Upper Gastrointestinal Tract
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How are bones formed?
As estrus progresses, the edema in the endometrial folds wanes so that it is minimal by the time of ovulation. After ovulation and development of the corpus luteum, the uterus is stimulated by progesterone , uterine tone increases, and the endometrial folds are no longer edematous. After 14—18 days of gestation, the endometrial folds are not readily palpable because of the gradual but marked increase in uterine wall thickness.
The length, width, and tone of the cervix are palpable per rectum; however, complete evaluation of the cervix requires direct palpation per vagina see Vaginal Examination. A cervical evaluation also serves as a bioassay, because the cervix changes in response to the steroid hormone status of the mare. During anestrus, ovarian steroid serum concentrations are low, and the cervix is either short, thin, and open or closed but readily opened.
After the first ovulation of the season and during subsequent periods of diestrus, serum progesterone concentrations are increased and the cervix is closed, with a long cylindrical shape. During estrus, serum progesterone concentrations are low, and estrogen concentrations are high; the cervix is relaxed and edematous. Visual speculum vaginal examination will allow further assessment of the character of the cervix. Urine in the vagina urovagina may be seen sporadically or be a chronic problem.
Mares with urovagina may have an abnormal voiding pattern, and the endometrium may show histologic evidence of chronic irritation. The neck of the bladder can be used to indicate the caudal boundary of the vagina during ultrasonography. The vagina can be imaged dorsal to the bladder and examined for any accumulation of echogenic fluid caudal to the cervix. A definitive diagnosis of urovagina requires direct observation of urine in the vagina via vaginoscopy.
Before an endometrial swab is taken, the nonpregnant status of the mare must be confirmed because the swabbing could lead to termination of a pregnancy see Pregnancy Determination in Horses. The perineum is cleansed with povidone-iodine scrub, rinsed, and dried. The operator dons a sterile sleeve or clean examination sleeve with the hand encased in a sterile glove.
A water-soluble lubricant free of bacteriostatic chemicals is placed on the back of the hand and lower arm. When obtaining an endometrial swab sample, the vestibule, vagina, and cervix must be passed. Care must be taken to avoid contamination of the swab by microorganisms in the structures caudal to the uterus that would hinder accurate interpretation of the culture results.
A double-guarded occluded uterine swab is gently guided through the cranial end of the cervix. Once inside the uterine body, the inner guard is advanced from the outer guard, and the swab is exposed to the uterine lumen for 30—60 sec. The swab tip is withdrawn into the inner guard, which is then withdrawn into the outer guard before the entire swabbing instrument is removed from the uterine body.
The swab tip is carefully placed into a transport system, which is vital to maintain viability of the organisms from the time of sample collection until aerobic culture in the laboratory. Stuart's carrier medium may maintain microorganisms for as long as 72 hr if stored at ambient temperature. A second endometrial sample may be taken immediately after the first or simultaneously with a uterine swab or cytology brush. This sample is then evaluated cytologically by rolling it onto a glass microscope slide, fixing and staining with a Romanowsky-type stain, and viewing it microscopically for evidence of neutrophils, debris, and microorganisms.
A low-volume uterine lavage can be performed in mares with negative culture results despite obvious clinical signs of endometritis.
Sterile saline 60— mL is infused into the uterus using a closed system with a small uterine catheter. Oxytocin 20 IU, IV is administered to enhance uterine evacuation. The effluent is collected by gravity flow into a sterile centrifuge tube and then centrifuged. The pellet is then swabbed, placed into transport media, and submitted for aerobic culture.
A second swab can be made of the pellet for cytologic examination after staining. In most cases, the mixed growth of a few miscellaneous microorganisms is not significant. A heavy growth of any microorganism should be considered significant unless obvious contamination has occurred. Clinical signs must be correlated with culture results to determine clinical significance and to develop a therapeutic plan. Isolation of an organism transmitted venereally, such as Taylorella equigenitalis requires a special culture system and certain strains of Pseudomonas and Klebsiella spp, is considered a significant finding.
Occasionally, microorganisms causing a pyometra may not be detected on aerobic culture, because products of the inflammatory reaction prohibit their growth. Aerobic culture results of the endometrial swab should be used as a diagnostic adjunct and not as the sole determinant in diagnosing a uterine infection. A positive culture result must be accompanied by evidence of inflammation for the diagnosis of endometritis to be made.
Mares exhibiting clinical signs of infection uterine fluid as seen on ultrasonographic examination per rectum, tail matting or uterine discharge, and the presence of inflammatory cells seen on a stained smear from a uterine sample with a positive endometrial swab are likely to have endometritis.
Inflammation seen on histologic evaluation of the endometrium confirms the diagnosis of endometritis. In these cases, the culture results are useful in determining the sensitivity of the causative microorganism and developing an antimicrobial treatment plan.
The following antibiotics see Table: Intrauterine Antibiotics for Use in Mares have been used for daily 3—7 days uterine infusion by diluting with sterile saline to an infusion volume of 60— mL.
Systemic administration of antibiotics may be considered if the microorganism, management situation, and ease of treatment indicate. Two doses of long-acting ceftiofur crystalline free acid 6. Gentamicin sulfate diluted with 20 mL sodium bicarbonate and 20 mL saline. An endometrial biopsy sample is usually obtained immediately after the endometrial samples have been procured.
It should be kept in mind that manipulation of the endometrium can quickly cause a neutrophilic response in the endometrium. Preparation for biopsy is the same as for taking a swab see above. The basket of the biopsy instrument should be kept closed during positioning to prevent accidental procurement of vagina, cervix, or examination glove. The instrument is manually guided with the gloved hand through the caudal genital tract into the uterine lumen.
While keeping the instrument in place within the uterus with the nongloved external hand, the gloved hand is carefully withdrawn from the genital tract and inserted into the rectum to allow positioning of the basket of the biopsy instrument at the ventral luminal surface of the base of a uterine horn.
The instrument jaws are then opened, the uterine wall is pressed into the side of the basket, and the jaws are closed. The jaws should be kept closed while the instrument is withdrawn from the genital tract. It is not unusual for a small amount of uterine bleeding to occur after biopsy. The biopsy procedure is not detrimental to fertility, and a mare can conceive from a breeding that occurred during an estrus when biopsy was performed.
The luminal contents may indicate the presence of uterine fluid or exudate. Epithelial cell height is related to hormone status; cells are cuboidal during anestrus and low to tall columnar during the breeding season.
Transepithelial cells may indicate active inflammation. The pattern, character, and location of inflammation indicate the chronicity of response—neutrophils indicate an acute reaction, and lymphocytes and plasma cells indicate a chronic reaction.
Focal or diffuse cellular distribution pattern, frequency of inflammatory cells, and degree of infiltration slight to severe relate to severity of inflammation.
Histologic evidence of significant inflammation, combined with a report of growth of microorganisms from aerobic culture of endometrial swab and the presence of clinical signs of infection uterine fluid, uterine discharge , support the decision that an endometrium would benefit from therapy to decrease inflammation.
Knowledge of the pattern of distribution and severity of periglandular fibrosis is prognostically useful. Periglandular fibrosis may interfere with endometrial gland function and may be a factor causing early embryonic death. Glandular distention normally develops during pregnancy, but widespread cystic glandular distention in the nonpregnant mare is undesirable.
Cystic glandular distention is often associated with periglandular fibrosis and may result from an accumulation of gland secretions proximal to the occlusion of the endometrial gland by periglandular fibrosis.
Endometria are classified in four categories that attempt to predict ability to carry a foal to term. Category I indicates no significant changes are present in the endometrium, and no treatment is required.
An endometrium with any notable periglandular fibrosis cannot be classified as Category I. Models should include labels. Students' respiration models should be completed independently and demonstrate their understanding of the respiratory system. As students work, walk around the room and support students. Answer questions and offer suggestions.
Share and display models. Extensions Practice vocabulary words by playing 'Password' with students. Make full-body models to show how other systems interact with the respiration system. Ask students to write a creative writing piece from the perspective of oxygen traveling throughout the body. Related Lessons Diffusion in the Respiratory System: Register to view this lesson Are you a student or a teacher?
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