Human Metabolism and Energy Balance

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Questions and Answers

What hormone is secreted by adipocytes?

Leptin (correct)

Insulin

Ghrelin

Cortisol

Which statement about leptin deficiency in obese individuals is true?

Leptin deficiency is rare in obese adults. (correct)

Obese individuals typically have elevated levels of leptin.

Leptin levels are irrelevant to obesity.

Most obese humans are deficient in leptin.

What neurotransmitter primarily stimulates food intake?

Neuropeptide Y (correct)

GABA

Serotonin

Dopamine

What does the first law of thermodynamics state?

Energy can be neither created nor destroyed. Signup and view all the answers

How is the basal metabolic rate best estimated?

When the person is resting after a 12-hour fast Signup and view all the answers

What does gluconeogenesis refer to?

Creating glucose from non-carbohydrate sources Signup and view all the answers

Which nutrient yields the most energy per gram when metabolized?

Fats Signup and view all the answers

During prolonged fasting, which energy stores become the primary source of glucose for the body?

Adipose tissue Signup and view all the answers

What enzyme is responsible for digesting fats?

Lipase Signup and view all the answers

Which process has the highest diet-induced thermogenesis after ingestion?

Proteins Signup and view all the answers

What is the primary role of high-density lipoproteins (HDLs)?

Carry cholesterol and phospholipids to the liver Signup and view all the answers

What occurs during deamination of amino acids?

Removal of nitrogen from the amino acid Signup and view all the answers

Which statement accurately describes gluconeogenesis?

It accelerates during starvation Signup and view all the answers

What is the effect of glucagon on the liver?

Stimulates gluconeogenesis Signup and view all the answers

Which process occurs in the mitochondria and breaks down fatty acids into two-carbon units?

Beta-oxidation Signup and view all the answers

What characterizes the hyperglycemic hyperosmotic state in type I diabetes?

Increased plasma glucose and blood osmolarity Signup and view all the answers

What hormone is produced by the alpha cells of the pancreas?

Glucagon Signup and view all the answers

How is body temperature primarily regulated?

By the hypothalamus Signup and view all the answers

Which condition can result from heat exhaustion?

Dehydration Signup and view all the answers

What does the presence of GLUT4 transporters indicate?

Enhanced glucose uptake in muscle and fat Signup and view all the answers

Study Notes

Adipocytes and Leptin

Adipocytes secrete leptin, a hormone.
Most obese humans are not deficient in leptin.

Brain Neurotransmitters and Food Intake

Neuropeptide Y is a brain neurotransmitter that stimulates food intake.

Thermodynamics and Energy Balance

The first law of thermodynamics states that energy cannot be created or destroyed.
Energy input must equal energy output.
One kilocalorie (kcal) is the energy needed to raise one liter of water by 1°C.
A bomb calorimeter measures heat produced from food combustion.

Metabolic Rate and Respiratory Quotient

Metabolic rate is determined by measuring heat release and oxygen consumption.
Respiratory quotient is highest for carbohydrates compared to proteins and fats.
Basal metabolic rate is best estimated when a person is resting after a 12-hour fast.

Metabolism and Anabolism

Metabolism encompasses all chemical reactions in an organism.
Anabolism is the synthesis of biomolecules, requiring energy input.
The brain primarily uses glucose for energy. Without it, brain cells die quickly.

Gluconeogenesis and Enzymes

Gluconeogenesis converts non-carbohydrate precursors into glucose (glycerol, amino acids, lactate).
Lipase is an enzyme that digests fats.
The liver and skeletal muscles store glucose as glycogen for energy.

Nutrient Energy Value

Fats provide the most energy per gram when metabolized.
Protein ingestion leads to the highest diet-induced thermogenesis.

Fasting State and Energy Sources

During fasting, adipose tissue releases glucose to support the body.
High-density lipoproteins (HDLs) carry cholesterol and phospholipids from tissues to the liver.

Amino Acid Metabolism

Deamination precedes amino acid metabolism for energy.
Nitrogen from amino acid metabolism is converted to urea and excreted by the kidneys.
Lipolysis breaks down fats into glycerol and fatty acids.

Fatty Acid Metabolism

Beta-oxidation breaks down fatty acids into two-carbon units within mitochondria.
Ketone bodies are harmful byproducts of fatty acid metabolism.

Pancreatic Hormones

Alpha cells in the pancreas produce glucagon.
Beta cells in the pancreas produce insulin.
Insulin is released when blood glucose levels are high ("fed" state).
Glucagon is released when blood glucose levels are low ("fasting" state).
Feeding and satiety centers are in the hypothalamus.

Absorptive and Fasting States

During the absorptive state (high blood glucose, insulin), the liver synthesizes glycogen.
During starvation, gluconeogenesis rapidly increases.
Thyroid hormones and epinephrine increase basal metabolic rate (BMR).

Insulin and its Function

Insulin stimulates glycolysis and inhibits gluconeogenesis.
Glucagon stimulates gluconeogenesis, mostly in the liver.
Insulin secretion is stimulated by parasympathetic neurons.
GLUT4 transporters are stored in vesicles and found in adipose and muscle tissue.

Diabetes and Hyperglycemic State

Dehydration can result from heat exhaustion and diabetes.
In type I diabetes, a hyperglycemic hyperosmotic state can occur. This means plasma glucose and blood osmolarity are elevated above normal.

Thermoregulation

Homeothermy involves maintaining a constant body temperature.
Convective heat loss involves warm air rising from the body.
Radiation is the primary method of heat loss from the body.
Heat loss is also promoted by sweating and dilated cutaneous blood vessels.
The hypothalamus governs responses to temperature changes.

Diabetic Responses to Carbohydrate Intake

Following carbohydrate ingestion in an insulin-deficient diabetic, protein breakdown and ketone production occur.

Treatment and Signs of Diabetes

Drugs can stimulate beta-cell insulin secretion.
High fatty acid metabolism increases ketone body levels.
Symptoms of type I diabetes include high blood glucose (hyperglycemia), glucose in urine (glucosuria), ketoacidosis, thirst, and excessive urination (polydipsia).

Type II Diabetes

In type II diabetes, insulin levels are often normal but cells are resistant to insulin's effects, suggesting a defect in the signal transduction pathway.

Basal Metabolic Rate

An individual needing to consume more calories to maintain weight = higher oxygen consumption, i.e. Bill consuming 20 liters of oxygen per hour.

Traveler's Diarrhea and Ketosis

Ketosis, increased blood urea, decreased blood pH, and increased gluconeogenesis are signs of using alternative energy sources due to reduced carbohydrate intake (as in traveler's diarrhea).

Insulin and Glucagon Actions

Insulin and glucagon, both peptide hormones that target liver cells, have opposite effects. This indicates that each hormone activates a different secondary messenger system.

Brown Fat

Brown fat is innervated by the sympathetic nervous system.
Brown fat is found in infants.
Brown fat helps with non-shivering thermogenesis.
Brown fat has a rich vascular supply.

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Description

This quiz explores key concepts related to human metabolism, including the roles of adipocytes and leptin, neurotransmitters affecting food intake, the principles of thermodynamics and energy balance, as well as metabolic rates. Test your understanding of how these components interact to regulate energy in the body.