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Explain question number 35 to 43 in full detail with the exam-oriented MBBS with flow chart and diagram only.

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MBBS BIOCHEMISTRY - Questions 35 to 43

Complete Exam-Oriented Notes with Flowcharts & Diagrams

Q.35 - GLYCOGEN METABOLISM + HORMONAL REGULATION

STRUCTURE OF GLYCOGEN

Glycogen = Branched polysaccharide of α-D-glucose
├── Primary bond: α(1→4) glycosidic linkage (straight chain)
├── Branch point: α(1→6) glycosidic linkage (every 8-14 residues)
└── Single molecule: up to 55,000 glucosyl residues

STORES:
  Liver glycogen  → ~100 g  → 10% fresh weight → Maintains BLOOD GLUCOSE
  Muscle glycogen → ~400 g  → 1-2% fresh weight → Fuel for MUSCLE CONTRACTION

A. GLYCOGEN SYNTHESIS (GLYCOGENESIS)

FLOWCHART: Glycogenesis

Glucose
   │ Hexokinase (muscle) / Glucokinase (liver) + ATP
   ▼
Glucose-6-phosphate (G6P)
   │ Phosphoglucomutase
   ▼
Glucose-1-phosphate (G1P)
   │ UDP-glucose pyrophosphorylase + UTP → PPi
   ▼
UDP-Glucose  ← [Activated form of glucose]
   │
   │ [Primer needed: Glycogenin protein - self-glucosylates]
   ▼
GLYCOGEN SYNTHASE  ← KEY ENZYME (rate-limiting)
   │ Adds glucose via α(1→4) bonds
   ▼
Linear chain ────────────────────────────────┐
                                              │ Branching Enzyme
                                              │ (Amylo-4,6-glucan transferase)
                                              │ Transfers 6-7 residues to C6-OH
                                              ▼
                                    BRANCHED GLYCOGEN

Key Points:

Glycogenin is the primer (self-glucosylating protein, first 7-8 glucose residues)
UDP-glucose is the activated donor of glucose
Pyrophosphate (PPi) hydrolysis drives the reaction forward (irreversible)

B. GLYCOGEN DEGRADATION (GLYCOGENOLYSIS)

FLOWCHART: Glycogenolysis

BRANCHED GLYCOGEN
   │
   │ Glycogen Phosphorylase (KEY enzyme)
   │ Cleaves α(1→4) bonds from non-reducing end
   │ Requires Pyridoxal Phosphate (PLP/Vit B6)
   │ Stops 4 residues before branch point
   ▼
Glucose-1-phosphate + Shortened chain (4 units from branch)
   │                        │
   │                        │ Debranching Enzyme (TWO activities):
   │                        ├─ Transferase: moves 3 of 4 residues to main chain
   │                        └─ Glucosidase: cleaves α(1→6) bond → FREE GLUCOSE
   │
   │ Phosphoglucomutase
   ▼
Glucose-6-phosphate
   │
   ├──────────────────────── MUSCLE (no glucose-6-phosphatase)
   │                              → Enters GLYCOLYSIS → ATP
   │
   └──────────────────────── LIVER (has glucose-6-phosphatase)
                                   │ Glucose-6-phosphatase (ER enzyme)
                                   ▼
                              FREE GLUCOSE → Blood

Memory Aid: "PhosPhorylase Phosphorylates - Phosphoglucomutase Moves - Phosphatase Frees"

C. HORMONAL REGULATION OF GLYCOGEN METABOLISM

╔══════════════════════════════════════════════════════════════╗
║          HORMONAL REGULATION (THE BIG PICTURE)               ║
╚══════════════════════════════════════════════════════════════╝

GLUCAGON / EPINEPHRINE (Catabolic hormones - Low blood glucose)
        │
        ▼
   G-protein coupled receptor
        │
        ▼
   Adenylate Cyclase ACTIVATED
        │
        ▼
   ATP ──→ cAMP ↑
        │
        ▼
   Protein Kinase A (PKA) ACTIVATED
        │
        ├──────────────────────────────────────┐
        ▼                                      ▼
Phosphorylase Kinase                  Glycogen Synthase
ACTIVATED (phosphorylated)            INACTIVATED (phosphorylated)
        │                                      │
        ▼                                      ▼
Glycogen Phosphorylase b               Glycogen Synthase b
→ Phosphorylase a (ACTIVE)             (INACTIVE form)
        │
        ▼
  GLYCOGENOLYSIS ↑                GLYCOGENESIS ↓
  (Glucose released)

══════════════════════════════════════════════════════════════

INSULIN (Anabolic hormone - High blood glucose)
        │
        ▼
   Tyrosine kinase receptor
        │
        ▼
   Phosphodiesterase ACTIVATED → cAMP ↓
        │
        ▼
   PKA INACTIVATED
        │                        Phosphoprotein Phosphatase-1 ACTIVATED
        │                              │
        ├──────────────────────────────┤
        ▼                              ▼
Phosphorylase a → Phosphorylase b    Glycogen Synthase b → Synthase a
(INACTIVE)                           (ACTIVE)
        │
        ▼
  GLYCOGENOLYSIS ↓               GLYCOGENESIS ↑

Summary Table: Hormonal Effects

Hormone	Blood Glucose	cAMP	Glycogen Synthase	Glycogen Phosphorylase	Net Effect
Glucagon	Low	↑	Inactive (b)	Active (a)	Glycogenolysis
Epinephrine	Stress	↑	Inactive (b)	Active (a)	Glycogenolysis
Insulin	High	↓	Active (a)	Inactive (b)	Glycogenesis
Cortisol	Low	-	Promotes synthesis	-	Glycogenesis (liver)

NOTE: GLYCOGEN STORAGE DISEASES (GSDs)

Type	Enzyme Deficient	Organ	Disease Name	Features
0	Glycogen Synthase	Liver	-	Hypoglycemia, hyperketonemia
I	Glucose-6-phosphatase	Liver/Kidney	Von Gierke	Severe fasting hypoglycemia, hepatomegaly, lactic acidosis
II	Lysosomal α-glucosidase	All organs	Pompe	Cardiomegaly, hypotonia, death <2 yrs
III	Debranching enzyme	Liver/Muscle	Cori	Mild hypoglycemia, short outer branches
IV	Branching enzyme	Liver	Andersen	Hepatosplenomegaly, fatal
V	Muscle phosphorylase	Muscle	McArdle	Exercise-induced cramps, myoglobinuria
VI	Liver phosphorylase	Liver	Hers	Hepatomegaly, mild hypoglycemia

Mnemonics:

"Very Poor Carbohydrate Absorption = Andersen's, McArdle's, Her's" for Types I, II, III, IV, V, VI
Von Gierke = Glucose can't exit liver (no G6Pase)
McArdle = Muscle can't break glycogen (ischemic forearm test: no lactate rise)

Q.36 - BLOOD GLUCOSE REGULATION + HORMONES + TYPES OF DIABETES MELLITUS

NORMAL BLOOD GLUCOSE LEVELS

Fasting plasma glucose: 70-100 mg/dL (3.9-5.6 mmol/L)
Postprandial (2h):     < 140 mg/dL
Impaired fasting glucose: 100-125 mg/dL
Diabetes mellitus:     ≥ 126 mg/dL (fasting) OR ≥ 200 mg/dL (random)

MECHANISMS OF BLOOD GLUCOSE REGULATION

╔══════════════════════════════════════╗
║    BLOOD GLUCOSE HOMEOSTASIS         ║
║         (Normal: 70-100 mg/dL)       ║
╚══════════════════════════════════════╝

GLUCOSE RISES (Fed state)             GLUCOSE FALLS (Fasting)
      │                                       │
      ▼                                       ▼
β-cells of Pancreas                   α-cells of Pancreas
release INSULIN                       release GLUCAGON
      │                                       │
      ▼                                       ▼
┌─────────────────────────┐      ┌───────────────────────────┐
│ INSULIN ACTIONS:         │      │ GLUCAGON ACTIONS:          │
│ • Glucose uptake ↑       │      │ • Glycogenolysis ↑ (liver) │
│ • Glycogenesis ↑         │      │ • Gluconeogenesis ↑        │
│ • Glycolysis ↑           │      │ • Lipolysis ↑              │
│ • FA synthesis ↑         │      │ • Ketogenesis ↑            │
│ • Protein synthesis ↑    │      └───────────────────────────┘
│ • Gluconeogenesis ↓      │
│ • Lipolysis ↓            │
└─────────────────────────┘
      │                                       │
      ▼                                       ▼
BLOOD GLUCOSE ↓ → Normal           BLOOD GLUCOSE ↑ → Normal

HORMONES AND THEIR ROLES IN GLUCOSE REGULATION

┌─────────────────┬──────────────┬────────────────────────────────────────┐
│ HORMONE          │ SOURCE        │ EFFECT ON BLOOD GLUCOSE                │
├─────────────────┼──────────────┼────────────────────────────────────────┤
│ Insulin          │ β-cells       │ ↓ Blood glucose (HYPOGLYCEMIC)         │
│ Glucagon         │ α-cells       │ ↑ Blood glucose (HYPERGLYCEMIC)        │
│ Epinephrine      │ Adrenal medulla│ ↑ BG (glycogenolysis, gluconeogenesis) │
│ Cortisol         │ Adrenal cortex│ ↑ BG (gluconeogenesis, insulin resist.) │
│ GH               │ Pituitary     │ ↑ BG (anti-insulin, lipolysis)         │
│ Thyroxine (T4)   │ Thyroid       │ ↑ BG (glycogenolysis, absorption ↑)    │
│ Somatostatin     │ δ-cells       │ ↓ BG (inhibits glucagon & insulin)     │
│ GLP-1            │ L-cells (gut) │ ↓ BG (incretin - stimulates insulin)   │
└─────────────────┴──────────────┴────────────────────────────────────────┘

NOTE: TYPES OF DIABETES MELLITUS

DIABETES MELLITUS
├── TYPE 1 (Insulin-Dependent DM / IDDM / Juvenile onset)
│   ├── Mechanism: Autoimmune destruction of β-cells
│   ├── Antibodies: Anti-GAD, Anti-islet cell, Anti-insulin
│   ├── HLA association: HLA-DR3, HLA-DR4
│   ├── Insulin: Absent (absolute deficiency)
│   ├── Body: Thin/normal weight
│   └── Treatment: INSULIN mandatory
│
├── TYPE 2 (Non-Insulin-Dependent / NIDDM / Adult onset)
│   ├── Mechanism: Insulin resistance + β-cell dysfunction
│   ├── Risk factors: Obesity, sedentary lifestyle, family history
│   ├── Insulin: Relative deficiency (secretion reduced later)
│   ├── Body: Obese
│   └── Treatment: Oral hypoglycemics → insulin if needed
│
├── GESTATIONAL DM (GDM)
│   ├── Onset: During pregnancy (usually 2nd/3rd trimester)
│   ├── Mechanism: Placental hormones → insulin resistance
│   └── Risk: Macrosomia, neonatal hypoglycemia
│
└── OTHER SPECIFIC TYPES (MODY, LADA, Secondary DM)
    ├── MODY: Maturity-Onset Diabetes of the Young (monogenic)
    ├── Secondary: Cushing's syndrome, acromegaly, pancreatitis
    └── LADA: Latent Autoimmune Diabetes in Adults

Diagnostic Criteria for DM (ADA)

Test	Normal	Pre-diabetes	Diabetes
FPG (mg/dL)	< 100	100-125	≥ 126
2h OGTT (mg/dL)	< 140	140-199	≥ 200
HbA1c (%)	< 5.7	5.7-6.4	≥ 6.5
Random glucose	-	-	≥ 200 + symptoms

Q.37 - ORAL GLUCOSE TOLERANCE TEST (OGTT)

DEFINITION

OGTT is a dynamic test that assesses the ability of the body to handle a standardized oral glucose load. It measures glucose disposal over time.

PROCEDURE FLOWCHART

PREPARATION (3 days before):
├── Unrestricted diet with ≥150g carbohydrate/day
├── Normal physical activity
└── Discontinue medications affecting glucose (thiazides, OCP, steroids)
        │
        ▼
FASTING (10-16 hours overnight)
        │
        ▼
MORNING (7:00-9:00 AM) - Ambulatory, seated patient
        │
        ▼
FASTING BLOOD SAMPLE (0 min) → Measure plasma glucose
        │
        ▼
GLUCOSE LOAD ADMINISTERED:
├── Non-pregnant adults: 75 g glucose in 300 mL water over 5 min
├── Children: 1.75 g/kg (max 75 g)
└── Pregnant (GDM screening): 100 g (3-hour test)
        │
        ▼
BLOOD SAMPLES at:
├── 30 min
├── 60 min
├── 90 min
└── 120 min (2 hours) ← KEY diagnostic sample
        │
        ▼
INTERPRET RESULTS

INTERPRETATION TABLE

┌──────────────────┬──────────────┬─────────────────┬───────────────┐
│ CATEGORY         │ FASTING (0h) │ 2-HOUR POST LOAD│ HbA1c         │
├──────────────────┼──────────────┼─────────────────┼───────────────┤
│ Normal           │ <100 mg/dL   │ <140 mg/dL      │ <5.7%         │
│ Impaired FG      │ 100-125      │ -               │ -             │
│ Impaired GT (IGT)│ <126         │ 140-199 mg/dL   │ -             │
│ Diabetes Mellitus│ ≥126 mg/dL   │ ≥200 mg/dL      │ ≥6.5%         │
└──────────────────┴──────────────┴─────────────────┴───────────────┘

OGTT Curve (Diagram)

Blood
Glucose                    NORMAL
(mg/dL) 300 ─               ╭────╮ DM
        280 ─              ╱      ╲─────────────────
        260 ─            ╱         ╲
        220 ─           ╱           ╲
        200 ─ ─ ─ ─ ─ ─╱─ ─ ─ ─ ─ ─ ╲─ DM threshold ─
        180 ─         ╱               ╲
        160 ─       ╱   IGT curve      ╲─────────────
        140 ─ ─ ─ ─╱─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ IGT threshold
        120 ─     ╱      ╭───╮          
        100 ─   ╱       ╱     ╲────────────── Normal
         80 ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ fasting level
         60 ─
              0   30   60   90  120  min
                     TIME (minutes)

INDICATIONS FOR OGTT

Diagnosis of Gestational Diabetes (GDM) - most common indication
Postpartum screening in GDM patients
Suspected Impaired Glucose Tolerance (IGT)
Borderline FPG (100-125 mg/dL)
Unexplained neuropathy/retinopathy despite normal FPG
Reactive hypoglycemia evaluation

CONTRAINDICATIONS

Acutely ill / hospitalized patients
Bed-ridden patients (impairs glucose tolerance)
Known diabetics on insulin (unnecessary, already diagnosed)
Post-gastrectomy (altered absorption - gives false results)

TYPES OF GTT

Oral GTT (OGTT) - Standard 75 g; most common
IV GTT - Used when GI absorption abnormal (e.g., malabsorption)
Cortisone GTT - Steroid given to unmask latent DM
3-hour 100g OGTT - For gestational diabetes
Prediabetes screening OGTT - Lower-dose screening

FACTORS AFFECTING OGTT (BOX 47.4 - Tietz)

Patient preparation: duration of fast, prior carb intake, medications (thiazides, OCP, steroids), age, weight, activity
During test: posture, anxiety, caffeine, smoking, time of day
Glucose administration: form (anhydrous vs monohydrate), quantity, rate of ingestion

Q.38 - METABOLIC DERANGEMENTS IN DIABETES MELLITUS + COMPLICATIONS + BIOCHEMICAL INDICES

METABOLIC DERANGEMENTS IN DM

INSULIN DEFICIENCY (Absolute - Type 1 / Relative - Type 2)
              │
              ▼
┌─────────────────────────────────────────────────────────────┐
│              METABOLIC CONSEQUENCES                          │
├────────────────────┬────────────────────────────────────────┤
│ GLUCOSE            │ LIPIDS            │ PROTEINS           │
├────────────────────┼───────────────────┼────────────────────┤
│ • GLUT-4 ↓         │ • Lipolysis ↑↑↑   │ • Proteolysis ↑   │
│ • Glycolysis ↓     │ • FFAs released   │ • Gluconeogenesis ↑│
│ • Glycogen synth ↓ │ • Ketogenesis ↑↑↑ │ • Muscle wasting  │
│ • Gluconeogenesis ↑│ • TG synthesis ↓  │ • Amino acids →   │
│ • HYPERGLYCEMIA    │ • Hypertriglycerid.│  glucose          │
│ • Glycosuria       │ • KETONEMIA       │ • Negative nitrogen│
│ • Osmotic diuresis │ • Ketonuria       │   balance         │
│ • Polydipsia       │ • KETONURIA       │                   │
│ • Polyuria         │                   │                   │
└────────────────────┴───────────────────┴────────────────────┘

COMPLICATIONS OF DIABETES MELLITUS

A. ACUTE COMPLICATIONS

ACUTE COMPLICATIONS:

1. DIABETIC KETOACIDOSIS (DKA) - TYPE 1
   ├── Cause: Absolute insulin deficiency + stress
   ├── Biochemistry: Glucagon↑ → lipolysis↑ → ketone bodies↑↑↑
   ├── Features: Hyperglycemia >250 mg/dL, Ketosis, Metabolic acidosis (pH<7.3)
   ├── Serum bicarbonate < 15 mEq/L
   ├── Anion gap ↑ (ketone bodies = unmeasured anions)
   └── Kussmaul breathing, fruity breath (acetone)

2. HYPERGLYCEMIC HYPEROSMOLAR STATE (HHS) - TYPE 2
   ├── Blood glucose very high (>600 mg/dL)
   ├── No significant ketosis (residual insulin prevents lipolysis)
   ├── Extreme dehydration, altered consciousness
   └── Serum osmolality >320 mOsm/kg

3. HYPOGLYCEMIA (Insulin-induced)
   ├── Blood glucose < 70 mg/dL
   ├── Symptoms: Sweating, tremors, confusion, seizures
   └── Counter-regulatory response: Glucagon, Epinephrine, Cortisol, GH

B. CHRONIC COMPLICATIONS

CHRONIC COMPLICATIONS: "Triopathy" = Neuropathy + Nephropathy + Retinopathy

PATHOMECHANISM:
Hyperglycemia (chronic)
        │
        ├──► POLYOL PATHWAY ↑
        │    Glucose → Sorbitol (aldose reductase)
        │    → Sorbitol accumulates → Osmotic damage
        │    → Affects: Lens (cataract), Nerves, Kidney, Retina
        │
        ├──► ADVANCED GLYCATION END PRODUCTS (AGEs)
        │    Glucose + Proteins → AGEs (non-enzymatic glycosylation)
        │    → Basement membrane thickening
        │    → Cross-linking of collagen → Vessel stiffness
        │
        ├──► PKC (Protein Kinase C) ACTIVATION
        │    DAG accumulation → PKC-β → VEGF↑ → Neovascularization
        │
        └──► OXIDATIVE STRESS ↑
             ROS formation → Endothelial dysfunction

MACROVASCULAR COMPLICATIONS:
├── Coronary Artery Disease (MI - leading cause of death)
├── Cerebrovascular disease (Stroke)
└── Peripheral vascular disease (Gangrene)

MICROVASCULAR COMPLICATIONS:
├── DIABETIC NEPHROPATHY: Kimmelstiel-Wilson nodules, proteinuria → CKD
├── DIABETIC RETINOPATHY: Non-proliferative → Proliferative (VEGF↑)
└── DIABETIC NEUROPATHY: Peripheral (glove & stocking pattern), Autonomic

OTHER:
├── Diabetic cardiomyopathy
├── Infections (impaired immunity)
└── Diabetic foot ulcers

BIOCHEMICAL INDICES OF DIABETIC CONTROL

┌────────────────────┬──────────────────────────────────────────────────┐
│ TEST               │ DETAILS                                           │
├────────────────────┼──────────────────────────────────────────────────┤
│ HbA1c (Glycated Hb)│ Reflects BG over PAST 2-3 MONTHS                 │
│                    │ Normal < 5.7%; Target for DM: < 7%                │
│                    │ Gold standard for long-term control               │
├────────────────────┼──────────────────────────────────────────────────┤
│ Fructosamine       │ Glycated albumin - reflects past 2-3 WEEKS        │
│                    │ Useful when HbA1c unreliable (hemolytic anemia)   │
├────────────────────┼──────────────────────────────────────────────────┤
│ Glycated albumin   │ Past 1-2 weeks control                            │
├────────────────────┼──────────────────────────────────────────────────┤
│ 1,5-Anhydroglucitol│ Reflects short-term (days) postprandial control   │
├────────────────────┼──────────────────────────────────────────────────┤
│ Urine glucose      │ Qualitative/quantitative; unreliable for control  │
│ (Glucosuria)       │ Renal threshold: ~180 mg/dL                       │
├────────────────────┼──────────────────────────────────────────────────┤
│ Microalbuminuria   │ Early nephropathy marker                          │
│                    │ 30-300 mg/day (normal < 30 mg/day)                │
├────────────────────┼──────────────────────────────────────────────────┤
│ C-peptide          │ Measures endogenous insulin secretion             │
│                    │ Low in T1DM; Normal/high in T2DM                  │
└────────────────────┴──────────────────────────────────────────────────┘

HbA1c Formula note: HbA1c = % of hemoglobin with non-enzymatic glycosylation at N-terminal valine of β-chain. It reflects glycemic control for 2-3 months (= RBC lifespan ~120 days).

Q.39 - METABOLIC PROCESSES IN SPECIFIC ORGANS: FASTING AND FED STATE

THE FED STATE (Post-Absorptive - First 2-4 hours after meal)

INSULIN ↑ (KEY SIGNAL OF FED STATE)
              │
              ▼
┌──────────────┬───────────────┬──────────────┬──────────────────┐
│    LIVER     │    MUSCLE      │   ADIPOSE    │     BRAIN        │
├──────────────┼───────────────┼──────────────┼──────────────────┤
│ • Glycolysis↑│ • Glucose      │ • Glucose    │ • Uses glucose   │
│ • Glycogen   │   uptake↑      │   uptake↑    │   freely         │
│   synthesis↑ │  (GLUT-4)      │  (GLUT-4)    │ (insulin-        │
│ • Fatty acid │ • Glycogen     │ • FA synthesis│  independent)   │
│   synthesis↑ │   synthesis↑   │  (lipogenesis)│                 │
│ • VLDL       │ • Protein      │ • TG stored  │                  │
│   secretion↑ │   synthesis↑   │ • Lipolysis↓ │                  │
│ • Gluconeo-  │               │              │                  │
│   genesis ↓  │               │              │                  │
└──────────────┴───────────────┴──────────────┴──────────────────┘

THE FASTING STATE (Progressive stages)

FASTING TIMELINE:
                                                    
[0-4 hrs]    [4-16 hrs]    [16-48 hrs]    [>48 hrs / Starvation]
FED→FASTING  Post-absorb.   EARLY FAST      PROLONGED FASTING
     │             │              │                   │
     ▼             ▼              ▼                   ▼
Insulin↓        Glucagon↑     Glucagon↑↑         Glucagon↑↑↑
                Glycogen-     Gluconeo-          Ketone bodies
                olysis        genesis↑↑          become main fuel
                (LIVER)       Lipolysis↑         for BRAIN

ORGAN-SPECIFIC FASTING METABOLISM

┌──────────────────────────────────────────────────────────────────┐
│                    LIVER (Central Metabolic Organ)                │
│                                                                  │
│ FASTING:                          FED:                           │
│ • Glycogenolysis ↑ (0-16h)        • Glycogenesis ↑               │
│ • Gluconeogenesis ↑ (>16h)        • Glycolysis ↑                 │
│   (from alanine, lactate,         • Fatty acid synthesis ↑       │
│    glycerol, glutamine)           • VLDL assembly ↑              │
│ • Ketogenesis ↑ (>16h)           • Gluconeogenesis ↓            │
│ • VLDL secretion ↑               • Urea synthesis ↑             │
│ • Fatty acid oxidation ↑         (from absorbed amino acids)     │
└──────────────────────────────────────────────────────────────────┘

┌──────────────────────────────────────────────────────────────────┐
│                    SKELETAL MUSCLE                                │
│                                                                  │
│ FASTING:                          FED:                           │
│ • Uses fatty acids (β-oxidation)  • Glucose uptake ↑ (GLUT-4)   │
│ • Uses ketone bodies (starvation) • Glycogen synthesis ↑         │
│ • Releases alanine & glutamine    • Protein synthesis ↑          │
│   (glucose-alanine cycle)        • FA synthesis (minor)          │
│ • Glycogen depleted after ~16h   • Glycolysis ↑                 │
└──────────────────────────────────────────────────────────────────┘

┌──────────────────────────────────────────────────────────────────┐
│                    ADIPOSE TISSUE                                 │
│                                                                  │
│ FASTING:                          FED:                           │
│ • Lipolysis ↑ (HSL activated)     • Lipogenesis ↑               │
│ • FFAs released → liver, muscle   • TG stored                    │
│ • Glycerol → liver gluconeo-      • Glucose uptake ↑ (GLUT-4)   │
│   genesis                         • Lipolysis inhibited          │
└──────────────────────────────────────────────────────────────────┘

┌──────────────────────────────────────────────────────────────────┐
│                    BRAIN                                         │
│                                                                  │
│ FASTING:                          FED:                           │
│ • MUST have glucose (early fast)  • Uses glucose exclusively     │
│ • After 2-3 days: adapts to       • GLUT-1, GLUT-3 (insulin-    │
│   KETONE BODIES (acetoacetate +   independent transporters)     │
│   β-hydroxybutyrate)             • 120g glucose/day             │
│ • Ketones can supply up to 75%   • Cannot use fatty acids        │
│   of brain's energy needs        (cannot cross BBB)             │
└──────────────────────────────────────────────────────────────────┘

┌──────────────────────────────────────────────────────────────────┐
│                    RED BLOOD CELLS (RBCs)                        │
│                                                                  │
│ ALL STATES:                                                      │
│ • ONLY uses glucose (no mitochondria)                            │
│ • Anaerobic glycolysis → Lactate                                 │
│ • Lactate → Liver → Glucose (Cori Cycle)                        │
│ • Never uses fats or ketones                                     │
└──────────────────────────────────────────────────────────────────┘

GLUCOSE-ALANINE CYCLE (Muscle-Liver)

MUSCLE                           LIVER
  │ Protein catabolism              │
  │ Amino acids                     │
  │ Transamination                  │
  │ Pyruvate + NH3 → ALANINE ──────►│
  │                                 │ Alanine aminotransferase (ALT)
  │ ◄──────────────── GLUCOSE ──────│ Alanine → Pyruvate + NH3
                                    │ Pyruvate → Gluconeogenesis
                                    │ NH3 → Urea cycle

Q.40 - LIPOPROTEINS: STRUCTURE, FUNCTION, METABOLISM + ATHEROSCLEROSIS

LIPOPROTEIN STRUCTURE

                    ┌───────────────────────────────┐
                    │      LIPOPROTEIN PARTICLE      │
                    │                                │
                    │  ┌─────────────────────────┐   │
                    │  │  HYDROPHOBIC CORE:        │   │
                    │  │  • Triacylglycerols (TG)  │   │
                    │  │  • Cholesteryl esters (CE)│   │
                    │  └─────────────────────────┘   │
                    │                                │
                    │  OUTER SHELL:                  │
                    │  • Phospholipids               │
                    │  • Free cholesterol            │
                    │  • APOLIPOPROTEINS             │
                    └───────────────────────────────┘

CLASSES OF LIPOPROTEINS

┌──────────────────────────────────────────────────────────────────────────┐
│               LIPOPROTEIN DENSITY SPECTRUM                                │
│                                                                          │
│ LARGEST/LEAST DENSE          →        SMALLEST/MOST DENSE               │
│                                                                          │
│  Chylomicron  →  VLDL  →  IDL  →  LDL  →  HDL                          │
│  (dietary)   (liver TG) (VLDL       (LDL  (Reverse                       │
│                          remnant)  receptor)cholesterol                  │
│                                          transport)                      │
└──────────────────────────────────────────────────────────────────────────┘

COMPOSITION:
                TG%    Cholesterol%   Protein%  ApoProtein
Chylomicron:    88        5              2       ApoB-48, ApoC-II, ApoE
VLDL:           55       20              8       ApoB-100, ApoC-II, ApoE
IDL:            31       35             19       ApoB-100, ApoE
LDL:            10       45             25       ApoB-100 (ONLY)
HDL:             5       20             50       ApoA-I, ApoA-II

LIPOPROTEIN METABOLISM FLOWCHART

EXOGENOUS PATHWAY (Dietary Lipids):

INTESTINE
├── Dietary TG + Cholesterol absorbed
├── Re-esterified in enterocytes
├── Packaged as CHYLOMICRONS (ApoB-48)
└── Secreted into lymphatics → Thoracic duct → Blood
          │
          ▼ ApoC-II activates Lipoprotein Lipase (LPL) on capillaries
    MUSCLE/ADIPOSE
          │ LPL hydrolyzes TG → FFAs + Glycerol (taken up by tissues)
          ▼
    CHYLOMICRON REMNANT (ApoE, ApoB-48 remain)
          │
          ▼ ApoE binds LDL receptor on LIVER
    LIVER takes up remnants → Cholesterol recycled

══════════════════════════════════════════

ENDOGENOUS PATHWAY (Liver-derived Lipids):

LIVER
├── Synthesizes TG + Cholesterol
├── Packages as VLDL (ApoB-100, ApoC-II, ApoE)
└── Secretes VLDL into blood
          │
          ▼ LPL action (same as above)
    IDL (Intermediate Density Lipoprotein)
          │
          ├── Taken up by LIVER (LDL receptor + ApoE)
          │
          └── Hepatic Lipase removes more TG
                    ▼
               LDL (ApoB-100 only)
                    │
                    ├── PERIPHERAL TISSUES: LDL receptor binds ApoB-100
                    │   → Endocytosis → Cholesterol released
                    │
                    └── LIVER: LDL receptor → cleared from blood

══════════════════════════════════════════

REVERSE CHOLESTEROL TRANSPORT (HDL):

PERIPHERAL TISSUES
└── Excess cholesterol efflux via ABCA1 transporter
          │
          ▼
    NASCENT HDL (ApoA-I from liver/intestine)
          │ LCAT (Lecithin:Cholesterol Acyltransferase) - activated by ApoA-I
          │ Free cholesterol → Cholesteryl ester → core of HDL (HDL matures)
          ▼
    MATURE HDL (large, spherical)
          │
          ├── Direct uptake by LIVER (SR-BI receptor)
          │
          └── CETP (Cholesteryl Ester Transfer Protein)
              Transfers CE to VLDL/LDL in exchange for TG
                    ▼
              LDL/VLDL (enriched with CE) → Liver

NOTE: ATHEROSCLEROSIS

PATHOGENESIS OF ATHEROSCLEROSIS (Response-to-Injury Hypothesis)

Step 1: ENDOTHELIAL DYSFUNCTION
├── Risk factors: Hypertension, smoking, hyperglycemia, hyperlipidemia
└── Endothelial cells → permeability↑, adhesion molecules↑

Step 2: LDL ENTERS INTIMA
└── Modified/Oxidized LDL (ox-LDL) formed

Step 3: MONOCYTE RECRUITMENT
└── Monocytes → Macrophages → Engulf ox-LDL via SCAVENGER RECEPTORS

Step 4: FOAM CELL FORMATION
└── Lipid-laden macrophages = FOAM CELLS
    → Visible as FATTY STREAK (earliest lesion)

Step 5: INFLAMMATION + SMOOTH MUSCLE PROLIFERATION
├── Cytokines (IL-1, TNF-α) attract smooth muscle cells (SMC)
├── SMC migrate from media to intima
└── SMC secrete collagen → FIBROUS CAP forms

Step 6: PLAQUE FORMATION (ATHEROMA)
├── Fibrous plaque = lipid core + fibrous cap
└── Advanced plaque: calcification, necrotic core

Step 7: PLAQUE COMPLICATIONS
├── STABLE plaque: thick cap → stable angina
├── UNSTABLE/VULNERABLE plaque: thin cap → rupture
│   → Thrombosis → MYOCARDIAL INFARCTION / STROKE
└── Calcification, aneurysm formation

KEY LIPID RELATIONSHIPS:
├── LDL ↑ (especially oxidized LDL) → ATHEROGENIC
├── HDL ↑ → ANTI-ATHEROGENIC (Reverse cholesterol transport)
├── Lp(a) → highly atherogenic
└── Small dense LDL (sdLDL) → most atherogenic

Apolipoproteins Quick Reference

ApoProtein	Lipoprotein	Function	Clinical Significance
ApoA-I	HDL	Activates LCAT, SR-BI ligand	Anti-atherogenic
ApoB-48	Chylomicron	Structural	Identifies dietary lipoproteins
ApoB-100	VLDL, IDL, LDL	LDL receptor ligand	Atherogenic; elevated in FH
ApoC-II	Chylomicron, VLDL	Activates LPL	Deficiency → hypertriglyceridemia
ApoE	Chylomicron, VLDL, IDL	Binds LDL receptor	ApoE4 → Alzheimer's risk

Q.41 - β-OXIDATION OF FATTY ACIDS: STAGES, ENERGETICS, DISORDERS

ACTIVATION & TRANSPORT INTO MITOCHONDRIA

CYTOSOL:
Free Fatty Acid (FFA)
        │ Fatty Acyl-CoA Synthetase (Thiokinase) + CoA + ATP → AMP + PPi
        ▼
Fatty Acyl-CoA
        │ (CANNOT enter mitochondria directly!)
        │ Carnitine Acyltransferase I (CAT-I) [Rate-limiting / KEY enzyme]
        │ + Carnitine → Acylcarnitine + CoA (CoA released in cytosol)
        ▼
INNER MITOCHONDRIAL MEMBRANE TRANSPORT
(Carnitine-acylcarnitine translocase)
        │
        ▼
MITOCHONDRIAL MATRIX:
Acylcarnitine
        │ Carnitine Acyltransferase II (CAT-II) + CoA
        ▼
Fatty Acyl-CoA (inside mitochondria) + Carnitine (returns to cytosol)

KEY: Malonyl-CoA (first intermediate in FA synthesis) INHIBITS CAT-I → prevents simultaneous synthesis and oxidation of fatty acids.

β-OXIDATION CYCLE (One round = removes 2-carbon unit as Acetyl-CoA)

┌─────────────────────────────────────────────────────────────────┐
│                    ONE CYCLE OF β-OXIDATION                      │
│                                                                 │
│  Fatty Acyl-CoA (n carbons)                                     │
│        │                                                        │
│        │ Step 1: ACYL-CoA DEHYDROGENASE (FAD → FADH₂)          │
│        ▼                                                        │
│  trans-Δ²-Enoyl-CoA                                             │
│        │                                                        │
│        │ Step 2: ENOYL-CoA HYDRATASE (H₂O added)               │
│        ▼                                                        │
│  L-3-Hydroxyacyl-CoA                                            │
│        │                                                        │
│        │ Step 3: 3-HYDROXYACYL-CoA DEHYDROGENASE (NAD⁺ → NADH) │
│        ▼                                                        │
│  3-Ketoacyl-CoA                                                 │
│        │                                                        │
│        │ Step 4: THIOLASE (+ CoA → thiolysis)                   │
│        ▼                                                        │
│  Acetyl-CoA  +  Fatty Acyl-CoA (shortened by 2C)               │
│                       │                                         │
│                       └── REPEAT CYCLE until all Acetyl-CoA     │
└─────────────────────────────────────────────────────────────────┘

Memory: "A-E-H-T" = Dehydrogenation, Hydration, Dehydrogenation, Thiolysis

ENERGETICS OF β-OXIDATION (Example: Palmitic Acid C16:0)

PALMITIC ACID (16 carbons, saturated)
= 7 cycles of β-oxidation
= 8 Acetyl-CoA produced

Each cycle yields:
├── 1 FADH₂  → 1.5 ATP (oxidative phosphorylation)
└── 1 NADH   → 2.5 ATP

Per cycle: 1.5 + 2.5 = 4 ATP

For 7 cycles: 7 × 4 = 28 ATP (from FADH₂ + NADH)

8 Acetyl-CoA × 10 ATP each (via TCA cycle) = 80 ATP

Total GROSS ATP = 28 + 80 = 108 ATP

Subtract activation cost: -2 ATP (ATP → AMP + PPi = 2 high-energy bonds)

NET ATP FROM PALMITATE = 106 ATP

Compare: Glucose (180g/mol) → ~30-32 ATP
         Palmitate (256g/mol) → ~106 ATP
         ∴ Fats yield ~2.5x more energy per gram than carbohydrates

β-OXIDATION OF SPECIAL FATTY ACIDS

ODD-CHAIN FATTY ACIDS (e.g., valproate metabolism):
└── Last cycle yields: Acetyl-CoA + PROPIONYL-CoA (3C)
    Propionyl-CoA → Methylmalonyl-CoA (Vitamin B12) → Succinyl-CoA → TCA

UNSATURATED FATTY ACIDS (e.g., Oleate C18:1, cis-Δ9):
└── Requires 2 extra enzymes:
    ├── Enoyl-CoA isomerase (changes cis to trans)
    └── 2,4-dienoyl-CoA reductase (for polyunsaturated FAs)
    → One fewer FADH₂ generated per double bond

NOTE: ASSOCIATED DISORDERS OF β-OXIDATION

┌─────────────────────────────────────────────────────────────────┐
│ DISORDER                     │ DEFECT      │ FEATURES           │
├──────────────────────────────┼─────────────┼────────────────────┤
│ MCAD Deficiency              │ Medium-chain│ Most common FAO    │
│ (Medium-Chain Acyl-CoA       │ Acyl-CoA    │ disorder; neonatal │
│ Dehydrogenase Deficiency)    │ Dehydrogenase│ hypoglycemia;      │
│                              │             │ SIDS risk          │
├──────────────────────────────┼─────────────┼────────────────────┤
│ Carnitine Deficiency         │ CAT-I/II or │ Hypoglycemia,      │
│                              │ Translocase │ cardiomyopathy,    │
│                              │             │ muscle weakness    │
├──────────────────────────────┼─────────────┼────────────────────┤
│ Jamaican Vomiting Sickness   │ Hypoglycin A│ Inhibits FAO;      │
│ (Ackee fruit poisoning)      │ inhibits    │ hypoglycemia,      │
│                              │ Acyl-CoA DH │ vomiting, death    │
├──────────────────────────────┼─────────────┼────────────────────┤
│ Refsum Disease               │ Phytanic acid│ Accumulation of   │
│                              │ α-hydroxylase│ phytanic acid;    │
│                              │             │ ataxia, neuropathy │
├──────────────────────────────┼─────────────┼────────────────────┤
│ Zellweger Syndrome           │ Peroxisomal │ Very long chain FA │
│ (Peroxisomal disorder)       │ biogenesis  │ accumulate;        │
│                              │ defect      │ neurodegeneration  │
└─────────────────────────────────────────────────────────────────┘

Q.42 - SYNTHESIS AND UTILIZATION OF KETONE BODIES + KETOSIS

SYNTHESIS OF KETONE BODIES (KETOGENESIS)

Site: LIVER MITOCHONDRIA only (liver cannot use ketones itself)

FLOWCHART: KETOGENESIS

Acetyl-CoA (from β-oxidation - excess in fasting/DM)
        │
        │ Thiolase
        ▼
Acetoacetyl-CoA
        │
        │ + Acetyl-CoA via HMG-CoA Synthase (mitochondrial)
        ▼
HMG-CoA (β-Hydroxy-β-Methylglutaryl-CoA)
        │
        │ HMG-CoA Lyase (Rate-limiting enzyme)
        ▼
     ┌──┴────────────────────┐
     ▼                       ▼
ACETOACETATE              ACETYL-CoA (recycled)
(First ketone body)
     │
     │ β-Hydroxybutyrate Dehydrogenase (NADH)
     ▼                        │
β-HYDROXYBUTYRATE             │ Spontaneous decarboxylation
(Predominant in DKA)          ▼
                          ACETONE (volatile - fruity breath)

UTILIZATION OF KETONE BODIES (Peripheral Tissues)

FLOWCHART: KETOLYSIS (in Muscle, Brain, Heart, Kidney)

β-HYDROXYBUTYRATE (from blood)
        │ β-Hydroxybutyrate Dehydrogenase
        ▼
ACETOACETATE
        │ Succinyl-CoA:Acetoacetate-CoA Transferase (THIOPHORASE)
        │ [KEY enzyme - ABSENT in LIVER - so liver cannot use ketones]
        │ + Succinyl-CoA → Succinate + Acetoacetyl-CoA
        ▼
ACETOACETYL-CoA
        │ Thiolase + CoA
        ▼
2 × ACETYL-CoA
        │
        ▼
TCA CYCLE → ATP

RULE: Liver MAKES ketones but cannot USE them. Brain USES ketones after adaptation.

REGULATION OF KETOGENESIS

INSULIN ↑ (Fed state):
├── Malonyl-CoA ↑ → Inhibits CAT-I → FA enter mitochondria ↓
└── Ketogenesis ↓

GLUCAGON ↑ / INSULIN ↓ (Fasting, DM):
├── Lipolysis ↑ → FFA → Liver → β-oxidation ↑
├── Malonyl-CoA ↓ → CAT-I active → FA enter mitochondria ↑
├── Acetyl-CoA floods TCA → OAA depleted (used in gluconeo-genesis)
└── Acetyl-CoA diverted to HMG-CoA → KETOGENESIS ↑↑↑

NOTE: KETOSIS IN STARVATION vs DIABETES MELLITUS

┌──────────────────────┬───────────────────────┬───────────────────────┐
│ FEATURE              │ STARVATION KETOSIS     │ DKA (Diabetic)        │
├──────────────────────┼───────────────────────┼───────────────────────┤
│ Insulin level        │ Low (but present)      │ Absent (Type 1)       │
│ Glucagon level       │ High                   │ Very high             │
│ Blood glucose        │ Low/normal             │ Very high (>250)      │
│ Ketone bodies        │ Moderate               │ Very high             │
│ Acidosis             │ Mild (compensated)     │ Severe (pH <7.3)      │
│ HCO₃⁻               │ Normal/slightly low    │ <15 mEq/L             │
│ Anion gap            │ Normal/mildly elevated │ High (>12)            │
│ Urine ketones        │ Present                │ Strongly positive     │
│ Treatment            │ Feed glucose           │ IV insulin + fluids   │
│ Cause                │ No food intake         │ Insulin deficiency    │
└──────────────────────┴───────────────────────┴───────────────────────┘

STARVATION KETOSIS SEQUENCE:
0-16h:  Liver glycogen depleted → Blood glucose maintained
16-48h: Gluconeogenesis from amino acids + glycerol
2-3 d:  Ketogenesis ramps up → Brain adapts to ketones
>1 wk:  Brain uses 75% ketones → Muscle protein spared

NORMAL KETONE BODY LEVELS

Normal blood: 0.1-0.2 mmol/L (mostly β-hydroxybutyrate)
Normal urine: <0.5 mmol/day
DKA: can reach 20-30 mmol/L
Ratio β-OHB : Acetoacetate = 3:1 (normally) → up to 10:1 (DKA)

Q.43 - TRIACYLGLYCEROL (TAG) SYNTHESIS, DEGRADATION, HORMONAL REGULATION + FATTY LIVER

SYNTHESIS OF TRIACYLGLYCEROL (Lipogenesis)

Sites: Liver (major), Adipose tissue, Intestine

FLOWCHART: TAG SYNTHESIS (Glycerol-3-phosphate Pathway)

GLUCOSE → Glycolysis → Dihydroxyacetone phosphate (DHAP)
                              │ Glycerol-3-phosphate Dehydrogenase
                              ▼
              Glycerol-3-phosphate (sn-glycerol-3-phosphate)
                              │
                              │ Acyl-CoA + Acyltransferase (Step 1)
                              ▼
                      Lysophosphatidate (1-acylglycerol-3-P)
                              │
                              │ + Acyl-CoA + Acyltransferase (Step 2)
                              ▼
                      Phosphatidate (1,2-diacylglycerol-3-P)
                              │
                              │ Phosphatidate Phosphatase (PAP/Lipin)
                              ▼
                      1,2-Diacylglycerol (DAG)
                              │
                              │ + Acyl-CoA + DAG Acyltransferase (DGAT)
                              ▼
                      TRIACYLGLYCEROL (TAG)
                      (Stored in adipose / secreted as VLDL from liver)

MONOACYLGLYCEROL PATHWAY (Intestine - during fat absorption):
2-Monoacylglycerol (from dietary TG digestion)
  + 2 Fatty Acyl-CoA → TAG (for chylomicron assembly)

DEGRADATION OF TRIACYLGLYCEROL (Lipolysis)

FLOWCHART: LIPOLYSIS

TRIACYLGLYCEROL (stored in adipocyte lipid droplet)
        │
        │ HORMONE-SENSITIVE LIPASE (HSL) - Rate-limiting [Step 1]
        │ (activated by phosphorylation via PKA)
        ▼
DIACYLGLYCEROL + Fatty Acid (1st FA released)
        │
        │ DAG Lipase
        ▼
MONOACYLGLYCEROL + Fatty Acid (2nd FA released)
        │
        │ MAG Lipase (ATGL: Adipose TG Lipase - actually Step 0)
        ▼
GLYCEROL + Fatty Acid (3rd FA released)
        │
        ▼
Glycerol → Blood → Liver → Gluconeogenesis
Fatty acids → Bound to albumin → Blood → Tissues (β-oxidation)
              [Liver: β-oxidation + Ketogenesis]
              [Muscle: β-oxidation → ATP]

Correction note: ATGL (Adipose Triglyceride Lipase) is actually the PRIMARY initiating lipase (Step 1); HSL mainly acts on DAG.

HORMONAL REGULATION OF TAG METABOLISM

┌──────────────────────────────────────────────────────────────────┐
│          HORMONAL REGULATION OF LIPOLYSIS / LIPOGENESIS          │
├────────────────┬────────────────────────────────────────────────┤
│ HORMONE        │ MECHANISM                │ EFFECT             │
├────────────────┼──────────────────────────┼────────────────────┤
│ Insulin        │ ↑ Phosphodiesterase      │ Lipogenesis ↑      │
│ (Anabolic)     │ cAMP↓ → PKA↓ → HSL↓     │ Lipolysis ↓        │
│                │ SREBP-1c activation      │ VLDL secretion ↑   │
├────────────────┼──────────────────────────┼────────────────────┤
│ Glucagon       │ ↑ Adenylate cyclase      │ Lipolysis ↑        │
│                │ cAMP↑ → PKA↑ → HSL↑     │ Lipogenesis ↓      │
├────────────────┼──────────────────────────┼────────────────────┤
│ Epinephrine    │ β-adrenergic→ cAMP↑      │ Lipolysis ↑↑       │
│                │ α-adrenergic→ cAMP↓      │ (major in stress)  │
├────────────────┼──────────────────────────┼────────────────────┤
│ GH/Cortisol    │ Induce lipases           │ Lipolysis ↑        │
├────────────────┼──────────────────────────┼────────────────────┤
│ Thyroxine      │ ↑ LPL, ↑ β-oxidation    │ FFA turnover ↑     │
├────────────────┼──────────────────────────┼────────────────────┤
│ Natriuretic    │ Activates PKG → HSL-P    │ Lipolysis ↑        │
│ peptides (ANP) │                          │                    │
└────────────────┴──────────────────────────┴────────────────────┘

NOTE: FATTY LIVER (HEPATIC STEATOSIS)

Definition: Accumulation of TG in hepatocytes (>5% of liver weight)

PATHOGENESIS FLOWCHART:

NORMAL BALANCE:
TG input to liver = TG output as VLDL
        │
        ▼
FATTY LIVER = TG INPUT > TG OUTPUT (imbalance)

CAUSES / RESPONSIBLE FACTORS:

┌──────────────────────────────────────────────────────────────┐
│               CAUSES OF FATTY LIVER                          │
├────────────────────────────┬─────────────────────────────────┤
│ ↑ TG INPUT:                │ ↓ TG OUTPUT:                    │
│ • Excess alcohol            │ • Apolipoprotein deficiency     │
│   → Acetaldehyde → NADH↑   │   (can't assemble VLDL)         │
│   → FA oxidation↓          │ • Choline deficiency            │
│   → FA synthesis↑          │   (phosphatidylcholine for VLDL)│
│ • Obesity/excess calories  │ • Protein malnutrition          │
│ • Diabetes (insulin resist.)│  (Kwashiorkor)                 │
│ • High fat diet             │ • CC14 poisoning               │
│ • Lipolysis ↑ (adipose)    │ • Tetracycline (inhibits VLDL)  │
│   → FFA flood liver         │ • Orotic acid (blocks VLDL)    │
└────────────────────────────┴─────────────────────────────────┘

PROGRESSION:
Simple Steatosis (Fatty Liver)
        │ Oxidative stress + Inflammation
        ▼
NASH (Non-Alcoholic SteatoHepatitis) - "second hit"
        │ Fibrosis
        ▼
Cirrhosis → Hepatocellular Carcinoma (HCC)

ALCOHOLIC FATTY LIVER (Special Note)

ALCOHOL → Acetaldehyde → Acetate
                  │
        Alcohol dehydrogenase + NAD⁺ → NADH↑↑
                  │
        ┌─────────────────────────────────────┐
        │ NADH/NAD⁺ RATIO ↑↑ effects:         │
        │ • Pyruvate → Lactate (gluconeo ↓)   │
        │ • OAA → Malate (TCA cycle ↓)        │
        │ • Acetyl-CoA → FA synthesis ↑       │
        │ • FA β-oxidation ↓ (NADH inhibits)  │
        │ • Glycerol-3-phosphate ↑ → TAG ↑    │
        └─────────────────────────────────────┘
                  │
                  ▼
        FATTY LIVER (Alcoholic Steatosis)
        Hepatomegaly, elevated AST:ALT > 2:1

BIOCHEMICAL MARKERS OF FATTY LIVER

Test	Fatty Liver	NASH	Cirrhosis
ALT/AST	Mildly ↑	↑↑	↑ or ↓
GGT	↑ (alcohol)	↑	↑
Alkaline phosphatase	Normal/↑	↑	↑
Bilirubin	Normal	Normal/↑	↑
Albumin	Normal	Normal	↓
Ultrasound	Echogenic	Echogenic	Nodular

QUICK REVISION SUMMARY TABLE (Q35-43)

┌──────┬───────────────────────────────────┬──────────────────────────────────────┐
│ Q No.│ TOPIC                              │ KEY EXAM POINTS                      │
├──────┼───────────────────────────────────┼──────────────────────────────────────┤
│  35  │ Glycogen Metabolism               │ Glycogenin primer; Glycogen synthase  │
│      │                                   │ vs Phosphorylase regulation by cAMP;  │
│      │ + Hormonal Regulation             │ Von Gierke (Type I), McArdle (V)      │
├──────┼───────────────────────────────────┼──────────────────────────────────────┤
│  36  │ Blood Glucose Regulation + DM     │ Counter-regulatory hormones = "CAGE"  │
│      │                                   │ Cortisol, Adrenaline, GH, Glucagon;   │
│      │ Types of DM                       │ Type 1 = autoimmune, Type 2 = insulin │
│      │                                   │ resistance                            │
├──────┼───────────────────────────────────┼──────────────────────────────────────┤
│  37  │ OGTT - Procedure + Interpretation │ 75g/300mL/5min; Fasting 10-16h;       │
│      │                                   │ 2h value ≥200 = DM; IGT = 140-199;   │
│      │ Contraindications + Types         │ GDM = 100g 3-hour test                │
├──────┼───────────────────────────────────┼──────────────────────────────────────┤
│  38  │ Metabolic Derangements in DM      │ DKA: no insulin → lipolysis → ketosis │
│      │                                   │ Polyol pathway → sorbitol → cataract  │
│      │ Complications + Indices           │ AGEs → basement membrane thickening;  │
│      │                                   │ HbA1c = 2-3 months control index      │
├──────┼───────────────────────────────────┼──────────────────────────────────────┤
│  39  │ Fed vs Fasting State              │ Fed = anabolic (insulin); Fasting =   │
│      │ Organ-specific metabolism         │ catabolic (glucagon); Brain adapts to │
│      │                                   │ ketones after 3 days starvation        │
├──────┼───────────────────────────────────┼──────────────────────────────────────┤
│  40  │ Lipoproteins + Atherosclerosis    │ ApoC-II activates LPL; ApoB-100 =    │
│      │                                   │ LDL receptor ligand; HDL is anti-     │
│      │                                   │ atherogenic (LCAT, SR-BI); Foam cells │
│      │                                   │ = macrophages + ox-LDL                │
├──────┼───────────────────────────────────┼──────────────────────────────────────┤
│  41  │ β-Oxidation + Energetics +        │ "A-E-H-T"; CAT-I = rate-limiting;    │
│      │ Disorders                         │ Palmitate → 106 ATP net; MCAD defic. │
│      │                                   │ → SIDS risk, neonatal hypoglycemia    │
├──────┼───────────────────────────────────┼──────────────────────────────────────┤
│  42  │ Ketone Bodies + Ketosis           │ HMG-CoA Lyase = rate-limiting;        │
│      │                                   │ Thiophorase absent in liver;          │
│      │                                   │ DKA vs starvation ketosis comparison  │
├──────┼───────────────────────────────────┼──────────────────────────────────────┤
│  43  │ TAG synthesis + degradation       │ Glycerol-3-P pathway; ATGL/HSL roles; │
│      │ + Hormonal regulation             │ NADH↑↑ in alcohol → fatty liver;      │
│      │ + Fatty liver                     │ VLDL blocked → TG accumulates         │
└──────┴───────────────────────────────────┴──────────────────────────────────────┘

HIGH-YIELD MNEMONICS

GLYCOGEN STORAGE DISEASES - "Oh Very Poor Carbohydrate And McArdle's Hurt People"
O=Type 0, V=Von Gierke, P=Pompe, C=Cori, A=Andersen, M=McArdle, H=Hers

COUNTER-REGULATORY HORMONES - "CAGE":
C=Cortisol, A=Adrenaline (Epinephrine), G=GH (Growth Hormone), E=Epinephrine (+ Glucagon)

KETONE BODIES - "BOAT":
B=Beta-hydroxybutyrate (major), O=Acetone (volatile), A=Acetoacetate (measured clinically)
T=Thiophorase (absent in liver)

APOLIPOPROTEINS:
ApoA = HDL (A for "Artery protection")
ApoB = Bad (LDL, atherogenic)
ApoC = Catalyst (activates LPL)
ApoE = Eating (liver uptake of remnants)

β-OXIDATION STEPS - "Doctor Has Three Assistants":
D=Dehydrogenation (FAD), H=Hydration, T=Thiol-Dehydrogenation (NAD), A=Attack by thiolase

Sources: Lippincott's Illustrated Reviews Biochemistry 8th ed.; Basic Medical Biochemistry - A Clinical Approach 6th ed. (Marks); Tietz Textbook of Laboratory Medicine 7th ed.

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