13- Nutrition Metabolism

Metabolism

total sum of all chemical reactions occurring in an organism

Cellular metabolisms

the chemical processes that occur within cells

Anabolism

ENERGY-REQUIRING reactions that join smaller molecules to form larger molecules

Catabolism

ENERGY-RELEASING reactions resulting in the breakdown of larger molecules to smaller ones

What does chemical energy released by the breakdown of organic molecules during cellular respiration generate?

ATP

ATP (Adenosine Triphosphate)

A molecule that stores energy from the breakdown of food and releases it when necessary to perform work

How does ATP energize other molecules in cells?

by transferring phosphate groups to those molecules

Mechanical work

helps cells change shape

Transport work

enables the transport of ions and other substances across membranes

Chemical work

drives the production of large molecules in the cell

Biochemical pathways

Controls the energy release from nutrients through a series of chemical reactions

-Small amounts of energy are released per reaction to synthesize ATP

Carbohydrate metabolism

cellular respiration

-Glycolysis (in cytoplasm)

-Citric Acid Cycle (in mitochondrial matrix)

-Electron Transport Chain (cristae folds)

-Aerobic/Anaerobic Respiration

Lipid Metabolism

Triglycerides are broken down into fatty acids and glycerol (lipolysis)

-99% body energy storage; 1% glycogen

-Takes place in mitochondria

What happens to proteins during digestion?

Digestion breaks apart proteins, which are quickly taken up by cells/liver.

What is the primary purpose of amino acids in protein metabolism?

Amino acids are used to synthesize needed proteins.

What is the secondary purpose of amino acids in protein metabolism?

Amino acids can be broken down to enter carbohydrate metabolism for energy.

How can amino acids be metabolized to produce ATP (option 1)?

Amino acids can be converted to pyruvic acid and acetyl-CoA.

What are the byproducts when the amine group is removed from amino acids (option 2)?

Ammonia, NADH, and a-keto acid are produced.

What happens to proteins during prolonged fasting or starvation?

Proteins are converted to pyruvic acid for energy.

Absorptive state

The period immediately after a meal (0-4 Hours)

-Glucose entering circulation is used by cells for immediate energy needs

What happens to nutrients during the absorptive state?

Nutrients are absorbed through the intestinal wall into the circulatory and lymphatic systems.

Where do nutrients travel after being absorbed in the absorptive state?

Nutrients travel to the liver.

How are nutrients processed in the liver during the absorptive state?

Nutrients are converted into energy storage molecules (glycogen, fatty acids, triglycerides) and proteins.

Where are triglycerides stored during the absorptive state?

Triglycerides are stored in adipose tissue.

Where is glycogen stored during the absorptive state?

Glycogen is stored in muscle.

How are stored nutrients used in tissues during the absorptive state?

Stored nutrients are used in tissues for energy.

Postabsorptive state

-Occurs late in the morning, late in the afternoon, or during the night after each absorptive state ends

-Blood glucose levels are maintained by the conversion of other molecules to glucose

What is the first source of blood glucose conversion?

Liver glycogen stores

How long do liver glycogen stores last for blood glucose conversion?

4 hours

What is the second source of blood glucose conversion after liver glycogen?

Muscle glycogen stores

What is the third source of blood glucose conversion?

Adipose tissue

What does the liver convert lactic acid into?

Pyruvic acid

What does the liver convert amino acids into?

a-keto acid, NADH, ammonia

What does the liver convert fatty acids into?

Ketones

Metabolic rate

the total amount of energy produced and used by the body per unit of time

How is metabolic rate estimated?

by measuring the amount of oxygen used per minute

-One liter of O2 consumed by the body produces 4.825 kcal of energy

Three ways to use metabolic energy

-Basal metabolism processing

-Muscle contraction

-Food

-Processing

Basal metabolic rate (BMR)

-Metabolic rate calculated in expended kilocalories per square meter of body surface area per hour

-Measured while a person is awake and at rest, without eating for 12 hours

-Higher males > females; Higher young> old

Thermoregulation

maintaining physiologic core body temperature by balancing heat generation with heat loss

How does the body generate heat?

as a byproduct of metabolic processes (thermogenesis)

-Heat is retained if the environment is too cold

-Heat is released if the environment is too hot

When do heat-generating mechanisms activate?

When the environmental temperature is less than the body temperature.

What is the primary goal of heat-generating mechanisms?

To increase heat production and reduce heat loss.

What are the main mechanisms of heat generation in the body?

Thyroid hormones, sympathetic nervous system activation, and shivering.

What role do thyroid hormones play in heat generation?

They are thermogenic, increase metabolic rate and O2 consumption, and stimulate Na+/K+ ATPase.

What happens when there are deficits or excess thyroid hormones?

They cause disturbances in body temperature regulation, leading to hyperthyroidism or hypothyroidism.

How does sympathetic nervous system activation contribute to heat production?

It stimulates B receptors in brown fat to increase metabolic rate and heat production, and a1 receptors in vascular smooth muscle to cause vasoconstriction.

What is the effect of sympathetic nervous system activation on blood flow?

It reduces blood flow to the surface of the skin.

What is shivering and its role in heat production?

Shivering is rhythmic skeletal muscle contraction and is the most potent mechanism for increasing heat production.

Which part of the brain reacts to cold to activate shivering?

The posterior hypothalamus.

What do the temperature centers in the posterior hypothalamus activate in response to cold?

They activate skeletal muscle alpha and gamma motoneurons to generate heat and raise body temperature.

What activates heat-dissipating mechanisms?

When the environmental temperature increases or the body must relieve excessive heat to maintain normal body temperature.

What are the two heat-release methods?

Radiation and Convection.

Where are the mechanisms for dissipating heat coordinated?

In the anterior hypothalamus.

What happens to skin blood vessel sympathetic activity when body temperature increases?

It decreases.

What is the result of decreased sympathetic activity in skin blood vessels?

Increased blood flow/shunting of blood through the skin arterioles.

What allows for heat to be lost through radiation and convection?

Increased blood flow to the skin, resulting in skin redness and warmth.

What happens to sweat gland sympathetic cholinergic fibers when body temperature increases?

There is increased activation, leading to increased sweating.

What is the cooling effect produced by increased sweating?

It helps to dissipate heat.

What are some behavioral changes to help dissipate heat?

Increasing skin exposure by removing clothing or fanning.

What is the role of the anterior hypothalamus in body temperature regulation?

It is the body's temperature regulation center.

What type of information does the anterior hypothalamus receive from skin thermoreceptors?

External environmental temperature information.

What type of information does the anterior hypothalamus receive from anterior hypothalamic thermoreceptors?

Internal core temperature information.

What happens if the core temperature is below the set-point?

Heat-generating and heat-retaining mechanisms are activated.

What happens if the core temperature is above the set-point?

Heat-dissipating mechanisms are activated.

Fever

Abnormal elevation in body temperature caused by pyrogenic cytokines (IL-1, IL-6, TNF-α) increasing the hypothalamic set-point temperature

Heat Exhaustion

A consequence of the body's responses to elevated environmental temperature; Excessive sweating leads to decreased ECF and fainting

Heat Stroke

Body temperature increases to the point of tissue damage; Core temperature increases to dangerous levels

Malignant Hyperthermia

Massive increase in metabolic rate, increased O2 consumption, & skeletal muscle heat production elevate body temperature to dangerous levels

Western nutritional diseases are the result of

-Diets high in processed foods (refined carbohydrates)

-Diets high in saturated fats

-Diets high in sugar consumption

-Diets low in fruit, vegetable, and whole grain consumption

What do poor dietary patterns contribute to?

The prevalence of several chronic diseases

Who is affected by Western nutritional diseases?

Millions globally, especially in developed nations

Common western nutritional diseases

-Obesity

-Type 2 Diabetes Mellitus

-Cardiovascular Diseases

What are the highest rates of obesity found in?

Developed countries

What percentage of U.S. adults were reported as obese in 2020 according to the CDC?

Approximately 42.4%

Which age groups are affected by obesity?

All age groups, with increasing rates in children and adolescents

What is one common Western nutritional disease caused by obesity?

Type 2 Diabetes Mellitus (NIDDM)

What is another common disease associated with obesity?

Cardiovascular Diseases

What syndrome is considered an underlying cause of obesity?

Metabolic Syndrome

Type 2 Diabetes Mellitus

-Affects about 10.5% of the U.S. population (CDC, 2020)

-Higher incidence in adults (increasing rates in children & adolescents)

What are the physiological impacts of T2DM?

-Hyperglycemia – Chronic elevated blood glucose levels

-Neuropathy – Nerve damage (extremities)

-Nephropathy – Kidney damage

-Retinopathy – Retinal damage

-CV risks – Increased risk of HTN, stroke, and heart disease

Cardiovascular Disease

-Leading cause of death globally

-Accounts for 1 in 4 deaths in the U.S. (CDC, 2020)

-Affects adults (risk increasing with age and lifestyle factors)

What are the physiological impact of cardiovascular disease?

-Atherosclerosis – Buildup of arterial plaque reduces blood flow & leads to ischemic events

-Hypertension – HBP strains CV system & leads to heart failure and stroke

-Heart Failure – Insufficient heart function

-Dyslipidemia – High cholesterol levels in blood

Metabolic Syndromes

-Affects about 34% of U.S. adults (CDC, 2020)

-Common in adults with obesity and a sedentary lifestyle

What are the physiological impacts of metabolic syndromes?

-Insulin Resistance – Leads to T2 DM and associated complications

-CV Risks – Increased risk of heart disease and stroke

-Liver Disease – Increased risk of non-alcoholic fatty liver disease (25% of population) and steatohepatitis (fat accumulation in liver cells causing inflammation)