Showing papers in "Journal of Anatomy in 1986"

The histology of tendon attachments to bone in man.

Abstract: Based on a parallel study of a wide range of human tendons from embalmed dissecting room subjects and from a study of dried bones, an explanation is offered for the well known similarity in gross appearance between the markings left by certain tendons (e.g. those of the rotator cuff) and by articular surfaces on dried bones. Epiphyseal tendons leave markings on bones that look like those left by articular surfaces. These tendons have a prominent zone of fibrocartilage at their attachment site and the deepest part of this is calcified, just as the deepest part of articular hyaline cartilage is calcified. After maceration of the soft tissues, the calcified (fibro) cartilage is left attached to the bone at articular surfaces and at the sites of tendon attachment. In all cases, the tissues separate at the basophilic tidemark between the calcified and uncalcified regions. This tidemark is smooth where there is much overlying uncalcified (fibro) cartilage and it is the smoothness that gives the typical appearance of the dried bone. Blood vessels do not generally traverse the tendon fibrocartilage plugs. Hence the areas are devoid of vascular foramina. The functional significance of tendon fibrocartilage is discussed with particular reference to supraspinatus. It is suggested that the uncalcified fibrocartilage ensures that the tendon fibres do not bend, splay out or become compressed at a hard tissue interface, and are thereby offered some protection from wear and tear. It is also suggested that the fibrocartilage plug of supraspinatus prevents the tendon from rubbing on the head of the humerus.

Node-like cells in the myocardial layer of the pulmonary vein of rats: an ultrastructural study.

Abstract: The myocardial layer of the pulmonary vein of adult rats was examined by electron microscopy. Among ordinary myocardial cells resembling those of the atrial myocardium, clear cells with structural features similar to those of sinus node cells were identified. They were distributed in the intrapulmonary, preterminal portion of the pulmonary vein. They appeared singly or in small groups among the ordinary myocardial cells. Their cytoplasm was characterised by a paucity of myofilaments, irregular disposition of myofilament bundles, small and oval mitochondria, absence of atrial specific granules and a wide cytoplasmic matrix between intracellular organelles. The intercalated discs of node-like cells were composed of small junctional specialisations. Nerve fibres containing small and large vesicles with and without dense cores were juxtaposed to the node-like cells over an intercellular space of more than 200 nm. Taking into consideration physiological data, the possibility is discussed that the node-like cells may have a potential pacemaking activity and represent an ectopic pacemaker centre in the pulmonary vein.

The Principles and Practice of Electron Microscopy

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Occurrence, distribution and origin of peptide-containing nerves of guinea-pig and rat male genitalia and the effects of denervation on sperm characteristics.

Abstract: A systematic immunohistochemical and radio-immunological survey of the occurrence, distribution and origin of the peptidergic nerve supply in guinea-pig and rat male genitalia is presented. Neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI), substance P and CGRP were detected in the genital organs of both species. The densities and distribution patterns of the peptidergic nerves were compared with those of the adrenergic nerves, as revealed by antibodies raised against dopamine-beta-hydroxylase (D beta H) and tyrosine hydroxylase (TH), and the general neuronal component, as revealed by antibodies raised against neurofilament proteins (NF). Bilateral transection of the hypogastric nerves, in the guinea-pig, resulted in a decrease of substance P-containing nerves in the vas deferens and of NPY-, PHI- and VIP-containing nerves in the seminal vesicle. Unilateral disconnection of the pelvic nerves caused a decrease of VIP, PHI, substance P and CGRP nerve supply in the ipsilateral vas deferens and cauda epididymidis in the guinea-pig. A marked reduction of noradrenergic and NPY-containing nerves was observed in the vas deferens and sexual accessory glands of rats, chemically sympathectomised by chronic injection of low doses of guanethidine. Conversely, increase of substance P and CGRP immunoreactivities were observed, particularly in the vas deferens. After guanethidine, the cauda epididymidis and vas deferens were distended with spermatozoa, suggesting paralysis of the ducts. Spermatozoa had a decreased percentage of attached cytoplasmic droplets, indicating prolonged retention in the ducts.

Gyrus formation in the cerebral cortex of the ferret. II: Description of the internal histological changes

Abstract: The internal changes within a developing gyrus of the ferret cerebral cortex were studied by recording (i) the changing length and direction of the radial tissue lines and (ii) the emergence of the tangential banding of the classical six cortical layers. Together these lines provided a coordinate net whose deformations during development gave an indication of the differential growth occurring within a gyrus. The changes in these features suggested that a gyrus was initiated by an area of local growth appearing in the subplate and then in the suprajacent segment of cortical plate. During subsequent growth there was tangential spreading of the more mature tissue at the gyral crown while at the site of the future sulci the cortical plate remained immature and growth was retarded. During later stages the majority of tangential growth occurred in the parasulcal area. At this site a very much thinner cortex was generated from a segment of cortical plate of the same depth and degree of nuclear crowding as elsewhere, implying that growth here was resolved into tangential spreading. The cells and fibres of the deeper cortical layers of the sulcal cortex eventually became tangentially orientated suggesting that they subserved a commissural function between the columnar systems of adjacent gyri. At the scale prevailing in the ferret, gyrus formation was seen as a configuration which tended to conserve both the total length of the cortical columns and the depth of the individual cortical layers.

The number and distribution of lymphoid follicles in the human large intestine.

Abstract: The density of mucosal lymphoid follicles has been determined in the large intestines of five sudden death victims. The specimens were fixed in acetic acid which made the follicles visible macroscopically. The estimated total number of follicles in the large intestine ranged from 12761 to 18432. The average density of follicles was 18.4 per cm2 in the caecum, 15.0 per cm2 in the colon and 25.4 per cm2 in the rectum. These results indicate that the density of lymphoid follicles has been grossly underestimated in the past where three to five follicles per cm2 have been accepted as normal. The cause for this major discrepancy is discussed as is its bearing on the diagnosis of lymphoid hyperplasia.

Gyrus formation in the cerebral cortex in the ferret. I. Description of the external changes.

Abstract: The external features of gyrus formation in the postnatal ferret cerebral cortex are described and correlated with certain internal changes. The observations indicate that gyri are formed by longitudinal and radial expansion of the cortical compartment occurring between relatively fixed areas which form the sulcal floors. The gyri were initially rounded with open sulci and the cerebrum had a rectangular outline when seen in lateral and dorsal view. By adult life the hemisphere had been subjected to considerable moulding by the growing skull, so that the frontal pole of the cerebrum became pointed while the sulcal walls became closely opposed and the gyral crowns flattened.

A study of weight transmission through the cervical and upper thoracic regions of the vertebral column in man.

Abstract: The role of the neural arch in weight transmission in the cervical and upper thoracic regions of the vertebral column has been investigated. Measurements at the levels of C2, C4, C6, C7, T1 and T5 vertebrae were made in 44 adult male vertebral columns. At each level, the area of the inferior surface of the body was compared with the area of the inferior articular facets, the pedicle index and the arch index; inclination of the pedicle in relation to the body was also measured. On the basis of these studies it was found that at C2 level the compressive force acting on the superior articular surfaces was transmitted to the inferior surface of the body and to the two inferior articular facets. From C2 to C7, compressive force is transmitted through three parallel columns - one anterior, formed by the bodies and intervertebral discs, and two posterior, formed by the articulations of the articular processes on either side. Due to the posterior curvature in the cervical region, the posterior columns here sustain more of the compressive force. From C7 level downwards, the compressive force is transmitted through two columns, i.e. one anterior formed by the bodies and intervertebral discs and one posterior formed by successive articulations of the laminae. Below C7 level, compressive force from the posterior column is partly transferred to the anterior column through the pedicles at T1 and T2. In the upper thoracic region, due to the anterior curvature, the main part of the compressive force is transmitted through the anterior column, which sustains even greater compressive force than is suggested by body area, with resulting increased stress.

Autonomic neuromuscular junctions: current developments and future directions.

Abstract: (1) The autonomic neuromuscular junction has been defined, with emphasis on the role of muscle effector bundles and en passage release of transmitter from extensive terminal nerve varicosities to diffuse to muscle across variable and often wide junctional clefts. (2) A multiplicity of neurotransmitters is described in the autonomic nervous system, including purines, peptides, amino acids and monoamines. The ultrastructural identification, projections, roles and interactions of the different nerve types have been discussed. (3) It has been suggested that the part played by peripheral neuroeffector control mechanisms has been underestimated and includes cotransmission, pre- and post-junctional neuromodulation, and the participation of locally released agents. (4) A time-lapse film was shown of the formation of autonomic neuromuscular junctions in culture, introducing questions relating to long-term 'trophic' influences in the autonomic nervous system.

Development of interstitial cells and ovigerous cords in the human fetal ovary: an ultrastructural study.

Abstract: Differentiation and subsequent regression of interstitial cells in the human fetal ovary was studied by light and electron microscopy in specimens obtained from twelve fetuses between 12 and 40 weeks of gestation. Interstitial cells possessing the ultrastructural features associated with steroid production first differentiate from fibroblast-like cells by 15 weeks. This occurs within the medullary fibrous tissue penetrating the cortex. The number of such cells is maximal at 18 weeks around the ovigerous cords in the inner half of the cortex. In addition, gap junction formation is seen in the pregranulosa cells forming ovigerous cords. From 21 to 31 weeks primordial follicles develop from ovigerous cords, which themselves develop from undifferentiated cortex, in a sequence that is most advanced in the medullary portion of the gonad and least advanced at its surface. During this time the interstitial cells decrease in number. They are not observed around the follicles, but are occasionally seen in the outer layer of the cortex which is still at the stage of ovigerous cords. At 40 weeks, growing follicles associated with several layers of enveloping theca cells are observed in the innermost region of the cortex. Interstitial cells are rare in all parts of the ovary. The development of interstitial cells independent of follicles in the human fetal ovary implies that such cells are distinct from theca cells, and that they correspond to the primary interstitial cells of other mammalian species. In addition anatomical and temporal relationships are observed between the interstitial cells, the ovigerous cords, developing primordial follicles and the formation of gap junctions in pregranulosa cells.

Ultrastructure of Leydig cells in human ageing testes.

Abstract: Ultrastructural study of Leydig cells in elderly men revealed the following Leydig cell types: (1) ultrastructurally normal Leydig cells (46.2%); (2) Leydig cells either with multiple cytoplasmic or intranuclear Reinke crystals or with numerous para-crystalline inclusions (6.1%); (3) multivacuolated Leydig cells with the cytoplasm almost filled by lipid droplets (16.7%; (4) dedifferentiated Leydig cells with poor development of agranular endoplasmic reticulum and mitochondria, and increased amounts of lipofuscin granules (22.3%); and (5) bi- or trinucleate Leydig cells (8.7%) showing either a normal (2.8%) or dedifferentiated (5.9%) cytoplasm. These results suggest an involution of Leydig cells with advancing age. A correlation between the proportion of altered Leydig cells and the decrease in testosterone and increase in luteinising hormone levels could be observed.

Ultrastructural evidence for fibril-to-fibril associations in articular cartilage and their functional implication.

Abstract: This study presents ultrastructural evidence for the presence of a variety of fibril-to-fibril interactions or associations in the architecture of the general matrix of articular cartilage. These interactions are believed to serve a higher purpose of repeatedly constraining an overall radial arrangement of fibrils into an array of oblique interconnecting segments thus creating a three dimensional meshwork within which the hydrated ground substance is constrained. It is argued that any reduction in these interfibrillar interactions will allow the oblique fibril segments to revert to a low energy radial configuration, thus explaining the presence of such arrays prominent in various degenerate forms of articular cartilage.

The effect of posture on diffusion into lumbar intervertebral discs.

Abstract: The diffusion of small solutes into the intervertebral discs of cadaveric lumbar motion segments was measured using a radioactive tracer technique. The motion segments were wedged and loaded to simulate erect posture and flexed sitting postures. The results show that erect posture favours diffusion into the anterior half of the disc compared to the posterior half. Flexed posture, by deforming the annulus fibrosus, reverses this imbalance.

Schmorl's nodes (intravertebral herniations of intervertebral disc tissue) in two historic British populations.

Abstract: The herniation of the nucleus pulposus into the vertebral body produces ectopic deposit of disc material which are known as Schmorl's nodes. This prolapsed disc tissue leaves characteristic deformations on the surface of the vertebral body and hence the incidence of this lesion can be studied in skeletal remains. This report describes the occurrence of Schmorl's nodes in TV8-SV1 in two historic adult British populations, one from Aberdeen and the other from London. In the Aberdeen group, both males and females showed a high incidence rate and severity of Schmorl's nodes. In the London group, the males had a similarly high affliction whereas the females were nearly free of the condition. The lesion had no significant predilection for any one particular vertebral surface. However, in males in both localities, the frequency of Schmorl's nodes was significantly higher in the thoracic region than in the lumbosacral region. In contrast, both groups of females showed similar node frequency in these two zones. The majority of Schmorl's nodes were localised in the central and central-posterior regions of the vertebral surface. When nodes occurred on successive vertebral surfaces, they often formed sequences showing similar shape and position. The aetiology of Schmorl's nodes is unclear. Various hypothetical causal factors were appraised in relation to the findings of this study. It was suggested that anomalies in vascular and/or notochordal regression may be related to the development of the lesion.

The morphology of Golgi-stained neurons in lamina II of the rat spinal cord.

Abstract: Golgi-stained neurons in Lamina II of the rat spinal cord were examined by light microscopy Stalked and islet cells similar to those seen in other species were found Stalked cells were present in large numbers in the dorsal part of the lamina where they made up nearly half the population of stained cells Islet cells were found throughout the lamina and constituted about one third of the total population In the ventral part of the lamina half of the stained cells did not fall into either category, but could be divided into groups on the basis of dendritic spread The axons of many of these cells either remained in Lamina II or passed ventrally into Lamina III Some of these cells may correspond to the stellate or the II-III border cells which have been seen in human spinal cord and cat medulla respectively

A quantitative ultrastructural comparison of alpha and gamma motoneurons in the thoracic region of the spinal cord of the adult cat.

Abstract: The cell bodies of motoneurons supplying both the levator costae and external intercostal muscles were identified after retrograde labelling with horseradish peroxidase. A quantitative ultrastructural comparison of cell bodies of large (greater than 40 microns) and small (less than 30 microns) diameter revealed that the intracellular appearance of large and small motoneurons was similar. However, small motoneurons had less than half the synaptic terminal frequency or cover of large motoneurons. Furthermore, only synapses of the S- and F-type were seen on small motoneurons, while S- T- F- and C-type terminals were consistently seen on large motoneurons. The variation between individual small motoneurons for various aspects of their synaptic features was more than twice that found for large motoneurons. No correlation between small motoneuronal ultrastructure and cell body diameter was found, although scatter diagrams of synaptic terminal cover against cell body size indicated the presence of two groups of small motoneurons: one with relatively high values for synaptic cover and the other with relatively low values. On the basis of the similarity of their cell body diameters to those of electrophysiologically identified alpha and gamma motoneurons, it is concluded that the large and small motoneurons examined in the present study are alpha and gamma motoneurons respectively. The synaptic difference found between alpha and gamma motoneurons is discussed in relation to both their different functional properties and the different natures of their respective peripheral targets.

Quantitation of the secretory cells of the ferret tracheobronchial tree.

Abstract: The tracheal epithelium of the ferret has few goblet cells while sero-mucous submucosal glands are present in large numbers throughout the length of the trachea and bronchi. The epithelium consists mainly of ciliated cells and of dark cytoplasmic non-ciliated cells that sometimes contain secretory granules. Any 'respiratory tract fluid' secreted into the ferret trachea is probably mainly glandular in origin. The epithelium contains neutrophils and a few mast cells and eosinophils. Nerve fibres are virtually absent from the epithelium, and this may be associated with a lack of the cough reflex from the ferret trachea. From a morphological point of view, the ferret trachea may well make a good model for the study of submucosal gland secretions.

The bill tip organ of the chicken (Gallus gallus var. domesticus).

Abstract: At the tip of the lower beak of the chicken there were found 15-20 specialised dermal papillae containing large numbers of mechanoreceptors. The Merkel or Grandry corpuscles were situated distally in the papillae and at the papillae base was a collection of Herbst corpuscles. The apex of the papillae, under the scanning electron microscope, appeared as a row of shallow pits on the surface of the beak just inside the mouth. These papillae resemble similar structures seen in other birds and are probably necessary for fine tactile discrimination.

The early origin of vertebral anomalies, as illustrated by a 'butterfly vertebra'.

Abstract: An anomalous (butterfly) eleventh thoracic vertebra in a fetus of 63 mm greatest length is described and graphic reconstructions (together with normal controls) are provided The cartilaginous hemicentra are separated by disc-like material Cartilaginous bars to adjacent vertebrae are present The neural arch is complete The notochord is not duplicated Only one comparable case in the embryonic period has been described previously After a discussion of cleft vertebrae in the human and in experimental animals, a developmental timetable of the appearance of several vertebral anomalies is provided The sensitive period for butterfly vertebrae, depending on the mode of origin, seems to be 3-6 postovulatory weeks More severe anomalies, such as the split notochord syndrome, appear earlier It is concluded that most of the vertebral anomalies discussed arise during the embryonic period proper, although the timing of a few, such as spina bifida occulta, extends into the early fetal period

Growth of the nasal septal cartilage of the rat in vitro.

Abstract: The nasal septal cartilage from 4 days old rats was cultured in a serum-free chemically defined medium for 10 days to establish the intrinsic capacity for growth. Moreover, to obtain an indication of the separating potential, the maximal pressure generated by this growth was determined in a specially designed in vitro pressure registration system. The results show that, though to a lesser extent in comparison with the same period in vivo, the nasal septal cartilage increased considerably in size while the shape was preserved. The greatest force was generated by the longitudinally growing rod-like base of the nasal septal cartilage; the smallest force was generated by growth in height. The in vitro growth behaviour and growth pressure characteristics of the nasal septal cartilage corresponded with those previously found for epiphyseal cartilage. The present results suggest a prominent role for the nasal septal cartilage in midfacial outgrowth in the rat.

A Golgi study of the sixth layer of the cerebral cortex. I. The lissencephalic brain of Rodentia, Lagomorpha, Insectivora and Chiroptera.

Abstract: A study of the morphological characteristics of the neurons in layer VI of the cerebral cortex was carried out using the rapid Golgi method in several lissencephalic species including Rodentia (rat, mouse, vole (Microtus agrestis) and hamster), Lagomorpha (rabbit), Insectivora (hedgehog) and in the Chiroptera the dwarf bat (Pipistrellus pipistrellus). There was a basic uniformity in the structure of the sixth layer. Main neuronal types in lamina VIa were large pyramidal neurons, triangular or atypical pyramidal cells, multiapical pyramidal neurons, inverted pyramids, fusiform neurons, Martinotti cells and bi-tufted cells. Main neuronal types in lamina VIb were medium sized, flattened pyramids, large and small horizontal neurons, horizontal pyramidal cells, fan shaped neurons and multipolar spinous neurons with long descending axons. Sparsely spinous and spine-free multipolar neurons with short axons were present in the two laminae of layer VI, but sparsely spinous neurons with axons similar to those found in basket cells of other layers of the cortex were observed mainly in lamina VIa. Neuronal subsystems were tentatively classified on the basis of the course of the axons. Pyramidal neurons, fusiform neurons, multiapical pyramidal cells, inverted pyramidal cells, fan shaped neurons and multipolar neurons with large descending axons were interpreted as being the main source of long projection and association connections. Large horizontal neurons were interpreted as possible ipsilateral association neurons because the horizontal course of the axons over long distances followed the boundary of the deeper region of the sixth layer. Three intracortical (association) subsystems were included. Axons of Martinotti cells and collateral ascending axons of pyramidal neurons (including multiapical pyramidal neurons) formed the ascending interlaminar fibrillary subsystem. Axons of small horizontal cells and horizontal collaterals of pyramidal neurons formed the horizontal intracortical subsystem. Sparsely spinous and spine-free multipolar neurons and bi-tufted cells were the main source of the local, non-horizontal fibrillary subsystem.

Cell production gradients in the developing ferret isocortex.

Abstract: The accumulation of cells within the cortical plate was studied in ferrets at two developmental ages. A survey method based on the presumed radial organisation of cortical neuron production was used to sample variations in cell production along the rostrocaudal and laterodorsal axes of the brain. The resulting cell counts confirmed the presence of a gradient of cortical plate formation, with a rostrolateral focus. These findings were discussed in relation to some recent teratological studies on brain development in ferrets, where there has been a lack of normative data.

A Golgi study of the sixth layer of the cerebral cortex. II. The gyrencephalic brain of Carnivora, Artiodactyla and Primates

Abstract: The sixth layer of the cerebral cortex has been studied by means of the Golgi method in Carnivora (dog and cat), Artiodactyla (cow and sheep), and Primates (human) brains; a basic structural uniformity being observed in all these species. Projection neurons of lamina VIa were large and medium sized pyramidal neurons (including atypical and multiapical), small pyramidal cells, and spinous multipolar neurons with long descending axons. Projection neurons of lamina VIb were medium sized pyramidal neurons and small pyramids, horizontal pyramids, inverted pyramidal cells, spinous multipolar neurons with long descending axons and large fusiform cells. Local circuit neurons of lamina VIa were Martinotti cells, basket neurons, neurogliaform cells, sparsely spinous neurons with whirled axons, spine-free multipolar cells and bipolar neurons. Local circuit neurons of lamina VIb were sparsely spinous and spine-free multipolar cells with short axons and bipolar neurons. Marked differences were observed between gyral, intermediate and fissural regions. Fusiform and bipolar neurons were vertically arranged in the former, but were tangentially orientated in intermediate and fissural regions; inverted pyramidal cells were present in the gyrus but horizontal pyramids were the respective cells in the intermediate and fissural zones. When compared with lissencephalic species, a great horizontal fibrillary system (which is vertically arranged in gyral regions) was observed in convoluted brains. Cells of origin were fusiform neurons, bipolar cells, horizontal and inverted pyramids and pyramidal neurons (the latter by means of horizontal axonal collaterals). The great development of this cortico-cortical association system in gyrencephalic species is considered to be a major step in neocortical evolution.

The adrenal and renal veins of man and their connections with azygos and lumbar veins.

Abstract: There exist many variations in the manner of formation, dimensions and place of termination of the central adrenal veins. In addition, some superficial adrenal veins may be substantial in size and may themselves drain directly into the renal veins and/or into other vessels which communicate with azygos and lumbar veins. This provides a route for venous adrenal blood to the heart via the azygos system and the superior vena cava rather than via the inferior vena cava. Variations in the formation and disposition of the renal veins are also described and the patterns of communication between somatic veins (including veins of the azygos and lumbar systems) and the left renal vein are illustrated and discussed in relation to the findings of others.

Vascular and neural changes in the rat optic nerve following induction of diabetes with streptozotocin.

Abstract: This study was undertaken to determine whether or not changes occur in blood vessels, axons or glia of the optic nerve as the result of streptozotocin-induced diabetes Diabetes was induced in 4 weeks old Sprague-Dawley rats At 12 and 16 weeks of age, the rats were killed and the optic nerves prepared for examination The number and density of blood vessels was found to be significantly increased in the diabetic rats No alteration in the structure of the blood vessels was noted A decrease in the percentage volume of axons and an increase in the percentage volume of glial elements accompanied the increase in blood vessels in the diabetic rats No difference was found in the spectrum of fibre diameters

Comparison of ear tissue regeneration in mammals.

Abstract: These studies, on a variety of laboratory, zoo and agricultural animals, show that the phenomenon of replacement of tissues lost in an ear punch is common to some other mammals as well as the rabbit, although the rabbit appears to be the most proficient in this process. It is suggested that the cartilage may be replaced in two ways, namely through the formation of a blastema as originally hypothesised by Markelova (Vorontsova & Liosner, 1960), and also from the perichondrium. The finding of bone tissue is supportive evidence enabling the suggestion that dedifferentiation, followed by deviant redifferentiation, does occur in the process of regeneration.

The numbers and types of muscle fibres in large and small breeds of pigs.

Abstract: M. semitendinosus and m. trapezius (portion) were removed from eight miniature pigs ranging from 21 to 160 days of age and eight age-control as well as eight weight-control commercial Large White pigs. Complete transverse frozen sections were obtained for each muscle sample and stained for various enzyme activities including myosin adenosine triphosphatase activity which enabled the identification of 'metabolic bundles'. This in turn enabled conclusions to be made about the prenatal development of the muscle in terms of primary and secondary myofibres. The Large White pigs contained 173% more muscle fibres in m. semitendinosus than did the miniature pigs. Primary myofibre number was found to be about four times more important than secondary to primary myofibre ratios in determining myofibre number in the two breeds of pigs. Both primary myofibre number and secondary to primary myofibre ratios were, however, significantly greater in Large White than in miniature pigs. When the age- and weight-control Large Whites were compared with the miniature pigs it was found that at any given live weight the miniature pigs had thicker myofibres whereas at the same age there was no significant difference. The total area of m. semitendinosus occupied by slow myofibres was about three times greater in the Large White pigs; the functional aspects of this are discussed. It was concluded that genetically smaller animals develop fewer muscle fibres in their muscles by a different mechanism to that exhibited by animals which are smaller due to nutritional deprivation in utero.

Ultrastructural changes in porcine mammary tissue during lactogenesis.

Abstract: Ultrastructural changes occurring in porcine mammary tissue were characterised between Day 90 of pregnancy and Day 4 of lactation. Porcine mammary tissue on Day 90 of pregnancy was composed of alveoli which contained negligible to moderate amounts of secretion. Epithelial cells of these alveoli were relatively undifferentiated. The appearance and distribution of cellular organelles suggested that mammary epithelial differentiation had been initiated by Day 105 of pregnancy in the pig. A further increase in intracellular lipid droplets and granular endoplasmic reticulum suggested that differentiation had progressed by Day 112. On the day of parturition, secretions within the alveolar lumina assumed the appearance of normal milk (as opposed to colostrum) and the epithelia displayed a distinct cellular polarity characteristic of lactating mammary tissue. By Day 4 of lactation, differentiation of epithelial cells appeared to be complete, with dilated cisternae of the granular endoplasmic reticulum and with numerous secretory vesicles. Elongated microvilli were present and numerous cells contained lipid droplets which were being extruded into the lumina. Data from this and previous studies indicate that lactogenesis in the pig occurs in two stages. Stage 1 occurs between Days 90 and 105 of pregnancy, and Stage 2 between Days 112 of pregnancy and early lactation when the predominant feature is active milk secretion.