Ch 1: Nutrient Intake, Digestion, Absorption, & Excretion Flashcards
Major inputs influencing appetite regulation include:
- Short term signals r/t meal ingestion transmitted by th gut-brain axis
- Signals associated with the energy stores that are mediated by leptin
- Signals deriving from LBM
What part of the brain regulates appetite?
Hypothalamus
What is the adipose tissue-derived hormone that acts on the hypothalamus to decrease PO intake and increase energy expenditure?
Leptin
What type of meals should be initiated to increase nutrient intake during nutrition rehabilitation of undernourished patients?
small frequent meals
Stomach size impacts PO intakes
Products of what macronutrient are shown to influence development of nausea?
fat digestion
What stimulates peristaltic waves in esophagus and gastric emptying?
vagus nerve
When the swallowing mechanism is bypassed (ex: NG feeds), the rate of gastric emptying is
faster or slower?
faster
Volume of chyme that empties into the cecum is
1500-2000 mL/d
Consistency of stool in ascending colostomies vs descending colostomies
- Ascending colon – receives liquid contents
- Transverse colon → descending colon: luminal contents become more solid
What is the rectal relaxation and subsequent urge to defecate 2/2 gastric distention by food called?
Gastrocolic reflex
Why type of motility is the last to recover following GI surgery?
Colon motility
MNT post-op management SBO
When feasible, provide PO/EN postop within 24 hours of surgery for optimal patient outcomes
* Failure to initiate EN in the immediate post-op period can delay return of bowel function
Why can EN can be initiated as soon as 6 hours after surgery?
EN can be initiated within 6 hours after surgery because motility returns quickly in the small bowel
What is Chronic Intestinal Pseudo-Obstruction (CIP)?
Motility disorder of peristalsis
- Most often affects small bowel, but can occur at any point in the GI tract
- Mechanical obstruction is absent, but presence of massively dilated bowel can prevent normal function
- Colonic pseudo-obstructions – complication of narcotic use, bed rest, or disease
Chronic Intestinal Pseudo-Obstruction (CIP)
MNT for CIP
- Small, frequent meals
- Emphasis on liquid forms of energy/protein
- MVI with minerals
- Consider elemental diets with MCTs if patient doesn’t tolerate polymeric nutrients
Chronic Intestinal Pseudo-Obstruction (CIP)
If patient has SIBO in CIP
add fat-soluble and B12 vitamins
Definitition of Diarrhea
2-3 liquid stools or >250 mL liquid stool/day
What losses occur with diarrhea?
Losses of sodium, potassium, and water
When evaluating diarrhea:
Labs and etiology
- Infectious process – a left shift with increased WBC
- Anemia – decreased Hgb from blood loss
- Dehydration – increased (s)Na and BUN
- Losses – decreased (s)Na and (s)K
- Acidosis – d/t hyperchloremia
- Alkalosis – d/t dehydration
Pseudomembranous colitis (PMC):
- intestinal inflammation in the colon
- The bacterium that causes PMC is Clostridium difficile
Why do you not want to use antiperistaltic agents with infectious diarrhea?
Slowing GI motility in setting of infectious diarrhea may increase the risk of bacterial translocation
MNT for PMC diarrhea
Evidenced-based diet recommendations for PMC diarrhea haven’t been established
Anecdotal MNT:
Clear liquids (caffeine free) → low lactose/fat/fiber diet
* Caffeine/stimulatory effects on GI motility
* Solids - addresses likely transient nutrient intolerances associated with suspected loss of brush border enzymes r/t diarrhea
Do ASPEN guidelines support the use of supplemental fiber in patients with Cdiff?
No
What patient population can receive soluble fermentable fiber in standard EN formulas?
Hemodynamically stable patients with noninfectious diarrhea
How do SCFAs help to control diarrhea?
By stimulating uptake of water and electrolytes by colonocytes
Colonic bacteria ferment fibers (FOS, inulin, pectin, guar gum, psyllium) to SCFAs.
SCFAs (esp Butyrate) are major energy sources for colonocytes
What patient population should not receive insoluble fiber?
Critically ill
What patient population should not receive any form of fiber (soluble or insoluble)?
Patients at risk for bowel ischemia
MNT for gastroparesis
- small, frequent meals;
- drinking fluids with meals;
- limiting dietary fat and fiber;
- maintain good glucose control.
- When necessary, feed past the pylorus
MNT for dumping syndrome
- slow reintroduction of solid food
- no simple sugars
- frequent small meals
- no liquids with meals
can try fiber to delay gastric emptying
What secretes saliva and how much do you excrete in a day?
- Secreted by parotid, submandibular, and sublingual glands
- Excrete 1000-1500 mL/d
What does saliva include?
- mucin for lubrication
- ptyalin (a-amylase; aka salivary amylase) - enzyme for starch digestion
- immunoglobulin A (IgA) and lysozyme for protection against oral bacteria
Hyposalivation
- Often occurs in obesity via increased leptin and decreased ghrelin
- Can lead to alterations in taste perception, chewing/swallowing problems, intolerance of spicy foods
Daily amount of gastric secretions:
2500 mL/d
What do the Parietal cells of the stomach secrete?
HCl and Intrinsic Factor
What do the Peptic (or chief) cells secrete?
pepsinogen and gastric lipase
Why do oxyntic glands secrete mucus?
To protect the gastric lining and duodenum from HCl
What happens when parietal cells are destroyed?
Destruction of parietal cells (ex: chronic gastritis) → development of
- achlorhydria (absence of acid)
- pernicious anemia
- B12 deficiency
What stimulates gastrin and acid production?
Caffeine and alcohol
Proton pump inhibitor
Interfere with H,K-ATP activity
H2-receptor antagonist
block histamine stimulation of acid production
Why do peptic ulcers develop and what meds are prescribed for management?
- Develop when gastric lining’s protective barrier against irritation/autodigestion is compromised
- PPI & H2 receptor antagonist
Function of bile
Central to fat digestion and absorption
* Emulsifier (bile salts)
* Aids absorption of digested fats into intestinal mucosa
Bile salts - how much does the body reabsorb per day?
90-95% reabsorbed in the terminal ileum
What do white stools mean?
bile acids are prevented from entering the colon (ex: biliary obstruction)
How many mL of alkaline, bicarbonate rich pancreatic juice is secreted daily into the duodenum via the sphincter of Oddi per day?
1500 mL/d
In normal circumstance the pancreas releases small amounts of enzymes into blood circulation. During acute pancreatitis, serum levels of what enzymes rise dramatically?
amylase and lipase
Fasted state without EN – peristalsis still occurs, even when NPO
gastric, biliary, pancreatic secretion amounts
- Gastric secretions: 500-1000 mL/d
- Biliary and pancreatic secretions: 1000-2000 mL/d
Composition of the chyme partially determines the composition of pancreatic juice
Pancreatic juice contains enzymes for 3 major macronutrients:
- CHO – pancreatic amylase
- Protein – pancreatic proteases
- Lipids – pancreatic lipase, cholesterol esterase, and phospholipase
What is the length of the small bowel?
can vary from 12-20 feet
(350-600 cm)
small bowel
Brush border
microvilli on the edge of the epithelium of the villi that is specialized for absorption
small bowel
Enterocytes
- a mucosal cell of the intestinal lining
- role in digestion is ensuring the uptake of ions, water, nutrients, vitamins and absorption of unconjugated bile salts
small bowel turnover
The loss of sloughed cells = how many grams of protein loss?
30g protein/day loss
Purpose of mucus in the colon
provides an adherent medium to hold feces together
Digestion of Starch
- Mouth – salivary a-amylase
- Stomach – salivary amylase inhibited by gastric acid
- Small bowel – pancreatic a-amylase
- Brush border enzymes – further digestion of oligosaccharides
Deficiency of lactase enzyme is common in which populations?
- African Americans
- Native Americans
- Asians
- Individuals of Mediterranean descent
Acquired disorders of brush-border enzyme deficiency is
- Usually transient and resolves in a short period of time
- Can be 2/2 gastroenteritis or protracted diarrhea with SB villous atrophy
Protein digestion:
- Stomach – pepsin
- Duodenum – pepsin is inactivated
- Pancreatic enzymes – continues protein digestion
- Colon – bacteria digest some of the remaining protein → ammonia
The amount of ammonia absorbed is decreased when:
- Reduced amount of bacteria (antibiotic administration)
- Colonic pH is low (after lactulose administration)
Ammonia absorption may be clinically relevant during
- GI bleeds (increased absorption)
- Liver disease (lack of conversion of enteric ammonia into urea) – can contribute to development of hepatic encephalopathy
Fat digestion:
- Mouth – lingual lipase
- Stomach – gastric lipase
- Duodenum – pancreatic lipase → where most fat digestion occurs
- Bile emulsifies fat globules into smaller globules to increase surface area where water-soluble lipase enzymes can act
- Bile salts → micelles
- Brush border: micelles transport monoglycerides and free fatty acids to be absorbed
Where does most fat digestion occur?
Duodenum via pancreatic lipase
Pancreatic insufficiency and impact on fat digestion:
fat is maldigested → patients have fatty, bulky, clay-colored stools
The absorptive area of the small intestine is approximately the same area as
a tennis court
What substances are absorbed in the stomach in appreciable amounts?
alcohol and aspirin
Na+ may be co-transported by carrier proteins with what?
amino acids or glucose
What does sodium-glucose transporter 1 (SGLT1) help the body absorb?
Glucose and galactose
SGLT-1 simultaneously transports Na+ and glucose or galactose
GLUT2
When intraluminal concentrations of glucose are high, glucose is absorbed via facilitated glucose transporter type 2 (GLUT2)
How is fructose absorbed?
Fructose absorption into mucosal cells – facilitated diffusion by GLUT5
High concentrations of Na+ in the chyme
increases glucose transport
Low concentrations of Na+
decrease glucose absorption
99% of protein consumed is absorbed before reaching what part of the bowel?
distal jejunum
What is recommended as a serum cholesterol-lowering intervention and why?
Nonabsorbable soy-based sterols reduce cholesterol absorption
How are fat-soluble vitamins absorbed?
Fat soluble vitamins are transported to the brush border within micelles (just like fatty acids)
How are water soluble vitamins absorbed?
Water soluble vitamins often require Na+ cotransporters for absorption
Folate is absorbed via
a proton-coupled folate transporter
Loss of parietal cells (gastrectomy, chronic gastritis) or loss of distal ileum may lead to what sort of deficiency?
B12 deficiency
What is primarily responsible for water absorption?
Small bowel and colon
Na+ facilitates absorption of
glucose, some amino acids, and bile acids
Which is why NaCl and glucose are in oral rehydration solutions
Protein facilitates the absorption of what?
calcium and magnesium
Why does the passage of feces continue during bowel rest?
because fecal contents include material other than food residue
MCTs
Water soluble
Hydrolyzed and pass through enterocytes directly into portal circulation
SCFAs
Produced in the colon by the action of bacteria on fermentable dietary fiber
Types of SCFAs formed:
acetate, propionate, and butyrate
Effects of SCFAs
- Increased sodium and water absorption
- Trophic effects on mucosal cells of the colon
- Inhibition of cholesterol synthesis in the liver
- Improvement of colonic and splanchnic circulation
- Enhancement of immunity through stimulation of the production of macrophages, T helper lymphocytes, neutrophils, and antibodies
- Acidification of colonic pH → lower solubility of bile acids and their conversion to cytotoxic bile acids; inhibits growth of pathogenic bacteria
What happens to the villi in low flow states (ex: circulatory collapse)?
Oxygen deprivation in the tips of the villi → ischemic death of villi → decreased absorptive capacity
Mucosal atrophy occurs during
- starvation
- stress
- PN
- bowel rest
the microvilli shorten
After 1 week of a protein deficient diet
Glutamine is a
principal metabolic fuel for intestinal cells
* Its absence may contribute to mucosal atrophy that accompanies bowel rest
Trickle feeds (10-20 ml/hr) can prevent mucosal atrophy in which patient patients?
low- to moderate-risk patients
- It will not achieve the desired EN clinical outcomes in high-risk patients
