TISSUESAND SUPPORTING SYSTEMS Movementis one of the essential features of living things.
Cellular movement isobserved in one-celled amoebas, ciliates, and flagellates. Flagella whip aboutto produce cellular motion, while cilia beat synchronously to propel a cell. Inanimals, movement is essential for locating food, escaping predators, andseeking mates.
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In many animals, themovement process is centered in the muscle cell, which contracts and relaxes.The contraction yields great force, which is applied against a surface by meansof a skeleton.SKELETONSkeleton is the bonyframework of the body which provides support, shape and protection of the softtissues and organs in animals. It enables animals to move from place to place. Forms and Componentof Skeleton:The three forms of skeleton are:-· Cuticles: The cuticle is composed of aprotein called chitin. Chitin is a non-living substance, hence, arthropodswhich are insects, crabs, scorpions, prawns etc with this type of skeletal materialcan only grow by “moulting” or “ecdysis” (process in which an organismsheds off its old skeleton and put on a new one).
· Bones: It is the major component of theskeleton. It consists of the living bone cells (osteocytes), protein fibres(collagen) and minerals (inorganic salts) which are mainly calcium phosphateand calcium carbonate. The inorganic makes the bone stronger and more rigidthan the cartilage. Examples of organisms which have bones are mainlyvertebrates which are the bony fishes, toads, crocodile, snakes, birds andmammals.
· Cartilages: Cartilage is a tissue found inthe skeleton of complex vertebrae. It consists of living cells (chondroblasts),carbohydrates and protein fibres. It is a firm, flexible material which cansupport great weight. It also acts as a shock absorber, cushioning the effectof bones moving against bones during movement.
Examples of organisms whichpossess cartilages are cartilaginous fishes like sharks, rays and mammals. There are three types of cartilageswhich are hyaline cartilage, fibro-cartilage and elastic cartilage.Types of Skeleton: The three main types of skeletonare:· Hydrostatic(Fluid) Skeleton:Many animals have a water-based skeleton, or hydrostatic skeleton.Hydrostatic skeletons do not contain hard structures, such as bone, for musclesto pull against.
Rather, the muscles surround a fluid-filled body cavity. In aworm, for example, movement occurs when muscle cells contract, and thecontractions squeeze internal fluid (the hydrostatic skeleton) against theskin, causing the worm to stiffen and the body to shorten and widen. Thesquirming motion of a worm also depends on a hydrostatic skeleton. Examples oforganisms with hydrostatic skeleton are worms, sea anemone, slug, earthwormetc.· Exoskeleton: This is the hard cuticle foundin arthropods (millipedes, insects, crabs) and other organisms. It performs thefunction of skeleton which as it lies outside the muscles is calledexoskeleton. The exoskeleton is made up of non-living substance called chitin.
Organisms with this type ofskeleton can only grow by a process called moultingor ecdysis (a process an organismsheds off its old skeleton, grow and later covered with a new one). Examples oforganisms with exoskeleton are the arthropods, hydra, snail, e.t.c.· Endoskeleton: The skeletons are found insidethe body of organisms. Muscles are attached to these skeletons inside the bodyof organisms. Endoskeletal animals grow by continuous increase in size and notby ecdysis.
Examples of organisms with this type of skeleton are mammals, aves,cartilaginous fishes, bony fishes, reptiles, amphibian e.t.c.
Axialand the Appendicular Skeleton Fig 13.1 The human skeleton showing the major bones of thebody.AxialSkeletonAxial skeleton is made up of theskull, vertebral column (backbone), the ribs and the breastbone (sternum).The skull: The mammalian skull is made up ofseveral flat bones which are joined together by means of joints called sutures. The three (3) major parts ofthe skull are the brain box or cranium which contains and enclose the brain the facialskeleton which supports the nose, eyes, e.t.c. and the jawswhich are made up of the upper jaw (maxilla)and lower jaw (mandible) whichcontains the teeth.
The skull gives the head its shape. It protects vital organsin the head e.g. eyes, nose & ears.
It bears the teeth which aids grindingof food.The vertebralcolumn: Itis the central supporting structure of the skeleton. It protects the spinalcord. In humans, there are 33 vertebrae. The vertebrae are held one to theother with strong ligaments called inter-vertebraldiscs. In mammals, thefive (5) different vertebrae are:· Cervicalvertebrae- Found in the neck region.· Thoracicvertebrae- Found in the chest region.
· Lumbervertebrae- Found in the upper abdomen.· Sacralvertebrae- Found in the lower abdomen.· Caudalvertebrae- Found in the tail region.Featuresof a Typical VertebraA typical vertebrae possess thefollowing features, these are: · Neuralcanal: Thisis the passage of the spinal cord.
· Neuralspine: Thisprojects upwards and dorsally for the attachment of muscles.· Transverseprocesses: -They project from the sides of each vertebrae for the attachment of muscles andligaments.· Centrum:- It is asolid piece of bone below the neural canal.· Facet: – This is a small, smooth, flator slight depressed area on a bone that is usually a point of contact withanother bone.
· Zygapophysis: – These are articular surfacesfor the articulation of successive vertebrae. They are grouped into two parts;- Pre-zygapophyses facing inwards and upwards and- Post-zygapophyses facing outward and downward. Cervical VertebraeThe cervicalvertebrae are found in the neck region. The first cervical vertebrae is calledthe atlas,the second is called axis.
The 3rd to 7thbones are the normal cervical bones.Characteristics ofAtlas· Theatlas vertebra has a large neural canal.· Ithas a flat and broad transverse process.· Theneural spine is very short -or absent.· Thecentrum is absent.· Ithas a vertebraterial canal for the passage of blood vessels.Function: Atlas allows the head to nod onit, as it fits into the occipital condyles of the skull.
Characteristics ofthe Axis· Theaxis has a broad and flat centrum.· Itarticulates with the atlas through the odontoid process.· Ithas a large, flattened neural spine.
· Thetransverse process is reduced to a pin-like structure.· Ithas a vertebraterial canal. Function: It allows the head to be turnedeasily i.e. twisting of the head.Thoracic VertebraeThoracic vertebrae are found inthe chest region. They are 12 in number in man.Characteristics of ThoracicVertebrae· Ithas a long prominent neural spine which projects upwards and backwards.
· Ithas a pair of short transverse process.· Thereis a presence of demifacets and articular surfaces for attachment of ribs.· Ithas a large neural canal and neural arch.
· Ithas a large cylindrical centrum. Functions: It aids the attachment of theribs, muscles of the shoulder and back are attached to neural spines. It alsoassists in breathing alongside with the ribs.
Lumber VertebraeThe lumbarvertebrae are found in the upper abdominal region. In man, they are five (5) innumber. Characteristics ofLumber Vertebrae· Itpossess a large, flattened transverse process.· Ithas broad and flat neural spine.· Ithas large and thick centrum.· Ithas well developed pre and post zygapophyses.
· Italso has two (2) extra paired projections for attachment of abdominal muscles. Functions: They provide attachment forabdominal muscles and they bear considerable weight of the body.Sacral VertebraeThe sacral vertebrae are found inthe lower abdominal region. In man, they are five (5) in number.
They fuse toform a structure called sacrum.Characteristics of SacralVertebrae· Ithas a narrow neural canal.· Ithas a neural spine that is highly reduced.· Ithas a large centrum.Function: They are joined to the pelvicgirdles to provide support, rigidity and strength.
Caudal VertebraeThe last vertebrae are the caudalvertebrae. It is found in the tail region. They are four (4) in number in man.
They fuse together to form a structure called coccyx. They have no neural spine, neural canal and transverseprocess. They support the tail and provide attachment for tail muscles. The Ribs: The ribs are long semi-circularrods connecting the thoracic vertebrae to the breastbone (sternum). There are12 pairs of ribs in humans. The first 7 pairs of ribs are called the true ribsbecause they are connected directly with the sternum in front by coastalcartilages. The next five pairs are called the false ribs because the 8thto 10th have a common connection with the sternum; each beingattached to the coastal cartilage of the rib above.
The 11th and 12thpair is called floating ribs because they have no connection at all with thebreast bone. AppendicularSkeletonThe appendicular skeleton is madeup of the pectoral girdle, pelvic girdle, fore limbs and the hind limbs.The Pectoral Girdle: The pectoral girdle is foundaround the shoulder in man. The bones of the pectoral girdle are the scapula(shoulder blade), the clavicle (collar bone) and coracoids. The scapula is a flat triangular bone.
Itis also called the shoulder blade. At the apex is a hollow or cavity called glenoid cavity into which the head ofthe humerus fits into from the shoulder joints. Above the glenoid cavity is asmall hook-shaped bone called coracoidbone. The Pelvic Girdle: The pelvic girdle is found aroundthe waist of man. It consists of two halves which are joined to each otherventrally and to the sacrum dorsally (top). The line of fusion of the two (2) halves is called pubis symphysis. Each half is called innominate bone. Each half is made up of three (3) bones which are;· Ilium· Ischium· Pubis They are fused together.
At thetop is the ilium which is the largest and longest of the three (3) bones. Theischium and pubis are fused together at the lower end. The ischium and pubisenclose an opening called “obturator foramen”. It is through this hole thatnerves, blood vessels and muscles pass. On the other surface of each half ofgirdle where the three (3) bones meet, there is a deep hollow or depressioncalled acetabulum where the head of the femur of the hind limb fits to form thehip joint. The Fore limb: The fore limb is made up of thehumerus, the ulna, the radius, carpals, metacarpals and phalanges. The Hind limb: The hind limb is made up of thefemur, tibia, fibula, tarsals, metatarsals and phalanges.
JOINTSA joint is a point or place wheretwo or more bones meet or articulate. Joints are held together firmly byligaments. Ligaments join bones to bones.Types of joints: The two types of joints are theimmovable (i.e. movement of bones of this joint is impossible e.g. skull) andmovable joints (i.
e. bones that make up this joint move over each other makingmovement possible).Typesof Movable Joints· Balland socket joints: Itallows movement in all directions (even up to 360o). This joint isfound in the shoulder and hip joints.· Hingejoints: Itallows movement in one direction only (i.e.
up to 360o). This jointis found in the elbow and knee joints.· Glidingor sliding joints: Thisjoint allows the sliding of bones over one another.
Examples of these jointsare found in the wrist and ankle.· Pivotjoints: Thisallows nodding or rotation of one part of the body on another. It is foundbetween the atlas and axis vertebrae.Structure of aJoint· Ligaments: These are tough partly elasticbands of tissue. They hold two (2) bones together at a joint. They join onebone to another. · Tendons: They are extensions ofconnective tissues which surround the muscles.
They are non-elastic in nature.They connect muscles to bones.· ArticularCartilage:These are found at the surface of bones at joint. They cushion bones byprotecting them from wear and tear during movement. They prevent thearticulating surface from being worn out due to friction.
· SynovialMembrane: Itis responsible for the secretion of synovial fluid.· SynovialFluid: Thisis the fluid secreted by the synovial membrane which lubricates the joints andreduces shock as well as friction between two (2) bones.· Capsule: Capsule is the space whichcontains the synovial fluid. How Muscles Acton Bones to Cause MovementMusclesare bundles of long thin cells enclosed in sheaths of connective tissues.
Muscle tissue consists of long cells called muscle fibres which have theremarkable ability to change their length and produce tension (pull). This isthe basis of the main function of muscle: to move the whole body or parts ofit. Muscles are attached to the bones by means of non-elastic, tough, whitishcord of fibrous materials called TENDONS.
Muscles can contract and relax. When a musclecontracts, it becomes shorter and thicker. Thus a pulling force is exerted onthe bone in which it is attached. When a muscle relaxes, it lengthens andbecomes thinner. Most muscles act in pairs called ANTAGONISTIC PAIRS, so that while one member iscontracting, the other is relaxing i.e. the muscles acts in opposite direction.
One member is called extensor andthis tends to extend or straighten a limb by its contraction; the other memberis called flexor, this bends orflexes the limb. Thus,muscles act in opposite directions in order to cause a bone to move. This aidsmovement of the body.
Muscles are attached to the bones at two points. One ofthe points of attachment is called the origin of the muscles. This is where themuscles are attached to an immovable or rigid bone e.g. shoulder blade.
Theother point of attachment is called insertion. This is where the muscles areattached to a movable bone e.g. radius.Movementof Forelimbs at the Elbow JointThemuscles of the upper arm on humerus are referred to as biceps and triceps.Bicep muscles are attached to the front of the humerus and are attached to thescapula by means of two (2) tendons. The triceps muscles are attached at theback of the humerus. The contraction and relaxation of these muscles bringabout bending and straightening of the limb.
The muscles are antagonisticmuscles, that is, they work together in pairs in opposite ways. When an impulse is received from thecentral nervous system, the biceps called the flexors contract by becoming shorter and thicker, and at the sametime, the triceps (extensors) relax.Since the tendons do not stretch, the shortening of the biceps result in a pullof the radius and as a result, the arm is bent. Onthe other hand, when the triceps muscle (extensor muscles) contract, becomingshorter and thicker at the same time, the biceps muscle (flexors) relax, aforce is exerted on the ulna and the arm is straightened as a result. Functions of Skeleton in ManThe functions of skeleton in maninclude:· Support: The rigid skeleton supports thebody. It also supports some vital organs and it maintains shape of the body.
· Protection: The skeleton protects importantand delicate organs of the body. The skull protects the brain and houses theinner structures of the ear and eyeball. The vertebral column protects thespinal cord and the ribcage protect the heart and lungs.
The pelvic girdleprotects the abdominal organs e.g. urinary bladder and female reproductivesystem.
· Movement: The several pieces of bonesmaking up the skeleton allow free movement of the body and limbs. The skeletonprovides a base for the attachment of muscles which bring about movement of thebody and limbs and it gives them the ability to bend and twist in any desireddirection. · Respiration: The ribcage together with themuscles attached to them assist in respiration (both inspiration andexpiration).· Manufactureof Blood Cells:The white and red blood cells are manufactured in the marrow of long bones.
· MuscleAttachment:Skeleton provides places for the attachment of muscles. Muscles are attached tobones by tendons.· Shape: Skeleton gives shape to thebody. Thus controlling growth rate in animals is not the function of theskeleton.
SUPPORTINGTISSUES IN PLANTSPlantspossess supporting tissues which give them definite shape, strength, rigidity etc.The supportingtissues in plant and mechanisms of support in plants are:· ParenchymaTissues: -They are found in the cortex of stem, phloem, root, leaf, xylem e.t.c. They arepacking tissues made up of thinned walled cells with a central vacuole each.The cells have intercellular air spaces.
They provide flexibility, firmness andturgidity to the stems of herbciceous (dicotyledonous) plants.· CollenchymaTissues: -They are usually located in the cortex of stems, roots and in the hypodermisjust beneath the epidermis. The cells have thick walls that are pronounced atthe corners. They provide strength and support in young growing plants. Theyalso give flexibility and resilience to plants i.e.
enable plants to bendwithout breaking.· SclenrenchymaTissues: -They are made up of cells which have very thick walls containing lignin,cellulose and other substances. There are two types of sclenrenchyma, these aresclereids and fibres. Hence, they provide rigidity, resilience, hardness andsupport to plants. It also provides flexibility to plants.· XylemTissues: -It is found mainly in the vascular tissues of stems, roots and leaves. Xylem ismade up of cells like tracheids (It aids the passage of water and dissolvedmineral salts), vessels, fibres and xylem parenchyma. It has a rigid thickwall.
Xylem provides support, strength and shape to the plant. It also conductswater and dissolved mineral salts from the roots to the leaves (i.e.
it is aconducting tissue).· PhloemTissues: -It is also located within the vascular bundles of all plants in roots, stemsand leaves. It is made up of four (4) cells. These are;ü Sieve tubes: These are living elongated cellsthat conduct mainly food.ü Phloem parenchyma: They provide strength andsupport to the plant. It also helps in food storage.
ü Phloem fibres: They also provide strength.ü Companion cells: They are small and short cellswhich also assist in the conduction of food substances.The function of phloem is toconduct manufactured food from their area of synthesis to areas where they areneeded.
It also provides support.· Epidermisor piliferous layer: -Epidermis is the outer covering of the leaves and stem while that of the rootis piliferous layer. They are one cell thick. They help in protection. Theyprevent the inner cells from injury, infection and loss of water.Cortex: – It is found between theepidermis and vascular bundles (xylem & phloem) of a dicotyledonous stem.
The cortex is made up of three (3) tissues which are the (i) collenchyma (onthe outside), (ii) the middle parenchyma and (iii) the inner epidermis (it isalso called starch sheet). It stores starch; hence, when stained with iodinesolution, it will turn blue black.· Cambium:- It isfound between the phloem and xylem.
This increase the size of cells (which iscalled secondary thickening or growth). It is responsible for the increase insize of the trunks of many trees. It makes the trees get wider.· Pith: – This is the central part ofthe stem. It is large and made of parenchyma and extends between the vasculartissue.
Functions ofSupporting Tissues in PlantsThe functions ofsupporting tissues in plants are;· Strengthening: Sclerenchyma and collenchyma providethe necessary strength required by plants.· Rigidity: Collenchyma, sclenrenchyma andwood fibres provide necessary materials to make the plant strong againstexternal forces.· Resilienceand Flexibility:The supporting tissues also provide the necessary materials which make theplant resilient and flexible thereby preventing the plants from being broken bythe bending and twisting movements caused by strong winds.· Protection: Some supporting tissues protectthe delicate parts of plant body e.g.
cambium.· DistinctShape:Supporting tissues generally give shapes to plants.· Conduction: Some supporting tissues,especially xylem and phloem tissues are known to conduct water and manufacturedfood respectively within the plant.