Disorders of Carbohydrate Metabolism – Core Vocabulary

Vocabulary flashcards covering major terms, enzymes, pathways, diseases, clinical features and complications related to disorders of carbohydrate metabolism as presented in the lecture notes.

Carbohydrate Metabolism

All biochemical processes responsible for the formation, breakdown and inter-conversion of carbohydrates in living organisms.

Monosaccharide

Single-unit sugar such as glucose, fructose or galactose.

Disaccharide

Two monosaccharides linked together; e.g. sucrose, lactose, maltose.

Glycogen

Branched polymer of glucose serving as the main storage carbohydrate in animals.

Hexosamine Pathway

Glucose-derived pathway producing UDP-GlcNAc for synthesis of glycoproteins and glycolipids.

Glycoconjugate

Molecule in which carbohydrate is covalently linked to protein or lipid (glycoprotein, glycolipid).

Gluconeogenesis

Formation of glucose from non-carbohydrate precursors such as lactate, glycerol or amino acids.

Glycogenolysis

Breakdown of glycogen to release glucose.

Essential Fructosuria

Benign disorder due to fructokinase deficiency causing fructose accumulation and urinary excretion.

Hereditary Fructose Intolerance

Severe disease from aldolase B deficiency leading to fructose-1-phosphate buildup, hypoglycaemia and liver dysfunction.

Classic Galactosaemia

Autosomal-recessive GALT deficiency with accumulation of galactose-1-phosphate causing failure to thrive, cataracts, jaundice.

Lactose Intolerance

Symptomatic malabsorption of lactose due to lactase deficiency resulting in osmotic diarrhoea and bloating.

Primary Lactase Deficiency

Age-related decline of lactase activity beginning after weaning; symptoms in adolescence/adulthood.

Secondary Lactase Deficiency

Transient loss of lactase from mucosal injury (infection, inflammation, coeliac disease, etc.).

Congenital Lactase Deficiency

Rare autosomal-recessive absence of lactase from birth producing severe neonatal diarrhoea.

Glycogen Storage Disease Type I (von Gierke)

Glucose-6-phosphatase deficiency causing fasting hypoglycaemia, hepatomegaly and lactic acidosis.

Glucose-6-Phosphatase

Enzyme that converts glucose-6-phosphate to free glucose during gluconeogenesis and glycogenolysis.

Glucose-6-Phosphate Dehydrogenase

First enzyme of pentose-phosphate pathway producing NADPH; distinct from glucose-6-phosphatase.

Glucose

Major energy substrate whose plasma concentration is tightly regulated between ~2.5–8 mmol/L.

Insulin

Pancreatic β-cell hormone lowering blood glucose by promoting uptake, glycogen synthesis and lipogenesis.

Counter-Regulatory Hormones

Hormones opposing insulin (glucagon, cortisol, catecholamines, growth hormone).

Glucagon

Pancreatic α-cell hormone that raises blood glucose via glycogenolysis and gluconeogenesis.

Hyperglycaemia

Abnormally high blood glucose concentration.

Hypoglycaemia

Blood glucose <3.0 mmol/L producing neuroglycopenic and sympathoadrenal symptoms.

Glucosuria

Presence of glucose in urine when blood concentration exceeds renal threshold or tubules are defective.

Fanconi Syndrome

Generalised proximal tubular dysfunction causing glucosuria, aminoaciduria and phosphate loss.

Diabetes Mellitus

Group of metabolic disorders characterised by chronic hyperglycaemia due to defects in insulin secretion, action or both.

Type 1 Diabetes Mellitus (T1DM)

Autoimmune β-cell destruction leading to absolute insulin deficiency; usually childhood onset.

Type 2 Diabetes Mellitus (T2DM)

Combination of insulin resistance and relative insulin deficiency; strongly linked to obesity and genetics.

Gestational Diabetes Mellitus (GDM)

Glucose intolerance first recognised during pregnancy; screened with 75-g OGTT at 24–28 weeks.

Monogenic Diabetes

Rare forms due to single-gene defects affecting β-cell function or insulin signalling (e.g. MODY).

Maturity-Onset Diabetes of the Young (MODY)

Autosomal-dominant diabetes presenting in youth; commonest form (MODY-2) involves glucokinase mutation.

Insulin Resistance

Reduced biological response of peripheral tissues to insulin, preceding hyperglycaemia in T2DM.

β-Cell Dysfunction

Inadequate insulin secretion in presence of insulin resistance and hyperglycaemia.

Lipotoxicity

β-cell impairment due to chronic elevation of free fatty acids.

Glucotoxicity

β-cell damage from persistent hyperglycaemia.

Incretin Effect

Augmented insulin release after oral vs intravenous glucose via gut hormones GIP and GLP-1.

Amyloid Deposition in Islets

Islet accumulation of amylin (IAPP) characteristic of T2DM contributing to β-cell loss.

Polyuria

Excessive urination caused by osmotic diuresis from glycosuria.

Polydipsia

Excessive thirst stimulated by hyperosmolarity.

Polyphagia

Excessive hunger due to negative energy balance in uncontrolled diabetes.

Diabetic Ketoacidosis (DKA)

Acute T1DM emergency with hyperglycaemia, ketonaemia and metabolic acidosis.

Hyperosmolar Hyperglycaemic State (HHS)

Severe hyperglycaemia and dehydration without significant ketosis; typical of T2DM.

Pre-Diabetes

State with impaired fasting glucose or tolerance (FPG 6.1-6.9 mmol/L; 2-h OGTT 7.8-11 mmol/L; HbA1c 5.7-6.3%).

Microvascular Complications

Diabetes-related damage to small vessels causing nephropathy, neuropathy and retinopathy.

Macrovascular Complications

Accelerated atherosclerosis in large arteries leading to MI, stroke and peripheral gangrene.

Advanced Glycation End Products (AGEs)

Irreversible proteins/lipids modified by glucose that cross-link matrices and bind RAGE to drive vascular damage.

Protein Kinase C Activation

Hyperglycaemia-induced DAG accumulation activating PKC isoforms and altering vascular permeability.

Polyol Pathway

Metabolic route converting glucose to sorbitol then fructose; excess sorbitol causes osmotic damage (e.g. cataract).

Diabetic Nephropathy

Kidney disease featuring microalbuminuria, glomerulosclerosis and eventual renal failure.

Microalbuminuria

Urine albumin 30-300 mg/24 h, earliest sign of diabetic nephropathy.

Nodular Glomerulosclerosis (Kimmelstiel-Wilson)

PAS-positive nodules in mesangium pathognomonic for diabetic nephropathy.

Diabetic Neuropathy

Peripheral nerve dysfunction due to metabolic and vascular injury; includes distal symmetric polyneuropathy and autonomic neuropathy.

Distal Symmetric Polyneuropathy

Stocking-glove sensory loss, pain and weakness beginning in toes, commonest diabetic neuropathy.

Autonomic Neuropathy

Dysfunction of autonomic nerves causing postural hypotension, bladder atony, erectile problems, etc.

Diabetic Retinopathy

Retinal microangiopathy progressing from non-proliferative changes to proliferative neovascularisation.

Non-Proliferative Diabetic Retinopathy

Earliest retinal changes: microaneurysms, haemorrhages, macular oedema and exudates.

Proliferative Diabetic Retinopathy

Formation of new fragile retinal vessels leading to haemorrhage, fibrosis and traction detachment.

Cataract (Diabetic)

Lens opacification from sorbitol accumulation within lens fibres.

Glaucoma (Diabetic)

Elevated intraocular pressure and optic nerve damage associated with diabetic microvascular changes.

Islet Autoantibodies

Markers of T1DM including anti-GAD, anti-IA-2, anti-ZnT-8 and anti-insulin antibodies.

Molecular Mimicry

Immune cross-reactivity where viral antigens resemble β-cell antigens, triggering autoimmunity in T1DM.

Ketogenesis

Hepatic production of ketone bodies from fatty acids during insulin deficiency.

Osmotic Diuresis

Water loss in urine driven by unreabsorbed solutes such as glucose.

Renal Threshold for Glucose

Blood glucose concentration (~10 mmol/L) above which glucose appears in urine.

SGLT2 Deficiency

Inherited defect of renal glucose transporter causing benign isolated glucosuria with normal blood glucose.

Fanconi Syndrome

Proximal tubular dysfunction with glucosuria, phosphaturia, aminoaciduria and bicarbonate loss.

Sulfonylureas

Oral hypoglycaemic drugs that stimulate insulin release; can cause hypoglycaemia.

Insulinoma

β-cell tumour secreting insulin, leading to fasting hypoglycaemia with high C-peptide and proinsulin.

Post-Prandial (Reactive) Hypoglycaemia

Symptoms of low glucose 2–4 h after meals, sometimes due to gastric bypass or NIPHS.

Acanthosis Nigricans

Velvety hyperpigmented skin thickening, often indicates severe insulin resistance.

Glucokinase

β-cell ‘glucose sensor’; catalyses glucose → glucose-6-phosphate; mutated in MODY-2.

Fructokinase

Hepatic enzyme phosphorylating fructose to fructose-1-phosphate; absent in essential fructosuria.

Fructose-1-Phosphate Aldolase B

Splits fructose-1-phosphate; deficiency causes hereditary fructose intolerance.

Galactose-1-Phosphate Uridyltransferase (GALT)

Converts galactose-1-P to UDP-galactose; deficiency produces classic galactosaemia.

Galactitol

Sugar alcohol formed from galactose; accumulates in lenses causing cataracts in galactosaemia.

HbA1c

Glycated haemoglobin reflecting average plasma glucose over ~3 months; ≥6.3 % indicates diabetes.

Oral Glucose Tolerance Test (OGTT)

Diagnostic test measuring plasma glucose 2 h after 75 g oral load.

Hexokinase

First glycolytic enzyme converting glucose to glucose-6-phosphate in most tissues.

Fanconi-Bickel Syndrome

(Mentioned indirectly) Glycogen storage disease with GLUT2 defect, causing renal glucosuria and hepatomegaly.

Ketone Bodies

Acetoacetate, β-hydroxybutyrate and acetone produced during prolonged fasting or insulin deficiency.

Kussmaul Breathing

Deep, laboured respiration seen in severe metabolic acidosis (e.g. DKA).

Osmolality

Measure of solute concentration; markedly elevated in HHS leading to mental status changes.

Microvascular Basement Membrane Thickening

Characteristic widespread change in diabetic microangiopathy affecting capillaries and non-vascular tissues.

Hyaline Arteriolosclerosis

Amorphous thickening of arteriolar walls; more severe in diabetic hypertension.

Nephrosclerosis

Kidney scarring from vascular lesions; includes granular surface and cortical thinning in diabetes.

Glomerular Mesangial Sclerosis

Diffuse increase in mesangial matrix seen in diabetic glomerulosclerosis.

Polyol Pathway Enzyme: Aldose Reductase

Converts glucose to sorbitol; high activity in lens, nerves and kidneys contributes to diabetic complications.

Protein Kinase C-β Inhibitors

Experimental drugs aimed at reducing diabetic microvascular damage by blocking PKC activation.

Sorbitol

Polyol accumulating in tissues when glucose is reduced; causes osmotic stress and oxidative damage.

Insulin-to-Glucagon Ratio

Key determinant of metabolic state; high after meals promotes storage, low during fasting promotes catabolism.

Ketone Body Utilisation

Peripheral conversion of β-hydroxybutyrate and acetoacetate to acetyl-CoA for energy during fasting.

Carbohydrate Metabolism

All biochemical processes responsible for the formation, breakdown and inter-conversion of carbohydrates in living organisms.

Monosaccharide

Single-unit sugar such as glucose, fructose or galactose.

Disaccharide

Two monosaccharides linked together; e.g. sucrose, lactose, maltose.

Glycogen

Branched polymer of glucose serving as the main storage carbohydrate in animals.

Hexosamine Pathway

Glucose-derived pathway producing UDP-GlcNAc for synthesis of glycoproteins and glycolipids.

Glycoconjugate

Molecule in which carbohydrate is covalently linked to protein or lipid (glycoprotein, glycolipid).

Gluconeogenesis

Formation of glucose from non-carbohydrate precursors such as lactate, glycerol or amino acids.

Glycogenolysis

Breakdown of glycogen to release glucose.