Physiology 31 Lecture
Chapter 22 – Metabolism & Energy Balance
I. Overview
A. The Brain and Food Intake
B. Energy Balance
C. Metabolism
D. Homeostatic Control of Metabolism
II. The __________ Controls Food Intake
A. Food intake is affected by ______logical, environmental, and social factors, as well as
_______logical mechanisms
B. Appetite is regulated by centers in the ___________
1. A _________ center produces a sensation of hunger. Loss of this center produces
__________ (loss of appetite) in animals
2. A _______ center produces a sensation of satisfaction. Damage to this area causes
____________ (overeating) and obesity
3. Hypotheses about the ____________ of hunger include
a. ____________ hypothesis – glucostats in the satiety center absorb glucose after a
meal and send inhibitory signals to the feeding center
b. ____________ hypothesis – adipocytes secrete the hormone leptin, which inhibits
the synthesis of neuropeptide Y, an appetite stimulant, and inhibits the storage of
additional fat
c. Fats and amino acids stimulate the duodenum to secrete ____, which suppresses
appetite
d. Merely __________ and swallowing food suppresses appetite
e. Hunger is stimulated by neuropeptide Y in the brain and the hormone _________,
secreted by the stomach, as well as hunger contractions in an empty stomach
III. Energy Balance
A. Body weight and __________ balance
1. Body weight is stable when average daily energy intake and output are _______
2. Body weight has a “_____ _______” that is determined partly by heredity
3. About 30-50% of the difference in weight between people is hereditary and the rest is
due to _________ habits, exercise, etc.
B. The _________ we eat provides the following
1. Materials for replacement of worn out bio__________ and cells
2. Fuel that provides _________ for all biological work, including
a. __________ work to move substances across cell membranes
b. _____________ work, such as skeletal muscle contraction and the movement of
intracellular vesicles
c. _____________ work used for growth, maintenance, and storage of information and
energy
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C. Energy Balance is reflected by a person’s ________ consumption
1. Oxygen consumption is equated to ___________ rate
a. Food energy is measured via a bomb ________ in which food is burned and the
resulting heat is measured in kilocalories
b. A ___________ (kcal = Calorie) is the amount of heat needed to raise the
temperature of one liter of water by 1°C
c. The metabolic energy of carbohydrates and proteins is ___ kcal/g, whereas that of
fats is ___ kcal/g
d. A food’s energy content can be calculated by multiplying the number of _______ of
each component by its _______ content
e. A person’s _________ expenditure may be determined by measuring their oxygen
consumption or CO2 production
1) __________ consumption is relatively constant at a rate of 1 L O2 per 4.5-5 kcal
of energy
2) The ratio of CO2 : O2 is known as the _________ ________ (RQ), and varies with
the composition of the diet
2. Many factors influence metabolic ________
a. __________ rate is the amount of energy released by the body in a given time (e.g.,
2,000 kcal/day)
b. Basal metabolic rate (______) is a person’s lowest metabolic rate (i.e., when resting
after a 12 hr. fast)
c. _______ that affect metabolic rate include age, gender, amount of lean muscle mass,
activity level, diet, hormones, and genetics
1) _________ – adult male BMR averages 1.0 kcal/hr, whereas average female
BMR is 0.9 kcal.hr, mainly due to a higher lean muscle mass/adipose tissue ratio
in males
2) Age – BMR ________ with age, partially due to decrease in muscle
3) Physical activity and muscle contraction ___________ the metabolic rate above
the BMR
4) Diet induced ____________ – metabolic rate increases after a meal due to
energy required to digest and absorb nutrients
a) ______ cause little heat production
b) ____________ increase heat production the most
5) Hormone effects – BMR is increased by _______ hormones and catecholemines,
as well as other peptides that regulate food intake
d. The two key ____________ to avoiding weight gain are
1) ______ less
2) ____________ more
3. Energy is stored in _______ & glycogen
a. An average adult male requires about ________ kcal/day
b. Carbohydrates, proteins, and fats we eat are broken down, absorbed, and used for
immediate ________ needs; excess nutrients are _________ as glycogen or fat
c. __________ is a glucose polymer stored in the liver and muscle cells, and may be
broken back down to _________ when needed
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d. Most of the body’s energy reserves are stored in _____, which has over ________ the
energy content of carbohydrates or proteins, but is more difficult for the body to
access
IV. Metabolism
A. ______________ is all the chemical reactions that extract, use, or store energy in the body.
Two types of metabolic __________ are
1. ___________ pathways, whereby small molecules are synthesized into larger ones
a. In the fed, or ____________ state, after a meal, products of digestion are absorbed,
used, and stored
b. _________ from the nutrients are transferred to high-energy compounds, or stored in
chemical ________ of other molecules
2. __________ pathways, in which large molecules are broken down to smaller ones
a. In the fasting, or _____________ state, nutrients are depleted from the blood, so the
body taps into its __________ reserves
b. Energy released by breaking chemical _____ is used to do work
B. The _______ of absorbed nutrients depends upon whether it is a carbohydrate, protein, or
fat
1. Carbohydrates are absorbed mostly as __________
a. Glucose is the main ________ source in the body
b. The _______ uses glucose exclusively as its energy source, except in times of
starvation
c. Excess glucose is stored as __________ (glycogenesis), or as _____ (lipogenesis)
d. If plasma glucose levels drop, the liver breaks glycogen down to glucose
(_______________) and releases it into the blood
2. Proteins are absorbed as _________ ______
a. Amino acids are used primarily for _________ synthesis
b. If glucose intake is low, certain amino acids can be converted into glucose in the
liver via ________________
C. Fats are absorbed mainly as ________ acids and _________
1. Fatty acids can be used as an ________ source by many tissues, or stored as
_____________ in adipose tissue
2. Glycerol and fatty acids can also be converted to glucose like products via
gluco__________ pathways during times of fasting
D. ___________ control metabolic pathways by changing enzyme activity
1. Metabolic pathways can move forward or backward by using different __________
2. _________ can stimulate some enzymes, while inhibiting others
a. __________ stimulates enzymes for glycogen synthesis, and inhibits enzymes for
glycogen breakdown
b. ___________ stimulates enzymes for glycogenolysis, and inhibits enzymes for
glycogenesis
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E. ____________ metabolism dominates in the fed (absorptive) state
1. _________ provides energy; once absorbed, it travels to the liver and other body
tissues. Glucose is used for:
a. _________, via cellular respiration
b. _____________ synthesis in the liver
c. _____________ synthesis in liver and muscle
d. Excess glucose is converted to ____ via: glucose → pyruvate → acetyl CoA →
fatty acids, and stored in adipose tissue
2. _________ _______ are used to synthesize proteins
a. Once absorbed, amino acids travel to the ______, where they are used to synthesize
_____proteins and ________ proteins (e.g., albumin, clotting factors, etc.)
b. Amino acids not used by the liver are used by cells to create structural proteins
(e.g., _______ and myosin) or functional proteins (e.g., _________ and
hormones)
c. If glucose is low, the liver converts AAs into intermediates for cellular
_____________
d. Excess AAs are converted to ____ via: amino acids → acetyl CoA → fatty acids,
and stored in adipose tissue
3. _______ are stored energy, and are transported in the blood as ______proteins - tiny
droplets of __________ and triglycerides coated with proteins and phospholipids.
Lipoproteins from higher to lesser density include
a. ____________ – produced in the small intestine and transport dietary lipids
throughout the body
b. High-density lipoproteins (_____) - “______” lipoproteins that pick up excess
cholesterol and transport it to the liver for excretion in _______
c. Low-density lipoproteins (____) – “_____” lipoproteins that carry cholesterol to
cells, and sometimes deposit it in blood vessel walls
d. Very low density lipoproteins (_____) – formed in the liver, they transport lipids
to _________ tissue for storage; when their triglycerides are removed, they
become LDLs
e. High _____s indicate heightened risk of cardiovascular disease; high _____ is
beneficial to cardiovascular health
F. ___________ metabolism dominates in the fasted (postabsorptive) state
1. The goal of fasted state metabolism is to maintain adequate plasma __________ levels,
because glucose is normally the only fuel the _______ can utilize
2. In _________ cells, glycogen is broken down to pyruvate or __________, which are
transported to the _______ and converted to glucose
3. ______________ in adipocytes are broken down to fatty acids and glycerol
a. __________ goes to the liver, where it is converted to glucose
b. _______________ are chopped into 2 carbon acetyl units via β-oxidation
1) Acetyl joins with Coenzyme A to form ______________, and is fed into the citric
acid cycle
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2) Excess fatty acid breakdown in the liver leads to the formation of __________
bodies, which are used by the brain for energy during starvation
3) Some ketone bodies are acidic, and can cause ___________, as occurs in
uncontrolled diabetes mellitus (recognized by the smell of acetone on a person’s
breath)
4. ___________ proteins may be broken down to AAs, which can be converted to glucose
products and used in cell ____________
a. Enzymes remove amino groups (___________) and form urea, which is excreted
b. Some deaminated AAs become _________ cycle intermediates and are used to make
ATP
c. Other AAs are converted to _________ and travel to the liver, where they are
processed to glucose
V. Homeostatic Control of Metabolism - occurs largely via ________ regulation
A. Pancreatic _________ (of Langerhans) secrete insulin and glucagon
1. Beta cells secrete _________
2. Alpha cells secrete __________ when glucose levels drop below 200 mg/dl, with
maximum secretion below 50 mg/dl
B. The ______ of insulin to glucagon in the blood keeps blood glucose levels within normal
range
1. Normal blood __________ levels range from about ____ mg/dl (fasted) to _____ mg/dl
(fed)
2. After a meal when plasma glucose levels begin to rise, _________ is secreted and
promotes glucose uptake into cells
3. Between meals when glucose levels drop, __________ is secreted, which causes
glycogenolysis and gluconeogenesis in the liver
C. ____________ is the dominant hormone in the fed state.
1. Factors that _______ insulin release during & after eating include
a. Plasma _________ concentration greater than 100 mg/dl
b. Increased plasma _______ ________ concentrations
c. GI hormones, such as _____, CCK, gastrin, and glucagon-like peptide 1 (GLP-1)
cause and anticipatory release of insulin
d. ________________ activity to the GI tract and pancreas after a meal
2. Sympathetic neurons and catecholamines released during stress _________ insulin
release, and stimulate gluconeogenesis
D. Insulin promotes ____________ by binding to a cell membrane tyrosine-kinase receptor
and lowering plasma glucose levels in several ways. _________
1. Increases glucose ____________ into most insulin-sensitive cells (i.e., adipocytes and
skeletal ______ cells) by causing the insertion of ________ transporters in their
membranes
2. Indirectly influences glucose transport into _______ cells through __________
transporters that remain in the cell membrane
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3. Enhances cellular _____ and __________ of glucose via
a. _____________ of enzymes for glycolysis, glycogen, and fat synthesis
b. ____________ of enzymes for glycogenolysis, gluconeogenesis, and lipolysis
4. Activates enzymes for protein __________, and inhibits enzymes that break down
proteins
5. Promotes the conversion of excess glucose and amino acids into triglycerides
(____________), and inhibits beta-oxidation of lipids
E. ____________ is the dominant hormone in the fasted state
1. Glucagon prevents ______________ (low plasma glucose levels)
2. Glucagon release is stimulated by declining plasma ________ and amino acid levels
between meals
2. Glucagon promotes __________ and gluconeogenesis in the liver, which increases
plasma glucose levels
F. Diabetes _____________ is a group of metabolic diseases
1. ___________ is a failure to produce insulin (type I diabetes) or reduced sensitivity of
insulin receptors on target cells (type II diabetes)
2. _________ diabetes (IDDM) usually begins in childhood due to the destruction of __
cells by autoantibodies. Symptoms include
a. Catabolism of __________ and adipose tissue
b. High plasma glucose levels (_____________)
c. Excessive urine production (_______) and glucose in the urine (__________)
d. Metabolic ___________ due to production of acidic ketones, which causes
1) Increased __________
2) Acidification of the ______
3) Hyper___________
4) Can result in ________ or even death
5) Treatment is ______ replacement with fluid and electrolyte therapy
e. Insulin must be _________ to control the symptoms. Too much insulin can cause
insulin _______
3. ______ diabetes (NIDDM) usually occurs in middle aged adults, but increasing in
overweight children; insulin is still secreted, but target cells are insulin __________
a. Symptoms are similar to type 1 diabetes, but usually less ____
b. Can often be controlled by ______ and ___________, but can eventually require
insulin injection if not controlled
4. Uncontrolled diabetes mellitus is the leading cause of adult ________, renal failure,
gangrene, and limb amputations