Digestion (week 1)

Question 1

why is digestion important?

Answer 1

every cell in the human body depends on it

Hippocrates: all disease begins in the gut (almost)

40% of people worldwide have some form of a functional gastrointestinal disorder

optimizing digestion = “root cause” or “upsteam” approach

drugs may alleviate symptoms or slow the progression of a disease, but may not restore optimal function

digestive dysfunction underlies many conditions, not just overt gastrointestinal conditions

Question 2

what is digestion?

Answer 2

the mechanical and chemical breakdown of food

food is reduced to molecules that the body is able to use for energy (ATP), structure, and function

the digestive system is made up of:
-gastrointestinal tract (tube/lumen)
-accessory digestive organs: brain, teeth, tongue, salivary glands, liver, gallbladder, pancreas

Question 3

digestion is a north to south process

Answer 3

one step will initiate or signal the start of the subsequent step. if we miss any step in the “north” part of the process, it can impact the subsequent steps

Question 4

3 phases of digestion

Answer 4

Cephalic phase:
-the brain is heavily involved in digestive processes (thought, sight, smell)
-chewing and swallowing

Gastric phase:
-food enters the stomach

Intestinal phase:
-food leaves the stomach and enters the small intestine

Question 5

North to South function - The Brain

Answer 5

sight and smell trigger salivary glands

cerebral cortez triggers gastric secretions

controls peristaltic movement

monitors hunger, satiety, and primes metabolic hormones like insulin

Question 6

North to South function - The Mouth

Answer 6

mechanical breakdown of food (mastication)

chemical breakdown of food (enzymes in saliva)

salivary solutes
-salivary amylase (carbs)
-lingual lipase (fats)

direct messaging to the CNS to prepare for the rest of the digestive process

Question 7

North to South function - The Esophagus

Answer 7

once food is swallowed it becomes a bolus

esophagus: additional salivary glands and peristaltic contractions

lower esophageal sphincter (LES) opens to release food into stomach

the LES closes to prevent reflux from stomach into the esophagus

Question 8

Anatomy of the stomach

Answer 8

5 regions:
-cardia
-fundus
-body (or corpus)
-antrum
-pylorus

lined with millions of secretory epithelial cells which produce hormones, acids, enzymes

four key types of secretory epithelial cell:
-G cells: secrete hormone gastrin
-Mucoid cells: secrete protective mucous
-Parietal cells: secrete hydrochloric acid and intrinsic factor
-Chief cells: secrete pepsinogen, a proteolytic enzyme

Question 9

North to South function - The stomach

Answer 9

bolus enters stomach and it expands

the presence of protein and other mechanical & neurological cues stimulate the release of gastrin

gastrin stimulates:
-mucous production
-gastric motility
-secretion of hydrochloric acid (HCl) and intrinsic factor (intrinsic factor helps you absorb vitamin b12)

Question 10

Roles of stomach acid

Answer 10

hydrochloric acid (HCl)
-lowers PH = increases acidity (average pH 1.5-3.0)
-stimulates release of pepsinogen and gastric for protein and fat digestion
-converts pepsinogen to active form, pepsin
-broke down protein into smaller polypeptides and single amino acids
-reduces the microbial populations of the food
-liberates nutrients from food complexes
-stimulates the release of protective mucous
-stimulates the contraction of the LES
-helps regulate “churn and burn” and gastric emptying

Question 11

Mucous Membrane

Answer 11

how does the stomach not digest itself? protective mucous

protects from injury, burning, ulcers, etc

contains bicarbonate ions to buffer against HCl

in small intestine, will house beneficial microbes and shuttle nutrients for absorption

Question 12

North to South function - The stomach

Answer 12

once food leaves the stomach it’s known as chyme

chyme is released through pyloric sphincter into the upper part of small intestine
-the movement of chyme through the pyloric sphincter is known as gastric emptying

gastric emptying will begin within 30 minutes of eating and can take up to 4-5 hours to complete

Question 13

North to South function - Small Intestine

Answer 13

primary site of absorption

longest portion: 22ft in length

surface area of a tennis court

three sections:
-duodenum
-jejunum
-ileum

ducts to connect to accessory organs (liver/gallbladder and pancreas)

Question 14

North to South function - duodenum

Answer 14

acidity of chyme triggers small intestine to secrete mucous and two hormones:
-secretin
-cholecystokinin (CCK)

these hormones enter bloodstream, communicate with organs and nervous system

small intestine acting as both digestive organ and endocrine organ

Question 15

North to South function - HCL

Answer 15

notice stomach acid’s role in north to south function:
-LES tightening
-gastric emptying/pyloric valve regulation
-signal accessory organs and intestinal wall to prepare for meal

Question 16

secretin’s effect on pancreas

Answer 16

brings pH up to neutral (~7.0)
-inhibiting HCL in stomach
-stimulating the pancreas to release bicarbonate

alkalization protects mucous membranes

pH optimizes pancreatic enzyme function

Question 17

cholecystokinin’s effect on pancreas

Answer 17

several signals, including CCK, stimulate pancreatic enzymes:
-protease: proteins
-amylase: carbs
-lipase: fats/lipids

pancreas: dual role
-digestive secretions = exocrine
-blood sugar regulation (insulin and glucagon) = endocrine

Question 18

cholecystokinin’s effect on liver/gallbladder

Answer 18

stimulates the gallbladder to release bile

satiety in brain

dietary fat increases CCK and satiety

bile salts are made in the liver, stored in the gallbladder

help to emulsify dietary fats and fat soluble vitamins

Question 19

Bile Salts

Answer 19

bile acids are converted to bile salts with both hydrophobic and hydrophilic sides

influence the balance of microbiota in the intestines

recycles via enterohepatic circulation

bile flow allows for:
-elimination of endogenous metabolic waste products
-elimination of exogenous medication and environmental toxins
-cholesterol homeostasis

Question 20

north to south function: small intestine

Answer 20

chyme moves past duodenum into jejunum and ileum

single cell layer of solumnar epithelial cells, enterocytes

inner mucous membrane comprised of three layers:
-the protective mucosal barrier (covering enterocytes)
-lamina propria connective tissue
-muscle fibers of the muscularis mucosae

epithelial cells spread over peaks and valleys called villi

villi covered in microvilli
-increase surface area of intestines
-nutrient absorption
-produce brush border enzymes
-serve as a selective barrier

two routes of absorption:
-transcellular (through the cell body, major route)
-paracellular (between cells, minor route)

tight junctions hold enterocytes together and regulate paracellular route

Question 21

Small intestine macronutrient breakdown

Answer 21

Carbs > simple sugars (absorption) or indigestible fibers, resistant starch, or FODMAPs

Proteins > amino acids and polypeptides (max 2-3 amino acids in length)

Lipids > free fatty acids, glycerol molecules, cholesterol esters, and fat soluble vitamins

Question 22

Peristalsis and Migrator Motor complex

Answer 22

peristalsis: involuntary contraction and relaxation moves contents through intestines

migrator motor complex (MMC) is active during fasted state

MMC involved in regulating metabolism, hunger signals, and maintaining a healthy microbial and immune balance in the intestines

changes in MMC associated with functional GI disorders

Question 23

north to south function: Large Intestine

Answer 23

ileocecal valve separates small intestine from large intestine

processes leftover chyme containing undigested food particles, water, sloughed off cells, waste for elimination

4 sections:
-cecum and ascending colon
-transverse colon
-descending colon
-sigmoid colon

recycles water and electrolytes

concentrates waste into feces

produces and absorbs vitamins

bowel flora synthesizes:
-vitamins K/B1/B2/B12
-short chain fatty acids: butyrate, acetate, propionate

primary site of the intestinal microbiome
-bacteria
-fungus
-viruses
-live on the surface of mucosa
-feed off of indigestible fiber

remnants form and leave the body as feces

Question 24

Gastrointestinal transit time

Answer 24

varies: 10-73 hours

average closer to 24-48 hours
-50% of stomach contents emptied in 2.5-3 hours and completely emptied within 4-5 hours
-50% emptying of small intestine within 2.5-3 hours
-transit through the colon 30-40 hours

Varies by: age, gender, physical activity, hydration, metabolic function. thyroid function, GI disorders, dietary composition

Question 25

Carbohydrate digestion

Answer 25

salivary enzymes begin the breakdown of sugars

minimal chemical or enzymatic carbohydrate digestion in the stomach

pancreatic and brush border enzymes in the small intestine/duodenum break complex carbohydrates down into absorbable monosaccharides:
-glucose, fructose, galactose
-undigested/absorbed resistant starch, fibers, FODMAPs will be passed into the colon for bacterial fermentation and bulking of stool

saccharide is another name for sugar

carbohydrate digestion is based on the ability to break glycosidic bonds between saccharides

microbes have different carbohydrate enzymes

basis for prebiotics, fibers, and some elimination diets

Question 26

Protein digestion

Answer 26

chewed and swallowed as bolus

HCL and pepsin in stomach cleavage of peptide bonds

amino acids move to small intestine, for additional breakdown by pancreatic proteases

microvilli in small intestine absorb amino acids

carried through bloodstream to parts of body

tissue repair, hormones, enzymes, muscle, etc

Question 27

Lipid digestion

Answer 27

lingual lipase starts lipid digestion

dietary fat in duodenum triggers release of CCK, which triggers release of bile

bile emulsifies larger fat droplets into small micelles

lipase is released into small intestine by pancreas, which continues fat breakdown

primary dietary lipids include triglycerides, phospholipids, and cholesterol esters
-triglycerides are hydrolyzed into monoglycerides (one glycerol bond to fatty acid chain), free fatty acids, and glycerol molecules
-phospholipids are hydrolyzed into free fatty acids and smaller phospholipid particles
-cholesterol esters are hydrolyzed to free cholesterol and free fatty acids

fat soluble nutrients

lipids are absorbed through the microvilli in the small intestine

pathway depends on size:
-glycerol molecules, short & medium chain fatty acids can be absorbed directly into blood stream
-long chain fatty acids, monoglycerides, fat soluble vitamins, and cholesterol will be incorporated into chylomicrons are absorbed into the lymphatic system

used for energy, stored fuel, immune balance, cell membrane synthesis & regulation, tissue repair, hormone function

Question 28

Food Combining Diets

Answer 28

the idea that some foods pair well and others do not

some plans categorize by dominant macronutrient, others by pH, etc

largely based on the observation that foods are digested at different speeds and require different enzymes to be digested

physiological perspective:
-humans have always eaten a combination of nutrients
-digestive tract can digest multiple macros at the same time
-whole foods contain multiple macronutrients
-enzymes are released regardless of whether certain macronutrients are present

Question 29

dietary pH vs systemic pH

Answer 29

pH of blood is tightly managed to ensure survival

pH compartmentalization in different tissues and secretions

breathing regulates system pH by exhaling carbon dioxide

kidneys regulate systemic pH:
-excrete hydrogen ions (H+) into urine
-recycle bicarbonate back into the bloodstream

buffering systems exist within individual cells

acidic foods increase the acidity of urine, but in most healthy individuals, they do not change to systemic pH

diets rich in alkaline minerals are always helpful

individuals with impaired kidney or lung function may need additional care

Question 30

Nervous System overview

Answer 30

Central nervous system (CNS) includes the brain and spinal cord

Peripheral nervous system (PNS) includes all of the nerves that exist outside of the brain and spinal cord

The PNS is further divided into the sensory division (also called afferent with an “a”) and the motor division (also called efferent with an “e”). You can remember this because “affect” is a verb – so think of being affected by the world around you…the beautiful sights, sounds, and
smells that tell you about your environment. Whereas effect is a noun – it is the result of your response - it is what you create. You receive information from the world through the afferent parts of the PNS, integrate it into the CNS, and then use the efferent nervous system to respond using the efferent nervous system.

Somatic is related to the more superficial parts of the body such as the musculoskeletal system and the skin, and is associated with voluntary functions like moving your body or touch

Visceral is related to the internal organs and glands and is associated with involuntary functions and sensations like heart rate or blood pressure. Visceral/efferent = ANS - autonomic nervous system

Question 31

Autonomic Balance

Answer 31

Sympathetic Nervous System:
-governs stress response
-fight or flight
-shuttles resources to immediate survival
-decreases gastrointestinal activity

Parasympathetic Nervous system:
-rest and digest
-increases blood flow to GI tract
-activates digestive functions

Question 32

Autonomic Balance

Answer 32

Dual innervation:
-sympathetic: thoracic nerve branches
-parasympathetic: cranial and sacral nerves
-vagus nerve connects the gut brain
-a dynamic balance between autonomic branches, spoken of in terms of tone or dominance
-vagus nerve connects the gut brain

increasing the parasympathetic tone before eating is an upstream “northernmost” approach to digestive wellness

Question 33

Enteric Nervous System

Answer 33

“Second brain”

complex neural network in the wall of digestive tract

functions on its own, as well as in coordination with central nervous system and endocrine system

two main plexuses (or systems):
-myenteric plexus: gastric motility
-submucosa plexus: gastric secretions and blood flow regulation

constant cross talk with brain to coordinate appetite, immune response, hormone secretions, intestinal barrier functions, and more

Question 34

Ghrelin - Neuroendocrine Regulation

Answer 34

-secreted from stomach
-stimulates hunger
-levels increase while fasting and decrease when fed

Question 35

Leptin - Neuroendocrine Regulation

Answer 35

-secreted from the adipose tissue
-acts as an appetite suppressant
-counter-regulatory to ghrelin’s signal
-tells the brain about food intake need over the long term
-dysregulation can result in leptin resistance and increased appetite

Question 36

Peptide YY - Neuroendocrine Regulation

Answer 36

-secreted from the ileum and upper large intestine after eating
-slows digestive transit to aid absorption and increase satiety
-high levels are associated with poor food intake, low levels are associated with increased food intake

Question 37

Glucagon-like peptide-1 (GLP-1) - Neuroendocrine Regulation

Answer 37

-secreted from the small and large intestines
-stimulated by food intake, slows gastric emptying, decreases appetite, and promotes the release of insulin to help regulate blood glucose levels
-GLP-1 receptor agonists are drug targets in the treatment of T2DM

Question 38

the gut microbiome

Answer 38

trillions of bacteria, fungi, viruses, parasites, and other microbes

~90% gut bacteria are obligate anaerobes (oxygen sensitive) making research challenging

genetic sequencing - human microbiome projects (launched 2007) initiated a new era in microbiome research

metabolic capacity 100x greater than the liver

Question 39

functions of the gut microbiome

Answer 39

-structural integrity of mucosal lining
-protections against pathogenic organisms
-metabolizes complex carbohydrates to produce SCFA’s
-synthesizes B vitamins and Vitamin K
-helps breakdown and metabolize polyphenols
-converts amino acids into neurotransmitters
-reduce antigenicity of foods and induce oral tolerance
-interfaces with our immune system

Question 40

Prebiotic

Answer 40

Refers to nutrients, primarily carbohydrates, that preferentially feed strains that are associated with health benefits. The key word here is preferentially – so we are selecting the nutrients that the beneficial strains thrive on, and are simultaneously less likely to fuel the growth of pathogenic strains

Question 41

Probiotic

Answer 41

Refers to the actual living organisms themselves (used to refer to the food and supplements that contain the microorganisms)

Question 42

Postbiotic

Answer 42

Refers to the metabolic byproducts from microbes, which are more and more recognized for eliciting biological responses in the host and other members of the microbiota

Question 43

Resident / indigenous

Answer 43

Strains of microbes that have a stable colony in your GIT. They often colonize in early life, and populations can ebb and flow over a lifetime based on environmental factors like the rest of the microbiota, diet, medications, health status, etc. Resident microbes can adhere to the surfaces of the intestines, taking up those parking places in your intestinal terrain. When we talk about altering the microbiome with prebiotics, we are generally talking about shifting the existing populations of resident microbes by altering their food supply, rather than ingesting new microbes (both are valid approaches).

Question 44

Commensal

Answer 44

Commensal is another term that often refers to healthy indigenous populations and the way they live in balance with a healthy level of non-competition that allows them all to “eat from the same dish,” so to speak. Webster’s dictionary defines commensalism as “a relation between two kinds of organisms in which one obtains food or other benefits from the other without damaging or benefiting it.”

Question 45

Transient

Answer 45

Microbiota consumed in things like food or supplements, but only remain in the GIT for 2-3 weeks after ingestion. While they may not adhere and set up permanent
colonies, they can still have a major impact on health while they are present. They can exert influences that help alter the resident terrain as well.

Question 46

Opportunisitc

Answer 46

Describes microbial populations that are not typically considered pathogenic in normal situations/levels but have become problematic after expanding their population in number or location as a result of certain environmental conditions. These microorganisms may be present in very small amounts in healthy individuals
while the immune system and commensal microbes are able to suppress populations but can escalate into an infection when the host immune system is compromised. An example is the overgrowth of candida that is normally present but may get overgrown after a course of antibiotics depletes the beneficial bacteria populations.

Question 47

Dysbiosis

Answer 47

-imbalances between the beneficial and harmful microbiota
-changes in population numbers, types, function, or shift in their location
-resident microbes can be healthy or problematic depending on the balance
-no one single type of dysbiosis
-altered ratio between the two major phyla groups, Firmicutes and Bacteroides
-complex ecosystems tend to self regulate = biodiversity is key

Question 48

Diet & the microbiome

Answer 48

-refined carbohydrates (a-cellular) linked to more inflammatory and less diverse microbial profile

-artificial sweeteners have varying impacts

-excessively high saturated fat and/or undigested protein content can have negative impacts, which are mitigated by the presence of fiber/prebiotics/polyphenols

-diets rich in fruits, vegetables, and fibers are clearly associated with a more robust and diverse gut microbiome

Question 49

Fermented Foods & Prebiotics

Answer 49

Probiotic rich/fermented foods:
-sauerkraut
-kimchi
-kefir
-miso
-natto
-kombucha

Prebiotic rich foods/indigestible fiber:
-legumes
-dandelion greens
-artichokes
-berries
-garlic, onion, leeks
-asparagus
-bananas
-seaweed
-flax

some dysbiotic conditions like SIBO should be approached with caution

some high FODMAP foods can worsen symptoms of gastrointestinal conditions like IBS

Question 50

microbiome across a lifetime

Answer 50

begins developing at time of birth, diversity matches adult by 2.5 years

maternal vaginal microbiome is primary source of inoculation in vaginal birth

prenatal exposure to antibiotics and C-section deliveries can delay or alter colonization

research into vaginal seeding and supplementation with pre and probiotic strains to support development of healthy microbiome:
-vaginal seeding: not currently endorsed by major gynecological organizations, research is ongoing
-pre and probiotics shown to restore normal microbial profiles in both infants exposed to antibiotics at birth and cesarian delivery by 6 months of age

prebiotic sugars, fatty acids, and immune factors in breast milk influence colonization

adding prebiotics to formula can promote microbiome diversity similar to breastfeeding

Question 51

microbiome disruptors

Answer 51

• Age
• Geographical location
• Environmental exposures
• Smoking
• Infections
• Chemical consumption including pesticides, insecticides, and herbicides( glyphosate)
• Chronic antibiotic or prescription medication use
• Poor dental hygiene
• High levels of stress and anxiety, or a history of trauma
• Regular alcohol consumption
• Excessive hygiene/lack of exposure to soil, plants, and other animals

Question 52

Antibiotics

Answer 52

overuse can promote dysbiosis

degree of impact and return to pre-treatment status depending on:
-microbiota before treatment
-age
-genetics
-diet & lifestyle
-duration of treatment, dosage, antibiotic class

can have far reaching effects throughout the body

concurrent use of oral probiotic supplements mitigates damages and reduces risk of opportunistic infection

Question 53

GALT

Answer 53

GALT = gut associated lymphoid tissue

~70% of total immune system

~80% of activated B cells

impacts intestinal permeability, food tolerance, immunity against pathogens, self recognition, dampen or amplify systemic inflammation

Peyer’s patches: lymphoid follicles in intestinal mucosa that contain immune cells: macrophages, T cells, B cells, and dendritic cells