The Systems Integration Case File

Front matter · The progressive project · ~15 minutes · Read before Chapter 1

Everyone who has ever taught this course has watched the same thing happen. A student can define cardiac output on Monday and glomerular filtration rate on Wednesday, and on Friday cannot explain why a failing heart makes the kidneys hold on to salt. The definitions are not the problem. The wiring between them is.

What this project is

Across the thirty-three chapters of this book you will build one thing: a complete, mechanistically connected model of a single human body under stress.

You build it six sentences at a time. Every chapter ends with a Case File entry that gives you new findings about one family and asks you to add the system you just learned to the model you already have. The entries accumulate. By Chapter 33 you will hold something most students do not assemble until their second clinical year — an integrated picture in which a change in one organ propagates, predictably, through all the others.

The rule that makes it work: every entry must connect the new system to at least two systems you have already added. Not "the kidney filters blood." Instead: "the kidney filters blood, and its filtration rate depends on the arterial pressure the heart generates (Ch. 18–19), and it adjusts that pressure by secreting renin, which through angiotensin II constricts arterioles and through aldosterone retains sodium, which raises blood volume, which raises preload, which raises the workload on a heart that is already failing."

That sentence is the entire skill. You will be able to write dozens like it.

The family

All four people below are fictional composites created for teaching. Their findings are constructed to illustrate normal physiology and its predictable failures; they are not case reports, and nothing about them is medical advice.

                        THE OSEI–BARRETT FAMILY
                   (all persons fictional; for teaching only)

   ADWOA MENSAH, 78 (she/her) ──────────┐
   Amara's mother. Lives independently. │
   Osteoporosis · presbycusis ·         │  ← the LIFESPAN thread
   cataract · mild cognitive change     │     (Ch. 5,6,15,25,30)
   The aging thread.                    │
                                        │
        ┌───────────────────────────────┘
        │
   AMARA OSEI, 45 (she/her) ─────────────────────────  THE INDEX PATIENT
   Charge nurse, night shift, 20 years. 5'5", 176 lb.  ← appears in ALL 33
   Presents Ch. 1 with chest discomfort + dyspnea.        chapters
   Story arc: metabolic syndrome → coronary disease
   → NSTEMI → heart failure with preserved EF
   → chronic kidney disease stage 3 → rehabilitation.
        │
        ├──────────────────────┐
        │                      │
   NIA OSEI-BARRETT, 24        TOBIAS "TOBY" REYES, 19 (he/him)
   (she/her)                   Amara's nephew. College soccer.
   Amara's daughter.           ACL rupture, Ch. 8.
   Marathon runner, PT         ← the MUSCULOSKELETAL and
   student. Pregnant from        EXERCISE thread
   Ch. 28.                       (Ch. 6,7,8,9,10,32)
   ← the EXERCISE and
     REPRODUCTIVE thread
     (Ch. 9,18,19,22,24,27,28,32)

Figure FM.3 — The Osei–Barrett family and the four narrative threads.

Described: A family diagram of four fictional people. Adwoa Mensah, 78, is Amara's mother and carries the aging thread through Chapters 5, 6, 15, 25, and 30. Amara Osei, 45, is the index patient who appears in all thirty-three chapters; she is a night-shift charge nurse whose story arc runs from metabolic syndrome through coronary disease, a non-ST-elevation myocardial infarction, heart failure with preserved ejection fraction, and stage 3 chronic kidney disease, to rehabilitation. Her daughter Nia Osei-Barrett, 24, is a marathon runner and physical therapy student who carries the exercise and reproductive threads and becomes pregnant in Chapter 28. Her nephew Tobias Reyes, 19, is a college soccer player who ruptures an anterior cruciate ligament in Chapter 8 and carries the musculoskeletal thread.

Amara Osei — the index patient

Forty-five years old. Charge nurse on a medical–surgical floor; twenty years of rotating night shift. Five feet five inches, 176 pounds (BMI 29.3). Two children. Her mother has osteoporosis and hypertension; her father died at 58 of a myocardial infarction.

She has known for three years that her blood pressure runs high and that her fasting glucose was "a little up" at her last physical, which was two years ago. She has not had time. Nurses famously do not.

In Chapter 1 she finishes a twelve-hour shift, feels a pressure in her chest that she attributes to reflux, and finally — after her daughter refuses to let it go — walks into her own emergency department.

Everything after that is physiology.

The canonical numbers

These values are fixed across the whole book. If a chapter contradicts one of them, that is an error — please report it.
Triage vitals (Ch. 1) BP 168/98 · HR 104 · RR 24 · T 36.8 °C · SpO₂ 96% · cool, pale, diaphoretic
Peak troponin I (Ch. 3, 18) 4.1 ng/mL at 12 hours
Diagnosis (Ch. 18) NSTEMI; 90% proximal left circumflex stenosis, stented
Ejection fraction (Ch. 18) 48%, with grade 2 diastolic dysfunction
HbA1c (Ch. 2, 16) 7.4% on admission → 6.6% at 18 months
eGFR (Ch. 26) 46 mL/min/1.73 m² — stage 3a CKD
Adwoa's DEXA T-score (Ch. 6) −2.9 at the femoral neck

The arc, chapter by chapter

You do not need to read this table now. It is here so you can see that the story is designed, not improvised, and so you can look ahead when a thread interests you.

Ch System added What happens in the Case File
1 Orientation, homeostasis Amara presents. Vital signs. Anatomical language for her symptoms. Which homeostatic variables are off?
2 Chemistry Her first labs. Electrolytes, glucose, lipids, pH. What each number is, chemically.
3 Cells Troponin appears in her blood. Why is a protein that belongs inside heart cells outside them?
4 Tissues What tissue types are dying, and what will replace them. Scar is not muscle.
5 Integumentary Cool, pale, diaphoretic skin — the first visible sign of a cardiovascular problem. Adwoa's fragile skin.
6 Bone tissue Adwoa's DEXA scan. Amara's vitamin D. Bone as the body's calcium bank.
7 Skeleton Amara's sternum, ribs, and why chest pain localizes so badly. CPR anatomy.
8 Joints Toby ruptures his ACL. Why intra-articular ligaments do not heal.
9 Muscle physiology Cardiac vs. skeletal muscle. Why heart muscle cannot be replaced. Statin myopathy risk.
10 Muscular system Cardiac rehabilitation begins. Which muscles, which loads, and why Valsalva is forbidden.
11 Neurons Why her chest pain radiated to her jaw and left arm. Referred pain, explained.
12 CNS Sleep deprivation from twenty years of nights. What the brain does to blood pressure.
13 PNS (sensory, somatic) Dermatomes and her radiating pain. Early sensory neuropathy in her feet.
14 Autonomic Her heart rate variability. Sympathetic tone. Why beta-blockers work.
15 Special senses Adwoa's cataract and hearing loss. Amara's early retinal changes.
16 Endocrine Insulin resistance quantified. Cortisol and night shift. The RAAS enters the story.
17 Blood Full CBC. Anemia begins. Platelets, clotting, and why she is on two antiplatelet drugs.
18 Heart The central chapter. Her ECG, her catheterization, her ejection fraction.
19 Vessels Her blood pressure decomposed into its parts. Why the number is high and what that costs.
20 Lymphatic The ankle edema on day 3. Where the filtered fluid goes when the heart cannot keep up.
21 Immunity The inflammatory response to infarcted muscle. Why healing and scarring are the same process.
22 Respiratory Obstructive sleep apnea diagnosed. Pulmonary edema explained. Her arterial blood gas.
23 Digestive A GI bleed on dual antiplatelet therapy. Reflux, and her night-shift eating.
24 Nutrition, metabolism Metabolic syndrome, fully assembled. Nia's marathon fueling as the contrast case.
25 Thermoregulation Circadian temperature and night shift. Heat tolerance during rehab. Adwoa's blunted response.
26 Urinary Her creatinine has drifted. Stage 3a CKD. The cardiorenal loop closes.
27 Reproductive Perimenopause and the loss of estrogen's vascular protection. Nia's cycle.
28 Development Nia is pregnant. Family history makes her preeclampsia risk real.
29 Genetics The family pedigree, drawn properly. Polygenic risk vs. single-gene disease.
30 Aging Adwoa at 78, Amara at 45, Nia at 24 — the same systems, three decades apart.
31 Fluid, acid-base A diuretic causes hypokalemia and metabolic alkalosis. Everything converges.
32 Exercise physiology Eighteen months of rehab. VO₂peak up 18% with no change in ejection fraction. Where did it come from?
33 Capstone The whole model, assembled and run forwards. What happens next, and why.

What you write each chapter

Each Case File entry ends with the same three prompts.

Your Case File entry — the standard format

1 · ADD (2–3 sentences). What does the system from this chapter contribute to Amara's picture? Be specific and use numbers where you have them.

2 · CONNECT (2–3 sentences). Link this system to at least two systems already in your file. State the direction of causation each time — A causes B, not A is related to B.

3 · PREDICT (1–2 sentences). Name one thing you now expect to find in a later chapter, and say why. Then, when you reach that chapter, come back and mark whether you were right.

The PREDICT step is the one students skip and the one that does the most. A prediction you wrote down and later have to grade is a completely different cognitive event from a prediction you merely thought about.

The scoring rubric (if your course grades this)

Instructors: the full rubric, with point values and sample entries at each level, is in the Instructor Companion.

Level What it looks like
4 — Integrated Names ≥2 prior systems, states direction of causation, identifies at least one feedback loop, uses the patient's actual numbers
3 — Connected Names ≥2 prior systems with correct causal direction, but treats connections as one-way
2 — Adjacent Names other systems but describes association rather than mechanism ("the kidney is related to blood pressure")
1 — Isolated Correct description of the new system with no connection to prior chapters

Most students start at level 1 or 2 around Chapter 3 and reach level 4 somewhere between Chapters 16 and 19 — usually the moment the renin–angiotensin–aldosterone system connects the heart, vessels, kidneys, and adrenal glands in a single loop, and the whole thing audibly clicks.

A note on studying a patient

Amara Osei is not real. But everything that happens to her happens to about a million real people a year in the United States alone, and if you are entering health care you will meet her within weeks of starting clinicals — a working adult in her forties, insured but under-cared-for, with three or four ordinary risk factors that nobody added up, who arrives because something finally hurt enough.

The purpose of this project is that when you meet her, you will not see a list of diagnoses. You will see a system.

Begin with Chapter 1 · The Human Body: An Orientation.