GI System Flashcards
What are the macronutrients involved with the GI tract?
Carbohydrates, Proteins and Fats/lipids
Why do we need nutrients?
- To make ATP (energy)
- To make new cell parts (building blocks)
- To maintain cellular function
What are the two functions of the GI tract?
Digestion and Absorption
What is physical digestion?
Breaks the food into smaller and smaller pieces.
Mouth: Chewing
Stomach: Propulsion and Retropulsion
What is chemical digestion?
Using enzymes to breakdown the molecular structure of nutrients into simpler forms
What are digestive enzymes?
Proteins that break down bonds in macromolecules into their smaller building blocks
In physical and chemical digestion, what are carbohydrates broken down to?
Physical Digestion:
- Polysaccharides (many)
- Disaccharides (2)
Chemical Digestion:
- Monosaccharides (1)
In physical and chemical digestion, what are proteins broken down to?
Physical Digestion:
- Protein (many)
Chemical Digestion:
- Amino acids (1)
- Short peptides (2-3)
In physical and chemical digestion, what are fats/lipids broken down to?
Physical Digestion:
- Triglycerides
Chemical Digestion:
- 2x Free fatty acids (1)
- Monoglyceride (1)
What are the 6 main parts of the GI Tract?
Mouth
Oesophagus
Stomach
Small Intestine
Large Intestine (colon)
Rectum and Anus
What are the 4 accessory organs of the GI tract?
Salivary Glands
Liver
Gall Bladder
Pancreas
What is Peristalsis?
Waves of smooth muscle contraction that move food through the GI Tract. (Muscle pinches behind the food to push it forward)
What are Sphincters? (3)
- A ring of muscle around the junction between parts of the tract
- Control entry into the next section of the tract
- Prevent Backwards Movement
How is the GI Tract regulated?
- Nervous System (external)
- Enteric Nervous System (local)
- Hormones
How does the Nervous System regulate the GI Tract?
CNS
- processes sight, smell, taste or thoughts of food
Parasympathetic
- Increases digestion
- Stimulates motility and secretion
Sympathetic
- Inhibits motility and secretion
How does the Enteric Nervous System regulate the GI Tract?
- Its a self contained system and able to function independently.
- It has a web of neurons that stimulate motility, secretion and absorption
How do Hormones regulate the GI Tract?
Gastrin
- Stimulates acid production in stomach
- Stimulates gastric (stomach) motility
What’s the function of the Mouth + Salivary Glands in the GI Tract?
Chewing:
- physical breakdown of the food
Saliva:
- Lubrication - making it easier to swallow
- Salivary Amylase Enzyme - initial chemical breakdown of carbohydrates
- Dissolves food - allows tasting
What’s the function of the Esophagus in the GI Tract? (3)
- Transport of materials to the stomach
- Food is moved via peristalsis
- Sphincter between esophagus and stomach prevent acid reflux
What’s the function of the Stomach in the GI Tract?
Storage
- relaxation of smooth muscles allows volume to increase without change in pressure
- must be able to store a meal or two to allow time for the food to be physically and chemically digested.
How much does the stomach expand after a large meal?
Expands by 4-6 times due to the smooth muscles that line the stomach itself
What physical digestion takes place in the stomach?
- Through peristalsis contractions to move chyme
- Propulsion: forwards - move chyme forwards
- Retropulsion: backwards - movement of chyme backwards (aided by pyloric sphincter)
Propulsion and Retropulsion creates mixing waves
What chemical digestion takes place in the stomach?
Protein Only
Stomach secretes:
- acid: pH 1.5-2 (unfolds the proteins) and
- pepsin: protein digesting enzyme (chops up the protein)
What are the 3 phases of Gastric Activity?
- Cephalic phase (Incoming Food)
- Gastric Phase (Food arrives in the stomach)
- Intestinal Phase (stomach –> intestine)
What is the Cephalic phase?
Function: Prepare the stomach for arrival of food
Responds to: Seeing, smelling, tasting or thinking about food
Triggers: Activation of the CNS –> increased parasympathetic activity
Outcome: increased secretion of acid, pepsin and mucus from cells in the stomach
What is the Gastric Phase?
Function: Maximise physical digestion and begin protein chemical digestion
Responds to: Stretch, increased pH, undigested food (esp protein)
Triggers: Activation of the Enteric Nervous System which causes increased release of Gastrin
Outcome: increased secretion of acid, pepsin and mucus, increased mixing waves
What is the Intestinal Phase?
Function: slow controlled release of food to small intestine (gastric emptying)
Responds to: Stretch of the small intestine (SI) wall, decreased pH, lipids and carbs in the intestine
Triggers: release of SI hormones
Outcome: Inhibition of the enteric nervous system innervating stomach, decreased secretion of acid and pepsin and decreased mixing waves
How does exercise impact gastric emptying?
High intensity exercise –> Increased sympathetic and decreased parasympathetic activity –> reduction in neural and hormonal control –> delayed gastric emptying (intestinal phase)
What’s the function of the Small Intestine in the GI Tract?
Completion of chemical digestion and absorption of 90% of nutrients
What’s the function of the Duodenum?
Bicarbonate and mucus secretion which protects the small intestine from stomach acid. (Bicarbonate is an alkaline chemical so it neutralises the incoming acid)
What’s the function of the Pancreas?
Digestive Enzymes - chemical digestion of protein, fat and carbohydrates
What’s the function of the liver?
Makes bile salts
What’s the function of the gall bladder?
Storage and release of bile salts - needed for the digestion and absorption of fat
What are the motility patterns occurring in the small intestine?
Peristalsis and Segmentation
What does peristalsis do in the small intestine?
Wavelike contractions that propel chyme through the small intestine to the large intestine
What does segmentation do in the small intestine?
Segmentation: rhythmic contraction and relaxing but no set pattern (pinches either side)
Important for chemical digestion
- mixes the digested food with pancreatic enzymes
- increases contact with intestinal wall/brush border
BUT
- it doesn’t move chyme through intestine
- not physical digestion
What’s the function of the large intestine (colon)?
- Bacteria will ferment any undigested food
- Absorption of vitamins, electrolytes and water
- Microbial Fermentation
- Forms and stores faeces, which comprises of: bacteria, old epithelial cells, undigested food matter, fibre and a little bit of water
How long does it take?
Mouth: about 1 minute
Esophagus: about 4-8 seconds
Stomach: 2-4 hours
Small Intestine: 3-5 hours
large Intestine (colon): 10 hours to several days
What are the three enzymes secreted from the pancreas into the duodenum?
Amylase
Protease
Lipase
What does amylase do?
- carbohydrating digesting enzyme
- breaks down starch into disaccharides (but these are still too big to be absorbed into the blood)
What does protease do?
- protein digesting enzyme
- breaks down the polypeptides (20+) into small polypeptides (10+) (but these are still too big to be absorbed into the blood)
What does lipase do?
- fat digesting enzyme
- breaks down the triglycerides into free fatty acids (2) and monoglyceride (1)
What is the brush border?
The microvilli on the cell wall of the small intestine. Finishes off the chemical digestion of carbs and proteins.
- Carbohydrates: Disaccharides –> monosaccharides
- Protein: Small polypeptides –> amino acids + short peptides (2-3)
Where does the majority of the absorption take place?
In the small intestine (90%).
The other 10% happens in the large intestine (the fine tuning)
How does the small intestine have a large surface area?
Due to the folds, called villi, on the intestinal lining. This increases the rate of absorption of nutrients.
What cells line the small intestine?
Epithelial cells
What is the lumen?
Inside tube of small intestine (with digested food)
What is the apical membrane?
Cell side exposed to digested material (lumen side)
What is the basolateral membrane?
Cell side exposed to interstitial space (blood side)
Whats the order of nutrient absorption in the small intestine?
Lumen –> Apical membrane –> through/between cell –> basolateral membrane –> interstitial space –> blood stream
Whats the sodium electrochemical gradient?
- High concentration (positive) outside cells and low (negative) inside cells.
- The electrochemical gradient for sodium is created by Na+/K+-ATPase pumps
- The sodium electrochemical gradient is used as a driving force for other substances eg. glucose (secondary active transport)
How are carbohydrates, in the form of glucose, absorbed?
- Apical Membrane: sodium-coupled secondary active transport (movement of Na+ downs its concentration gradient to drive glucose transport against its concentration gradient)
- Basolateral Membrane: Facilitated diffusion (glucose transporter drives glucose transport down its gradient)
- Water follows by osmosis
What are the sources of Amino acids?
- Diet
- Old gastrointestinal cells (recycled)
- Digestive Enzymes
How is protein, in the form of amino acids and short peptides, absorbed?
- Apical Membrane: sodium-coupled secondary active transport
- Basolateral Membrane: facilitated diffusion (amino acids transporter)
- Driven by: sodium electrochemical gradient
- Water follows by osmosis
Why are fats essential?
- Important energy source
- Essential for cell growth, division & maintained the plasma membrane
- Cholesterol used to make steroid hormones
- Formation of cells (phospholipid bilayer)
How is fat absorbed?
- Lipids get surrounded by bile salts from the gall bladder
- Breakdown into smaller droplets via segmentation = emulsification
- Lipase enzymes get released from pancreas to break it down into free fatty acids + monoglyceride
- The bile salts then surround the droplets and form micelles
- The Monoglyceride’s + fatty acids enter the cell via simple diffusion and the bile salts are reabsorbed & recycled
- Monoglyceride and fatty acids are reassembled into triglycerides + other lipids
- These are repackaged into chylomicrons (special form of fat) and absorbed into the bloodstream
At rest, how much of CO is supplied to GI organs?
25%
During light exercise, how much of CO is supplied to GI organs?
12%
During heavy exercise, how much of CO is supplied to GI organs?
3%
What happens during exercise to blood flow?
Increased SNS activity –> constriction of vessels to abdominal organs –> decreased blood flow to GI organs –> decreased absorption of nutrients
Decreased PNS activity –> decreased ENS activity –> decreased motility and digestion
Blood flow to abdominal viscera during heavy exercise?
Reduced blood flow
- decreased absorption
Blood flow to skin during heavy exercise?
Increased blood flow
- increased heat loss demand
Blood flow to skeletal muscles during heavy exercise?
Increased blood flow
- increased O2 demand
- increased CO2 production
- increased metabolic waste production
What is exercise-induced nausea?
Blood flow to GI tract and stomach is redirected to the working muscles.
This slows digestion and causes discomfort
Causes of nausea? (6)
- Eating too soon
- High intensity exercise
- Over hydration and dehydration
- Exercising in the heat
- Exercising at high altitudes
- Supplements and Medications
What is a side stitch also known as?
An exercise-related transient abdominal pain
What are the 3 potential causes of stitch?
- Food in stomach –> increased blood flow to digestive tract and reduced blood flow to diaphragm –> diaphragm cramping and causes side stitch
- Ligaments that connect your diaphragm to internal organs are over stretched –> causes spasms
- Friction between the membranes that line your abdominal wall and the membrane that line your abdominal organs
How to prevent side stitch? (4)
- No eating 2-3 hours before exercise
- Avoiding foods and drinks that are concentrated in sugars before exercise
- Warming up before you start exercising
- Regulating your breathing
What is a food coma?
Post Prandial Somnolence aka food coma refers to the sense of fatigue, sleepiness or decreased energy levels following a meal.
What causes a food coma?
Eating meals high in protein and carbohydrates:
- Increased absorption/production of tryptophan –> increased serotonin production –> sleepiness
- Increase PSNS activity –> increased motility and digestion –> sleepiness
How to prevent a food coma? (6)
- going for a walk
- eating smaller portions more often
- taking an afternoon nap
- balancing meals
- getting more sleep at night
- keeping a food diary
What is the gut microbiome?
Trillions of micro-organisms, mainly comprising of bacteria, that live in your intestinal tract and are involved in functions critical to your health and wellbeing.
Why is gut microbiota important? (6)
- Helps the body digest certain foods eg. dietary fibre
- Produces some vitamins eg. B12, folate, k
- Regulates energy metabolism
- Defends against harmful micro-organisms
- Provides signals for the development and function of the immune system
- Influences gut-brain communication for optimal gut and brain function
How does diet effect the gut microbiome?
The type and amount of protein, fat and carbohydrates present in the diet influence the composition of the gut microbiota in the body.
- Healthy diet - promotes better gut and mental health
- Unhealthy diet - promotes diseases and poor mental health
How does exercise effect the gut microbiome?
More exercise –> more bacterial diversity –> better health
What is symbiosis?
Healthy gut bacterial diversity caused by healthy diet + active lifestyle.
The microbiota is balanced due to higher levels of beneficial gut bacteria.
Reduced risk of diseases and disorders.
What is Dysbiosis?
Decrease gut bacterial diversity caused by poor diet + sedentary lifestyle.
The microbiota is imbalanced due to higher levels of pro-inflammatory bacteria.
Increased risk of diseases and disorders.
