Collection · COL-03
Inside the Body
Cells, organelles, bacteria-eating immune cells, the things floating in your eyes, blood moving through living vessels, veins sealed shut from the inside, red cells bent into sickles, heart pumps that work from outside a child's chest, lungs that give way to sudden pressure and the scanners that image you.
Emotions, mood and brain chemistry now have their own collection, COL-13 The Brain.
Free PDF: every quick fact with its ID, the write-ups, sources and a quiz with an answer key.
What Is in Inside the Body?
27 case files on what is working, floating and hiding inside you. Eukaryotic cells contain specialized organelles, each with its own job. DD-003 Vaults are hollow, barrel-shaped particles in most of our cells (about 10,000 per cell), each built from 78 copies of one protein, and nobody knows for sure what they do. DD-015
The Case Files, in Order
- 01
DID YOU
KNOW?EukaryoticDD-003 - 02
DID YOU
KNOW?The VaultDD-015 - 03
DID YOU
KNOW?Starry EyedDD-001 - 04
DID YOU
KNOW?MacrophagiaDD-044 - 05
DID YOU
KNOW?Blood WatchDD-649 - 06
DID YOU
KNOW?SclerotherapyDD-597 - 07
DID YOU
KNOW?Sickled CellsDD-613 - 08
DID YOU
KNOW?Berlin HeartDD-577 - 09
DID YOU
KNOW?ImploderDD-593 - 10
DID YOU
KNOW?An MRI's SkeletonDD-290 - 11
DID YOU
KNOW?I Wanted You to Know...DD-265I Wanted You to Know...
Every heartbeat starts with a spark from the sinoatrial node.
Open case file → - 12
DID YOU
KNOW?Bacteria HuntersDD-309Bacteria Hunters
Phages are the most numerous biological entities on Earth, yet the idea of using them as medicine was largely sidelined in the West by antibiotics; rising antibiotic resistance is why that century-old idea is back.
Open case file → - 13
DID YOU
KNOW?Your Heart in a GlassDD-315 - 14
DID YOU
KNOW?Embryonic DevelopmentDD-333Embryonic Development
The earliest stage of an embryo involves a lot of division with no growth at all, and the real reorganization comes later, when cells sort themselves into layers.
Open case file → - 15
DID YOU
KNOW?Blood DestructionDD-395Blood Destruction
Malaria remains one of the deadliest infectious diseases, concentrated overwhelmingly in Africa, and its long fight with humans has reshaped both medicine and the human genome.
Open case file → - 16
DID YOU
KNOW?Articulated ProsthesisDD-438Articulated Prosthesis
Myoelectric hands read electrical signals from the user's muscles.
Open case file → - 17
DID YOU
KNOW?Rabies CraziesDD-420 - 18
DID YOU
KNOW?Root of the ProblemDD-448 - 19
DID YOU
KNOW?Seeing Things DifferentlyDD-454Seeing Things Differently
Laser eye surgery reshapes the cornea to fix blurry vision.
Open case file → - 20
DID YOU
KNOW?Face CreatorDD-465 - 21
DID YOU
KNOW?MAiDDD-487 - 22
DID YOU
KNOW?Lens CrafterDD-492 - 23
DID YOU
KNOW?Shifty PeripheryDD-502 - 24
DID YOU
KNOW?Cell DeathDD-523 - 25
DID YOU
KNOW?Wet ResponseDD-525 - 26
DID YOU
KNOW?HHSDD-539 - 27
DID YOU
KNOW?AI Surgery IIDD-549
Collection Quiz
All quizzes →54 questions from all 27 case files in Inside the Body. Test Your Knowledge: answers are revealed instantly.
Which organelle holds the cell's DNA and controls gene expression?
- Golgi apparatus
- Ribosome
- Nucleus
- Lysosome
Show the answer
Answer: C. Nucleus Now You Know: The nucleus holds the cell's DNA and controls gene expression. Source: DD-003 · Eukaryotic · Write-up · Exhibit A (Nucleus), from the Reel
Which organelles produce energy through cellular respiration?
- Mitochondria
- Peroxisomes
- Ribosomes
- Golgi apparatus
Show the answer
Answer: A. Mitochondria Now You Know: Mitochondria produce the cell's energy through cellular respiration. Source: DD-003 · Eukaryotic · Write-up · Exhibit D (Mitochondria), from the Reel
Why are vaults called 'vaults'?
- They lock away the cell's DNA
- Under the microscope they look like the arches of a cathedral's vaulted ceiling
- They were found inside bank-vault-like membranes
- They store the cell's energy reserves
Show the answer
Answer: B. Under the microscope they look like the arches of a cathedral's vaulted ceiling Now You Know: Kedersha and Rome named them for their resemblance to the multiple arches of cathedral vaults. Source: DD-015 · The Vault · Write-up · Exhibit A (Found by accident in 1986) · Isolation and characterization of a novel ribonucleoprotein particle (Kedersha & Rome, J. Cell Biol. 1986); The key to 'the vault' (California NanoSystems Institute, UCLA, May 27, 2024)
Roughly how many vaults does a typical human cell contain?
- About 10
- About 10,000
- About 10 million
- Exactly one
Show the answer
Answer: B. About 10,000 Now You Know: Most human cells have around 10,000 vaults; some immune cells may have up to 100,000. Source: DD-015 · The Vault · Write-up · Exhibit B (Big and everywhere) · Isolation and characterization of a novel ribonucleoprotein particle (Kedersha & Rome, J. Cell Biol. 1986); The vault complex (van Zon et al., Cell Mol Life Sci 2003, via PMC); How a scientist's lifelong obsession with vaults could transform medicine (UCLA Health)
Where in the eye are asteroid bodies found?
- The cornea
- The lens
- The vitreous gel
- The tear film
Show the answer
Answer: C. The vitreous gel Now You Know: They sit in the vitreous humor, the gel that fills the eyeball. Source: DD-001 · Starry Eyed · Write-up · Exhibit A (Stars in the vitreous) · Prevalence and associations of asteroid hyalosis: the Beijing Eye Study (BMC Ophthalmology, 2022); Asteroid Hyalosis (EyeWiki, American Academy of Ophthalmology)
What are asteroid bodies mainly made of?
- Iron and protein
- Calcium, phosphate and lipids
- Ice crystals
- Cholesterol only
Show the answer
Answer: B. Calcium, phosphate and lipids Now You Know: They're lipids complexed with calcium, phosphate and oxygen, with an apatite-like structure. Source: DD-001 · Starry Eyed · Write-up · Exhibit B (What they're made of) · Ultrastructure and composition of asteroid bodies (Winkler & Lünsdorf, IOVS 2001; PubMed); Global prevalence of asteroid hyalosis: systematic review and meta-analysis (Acta Ophthalmologica, 2020); Prevalence and associations of asteroid hyalosis: the Beijing Eye Study (BMC Ophthalmology, 2022)
What does 'macrophage' mean?
- Small cell
- Big eater
- White blood
- Fast mover
Show the answer
Answer: B. Big eater Now You Know: From the Greek makros (big) and phagein (to eat). Source: DD-044 · Macrophagia · Write-up · Exhibit A (Big eaters) · Origins, Biology, and Diseases of Tissue Macrophages (PMC)
What are antibodies and complement proteins that tag a microbe for eating called?
- Opsonins
- Lysosomes
- Ribosomes
- Hormones
Show the answer
Answer: A. Opsonins Now You Know: Opsonic receptors bind these tags. Source: DD-044 · Macrophagia · Write-up · Exhibit B (Two ways to spot a target) · Uribe-Querol & Rosales, Control of Phagocytosis by Microbial Pathogens (Frontiers in Immunology, 2017); Uribe-Querol & Rosales, Phagocytosis: Our Current Understanding of a Universal Biological Process (Frontiers in Immunology, 2020); Phagocytosis (StatPearls, NCBI Bookshelf)
Who described capillaries in 1661?
- Marcello Malpighi
- Louis Pasteur
- Robert Koch
- Marie Curie
Show the answer
Answer: A. Marcello Malpighi Now You Know: He looked at a frog's lung. Source: DD-649 · Blood Watch · Write-up · Exhibit A (Malpighi's capillaries) · Hwa & Aird (2007): The history of the capillary wall, doctors, discoveries, and debates, American Journal of Physiology
What did Rudolph Wagner see in 1839?
- White blood cells rolling along vessel walls
- The first virus
- DNA
- A heart transplant
Show the answer
Answer: A. White blood cells rolling along vessel walls Now You Know: In a frog's webbed foot. Source: DD-649 · Blood Watch · Write-up · Exhibit B (Rolling white cells) · Granger & Senchenkova: Inflammation and the Microcirculation, Historical Perspectives (NCBI Bookshelf); Intravital microscopy in historic and contemporary immunology, Immunology & Cell Biology (PMC)
What does a sclerosant damage?
- The vein's inner lining
- The skin's surface
- The bone
- The nerve
Show the answer
Answer: A. The vein's inner lining Now You Know: The endothelium. Source: DD-597 · Sclerotherapy · Write-up · Exhibit A (Damage on purpose) · StatPearls (NCBI Bookshelf): Sclerotherapy; DermNet: Sclerotherapy
What kind of agent is polidocanol?
- A detergent
- An antibiotic
- A painkiller
- A vitamin
Show the answer
Answer: A. A detergent Now You Know: It breaks down the lining's cell membranes. Source: DD-597 · Sclerotherapy · Write-up · Exhibit B (Detergents lead) · StatPearls (NCBI Bookshelf): Sclerotherapy; Sclerotherapy for lower limb telangiectasias, Cochrane review (PMC)
What is the abnormal hemoglobin in sickle cell disease called?
- Hemoglobin S
- Hemoglobin A
- Hemoglobin F
- Hemoglobin C
Show the answer
Answer: A. Hemoglobin S Now You Know: It forms rigid strands. Source: DD-613 · Sickled Cells · Write-up · Exhibit A (One swap) · Sundd, Gladwin & Novelli (2019), Pathophysiology of Sickle Cell Disease, Annual Review of Pathology; Wikipedia: Sickle cell disease
When does hemoglobin S form rigid strands?
- After it releases oxygen
- Only in the lungs
- When it's cold
- After eating
Show the answer
Answer: A. After it releases oxygen Now You Know: In the tissues, where oxygen is delivered. Source: DD-613 · Sickled Cells · Write-up · Exhibit A (One swap) · Sundd, Gladwin & Novelli (2019), Pathophysiology of Sickle Cell Disease, Annual Review of Pathology; Wikipedia: Sickle cell disease
Where do the EXCOR's blood pumps sit?
- Outside the body
- Inside the chest
- In the abdomen
- Inside the heart
Show the answer
Answer: A. Outside the body Now You Know: That's what paracorporeal means. Source: DD-577 · Berlin Heart · Write-up · Exhibit A (Pumps outside the body) · FDA: HDE approval letter and summary, Berlin Heart EXCOR Pediatric VAD (H100004), December 16, 2011
What drives the EXCOR's pumps?
- Air pressure
- Magnets
- A hand crank
- Springs
Show the answer
Answer: A. Air pressure Now You Know: Air pulses flex a membrane in each pump. Source: DD-577 · Berlin Heart · Write-up · Exhibit B (Driven by air) · FDA: HDE approval letter and summary, Berlin Heart EXCOR Pediatric VAD (H100004), December 16, 2011
Why doesn't slowly rising pressure crush a diver?
- The body is mostly water, which barely compresses
- Wetsuits hold back the pressure
- Pressure doesn't rise underwater
- Divers hold their breath
Show the answer
Answer: A. The body is mostly water, which barely compresses Now You Know: The danger is in sudden changes and air spaces. Source: DD-593 · Imploder · Write-up · Exhibit A (Water doesn't squeeze) · NOAA National Ocean Service: How does pressure change with ocean depth?; Wikipedia: Blast injury
Which parts of the body are most vulnerable to pressure injury?
- Air-filled spaces like the lungs
- Bones
- Fingernails
- Hair
Show the answer
Answer: A. Air-filled spaces like the lungs Now You Know: This is called barotrauma. Source: DD-593 · Imploder · Write-up · Exhibit B (Air is the weak point) · Wikipedia: Blast injury
What does MRI use to image the body?
- A strong magnet and radio waves
- X-rays
- Ultrasound
- Visible light
Show the answer
Answer: A. A strong magnet and radio waves Now You Know: The signals come from hydrogen nuclei. Source: DD-290 · An MRI's Skeleton · Write-up · Exhibit A (Magnets and radio) · NIBIB (NIH): Magnetic Resonance Imaging (MRI)
Do MRI gradient coils spin?
- No, they're stationary
- Yes, rapidly
- Only during startup
- Only in old models
Show the answer
Answer: A. No, they're stationary Now You Know: They vary the field electrically. Source: DD-290 · An MRI's Skeleton · Write-up · Exhibit B (Gradient coils) · NIBIB (NIH): Magnetic Resonance Imaging (MRI)
What is the heart's natural pacemaker?
- The sinoatrial node
- The aorta
- The lungs
- The bundle of His
Show the answer
Answer: A. The sinoatrial node Now You Know: It fires the first impulse. Source: DD-265 · I Wanted You to Know... · Write-up · Exhibit A (Pacemaker) · Wikipedia: Cardiac cycle; Wikipedia: Sinoatrial node
Which chambers contract first?
- The atria
- The ventricles
- The lungs
- The valves
Show the answer
Answer: A. The atria Now You Know: Then the ventricles. Source: DD-265 · I Wanted You to Know... · Write-up · Exhibit B (Atria first) · Wikipedia: Cardiac cycle
What do phages infect?
- Bacteria
- Humans
- Plants only
- Rocks
Show the answer
Answer: A. Bacteria Now You Know: Only bacteria. Source: DD-309 · Bacteria Hunters · Write-up · Exhibit A (Outnumbering all life) · Wikipedia: Bacteriophage
What do they inject?
- Genetic material
- Oxygen
- Sugar
- Water
Show the answer
Answer: A. Genetic material Now You Know: DNA or RNA. Source: DD-309 · Bacteria Hunters · Write-up · Exhibit A (Outnumbering all life) · Wikipedia: Bacteriophage
What are heart muscle cells called?
- Cardiomyocytes
- Neurons
- Erythrocytes
- Osteocytes
Show the answer
Answer: A. Cardiomyocytes Now You Know: Cardiac cells. Source: DD-315 · Your Heart in a Glass · Write-up · Exhibit A (Cardiomyocytes) · Wikipedia: Cardiac muscle cell
Which proteins contract?
- Actin and myosin
- Keratin
- Collagen
- Insulin
Show the answer
Answer: A. Actin and myosin Now You Know: In myofibrils. Source: DD-315 · Your Heart in a Glass · Write-up · Exhibit B (Impulses) · Wikipedia: Cardiac muscle cell
What is the first cell?
- A zygote
- A neuron
- A blastocyst
- A gamete
Show the answer
Answer: A. A zygote Now You Know: Fertilized. Source: DD-333 · Embryonic Development · Write-up · Exhibit A (Dividing without growing) · Wikipedia: Embryonic development
What are early divisions called?
- Cleavage
- Mitosis only
- Meiosis
- Fusion
Show the answer
Answer: A. Cleavage Now You Know: Rapid. Source: DD-333 · Embryonic Development · Write-up · Exhibit A (Dividing without growing) · Wikipedia: Cleavage (embryo)
What causes malaria?
- Plasmodium parasites
- A virus
- Bacteria
- Fungi
Show the answer
Answer: A. Plasmodium parasites Now You Know: Protozoa. Source: DD-395 · Blood Destruction · Write-up · Exhibit A (The current toll) · Wikipedia: Malaria
Which mosquitoes spread it?
- Female Anopheles
- Male Aedes
- All flies
- Ticks
Show the answer
Answer: A. Female Anopheles Now You Know: Vector. Source: DD-395 · Blood Destruction · Write-up · Exhibit B (Nobel-winning detective work) · Wikipedia: Malaria
What controls a myoelectric hand?
- Muscle signals
- Voice
- Eye blinks
- Breath
Show the answer
Answer: A. Muscle signals Now You Know: Electrodes. Source: DD-438 · Articulated Prosthesis · Write-up · Exhibit A (Joints) · Wikipedia: Prosthesis
Where are sensors placed?
- On the skin
- In the bone
- On the shoe
- In the mouth
Show the answer
Answer: A. On the skin Now You Know: Residual limb. Source: DD-438 · Articulated Prosthesis · Write-up · Exhibit B (Myoelectric) · Wikipedia: Myoelectric prosthesis
How does rabies spread?
- Bites or scratches
- Air
- Water
- Food
Show the answer
Answer: A. Bites or scratches Now You Know: Saliva. Source: DD-420 · Rabies Crazies · Write-up · Exhibit A (Spread) · Wikipedia: Rabies
How does it reach the brain?
- Along nerves
- Through blood only
- Via lungs
- Through skin
Show the answer
Answer: A. Along nerves Now You Know: Peripheral nerves. Source: DD-420 · Rabies Crazies · Write-up · Exhibit B (Route) · Wikipedia: Rabies
What is removed?
- The pulp
- The enamel
- The gum
- The jaw
Show the answer
Answer: A. The pulp Now You Know: Soft tissue. Source: DD-448 · Root of the Problem · Write-up · Exhibit A (Pulp) · Wikipedia: Root canal treatment
What fills the canals?
- Gutta-percha
- Gold
- Cement only
- Wax
Show the answer
Answer: A. Gutta-percha Now You Know: Rubbery. Source: DD-448 · Root of the Problem · Write-up · Exhibit B (Removal) · Wikipedia: Root canal treatment
What is reshaped?
- Cornea
- Retina
- Lens
- Iris
Show the answer
Answer: A. Cornea Now You Know: Front of eye. Source: DD-454 · Seeing Things Differently · Write-up · Exhibit A (Goal) · Wikipedia: LASIK
LASIK stands for laser-assisted in situ...?
- Keratomileusis
- Keratitis
- Myopia
- Lenticule
Show the answer
Answer: A. Keratomileusis Now You Know: Term. Source: DD-454 · Seeing Things Differently · Write-up · Exhibit B (Target) · Wikipedia: LASIK
Which cells migrate?
- Neural crest
- Red blood
- Muscle
- Fat
Show the answer
Answer: A. Neural crest Now You Know: Embryo. Source: DD-465 · Face Creator · Write-up · Exhibit A (Start) · Wikipedia: Human embryonic development
How many segments?
- Five
- Two
- Ten
- One
Show the answer
Answer: A. Five Now You Know: Prominences. Source: DD-465 · Face Creator · Write-up · Exhibit B (Cells) · Wikipedia: Human embryonic development
MAiD stands for?
- Medical assistance in dying
- Medical aid insurance deal
- Mandatory aid
- None
Show the answer
Answer: A. Medical assistance in dying Now You Know: Term. Source: DD-487 · MAiD · Write-up · Exhibit A (Term) · Wikipedia: Medical assistance in dying
Country using the term?
- Canada
- Japan
- Brazil
- Egypt
Show the answer
Answer: A. Canada Now You Know: Canada. Source: DD-487 · MAiD · Write-up · Exhibit B (Legal in) · Wikipedia: Medical assistance in dying
RGP means?
- Rigid gas permeable
- Really good plastic
- Red glass pane
- None
Show the answer
Answer: A. Rigid gas permeable Now You Know: Type. Source: DD-492 · Lens Crafter · Write-up · Exhibit A (Methods) · Wikipedia: Contact lens
Custom lenses are often?
- Lathed
- Painted
- Blown
- Woven
Show the answer
Answer: A. Lathed Now You Know: Machined. Source: DD-492 · Lens Crafter · Write-up · Exhibit B (RGP) · Wikipedia: Contact lens
Which cells dominate the periphery?
- Rods
- Cones
- Neurons only
- Lens cells
Show the answer
Answer: A. Rods Now You Know: Light-sensitive. Source: DD-502 · Shifty Periphery · Write-up · Exhibit A (Strength) · Wikipedia: Rod cell
Center of retina has?
- Cones
- Only rods
- No cells
- Blood
Show the answer
Answer: A. Cones Now You Know: Fovea. Source: DD-502 · Shifty Periphery · Write-up · Exhibit B (Cells) · Wikipedia: Rod cell
Programmed cell death?
- Apoptosis
- Necrosis
- Mitosis
- Osmosis
Show the answer
Answer: A. Apoptosis Now You Know: Controlled. Source: DD-523 · Cell Death · Write-up · Exhibit A (Type) · Wikipedia: Apoptosis
Key enzymes?
- Caspases
- Amylases
- Lipases
- Kinases only
Show the answer
Answer: A. Caspases Now You Know: Dismantlers. Source: DD-523 · Cell Death · Write-up · Exhibit B (Contrast) · Wikipedia: Apoptosis
Controlled by?
- Autonomic nervous system
- Bones
- Muscles only
- Hair
Show the answer
Answer: A. Autonomic nervous system Now You Know: Automatic. Source: DD-525 · Wet Response · Write-up · Exhibit A (Cause) · Wikipedia: Wrinkle
What constricts?
- Blood vessels
- Bones
- Nails
- Hair
Show the answer
Answer: A. Blood vessels Now You Know: Volume. Source: DD-525 · Wet Response · Write-up · Exhibit B (Control) · Wikipedia: Wrinkle
Program it runs?
- Medicare
- Social Security
- NASA
- Amtrak
Show the answer
Answer: A. Medicare Now You Know: Health. Source: DD-539 · HHS · Write-up · Exhibit A (Role) · Wikipedia: United States Department of Health and Human Services
Agency it oversees?
- CDC
- FBI
- EPA
- IRS
Show the answer
Answer: A. CDC Now You Know: Public health. Source: DD-539 · HHS · Write-up · Exhibit B (Origin) · Wikipedia: United States Department of Health and Human Services
What is filtered?
- Tremor
- Light
- Sound
- Blood
Show the answer
Answer: A. Tremor Now You Know: Steadiness. Source: DD-549 · AI Surgery II · Write-up · Exhibit A (Scale) · Wikipedia: Robot-assisted surgery
Motion scaling does?
- Shrinks movements
- Speeds them
- Stops them
- Records them
Show the answer
Answer: A. Shrinks movements Now You Know: Precision. Source: DD-549 · AI Surgery II · Write-up · Exhibit B (Imaging) · Wikipedia: Robot-assisted surgery