Exam 1 · Week 2 · BIO 280 Pathophysiology
M2 · Pathogens · Immunity · UTI
What each pathogen is, the two arms of immunity, what the white cell differential is telling you, and why UTI looks like confusion in an older adult.
▸M2Pathogens · Immunity · UTIWeek 2
💡 The one idea
The pathogen decides the treatment; the immune response decides the symptoms. Fever, swelling, pus and fatigue are not the organism — they are the body's answer to it.
Antibiotics work on bacteria. Nothing in that class touches a virus.
🦠 The pathogens
| Type | What it is | Treated with |
|---|---|---|
| Bacteria | Single-celled, no nucleus, reproduce on their own. Gram positive vs negative is a cell wall difference and it changes the drug. | Antibiotics |
| Virus | Genetic material in a coat. Not alive on its own — it must hijack a host cell to reproduce. | Antivirals; mostly supportive |
| Fungi | Yeasts and molds. Thrive when normal flora or immunity is knocked down — after antibiotics, in diabetes, in immunosuppression. | Antifungals |
| Parasites | Protozoa and helminths; live on or in a host at its expense. | Antiparasitics |
| Prions | Misfolded protein. No genetic material at all, and not destroyed by normal sterilization. | None |
Giving an antibiotic for a viral illness does not help and it breeds resistance. This is the most commonly tested point in the whole module.
🛡️ Two lines of defense
- Innate (non-specific) — born with it, responds in minutes to hours, the same way every time, no memory. Skin and mucous membranes, stomach acid, normal flora, the inflammatory response, fever, complement, neutrophils, macrophages, natural killer cells.
- Adaptive (specific) — learned, takes days the first time,
and it remembers. This is why the second exposure is milder, and it is what
vaccines are for.
- Humoral — B cells → plasma cells → antibodies. Works on things outside the cell: bacteria, toxins, free virus.
- Cell-mediated — T cells. Works on things inside the cell: virally infected cells, cancer cells, transplanted tissue. Helper T (CD4) directs; cytotoxic T (CD8) kills.
IgM is the first antibody to appear — it means a current infection. IgG comes later, stays for years, and crosses the placenta — it means past infection or immunity.
⭐ Reading the differential
| Cell | Share | Raised means |
|---|---|---|
| Neutrophils | ~55–70% | First responder. High = bacterial infection. |
| Lymphocytes | ~20–40% | B and T cells. High = viral. |
| Monocytes | ~2–8% | Become macrophages. High = chronic infection, TB. |
| Eosinophils | ~1–4% | Allergy and parasites. |
| Basophils | <1% | Release histamine — allergic and inflammatory. |
Never eat butter, better eat bacon — Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils, in descending order.
A left shift means immature neutrophils (bands) are being pushed out early. The marrow is being emptied faster than it can mature cells — that is a severe bacterial infection.
🚨 Neutropenia — the fever is the emergency
In a neutropenic patient a single temperature of 38°C /
100.4°F is a medical emergency, even if they look well.
With too few neutrophils there are not enough cells to make pus, redness or swelling. The usual signs of infection are absent. Fever may be the only thing the body can still produce — so it gets treated as sepsis until proven otherwise.
🦶 Urinary tract infection
E. coli causes the large majority, and it arrives from the perineum. Women are affected far more often because the female urethra is short and close to the anus.
| Lower (cystitis) | Upper (pyelonephritis) | |
|---|---|---|
| Where | Bladder, urethra | Kidney |
| Signs | Dysuria, frequency, urgency, suprapubic pain, cloudy or foul urine | Fever, chills, flank / CVA tenderness, nausea, vomiting |
| Severity | Uncomfortable | Can scar the kidney and seed the blood |
Urinalysis: positive leukocyte esterase (white cells present) and positive nitrites (gram-negative bacteria converting nitrate). Culture identifies the organism and its sensitivities — culture before antibiotics.
⭐ In an older adult, UTI looks like confusion
New confusion, falling, or a sudden functional decline in an older adult is a UTI until proven otherwise — often with no dysuria, no urgency and no fever at all. The blunted immune response and altered temperature regulation take the classic signs away.
Sudden change in mental status in an older adult → check the urine.
🎯 Module quiz
Questions for this module.
Nothing here yet — drop it in when you have it