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Free Animated Health Science Diagrams

Endocrinology, metabolism, neuroscience, immunology, gut, sleep, cardiovascular. The body, made legible.

324 live For: Health bloggers · Science journalists · Medical educators · Wellness writers · Biohackers

Animated explainers for the human body at the cellular and systemic level. Hormone curves, metabolic pathways, neuroscience cascades, immune responses, sleep architecture, cardiovascular dynamics. Built with peer-review-grade accuracy and the visual restraint a textbook would envy.

What this is
Free, embeddable, animated diagrams covering health science topics (endocrinology & hormones, metabolism & energy, cell biology, neuroscience, and more).
Who uses it
Health bloggers · Science journalists · Medical educators · Wellness writers · Biohackers
How to embed
Copy one line of HTML per diagram. No signup. No watermark. Works in WordPress, Webflow, Ghost, Substack, plain HTML.
Diagrams in this category
324 live (total in catalog: 324).
License
Free forever. The diagram and editorial explainer text are served from scrollchart.com so they can be updated over time to reflect new research.
URL
scrollchart.com/categories/science
Highlights

What you will find here

  • Endocrinology: cortisol, insulin, GH, thyroid, sex hormones
  • Metabolism: ATP, glycolysis, beta-oxidation, mTOR, AMPK
  • Neuroscience and sleep architecture
  • Immune cascades and inflammation resolution
  • Gut microbiome and cardiovascular dynamics
Sub-categories

10 topic areas in Health Science

Endocrinology & hormones

Cortisol, insulin, GH, thyroid, leptin, ghrelin, T, E2, HPA axis.

53 live
Metabolism & energy

ATP, glycolysis, beta-oxidation, GLUT4, mTOR, AMPK, ketogenesis.

71 live
Cell biology

Membrane transport, organelles, autophagy, apoptosis, mitosis.

37 live
Neuroscience

Action potential, neurotransmitters, synaptic plasticity, brain regions.

22 live
Immune system & inflammation

Innate vs adaptive, cytokine cascades, NF-kB, resolution pathways.

24 live
Gut & microbiome

Microbial diversity, SCFAs, gut-brain axis, leaky gut, dysbiosis.

27 live
Sleep & circadian

Hypnogram, REM/NREM cycles, circadian phase, jet lag, shift work.

26 live
Cardiovascular

Cardiac cycle, blood pressure, atherosclerosis, lipid metabolism.

27 live
Respiratory

Gas exchange, V/Q matching, breathing mechanics, altitude.

14 live
Aging & longevity

Hallmarks of aging, telomeres, senescence, longevity pathways.

23 live
Catalog

Browse Health Science diagrams

All categories →

Metabolism & energy 71 live

ATP, glycolysis, beta-oxidation, GLUT4, mTOR, AMPK, ketogenesis.

Health Science Rich

Three-Tier Fat Clearance

Fat loss requires all three tiers: lipolysis (release), albumin transport, and mitochondrial beta-oxidation.
Health Science Medium

ATP: The Cellular Energy Currency

ATP hydrolysis to ADP releases ~30 kJ/mol; the cell turns over its body weight in ATP daily.
Health Science Rich

Glycolysis: 10-Step Pathway

Glucose to two pyruvates across ten enzymatic steps, net yield 2 ATP and 2 NADH.
Health Science Rich

Krebs (TCA) Cycle

Acetyl-CoA enters, two CO2 exit, three NADH and one FADH2 are produced per turn.
Health Science Rich

Electron Transport Chain

NADH and FADH2 feed electrons through Complexes I-IV, pumping protons that drive ATP synthase to produce ~28-30 ATP per glucose.
Health Science Rich

Beta-Oxidation of Fatty Acids

Long-chain fatty acids enter mitochondria and shed two carbons per cycle as acetyl-CoA, yielding 7 FADH2, 7 NADH, and 8 acetyl-CoA from one palmitate.
Health Science Rich

GLUT4 Vesicle Translocation

Insulin signaling drives GLUT4-loaded vesicles to fuse with the membrane, opening glucose entry. Exercise activates the same translocation independently via AMPK.
Health Science Rich

mTORC1 Amino Acid Sensing

Leucine and arginine signal through Sestrin/CASTOR/GATOR to activate Rag GTPases, anchoring mTORC1 to the lysosome.
Health Science Rich

AMPK Energy Stress Sensor

Rising AMP:ATP activates AMPK (via LKB1/CaMKK2), switching off mTORC1/ACC/SREBP1c and switching on CPT1/GLUT4/ULK1 for PGC-1alpha-driven mitochondrial biogenesis.
Health Science Medium

Ketogenesis Pathway

Hepatic acetyl-CoA from fatty-acid oxidation condenses into acetoacetate, BHB, and acetone.
Health Science Rich

Gluconeogenesis: Glucose from Scratch

Liver synthesizes new glucose from lactate, glycerol, and amino acids when carbs run low.
Health Science Medium

Cori Cycle

Muscle exports lactate; liver imports it and rebuilds glucose, which returns to muscle.
Health Science Medium

Glycogen Synthesis and Breakdown

Glycogen synthase builds branches; glycogen phosphorylase cleaves them; insulin and glucagon flip the switch.
Health Science Medium

De Novo Lipogenesis

Excess carbs convert to acetyl-CoA, then via ACC and FAS to palmitate and triglycerides.
Health Science Rich

Lipolysis Cascade: From Stimulus to Free Fatty Acids

Catecholamines bind beta-adrenergic receptors, cAMP rises via Adenylyl Cyclase, PKA activates HSL and ATGL, triglycerides break to FFA and glycerol.
Health Science Medium

Protein Synthesis vs Breakdown

Net protein balance is the difference between synthesis and breakdown; meals shift the balance positive, fasting negative.
Health Science Rich

Urea Cycle

Liver disposes of ammonia via the urea cycle; five steps span mitochondrion and cytosol.
Health Science Medium

Three Fates of Pyruvate

Pyruvate becomes acetyl-CoA (aerobic), lactate (anaerobic), or oxaloacetate (gluconeogenesis).
Health Science Medium

UCP1 Thermogenesis in Brown Fat

Cold triggers SNS norepinephrine -> beta-3-AR -> cAMP -> PKA -> UCP1 activation; the proton gradient short-circuits to heat instead of ATP.
Health Science Medium

Metabolic Flexibility

Healthy metabolism switches between glucose and fat oxidation as substrate availability shifts; insulin resistance flattens this.
Health Science Simple

TDEE Components

Basal metabolic rate, NEAT, exercise, and thermic effect of food sum to total daily energy expenditure.
Health Science Rich

TDEE Components (Animated)

Animated donut breaking down Total Daily Energy Expenditure into BMR, NEAT, EAT, and TEF, with state pills cycling through 4 activity levels (sedentary, light, active, athlete) so wedges resize and the kcal total updates live.
Health Science Medium

Glycemic Response Curve

Same carb load produces sharp spike from refined sugar, gentler curve from fiber-rich whole foods.
Health Science Rich

Iron Metabolism

Dietary iron absorption, transferrin transport, ferritin storage, hepcidin master regulator.
Health Science Medium

Cholesterol Synthesis (HMG-CoA Reductase)

Acetyl-CoA condenses through HMG-CoA to mevalonate; HMG-CoA reductase is the rate-limiting and statin-target step.
Health Science Medium

Metabolic Stages of Fasting

Glycogen depletion (0-24h), gluconeogenesis dominance (24-72h), ketosis adaptation (72h+).
Health Science Simple

Mitochondrial Density Grid

Endurance training multiplies mitochondrial density; sedentary muscle stays sparse.
Health Science Medium

Glucose to Ketone Fuel Switch

Two parallel fuel pipelines show glucose dimming and ketones flowing as the fasting threshold valve flips around hour 14-16.
Health Science Simple

Fat Cell Shrinkage During a Deficit

Adipocytes shrink as triglycerides mobilize out across a 12-week deficit; cell count stays constant while cell volume drops up to 67%.
Health Science Medium

TDEE Breakdown: Pie to Bar

TDEE components shown first as a pie chart, then decomposed into individual bars for clarity.
Health Science Simple

Lipolysis: Fat Cell Opening and FFA Release

A fat cell unlocks as HSL activates; free fatty acids stream into the bloodstream in an animated cascade.
Health Science Medium

TDEE Waterfall Breakdown

Energy expenditure as a waterfall: each component subtracts from total daily calories to reach zero.
Health Science Medium

Ketone Bodies: Signal, Not Just Fuel

Visceral fat lipolysis drives hepatic ketogenesis; BHB and acetoacetate signal metabolic shift and serve as alternative fuel for brain, muscle, and breath.
Health Science Rich

Fat Loss Signaling Pathway

From catecholamine stimulus to FFA release: the complete cAMP/PKA/HSL cascade inside an adipocyte, with insulin/PDE3B as the dominant inhibitory input.
Health Science Rich

From Lipolysis to Beta-Oxidation

The two-step journey of stored fat: BREAK (lipolysis in the fat cell) and BURN (beta-oxidation in muscle mitochondria), connected by albumin-bound bloodstream transport.
Health Science Medium

Portal Vein Fat Delivery to Liver

Visceral fat FFAs travel via the portal vein directly to the liver, bypassing systemic dilution and delivering a concentrated lipid load that drives hepatic fat accumulation.
Health Science Medium

Visceral vs Subcutaneous Fat Drainage Routes

Anatomical comparison of two drainage routes: visceral fat via portal vein to liver vs subcutaneous fat via systemic veins with 6-8x dilution.
Health Science Rich

PPAR-alpha: Nuclear Switch for Fat Burning

PPAR-alpha activated by FFAs or fibrate drugs heterodimerizes with RXR, binds PPRE, and transcribes CPT1, beta-oxidation enzymes, and ketogenic genes.
Health Science Medium

Re-esterification: The Hidden Fat Recycling Loop

30-50% of liberated FFAs at rest are re-esterified back to triglyceride inside or near the adipocyte, meaning lipolysis alone does not equal fat loss.
Health Science Medium

FFA Release and Clearance Timeline

A 60-minute plasma FFA curve from catecholamine surge to beta-oxidation, with a re-esterification risk window if FFAs are not cleared within 3-4 hours.
Health Science Rich

Liver Detoxification: Phase I and II

CYP450 enzymes (Phase I) oxidize toxins to reactive intermediates; Phase II conjugation enzymes add polar groups to neutralize and enable excretion.
Health Science Medium

Muscle as a Metabolic Sink

Greater lean muscle mass raises resting fat oxidation via elevated mitochondrial density, GLUT4 expression, AMPK activity, and RMR.
Health Science Rich

Cold Exposure and UCP1 Thermogenesis

Cold activates brown adipose tissue via beta-3 adrenergic signaling; UCP1 uncouples the mitochondrial proton gradient to produce heat instead of ATP.
Health Science Rich

Metabolic Fuel Switching

The body switches between glucose, fat, and ketone oxidation based on fuel availability, exercise intensity, and hormonal signals.
Health Science Rich

AMPK and Mitochondrial Biogenesis

AMPK senses low ATP:AMP ratio, activates PGC-1alpha, and drives new mitochondrial synthesis.
Health Science Rich

Glutathione Synthesis and Redox Cycle

Glutathione (GSH) is the cell's master antioxidant; reduced by GR using NADPH and oxidized by GPx while quenching ROS.
Health Science Rich

Alpha-2 vs Beta-3 Adrenergic Receptors

Alpha-2 receptors suppress lipolysis via Gi signaling; beta-3 receptors activate it via Gs/cAMP. Belly fat has up to 10x more alpha-2, explaining stubborn fat resistance.
Health Science Rich

Blood Flow Rebound in Fasted Training

Isometric compression followed by HIIT floods stubborn fat depots with catecholamines during a 2-5 minute reactive hyperemia window, overcoming alpha-2 resistance.
Health Science Rich

Catecholamine Fat Cell Cascade

HIIT triggers adrenal medulla release of adrenaline, which binds beta receptors, raises cAMP via PKA, activates HSL and ATGL, and cleaves triglycerides to FFAs.
Health Science Rich

Cyclic Liberation and Clearance

Alternating HIIT bursts and aerobic clearance cycles are repeated 5-6 times per session. FFAs not cleared in 3-4 hours re-esterify, making the aerobic window critical.
Health Science Rich

Growth Hormone Fasted Cascade

GH released by type IIa fiber recruitment peaks around 30 minutes post-trigger and drives lipolysis via JAK-STAT, bypassing the alpha-2 adrenergic barrier in stubborn fat.
Health Science Rich

Insulin's Triple Block on Lipolysis

Elevated insulin simultaneously blocks HSL, inhibits CPT-1, and upregulates alpha-2 receptors, creating a triple suppression of fat mobilization and oxidation.
Health Science Rich

Portal Vein Visceral Fat Pathway

Visceral fat FFAs drain directly into the portal vein and reach the liver first. With low glycogen, the liver oxidizes them. With high glycogen, they are repackaged as VLDL.
Health Science Rich

Three-Tier Fat Clearance (Animated)

Animated per-cycle breakdown of the HIGH/MODERATE/LOW intensity tiers, totaling 6 minutes clearance per cycle across 6 cycles for 36 minutes plus final clearance.
Health Science Rich

Woosh Effect and Fat Cell Apoptosis

Fat cells fill with water after lipolysis, masking scale progress. A cortisol drop triggers the woosh release. Shrunken cells then enter a 3-8 week apoptosis window that can permanently reduce fat cell count.
Health Science Rich

Cell Membrane Transport

The phospholipid bilayer controls what enters and leaves every cell via integral proteins, GLUT transporters, ion channels, and carrier proteins.
Health Science Rich

Free Fatty Acid Timeline During Fasting

Plasma FFA rises steeply through the first 2-4 hours of fasting, plateaus as adipose release meets oxidative clearance, and drives hepatic ketogenesis.
Health Science Rich

Ketogenesis Cycle

The liver converts excess acetyl-CoA from beta-oxidation into acetoacetate, beta-hydroxybutyrate, and acetone, which fuel brain and muscle during low-carbohydrate states.
Health Science Rich

Lipolysis to Beta-Oxidation

From HSL activating in the adipocyte to the beta-oxidation spiral in muscle mitochondria: the complete fat-burning pathway.
Health Science Rich

Omega-6 in Cell Membranes

Dietary linoleic acid incorporates into membrane phospholipids as arachidonic acid, setting the balance between pro-inflammatory and anti-inflammatory eicosanoids.
Health Science Rich

PPAR-Alpha Fat Burning Switch

PPAR-alpha is a nuclear receptor activated by fatty acids and fibrate drugs that upregulates the full gene program for mitochondrial beta-oxidation.
Health Science Rich

Responsive vs Stubborn Fat

Regional fat differences in alpha-2 receptor density, blood flow, and catecholamine sensitivity explain why belly fat mobilizes easily while hip/thigh fat resists.
Health Science Rich

Sink Strategy for Blood Glucose

Skeletal muscle acts as the primary glucose sink, especially via exercise-induced GLUT4 translocation that works independently of insulin.
Health Science Rich

Three Phases of a Fat-Loss Cut

A prolonged cut progresses through rapid water and glycogen loss, a plateau driven by metabolic adaptation, and a slower recomposition phase.
Health Science Rich

Woosh Effect Fat Cell Mechanism

After significant fat loss, adipocytes transiently fill with water before releasing it, causing a sudden scale drop days or weeks after true fat loss has occurred.
Health Science Medium

Resting Metabolic Rate Determinants

RMR breakdown: fat-free mass 60%, organ mass 20%, fat mass 5%, age/sex/genetics ~15%.
Health Science Medium

Oral Glucose Tolerance Test Curves

OGTT 0/30/60/90/120 min glucose curves: normal vs impaired glucose tolerance vs diabetic thresholds.
Health Science Rich

Liver Detoxification: Phase I and II

CYP450 oxidation (Phase I) generates reactive intermediates; Phase II conjugation neutralizes them for excretion.
Health Science Rich

Pentose Phosphate Pathway

Glucose-6-phosphate branches from glycolysis into the PPP, generating 2 NADPH and ribose-5-phosphate per turn; the non-oxidative phase returns F6P and G3P to glycolysis.
Health Science Rich

Glycemic Response Mechanism

A mixed meal triggers a 45-min glucose peak (normal: 140 mg/dL), first-phase and second-phase insulin secretion, and GLP-1/GIP incretin amplification; in T2D, first-phase is lost and peak exceeds 250 mg/dL.
Health Science Rich

Metformin Mechanism of Action

Metformin mildly inhibits mitochondrial Complex I, raising AMP/ATP and activating AMPK; AMPK phosphorylates CRTC2 to block PEPCK/G6Pase transcription, cutting hepatic glucose output 30-40%, while AS160 phosphorylation drives GLUT4 translocation.

Endocrinology & hormones 53 live

Cortisol, insulin, GH, thyroid, leptin, ghrelin, T, E2, HPA axis.

Health Science Rich

Type 1 vs Type 2 Diabetes

Autoimmune beta-cell destruction (T1D) vs insulin resistance with progressive beta-cell exhaustion (T2D): clinical comparison.
Health Science Medium

Cortisol Circadian Curve

Cortisol surges 30-45 minutes after waking, then declines exponentially through the day to a midnight nadir.
Health Science Rich

HPA Axis Stress Response Cascade

Hypothalamus CRH triggers pituitary ACTH, driving adrenal cortisol; cortisol closes the negative feedback loop.
Health Science Medium

Insulin and Glucose Response Curves

Postprandial glucose rises, insulin follows minutes later, both return to baseline within 2-3 hours.
Health Science Rich

Thyroid Axis Hierarchy

TRH to TSH to T4 to T3 with peripheral conversion and negative feedback.
Health Science Medium

Leptin Satiety Signal

Adipocytes secrete leptin proportionate to fat mass; hypothalamus reads it as a fullness gauge.
Health Science Medium

Leptin Resistance

Chronically high leptin downregulates hypothalamic receptors; the satiety signal stops registering.
Health Science Medium

Ghrelin Meal Cycle

Ghrelin rises before expected meals and falls sharply after eating; the hunger oscillator.
Health Science Simple

Testosterone Diurnal Rhythm

Testosterone peaks in early morning, drops 30-40% by evening in young men.
Health Science Simple

Testosterone Age Decline

Average male testosterone falls 1-2% per year after age 30.
Health Science Medium

Estradiol Across the Menstrual Cycle

E2 climbs through follicular phase, peaks at ovulation, dips, then rises again in the luteal phase.
Health Science Medium

Progesterone in the Luteal Phase

Progesterone rises sharply after ovulation, sustains the endometrium, falls if no implantation.
Health Science Rich

Full Menstrual Hormone Overlay

LH surge at ovulation, FSH follicular rise, estradiol follicular peak, and progesterone luteal rise across 28 days.
Health Science Medium

Menopause Hormone Transition

Perimenopausal estradiol becomes erratic, then drops; FSH rises as ovarian output fails.
Health Science Rich

Aldosterone and the RAAS Cascade

Renin to angiotensin II to aldosterone, regulating sodium, potassium, and blood pressure.
Health Science Medium

ADH and Fluid Balance

Plasma osmolality rises, posterior pituitary releases ADH, kidney conserves water.
Health Science Rich

Parathyroid Calcium Regulation

Low serum calcium triggers PTH; PTH mobilizes bone calcium and activates vitamin D for gut absorption.
Health Science Simple

Calcitonin: PTH Counterweight

High calcium triggers calcitonin from C cells; bone resorption is suppressed.
Health Science Medium

Glucagon Counter-Regulation

Falling glucose triggers alpha-cell glucagon; liver releases glucose via glycogenolysis and gluconeogenesis.
Health Science Medium

Epinephrine: Fight-or-Flight Surge

Stressor triggers adrenal medulla, epinephrine spikes within seconds, mobilizes glucose and raises HR.
Health Science Simple

Oxytocin Release Triggers

Touch, eye contact, breastfeeding, and orgasm all trigger oxytocin from posterior pituitary.
Health Science Simple

Melatonin Nightly Curve

Melatonin starts rising at dusk, peaks 02:00-04:00, falls to near zero by mid-morning.
Health Science Rich

Insulin Signaling Cascade and Resistance Mechanism

Normal IRS-1/PI3K/Akt/GLUT4 pathway shown alongside the DAG/PKC-theta/Ser307 block that causes insulin resistance.
Health Science Medium

Acute Stress Cortisol Response

Cortisol rises 15 to 20 minutes after stress onset, peaks at 30 minutes, normalises by 60 to 90 minutes.
Health Science Medium

CRH and ACTH Pulsatile Release

CRH and ACTH are secreted in synchronized pulses every 60-90 minutes; cortisol amplifies the rhythm.
Health Science Simple

Sex Hormone Binding Globulin (SHBG)

SHBG binds testosterone and estradiol, controlling free hormone availability.
Health Science Rich

HPG Axis (Reproductive)

Hypothalamus GnRH to pituitary LH/FSH to gonadal sex-hormone production with negative feedback.
Health Science Medium

Thyroid Set-Point and Lab Interpretation

TSH-T4 inverse relationship with reference bands and individual set-point variation.
Health Science Medium

GH-IGF-1 Feedback Loop

GH stimulates hepatic IGF-1; IGF-1 feeds back to suppress GH at hypothalamus and pituitary.
Health Science Medium

POMC and its Hormone Derivatives

Single POMC precursor cleaves into ACTH, alpha-MSH, beta-endorphin, and others.
Health Science Medium

Hormone Receptor Binding

A ligand descends from extracellular space, docks into its receptor pocket, and triggers a downstream cascade.
Health Science Medium

HPA Axis Hormone Cascade

CRH to ACTH to cortisol: a three-tier cascade with stress input and negative feedback loop.
Health Science Medium

Insulin Response Overlay: Multi-Meal vs Fasting Window

24-hour insulin overlay comparing typical multi-meal spikes against a time-restricted eating pattern with a visible lipolysis window.
Health Science Medium

Growth Hormone Pulsatile Secretion

GH is released in sharp pulses across 24 hours; the dominant pulse during slow-wave sleep drives the majority of daily lipolytic GH action.
Health Science Medium

Sleep Quality and GH Pulse Amplitude

Good sleep delivers a dominant GH pulse at slow-wave onset; poor sleep fragments this pulse, reducing nightly lipolytic GH action.
Health Science Rich

Insulin Triple-Lock on Fat Mobilization

Elevated insulin simultaneously locks HSL (cAMP depletion), CPT1 (malonyl-CoA block), and alpha-2 receptors (future brake upregulation), sealing the fat cell on three fronts.
Health Science Medium

Alpha-2 Locked Fat Cell

In alpha-2 dominant depots, catecholamine signals and effort arrows bounce off a padlocked fat cell; the Gi/cAMP suppression pathway is the reason.
Health Science Medium

Alpha-2 vs Beta-3 Receptor Pathways in Fat Cells

Adrenaline splits at the fat cell: beta-3 pathway raises cAMP and unlocks lipolysis; alpha-2 pathway lowers cAMP and blocks it.
Health Science Medium

Insulin Triple Block on Lipolysis

Elevated insulin simultaneously suppresses HSL, blocks CPT1 mitochondrial import, and upregulates alpha-2 receptors, locking fat on three fronts.
Health Science Simple

Alpha-2 Receptor Dominance in Stubborn Fat

Alpha-2 stop receptors outnumber beta-3 go receptors by up to 10:1 in lower belly fat, explaining why it resists conventional fat loss.
Health Science Medium

Cortisol vs Testosterone Balance

Cortisol rises under stress and suppresses testosterone; recovery re-establishes the anabolic window.
Health Science Medium

GH Critical Release Window

Mechanical compression transiently restricts blood flow; the post-compression reactive hyperemia window is when GH-driven lipolysis peaks.
Health Science Rich

Cortisol vs Testosterone Balance

Cortisol and testosterone share the pregnenolone precursor; chronic stress steals substrate from the androgen pathway, suppressing testosterone at three levels.
Health Science Rich

Sleep Growth Hormone Pulse

The largest daily GH pulse occurs in the first slow-wave sleep cycle, driving overnight IGF-1 rise, tissue repair, and fat mobilization.
Health Science Rich

HPA Axis Stress Response

Stress activates the hypothalamus-pituitary-adrenal axis; CRH -> ACTH -> cortisol. Chronic activation suppresses immunity, metabolism, and reproductive function.
Health Science Rich

HPA Axis Feedback Loop

Stress -> hypothalamus CRH -> pituitary ACTH -> adrenal cortisol -> negative feedback closes the loop.
Health Science Rich

Insulin Sensitivity: OGTT Response Curves

Oral glucose tolerance test 2-hour curve: insulin-sensitive vs insulin-resistant response patterns.
Health Science Medium

Hormone Half-Life Comparison

Cortisol 60-90 min vs testosterone 10-100 min vs estradiol 13h vs thyroxine 7 days: half-lives compared.
Health Science Medium

Estrogen and Progesterone: 28-Day Cycle

Estradiol peaks day 13 at ovulation; progesterone rises in the luteal phase, peaking day 21.
Health Science Rich

Thyroid Axis: TRH - TSH - T4 - T3

Hypothalamus TRH -> pituitary TSH -> thyroid T4/T3 -> tissue targets; negative feedback loop.
Health Science Rich

mTOR vs AMPK: Growth vs Longevity

Nutrient surplus activates mTOR (growth, anabolism); energy stress activates AMPK (autophagy, longevity).
Health Science Rich

Sirtuins and Longevity

NAD+ activates SIRT1/3 -> DNA repair, mitochondrial biogenesis, glucose homeostasis, extended healthspan.
Health Science Medium

Vitamin D Status Curve

Serum 25(OH)D: deficient <30, insufficient 30-50, sufficient 50-100, high-normal 100-150, toxic >150 nmol/L.

Cell biology 37 live

Membrane transport, organelles, autophagy, apoptosis, mitosis.

Health Science Rich

Tyrosinase - Melanin Pathway

Tyrosinase converts tyrosine to DOPA and dopaquinone; branches to eumelanin (brown/black) or pheomelanin (red/yellow).
Health Science Rich

Membrane Transport Mechanisms

Passive diffusion, facilitated diffusion, primary active, secondary active, vesicular transport.
Health Science Rich

Cellular Organelles Atlas

Nucleus, mitochondrion, ER, Golgi, lysosome, peroxisome - what each does and how they connect.
Health Science Rich

Autophagy Stages

Initiation, nucleation, elongation, maturation, fusion with lysosome, degradation, recycling.
Health Science Rich

Apoptosis: Intrinsic and Extrinsic Pathways

Death receptor (extrinsic) and mitochondrial (intrinsic) routes converge on caspase-3 execution.
Health Science Medium

Mitosis Phases

Prophase, prometaphase, metaphase, anaphase, telophase, cytokinesis - one cell to two.
Health Science Medium

Meiosis vs Mitosis

Mitosis preserves chromosome number; meiosis halves it and shuffles via crossover and independent assortment.
Health Science Rich

Cell Cycle Checkpoints

G1/S, G2/M, and spindle assembly checkpoints gate progression and prevent cancer.
Health Science Rich

ER Stress and the Unfolded Protein Response

Misfolded protein accumulation triggers PERK, IRE1, and ATF6 to restore homeostasis or trigger apoptosis.
Health Science Rich

Mitophagy: Damaged Mitochondria Recycling

PINK1 and Parkin tag depolarized mitochondria with ubiquitin; autophagy machinery clears them.
Health Science Medium

Lysosomal Degradation

Acid hydrolases inside the lysosome break proteins, lipids, nucleic acids, and carbohydrates into monomers.
Health Science Medium

Sodium-Potassium Pump

Na/K-ATPase exports 3 Na, imports 2 K per ATP, sustaining the membrane potential and ionic homeostasis.
Health Science Medium

Endocytosis Modes

Phagocytosis (large particles), macropinocytosis (fluid), clathrin-mediated and caveolae-mediated (receptor-specific).
Health Science Rich

Aquaporin Water Channels

AQP-2 tetramers pass 3 billion water molecules per second while the NPA selectivity filter blocks protons, ions, and all solutes larger than water.
Health Science Rich

Gap Junction Communication

Connexin hemichannels from adjacent cells dock into a 12-subunit gap junction, directly linking cytoplasms and enabling transfer of ions, cAMP, and calcium waves.
Health Science Medium

Protein Folding and Chaperones

Hsp70 and Hsp60/chaperonins shepherd nascent and stressed proteins to their native fold.
Health Science Rich

Ubiquitin-Proteasome System

E1-E2-E3 enzyme cascade tags damaged proteins with polyubiquitin; 26S proteasome shreds them.
Health Science Medium

Resting Membrane Potential

K+ leak channels and Na/K-ATPase establish a resting potential of approximately -70 mV.
Health Science Medium

Mitochondrial Membrane Potential

ETC pumps protons creating ~150 mV across inner membrane; collapse triggers apoptosis.
Health Science Simple

Three Cell Junction Types

Tight junctions (seal), adherens/desmosomes (anchor), gap junctions (communicate).
Health Science Medium

Stem Cell Hierarchy

Totipotent, pluripotent, multipotent, oligopotent, unipotent - widening differentiation as potency narrows.
Health Science Rich

Cellular Senescence (SASP)

Damaged cells exit cycle but stay metabolically active, secreting pro-inflammatory SASP factors.
Health Science Rich

Cell Death Mechanisms: Apoptosis Cascade

Four-stage linear sequence: stressed cell -> BAX/BAK pores in mitochondria -> caspase-9/3 execution -> macrophage cleanup. Apoptosis vs necrosis comparison included.
Health Science Medium

Cell Membrane Fluidity

Healthy membranes (unsaturated fats, EVOO) are fluid and permeable; seed-oil-rich membranes are rigid and block receptor signaling.
Health Science Medium

DNA Repair Pathways

BER for oxidised bases, NER for bulky adducts, NHEJ and HR for double-strand breaks - four pathways guarding genome integrity.
Health Science Medium

Fat Cell Apoptosis Pathways

Intrinsic (mitochondrial) and extrinsic (death receptor) apoptosis cascades converge on caspase-3 to execute adipocyte programmed death.
Health Science Rich

Glutathione Synthesis and Recycling

GSH is built from glutamate, cysteine, and glycine via two-step ATP-dependent ligation; oxidized GSSG is regenerated by glutathione reductase + NADPH.
Health Science Rich

Photobiomodulation Mechanism

Red and near-infrared light (630-850 nm) is absorbed by cytochrome c oxidase, increasing electron transport efficiency, ATP output, and downstream signaling.
Health Science Rich

Mitophagy: Damaged Mitochondria Clearance

PINK1 accumulates on depolarized mitochondria, recruits Parkin, which ubiquitinates outer membrane proteins, triggering autophagic engulfment.
Health Science Rich

ROS Defense System

Superoxide dismutase, catalase, and glutathione peroxidase form a hierarchical antioxidant cascade neutralizing superoxide, hydrogen peroxide, and lipid peroxides.
Health Science Rich

Senescent Cell Clearance Mechanisms

Immune surveillance by NK cells and macrophages, plus senolytic compounds, clear growth-arrested senescent cells that secrete the inflammatory SASP.
Health Science Medium

Light Wavelength Tissue Penetration Depth

Red (630-700 nm) penetrates to dermis; near-infrared (800-1100 nm) reaches muscle and bone; UV is absorbed in the epidermis.
Health Science Rich

Electron Transport Chain

NADH and FADH2 donate electrons through four mitochondrial membrane complexes; the resulting proton gradient drives ATP synthase to produce ATP.
Health Science Rich

Apoptosis vs Necrosis

Programmed apoptosis dismantles the cell in an orderly, immunologically silent process; necrosis is uncontrolled rupture that triggers inflammation.
Health Science Rich

Collagen Synthesis and Degradation

Fibroblasts build collagen with vitamin C as cofactor; matrix metalloproteinases regulate turnover; the balance determines tissue strength and repair.
Health Science Rich

Myonuclear Domain Theory

Each muscle fiber nucleus controls a fixed volume of sarcoplasm; adding nuclei through satellite cell fusion enables growth beyond the single-nucleus ceiling, and they persist after detraining.
Health Science Rich

Myostatin Muscle Limit

Myostatin is a TGF-beta family protein that signals through ActRIIB and SMAD2/3 to suppress satellite cell proliferation and limit muscle fiber size.

Gut & microbiome 27 live

Microbial diversity, SCFAs, gut-brain axis, leaky gut, dysbiosis.

Health Science Medium

Microbial Diversity (Shannon Index)

High Shannon diversity correlates with metabolic and immune health; Western diets compress it.
Health Science Rich

SCFA Production from Fiber

Colonic bacteria ferment fiber to acetate, propionate, butyrate - fuel for colonocytes and systemic signals.
Health Science Rich

Gut-Brain Axis

Vagus, immune, endocrine, and metabolite routes connect gut microbes to brain function.
Health Science Rich

Leaky Gut (Increased Intestinal Permeability)

Tight-junction disruption lets LPS and antigens cross into circulation, driving systemic inflammation.
Health Science Medium

Dysbiosis Patterns

Loss of diversity, bloom of pathobionts, depletion of keystone species - three signatures of dysbiosis.
Health Science Medium

Prebiotic Fiber Types

Inulin, FOS, GOS, resistant starch, beta-glucan, pectin - which microbes ferment which fibers.
Health Science Medium

Probiotic Strains

Strain-specific effects: L. rhamnosus GG (diarrhea), B. lactis (constipation), S. boulardii (C. diff).
Health Science Medium

Fecal Microbiota Transplant

Donor stool processed and infused via colonoscopy, capsule, or NJ tube to reset recipient microbiome.
Health Science Rich

Bile Acid Pool and Microbiome

Microbes deconjugate primary bile acids to secondary; secondary BAs signal via FXR and TGR5.
Health Science Medium

GLP-1 Pathway: L Cell to Beta Cell

Nutrients trigger ileal L cells to release GLP-1; it amplifies insulin secretion, slows gastric emptying, suppresses glucagon, and drives satiety. GLP-1 RAs (semaglutide) mimic this cascade.
Health Science Medium

Microbiome Recovery After Antibiotics

Diversity crashes within days; partial recovery over weeks; full recovery may take 6+ months.
Health Science Rich

Tryptophan-Kynurenine Axis

Microbes shunt tryptophan toward indole metabolites; inflammation diverts host tryptophan to kynurenine.
Health Science Simple

Fermented Foods and Inflammation

High fermented-food diets raise diversity and lower inflammatory markers within 10 weeks.
Health Science Medium

TMAO from Gut Microbes

Microbes metabolize choline and carnitine to TMA; liver oxidizes to TMAO; high TMAO predicts CV risk.
Health Science Medium

Short Bowel Microbiome Adaptation

After resection, remaining bowel undergoes structural and microbial adaptation over months.
Health Science Medium

Microbiome Shifts with Age

Diversity drops, Bifidobacterium falls, Proteobacteria rise; centenarians show distinct signatures.
Health Science Medium

SIBO: Small Intestinal Bacterial Overgrowth

Bacteria normally confined to colon overgrow in small intestine, fermenting carbs prematurely.
Health Science Medium

Prebiotic Fiber to SCFA Production

Dietary fiber resists digestion, reaches the colon, and is fermented by Firmicutes and Bacteroidetes into short-chain fatty acids: acetate, propionate, and butyrate.
Health Science Rich

Probiotic Colonization and Gut Wall Interaction

Probiotic bacteria colonize the mucus layer, compete with pathogens via competitive exclusion, and communicate with the mucosal immune system to promote Treg induction and IgA production.
Health Science Rich

Digestive Enzyme Cascade

Salivary amylase in the mouth to pancreatic lipase/protease to small intestine brush-border peptidases: each site adds enzymes as food moves through the GI tract.
Health Science Rich

Gut Barrier Permeability

Tight junction proteins (claudin, occludin, ZO-1) seal epithelial gaps; inflammation or dysbiosis causes leaky gut.
Health Science Rich

Digestive Enzyme Cascade

Salivary amylase, gastric pepsin, pancreatic lipase and proteases, and brush-border enzymes sequentially break down carbohydrates, proteins, and fats through the GI tract.
Health Science Rich

Gut Barrier and Tight Junctions

Claudin, occludin, and ZO-1 proteins form the tight junction seal between enterocytes; zonulin release and inflammation open the paracellular pathway.
Health Science Rich

Intestinal Parasite Lifecycle

Common intestinal parasites (Giardia, Cryptosporidium, helminths) follow a fecal-oral or soil-transmitted cycle with distinct host and environmental stages.
Health Science Rich

Prebiotic to SCFA Pathway

Dietary fiber is fermented by colonic bacteria to short-chain fatty acids (butyrate, propionate, acetate), which fuel colonocytes, regulate immunity, and cross the gut-brain axis.
Health Science Medium

Gut Microbiome Diversity by Diet

Shannon diversity index by diet type: Western vs Mediterranean vs plant-rich vs fermented-food-rich, with SCFA production noted.
Health Science Rich

Gut-Brain Axis via Vagus Nerve

Vagal afferent fibers carry gut microbiome signals (SCFAs, serotonin) to the brain; bidirectional communication affects mood and cognition.

Cardiovascular 27 live

Cardiac cycle, blood pressure, atherosclerosis, lipid metabolism.

Health Science Rich

Cardiac Cycle

Atrial systole, ventricular systole, ventricular diastole - pressures, volumes, valve events.
Health Science Rich

Blood Pressure Regulation

Baroreflex (seconds), RAAS (minutes-hours), pressure natriuresis (days) - three time scales.
Health Science Rich

Atherosclerosis Progression

Endothelial dysfunction -> LDL infiltration -> foam cells -> fatty streak -> fibrous plaque -> rupture.
Health Science Rich

Lipoprotein Trafficking

Chylomicrons from gut, VLDL/IDL/LDL from liver, HDL reverse transport - the lipid economy.
Health Science Medium

ECG Waves: P-QRS-T

P (atrial depolarization), QRS (ventricular depolarization), T (ventricular repolarization).
Health Science Medium

Frank-Starling Curve

Stroke volume rises with end-diastolic volume up to a point; failing hearts shift the curve down.
Health Science Rich

Preload, Afterload, Contractility

Three independent levers determining stroke volume - mapped onto pressure-volume loops.
Health Science Rich

Myocardial Infarction Timeline

Coronary occlusion -> ischemia -> infarction -> remodeling - minutes to weeks.
Health Science Medium

Common Arrhythmias

Bradycardia, tachycardia, AFib, AFlutter, V-tach, V-fib - rhythm strips compared.
Health Science Medium

Baroreflex Loop

Carotid stretch sensors -> brainstem -> SNS/PNS -> HR and vascular tone in seconds.
Health Science Medium

Capillary Starling Forces

Hydrostatic pushes fluid out arterial end; oncotic pulls it back venous end; lymph clears the rest.
Health Science Medium

Venous Return Mechanisms

Skeletal muscle pump, respiratory pump, valve cusps, venous tone - how blood gets back uphill.
Health Science Rich

Hypertension Pathophysiology

Genetics + lifestyle -> sympathetic overdrive, RAAS dysregulation, endothelial dysfunction -> sustained high BP.
Health Science Rich

Heart Failure Spectrum

HFrEF (low EF) vs HFpEF (preserved EF, stiff ventricle) - distinct mechanisms, overlapping symptoms.
Health Science Medium

Exercise and Cardiac Output

CO rises 4-6x with exercise via increased HR and stroke volume; trained heart achieves higher SV at lower HR.
Health Science Medium

Lipid Panel Components

Total chol, LDL, HDL, TG, non-HDL, ApoB, Lp(a) - what each value means and predicts.
Health Science Medium

Statin Mechanism

HMG-CoA reductase inhibition lowers liver cholesterol synthesis, upregulates LDL receptor, clears LDL.
Health Science Medium

Aortic Stiffness with Aging

Aortic compliance falls with age, raising systolic BP and pulse pressure.
Health Science Simple

Blood Volume Distribution

~70% of blood sits in veins; sympathetic activation moves it centrally on demand.
Health Science Medium

Coronary Circulation

LAD, LCx, RCA territories; perfusion happens during diastole only.
Health Science Simple

Sodium and Blood Pressure

Salt-sensitive individuals see sharper BP response to dietary sodium; non-sensitive show flat curve.
Health Science Medium

Endothelial Function and Nitric Oxide

Healthy endothelium releases NO via eNOS; oxidative stress and ADMA inhibit it, raising vascular tone.
Health Science Rich

Nitric Oxide and Vasodilation

L-arginine via eNOS generates NO, activating sGC/cGMP/PKG signaling to relax smooth muscle. Exercise and dietary nitrates boost the pathway.
Health Science Rich

Poor Blood Flow and Stubborn Fat

Subcutaneous vasoconstriction in alpha-2-dense fat depots strands mobilized FFA locally, allowing re-esterification to cancel the lipolysis that already occurred.
Health Science Medium

Kidney Function and eGFR by Age

eGFR by age: normal 90-120 mL/min/1.73m2, CKD stages 1-5 thresholds, age-related decline.
Health Science Rich

Cholesterol to Plaque Pathway

LDL enters arterial wall, oxidizes, foam cells form, plaque develops; HDL reverse transport opposes it.
Health Science Medium

Heart Rate Variability: Autonomic Balance

High HRV indicates parasympathetic dominance and recovery; low HRV indicates sympathetic stress. 24-hour HRV pattern.

Sleep & circadian 26 live

Hypnogram, REM/NREM cycles, circadian phase, jet lag, shift work.

Health Science Rich

Sleep Hypnogram: Five Stages Across the Night

Full-night hypnogram: N1, N2, N3, REM across 4-5 cycles; deep sleep front-loaded, REM expands toward morning.
Health Science Medium

Hypnogram: A Night of Sleep

NREM 1-3 and REM cycle every 90 minutes; deep sleep dominates first half, REM the second.
Health Science Medium

REM vs NREM Physiology

REM: brain-active, muscle-paralyzed, vivid dreams. NREM: brain-quiet, body-restorative.
Health Science Rich

Suprachiasmatic Nucleus: The Master Clock

SCN entrains to light via retinohypothalamic tract; broadcasts ~24h timing to peripheral clocks.
Health Science Medium

Jet Lag and Phase Shift

Eastward travel requires phase advance (harder); westward requires phase delay (easier).
Health Science Medium

Shift Work Circadian Disruption

Working nights forces a chronic circadian misalignment with metabolic and cancer risks.
Health Science Medium

Two-Process Model: Sleep Pressure

Process S (homeostatic adenosine pressure) plus Process C (circadian alerting) determine sleep timing.
Health Science Medium

Caffeine Blocks Adenosine

Caffeine binds A1/A2A receptors competitively, masking accumulated sleep pressure.
Health Science Medium

Light Suppresses Melatonin

Even ~10 lux of evening light cuts melatonin in half; bright phone screens delay sleep onset.
Health Science Simple

Core Body Temperature and Sleep

CBT must drop ~1 C for sleep onset; rises again in early morning to drive waking.
Health Science Simple

Chronotype Distribution

Larks, owls, and the bell curve of biological wake times across the population.
Health Science Medium

Sleep Deprivation: Cognitive Decline

After 17 hours awake, performance equals 0.05% BAC; after 24, equals 0.10%.
Health Science Simple

Sleep and Immune Function

Less than 6h sleep reduces vaccine antibody response by 50%; nights of <5h triple cold susceptibility.
Health Science Medium

Sleep Apnea Oxygen Desaturation

Repeated airway collapse drops SpO2; sympathetic surges fragment sleep and elevate CV risk.
Health Science Simple

REM Cycle Lengthening

REM bouts grow from ~10 min in cycle 1 to ~45 min in cycle 5.
Health Science Simple

Social Jet Lag

Weekday-weekend sleep timing mismatch causes a chronic mini-jetlag with metabolic costs.
Health Science Medium

Sleep and Memory Consolidation

NREM consolidates declarative memory via hippocampal-cortical replay; REM consolidates emotional and procedural.
Health Science Medium

Orexin and Wake Stability

Lateral hypothalamic orexin neurons stabilize wake; their loss causes narcolepsy.
Health Science Medium

Sleep Changes with Age

Total sleep stable; deep sleep falls 60-80% from age 20 to 70; awakenings increase.
Health Science Medium

Melatonin and Blue-Light Suppression

Evening blue-light exposure delays DLMO by 1-3 hours and blunts melatonin peak amplitude.
Health Science Rich

Circadian Clock Mechanism

SCN master clock drives 6 hormone rhythms across 24 hours. All curves computed from Gaussian peak distributions; morning/noon/evening/night phases shown simultaneously.
Health Science Medium

Adenosine Sleep Pressure

Adenosine accumulates during waking hours and binds A1/A2A receptors to increase sleep pressure; caffeine competes for these receptors and masks the drive to sleep.
Health Science Rich

Circadian Rhythm: The Molecular Clock

CLOCK/BMAL1 drive a transcription-translation feedback loop with a ~24-hour period; light resets the SCN master clock daily.
Health Science Rich

Sleep Cycle Stages: 8-Hour Night

4-5 cycles of N1/N2/N3/REM across 8 hours; deep sleep front-loaded, REM back-loaded.
Health Science Medium

Circadian Cortisol Curve

24-hour cortisol: cortisol awakening response peak ~8am, ultradian pulses, midnight nadir.
Health Science Medium

Melatonin Suppression by Evening Light

Evening light delays DLMO by 1-3 hours and blunts melatonin peak, pushing sleep onset later.

Immune system & inflammation 24 live

Innate vs adaptive, cytokine cascades, NF-kB, resolution pathways.

Health Science Medium

Innate vs Adaptive Immunity

Innate is fast and generic; adaptive is slow, specific, and remembers.
Health Science Rich

Pro-Inflammatory Cytokine Cascade

TNF-alpha, IL-1, IL-6 amplify locally and systemically; IL-10 and TGF-beta resolve.
Health Science Rich

NF-kB Activation Pathway

TLR/TNF receptor -> IKK -> phosphorylates IkB -> NF-kB enters nucleus -> transcribes inflammatory genes.
Health Science Rich

NLRP3 Inflammasome

Two-signal activation assembles NLRP3-ASC-caspase-1; cleaves pro-IL-1-beta to active IL-1-beta.
Health Science Rich

Complement Cascade

Three pathways converge on C3, opsonization, MAC formation, and inflammation.
Health Science Medium

Antibody Isotypes

IgM, IgG, IgA, IgE, IgD: structures, locations, and roles compared.
Health Science Rich

T Cell Activation

Naive T cell needs TCR signal, costimulation (CD28-B7), and cytokines to clonally expand.
Health Science Medium

T Helper Subsets

Th1, Th2, Th17, Treg - four flavors of CD4 T cell with distinct cytokines and roles.
Health Science Rich

B Cell Class Switching

Activation-induced cytidine deaminase (AID) drives DNA recombination switching IgM to IgG/A/E.
Health Science Rich

MHC Class I vs II Antigen Presentation

MHC-I displays cytosolic peptides to CD8; MHC-II displays endocytosed peptides to CD4.
Health Science Medium

Inflammation Resolution

Specialized pro-resolving mediators (resolvins, protectins, maresins) actively switch off inflammation.
Health Science Medium

M1 vs M2 Macrophage Polarization

M1 is classically activated and pro-inflammatory; M2 is alternatively activated and pro-resolving.
Health Science Rich

Neutrophil Extracellular Traps

Neutrophils extrude DNA-histone webs decorated with antimicrobial proteins to ensnare pathogens.
Health Science Medium

Fever and the Hypothalamic Set-Point

IL-1, IL-6, TNF cross blood-brain barrier signal, raise PGE2, reset hypothalamic set-point upward.
Health Science Medium

Chronic Low-Grade Inflammation

Persistent CRP, IL-6 elevation drives metabolic dysfunction, atherosclerosis, neurodegeneration.
Health Science Medium

Vaccine Antibody Response

Primary response is slow and IgM-dominant; secondary is fast, large, and IgG-dominant.
Health Science Rich

Cytokine Storm

Runaway IL-6/TNF feedback drives multi-organ damage in severe infection (sepsis, severe COVID).
Health Science Rich

Gut-Immune Axis

Peyer patches, M cells, IgA in lumen; ~70% of immune cells reside in gut.
Health Science Rich

Pyroptosis: Inflammatory Cell Death

Caspase-1 cleaves gasdermin-D, which forms membrane pores, cell swells and bursts releasing inflammatory contents.
Health Science Rich

ROS Antioxidant Defense System

Superoxide from multiple cellular sources is dismutated by SOD to H2O2, then neutralized by catalase and glutathione peroxidase, with NADPH from the pentose phosphate pathway regenerating the system.
Health Science Medium

ROS Hormesis Curve

Low-dose ROS from exercise, cold, and fasting activates NRF2 and adaptive pathways; high-dose ROS causes damage. The inverted-U relationship is the basis for exercise and stress tolerance.
Health Science Medium

Innate vs Adaptive Immunity Response Curves

Innate fires within hours, peaks day 1-2, and fades; adaptive activates day 3-4, peaks day 10-11, then forms memory.
Health Science Medium

Acute vs Chronic Inflammation Time Course

Acute spike with resolution vs chronic low-grade plateau; CRP and IL-6 as biomarkers.
Health Science Rich

Immune Response Timeline: Innate to Adaptive

Innate (0-12h) -> adaptive cellular T cell (1-7d) -> adaptive humoral antibody (7-21d); antibody titer curve.

Aging & longevity 23 live

Hallmarks of aging, telomeres, senescence, longevity pathways.

Health Science Rich

Twelve Hallmarks of Aging

Genomic instability, telomere attrition, epigenetic drift, proteostasis loss, etc. - the canonical 12.
Health Science Medium

Telomere Shortening Across Cell Divisions

TTAGGG caps shrink ~50-100 bp per division; below critical length cells senesce or undergo apoptosis.
Health Science Medium

Telomere Attrition

Telomeres shorten with each division; below a critical length, cells senesce or die.
Health Science Rich

Longevity Pathways

Caloric restriction -> AMPK, sirtuins, FoxO; mTOR inhibition; insulin/IGF-1 reduction.
Health Science Rich

Senescent Cell Accumulation

Senescent cells accumulate with age, secrete SASP, damage local tissue; senolytics clear them.
Health Science Medium

NAD+ Decline with Age

Tissue NAD+ falls 50% from young adult to old age, limiting sirtuin and PARP activity.
Health Science Rich

Sirtuin NAD-Dependent Deacetylation

SIRT1-7 use NAD+ to deacetylate histones and proteins, reprogramming gene expression and metabolism.
Health Science Rich

Rapamycin and mTOR Inhibition

Rapamycin binds FKBP12, inhibits mTORC1; extends lifespan in every model tested.
Health Science Medium

Caloric Restriction

20-40% energy restriction extends lifespan and healthspan via overlapping pathways: AMPK, sirtuins, autophagy.
Health Science Medium

Biological vs Chronological Age

Epigenetic clocks (Horvath, GrimAge) measure biological age; same chronological age can differ by decades.
Health Science Rich

Mitochondrial Decline with Age

Mitochondrial number, function, and quality control all degrade; ROS rise; mtDNA mutations accumulate.
Health Science Medium

Epigenetic Drift

DNA methylation patterns drift with age - some sites lose methylation, others gain it.
Health Science Simple

Hayflick Limit

Normal somatic cells divide ~50 times before senescence; cancer and stem cells bypass via telomerase.
Health Science Rich

FoxO Longevity Genes

FoxO3 variants associate with extreme longevity; transcribe stress-resistance and antioxidant genes.
Health Science Simple

Blue Zone Common Patterns

Plant-forward diet, daily movement, social embeddedness, purpose, modest CR - the converging signals.
Health Science Rich

Senolytic Mechanism

Drugs that disrupt senescent-cell anti-apoptotic networks (BCL-2, PI3K) trigger their selective death.
Health Science Rich

Immunosenescence and Inflammaging

Thymic involution, T-cell repertoire contraction, chronic low-grade inflammation drive age-related disease.
Health Science Rich

Senescent Cell SASP: The Damage-Secreting Factory

Senescent cells permanently halt division but remain metabolically active, secreting a pro-inflammatory SASP cocktail that damages neighboring tissue, promotes bystander senescence, and drives age-related pathology.
Health Science Rich

Senolytic Strategy: Clearing Senescent Cells

Senescent cells survive by overexpressing BCL-2 anti-apoptotic proteins. Senolytic drugs (dasatinib+quercetin, fisetin, navitoclax) disrupt this survival network, selectively triggering senescent cell apoptosis.
Health Science Rich

NAD+ Lifecycle and Salvage

NAD+ is synthesized from tryptophan and vitamin B3 precursors, consumed by sirtuins and PARPs, and regenerated via the salvage pathway.
Health Science Rich

DNA Methylation Biological Clock

CpG methylation patterns drift with age; epigenetic clocks (Horvath, Hannum) predict biological age from methylation data.
Health Science Rich

Autophagy Induction by Fasting

Fasting hours timeline: 12h glycogen depleted, 16-24h ketosis and autophagy ramps up, 48h+ peak autophagy.
Health Science Rich

Oxidative Stress Cascade

ROS generation -> lipid, protein, DNA damage -> antioxidant defenses -> repair vs accumulate decision.

Neuroscience 22 live

Action potential, neurotransmitters, synaptic plasticity, brain regions.

Health Science Rich

Voltage-Gated Calcium Channel Signaling

Membrane depolarization opens Cav channels; Ca2+ influx triggers calmodulin, calcineurin, and NFAT-driven gene expression.
Health Science Rich

Four Dopamine Pathways

Mesolimbic (reward), mesocortical (cognition), nigrostriatal (motor), tuberoinfundibular (prolactin).
Health Science Medium

Major Neurotransmitters at a Glance

Glutamate, GABA, dopamine, serotonin, norepinephrine, acetylcholine in one table: type, receptors, function, pathology, drug examples.
Health Science Medium

Serotonin Pathways

Raphe nuclei project broadly through cortex, limbic system, and brainstem; gut produces 90% of body serotonin.
Health Science Rich

BDNF and Neuroplasticity

Exercise triggers BDNF release; TrkB binding activates CREB; new synapses, LTP, and hippocampal neurogenesis follow. Decline triggers and support factors shown.
Health Science Rich

BDNF Signaling Cascade

Exercise and learning raise BDNF; TrkB signaling drives dendritic spine growth and survival.
Health Science Medium

Major Brain Regions

Frontal lobe, parietal, temporal, occipital, cerebellum, brainstem, limbic structures - what each does.
Health Science Medium

Limbic System

Hippocampus, amygdala, cingulate, hypothalamus - the emotion and memory loop.
Health Science Medium

Voltage-Gated Ion Channels

Na+, K+, Ca2+, Cl- channels open and close based on membrane voltage; the molecular basis of excitability.
Health Science Rich

Glymphatic System

CSF flushes through brain interstitium during sleep, clearing metabolic waste including amyloid-beta.
Health Science Medium

Adult Neurogenesis

Hippocampal dentate gyrus produces new neurons throughout life; exercise and learning amplify the rate.
Health Science Medium

Ascending Pain Pathway

Nociceptor -> dorsal horn -> spinothalamic tract -> thalamus -> somatosensory cortex.
Health Science Medium

Sympathetic vs Parasympathetic

Fight-or-flight against rest-and-digest, with major target organs and effects compared.
Health Science Medium

Vagus Nerve and HRV

Parasympathetic vagal tone regulates HR variability; high HRV = healthy autonomic flexibility.
Health Science Rich

Sleep-Wake Circuits

Ascending arousal system vs sleep-promoting VLPO; orexin from hypothalamus stabilizes wake state.
Health Science Medium

Memory Consolidation Cycle

Encoding in hippocampus, consolidation via sleep replay, gradual transfer to neocortical storage.
Health Science Rich

Dopamine Reward Circuit

VTA projects to nucleus accumbens (reward), PFC (cognition), and substantia nigra to striatum (motor); reward prediction error signals encode learning.
Health Science Rich

GABA / Glutamate Balance

GABA is the brain's main inhibitory signal; glutamate is the main excitatory signal; their balance governs arousal, anxiety, and cognition.
Health Science Rich

Pain Neuroscience

Pain is a brain output, not a tissue readout. Nociception, central sensitization, and descending modulation all shape what reaches consciousness.
Health Science Rich

Neurotransmitter Synthesis Pathways

Serotonin from tryptophan, dopamine from tyrosine, GABA from glutamate, acetylcholine from choline: four animated synthesis routes in one diagram.
Health Science Rich

Dopamine Reward Loop

Dopamine encodes prediction errors, not just pleasure; the mesolimbic pathway drives motivation, learning, and the neural basis of addiction.
Health Science Rich

Dopamine Reward Cycle: Phasic vs Tonic

Phasic dopamine spikes on rewards and cues; tonic baseline sets sensitivity; chronic stimulation collapses tonic, driving tolerance.

Respiratory 14 live

Gas exchange, V/Q matching, breathing mechanics, altitude.

Health Science Medium

Alveolar Gas Exchange

O2 diffuses in, CO2 out across the 0.5 micron alveolar-capillary membrane in under a second.
Health Science Rich

Oxygen-Hemoglobin Dissociation Curve

Sigmoid curve; right shift (Bohr) releases more O2 in tissues; left shift binds tighter in lungs.
Health Science Rich

V/Q Matching

Ventilation and perfusion gradient down the lung; mismatch creates dead space (high V/Q) or shunt (low V/Q).
Health Science Medium

Breathing Mechanics

Diaphragm contracts (inhale) and relaxes (exhale); accessory muscles add capacity at high demand.
Health Science Medium

Lung Volumes and Capacities

TV, IRV, ERV, RV, plus IC, FRC, VC, TLC - the spirometric building blocks.
Health Science Rich

Altitude Adaptation

Acute hyperventilation, days-weeks EPO and 2,3-BPG, months structural lung and capillary changes.
Health Science Medium

Asthma: Bronchospasm and Inflammation

Trigger to mast-cell degranulation to bronchoconstriction, edema, mucus to airflow obstruction.
Health Science Medium

COPD and Emphysema

Chronic inflammation destroys alveolar walls; air-trapping, hyperinflation, reduced gas exchange surface.
Health Science Rich

Respiratory Control Center

Medullary DRG/VRG and pontine groups set rhythm; chemoreceptors adjust based on PCO2 and PO2.
Health Science Medium

CO2 Transport in Blood

Three forms: bicarbonate (~70%), Hb-bound carbamino (~23%), dissolved (~7%).
Health Science Rich

Pulmonary Hypertension

Sustained pulmonary arterial pressure elevation strains right heart; causes range from PE to PAH.
Health Science Medium

Pulmonary Embolism: V/Q Mismatch

Embolus blocks perfusion in a region; ventilated but unperfused = dead space; hypoxemia ensues.
Health Science Medium

Obstructive Sleep Apnea Mechanics

Pharyngeal muscle relaxation collapses airway; arousal restores patency; cycle repeats hundreds of times.
Health Science Medium

Carbon Monoxide Poisoning

CO binds Hb 240x stronger than O2; left-shifts curve, drops O2 delivery, masks pulse-ox.
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