Microvascular anatomy of the pig eye: scanning electron microscopy of vascular corrosion casts

The microvasculature of the eye of 10 pigs was investigated using scanning electron micrographs of corrosion casts. The ciliary body, iris and bulbar conjunctiva were supplied by the iridociliary ring artery via the long posterior ciliary artery. Capillaries of the ciliary process were of large diameter (23.2-27.5 microm) with an irregular bore, forming a thoroughfare channel draining blood in the ciliary arterioles into the pars plana venous vessels. Arterioles and venules in the iris exhibited a zigzag or spiral features. The third palpebra was supplied by the anterior ciliary artery. The capillary bed of the third palpebra was dense and was formed by many rows of fine hair-pin loops. Capillaries in the bulbar conjunctiva formed a sparse network disposing approximately parallel to the epithelium and formed a well-developed venous plexus, draining into the vortex veins. Retinal arterioles formed a slender and long course to capillaries. Retinal capillaries were extremely thin (3.0-4.0 microm in diameter). The choroid was supplied by the short posterior ciliary arteries. Choroidal arterioles exhibited a thick and short course to the choriocapillaris. The choriocapillaris was flat and sinusoid-like (8.9-13.9 microm in diameter), forming a dense sheet-like network. Blood from the choroid emptied into the episcleral vein via the vortex vein. Blood from the retina was drained by the posterior ciliary veins. The functional significance of this vascular architecture was discussed.     

Microvasculature of the hamster eye: scanning electron microscopy of vascular corrosion casts

The architecture of the retina, choroid and anterior eye segment was investigated in 12 Syrian hamsters using scanning electron micrographs of methylmethacrylate corrosion casts. The hamster eye receives its primary blood supply from the long posterior ciliary artery, which directly enters the optic nerve head, and divides into three branches: the central retinal artery and medial and lateral long posterior ciliary arteries. In the retina the central retinal artery divides into six radiating branches. Retinal arterioles form a slender and long course to capillaries. Retinal capillaries are extremely thin in diameter and form a sparse capillary network. The choroid is supplied by the long posterior ciliary arteries. Choroidal arterioles exhibit a thick and short course to the choriocapillaris. The choriocapillaris is thick and sinusoid-like, forming a dense network in the choroid. The ciliary body, iris and bulbar conjunctiva are supplied by the anterior ciliary arteries, which are branches of the long posterior ciliary arteries. Capillaries supplying the anterior margin of the ciliary process are large in diameter with an irregular bore, forming a thoroughfare channel draining blood in the ciliary arterioles into the pars plana vessels. Blood from the retina is drained by the central retinal veins. Venules from the anterior eye segment empty into the vortex veins via the pars plana vessels. Venous blood from the choroid is drained only by vortex veins via the choroidal veins. The functional significance of the vascular architecture and species differences are discussed.     

Microvasculature of the rat eye: scanning electron microscopy of vascular corrosion casts

Methylmethacrylate castings of the eye microvasculature were prepared from 10 Spargue-Dawley rats and studied by electron microscopy. The choroidal arterioles are larger in diameter than retinal arterioles, and have a shorter course to choroidal capillaries than retinal arterioles to retinal capillaries. Retinal capillaries are extremely thin in diameter and form a sparse retinal capillary network. The choriocapillaris is large and sinusoid-like, forming a compactly arranged network in the choroid. These differences in the microvasculature between the choroid and retina help explain the differences in ocular hemodynamics; that is, the blood flow in the choroid is faster than that in the retina. Capillaries of the iris show a zigzag configuration, which may be an accommodation for dilation and constriction of the pupil. Capillaries of the ciliary body are of large diameter forming leaf-like configurations, presumably to contribute to the secretion of the aqueous humor. Capillaries of the conjunctiva exhibit a somewhat coiled configuration, the arrangement of which reduce tension of the conjunctiva vessels caused by eyeball movement. Intra-arterial cushions, which control blood flow at the branching sites, are found in both choroidal or retinal arterioles.     

The vascular bed in the rabbit ear: microangiography and scanning electron microscopy of vascular corrosion casts

The vascular bed of the rabbit ear has been studied with light microscopy, microangiography and scanning electron microscopy of resin casts in a series of 20 ears. The major arteries supplying the ear were the central and rostral auricular branches of the caudal auricular artery. The caudal auricular branch was not observed, except as a small vessel supplying the rostral auricular base. The central auricular branch supplied blood to most of the auricular integument and was surrounded by capillaries extended from those supplying the skin. The periarterial capillaries formed a fine, compact network in the tunica media and were closely related to the central auricular branch. Evidence is presented suggesting that this vascular mechanism has a counter-current heat-exchange function for regulating body temperature. The artery had the well-developed internal elastic lamina and intimal cushions that regulate blood flow at the branching sites. A number of arteriovenous anastomoses were also observed between arterioles and venules, particularly in marginal regions of the ear. The intimal cushions and arteriovenous anastomoses might play an additional role in thermoregulation by regulating local blood flow in the ear.     

Microvasculature of the retina, ciliary processes and choroid in the North American raccoon (Procyon lotor) eye: a scanning electron microscopic study of corrosion casts

We have studied the vasculature of the retina, ciliary processes and choroid in the North American raccoon (Procyon lotor), a nocturnal mammal, using light and scanning electron microscopic examination of corrosion casts. We carried out an identical study in the crab-eating macaque (Macaca fascicularis), which forages only during the daytime, in order to compare the ocular vasculature with that of nocturnal mammals. Our observations in raccoons demonstrated a photoreceptor layer associated with rich lymph and a poorly vascularized retina. The meridian region of the eye, which lies in the horizontal plane and pass around the optic disc, had a markedly sparse capillary network. This horizontal sparse vascular band may correspond to a visual streak. Ciliary process capillaries were delicate, and formed a well-developed and compact network. Choriocapillaries were quite thin and formed a coarse capillary network. This contrasted with the dense retinal and well-extended choroidal capillary networks noted in the macaques. Our findings suggest that the sparse retinal capillary network in raccoons is extremely beneficial for photon capture, thereby allowing the raccoon to see well at night, as the retinal vessels restrict the inflow of photons toward the photoreceptors. The well-developed lymph probably compensates for the sparse retinal capillaries and choriocapillaries and nourishes the retina in the nocturnal raccoon.     

Functional anatomy of the footpad vasculature of dogs: scanning electron microscopy of vascular corrosion casts

Dogs are well adapted to cold climates and they can stand, walk and run on snow and ice for long periods of time. In contrast to the body trunk, which has, dense fur, the paws are more exposed to the cold due to the lack of fur insulation. The extremities have a high surface area-to-volume ratio, so they lose heat very easily. We offer anatomical evidence for a heat-conserving structure associated with dog footpad vasculature. Methylmethacrylate vascular corrosion casts for scanning electron microscopy, Indian ink-injected whole-mount and histological specimens were each prepared, in a series of 16 limbs from four adult dogs. Vascular casts and Indian ink studies showed that abundant venules were arranged around the arteries supplying the pad surface and formed a vein-artery-vein triad, with the peri-arterial venous network intimately related to the arteries. In addition, numerous arteriovenous anastomoses and well-developed venous plexuses were found throughout the dermal vasculature. The triad forms a counter-current heat exchanger. When the footpad is exposed to a cold environment, the counter-current heat exchanger serves to prevent heat loss by recirculating heat back to the body core. Furthermore, the arteriovenous anastomoses shift blood flow, draining blood to the skin surface, and the venous plexuses retain warm blood in the pad surface. Hence, the appropriate temperature for the footpad can be maintained in cold environments.     

Functional anatomy of the ocular circulatory system: vascular corrosion casts of the cetacean eye

OBJECTIVE: To examine the functional anatomy of the ocular circulation in four bottlenose dolphins (Tursiops truncatus) and five melon-headed whales (Peponocephala electra). PROCEDURE: Eyes were obtained postmortem from whales that died while in captivity and/or were found beached. Specimens from whales were investigated using scanning electron microscopy (SEM) of vascular corrosion casts and histology. The thermal characteristics of live dolphin eyes were measured using an infrared imaging system. RESULTS: The whale eye receives its primary blood supply from the ophthalmic rete, which extends just behind the eyeball. The ophthalmic rete diverges from the basilar rete and the cervical rete via the posterior thoracic artery. The iris and ciliary processes are supplied by iridic arteries via the major arterial circle that is located around the iris edge. The retinal vessels show the holangiotic type. Choroidal arteries run in parallel arrays so as to interdigitate the densely packed choroidal veins. The venules in the conjunctival fold and palpebral conjunctiva form a well-developed venous plexus. Thermographic examination revealed that the eye shows a substantially higher degree of thermal emission than adjacent skin areas. CONCLUSIONS: The cetacean eye is characterized by a unique vascular pattern and multivessel plexuses, which are quite different from those of terrestrial mammals. This suggests that the ocular vasculature might function as a thermoregulatory system so that the appropriate operating temperature for the photoreceptors can be maintained in a deep and cold aquatic environment. The distinctive plexuses in the orbit might also be for pooling blood in the eye to conserve oxygen during dives. The ophthalmic rete might play a role in a pressure-damping effect on cetacean ocular circulation as well.     

Tubular contents of equine dentin: a scanning electron microscopic study

The dentinal tubules of 20 permanent equine incisors were investigated by scanning electron microscopy. Occlusal surfaces and longitudinal fracture planes of both etched and undecalcified teeth were examined. Three different types of structure were observed inside the dentinal tubular lumen. Odontoblastic processes could only be visualized in the circumpulpal parts of the tubules. The more peripheral parts were empty or housed cylindrical structures that probably correspond to the laminae limitantes. Collagen fibres were frequently observed in the tubular lumina and were most numerous in the circumpulpal parts of the tubules.     

A scanning electron microscopic study of the vascular system of the bovine hind limb claw

The vascular organisation of the hind limb claws of clinically normal cattle was studied using scanning electron micrographs of plastic corrosion casts. The microvasculature of the dermal papillae and lamellae was demonstrated. A consistent vascular pattern was observed in the dermal papillae of the periople, coronary margin, sole and bulb. Ultrastructurally, the papillar vasculature consisted of a central artery and vein surrounded by a fine network of interconnected capillaries and venules. Arteriovenous anastomoses, connecting the central artery and vein, and peripherally situated arteriovenous loops were recognised in the terminal papillae of the white zone only. Arteriovenous anastomoses, focal enlargements and distension of the capillary bed were located within the interior half of the dermal lamellae. Numerous arteriovenous anastomoses were present throughout the entire dermis of the claw and were situated predominantly at the base of the dermal papillae and lamellae. The anastomoses and focal capillary enlargements may influence the blood flow in normal conditions and may play a significant role in the pathophysiology of bovine laminitis and sole ulceration.     

Light and scanning electron microscopic study on the blood vascular system of the donkey placenta

The donkey placenta is diffuse and epitheliochorial with numerous microplacentomes consisting of a fetal microcotyledonary and a maternal microcaruncular part. The microplacentomal vasculature during the last third of pregnancy has been investigated by light microscopy in comparison to scanning electron microscopy of the materno-fetal contact surface and corrosion casts of blood vessels after plastic instillation from either the microcotyledonary or the microcaruncular side, and, for the first time in a perissodactyle, from both sides. Morphological data were semiquantitatively evaluated. The supplying parts of both, the microcotyledonary and the microcaruncular vascular system are strictly proximo-distally oriented, thus reaching the capillary systems or working parts in the shortest way possible. The straight course of the vasculature, particularly on the fetal side, suggests the occurrence of venulo-arteriolar back diffusion. The fetal capillary system consists of convolutes confronting the maternal septal capillary complexes in a countercurrent way. This materno-fetal blood flow interrelationship is highly efficient in terms of placental exchange, which is further supported (1) by dilations and increasing coiling of the fetal venular capillary limbs in particular and (2) by a decrease in the interhaemal distance from 12.5 to 7.2 microm between the two capillary systems. Besides the countercurrent blood flow interrelationship, some maternal branch arterioles reach the septal capillary system from the maternally oriented pole of the microplacentome or microcaruncle, respectively, resulting in the less efficient crosscurrent blood flow. Hence, in the donkey placenta fetal and maternal blood vessels meet in a mix of countercurrent and crosscurrent flow patterns.     

Cellular architecture of the synovium in the tendon sheath of horses: an immunohistochemical and scanning electron microscopic study

The intimal lining cells of the synovium in joints have been studied morphologically and histochemically and shown to consist of macrophagic cells (type A) and fibroblast-like cells (type B). It is believed that the structure of the synovium in the tendon sheath is similar to that in the joint, but there have been only a few morphological studies of the tendon sheath. The present study revealed the cellular architecture of synovium in the tendon sheath of horses by histochemistry and scanning electron microscopy (SEM). Like the joint, the inner surface of the tendon sheath was covered with a cell-rich intimal layer. Acid phosphatase-positive A cells accumulated in the mesotendon but few in other regions. B cells were selectively immunolabeled with protein gene product (PGP) 9.5 antiserum and distributed in the entire length of the synovial intima in the tendon sheath. The synovial intima consisted of a surface layer rich in the processes of B cells and a deep layer containing cell bodies of B cells. Using SEM, B cells could be classified into two types according to the morphology of their processes. B cells of dendritic type were located mainly in the joint-side of the tendon sheath and extended branched processes to form a meshwork on the intimal surface. B cells of flat type were located in the skin-side of the tendon sheath and in the mesotendon. Their membranous processes extended in a horizontal direction and covered the intimal surface, resembling epithelium. It appears likely that the morphology and distribution of synovial intimal cells are influenced by various factors, such as the nature of the underlying tissues and the magnitude of mechanical stress.     

Vasculature of the ophthalmic rete in night herons (Nycticorax nycticorax): scanning electron microscopy of corrosion casts

Vasculature of the ophthalmic rete (rete ophthalmicum) in the night heron (Nycticorax nycticorax) was studied using scanning electron microscopy of vascular corrosion casts and light microscopy on tissue sections. Most blood to the eyeball and a lesser volume of blood to the brain passed through the ophthalmic rete via the external ophthalmic artery. The collateral retial arterioles originated from the external ophthalmic artery forming a flat and fusiform-shaped arterial network at the ventrotemporal region of the eyeball. The arterial network was intermixed with a similar complex of the veins from the eye. The ophthalmotemporal artery, which supplied the eyeball posteriorly, and supraorbital and infraorbital arteries, which supplied the eyeball anteriorly, originated from the rete. Blood from the eye, which is a site of potential heat loss, drained into the ophthalmic rete via the ophthalmotemporal vein. On the casts of retial arterioles, slit-like cleavages at branching sites representing flap valves, which might play a role as sluice valves, were seen. In addition, marks of circularly running grooves, which might represent tufts of smooth muscle cells and might contribute to a sphincter activity, were observed. These anatomical specializations of the avian ophthalmic rete, involving parallel arrangement of arteries and veins, may function to facilitate counter-current heat exchange and to regulate blood pressure and volume to the eye and the brain.     

Three-dimensional microvascolature remodeling study of pig periovulatory follicles using vascular corrosion casts

Veterinary Research Communications -     

Influence of biotin supplementation on pig claw horn: a scanning electron microscopic study

Observations made with a scanning electron microscope of the claw horn and underlying soft tissues of young pigs fed a normal diet supplemented with 1 mg d-biotin/kg of feed were compared with observations on a similar group receiving no additional biotin. Supplementary biotin affected the structure of the coronary epidermis; there was an increase in the density of the horn tubules in the stratum medium, the horny squames in the stratum medium were more tightly packed and the tubules were more clearly defined in the pigs receiving biotin. The width of the band of intertubular horn adjacent to the laminae was greater in the claws of control pigs.     

The distribution of intratubular dentine in equine incisors: a scanning electron microscopic study

The distribution of intratubular (peritubular) dentine was studied by scanning electron microscopy in 12 equine incisor teeth. High levels of intratubular dentine were found in the peripheral regions of the dentine. In these areas, a marked asymmetry occurred, as intratubular dentine was predominantly deposited onto the side of the dentinal tubular walls nearest to the dentino-enamel junction. The quantity and asymmetry of intratubular dentine were reduced towards the centre of the tooth. The significance of these variations in the amount and distribution of intratubular dentine between the different dentinal regions is discussed.     

A scanning electron microscopic study of the equine upper respiratory tract

The surface features of the upper respiratory tract of 20 clinically normal horses of various ages and types were studied with scanning electron microscopy. In the rostral part of the nasal cavity, there was a wide zone of non-ciliated epithelium whereas, caudally, the surface was well ciliated. This latter type of epithelium extended into the nasopharynx and guttural pouches although scattered areas of non-ciliated microvillous cells were also found.