Alex Chacon and Jesse Felts
9-30-13
1.
2.
3.
4.
Introduce energy balance as a key
component of homeostasis
Overview the breakdown of energy output
and define basal metabolic rate
Discuss hormonal control of energy balance
throughout the body
Introduce the thyroid as a regulator of basal
metabolic rate (BMR)

The property of a system that regulates its
internal environment and tends to maintain a
stable, relatively constant set of conditions
◦
◦
◦
◦
◦
pH
Temperature
Solute concentration
Energy balance
Etc.




Weight maintenance
Satiety
Stress control and psychological wellness
Energetic requirement for many cellular
functions
◦ ATP, ADP, cAMP, GTP
Input
Output
U.S. Department of Health and Human Services

The set of life-sustaining chemical
transformations within the cells of living
organisms
◦ Catabolism – breakdown of organic components
(sugar, fat, protein) for the purpose of harvesting
energy
◦ Anabolism – synthesis of cellular components such
as lipids, proteins, and nucleic acids

Breaks large molecules into small
◦ Polysaccharides, lipids, nucleic acids, proteins 
monosaccharides, FAs, nucleotides, amino acids

Degradation of monomers to release energy
◦ Glycolysis, Citric Acid Cycle, Electron Transport
Chain  ATP + heat
◦ Gluconeogenesis – breakdown of fat and protein to
form glucose
◦ Glycogenolysis – breakdown of glycogen  glucose

Constructs large molecules from smaller ones
◦ Often powered by ATP hydrolysis
◦ Simple  complex

Growth and maturation
◦ Ex. bone mineralization
◦ Ex. muscle hypertrophy

TEF – thermic effect of food: energy used in
digestion, absorption and distribution of
nutrients

Energy used by normal cellular process at rest
◦ Breathing, body temperature regulation, cardiac
contractions.
◦ 60-70% of your total daily output
◦ Fat is the main energy source burned
 70% of ATP
 30% of ATP is from carbohydrates

What organ system uses the most energy in
the entire body?


Age: younger people have higher BMRs
Growth: children and pregnant woman have
higher BMRs
◦ Cell replication and division

Body composition: lean tissue masshigher
BMR
◦ Muscles burn energy even at rest
◦ Maintaining posture and muscle tone



Diet and exercise
“Input” and “output”
Exercise recommendations for adults (CDC):
◦ 150 min/wk of moderate-intensity aerobic activity
◦ Muscle-strengthening activities 2 days/week

Diet:
◦ balance calories with physical activity while
maintaining healthy nutrition



4 kcal / gram of carbohydrates
4 kcal / gram protein
9 kcal / gram fat


There are hundreds of metabolic diseases
Some are more directly related to Energy
balance:
◦ Diabetes, hyperthyroidism, hypothyroidism, obesity

What are the three categories of energy
output?
◦ What is the biggest one under your control?

Cause; in general:
◦ Input > output
◦ Diet, Exercise, Genetic susceptibility

Classification

Association of obesity with many other
medical conditions1:
◦ Insulin resistance, glucose intolerance, diabetes
mellitus, hypertension (high blood pressure),
dyslipidemia (high cholesterol), sleep apnea,
arthritis, hyperuricemia, gall bladder disease, and
certain types of cancer. (Pi-Sunyer 2010)

Leading preventable cause of death
worldwide (Barness 2007)

Biochemical function determined by necessity
◦ May liberate, store, or transform energy containing
molecules
◦ Facilitate transport of molecules

Secretion of hormones regulated by feedback
mechanisms
◦ Positive feedback - rare
◦ Negative feedback – most common in endocrine
systems



Stress hormone
Acts systemically
Synthesized by zona fasciulata of adrenal
cortex in response to ACTH secretion by the
pituitary gland
1.
2.
3.
Stress induces Corticotropin Releasing
Hormone (CRH) released by hypothalamus
Adrenocortropic hormone (ACTH) secreted
by pituitary into vascular system
ACTH binding to adrenal cells in zona
fasciulata  biosynthesis and release of
cortisol into vascular system

Diverts energy from low priority activities to
survive immediate threats (brain activity, etc.)
Increases gluconeogenesis and glycogenolysis in liver
Activates anti-stress and anti-inflammatory pathways
Facilitates the efficacy of epinephrine/NorEp
Counteracts insulin and inhibits peripheral glucose
uptake
◦ Shuts down reproductive system
◦ Decreases bone and muscle formation
◦
◦
◦
◦

Heightened in the morning to prepare for a new
day

Increase levels
◦ Prolonged physical
and/or mental stress
◦ Burnout
◦ Starvation
◦ Caffeine
◦ Sleep deprivation

Decrease levels
◦ De-stress and de-tox
activities
 Massage, music, yoga,
dancing
◦ Laughing and
happiness
◦ Black tea
◦ Fish oil
◦ High levels of cortisol
 negative feedback.



“Fight or flight” response
Acts systemically
Hormone AND neurotransmitter synthesized
in central nervous system and adrenal
medulla from tyrosine and phenylalanine
1.
2.
3.
Stress induces Sympathetic Nervous System
(SNS) activation and ACTH release by the
pituitary gland
Preganglionic sympathetic fibers and ACTH
stimulate adrenal cells to produce adrenal
precursors from tyrosine and phenylalanine
Adrenal enzymes convert precursors 
norepinephrine  epinephrine and release
from the adrenal glands into the vascular
system

Prepares the body to expend high amounts of
energy in a short period of time
◦
◦
◦
◦

Increases HR, BP, RR
Stimulates glycogenolysis
Triggers lipolysis
Facilitates stronger muscle contraction
Shunts blood and energetic molecules from
non-vital tissues



Cortisol increases epinephrine synthesis from
precursors in the adrenal medulla
No feedback mechanism
Action is terminated upon reuptake into
nerve terminal endings, dilution, and
catabolism by various tissues


Intro video:
http://www.youtube.com/watch?v=VCpjv8Yc
Uow


Major player in managing metabolism
Hormones:
◦ T3 (triiodothyronine)
◦ T4 (thyroxine)
◦ Calcitonin
 Reduces blood Ca2+

What key element is incorporated in T3 and
T4?



Increase metabolism of proteins and
carbohydrates
Increases basal metabolic rate
Other important effects:
◦ Increase heart rate, ventilation rate, increases
sympathetic activity, and aids in brain development





Low levels of thyroid hormones
release of thyrotropin-releasing hormone
(TRH) by hypothalamus
release of thyroid-stimulating hormone
(TSH) by anterior pituitary gland
T3 and T4 produced
Negative feedback loop

Hyperthyroidism
◦ Excess T3 and/or T4
◦ Every function of the body tends to speed up

Hypothyroidism
◦ Deficiency of T3 and/or T4
◦ Low metabolism
◦ Most common cause?

Goiter
◦ Swelling of thyroid gland




Barness LA, Opitz JM, Gilbert-Barness E (December
2007). "Obesity: genetic, molecular, and
environmental aspects". Am. J. Med. Genet.
A 143A(24): 3016–
34. doi:10.1002/ajmg.a.32035. PMID 18000969.
Forrest D, Visser TJ. 2013. Thyroid Hormone
signaling. Biochim Biophys Acta. 1830(7):3859. doi:
10.1016/j.bbagen.2013.03.001
Pi-Sunyer FX. Comorbidities of overweight and
obesity: current evidence and research issues. St.
Luke's-Roosevelt Hospital Center, Columbia
University College of Physicians and Surgeons, New
York, NY 10025, USA.
"Dietary Guidelines for Americans,
2010." Health.gov.