Answers to the sample questions

          1.    a.T    b.F    c.F    d.F    e.T

              In the eyelids:

          • the orbital septum extends forward and thicken into the tarsal plate within the eyelid
          • the meibomian gland secrete lipid rich secretion which is an important component of the tear film
          • the orifices of the meibomain glands are found posterior to the root of the eyelashes
          • there are about 30 meibomian glands in the upper tarsal plate and slightly fewer in the lower tarsal plate
          • the lower eyelid is supplied by branches of infraorbital nerve (a division of maxillary nerve ) and infratrochlear nerve ( a branch of the ophthalmic nerve)
           

          2.    a.T    b.F    c.T    d.F    e.T

              The inferior rectus muscle:

          • is inserted about 6.5 cm from the limbus
          • arises from the tendinous ring
          • is innervated by the inferior branch of the oculomotor nerve which enter the muscle on its superior surface
          • is attached to the lower lid via a band of connective tissue
          • has the following action: depression, medial rotation of the eye ball and extorsion. The effect of depression is greatest when the eyeball is abducted
          • lies inferior to the inferior oblique muscle
           

          3.    a.F    b.F    c.T    d.T    e.F
           

            The ciliary ganglon is found between the optic nerve and the lateral rectus muscle contains:
          • parasympathetic ganglion which receives its parasympathetic preganglion fibres from the Edinger-Westphal nucleus and supply the sphincter papillae
          • sensory fibres from the eyeball
          • sympathetic postganglionic fibres from the superior cervical    sympathetic ganglion which supply the dilator pupillae
           

          4.    a.T    b.T    c.T    d.T    e.T

              The nasociliary nerve supplies:

          • the sphenoidal sinus and the ethmoidal sinus via the posterior ethmoidal nerve
          • the cornea via the long ciliary nerves
          • the lacrimal sac via the infratrochlear nerve
          • the dilator pupillae via the long ciliary nerve
           

          5.    a.F    b.F    c.F    d.T    e.T

              The cornea:

          • is thicker peripherally (about 1.2 mm) than centrally (average 0.5 to 0.6 mm)
          • contains about 350,000 cells ( about 3 to 4000 cells per square mm) at birth, the number decreases with age
          • contains Descemet's membrane which is produced by the endothelium and forms its basement membrane
          • contains flattened keratocytes within the stroma. Other cells such as macrophages,lymphocytes or neutrophils may be seen
          • has a refractive index of 1.83
           

          6.    a. T    b.T    c.F    d.T    e.T

              The vitreous:

          • is a viscoelastic gel containing 98% water
          • has in it the main constituent of  type II collagen fibres which contains hyalonuric acid molecules
          • is firmly attached to the following:

            •         * the pars plana via the vitreous base
                    * the posterior lens capsule
                    * around the optic disc
                    * along the blood vessels
           

          7.    a.F    b.T    c.T    d.F    e.T

              The globe:

          • is closer to the orbital roof than the orbital floor
          • is closer to the lateral wall than the medial wall
          • has a vertical diameter less than the anteroposterior diameter (23 vs 24 mm on average)
          •  has an anterior segment which form 1/6 of the circumference
          •  is least protected laterally
           

          8.     a.T    b.T    c.F    d.F    e.T

              The lacrimal gland:

          • contains two parts: palpebral and orbital parts. The former is about 1/3 the size of the later
          • contains 12 ducts that originate from the orbital part and pass into the palpebral parts and open into the superior conjunctival fornix
          • surgical excision of the palpebral part will cause scarring of the ducts whereas removal of the orbital part will remove the nerve innervation and therefore excision of either part will affect tear secretion
          • receives its secretomotor nerve from the facial nerve
          • contains lymphatic system that drains into the parotid gland
           

          9.    a.T    b.T    c.F    d.F    e.F

              The lacrimal drainage system:

          • the upper lacrimal punctum is medial to the lower punctum
          • contains stratified squamous cells which line the canaliculi
          • contains nasolacrimal duct which is narrowest in the middle than either end
          • ontains nasolacrimal duct which runs downwards, backward and laterally to the inferior  meatus
          • blockage is usually due to failure of the lower end of the nasolacrimal duct becoming patent
           

          10.     a.F    b.F    c.T    d.T    e.F

              The cells of the retinal pigment epithelium:

          • are of ectoderm origin
          • are taller in the fovea and become flattened towards the periphery
          • contain melanin granules which absorb excess light and prevent radical damage to the cells
          •  phagocytose the photoreceptors segment and store vitamin A and therefore play an important part in the regeneratoin of photoreceptors
          • forms the outer blood-retina barrier
           

          11.    a.T    b.T    c.T    d.F    e.F

              Optic chiasm:

          • is found at the junction of the anterior wall and the floor of third ventricle
          • is posterior and inferior to the olfactory tracts
          • has the internal carotid arteries lying immediately lateral to it
          • is separated from the mamillary body by the pituitary stalk
          •  has the oculomotor nerves lying on its lateral side
           

          12.    a.T    b.T    c.T    d.F    e.T

              The facial nerve:

          • has a nucleus which lies in the floor of the fourth ventricle
          • the fibres exist the brain stem between the pons and the inferior cerebellar peduncle
          • transmits taste fibres from the anterior half of the tongue via chorda tympani
          • gives off greater petrosal nerve (Note: not deep petrosal nerve) which mediate tear secretion
          • contains tympani branches which are sensory nerve supplying the external acoustic meatus  and the pinna
           

          13.    a.T    b.F    .T    d.F    e.F

                  Cerebrospinal fluid:

          • found in the subarachnoid space ie between the pia mater and the arachnoid
          • normal amount is 130 ml and the intracranial pressure is 100 ml of water (varying between 60 to 150 ml of water)
          • is produced by choroidal plexi by the lateral ventricle, third ventricle and the fourth ventricle
          •  contains half the concentration of glucose found in the plasma. Few cells and trace protein  are found in normal people
           

          14.    a.T    b.T    c.F    d.T    e.F
           
                  The parotid gland:

          • is the largest salivary gland and contains serous acini
          •  the secretomotor nerve arises from the parasympathetic component within the glossopharyngeal nerve. It then travels within the lesser petrosal nerve which synapses in the otic ganglion. The post-ganglionic nerve reach the gland via the auriculotemporal   nerve.
           

          15.    a.F    b.F    c.T    d.T    e.T

              In the anatomy of the head and neck:

          • the lymph from the upper lid drains into the superficial parotid gland
          • the facial nerve derives from the second pharyngeal arch
          • branch of the ophthalmic division of the trigeminal nerve supply the scalp as far back as the scalp
          • a lateral harelip (cleft lip) results from the failure of fusion between the maxillary process and   the medial nasal process
           

          16.    a.T    b.T    c.T    d.T    e.T
           
              Development of the eye:

          •  the face including the orbit begins its development in the 4th week of gestation and is completed by 10th week
          • the orbit is formed from fusion between the lateral nasal process and the maxillary process
          • the upper lids arise from the fronto-nasal process whereas the lower eyelids from the maxillary process
          • the nasolacrimal groove forms along the fusion between the lateral nasal swelling and the maxillary process. The ectoderm in the groove invaginates to form nasolacrimal duct
           

          17.    a.T    b.F    c.F    d.F    e.T

              The following structures are of ectodermal origin:

          •     retina
          •     retinal pigment epithelium
          •     epithelium of the ciliary body
              The sclera, iris stroma and the ciliary body are derived from the mesenchyme
           

          18.    a.T    b.F    c.F    d.T    e.T
           
              The hyaloid artery:

          • comes off the dorsal ophthalmic artery and supplies the lens and the inner layer of the optic cup
          • the choroidal circulation arises from the long and short posterior ciliary arteries and do not communicate with the hyaloid artery
          • regresses before birth
          • Mitterdorf's dot is the anterior remnant of the hyaloid artery whereas the Bergmeister's papillae is the posterior remnant
          • forms vascular propria lentis which supplies the lens
           
          19.    a.T    b.F    c.T    d.T    e.F

              Lens development:

          •  the lens first appears as a disc-shaped thickening on the ectoderm at 27th day gestation
          • lens arises from the ectoderm
          • lens vesicle becomes separated from the surface ectoderm at the 33rd day gestation and contains a single layer of epithelial cells
          • embryonic nucleus is formed from the primary lens fibres. The foetal lens arises from the secondary fibres and contains Y sutures
          • the foetal lens is spherical but as the lens grows it becomes ellipsoid
           

          20.    a.F    b.T    c.F    d.F    e.T
           
              The first pharyngeal arch gives rise to:

          • artery: terminal branch of maxillary artery
          • skeletal elements: incus, malleus, mandible, maxilla, zygomatic, squamous portion of temporal bone
          • muscles: muscles of mastication (temporalis massenter and pterygoids), myelohyoid, anterior belly of the digastric, tensor tympani and tensor veli palatini
          • cranial nerve: maxillary and mandibular divisions of trigeminal nerve
              Muscle of facial expression including orbicularis and facial nerve arise from the second pharyngeal arch. The common carotid artery arises from the third pharyngeal arch
           

          21.    a.F    b.T    c.T    d.T    e.T
           
              The glucagon:

          • is a polypeptide hormone secreted by the alpha islet cell of pancrease
          • stimulates the release of glucose from glycogen storage in the liver ( glucogenolysis)
          • stimulates the synthesis of glucose in the liver (glycogenolysis)
          • has a positive inotropic effect on the myocardium
           

          22.    a.F    b.T    c.T    d.F    e.T
           
              Vergence movement:
              - is a tracking movement which is slower than pursuit movement
              - is voluntary but can be stimulated by blurred images on the retina
              - is required for binocular single vision and stereopsis
              - is limited by the near point and the far point of accommodation
           

          23.    a.F    b.F    c.T    c.F    e.T

              During accommodation:

          • the ciliary muscle contracts and thus the lens becomes thicker
          • the pupils constrict and therefore both the field of vision and the amount of light entering the eye are reduced
           

          24.    a.T    b.F    c.F    d.F    e.T

                  Binocular vision:

          • horopter represents the line in which all points along it will fall on the corresponding retinal point
          • points in front of the horopter will stimulate bitemporal retina whereas those distal to it on binasal retina
          • withint the Panum's area, point in front and distal to the horopter is perceived singly. Panum's area is wider in the periphery than in the centre
          • sensory fusion refers to cortical integration of the images perceived by the two eyes whereas motor fusion refers to the correct alignment of the extraocular muscle on a target of interest
           

          25.    a.F    b.T    c.T    d.F    e.T

              The eye movement:

          • saccade is controlled by contalateral supranuclear centre with a latency of 100 ms and velocity of 100 degrees per second
          • pursuit movement is controlled by ipsilateral supranuclear centre with a latency of 150ms and velocity of 30-50 degrees per second. A slow moving object is needed to elicite the pursuit movement
          • the superior colliculus is an important centre for possessing the visual image and contor control
          • the cerebellum mediate the vestibulo=ocular reflex and help to stabilize the retinal image
           

          26.    a.T    b.T    c.T    d.F    e.T

              Entopic phenomenon:

          • visual perceptions that are produced by the sturctures of one's own eyes
          • can be produced by cells in the vitreous or unformed images through palpation of the eyeball
          • when viewed through a pinhole against an uniformly illuminated background, the edge of one's pupil can be seen
          • asteroid hyalosis seldom produces significant visual problem
          • Haidinger's brushes are produced when one viewed a diffusely illuminated plane-polarised blue light. It is produced by the outer plexiform layers of the retina
           

          27.    a.T    b.T    c.T    d.F    e.T

              The intraocular pressure flutuate:

          • seasonally being higher in the winter
          • diurnally with the cicadian rhythem being higher in the morning
          • with eye movement being higher when the eye is moved away from the primary position
          • with fluid intake; the intraocular pressure increases with increase body fluid
           

          28.    a.T    b.T    c.F    d.F    e.T

              The tear film:

          • has a convex surface and therefore contribute to the refractive index of the eye
          •  has three layers: mucous, aqueous and lipid. The thickness is about 8 to 10 um
          •  the break up time is about 30 seconds
          •  tear production is inhibited by atropine
           

          29.    a.T    b.T    c.T    d.F    e.F
           
              The lens:

          • has a higher refractive index in the central part of the lens
          • contains a higher potassium concentration ( 125 mmole perkg lens water) than sodium (17 mmol perkg lens water)
          • has a higher concentration of sorbitol in diabetes mellitus. Excessive glucose is reduced to sorbitol by aldose reductase
          • 85% of glucose is metabolised by anerobic glycolysis and only 15% by aerobic glycolysis
          • conatins nucleated cells mainly on its anterior surface
           

          30.    a.T    b.T    c.T    d.F    e.T

              During dark adaptation:

          • Purkinje's effect is seen in which there is a shift in peak spectral sensitivity from 555nm to 505 nm with dark adaptation
          • rods are 1000 times more sensitive than cones
          • animals with only rods exhibit only monophasic change
          • it may take up to 30 minutes
          • it is delayed in hypovitaminosis A
           

          31.    a.T    b.F   c.T    d.T    e.F

              Phototransduction

          • dark current is present in the dark
          • in the presence of light, the sodium channels close and give rise to hyperpolarisation
          • 11 cis-retinal molecules are converted into trans-retinal
          •  transducin is important in converting GDP to GTP
           

          32.    a.T    b.F    c.T    d.T    e.T
           
              Blood retinal barrier:

          • the outer blood retina barrier is formed by retinal pigment epithelium cells and their junctions
          • the inner blood retina barrier is formed by endothelial cells of the capillaries of the retinal artery and their junctions
          • inhalation of 10% carbon-dioxide causes dilatation of blood vessels but does not break down the blood retinal barrier
           

          33.     a.T    b.F    c.F    d.F    e.T

              The aqueous humour:

          • the rate of formation is between 2 to 3 ul/minute
          • it has a very low protein concentration compared with the blood the ascorbate is between 10 to 50 times that of the plasma
          • glucose is lightly lower than that of the plasma
          • the lactic acid is higher than that of the plasma
           

          34.     a.F    b.T    c.F    d.T    e.T

              ERG:

          • records retinal activity
          • can be performed on anesthetized patients
          •  it is not affected by the ganglion cells and therefore not affected by optic neuritis
          • is normal in patient with amblyopia
          • contains upgoing a wave produced by photoreceptors and downgoing b wave produced by Muller and bipolar cells
          • dark adaptation increases the amplitude a and b wave as well as the latency
           

          35.    a.T    b.F    c.F    d.F    e.T
           
              EOG:

          • is an indirect measure of the standing potential of the eye
          • depends on a normal retinal pigment epithelium
          • requires co-operation of the patient who moves the eyes back and forth over a specific distance
          • the light response is higher than dark response
          • the result is given as a ratio between light to dark response. The normal ratio is more than 180%
          •  in Best's disease, the EOG is abnormal early on in the disease
           

          36.    a.T    b.F    c.T    d.T    e.F

              Stretch reflex:

          • is a monosynaptic reflex characterized by knee and ankle jerk. It opposes muscle stretching and the response time is short at 1 msec
          • its amplitude is inhibited by impulses from Golgi tendon organs
          • originates in the muscle fibers and the impulse is sent along the type Ia fibers
          • gamma efferent fibers are excitatory nerve fibers which supply the muscle spindles. Impulses along these fibers increases the intensity of the reflex
          • is increased in upper motor neurone lesion
           

          37.    a.F    b.T    c.T    d.F    e.F
           
              Glycocylated haemoglobin:

          • is found in normal population but the percentage is lower than diabetic patients
          • the risk of renal damage such as microalbuminuria increases when HbA 1c exceeds 8.1%
          • it involves the non-enzymatic binding of a hexose to the N-terminal amino acid of the beta-chain
          • glycocylated serum proteins such as fructosamine are more accurate than glycocylated haemoglobin
          • patients with sickle cell disease and haemolytic diseases have decreased survival span of red blood cells and therefore glycosylation is reduced
           

          38.    a.T    b.F    c.T    d.F    e.T

              Autonomic nervous system:

          • the cell bodies of the sympathetic nerves are found mainly in the lateral horn of the spinal cord
          • the preganglionic sympathetic fibers are longer than preganglionic parasympathetic fibers because sympathetic preganglionic fibers lie relatively close to their emergence from the spinal cord whereas parasympathetic relays are near or in the walls of the tissue or organs supplied
          • acetylocholine is found in autonomic ganglia
          • botulin toxin inhibits the exocytosis of acetylcholine in the preganglionic fibers
          • hemicholinum inhibits the uptake of choline and therefore synthesis of acetylcholine
           

          39.    a.F    b.F    c.T    d.T    e.T

              Blood coagulation:

          • heparin increases the activity of anti-thrombin III which inhibits the clotting cascade
          • vitamin K is used in liver to produce clotting factors and on its own has no anti-coagulation effect
          • thrombin is important in the clotting cascade by releasing fibrin from fibrinogen
          • platelets are essential for clotting
          • factors II, VII, IX and X are produced in liver with vitamin K
           

          40.    a.F    b.F    c.T    d.T    e.T
           
              The inner ear:

          • the tunnel of the Corti is filled with cortilymph
          • the lowest tone that can be heard is 30 Hz
          • the perilymph is identical to cerebrospinal fluid and in infants this may communicate with the subarachnoid fluid
          • the longest fibers of the basilar membrane are found at the apex
          • the maculae of the utricles detect linear acceleration
           

          41.    a.F    b.F    c.T    d.F    e.T

               Interferon:

          • is a glycoprotein produced by T lymphocytes and macrophages
          • are of three types: alpha, beta and gamma
          • has non-specific antiviral properties
          • its effects include:
                  * direct antiproliferative action on tumour and virus infected cells
                  * activation of natural killer cells and macrophages
                  * increased expression of class I HLA antigen on tumour or infected
                    cells
           

          42.    a.T    b.T    c.T    d.T    e.T

              Gram negative bacteria:

          •  proteus vulgaris and serratia marcescans have been reported in endophthalmitis and keratitis
          • haemophilus influenza can cause bacterial ocnjunctivitis
          • moraxella lacunata is a gram negative diplococci that produces corneal ulcerations most often after trauma in debilitated patients, diabetes and alcoholics
          • pseudomonas aeruginosa causes a serious infection which can lead to perforation and is the most common organisms associated with contact lens keratitis
           

          43.    a.T    b.F    c.F    d.F    e.F
           
              Antibiotics:

          • fusidic is effective against Staphylococcus aureus but resistance can occur easily
          • rifampicin has been used in the prophylaxis against meningecoccus
          • vancomycin is ineffective against endophthalmitis is given intravenous as the drug penetration into the vitreous cavity is poor
          • gentamicin is effective against mainly Gram negative bacteria
          • penicillin is ineffective against Gram negative bacilli
           

          44.    a.F    b.F    c.F    d.T    e.F

              Endotoxins:

          • are lipopolysaccharides derived from the cell wall of gram negative bacteria
          • are heat stable (cf with exotoxin)
          •  non-antigenic (cf with exotoxin)
          •  cause septicaemia and fever
          •  activates the alternative complement pathway
           

          45.    a.F    b.T    c.T    d.F    e.T

              Viruses associated with human cancer:

          • Epstein-Barr virus is associated with Burkitt's lymphoma and nasopharyngeal carcinoma
          • human papilloma is asscoaited with cervical cancer
          • hepatitis type B is associated with hepatic cancer
          • human immunodeficiency virus is associated with Kaposi's sarcoma and non-Hodgkin's lymphoma of the central nervous system
           

          46.    a.T    b.T    c.T    d.T    e.T

              Acute inflammation:

          • complete resolution is seen if the lesion is small and the tisuse involve can undergo complete regeneration
          • abscess is an example of a localised suppurative inflmmation. It is produced by the deep seeding of the pyogenic bacteria into a tissue
          • chronic inflmmation can occur if the inciting agent were removed
          • repair by connective tissue can lead to scar tisuse formation and loss of function
           

          47.    a.T    b.F    c.F    d.T    e.F
           
              Carbonic anhydrase inhibitors cause:

          •    metabolic acidosis
          •    hypokalaemia
          •    hyponatraemia
          •    renal calculi but not hypercalcaemia
          •    fatigue and paraesthesia of limbs
          •    Steven-Johnson's syndrome
           

          48.    a.F    b.F    c.T    d.F    e.F

              Anticholinesterase:

          • inactivate the cholinesterase and allow the chemical transmitter ie. acetylcholine to persist and produce intense effect
          • stimulate the parasympathetic pathway and therefore:
                      * the sphincter muscle of the iris becomes contricted
                      * the ciliary muscle contract and increases accommodation

              The blood vessels of the conjunctiva and the upper lids are controlled mainly by the sympathetic pathway.
           

          49.    a.T    b.F    c.T    d.F    e.T

              Accommodation:

          •  is controlled by the parasympathetic autonomic system
          •  is imparied by parasympathetic antagonists which affect the ciliary body and this include:
                      * atropine
                      * cylopentolate
                      * tropicamide
                      * phenothiazine
           

          50.    a.F    b.T    c.F    d.T    e.F

              Chloroquine:

          • at the equivalent dose is more toxic to the retina than the hydroxychloroquine
          • causes corneal deposition and anterior subcapsular cataract neither of which is of visual significance
          • bound to the melanin in the retinal pigment epithelium and is thought to be the reason for its toxicity
          • causes bull's eye maculopathy which may progress despite stopping the medication
           

          51.    a.T    b.F    c.F    d.T    e.T

              The concentration of adrenaline in the synaptic cleft is increased in:

          • the presence of cocaine which inhibits adrenaline reuptake
          • the presence of MAO inhibitors which blocks the metabolism of adrenaline by MAO. Although COMT is also involved in the metabolism of adrenaline this occurs in the blood stream
          • the presence of noradrenaline receptor blockers and partial agonist of noradrenaline receptors.
           

          52.    a.F    b.T    c.T    d.F    e.F

              The nucleic acids:

          • the purine and pyrimidine in the DNA are bound by ionic bonds
          • in RNA thymidine is replaced by uracil
          • intron is the region of DNA which generates that part of precursor RNA which is excised during transcription and does
          • not form mRNA and therefore does not specify the primary structure of the gene product
          • exon is the region of DNA which generates that part of precursor RNA which is not excised during transcription and forms mRNA and thus specifies the primary structure of the gene product
          • there are more introns than extrons in the DNA
          • histone is a protein which is rich in lysine and arginine and found in association with DNA in chromosomes
           

          53.    a.F    b.F    c.T    d.F    e.T
           
              Allergic reaction:

          •  Arthus reaction is not cell-mediated. It is type III hypersensitivity reaction and can be defined as a localised area of tissue necrosis resulting from acute immune complex vasculitis usually found in the skin
          • anaphylaxis is a type I reaction and occur in patients who have had previous exposure to the offending agents for example anaphylactic reaction to fluorescein angiography may be due to previous exposure to iodine in sea food
          • contact dermatitis and Mantoux test are both type IV reaction characterized by cell-mediated hypersensitivity
          • urticaria is a type I hypersensitivity reaction characterized by localised mast cell degranulation and resultant dermal microvascular hyperpermeability, culminating in prutitic wheals.
           

          54.    a.F    b.F    c.T    d.T    e.T

              Immunoglobulin A:

          • exists as a dimer whereas Ig M is a pentamer and therefore heavier
          • is excreted in the tear and breast milk
          • can activate complement by the alternative pathway
          • is ineffective against gonococcus
           

          55.    a.T    b.F    c.T    d.F    e.T

              Viruses:

          • contain nuclei acids which are either DNA or RNA
          • HIV virus is a retrovirus and contains RNA
          • cytomegalovirus is a herpes virus and contains DNA, it is not sensitive to acyclovir
          • induce interferon production which inhibits viral replication
           

          56.    a.T    b.F    c.T    d.T    e.T

              Virulence factors:

          • can be exotoxins or endotoxins (such as the cell wall of Haemophilus influenza)
          • M protein on some bacteria prevent phagocytosis
          • pili on gonococcus allow them to adhere to mucosal surface
              Beta lactamase or penicillaminase hydrolyses penicillin but has no direct effect on host tissue
           

          57.    a.F    b.F    c.F    d.T    e.T
           
              Synthesis of neurotransmitter:

          • both MAO and COMT are involved in the breakdown of adrenaline and noradrenaline
          • cholinesterase is responsible for the breakdown of acetylcholine
           

          58.    a.T    b.T    c.T    d.F    e.T

              Mitochondrial DNA are transmitted via the maternal line only. This is because the mitochondrial DNA is found only in the  ovum and not in the spermatozoan. Mitochondrial DNA is expressed in mitochondria rich tissue such as the muscles, the neural tissues and the myocardium. Patients with mitochondrial disorders are therefore liable to develop myopathy and cardiomyopathy. DNA in the mitochondria are coded for enzymes involved in oxidation and energy production.
           

          59.    a.F    b.T    c.F    d.T    e.F
           
              HLA antigen:

          •  the gene is coded by chromosome 6
          •  can be divided into two classes:
              • * class I antigen is found on the surface of all nucelated cells. The main function is to allow cytotoxic T-lymphocytes to recognise and eleminate virus-infected cells
              * class II antigens are found on cells that interact with T-lymphocytes for example Langerhans' cell. Their functions are to innitiate an immune response
          • although graft rejection is reduce with HLA matching. Some rare transplant tissues such as heart are limited to ABO matching
           

          60.    a.F    b.T    c.T    d.T    e.F

              There are 22 pairs of autosomal chromosome and one pair of sex chromosome. Due to meiosis only 23 chromosomesare found in the germinal cell. Female has two X chromosomes but only is activated and the other stay domant as the Barr body. In Klinefelter's syndrome, the male cell has an extra X chromosome.
           
           

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