Elementary Anatomy and Physiology.

Timaru Herald, Volume LXXXI, Issue 12480, 17 September 1904, Page 2 (Supplement)

Elementary Anatomy and Physiology.

LECTURE XIII. tDelivcred to Teachers under the Auspices of the South Canterbury Education Board by Dr. Barclay.) Structure and Uses of Epithelium, Connective Tissue, Adipose Tissue, Cartilago, Tendon, Ligament. Epithelium is the name applied to those cells in the body that line the various cavities and ducts, coven the mucous and serous membranes, and formi the superficial layers of the skin. It is essentially a covering layer. When it lines inner cavities, such as the inside of the heart or the blood vessels, it is sometimes spoken of as endothelium. COLUMNAR epithelium we have already seen. If we think of it as composed of oblong cells sitting on a basement membrane, we can construct the other varieties of it, for they are all modifications of the prototype. Now squeeze large number of these cells whose walls are roughly pftrallel, and the result is that they are shortened and their corners rounded off. Such are the hexagonal liver cells. This type of epithelium is called GLANDULAR EPITHELIUM. When the columnar'cells of the deeper layers of the skin are squeezed up to the surface, they lose their nuclei, ind are shed when they become dried up. In the process of being flattened hev are spread out and assume n lesselated form, called SQUAMUK EPITHELIUM, a scaly form of it. Seme cells have hair-like procesises projecting from them. These wave lik = a field of corn before a wiiul, all the ciliaa, as the fine hairs are called, mov- | ing in the same direction. This epithelium is columnar-shaped, but it is called CILIATED EPITHELIUM. It is of great use in the respiratory passages, "'here, i waving upwards, it carries up the mucus ; secretion of the lining membrane. CONNECTIVE TISSUE binds the various active parts of an organ together. It consists of cells and fibres. One variety is called AREOLAR. In it the fibres form a regular mesh work interlacing in all directions. Little cavities or areolae are left here and there, and they are occupied by branched cells called the connective tissue corpuscles. The fibres are usually white, but some are yellow, and these "'have all the properties of elastic. ' Where they are abundant the tissue is spoken of as yellow elastic tissue. Areolar tissue is found beneath the skin as well as binding together organs. ADIPOSE TISSUE or fat is a variety of connective tissue in which the spaces are filled by fat cells. CARTILAGE is bluish-white, and consists of a ground substance or matrix, with nucleated cells in it. When the matrix is smooth, like glass, it is said to form HYALINE cartilage. If there is much fibrous tissue in it, it is called white fibro-cartilage. If there is yellow elastic tissue in the matrix, it is called yellow fibro-cartilage. Hyaline cartilage is seen best in the Articular cartilage lining the ends of the bones in joints; white fibro-cartilage we have seen in the "intervertebral discs; and the yellow variety is seen in the external ear and epiglottis. I

MUSCLE. Its Varieties. Muscular Movement, Relation of Muscles to Nerves. Voluntary muscle is red and striated; involuntary muscle is pale or white, and i is ur.striated. A tendon is jUst- bundles of connective tissue longitudinally arranged, with cells in. their interior. They move in sheaths which are moistened by a mucous fluid. Ligaments again are interlacing masses of white fibrous tissue. Muscle consists of fleshy material bound together by connective tissue. Striated muscle is "thus divided up, perimysium surrounding it. Within the containing membrane are bundles of fibres called- fasciculi. The fasciculi can be split into, fibres The fibres are surrounded by the structureless membrane the sarcolemmu, and are composed of still minuter fibres called fibrillae. The term striated is derived from the fact that the fibres when examined under the microscope are seen to consist, of alternate light and dark stripes, giving to the muscle itself a characteristically striated appearance, while across the liplit areas a litis of black dots may be seen, forming KRAUSF.'S membrane. " The development of this cross and longitudinal striation is closely connected with the evolution and specialisation of the muscular function, i.e.. contraction. Contractility is. among others, a function of all undifferentiated protoplasm. Cells so constituted can only effect and weak contractions. Directly a specialisation of function is nectssa.iv, anil some coil or part of a cell has to contract rapidly in response to some stimulus from vithui ( or without, we find ,1 differentiation of form and internal structure. Each o-

brilla is supposod to consist of a number ] jf contractilo element* called Sarcous elements embedded in a granular material m >;ircoplasm. The latter »eoms to feed tho fonner, as it is present in various quantities in different muscle*, in proportion to the amount of sustained work each has to do. , When muscle contracts t'licro is a reversal of the light and dark bunds. Tho sarcous elements in contracting bulge and squeeze out the gianiilar embedding material, the sareoplusm, into tho light area. Thus the previous light band becomes darker, and the dark area lighter. Each muscle has entering it a nerve that conveys impulses to it, to cause it to contract, and also one that carries oif messages nf sensation from it to the brain. The motor nerves terminate in special structures called motor-end plates. First the nerve inns into the muscle, then the medullary sheajh abruptly ceases, and tho neurilemma becomes continuous with the sarcolemnla, and the aXis cylinder ramifies among the savcous elements. The usual stimulus to muscle contraction is of course a message conveyed from the brain along a motor nerve. If, however, you separate a muscle from the living bedy of nn animal, with its nerve attached, you will find that it trill contract if you apply an electric current to the ntive, or if you pinch it. or if you apply strong salt solution to it. Similarly, if these irritants tire npplicd to the muscle itself, and not to the nerve, it will still contract. Now these irritants are in order electrical, mechanical and chemical, and they all produce analogous effects. Tho ends of the | nerves in muscles can bo paralysed by a drug called curare, and when this is done still direct stimulation of the muscle fibres will cause contraction, thougUi stimulation of nerve will fail. This prove* decisively that muscular tissue has contractile powers apart from tho nervous supply altogether. When a muscle contracts it obviously becomes bulkier in the middle. When excited through it* nerve the contraction begins at tho end plates and spreads in all directions, but this takes time, so that the whole muscle does not contract at tlie same instant. But if while sending a current through-it, and before it has reached its height of contraction, another stimulus is sent through it. such as an electric shock, then the one stimulus is piled up on the other nnd the contraction will bo mudi • stronger. This is spoken of as the summation of stimuli. Suppose that the stimuli come so rapidly after one another that the muscle has no time to relax, but is kept all the time at the height of theM the condition is spoken of as TETANU, of the muscle. It is this state that i* found in tetanus or lock-jaw—one of continued tonic contraction. In performing work a muscle develop* heat ju*t a* ttf> engine does. A thermometer can be placed in the thigh muscles of a large animal and the spinal cord stimulated by electricity, and the thermometer show* at once a rise of temperature. The muscle plawna, or fluid portion, has the power to clot just like blood, and after death it docs so, producing the shortening and stiffening of the muscle known as Rigor Mortis. At the *ame time it changes from being alkaline m reaction to become acid, from tlio + developmeit of sarcolaotic aeid, and it gives off carbonic acid pa* and evolves heat.