Protein Flashcards
What are the nutritionally essential amino acids?
Phenylalanine, isoleucine, leucine, lysine, methionine, threonine, tyrptophan, valine, and histidine
Describe the main functions of proteins and amino acids
- Growth, maintenance, and movement: proteins form integral parts of most body structures (skin, tendons, membranes, muscles, organs, bones). Support growth and repair of body tissues
- Enzymes: facilitate chemical reactions
- Hormones: some are made of proteins, functioning as messengers and signals and regular body processes
- Immunity: antibodies, cytokines, and chemokines are proteins; regulate gene transcription and translation through mTOR signaling pathway
- Fluid and electrolyte balance: help maintain fluid volume and the composition of body fluids
- Acid-base balance: act as buffers
- Transportation and storage: transport substances (lipids, vitamins, minerals, and oxygen); some store a specific micronutrient
What are the 4 levels of protein structure?
Primary structure, secondary structure, tertiary structure, quaternary structure
Name some examples of transport proteins
Hemoglobin (carries oxygen from lungs to the cells)
Lipoprotein (transports lipids around the body)
Retinol-binding protein (transports retinol from liver to target tissues)
Albumin
Prealbumin
What are the secretory sites, main target sites, and functions of Gastrin?
Secreted in pyloric antrum, duodenum, and pancreas
Target site is parietal cell
Acid secretion, gastric contraction
What are the secretory sites, main target sites, and functions of Secretin?
Secreted in duodenum
Main target site is pancreas
Water and bicarbonate secretion
What are the secretory sites, main target sites, and functions of Cholecystokinin?
Secreted in duodenum and jejunum
Main target sites are pancreas and gallbladder
Pancreatic enzyme secretion, gall bladder contraction
What are the secretory sites, main target sites, and functions of Gastric inhibitory peptide?
Secreted in duodenum and jejunum
Main target site is pancreas
Insulin secretion
What are the secretory sites, main target sites, and functions of Glucagon-like peptide-1?
Secreted in small intestine (L cell)
Main target site is pancreas
Insulin secretion
What are the secretory sites, main target sites, and functions of Glucagon-like peptide-2?
Secreted in small intestine (L cell)
Main target site is small intestine
Intestinal growth (crypt cell)
What are the secretory sites, main target sites, and functions of Peptide YY?
Secreted in small intestine (L cell)
Main target site is brain stem
Slowing the gastric emptying, reducing appetite
What are the secretory sites, main target sites, and functions of Somatostatin?
Secreted in pyloric antrum, hypothalamus
Main target sites are GI tract, pituitary gland
Suppressing the release of GI hormones
What are endogenous sources from which protein enters the GI tract?
Desquamated mucosal cells, digestive enzymes, other glycoproteins such as mucus
Which amino acids are the most rapidly absorbed?
Methionine, leucine, isoleucine, and valine
What percent of dietary protein is absorbed as dipeptides and tripeptides? What percent is absorbed as free amino acids?
67% and 33%
What are the limitations of of free amino acid formulas in the clinical setting?
Higher osmolality, less palatable, cost more. Elemental formulas vs polymeric did not show and advantage with the former for patients with Crohn’s disease
What factors affect the accuracy of nitrogen balance measurement?
Renal dysfunction, errors in estimating intake, or incomplete collection of urine, stool, fistula, or ostomy losses may affect balance results
What is the formula for calculating nitrogen balance (NB)?
NB = Nitrogen Intake - Nitrogen Output
What is the formula for calculating Nitrogen Output (g/day)?
Nitrogen Output (g/day) = [Urinary Urea Nitrogen (mg/100 ml) x Urinary Volume (L/d)/100] + 20% of Urinary Urea Losses + 2 gm
What are the best ways to evaluate protein adequacy after traumatic injury?
Nitrogen Balance; made easier when the sole nutrition source is PN or EN. Clinical guidelines help define protein requirements in critical illness, but it is often necessary to adjust protein goals depending on the clinical condition of the patient (eg, worsening renal function where protein may need to be decreased).
Describe the characteristics of arteriovenous amino acid differences across organs as a measure of protein metabolism
Invasive method
A tracer amino acid should be infused
Samples of blood are obtained from both the arterial and venous catheter
The measurements are made across muscle beds