Anal Special †Nr. 12
Additional file 2: Simple logistic regression analyses of the factors associated with ever seeking medical advice for rectal bleeding and change in bowel habit. Simple logistic regression analyses of socio-demographic, clinical and psychosocial factors association with early medical advice seeking. (DOCX 25 KB)
Anal Special – Nr. 12
Phylum From this point on, all animals covered in the Zoo Lab website have primary bilateral symmetry and are triploblastic, that is, three true germ layers (the ectoderm, mesoderm and endoderm) are formed during gastrulation of the blastula stage of development. While radial symmetry may be well suited for sessile or slow-moving forms, animals that are active in seeking food, shelter and mates require a new body plan. Bilateral symmetry coupled with cephalization solves these problems. The anterior end moves forward and the posterior follows. The dorsal side is kept facing up and the ventral side is kept down and usually specialized for locomotion.The bilateral grade of metazoans is further subdivided into two main divisions: the protostomes and deuterostomes, which are separated on the basis of a number of embryological differences. Evidence from sequence analysis of the small-subunit ribosomal gene suggests that some time after ancestral deuterostomes and protostomes diverged from one another during the Cambrian period, protostomes split into two large groups (superphyla), the Ecdysozoa and Lophotrochozoa. In this lab we will examine one acoelomate lophotrochozoan phylum and several smaller pseudocoelomate and eucoelomate lophotrochozoan phyla.
The Phylum Platyhelminthes contains over 20,000 free-living and parasitic species of acoelomate animals called flatworms. In flatworms, the body that is flattened dorsoventrally, with the mouth and genital pore usually located in a ventral position. The space between the gut and outside is filled with mesodermal muscle fibers and undifferentiated parenchyma. Although fluid-filled spaces in the parenchyma serve as a hydrostatic skeleton for support and to aid in internal transport, the animals lack a body cavity, which is why they are called acoelomate. Most free-living flatworms have a gastrovascular-type digestive system (a mouth is present but no anus), while parasitic forms generally have no digestive system.Flatworms have a centralized nervous system consisting of pair of cerebral ganglia and longitudinal nerve cords connected to transverse nerves. The excretory system (absent in some forms) consists of two lateral canals with protonephridia bearing flame cells. Although many flatworms are free-living, the phylum includes some very important parasitic species as well.In terms of reproduction, flatworms can reproduce sexually or asexually. Most species are monoecious but practice cross fertilization. Many freshwater turbellarians can reproduce asexually by fission in which the animal simply divides into two halves, each of which regenerates the other half. In some turbellarians (as it is in most other animals), the yolk that provides nutrition for the developing embryo is containing within the egg cell itself, a condition described as endolecithal. In the monogeneans, trematodes and cestodes (as well as in a few turbellarians), yolk is contributed by cells released from organs called yolk glands, and the eggs are therefore described as ectolecithal. Development may be direct or indirect.
The Phylum Acanthocephala contains about 1,000 species of parasitic animals called spiny-headed worms, all of which are endoparasites in the intestinal tracts of vertebrates (especially fishes). Two hosts are required to complete the life cycle, and the juveniles are parasites of crustaceans and insects. Most species are quite small (less than 40 mm). Spiny-headed worms have an eversible proboscis covered with recurved spines that provides a means of attachment in the host's intestine. Eggs pass out host and are eaten by certain insects or crustaceans where they hatch and go through several developmental stages. When the intermediate host is eaten by a bird, mammal or fish, the larva inside attaches to the intestinal wall with its spiny proboscis.
This slide shows a stained whole mount of the Oriental liver fluke (Clonorchis sinensis), an important trematode parasite of the humans in many regions of Asia, especially China, Southeast Asia and Japan. Humans are infected by eating raw or poorly cooked fish containing the encysted metacercariae. After being ingested, these cysts dissolve in the intestine, releasing the young flukes which then migrate to the bile duct and liver.
This slide contains stained sections of the dog tapeworm Diplydium caninum taken from four different regions. The anterior most portion contains the scolex, a specialized attachment organ that often contains hooks and/or suckers. The rest of the body is divided into a linear series of segments called proglottids, each of which contains a complete set of reproductive organs. The youngest proglottids in the first part of the strobila (body) of the tapeworm are immature, while those in the middle are mature. The oldest terminal proglottids are gravid, which means they are filled with eggs. Dogs and cats can become infected by eating adult fleas (the intermediate hosts) containing cysticercoid larvae.
This slide shows several zooids of the freshwater ectoproct Plumatella. Note the conspicuous lophophores. These feeding devices consist of masses of ciliated tentacles borne on ridges surrounding the mouth. In addition to reproducing by budding, freshwater bryozoans reproduce asexually by means of special resistant bodies called statoblasts (not visible on this slide). These dark, disc-shaped structures (which are similar to the gemmules of freshwater sponges) are produced during the summer and fall, and can remain dormant until environmental conditions improve in the spring.
This slide shows a pair of adult blood flukes in copulation. Blood flukes differ from most other flukes by being dioecious (i.e., having separate sexes). Males are larger and have a large, ventral groove called a gynecophoric canal posterior to the ventral sucker that holds the smaller (more darkly stained) female during copulation, which is continuous. Schistosoma mansoni is one of the three species of blood flukes responsible for the disease in humans called schistosomiasis. Humans get infected when the tailed cercaria larvae (which escape from freshwater snails that serve as their intermediate hosts) burrow into the exposed skin of individuals bathing, swimming or working in such habitats.
This 60-year-old female presented with a 2-month history of headache, vertigo, amnesia. A right brachio-crural hemiparesis, right homonymous hemianopsia and sensorial dysphasia was evident. A CT scan revealed a left occipital lesion. MRI scan was not performed because the patient had an anal sphincter stimulator. Three years before thyroidectomy for a follicular carcinoma was performed. A total body CT scan was negative. A left occipital craniotomy was carried out and a solid mass was totally excised. A diagnosis of GNB was made from histopathological examination and immunohistochemistry. Post-operatively the patient recovered from the hemiparesis while the visual disturbances persisted. She underwent fractioned radiotherapy (60 Gy) and chemotherapy with Temozolomide. She remained disease free 18 months after diagnosis. A CT scan showed no evidence of recurrence. 041b061a72