Objective Data Leading to a Proctosigmoiditis Diagnosis

Scenario
A.O. is a 28-year-old woman who presents to your clinic with complaints of rectal bleeding and weakness. Five days ago, she noticed bright red blood in her stools. Furthermore, she reports that her daily bowel movements have increased to five or six with significant diarrhea. She has been weak for approximately three days. She has not traveled outside of the city, been hospitalized, or received antibiotics recently.
A proctosigmoidoscopy was conducted three days after the patient's discharge from the acute care clinic. A significant pseudopolyps formation could be seen. Biopsies of the colon revealed erosions of the mucosa and ulcerations into the submucosa with mixed acute (i.e., neutrophils) and chronic (lymphocytes and macrophages) inflammatory cells. No dysplastic cells suggesting the development of colon carcinoma were seen. No multinucleated giant cells suggesting Crohn's disease were seen. Inflammation and ulceration were limited to the rectum and sigmoid colon only. Crypts of Lieberkühn were intensely inflamed. Marked hemorrhaging of capillaries in the mucosa was also observed.
Laboratory Blood Test Results
Na+ = 143 meq/L
BUN = 20 mg/dL
Plt = 315,000/mm3
AST = 33 IU/L
K+ = 3.2 meq/L
Cr = 1.1 mg/dL
PO4-3 = 4.0 mg/dL
ESR = 24 mm/hr
ALT = 41 IU/L
Cl- = 108 meq/L
Hb = 10.8 g/dL
CRP = 1.5 mg/dL
T bilirubin = 0.9 mg/dL
Alb = 3.1 g/dL
HCO+3 = 18 meq/L
Hct = 36%
Ca+2 = 8.9 mg/dL
PT = 11.3 sec
Glu, fasting = 132 mg/dL
WBC = 9,400/mm3
Questions
What is the relevance of the last sentence in the first paragraph: "She has not traveled outside of the city, been hospitalized, or received antibiotics recently"?
Explain your answer in detail.
What is the diagnosis? Explain your answer. Why and how did you come up with this diagnosis?
Identify eight abnormal laboratory blood test values and provide a brief pathophysiological explanation for each of them.