rush Flashcards
During simple starvation, gluconeogenesis is important for:
A. Glycogen storage
B. Lipogenesis to continue to allow adequate fat storage
C. Protein synthesis to progress to allow muscle health
D. Tissues that use only glucose for fuel, such as the brain
and blood, and are dependent on this process
E. None of the above
Simple starvation results when nutrient intake does
not meet energy requirements. Energy expenditure characteristically decreases to help match energy intake, and metabolic responses occur to preserve the muscle mass. In early fasting, glycogenolysis
is the first energy source, followed by gluconeogenesis to maintain a glucose supply to obligate glucose users such as the brain, blood,
renal medulla, and bone marrow. Gluconeogenesis requires alanine,
glycerol, and lactate; therefore the focus of other organ systems in
early fasting is to provide these substrates to the liver.
Initially, during early fasting, the glycogen derived from glycogenolysis supplies glucose for obligatory glucose-using tissues. Lipogenesis is curtailed. The Cori cycle is then activated, which allows glucose
to be converted back to lactate through glycolysis in the peripheral
tissues. Skeletal muscle releases alanine via the alanine cycle. Through
these reactions, alanine and lactate are created for gluconeogenesis.
Which amino acid is released in large amounts to be used by the liver during simple starvation? A. Valine B. Serine C. Glutamine D. Cysteine E. Homocysteine
Protein metabolism adapts to starvation as
follows: (1) the synthesis of protein decreases because energy
sources for production are not available, (2) protein catabolism is
reduced as other fuels become the primary sources of energy for
many tissues, and (3) decreased ureagenesis and urinary nitrogen
loss reflect protein sparing (in the initial stages of starvation, the
rate of urea nitrogen loss is greater than 10 g/day, with a decline to
less than 7 g/day after weeks of starvation). Alanine, glutamine,
and glycine are released in large amounts to be used by the liver
and kidney for net glucose formation.
A 24-year-old male is made nil per os (NPO) after midnight for lipoma removal the next day. His case is delayed until early evening, and he enters simple starvation. In this patient,
glucagon mobilizes which of the following?
A. Glycogen from muscle tissue
B. Liver glycogen
C. Insulin to improve the cellular uptake of glucose
D. Glucose to the liver for storage
E. None of the above
Carbohydrates can be classified as complex (polysaccharides) or simple (mono- and disaccharides). Carbohydrate
digestion starts in the mouth with salivary amylase, which hydrolyzes polysaccharide bonds, and continues with pancreatic amylase
and the enzymes sucrase, lactase, maltase, and isomaltase from
intestinal epithelial cells to yield monosaccharides.
Glucose, a monosaccharide, is the preferred fuel in humans,
with all the metabolism beginning or ending with this hexose.
Glucose is transported to the liver via the portal circulation and
goes on to form pyruvate, glycogen, or fat in adipose tissue.
Glycogen is the stored form of carbohydrates and is present
in the liver and the skeletal muscle; the liver glycogen is for general
use and can be mobilized at any time using the enzymeglucose-6-phosphatase, whereas muscles lack this enzyme and
therefore conserve their glycogen for exclusive muscle use.
In times of fasting, glucagon activates the enzyme glycogen
phosphorylase to facilitate glycogenolysis. Glucagon also inhibits
glycogen synthase, preventing the formation of new glycogen. Glycogenolysis can provide glucose supplies for 12 to 24 h of fasting
A patient presents with lymphoma and a left pleural effusion;
upon drainage, the fluid is noted to be chylous. In which of
the following is he likely to be deficient?
A. Short-chain fatty acids
B. Medium-chain fatty acids
C. Long-chain fatty acids
D. Calcium
E. Vitamin B12
Fat absorption is through the small intestine and
the lymphatics.
Medium- and short-chain free fatty acids enter the enterocyte through simple diffusion and are transported from there into
the portal system. Triacylglycerides (TAGs), cholesterol, and
lipids are broken down by pancreatic lipase, cholesterol esterase,
phospholipase, and bile salts to form micelles and free fatty acids
in the intestine. Micelles contain bile salts, long-chain fatty acids,
and cholesterol. The micelles then fuse with the enterocyte membrane and from there undergo breakdown in the enterocyte.
TAGs are then resynthesized and form chylomicrons with
phospholipids and cholesterol. These, along with long-chain fatty
acids, enter the lymphatics to empty into the thoracic duct.
Chylothorax and other lymphatic or thoracic duct disruptions can
result in a profound deficiency of TAGs and long-chain fatty acids.
A patient presents with a 55% total body surface area
(TBSA) burn. Early enteral feeds are started per protocol,
and the burn unit director considers glutamine supplementation. Glutamine is an amino acid that:
A. Is categorized as an essential amino acid
B. Is found only in muscle tissue
C. Has been shown to be conditionally essential during
stress
D. Maintains stable levels in plasma during stress
E. Can be eliminated from the diet during times of stress
ANSWER: C
COMMENTS: Body proteins are made up of 20 different amino
acids, each of which has a different metabolic rate and function in
the body. There are three categories of amino acids: (1) essential
amino acids, which cannot be synthesized by the body; (2) nonessential amino acids, which can be synthesized de novo in the body;
and (3) conditionally essential amino acids, which consist of nonessential amino acids that are considered essential during stress or
trauma if their use exceeds the body’s capacity for synthesis and
an outside source is required.
Glutamine, the most abundant amino acid in the body, is a
conditionally essential amino acid; it accounts for 50% of the amino
acids in muscle, and its concentrations can fall during times of CHAPTER 4 / Nutrition, Metabolism, and Fluid and Electrolytes 51
stress because of the body’s inability to meet increases in body
requirements for the amino acid. Glutamine is the major amino acid
for intestinal mucosa, and some evidence shows improved outcomes in burn patients with glutamine supplementation. Other conditionally essential amino acids include arginine and tyrosine.
Which amino acids are classified as essential, can be
metabolized outside the liver, and are a local source of
energy for muscle?
A. Leucine, isoleucine, and valine
B. Alanine, arginine, and lysine
C. Ethionine, glutamine, and lysine
D. Phenylalanine, tyrosine, and histidine
E. None of the above
A
COMMENTS: Essential amino acids are those that cannot be
synthesized and must be obtained in the diet. The essential amino
acids are valine, leucine, isoleucine, methionine, lysine, threonine,
phenylalanine, and tryptophan. Of these, valine, leucine, and isoleucine are branched-chain amino acids; this makes them less susceptible to first-pass metabolism and less amenable to breakdown
in the liver. They are easily broken down by muscle and therefore
provide an energy source to skeletal muscle. The breakdown products of these amino acids are alanine and glutamine.
A 65-year-old woman with recently diagnosed nonobstructing
colon cancer presents to schedule a right hemicolectomy. She has
read about nutrition and healing after her surgery and asks how
she can optimize her protein intake. What are the dietary protein
recommendations for a 60-kg woman with intact protein stores?
A. 0.7 to 0.8 g/kg/day (42 to 48 g/day)
B. 0.9 to 1.0 g/kg/day (54 to 60 g/day)
C. 1.2 to 1.5 g/kg/day (72 to 90 g/day)
D. 2 to 4 g/kg/day (120 to 240 g/day)
E. 5 to 6 g/kg/day (300 to 360 g/day)
A
COMMENTS: The dietary protein requirement for adults is 0.8 g/
kg/day; that is, approximately 20% of the calories consumed should
be in the form of protein. One gram of nitrogen equals 6.24 g of
protein. In patients undergoing acute stress such as that of surgery,
protein intake should rise to 1.2 to 1.5 g/kg/day; in patients with
severe stress, such as burns or large nonhealing wounds, protein
requirements may rise to 2 to 4 g/kg/day. For burn patients, protein
requirements may be calculated by the following formula:
Protein= 1.5 g/kg/day + (3 g × % TBSA burn)
A patient presents with a perforated Meckel’s diverticulum
and undergoes terminal ileal resection with reanastomosis.
He subsequently develops poor reabsorption of bile acids.
What is the primary substrate for the formation of bile acids?
A. Cholesterol
B. Triglycerol
C. Triglycerides
D. Phospholipids
E. Insulin
ANSWER: A
COMMENTS: Three main forms of fat are found in the body:
glycerides, phospholipids, and sterols. Glycerides, principally triglycerides and triglycerol (fatty acid and glycerol), are the storage
forms of fat and are the most abundant forms in food; they account
for approximately 95%–98% of ingested fat and the fat in tissues.
Triglycerides store calories, protect organs, and act as insulators.
Phospholipids are ingested in small amounts and are main constituents of cell membranes and myelin sheaths; they are the substrates for prostaglandins, leukotrienes, and thromboxanes. Sterols
consist primarily of cholesterol. Cholesterol is the substrate for the
formation of bile acids (the primary bile acids are cholate and
chenodeoxycholate) and steroid hormones (aldosterone, progesterone, estrogen, and androgens).
A 26-year-old patient presents with abdominal pain, weight
loss, and steatorrhea. He is found to have severe terminal
ileal involvement and structuring. In which of the following
vitamins is he least likely to be deficient?
A. Vitamin A
B. Vitamin D
C. Vitamin E
D. Vitamin C
E. Vitamin K
ANSWER: D
COMMENTS: Vitamins can be either water soluble (vitamin C
and B vitamins—thiamin, niacin, riboflavin, folate, vitamin B6,
vitamin B12, biotin, and pantothenic acid) or fat soluble (vitamins
A, D, E, and K). Patients with steatorrhea, as seen in those with an
absent or damaged terminal ileum or those with pancreatitis, can
present with deficiencies of the fat-soluble vitamins.
The following are the classic signs of vitamin deficiency:
Vitamin A—dermatitis, night blindness, and poor wound healing
Vitamin D—bone demineralization and osteopenia
Vitamin E—increased platelet aggregation and decreased red
blood cell survival
Vitamin K—bruising and hemorrhage
Which of the following is not a component of the Harris– Benedict equation? A. Weight B. Height C. Age D. Gender E. % Lean body mass
COMMENTS: The Harris–Benedict equation can be used to predict the basal metabolic rate of a given patient at rest. The equation factors in weight, height, age, and gender form an estimation of caloric needs. It is not an infallible estimate but is commonly used as baseline estimation.
In general, a patient’s diet should be broken into 20% protein,
30% fat, and 50% carbohydrates. Protein needs may increase in the postsurgical state or when significant wound healing is necessary,
as in burns. Trauma, surgery, sepsis, pregnancy, lactation, and fever
can increase basal metabolic needs significantly
A 75-year-old female presents with ductal carcinoma in situ
for simple mastectomy. She has marked muscle wasting on
examination and admits to a poor diet. Which of the
following values is most predictive of postoperative
mortality?
A. Serum sodium
B. Serum albumin
C. Serum protein
D. Serum creatinine
E. Serum glucose
ANSWER: B
COMMENTS: Nutritional assessment of surgical patients involves
evaluation for preexisting malnutrition, comorbidities, risk factors
for malabsorption, and substance dependency. A number of laboratory tests may be performed based on the patient’s individual risk
factors. Multiple test values and anthropomorphic measurements
have been used to evaluate the risk of nonhealing and complications
after surgery; however, only serum albumin has been found to
correlate directly with morbidity and mortality. Preoperative
albumin levels less than 3 g/dL are associated with an increased
risk of developing serious complications within 30 days of surgery,
including sepsis, acute renal failure, coma, failure to wean from
ventilation, cardiac arrest, pneumonia, and wound infection. A
serum albumin level greater than 4.5 carries a <1% risk of mortality, less than 3 carries a 9% risk, and less than 2 carries a 30% risk.
A 55-year-old woman presents with pneumoperitoneum
and is found to have a perforated gastric ulcer with gross
intraabdominal spillage. Subsequently, she has sepsis and a
prolonged intubation, and tube feeds are started. Which of
the following visceral proteins is the best indicator of her
immediate nutritional status?
A. Prealbumin
B. Albumin
C. Transferrin
D. Total protein
E. Serum globulin
ANSWER: A
COMMENTS: In patients with a prolonged lack of nutrition,
serum markers of nutrition are a helpful way of assessing the
adequacy of nutritional supplementation. Serum total protein levels
are nonspecific and can be elevated by viral or autoimmune disease
processes. Levels of serum albumin, which has a half-life of 18 to
21 days, are helpful in the outpatient setting to assess general nutrition but are poorly reflective of short-term changes while hospitalized. Serum transferrin is commonly used but has a half-life of 8
to 10 days, again reflecting too long a time period to provide dayby-day assessments. Serum prealbumin has a half-life of 10 h to 2
days, depending on which isotype is used, and is commonly
obtained to assess the response to supplementation.
Of note, all of these markers are hepatic acute-phase reactants
and can decrease in times of stress; therefore the trend is more
significant than the absolute value.
A patient presents to the trauma bay after a house fire with a
65% TBSA burn. He is intubated and remains in the burn
unit for 5 days, after which he enters the hypermetabolic
flow phase of stress metabolism. Hyperglycemia during stress
hypermetabolism can be attributed to:
A. Increased insulin resistance
B. Increased glycogen storage
C. Decreased lipolysis
D. Increased glycogenesis
E. Increased insulin uptake
ANSWER: A
COMMENTS: In contrast to simple starvation, activation of stress
hypermetabolism occurs following surgery, trauma, or sepsis to
provide energy and substrates for tissue repair and to activate
immune function and the inflammatory response. In the initial
period, known as the ebb phase, a decline in oxygen consumption
is seen, along with poor circulation, fluid imbalance, and cellular
shock lasting 24 to 36 h. As the body adapts (flow or plateau
phase), enhanced cellular activity and increased hormonal stimulation take place and lead to an elevated metabolic rate, body temperature, and nitrogen loss. This phase can last days, weeks, or
months.
Both phases are characterized by hyperglycemia. In the ebb
phase, patients manifest impaired glucose tolerance. In the flow
phase, patients display frank insulin resistance.
In the hypermetabolic phase, glycogen storage is attenuated
and lipogenolysis is increased in an effort to keep up with the
grossly increased metabolic demands of wound healing.
In the patient above, stress hypermetabolism is characterized
by:
A. Decreased body temperature
B. Hypoglycemia and glycogenesis
C. Fluid imbalance and increased resting metabolic rate
D. Decreased gluconeogenesis and proteolysis
E. Decreased urinary protein retention
ANSWER: C
COMMENTS: The earliest stages of hypermetabolism are characterized by increases in gluconeogenesis, resting energy expenditure
(REE), proteolysis, ureagenesis, and urinary nitrogen loss. Clinical signs include tachypnea, increased body temperature, and tachycardia, with laboratory results showing increased leukocytosis, hyperlactatemia, azotemia, and hyperglycemia. Liver production of
glucose during stress is increased through gluconeogenesis and glycogenolysis (Cori cycle), which are stimulated by endocrine (hormonal) changes: increased cortisol, increased glucagon, increased
catecholamines, and decreased insulin. Overall use of protein as an
oxidative fuel source by the liver is increased, and typically, there is
increased turnover of branched-chain amino acids.
A 59-year-old woman remains intubated due to sepsis after
perforated diverticulitis. She has failed multiple trials of
extubation due to hypercapnia, which you suspect to be due
to overfeeding. Which of the following RQs is characteristic
of overfeeding?
A. 0.75
B. 0.85
C. 0.90
D. 1.0
E. 1.05
ANSWER: E
COMMENTS: Calculation of the RQ allows the clinician to alter
the nutrient content of feedings to optimize the macronutrient
intake. The RQ is the ratio of CO2 expired (Vco2) to the amount of
O2 inspired (Vo2): RQ = Vco2/Vo2.
The RQ is reflective of the type of energy expenditure. CO2
is produced when carbohydrates are converted to fat; therefore an
elevated RQ (1.0) indicates pure carbohydrate metabolism, and an
RQ of >1.0 indicates conversion of carbohydrates into fat and
therefore overfeeding.
An RQ of 0.7 is consistent with pure fat metabolism (starvation), 0.8 with pure protein metabolism, and 0.83 with a balanced
metabolism. A high RQ, by definition, causes hypercapnia and can
lead to difficulty to wean from the ventilator
