医学专英课本chapterBody structure

1、Chapter 2 Body StructureOrganization of the BodyBefore taking a look at the whole human body, we need to examine its parts. The human organism consists of cells, tissues, organs, and systems. These components are arranged in a hierarchical（分层的，分体系的）manner. That is, cells come together to form tissue

2、s, tissues come together to form organs, organs come together to form systems, and all the systems come together to form the whole organism.CellsAn adult human body consists of about seventy-five trillion cells. These cells have much in common, yet those in different tissues vary in a number of ways

3、.Cells vary considerably（相当地）in size. We measure cell sizes in units called micrometers. A micrometer equals one thousandth of a millimeter and is symbolized m. A human egg cell is about 140m in diameter and is just barely visible to an unaided eye. This is large when compared to a red blood cell, w

4、hich is about 7.5m in diameter, or the most common white blood cells, which vary from 10-12m in diameter. On the other hand, smooth muscle cells can be between 20 and 500m long.Cells also vary in shape, and typically their shapes are closely related to their functions. For instance（例如）, nerve cells

5、often have long, threadlike extensions that transmit nerve impulse from one part of the body to another. Epithelial cells that line the inside of the mouth are thin, flattened, and tightly packed, somewhat like floor tiles. Muscle cells, which contract to pull structures closer together, are slender

6、（细长的） and rod-like, with their ends attached to the parts they move. They are filled with contractile proteins. An adipose cell is little more than a blob of fat. A B lymphocyte is an antibody factory. fig.2.1 Fig.2.1 Nerve cell, muscle cell，red blood cells and sperm cellA cell consists of two major

7、 partsthe nucleus and the cytoplasm. The nucleus is innermost and is enclosed by a thin membrane called the nuclear envelope. The cytoplasm is a mass of fluid that surrounds the nucleus and is itself encircled by an even thinner cell membrane (also called plasma membrane). Within the cytoplasm are s

8、pecialized structures called cytoplasmic organelles that perform specific metabolic functions. The nucleus, on the other hand, directs the overall（全部的）activities o the cell. The nucleus is also considered to be an organelle. fig.2.2Fig.2.2 Structure of cellTissuesIn all complex organisms, cells are

9、organized into layers or groups called tissues. Although the cells of different tissues vary in size, shape, arrangement, and function, those within a tissue are quite similar.Usually tissue cells are separated by nonliving, intercellular materials that the cells secrete. These intercellular materia

10、ls vary in composition from one tissue to another and may be solid, semisolid, or liquid. The tissues of the human body include four major types: epithelial tissues, connective tissues, muscle tissues, and nervous tissues. These tissues are organized into organs that have specialized functions.Epith

11、elial tissues are widespread throughout the body. They cover all body surfacesinside and outand are major tissues of glands.Since epithelium covers organs, forms the inner lining of body cavities, and lines hollow organs, it always has a free surfaceone that is exposed to the outside or to an open s

12、pace internally. As a rule, epithelial tissues lack blood vessels. However, they are nourished by substances that diffuse from underlying connective tissues, which are well supplied with blood vessels. fig.2.3 Fig. 2.3 Epithelium tissueConnective tissues occur throughout the body and are the most ab

13、undant type of tissue by weight. They bind structures together, provide support and protection, serve as frameworks, fill spaces, store fat, produce blood cells, protect against infections, and help repair tissue damage. Connective tissue cells are usually able to reproduce. These tissues have varyi

14、ng degrees of vascularity, but in most cases, they have good blood supplies and are well nourished. Some connective tissues, such as bone and cartilage, are quite rigid. Loose connective tissue, adipose connective tissue, and fibrous connective tissue are more flexible. fig.2.4 Fig. 2.4 Connective t

15、issueMuscle tissues are contractile; that is, their elongated cells, or muscle fibers, can shorten and thicken. As they contract, muscle fibers pull at their attached ends, which move body parts. Skeletal muscle tissue is found in muscles that usually are attached to bones and that we control by con

16、scious effort. For this reason, it is often called voluntary muscle tissue. These long and threadlike cells have alternating light and dark cross-markings called striations（横纹）.Smooth muscle tissue is called smooth because its cells lack striations. This tissue is found in the walls of hollow intern

17、al organs, such as the stomach, intestines, urinary bladder, uterus, and blood vessels. Unlike skeletal muscle, smooth muscle usually cannot be stimulated to contract by conscious efforts. Thus, it is a type of involuntary muscle tissue.Cardiac muscle tissue occurs only in the heart. Its cells, whic

18、h are striated, are joined end to end. The resulting muscle fibers are branched and interconnected in complex networks. Each cell within a cardiac muscle fiber has a single nucleus. At its end, where it touches another cell, is a specialized intercellular junction called an intercalated disk（闰盘）, wh

19、ich is seen only in cardiac tissue. Cardiac muscle, like smooth muscle, is controlled involuntarily and, in fact, can continue to function without being stimulated by nerve impulses. This tissue makes up the bulk（大部分） of the heart and pumps blood through the heart chambers and into blood vessels. fi

20、g.2.5 Fig. 2.5 Skeletal muscle, cardiac muscle and smooth muscleNervous TissuesNervous tissues are found in the brain, spinal cord, and peripheral nerves. The basic cells are called nerve cells, or neurons, and they are among the more highly specialized body cells. Neurons are sensitive to certain t

21、ypes of changes in their surroundings. They respond by transmitting nerve impulses along cytoplasmic extensions (nerve fibers) to other neurons or to muscles or glands. As a result of the extremely complex patterns by which neurons are connected with each other and with muscle and gland cells, they

22、are able to coordinate, regulate, and integrate many body functions. fig.2.6Fig. 2.6 Nervous tissueOrgan SystemsThe human organism consists of several organ systems. Each system includes a set of interrelated organs that work together to provide specialized functions. The maintenance of homeostasis

23、depends on these organ systems working together in a coordinated manner. Major organs in each system and their functions are as follows: (Table 2.1)Table 2.1 Organ SystemsSystemMajor OrgansMajor functionsIntegumentaryskin, hair, nails, sweat glands, sebaceous glands（皮脂腺）protect tissues, regulate bod

24、y temperature, support sensory receptorsMusculoskeletalbones,ligaments cartilages,tendonprovide framework, protect soft tissues, provide attachments for muscles, produce blood cells, store inorganic salts; cause movements, maintain posture, produce body heatCardiovascularheart, arteries, veins, capi

25、llariesmove blood through blood vessels and transport substances throughout body respiratorynasal cavity, pharynx(咽) larynx, trachea, bronchi, lungsintake and output of air, exchange of gases between air and blooddigestivemouth, tongue, teeth, salivary glands, pharynx, esophagus, stomach, liver, gal

26、lbladder, pancreas, small and large intestinesreceive, break down, and absorb food; eliminate unabsorbed materialurinary kidneys, ureters, urinary bladder, urethraremove wastes from blood, maintain water and electrolyte balance, store and transport urinereproductivemale: scrotum（阴囊）, testes, epididy

27、mides, vasa deferntia, seminal vesicles, prostate gland, bulbourethral glands, urethra, penisfemale: ovaries, uterine tubes, uterus, vagina, clitoris, vulvaproduce and maintain sperm cells, transfer sperm cells into female reproductive tractproduce and maintain egg cell; receive and transport sperm

28、cells; support development of an embryo and function in birth processendocrine glands that secrete hormones control metabolic activities of body structuresnervous brain, spinal cord, nerves, sense organsdetect changes, receive and interpret sensory information, stimulate muscles and glandslymphatic

29、lymphatic vessels, lymph nodes, thymus, spleenreturn tissue fluid to the blood, carry certain absorbed food molecules, defend the body against infectionAnatomical TerminologyAnatomical PositionThe anatomical position is used when describing the positions and relationships of a structure in the human

30、 body. A body in the anatomical position is standing erect with the arms at the side of the body, the palms of the hands facing forward and the eyes looking straight ahead. In addition, the legs are parallel with the feet and the toes pointing forward. For descriptive purposes the assumption is alwa

31、ys that the person is in the anatomical position even if the body or parts of the body are in any other position. fig.2.7Fig. 2.7 Anatomical position and relative positionRelative PositionTerms of relative position are used to describe the location of one body part with respect to another. They incl

32、ude the following:1. Superior (or cephalic) means a part is above another part, or closer to the head. (The thoracic cavity is superior to the abdominopelvic cavity.)2. inferior (or caudal) means situated below another part or toward the feet. (The neck is inferior to the head.)3. Anterior (or ventr

33、al) means toward the front. (The eyes are anterior to the brain.)4. Posterior (or dorsal) is the opposite of anterior, it means toward the back. (The pharynx is posterior to the oral cavity.)5. Medial relates to an imaginary midline dividing the body into equal right and left halves. A part is media

34、l if it is closer to this line than another part. (The nose is medial to the eyes.)6. Lateral means toward the side with respect to the imaginary midline. (The ears are lateral to the eyes.)7. Proximal is used to describe a part that is closer to the trunk of the body or closer to another specified

35、point of reference than another part. (The elbow is proximal to the wrist.)8. Distal is the opposite of proximal. It means a particular body part is farther from the trunk or farther from another specified point of reference than another part. (The fingers are distal to the wrist.)9. Superficial mea

36、ns situated near the surface (The epidermis is the superficial layer of the skin.) Peripheral also means outward or near the surface. It is used to describe the location of certain blood vessels and nerves. (The nerves that branch from the brain and spinal cord are peripheral nerves.)10. Deep is use

37、d to describe parts that are more internal. (The dermis is the deep layer of the skin.)11. Supine means the body lying horizontally and facing upward. (The patient is in the supine position for abdominal surgery.)12. Prone means the body lying horizontally and facing downward. (The patient is placed

38、 in the prone position for spinal surgery.) fig.2.8Fig. 2.8 Supine and prone positionBody SectionsTo observe the relative locations and arrangements of internal parts, it is necessary to cut or section the body along various planes. The following terms are used to describe such planes and sections:1

39、. Sagittal (or median) refers to a lengthwise cut that divides the body into right and left portions. If a sagittal section passes along the midline and divides the body into equal parts, it is called median (midsagittal).2. Transverse (or horizontal ) refers to a cut that divides the body into supe

40、rior and inferior portions.3. Coronal (or frontal) refers to a section that divides the body into anterior and posterior portions.Sometimes a cylindrical organ such as a blood vessel is sectioned. In this case, a cut across the structure is called a cross section, an angular cut is called an oblique

41、 section, and a lengthwise cut is called a longitudinal section. fig.2.9Fig. 2.9 body sectionsBody RegionsA number of terms designate body regions. The abdominal area, for example is subdivide into nine regions as anatomical divisions of the abdomen as follows:1. Right hypochondriac: Right lateral r

42、egion of upper row beneath the lower ribs.2. Epigastric: Middle area of upper row above the stomach.3. Left hypochondriac: Left lateral region of the upper row beneath the lower ribs.4. Right lumbar: Right lateral region of the middle row at the waist.5. Umbilical: Central area over the navel.6. Lef

43、t lumbar: Left lateral region of the middle row at the waist.7. Right iliac: Right lateral region of the lower row at the groin.8. Hypogastric: Middle region of the lower row beneath the navel.9. Left iliac: Left lateral region of the lower row at the groin.fig.2.10Fig. 2.10 Abdominopelvic divisionT

44、he abdominal area also may be subdivided into the following four quadrants as clinical divisions of the abdomen by visualizing two imaginary lines. One line is horizontal and the other one is vertical, crossing at the navel.1. Right upper quadrant (RUQ): Contains majority of liver, gallbladder, smal

45、l portion of pancreas, right kidney, small intestines, and colon.2. Right lower quadrant (RLQ): Contains small intestines and colon, right ovary and fallopian tube, appendix, and right ureter.3. Left upper quadrant (LUQ): Contains small portion of liver, spleen, stomach, majority of pancreas, left k

46、idney, small intestines, and colon.4. Left lower quadrant (LLQ): Contains small intestines and colon, left ovary and fallopian tube, and left ureter.Some organs, such as the uterus and urinary bladder, fall half in the right quadrant and half in the left quadrant. Therefore, some organs are referred

47、 to as midline organs. fig.2.10Body Cavities The human organism can be divided into an axial（同轴的） portion, which includes the head, neck, and an appendicular（四肢的） portion, which includes the upper and lower limbs. Within the axial portion are two major cavitiesa dorsal（背部的） cavity and a larger ventr

48、al（腹部的） cavity. The organs contained within such a cavity are called viscera（内脏）. The dorsal cavity can be subdivided into two partsthe cranial cavity, which houses the brain, and the vertebral canal (spinal cavity), which contains the spinal cord and is surrounded by sections of the backbone (verte

49、brae). The ventral cavity consists of a thoracic cavity and an abdominopelvic cavity.The thoracic cavity is separated from the lower abdominopelvic cavity by a broad, thin muscle called the diaphragm（膈肌）. When it is at rest, this muscle curves upward into the thorax like a dome（圆屋顶）. When it contrac

50、ts during inhalation（吸气）, it presses down upon the abdominal viscera. The wall of the thoracic cavity is composed of skin, skeletal muscles, and various bones. Within it are the lungs and a region between the lungs, called the mediastinum. The mediastinum separates the thorax into to compartments th

51、at contain the right and left lungs. The remaining thoracic visceraheart, esophagus, trachea, and thymus glandare located within the mediastinum.The abdominopelvic cavity, which includes an upper abdominal portion and a lower pelvic portion, extends from the diaphragm to the floor of the pelvis. Its

52、 wall consists primarily of skin, skeletal muscles, and bones. The viscera within the abdominal cavity include the stomach, liver, spleen, gallbladder, and the small and large intestines.The pelvic cavity is the portion of the abdominopelvic cavity enclosed by the pelvic bones. It contains the termi

53、nal end of the large intestine, the urinary bladder, and the internal reproductive organs. fig.2.11Fig. 2.11 Body cavitiesSmaller cavities within the head include the oral cavity, nasal cavity, orbital cavities and middle ear cavities.The walls of the right and left thoracic compartments, which cont

54、ain the lungs, are lined with a membrane called the parietal pleura. The lungs themselves are covered by a similar membrane called the visceral pleura. (Parietal refers to the membrane attached to the wall of a cavity, and visceral refers to one that is associated with an internal organ, such as a l

55、ung.)The parietal and visceral pleural membranes are separated by a thin film of watery fluid that they secrete. Although there is normally o actual space between these membranes, the potential space between them is called the pleural cavity.The heart, which is located in the broadest portion of the

56、 mediastinum, is surrounded by pericardial membranes. A thin visceral (epicardium) covers the hearts surface and is separated from a much thicker, fibrous parietal pericardium by a small amount of serous fluid. The potential space between these membranes is called the pericardial cavity.In the abdom

57、inopelvic cavity, the lining membranes are called peritoneal membranes. A parietal peritoneum lines the wall, and a visceral peritoneum covers each organ in the abdominal cavity. The potential space between these membranes is called the peritoneal cavity.Vocabularies1. appendicular 7ApEn5dikjulE 四肢的2. cartilage5kB:tilidV 软骨3. caudal5kC:dl 尾部的4. cephalicsI5fAlIk 头部的5. cylindricalsI5lIndrIk(E)l圆柱体的6. diaphragm. 5daiEfrAm 横膈膜7. dorsal5dC:sEl