BIO 304 . Human Anatomy & Physiology . Week 7

Week 7 Workbook — Immune, Respiratory & GI

Days 25 through 28 . Print one packet, work the whole week.

Print this whole packet at the start of the week and use it as you work through the videos and interactive notes for the days listed below. Each day starts on a fresh page so it’s easy to keep them organized.

Day 25 · Lymphatic System & Innate Immunity
Day 26 · Adaptive Immunity
Day 27 · Respiratory Anatomy & Mechanics
Day 27 · Gas Exchange & Transport
Day 28 · GI Tract Anatomy & Motility
Day 28 · Digestion & Absorption

Day 25

Lymphatic System & Innate Immunity

BIO 304 . WEEK 7 . MONDAY . LAB WORKBOOK

Lymphatic System and Innate Immunity

Lymph nodes, vessels, spleen, thymus; barriers, phagocytes, NK cells, inflammation, complement, fever.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

Part 1 of 2

Anatomy Lab

1A. What you will draw

The lymphatic system both drains tissue fluid and houses the first line of immune defense. Today you'll draw the major lymphatic structures across the body, then a close-up of an inflammatory response in a tissue.

Box A. Major lymphatic structures

Directions

Draw a simple body outline.
Lymph nodes: cluster small ovals at the cervical (neck), axillary (armpit), and inguinal (groin) regions. Label each cluster.
Thymus: in the upper chest behind the sternum. Label (note: large in childhood, atrophies with age).
Spleen: in the upper left abdomen, behind the stomach. Label.
MALT (mucosa-associated lymphoid tissue): mark tonsils in the throat, Peyer's patches in the small intestine, and appendix. Label.
Draw a network of lymphatic vessels running through the body, with two large terminal ducts emptying into veins near the heart: thoracic duct (drains most of the body, empties into the left subclavian vein) and right lymphatic duct (drains right upper body, empties into the right subclavian vein). Label.

Draw here. Sketch by hand.

Box B. Acute inflammation in a tissue

Directions

Draw a section of tissue with a small injury (e.g., a splinter introducing bacteria).
Show a nearby blood capillary. Add arrows pointing OUT from the capillary indicating vasodilation and increased permeability.
Show fluid leaking from the capillary into the tissue, causing edema (swelling). Label.
Draw neutrophils squeezing through the capillary wall (diapedesis or extravasation) and migrating toward the bacteria. Label.
Draw the neutrophils phagocytosing bacteria. Label.
Mark the four cardinal signs of inflammation around the site: redness (rubor), heat (calor), swelling (tumor), pain (dolor). Add Latin names if you want.

Draw here. Sketch by hand.

1C. Structures to label (22)

After you finish each drawing, label every structure below directly on your sketch.

Lymph node
Cervical nodes
Axillary nodes
Inguinal nodes
Thymus
Spleen
Tonsils
Peyer's patches
Appendix
Lymphatic vessel
Thoracic duct
Right lymphatic duct
Vasodilation
Increased permeability
Edema
Neutrophil
Diapedesis (extravasation)
Phagocytosis
Redness
Heat
Swelling
Pain

Part 2 of 2

Physiology Lab

2A. Innate defense table

Fill in the table classifying innate immune defenses by category. After the table, answer the two follow-up questions.

Category	Example	Mechanism of defense
Physical barrier	Skin
Chemical barrier	Stomach acid (low pH)
Phagocyte	Neutrophil
Phagocyte	Macrophage
Cytotoxic innate cell	Natural killer (NK) cell
Chemical mediator	Complement
Whole-body response	Fever
Local response	Inflammation

Fever is a regulated rise in body temperature in response to infection. Explain mechanistically why a moderate fever is BENEFICIAL during a bacterial infection. Why is very high fever (over 41 C) dangerous?

Complement is a cascade of plasma proteins that can punch holes in bacterial membranes. Explain the term 'cascade' in this context, and how this design lets a small initial signal produce a large response.

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

1. A patient has a breast tumor removed along with several axillary lymph nodes. Predict the long-term consequence in the arm on that side, and explain mechanistically why this complication occurs (lymphedema).

2. A patient is taking corticosteroids long-term and develops infections easily. Explain mechanistically how corticosteroids suppress the innate immune response (consider phagocyte activity, inflammation, fever response).

3. Compare innate and adaptive immunity in one paragraph: speed of response, specificity, memory, and which cells are involved. Why does the body need BOTH systems?

3. What to submit

Complete both the Anatomy Lab (your own drawings, hand-labeled, plus the structures list) and the Physiology Lab (activity and synthesis questions). Photograph or scan every page and upload to Canvas before the deadline listed on the schedule. Hand-drawn, hand-labeled work is the integrity mechanism for this course. Typed or AI-generated diagrams are not accepted.

Day 26

Adaptive Immunity

BIO 304 . WEEK 7 . TUESDAY . LAB WORKBOOK

Adaptive Immunity

B cells, T cells, antibodies, antigen presentation, memory.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

Part 1 of 2

Anatomy Lab

1A. What you will draw

Adaptive immunity is specific (recognizes a particular pathogen) and has memory (responds faster on second exposure). Today you'll draw the two main effector cell types side by side, then an antibody up close.

Box A. B cell vs T cell action

Directions

Left half: a B cell encountering a free-floating antigen (e.g., a bacterial toxin). Draw the antigen binding the B cell receptor on the surface. Show the B cell differentiating into a plasma cell (label, with rough ER for antibody synthesis) and a memory B cell. Draw antibodies leaving the plasma cell into the surroundings.
Right half: a cytotoxic T cell (CD8) encountering an infected host cell. The infected cell presents a viral antigen on its surface bound to MHC class I (draw both). The T cell's T-cell receptor (TCR) binds the MHC-I + antigen complex. The T cell releases perforin and granzymes, punching the infected cell and triggering apoptosis. Draw the infected cell dying.
Label B cell, plasma cell, memory B cell, antibody on the left. Label cytotoxic T cell, TCR, MHC I, perforin/granzyme, apoptosis on the right.

Draw here. Sketch by hand.

Box B. Antibody structure

Directions

Draw a single antibody molecule as a Y shape.
Show four protein chains: two heavy chains (long) forming the stem and inner arms of the Y, two light chains (short) on the outer arms. Label.
Draw disulfide bonds (small dashes) connecting the chains.
Color or shade the TOPS of the two arms differently from the rest: these are the variable regions where antigen binding happens. Label antigen-binding site (two per antibody).
The rest of the molecule is the constant region. Label.
Below the antibody, draw a small antigen with surface features (epitopes) that fit the antigen-binding sites. Show the antibody-antigen binding.

Draw here. Sketch by hand.

1C. Structures to label (19)

After you finish each drawing, label every structure below directly on your sketch.

B cell
Plasma cell
Memory B cell
B cell receptor
Antibody
Cytotoxic T cell (CD8)
Helper T cell (CD4)
T cell receptor (TCR)
MHC class I
MHC class II
Perforin
Granzyme
Apoptosis
Heavy chain
Light chain
Variable region
Constant region
Antigen-binding site
Antigen (epitope)

Part 2 of 2

Physiology Lab

2A. Primary vs secondary immune response

Draw a graph (x-axis = time in days, y-axis = antibody concentration in blood) showing the primary vs secondary antibody response. On Day 0, the patient is exposed to antigen X. On Day 30, exposed again. Then answer the questions.

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

1. Explain how a vaccine works using the primary vs secondary response. Why does a vaccine produce immunity even though no real infection ever occurred?

2. HIV preferentially infects and destroys helper T cells (CD4). Predict the consequences for both the B cell response and the cytotoxic T cell response, and explain why HIV patients eventually develop opportunistic infections (AIDS).

3. Autoimmune disease occurs when adaptive immunity targets self tissues. Pick one autoimmune disease (e.g., Type 1 diabetes, rheumatoid arthritis, lupus, multiple sclerosis). Identify which self tissue is targeted and predict the consequences when adaptive immunity attacks that tissue.

3. What to submit

Day 27

Respiratory Anatomy & Mechanics

BIO 304 . WEEK 7 . THURSDAY . LAB WORKBOOK

Respiratory Anatomy and Mechanics

Upper and lower airways, alveoli, and how the chest moves air.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

Part 1 of 2

Anatomy Lab

1A. What you will draw

Air follows a specific path from nose to alveolus. The chest pulls air in and pushes it out by changing its own volume. Today you'll draw the respiratory tract from above, then a side view showing inspiration vs expiration.

Box A. Respiratory tract from nose to alveoli

Directions

Draw a head and chest in front view.
Label, in order from top to bottom: nasal cavity, pharynx, larynx, trachea, primary bronchi (right and left), secondary bronchi, tertiary bronchi, bronchioles, terminal bronchioles, respiratory bronchioles, alveolar ducts, alveoli.
At the bottom, draw a cluster of grape-like alveoli wrapped in capillaries.
Note: conducting zone = nose through terminal bronchioles (no gas exchange, just airflow). Respiratory zone = respiratory bronchioles through alveoli (gas exchange happens here).
Add the epiglottis at the top of the larynx (closes during swallowing).

Draw here. Sketch by hand.

Box B. Inspiration vs expiration

Directions

Draw two side views of the thorax side by side.
LEFT silhouette: inspiration. Diaphragm contracts and flattens (moves DOWN). External intercostals contract, lifting the rib cage UP and OUT. Thoracic volume INCREASES, pressure DROPS, air flows IN.
RIGHT silhouette: expiration (quiet). Diaphragm relaxes and domes upward. Rib cage drops. Thoracic volume DECREASES, pressure RISES, air flows OUT.
Label diaphragm position, external intercostals, ribs, lung volume change, airflow direction.
Below the silhouettes, write Boyle's Law: at constant temperature, pressure and volume are inversely related. Note that inspiration is an ACTIVE process (muscle contraction); quiet expiration is PASSIVE (elastic recoil).

Draw here. Sketch by hand.

1C. Structures to label (18)

After you finish each drawing, label every structure below directly on your sketch.

Nasal cavity
Pharynx
Larynx
Epiglottis
Trachea
Primary bronchus
Bronchioles
Terminal bronchiole
Respiratory bronchiole
Alveolar duct
Alveolus
Conducting zone
Respiratory zone
Diaphragm
External intercostal muscles
Visceral pleura
Parietal pleura
Pleural cavity

Part 2 of 2

Physiology Lab

2A. Lung volumes and capacities

Sketch a single spirometry tracing (volume vs time) on the lines below. Then label the four primary volumes and the four derived capacities.

1. Tidal volume (TV): the volume of air moved in a single normal quiet breath. Typical value?

2. Inspiratory reserve volume (IRV): the extra air you can breathe IN above a normal inspiration.

3. Expiratory reserve volume (ERV): the extra air you can breathe OUT below a normal expiration.

4. Residual volume (RV): the air remaining in the lungs after maximum expiration. Why is some always left?

5. Vital capacity (VC = TV + IRV + ERV): the largest volume you can move from a maximum inspiration to a maximum expiration.

6. Total lung capacity (TLC = VC + RV): everything the lungs can hold.

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

1. A patient has a pneumothorax (air enters the pleural cavity, breaking the seal between visceral and parietal pleura). Predict what happens to the affected lung and explain mechanistically why it collapses.

2. Compare obstructive (e.g., COPD, asthma) vs restrictive (e.g., pulmonary fibrosis) lung disease. Predict how each affects lung volumes (TV, IRV, FEV1, TLC) and explain the mechanical reason behind each pattern.

3. Surfactant is a lipid-protein mixture in the alveoli that reduces surface tension. Premature infants often lack adequate surfactant (respiratory distress syndrome). Predict the consequence for alveolar inflation and explain why this is life-threatening.

3. What to submit

Day 27

Gas Exchange & Transport

BIO 304 . WEEK 7 . THURSDAY . LAB WORKBOOK

Gas Exchange and Transport

External and internal respiration; how O2 and CO2 ride the bloodstream.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

Part 1 of 2

Anatomy Lab

1A. What you will draw

Gas exchange happens twice in every breath cycle: at the alveoli (external respiration, lungs pick up O2 and drop CO2) and at the tissues (internal respiration, tissues pick up O2 and dump CO2). Draw both interfaces and how hemoglobin transports the load.

Box A. Alveolus and tissue gas exchange

Directions

Draw two panels side by side: the alveolus (LEFT) and a body tissue (RIGHT).
Left panel: an alveolus with air inside. PO2 in alveolus is about 104 mmHg, PCO2 is about 40 mmHg. Wrap the alveolus with a pulmonary capillary. Blood entering the capillary has PO2 about 40, PCO2 about 45. Show O2 diffusing INTO the blood and CO2 diffusing OUT to the alveolus. By the time blood leaves, PO2 is ~100 and PCO2 is ~40.
Right panel: a tissue cell. Inside the cell, PO2 is about 40 and PCO2 is about 45 (because the cell is consuming O2 and making CO2). Wrap the tissue with a systemic capillary. Blood entering has PO2 ~100, PCO2 ~40. Show O2 diffusing INTO the tissue and CO2 diffusing OUT to the blood. By the time blood leaves, PO2 is ~40, PCO2 is ~45.
Add labels: external respiration (lungs), internal respiration (tissues). Note: diffusion goes down partial pressure gradients.

Draw here. Sketch by hand.

Box B. Hemoglobin transports O2

Directions

Draw a hemoglobin molecule schematically: four globin chains (subunits) clustered, each containing a heme group with a central iron (Fe). Label one heme.
Show the hemoglobin in two states: deoxyhemoglobin (no O2 bound) and oxyhemoglobin (4 O2 molecules bound, one per heme).
Draw a hemoglobin LOADING in the pulmonary capillary (high PO2): O2 binds.
Draw a hemoglobin UNLOADING in a tissue capillary (low PO2): O2 dissociates.
Note: hemoglobin shows cooperative binding (first O2 makes the next easier to bind), producing the S-shaped saturation curve.
Below, note three factors that promote unloading: low pH, high PCO2, high temperature (the Bohr effect). These are all features of active tissue.

Draw here. Sketch by hand.

1C. Structures to label (13)

After you finish each drawing, label every structure below directly on your sketch.

Alveolus
Pulmonary capillary
PO2 (high in alveolus, low in tissue)
PCO2 (low in alveolus, high in tissue)
External respiration
Internal respiration
Hemoglobin
Globin chain
Heme group
Iron (Fe)
Oxyhemoglobin
Deoxyhemoglobin
Bohr effect

Part 2 of 2

Physiology Lab

2A. Oxygen-hemoglobin dissociation curve

Sketch the oxygen-hemoglobin dissociation curve on a graph. x-axis: PO2 (0 to 100 mmHg). y-axis: percent hemoglobin saturation (0 to 100). Then answer the questions below.

1. At PO2 = 100 mmHg (lung capillary), what is hemoglobin saturation?

2. At PO2 = 40 mmHg (tissue capillary at rest), what is saturation?

3. Why is the curve S-shaped (sigmoidal) rather than linear?

4. Predict the direction the curve SHIFTS when blood pH drops, PCO2 rises, or temperature rises. What does the shift accomplish at the tissue?

5. A patient is given high-FiO2 oxygen therapy, raising arterial PO2 from 100 to 200 mmHg. Predict the change in hemoglobin saturation (it doesn't double).

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

1. Carbon monoxide (CO) binds hemoglobin with about 200 times the affinity of O2 and forms carboxyhemoglobin. Predict the effects on (a) hemoglobin saturation, (b) the dissociation curve, (c) O2 delivery to tissues. Why is CO poisoning so dangerous even at low concentrations?

2. Most CO2 in the blood is transported as bicarbonate (HCO3-), formed inside red blood cells by carbonic anhydrase. Trace this pathway: CO2 enters the RBC, becomes carbonic acid, then dissociates. Where does the H+ go, and where does HCO3- go?

3. An athlete in heavy exercise has muscle PCO2 high, pH low, and temperature elevated. Predict (using the Bohr effect) what happens to hemoglobin's affinity for O2 at the muscle, and why this is exactly what the muscle needs.

3. What to submit

Day 28

GI Tract Anatomy & Motility

BIO 304 . WEEK 7 . FRIDAY . LAB WORKBOOK

GI Tract Anatomy and Motility

Mouth to anus, plus the accessory organs that empty into the tract.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

Part 1 of 2

Anatomy Lab

1A. What you will draw

The GI tract is a tube from mouth to anus. Food and chyme move through it by two main mechanisms: peristalsis (propulsion) and segmentation (mixing). Today you'll draw the GI tract with accessory organs, then the wall layers common to most segments.

Box A. GI tract with accessory organs

Directions

Draw a body outline (head and torso).
Label, in order, the tube of the GI tract: mouth (oral cavity), pharynx, esophagus, stomach (J-shaped, in the upper left abdomen), small intestine (long coiled tube with 3 parts: duodenum, jejunum, ileum), large intestine (frames around the small intestine: cecum/appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum), anus.
Now add accessory organs (they don't carry food but contribute to digestion): salivary glands near the mouth, liver in the upper right abdomen, gallbladder under the liver, pancreas behind the stomach.
Show ducts: bile duct from liver and gallbladder, pancreatic duct from pancreas, both emptying into the duodenum.
Label every structure.

Draw here. Sketch by hand.

Box B. GI wall layers (cross-section)

Directions

Draw a cross-section of a typical GI tube (e.g., small intestine). Show the lumen in the center.
From the lumen outward, label four layers:
Mucosa (innermost): epithelium + lamina propria + muscularis mucosae. This is the absorptive surface; in the small intestine, show villi projecting into the lumen.
Submucosa: connective tissue with blood vessels and the submucosal nerve plexus. Label.
Muscularis externa: usually two layers of smooth muscle, an inner circular and an outer longitudinal. Between them runs the myenteric nerve plexus. These layers produce peristalsis and segmentation. Label.
Serosa (outermost): thin layer of mesothelium and connective tissue (the visceral peritoneum). Label.

Draw here. Sketch by hand.

1C. Structures to label (27)

After you finish each drawing, label every structure below directly on your sketch.

Oral cavity
Pharynx
Esophagus
Stomach
Duodenum
Jejunum
Ileum
Cecum
Appendix
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Rectum
Anus
Salivary glands
Liver
Gallbladder
Pancreas
Bile duct
Pancreatic duct
Mucosa
Submucosa
Muscularis externa
Serosa
Circular muscle layer
Longitudinal muscle layer

Part 2 of 2

Physiology Lab

2A. Peristalsis vs segmentation

Compare the two main GI motility patterns by filling in the table. Then answer the follow-up questions.

Property	Peristalsis	Segmentation
Primary function (propulsion / mixing)
Direction of movement
Where dominant in GI tract
Muscle layers involved
Wave pattern

Trace a bite of food from the moment it enters the mouth to the moment chyme leaves the stomach. Identify which motility patterns dominate at each step and approximately how long each stage takes.

Defecation is a complex motor act involving both involuntary smooth muscle (internal anal sphincter) and voluntary skeletal muscle (external anal sphincter). Explain why a patient with a high spinal cord injury loses voluntary control but may still defecate reflexively.

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

1. Dysphagia (difficulty swallowing) can result from problems with the pharynx, the esophagus, or the lower esophageal sphincter. Predict the symptoms in each case, and which patient population is most affected by each.

2. Gastroparesis (delayed gastric emptying) is a common complication of diabetes. Predict the patient's symptoms after a meal and explain why dampened autonomic input to the stomach reduces its motility.

3. Irritable bowel syndrome (IBS) is characterized by altered motility, often producing either diarrhea (too fast) or constipation (too slow). Predict what changes in segmentation and peristalsis would produce each pattern.

3. What to submit

Day 28

Digestion & Absorption

BIO 304 . WEEK 7 . FRIDAY . LAB WORKBOOK

Digestion and Absorption

What breaks down where, and how nutrients cross into the blood.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

Part 1 of 2

Anatomy Lab

1A. What you will draw

Digestion happens stepwise: mechanical and chemical. Absorption is largely the job of the small intestine, whose villi enormously expand surface area. Today you'll draw a villus close-up, then the macronutrient digestion pathways.

Box A. Intestinal villus close-up

Directions

Draw a single intestinal villus: a finger-like projection into the lumen.
Label the lumen at the top.
Show the villus surface lined by absorptive epithelial cells (enterocytes), each with microvilli (brush border) facing the lumen. Label both.
Inside the villus, draw a network of blood capillaries (label) and one central lac#0B1530 (a lymphatic capillary running up the center). Label.
Add a goblet cell (mucus-secreting) in the epithelium. Label.
Note the principle: water-soluble nutrients (amino acids, monosaccharides) enter the blood capillaries; fat-soluble nutrients (chylomicrons, fatty acids in lipid form) enter the lac#0B1530s and travel via lymph.

Draw here. Sketch by hand.

Box B. Macronutrient digestion pathways

Directions

Draw three parallel pathways: Carbohydrates, Proteins, Fats. Each pathway shows where digestion begins, where it continues, and what the final absorbed product is.
Carbohydrates: starch (mouth, salivary amylase begins) > starch (stomach, no digestion) > maltose (small intestine, pancreatic amylase) > glucose (small intestine, brush-border enzymes like maltase). Absorbed: monosaccharides into blood.
Proteins: protein (mouth, no digestion) > peptides (stomach, pepsin) > shorter peptides (small intestine, pancreatic proteases) > amino acids (small intestine, brush-border peptidases). Absorbed: amino acids into blood.
Fats: triglycerides (mouth, no digestion) > triglycerides (stomach, minor lingual lipase) > emulsified fat droplets (small intestine, bile salts from gallbladder) > monoglycerides + fatty acids (small intestine, pancreatic lipase). Absorbed: re-formed triglycerides as chylomicrons into lac#0B1530.
Label each enzyme, its source (which organ), and the products at each step.

Draw here. Sketch by hand.

1C. Structures to label (18)

After you finish each drawing, label every structure below directly on your sketch.

Villus
Microvilli (brush border)
Enterocyte
Goblet cell
Lumen
Blood capillary
Lac#0B1530
Salivary amylase
Pepsin
Pancreatic amylase
Pancreatic protease (trypsin)
Pancreatic lipase
Brush-border enzymes
Bile salts
Glucose
Amino acid
Fatty acid + monoglyceride
Chylomicron

Part 2 of 2

Physiology Lab

2A. Enzyme, source, substrate, product

Fill in the table to map each major digestive enzyme.

Enzyme	Source organ	Substrate	Product
Salivary amylase
Pepsin
Pancreatic amylase
Trypsin (and other pancreatic proteases)
Pancreatic lipase
Maltase (brush border)
Lactase (brush border)

Lactose intolerance is caused by deficiency of the brush-border enzyme lactase. Predict the patient's symptoms after consuming dairy, and explain why undigested lactose causes osmotic diarrhea and bacterial gas production.

Bile salts are NOT enzymes, yet they are essential for fat digestion. Explain mechanistically how bile salts contribute to fat digestion without breaking any chemical bonds themselves (think: emulsification).

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

1. Celiac disease is an autoimmune reaction to gluten that damages and flattens intestinal villi. Predict the consequences for nutrient absorption and the patient's symptoms (weight loss, anemia, fatigue, diarrhea).

2. A patient has their gallbladder removed (cholecystectomy). Predict the effect on fat digestion immediately after surgery and over the long term. Why can the patient still digest fats, just less efficiently?

3. Pancreatic insufficiency (e.g., from cystic fibrosis or chronic pancreatitis) leads to malabsorption of all three macronutrients, but fat malabsorption is most pronounced. Explain mechanistically why fat absorption is hit hardest.