Mineral and bone disorder of kidney disease, drawn as a map whose arrows say raises, suppresses or deposits, and whose dashed lines admit which links remain unproven. Searches like "mn 551 unit 8 assignment example", "mn551 unit 8 sample" and "mn551 unit 8 example" land here.
Mineral and Bone Disorder in Stage 4 Chronic Kidney Disease: A Concept Map With Labeled Connectors and a Defense of Its Hardest Links
[Student Name]
Purdue University Global
MN551: Advanced Physiology and Pathophysiology
Unit 8 Assignment
[Instructor Name]
[Date]
The patient is a composite built for teaching. No real patient is described.
The Case at the Center of the Map
The map is built around a composite 61-year-old retired machinist with stage 4 chronic kidney disease and an estimated glomerular filtration rate of 22 mL/min/1.73 m2. He reports generalized itching that keeps him awake and a dull ache in both shins. His laboratory values show phosphate 5.6 mg/dL, calcium 8.4 mg/dL, intact parathyroid hormone (PTH) 310 pg/mL, 25-hydroxyvitamin D 22 ng/mL and alkaline phosphatase 168 U/L. A plain film of his lower legs taken for the shin pain shows linear calcification along both superficial femoral arteries. Each of these findings appears as a node on the right side of the map, and every one of them can be followed leftward to a single starting point.
The Map, Column by Column
Key: a solid connector marks a link supported by strong human evidence; a dashed connector marks a link supported mainly by experimental models, keyed to its citation; a dotted connector marks a link whose mechanism remains poorly understood. Every connector carries a verb.
Column 1, initiating event. Falling nephron mass REDUCES filtered phosphate load (solid). This is the only node on the map with no arrow pointing into it.
Column 2, first responses. Phosphate retention STIMULATES osteocyte secretion of FGF23 (solid). FGF23 INCREASES phosphate excretion per remaining nephron (solid). FGF23 SUPPRESSES renal 1-alpha-hydroxylase (solid). Reduced 1-alpha-hydroxylase activity LOWERS calcitriol (solid). Falling nephron mass also REDUCES 1-alpha-hydroxylase capacity directly (solid).
Column 3, the parathyroid branch. Low calcitriol REDUCES intestinal absorption of calcium (solid). Low calcitriol RELEASES the parathyroid glands from vitamin D receptor inhibition (solid). Falling serum calcium STIMULATES PTH secretion through the calcium-sensing receptor (solid). Phosphate retention STIMULATES PTH secretion (solid). Sustained stimulation PRODUCES parathyroid hyperplasia (solid). PTH MOBILIZES calcium and phosphate from bone (solid), and this connector loops back into the phosphate retention node in column 2, closing a feedback cycle.
Column 4, outcomes. High PTH ACCELERATES osteoclastic bone resorption, producing high-turnover bone disease with the shin ache and raised alkaline phosphatase (solid). A raised calcium-phosphate product DEPOSITS mineral in the arterial media (solid). Phosphate CONVERTS vascular smooth muscle cells toward an osteoblast-like phenotype (dashed; Jono et al., 2000). FGF23 INDUCES left ventricular hypertrophy (dashed; Faul et al., 2011). FGF23 PROMOTES vascular calcification (dashed). Uremic toxins, PTH and mineral imbalance CONTRIBUTE to pruritus (dotted; Mettang & Kremer, 2015).
Reading the Map Backward From One Finding
The test of the map is whether any outcome can be followed leftward to the entry node without a gap. Take the shin ache. It sits on the high-turnover bone node in column 4, reached by the connector from high PTH. PTH is high for three reasons drawn in column 3: low serum calcium acting on the calcium-sensing receptor, phosphate retention acting on the glands directly, and low calcitriol releasing the glands from inhibition. Low calcitriol traces back to FGF23 suppressing 1-alpha-hydroxylase and to the lost renal mass that housed the enzyme. Both trace to falling nephron mass. Each step along that path carries a verb, so a reader following it learns how each node changes the next, not only that they are related.
The same test works for this patient's laboratory values. His phosphate of 5.6 mg/dL is high even though FGF23 has been increasing excretion per nephron for years, which tells the reader that at an estimated filtration rate of 22 the remaining nephrons can no longer excrete the load. His PTH of 310 pg/mL and alkaline phosphatase of 168 U/L sit on the parathyroid branch and the bone node. The map places every one of his numbers at the node that produces it. His 25-hydroxyvitamin D of 22 ng/mL adds a second, independent input to the calcitriol node, since the kidney cannot make calcitriol from substrate it does not have, and the map shows that input as a separate arrow rather than folding it into kidney loss.
Defending the Order of the Two Hormones
The first labeling decision a grader might question is why FGF23 and PTH sit in separate branches, with FGF23 drawn earlier. The answer is timing. In a large chronic kidney disease cohort, FGF23 rose as glomerular filtration fell before PTH or serum phosphate moved outside their normal ranges, which means the first detectable response to phosphate retention is FGF23 (Isakova et al., 2011). Drawing the two hormones on one line would imply they rise together and would hide the order that explains why phosphate stays normal for so long in early disease. FGF23 holds phosphate in range by increasing its excretion per nephron, at the cost of suppressing calcitriol. That cost is what sets the parathyroid branch in motion, so the map places the hormones in sequence, not in parallel.
The feedback loop is the second decision. PTH was drawn with an arrow returning to the phosphate node because PTH-driven bone resorption releases phosphate as well as calcium. In a kidney that can no longer excrete the extra load, the hormone that began as a response to mineral imbalance adds to the phosphate burden. A map without that arrow would describe a straight line where the physiology runs in a circle, and it could not explain why PTH keeps climbing in late disease.
Defending the Line Styles
The vascular calcification node receives two different arrows, and they are drawn differently on purpose. The arrow from the calcium-phosphate product is solid, because mineral deposition in the arterial media of patients with advanced kidney disease is well documented and fits this patient's radiograph. The arrow from phosphate to a change in the smooth muscle cells themselves is dashed. Jono et al. (2000) showed that raised phosphate drives cultured vascular smooth muscle cells to calcify through a sodium-dependent phosphate cotransporter, which makes the link plausible, but the evidence comes from cell culture rather than from people.
The FGF23 arrow to the heart is also dashed. Faul et al. (2011) produced left ventricular hypertrophy by giving FGF23 to rodents and linked higher levels to hypertrophy in a human cohort, but a direct causal effect in patients has not been established, and FGF23 rises alongside many other risks. Drawing that link as solid would overstate what is known. Pruritus is dotted because its mechanism remains uncertain; uremic toxins, immune dysregulation, the opioid system and mineral imbalance have each been proposed, and no single pathway explains most cases (Mettang & Kremer, 2015). The dotted line tells the reader that this patient's worst symptom is also the least understood.
The map also reflects current guidance on what to measure. The KDIGO work group describes the disorder as a combination of laboratory, bone and vascular abnormalities, which is why the right side of the map has three outcome nodes rather than one (Kidney Disease: Improving Global Outcomes CKD-MBD Update Work Group, 2017). Each of those nodes is visible in this one patient.
References
Faul, C., Amaral, A. P., Oskouei, B., Hu, M., Sloan, A., Isakova, T., Gutiérrez, O. M., Aguillon-Prada, R., Lincoln, J., Hare, J. M., Mundel, P., Morales, A., Scialla, J., Fischer, M., Soliman, E. Z., Chen, J., Go, A. S., Rosas, S. E., Nessel, L., ... Wolf, M. (2011). FGF23 induces left ventricular hypertrophy. Journal of Clinical Investigation, 121(11), 4393-4408. https://doi.org/10.1172/JCI46122
Isakova, T., Wahl, P., Vargas, G. S., Gutiérrez, O. M., Scialla, J., Xie, H., Appleby, D., Nessel, L., Bellovich, K., Chen, J., Hamm, L., Gadegbeku, C., Horwitz, E., Townsend, R. R., Anderson, C. A. M., Lash, J. P., Hsu, C.-Y., Leonard, M. B., & Wolf, M. (2011). Fibroblast growth factor 23 is elevated before parathyroid hormone and phosphate in chronic kidney disease. Kidney International, 79(12), 1370-1378. https://doi.org/10.1038/ki.2011.47
Jono, S., McKee, M. D., Murry, C. E., Shioi, A., Nishizawa, Y., Mori, K., Morii, H., & Giachelli, C. M. (2000). Phosphate regulation of vascular smooth muscle cell calcification. Circulation Research, 87(7), e10-e17. https://doi.org/10.1161/01.RES.87.7.e10
Kidney Disease: Improving Global Outcomes CKD-MBD Update Work Group. (2017). KDIGO 2017 clinical practice guideline update for the diagnosis, evaluation, prevention, and treatment of chronic kidney disease-mineral and bone disorder (CKD-MBD). Kidney International Supplements, 7(1), 1-59. https://doi.org/10.1016/j.kisu.2017.04.001
Mettang, T., & Kremer, A. E. (2015). Uremic pruritus. Kidney International, 87(4), 685-691. https://doi.org/10.1038/ki.2013.454
How this MN551 Unit 8 example is structured
The map is built so that any outcome can be followed leftward, arrow by labeled arrow, to the starting node, with no unlabeled line anywhere on the page. Connector verbs are specific: stimulates, suppresses, reduces absorption of, deposits in. Feedback is drawn explicitly, including the loop in which rising PTH mobilizes bone phosphate and worsens the retention it began responding to. Honesty is part of the design. Links with strong human evidence, such as FGF23 rising before PTH, are solid. Links supported mainly by experimental models, such as FGF23 acting directly on cardiac muscle or phosphate pushing vascular smooth muscle toward a bone-like phenotype, are dashed and keyed to a citation. Pruritus carries a dotted connector because its mechanism remains poorly understood. The narrative explains each line style and justifies the calls a grader is most likely to question.
Get an MN551 Unit 8 example written to your instructions
Name the condition your MN551 Unit 8 map must address; the prompt, any template and the rubric are the other three pieces. The first map is free, returned in 24-48h, with every connector labeled by a verb, feedback drawn where it exists, and line styles separating what is established from what remains debated. The paper above is an original model document written by our desk, not a submitted student paper and not an official Purdue University Global document.
MN551 Unit 8 questions, answered
What software should the map be drawn in?
Whatever your section accepts. Many students use a diagramming tool or presentation slides exported to PDF, and some sections allow a clear hand drawing photographed at good resolution. Format matters less than legibility: labels readable without zooming, arrows that do not cross ambiguously, and a key the grader can find.
How many nodes is right?
Enough to leave no step implied. For a condition like this one, twenty to thirty nodes usually carry the chain without crowding. An arrow hiding two events is better split, and three boxes saying the same thing are better merged. The test is whether each connector could be defended in one sentence.
Does the map need references?
Increasingly, yes, especially for links that are not textbook standard. A small citation key tied to numbered arrows is enough. The sample cites the disputed links specifically, since those are where a grader is most likely to ask for support, and leaves standard physiology unreferenced unless the rubric asks otherwise.