Metabolism: Lactate and Starvation

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Questions and Answers

Which condition is most commonly related to excessive insulin production, potentially causing hypoglycaemia?

Calcitonin-secreting tumours

Insulinoma (correct)

Carcinoid syndrome

Hypopituitarism

What is a potential cause of hypoinsulinaemic hypoglycaemia?

Insulin receptor antibodies

Primary hyperaldosteronism

Severe liver disease (correct)

Adrenal hyperplasia

Which of the following conditions might result in elevated C-peptide levels during hypoglycaemia?

Insulinoma (correct)

Alcohol-induced hypoglycaemia

End-stage renal disease

Accidental insulin overdose

What signifies the presence of insulin receptor antibodies in a hypoglycaemia patient?

Possible autoimmune response causing hypoglycaemia Signup and view all the answers

Which condition is NOT associated with reactive hypoglycaemia?

Type 1 diabetes mellitus Signup and view all the answers

What is the primary metabolic priority during starvation?

To provide sufficient glucose to the brain Signup and view all the answers

How long can a human survive without food under dehydration conditions?

Only for a few days Signup and view all the answers

What nutrient provides the largest energy reserve in a well-nourished 70 kg man?

Triacylglycerol Signup and view all the answers

Which process contributes the least to glucose production during prolonged starvation?

Degradation of fatty acids Signup and view all the answers

What happens to blood glucose levels during the first day of starvation?

They are maintained above 50 mg/dL Signup and view all the answers

How long can glycogen reserves typically last during starvation?

About one day Signup and view all the answers

What metabolic change occurs in response to low blood glucose during starvation?

Increased secretion of glucagon Signup and view all the answers

Which amino acids serve as a source of glucose during starvation?

Amino acids from protein breakdown Signup and view all the answers

What is the main strategy to preserve protein during starvation?

Shift fuel usage to fatty acids and ketone bodies Signup and view all the answers

What is the primary reason for the accumulation of lactate in the blood during conditions of tissue hypoxia?

Inhibition of gluconeogenesis due to low oxygen availability Signup and view all the answers

Which physiological process primarily occurs in the liver to convert lactate back into glucose?

Gluconeogenesis Signup and view all the answers

Why is anaerobic glycolysis particularly favored during high-intensity physical activity?

ATP levels are unable to be restored via the TCA cycle Signup and view all the answers

Which of the following factors can lead to pathological lactic acidosis?

Increased anaerobic glycolysis without sufficient oxygen Signup and view all the answers

What happens to lactate production under aerobic conditions compared to anaerobic conditions?

Lactate is consumed faster than it is produced Signup and view all the answers

Which statement best describes the role of adrenalin during muscular contraction?

It stimulates glycogenolysis and initiates glycolysis Signup and view all the answers

When lactate accumulates in the blood during shock syndrome, what is primarily affected in the body’s metabolic pathways?

Impairment of TCA cycle and gluconeogenesis Signup and view all the answers

What is the fasting plasma glucose concentration that indicates a diagnosis of diabetes mellitus?

Greater than or equal to 126 mg/dl Signup and view all the answers

Which condition does NOT affect the use of HbA1c for diagnosing diabetes?

Healthy individuals Signup and view all the answers

What is the threshold plasma glucose concentration for diagnosing hypoglycaemia?

Below 2.5 mmol/L Signup and view all the answers

Which of the following symptoms is NOT typically associated with hypoglycaemia?

Ketoacidosis Signup and view all the answers

What effect does a rapid fall in glucose concentration have on the body?

Increased adrenaline secretion Signup and view all the answers

Which of the following conditions is a potential cause of hyperinsulinaemic hypoglycaemia?

Insulinoma Signup and view all the answers

What is the significance of collecting a blood sample into a tube containing an inhibitor of glycolysis for diagnosing hypoglycaemia?

It allows accurate measurement of glucose levels Signup and view all the answers

What does a glycated haemoglobin (HbA1c) level greater than 6.5% indicate?

Diagnostic of diabetes mellitus Signup and view all the answers

Which of the following statements about symptoms of hypoglycaemia is true?

Symptoms may occur even at higher glucose levels following a rapid decline Signup and view all the answers

In chronic kidney disease, how does HbA1c interpretation change?

It becomes less reliable Signup and view all the answers

What metabolic process is primarily initiated by the liver during starvation?

Gluconeogenesis Signup and view all the answers

Which substrate is primarily used by the brain for energy after three days of starvation?

Ketone bodies Signup and view all the answers

What happens to glycolysis in the liver as acetyl-CoA levels rise during starvation?

It is inhibited. Signup and view all the answers

What is the primary source of glucose precursors during prolonged fasting?

Muscle protein breakdown Signup and view all the answers

During starvation, what causes the liver to produce large quantities of ketone bodies?

Depletion of oxaloacetate for the TCA cycle. Signup and view all the answers

How much glucose does the brain typically need per day during starvation after the first day?

40 grams Signup and view all the answers

What role do ketone bodies play for the heart during fasting?

They replace glucose as a main fuel source. Signup and view all the answers

What determines the duration of starvation that is compatible with life?

Size of triacylglycerol depot. Signup and view all the answers

What occurs to the breakdown rate of muscle during the later stages of starvation?

It decreases significantly. Signup and view all the answers

What is the primary source of energy for muscles in a low insulin state during starvation?

Fatty acids Signup and view all the answers

Study Notes

Lactate Production and Lactic Acidosis

Lactate is a byproduct of anaerobic glycolysis
Physiological lactic acidosis occurs during strenuous exercise, where the rate of glycolysis outpaces the availability of oxygen
The lactate produced is transported to the liver where it's converted back to glucose via gluconeogenesis (Cori cycle)
Pathological lactic acidosis arises from conditions that impair the TCA cycle or gluconeogenesis, or increase the rate of anaerobic glycolysis
Tissue hypoxia, like shock, can significantly contribute to lactic acidosis

Metabolic Adaptations in Prolonged Starvation

Starvation is the complete cessation of food intake
The body's survival period during starvation hinges on the fat reserves in adipocytes
More TAG content in adipocytes equates to a longer starvation survival time
Carbohydrate reserves exhaust quickly in starvation, typically within a day
During starvation, blood glucose levels are maintained above 50 mg/dL
Initially glucose supplies the brain and other essential tissues
Later, the body utilizes fatty acids and ketone bodies to fuel the body (especially the brain) which reduces muscle breakdown

Hyperglycemia

Hyperglycemia is elevated blood glucose levels, typically fasting levels above 100 mg/dL or postprandial levels above 140 mg/dL
Causes include diabetes mellitus (low insulin production/action), hyperactivity of anti-insulin hormones, glucagonoma, and prolonged steroid hormone treatment
Types of Diabetes Mellitus:
Type 1 (previously insulin-dependent): Characterized by insulin deficiency and susceptibility to ketoacidosis. Often presents in childhood/adolescence
Type 2 (previously non-insulin-dependent): The most common type, involving insulin resistance and often associated with obesity. Typically presents in adulthood.
MODY (Maturity Onset Diabetes of the Young): Inherited forms of diabetes
Gestational Diabetes Mellitus (GDM): A type of diabetes that develops during pregnancy.

Metabolic Syndrome/Insulin Resistance Syndrome

Characterized by an aggregation of lipid and non-lipid risk factors of metabolic origin
One definition is having three or more of the following features:
Abdominal obesity (male >102cm, female > 88cm)
Fasting plasma triglycerides > 1.7 mmol/L
Fasting plasma HDL Cholesterol (<1.0 mmol/L in males, <1.3 mmol/L in females)
Blood pressure >=130/85 mmHg
Fasting blood glucose >= 5.5 mmol/L

Acute Metabolic Complications of Diabetes Mellitus

Hypoglycemia: Characterized by low blood glucose levels
accidental overmedication
Precipitating causes include too high a dose of insulin or hypoglycemic drug; conversely, the patient may have missed a meal or taken excessive exercise after the usual dose of insulin or (OHD).
Symptoms include sweating, dizziness, palpitation, headaches, and may progress to coma if untreated
Causes include inappropriate insulin levels (e.g., insulinoma), exogenous insulin overdose, and certain drugs (sulphonylureas).
Diabetic Ketoacidosis (DKA): Characterized by elevated blood glucose, ketones, and metabolic acidosis
Often precipitated by infection, acute myocardial infarction, or vomiting.
Symptoms include nausea/vomiting, drowsiness, thirst, abdominal pain, and possibly confusion/coma.
The clinical consequences of DKA are primarily due to hyperglycemia, causing hyperosmolarity, metabolic acidosis, and glycosuria (excess glucose in urine).
Hyperosmolar Hyperglycemic State (HHS): Similar to DKA but without significant ketoacidosis; often seen in older patients. Characterized by very high blood glucose levels (~ > 600 mg/dL) and more marked hyperosmolality.

Investigations for Diabetes Mellitus

Urine Glucose Testing: Used in screening, glycosuria (glucose in urine) indicates high blood sugar
Blood Glucose Testing: Standard method, fasting levels >126mg/dL or random > 200 mg/dL (or above) confirm diabetes mellitus
Oral Glucose Tolerance Test (OGTT): Assesses how the body processes glucose over time.
Glycated Hemoglobin (HbA1c): Measures average blood glucose over the previous 8-12 weeks. An HbA1c >6.5% is a diagnostic criterion for diabetes mellitus.

Hypoglycemia

Hypoglycemia is a low blood glucose level (<2.5mmol/L)
Symptoms include headache, dizziness, irritability, excessive hunger, excess sweating, tachycardia, and progression to potentially permanent brain damage or death when untreated.
Causes vary, but broadly include:
Hyperinsulinaemic hypoglycaemia (excessive insulin) due to:
Pancreatic tumours (insulinomas)
Pancreatic hyperplasia
Exogenous insulin or diabetic medications
Certain drugs
Hypoinsulinaemic hypoglycaemia (low or absent insulin) due to:
Endocrine issues (e.g., adrenal, pituitary, or thyroid problems)
Liver or kidney failure
Reaction to glucose load, rapid absorption of glucose after ingestion
Alcohol-induced

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Description

This quiz covers two critical metabolic processes: lactate production during anaerobic glycolysis and the physiological effects of lactic acidosis, as well as the body's adaptations during prolonged starvation. Understand how the body manages energy under stress and the metabolic pathways involved in these conditions.