National Licensure Examination for Veterinarians Veterinary Histology, Embryology & Developmental Anatomy: practice questions

D. Blue or green

Masson's trichrome colours collagen blue or green (depending on the fibre stain used) and muscle and cytoplasm red, which is why it is used to assess fibrosis. Red collagen is the result with van Gieson's stain, where muscle is yellow; black fibres are seen with silver or Verhoeff's elastic stain.

Further reading: Bancroft's Theory and Practice of Histological Techniques

D. Six connexin subunits

A connexon is a hexamer of six connexins; two connexons in apposed membranes form one channel. Twelve is the number of connexins in a complete channel (two connexons), which is the common slip; claudins belong to tight junctions and cadherins to adherens junctions and desmosomes.

Further reading: Eurell and Frappier, Dellmann's Textbook of Veterinary Histology

D. Pseudostratified columnar ciliated epithelium with goblet cells

The conducting airway is lined by pseudostratified columnar ciliated epithelium with goblet cells, the mucociliary escalator. It looks layered because nuclei are at different heights, but every cell touches the basement membrane. Stratified squamous epithelium is found in the nasal vestibule and pharynx; transitional epithelium lines the urinary tract.

Further reading: Eurell and Frappier, Dellmann's Textbook of Veterinary Histology

A. Monocyte-macrophage lineage

Osteoclasts form by fusion of precursors of the monocyte-macrophage lineage from bone marrow, which is why they are multinucleated and TRAP-positive. Osteoprogenitor cells of mesenchymal origin give rise to osteoblasts and osteocytes, the tempting but wrong choice.

Further reading: Eurell and Frappier, Dellmann's Textbook of Veterinary Histology

A. Camelids such as camels, llamas and alpacas

Camelids are the only mammals with oval erythrocytes; like other mammalian red cells they lack a nucleus. Birds and reptiles also have oval red cells, but theirs are nucleated. Horse and cat red cells are round discs that form rouleaux; goat red cells are round and very small.

Further reading: Eurell and Frappier, Dellmann's Textbook of Veterinary Histology

B. Horses do not release reticulocytes into the blood, even during regeneration

Unlike dogs and cats, horses retain reticulocytes in the marrow until they mature, so their absence in blood does not rule out regeneration; marrow aspiration or serial red-cell indices are needed to judge the response. Concluding aplasia from the blood smear alone is the classic error.

Further reading: Eurell and Frappier, Dellmann's Textbook of Veterinary Histology

C. Allantoic cavity

Influenza and Newcastle disease viruses grow to high titre in the allantoic cavity, and the allantoic fluid is harvested and tested by haemagglutination. The chorioallantoic membrane is used for poxviruses, which produce pocks, and the yolk sac for chlamydiae and rickettsiae.

Further reading: McGeady et al., Veterinary Embryology; Noden and de Lahunta, The Embryology of Domestic Animals

D. Placental vascular anastomosis exposes the female twin to male hormones and cells

In the freemartin, the chorioallantoic circulations of the twins fuse early in gestation, so anti-Mullerian hormone and cells from the male reach the female; her gonads and Mullerian derivatives fail to develop and her vagina is short. Her blood shows XX/XY leucocyte chimerism, which is used for diagnosis.

Further reading: Zachary, Pathologic Basis of Veterinary Disease

C. Molecular, Purkinje cell, granular

The cerebellar cortex has an outer molecular layer, a single row of Purkinje cells, and an inner granular layer packed with granule cells. Pyramidal cells are the output neurons of the cerebral cortex, which has six layers.

Further reading: Eurell and Frappier, Dellmann's Textbook of Veterinary Histology

A. Interventricular foramina, third ventricle, aqueduct, fourth ventricle, lateral apertures

CSF made mainly by the choroid plexuses flows from the lateral ventricles through the interventricular foramina to the third ventricle, through the mesencephalic aqueduct to the fourth ventricle, and out through the lateral apertures into the subarachnoid space, where arachnoid villi absorb it. Obstruction at the narrow aqueduct causes hydrocephalus.

Further reading: de Lahunta, Veterinary Neuroanatomy and Clinical Neurology