up of cells, the interstitium, and fibers. It is characterized by a loose distribution of cells and a large number of interstitial cells. Connective tissue mainly includes: loose connective tissue, dense connective tissue, adipose tissue, cartilage, bone, blood and lymph and so on. They have support, bonding, nutrition, defense, repair and other functions.
The Belgian physician Vesarius published the book Anatomy of the Human Body, challenging Galen's doctrine of the "Trinity". The Spanish physician Servit found a small circulatory system of blood, proving that blood flows from the right ventricle to the lungs, through a zigzag route to the left ventricle. Through a large number of animal anatomy experiments, the British anatomist Harvey published "Theory of Heart Movement" and other works, which systematically explained the law of blood movement and the working principle of the heart. He pointed out that the heart is the center and source of blood movement. This major discovery made him the originator of modern physiology.

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