Features: Double-sided slightly concave disc shape, thinner in the center and thicker around the periphery, with a larger surface area

Function: Carrying and transporting oxygen and carbon dioxide

Characteristics: They are slender cylindrical multinucleated cells with alternating light and dark horizontal stripes.

Function: Contract quickly and forcefully

Features: There are many protrusions

Role: Receive, integrate and transmit information

Features: Cells are tightly arranged, single or multi-layered, with little intercellular matrix

Function: Protection, secretion, absorption

Features: loosely arranged cells, abundant intercellular matrix, and diverse shapes

Function: Support, connect, protect, nourish

Features: Has contraction and relaxation functions

Function: contraction, relaxation

Features: Composed of nerve cells and glial cells

Function: support, nutrition, insulation, protection

Function: Store and digest food

Features: Left upper abdomen, sac-like

Stomach wall composition

Composition: Nephron

Composition: respiratory tract, lungs

Function: Maintain the stability of oxygen and carbon dioxide concentrations in extracellular fluids

Composition: Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus and other digestive organs Digestive gland organs such as liver, pancreas and salivary glands

Function: The human body digests food and absorbs nutrients

Composition: kidney, ureter, bladder, urethra

Function: Excrete metabolic waste from the body

plasma

blood cells

blood

blood cells

tissue fluid

extracellular fluid

tissue cells

The stability of the human body's internal environment is closely related to the physiological activities of the human body's circulatory system, respiratory system, digestive system, and urinary system.

It is the immediate environment in which cells carry out metabolism. The oxygen and nutrients required for cell metabolism can only be taken in directly from the internal environment, while the carbon dioxide and metabolic end products produced by metabolism can only be discharged directly into the internal environment, and then transported through the blood circulation and transported by the respiratory system and excretory organs. Excreted from the body.

It is also the place where cells live and move. It must create a suitable environment for cells and provide the physical and chemical conditions necessary for cells to survive and move normally.