TISSUES (Part 1)

CHAPTER IV TISSUES To grasp an understanding of the various tissues properly, a brief description of the cells from which they are developed, embryologically, will be necessary. The Ovum. — The ovary secretes a cell, the original cell of the female human body, called the ovum. The ovum consists of a limiting wall, the vitelline membrane, enclosing the protoplasm, vitellus, which consists of two parts — the dentoplasm or nutritive yolk, and the animal protoplasm or formative yolk. Within the vitellus is found the nucleus or germinal vesicle, which contains the nucleolus or germinal spot. Before an ovum can develop into an offspring it must undergo numerous complex changes. The two most important phenomena are defined as maturation and fertilization. Maturation. — Maturation or ripening is the process taking place in the ovum, which prepares it for the reception of the male element — spermatazoon, where its contained chromatin and a small part of the proto- plasm are collected into the form of two minute structures called polar bodies, when a modified cell reproduction or karyokinesis occurs. This reproduc- tion must take place before ova can be fertilized. Fertilization.^ — ^This is the process in which the male and female units — the ovum and spermatozoon — unite to form a complete and perfect cell, by division, which ultimately develops into cells which form the tissues of the whole body. The male element or spermatozoon or spermium con- sists of a head, middle-piece, and tail. After entering 36 TISSUES Fig. 2 Fi« 3 FiQ. 4 Fia. 5 Fig. 6 i^50 t:- '■■4^' Diagrams illustrating cell division — karyokinesis. THE OVUM 37 Fig, 7 Fia. 8 \ Semidiagrammatic representation of the processes of cell and nuclear division (karyokinesis) in Ascaris megalocephala. (After Kostanecki.) Fig. 2. — Resting cell. Fig. 3. — Division of centrosome. Fig. 4. — Prophase — centrosomes at the 'poles; radiation well-developed; chromatin net-work broken up into four chromosomes. Fig. 5. — Mother-star stage (monaster); chromosomes arranged at the equator. Fig. 6. — Metaphase; the longitudinally divided chromatin filaments moving toward the poles. Fig. 7. — Anaphase; beginning of division of cell body. Fig. 8. — Division of cell body almost completed; the central spindle shows the beginning of the intermediate bodies. the ovum the head and middle-piece, representing the nucleus and centrosome, respectively, of a cell from the testicle (the male organ, the cells of which secrete the spermatozoon) form eight chromosomes. The chromatin of the germinal vesicle of the ovum also forms eight chromosomes. The process continues within the cell until thirty-two chromosomes are de- veloped by longitudinal cleavage; these are subdivided into sixteen chromosomes, which enter each diaster or daughter cell. 38 TISSUES I R Sp Fig. 11 Fig. 12 // R Sp Stages in the fertilization of Physa fontinalis. Wierzejski.) (After Kostanecki and Fig. 9. — Mother-star stage passing into metakinesis for the formation of the first polar body. The spermatozoon is enclosed in the egg in toto. Fig. 10. — Formation of first polar body; centrosome divided. Fig. 11. — First polar body formed. Monaster stage for the formation of the second polar body. Sperm radiation is separated from the sperm nucleus. Fig. 12. — Formation of the second polar body. Sperm radiation with two centrosomes near the vesicular sperm nucleus. THE OVUM 39 Fig. 43 (^^^-^')-// R K FA K Fig. 14 / R K- II R K- FA K \ ^pK ■^i> ;^^ ^ St Fig. 16 / F >7' -%^ Fig. 13. — Two polar bodies above. Egg nucleus has become vesicular. Sperm radiation has increased in size. Fig. 14. — Egg and sperm nuclei approach one another. The sperm radia- tion and the centrosomes move apart. Fig. 15. — Egg and sperm nuclei closely approximated. The centrosomes arrange themselves on opposite sides. Fig. 16. — The chromosomes of the egg and sperm nuclei form a monaster stage to give rise to two new cells. CSpK, central spindle; EiK, egg nucleus; IFSp, first spindle after fertiliza- tion; G, tail of spermatozoon; IRK, first polar body; II RK, second polar body; IRSp, first polar spindle; IIRSp, second polar spindle; SpC, centro- some of spermatozoon; SpK, sperm nucleus; SpSt, sperm radiation. 40 TISSUES After fertilization the ovum divides and redivides into numerous cells, forming an irregular mass termed the mulberry mass or morula. The latter collection of cells divides again into an outer and inner cell mass called the blastula. The outer mass is supposed to dis- appear, while the inner continues to develop and forms two layers — an outer, the ectoderm or epiblast, and an inner, the entoderm or hypoblast. This is termed the gastrala or diploblast. A third layer is developed from the two former layers, each setting aside a few cells which develop the third layer, termed the mesoderm or mesoblast, that lies between the two layers. The formation receives the name of blastodermic •vesicle or triploblast. All tissues of the body are composed of cells arising from the cells in the original three layers of the triplo- blast or blastodermic vesicle. Tissues, which are always studied microscopically, consist of cells held together by an intercellular cement, and perform a definite function; thus they may be supportive, as bone, etc., or functional, as the liver, etc. All the tissues to be seen and understood in their minute arrangement are first treated by histologic methods in the laboratory by hardening, sectioning, fixing, dehydrating, staining, etc., and are then observed under the microscope. This process is not essential to the nurse's knowledge, but should she desire a complete understanding of the subject she should refer to the standard works on histology. Tissues are divided into epithelial, comiective, muscle, and nerve Epithelial Tissue or Epithelium. — They may be pro- tective, as the cells of the skin and conjunctiva of the eye; secretive, as the cells of the pancreas, parotid gland, etc.; excretive, as the cells of the kidneys; to prevent friction, as those seen in the cells of the synovial sacs between the articulating cartilages of joints, peritoneum, and layers of pleura. Epithelial SQUAMOUS CELLS 41 cells line cavities that normally communicate with the air/ except the pleural, peritoneal, and synovial sacs, and between the articulating cartilages of joints. Epithelial cells are classified usually as: (1) squa- mous, simple and stratified; (2) columnar, simple, modi- fied, and stratified; (3) ciliated, simple and stratified; (4) prickle cells; (5) goblet cells; (6) transitional cells; (7) pigment; (8) neuro-epithelial; (9) glandular. Ftg 17 Flat epithelial cells isolated from the oral mucous membrane of man. X 375 (Szymonowicz.) 1. Squamous Cells. — (a) Simple squamous cells con- sist of a single layer of flattened elements, each con- taining a nucleus, usually situated in the centre and oval in form. They are found in the alveoli of the lungs, ventricle of brain, descending limb of Henle's loop in the kidney, and Bowman's capsule of kidney. (6) The stratified squamous cells consist of layers of cells one on top of the other. The lowest layer, the germinal stratum, is arranged in columns, those above being polygonal. As the surface is reached the cells become more flattened, forming the squames or scales. These cells are usually found when they afford the most protection, as the skin (epidermis) 42 TISSUES lining the mouth cavity, pharynx, esophagus, epiglottis, vocal cords, and the anus and vagina. Fia. 18 Diagram of flat epithelium. I, seen from above; II, seen from the side after transverse section on the line m. (a) cell boundaries as straight lines; (6) cell boundaries as wavy lines. (Szymonowicz.) .,.1 Q Q 0/0 1 1 ■ n 0 . JlVlilLllUH 0 6 (? K Umu 0 ^w Wc 00(0^6^^ 9Y9 Yeie I •T'/ »Ye 1 oToY Diagrams of epithelium: o, nuclei at various levels; b, stratified pave- ment epitheUum; c, stratified cylindrical epithelium, ciliated at the right. (Szymonowicz.) 2. Columnar Cells. — (a) Simple columnar cells are arranged in tall columns consisting of a single layer with a nucleus situated at the base of each cell. They are found in the stomach and intestinal tract, anterior portion of the male urethra, glands of Cowper and Bartholin, prostate, gall-bladder, seminal vesicles, and many gland ducts. Low columnar cells are often called cuboidal. GOBLET CELLS 43 (6) Modified or pseudostratified cells are simple columnar or ciliated cells in which the nuclei are at different levels, thus giving the appearance of several layers of cells. These cells are found as ciliated elements in the oviduct, uterus, and middle ear, and as non-ciliated elements in the seminal vesicles and prostate. (c) Stratified columnar cells consist of numerous layers of cells arranged one upon another. They are found in the lining membrane of the vas deferens (male), membranous urethra, and ducts of some glands. 3. Ciliated Cells. — (a) Simple ciliated cells are ar- ranged in a single layer of columnar cells which have upon their exposed surface fine cilia or hair-like pro- cesses; they possess motion that is always directed toward the outlet of the organ in which they are located. They are found in the smaller bronchioles, spinal canal, accessory spaces of the nasal cavities, and the ventricles of the brain. (6) Stratified ciliated cells are the same as the stratified columnar, with the cilia attached only to the cells of the exposed layer. These cells are found in the epididymis (male), first portion of the vas deferens (male). Eustachian tube, upper part of the pharynx, larynx, ^^Q- 20 trachea, and nasal tract. 4. Prickle Cells. — These are polygonal elements that possess little spines, which project from the sides of the cells, and pass to meet spines of other cells, thus preventing the cells from meeting, at the same time forming inter- prickie ceiis. (Gerrish.) cellular bridges or spaces. They are found in the epidermis (skin) just above the genetic layer. 5. Goblet Cells. — These are cells resembling the cylindric type, distended with a secretion called 44 TISSUES mucin. On filling they resemble a goblet. When the secretion has been discharged these cells become long and slender, the part containing the nucleus extending on either side. They are found in the gastro-intestinal and respiratory tracts. ail Cell body Nucleus — FiQ. 21 Impression made by neighboring cell Mucus — Oxflet Cell membrane i- — Protoplasm 'iijL. — yuclens Two ciliated cells and two goblet cells isolated from the frog's esophagus. X 520. 6. Transitional Cells. — These are stratified cells be- longing to neither the squamous or columnar groups. They are polygonal; found in the pelvis of the ureter, in the ureter, bladder, the first part of the male and almost the entire length of the female urethra. 7. Pigmented Cells. — These are polygonal or colum- nar in shape, the protoplasm containing pigment. They are found in the epidermis of the colored races, and around the nipple and genitals of the Caucasians, as polygonal cells, and in the retina of the eye where they assume the columnar shape. 8. Neuro-epithelial Cells. — These are cells which have become so differentiated as to perform a special sense function. These are found in the retina of the eye, in GLANDS 45 the internal ear (hair cells), in the olfactory mucous membran^, in the taste-buds of the tongue, and tactile cells in the epidermis. 9. Glandular Cells. — These are found in the pancreas, liver, etc., and their shape varies according to the gland in which they are found. Mucous Membranes. — All the surfaces of the gastro- intestinal and pulmonary tracts, genito-urinary appar- atus, etc., within the body are covered by epithelial cells, called mucous membranes, These membranes are protected in the various organs by a superficial layer of cells — their variety depending on the tissue they are found in — which we have described above. Beneath this layer the cells rest upon a delicate base- ment membrane, the next layer is the tunica propria consisting of a layer of fibro-elastic tissue. Within this layer are lodged the capillary bloodvessels, nerves, lymphatic spaces or channels, and, in certain organs, glands and lymphoid tissue. These thin layers, are seen resting on a fourth peripheral layer, called the muscularis mucosae, consisting of involuntary (not under the control of the will), non-striated muscle tissue. This layer is sometimes wanting in some tissues. The above mucous membranes line cavities which communicate with the air. Their cells usually secrete a substance called mucin. Glands. — Glands are considered under the classifica- tion of epithelial tissues. They are simply various shaped pouches or tubes of mucous membranes grow- ing out from the superficial surface of the tissue in which they are located. All glands are lined with epithelial cells arranged in different groups, and possessing a physiologic function. These groups of cells are the units from which the organs develop their secretions. Glands are subdivided into (1) tubular, simple, branched, coiled, compound; (2) tubulo-alveolar ; (3) alveolar, or racemose glands, simple and compound. 46 TISSUES These different shaped glands are lined by epithelial cells, depending on the situation and function. Their secretions are liquid, and may be serous, mucous, or mixed, which the lining cells secrete as needed by the organ to perform its physiologic function. Fig. 22 Tubular glaads. Alveolar glands. ^J^ m'dm Diagram of various forms of glands; a, duct; x, simple tubule; xx, simple alveolus. (After Szymonowicz.) Serous Membranes. — They are membranes covered by a single layer of flattened cells, with a large pro- jecting nucleus; these cells are held together by a intercellular cement. They are termed endothelial cells. Serous membranes never have a basement membrane and line cavities that do not communicate with the air. These membranes appear smooth, CONNECTIVE TISSUES 47 glisteniag, and transparent. Openings called stomata are said to be present between the cells, but they are supposed to be artefacts according to the latest teach- ing. Serous membranes line joint-cavities, bursse, tendon sheaths, circulatory and lymphatic systems, and the pleural, pericardial, and peritoneal cavities. Fig. 23 Fia. 24 White fibrous tissue. (Gerrish.) Yellow fibrous tissue. (Queckett.) Connective Tissues. — The connective tissues of the body are the elements entering into the formation of the more permanent structures of the body, such as bones, cartilages, ligaments, those holding fat in position, those used as' coverings for muscles — as fascia, as sheaths for bloodvessels, and nerves, as supports for cells of glands and organs, and those binding membranes to underlying organs, as the pleura and peritoneum to the lungs and abdominal 48 TISSUES organs respectively. The connective tissues are derived from the mesoderm. They are classified as follows: (1) fibrous; (a) loose, (h) dense; (2) yellow elastic; (3) mucous; (4) retiform; (5) mixed or areolar; (6) adipose or fatty; (7) l3rmphoid; (8) cartilage; (9) bone; (10) dentin (teeth); (11) blood. 1. Fibrous Tissue. — (a) The loose variety consists of fine thread-like fibers held in bundles by a small quantity of cement substance, and scattered through- out those groups of fibrils are seen a few cells. This variety is mostly for the support of capillary blood- vessels, the capsules of organs, and as a suppurative element in the tunica propria and submucosa in the mucous membrane of the respiratory and alimentary tracts. (6) The dense variety differs from the former in the fibrils being thicker and the bundles larger. The dense is best seen in tendons of muscles, when it occurs as parallel bundles. Seen under the microscope on a cross-section the whole structure is seen surrounded by a loose sheath of fibers, the epitendineum, from which septa are seen passing into and dividing it into dis- tinct or separate bundles of fibers, the peritendineum. The tendon cells are seen arranged in rows lying between the individual bundles of fibers. White fibrous tissue is very strong, inelastic, is pearly white in color, as seen when the skin is removed and dissections made of ligaments and tendons. It serves as a stocking-like covering to muscles, where it is termed fascia; and is seen as a bluish-white mem- brane reinforcing muscles and strengthening their insertions to bones, particularly in the region of joints, called an aponeurosis. 2. Yellow Elastic Tissue.^ — This, as the name implies, possesses elasticity; the fibrils are coarser than the white variety. It is found in the ligamentum nuchse, which extends from the occipital bone to the spinous CONNECTIVE TISSUES 49 processes of the cervical vertebra, along the vertebral column, where it is reinforced by white fibrous tissue, also in the ligamentum subflava, in the vertebral column, in bloodvessels, and in the skin. 3. Mucous or Embryonic Tissue. — This is found in the umbilical cord of the fetus. It is at first homo- geneous, then later fibers both white and elastic develop, the former in bundles, the latter generally single. Among these fibers are a few scattered, mostly spindle- shaped, some stellate, and some round cells. Fig. 25 Areolar tissue, composed of bundles of white fibrous tissue and branched strands of yellow fibrous tissue loosely intertwined. (Gerrish.) 4. Retiform or Reticulum Tissue. — This forms the frame-work of glands and gland-like organs. The fibrils are arranged in delicate bundles, in the meshes 4 50 TISSUES of which are the functionating cells of the glands. The cells of this variety are mostly stellate. 5. The Mixed or Areolar Tissue. — This contains both white and elastic tissue. It shows a net-work of fine white fibrils, with elastic fibrils scattered throughout, and they are usually branched. The cellular elements scattered among these fibrils are stellate, plasma, and wandering forms. Areolar tissue is very fine, delicate, loose in texture, and binds the skin to the underlying fasciae, and lies between muscles. 6. Adipose or Fatty Tissue. — This is white fibrous tissue, in which fat cells are deposited. In the living body it is liquid at the temperature of the body. It can only be seen in the tissues under the microscope after special preparation. It is essential to know, how- ever, that it is found and