Note how the proportion of acidophilic (eosin positive cytoplasm), basophilic (h

Question

Note how the proportion of acidophilic (eosin positive cytoplasm), basophilic (hemotoxylin positive cytoplasm), and clear cells differ between the lobes. It may be necessary to examine under 10X or 20X power to view acidophil and basophil staining. Lactotrophs (secrete PRL) and somatotrophs (secrete GH) are acidophillic, and gonadotrophs (secrete LH & FSH) and thyrotrophs (secrete TSH) are basophilic. Corticotrophs (secrete ACTH) are either mildly basophilic or clear. Neurons that produce oxytocin and vasopressin (ADH) have clear cytoplasm under H&E staining. Under 10X or 20X objectives, compare and contrast the relative volume of the three pituitary lobes within the cheetah and rat: 6.1. In each of the species, compare the relative size of the lobes within the pituitary gland: a) Which of the 3 lobes is the largest within that species (relative to its other lobes)? For example, is the anterior lobe the largest in both species? 2 points 6.2. Based on your examination of the pituitary glands, which species would you predict would have the best capability for kidney water retention? Briefly explain what about the pituitary gland histology lends support to your hypothesis? 2 points

Explanation / Answer

The pituitary gland controls the function of the kidney. The anterior lobe of the pituitary accounts for nearly 80% of the pituitary while the rest is the posterior lobe. The anterior lobe produces the hormones: growth hormone, thyroid stimulating hormone, adrenocorticotropic hormone (ACTH), follicle stimulating hormone, luteinizing hormone, prolactin, endomorphins, enkephalins, and beta melanocytes stimulating hormone. The ACTH hormone acts on the adrenal gland and induces synthesis of cortisol. Posterior lobe produces vasopressin and oxytocin.

The hormone vasopressin or anti-diuretic hormone (ADH) is involved in water retention in kidneys. ADH is the anti-diuretic hormone in human body. ADH in involved in hydro-osmotic effect wherein it promotes the reabsorption of water from the tubular fluid in the collecting duct of the kidneys. ADH has not much effect on rate of Na+ reabsorption. ADH also cause vasoconstriction in the arterioles and increases the arterial blood pressure.

Normally, ADH is secreted by hypothalamus when there is increased osmolarity in serum and then transported to the posterior pituitary gland. Hyperosmolarity and depletion of circulating volume, sensed by Osmoreceptors and baroreceptors respectively trigger ADH secretion. Osmoreceptors are present in hypothalamus while baroreceptors are present in the carotid sinus, aortic arch, and left atrium.ADH travels via the circulatory system to kidneys and binds vasopressin/ADH receptors on the distal convoluted tubule. As a result, aquaporin channels move from cytoplasm to apical membrane of the tubules. Water is reabsorbed out of the collecting ducts through these channels into the bloodstream. As s result, there is increased osmolarity of urine excreted. Decreased serum osmolarity cause reduction of ADH secretion.

The Cheetah has larger lobes than the rat (I presume it includes the posterior lobes as well as per your experimental results. If not, please check which species has larger posterior lobe and change accordingly). The Cheetah will therefore have better water retention capacity in kidneys. The number of neurons that produce oxytocin/ vasopressin should be higher in the cheetah than the rat as the posterior lobe is enlarged. These neurons will have a clear cytoplasm when observed with Haemotoxylin Eosin staining. It may not be possible to distinguish between oxytocin and vasopressin-secreting neurons as both have a clear cytoplasm. These are non-myelinating axon containing neurons. The eosin will lightly (nearly white-pinkish cytoplasm) stain these neurons. Only immunostaining with specific antibodies to ADH and oxytocin will confirm which hormones are produced by which neurons in posterior pituitary.

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