physio GI Flashcards
What are nutrients?
Most nutrients are usd for metabolic fuel, but some are for cell structure and molecular synthesis. They are substances in food needed for growth, maintenance, and repair.
What are the 3 main types of nutrients?
Macronutrients, micronutrients, and essential nutrients
Define macronutrients
Three major nutrients that make up the bulk of digested food: carbs, lipids/fats, and proteins
Define micronutrients
Two other nutrients that are required, but only in small amounts: vitamins and minerals
Define essential nutrients
Nutrients that must be eaten because the body cannot synthesize these from other nutrients. Water is required, so technically it is a nutrient.
What is an example of a non essential nutrient?
Cholesterol because our body makes it, but generally our diets are high in cholesterol
What are the functions of carbs?
They are the primary energy source for the body (especially for the brain and muscles). It is stored as glycogen in liver and muscles
What are the types of carbs?
- Simple sugars (monosaccharides and disaccharides) eaten in milk, fruits, honey (less nutritious from candy)
- Complex carbs (polysaccharides, starch, fiber)- whole grains (brown rice, oats), vegetables (potatoes, corn), legumes (beans, lentils)
Which type of carbs should be the focus of patient intake?
Complex carbs
How are carbs digested?
Enzymatic in stomach, mouth, small intestine
How are carbs absorbed?
In the duodenum and jejunum
How do carbs affect glucose?
Fuel most used by cells to make ATP
Some cells use fat for energy, however, neurons, and RBCs rely entirely on glucose
Excess glucose is converted to glycogen or fat, then stored
How are carbs used in glycogenesis?
occurs in the liver and muscle cells when the glucose level drops in the blood. Phosphorylase kinase and glycogen phosphorylase are the key enzymes
How are carbs used in glucogenesis?
Glucogenesis is the process of the glucose synthesis from non-carbohydrate sources, such as amino acids and liquids. Happens in the liver and kidneys when all the stored glycogen has been used. Pyruvate carboxylase, PEP carboxykinase. Glucose 6-phosphate, and fructose 1, 6-biphosphate are regulatory enzymes
How does insulin help with our glycogen stores?
It helps by increasing the uptake of glycogen
How are carbs used in glycogen synthesis?
Glycogen synthesis is synthesizing glycogen from glucose. Occurs when excess glucose is stored as glycogen. Synthesis occurs in the liver and muscle cells.
What is the recommended daily allowance of carbs for adults?
130 g
How are carbs obtained from the diet?
Should consist mostly of complex carbohydrates (whole grains and vegetables)
Simple carbohydrates should be limited as high amounts of sugars can lead to obesity, as well as nutritional deficiencies
What are the two types of lipids?
Triglycerides and cholesterol
What are the three types of triglycerides?
Saturated fats, trans fat, unsaturated fats
What are triglycerides?
These are neutral fats that are most abundant
What are saturated fats?
Animal fats (fatty meats, butter, cheese), tropical oils (coconut, palm oil)
What are trans fat?
Processed and fried food such as margarine, spreads, vegetable shortening, fast food
What are unsaturated fats?
(mono and polyunsaturated) nuts, plant oils, certain fish (salmon, tuna which have omega-3), olives, avocados
How are lipids digested?
Bile emulsifies fats, lipases break them down into fatty acids and monoglycerides
What is cholesterol?
Found in egg yolk, meats, organ meats, shellfish, and milk products
Liver makes 85% of cholesterol
How are lipids absorbed?
Through enterocytes, re-formed into triglycerides, and transported via chylomicrons
What are the functions of lipids?
Adipose tissue offers protection, insulation, fuel storage.
Phospholipids essential in myelins heaths and all cell membranes.
Cholesterol stabilizes membranes; precursor of bile salts, steroid hormones.
Prostaglandins → smooth muscle contraction, BP control, inflammation
Major fuel of hepatocytes and skeletal muscle
Help absorb fat-soluble vitamins
What is the phospholipid bilayer made up of?
Phospholipid, triglyceride, and cholesterol
What are the dietary requirements of lipids?
Fats: should represent 20-35% of total calorie intake
Saturated fats: limited to 10% or less of total fat intake
Cholesterol: not required in diet
What is lipogenesis?
Triglyceride synthesis that occurs when cellular ATP and glucose levels are high. Dietary glycerol and fatty acids not needed for energy are stored as triglycerides
50% is stored in adipose tissue; the other 50% is deposited in other areas. Glucose is easily converted to fat
What is lipolysis?
Breakdown of stored fats into glycerol and fatty acids, reverse of lipogenesis. Fatty acids are actually preferred by liver, cardiac muscle, and resting skeletal muscle for fuel. Lipolysis is accelerated when carbohydrate intake is inadequate
How does the body metabolize lipids?
With the metabolism of large amounts of fatty acids, ketone bodies (ketones) are formed which can cause ketosis
What is ketosis?
Accumulation of ketone bodies in blood can lead to ketosis. Common in starvation, unwise dieting, or diabetes melitus (usually occurs in T1D). Ketone bodies are also excreted in urine. Ketones are acidic, so a buildup of these molecules can lead to metabolic acidosis, which can cause dangerously low pH levels. Patient’s breath can smell fruity from vaporizing acetone. Also, breathing becomes rapid as lungs try to release CO2 to raise pH
How is cholesterol used in the body?
Is not used as an energy source. It is the structural basis of bile salts, steroid hormones, and Vitamin D. Major component of plasma membranes. 15% of blood cholesterol is ingested, with rest made in the body, primarily by the liver. Lost from body when metabolized or excreted in bile salts that are lost in feces
How is cholesterol transported?
Through lipoproteins that can transport water-insoluble cholesterol and triglycerides through blood
What are the types of lipoproteins?
HDLs and LDLs
What are HDLs?
High density lipoproteins, which have the highest protein content. They transport excess cholesterol from peripheral tissues to live to be broken down and secreted into bile. Deliver cholesterol to the liver to be secreted.
What are LDLs?
Low density lipoproteins which have the highest cholesterol count. They transport cholesterol to peripheral tissues for membranes, storage, or hormone synthesis. Deliver cholesterol to cells for storage and is a major tributary to atherosclerosis.
How do we get proteins from our diet?
Animal products (eggs, milk, fish, most meals), as well as soybeans, are considered complete proteins that contain all needed essential amino acids.
Legumes, nuts, and cereals contain incomplete proteins (lack some essential amino acids)
Legumes and cereal grains together contain all essential amino acids
How are proteins used in the body?
They are structural materials in cells such as keratin (skin), collagen and elastin (connective tissue), and muscle proteins. Immune function and tissue repair
How much protein is required in our diet?
Needs reflect age, size, metabolic rate, nitrogen balance
Rule of thumb: daily intake of 0.8 per kg body weight. American diet provides more than needed
What are complete proteins?
Eggs, milk, milk products, meat (fish, poultry, pork, beef, lamb), soybeans
What are incomplete proteins?
Legumes (lima beans, kidney beans, lentils), nuts, seeds, grains and cereals, vegetables
How are vitamins absorbed in the small intestine?
Fat soluble vitamins: A, D, E, K (stored in liver and adipose tissue)
Water soluble vitamins: vitamins C and B-complex vitamins; B12 however it is so large it requires intrinsic factor in the stomach
How are water and minerals absorbed in the small intestine?
K, Mg, Na+, phosphate, calcium are important for health and fluid balance.
Trace minerals: iron, zinc, iodine
What are the requirements in our diet for vitamins and minerals?
Dangerous free radicals are generated during normal metabolism.
Vitamins C, E, and A and mineral selenium are antioxidants that neutralize these free radicals: broccoli, cauliflower, brussel sprouts are all good sources of vitamins A and C.
Megadoses of vitamins are useless and may actually cause serious health problems, depending on the vitamins involved.
What happens when we take excess vitamins?
We will overwhelm the kidneys and the liver
What are the functions of the GI system?
Digestion
Motility (peristalsis): clamping and pushing of the stomach and esophagus to move food (chyme) down
Absorption
Secretion
What are the muscles of mastication?
Temporalis, masseter, lateral pterygoid, and medial pterygoid
What is the function of the temporalis muscle?
Elevation and retraction
What is the function of the masseter muscle?
elevation
What is the function of the lateral pterygoid?
Protrusion and side to side to side movements
What is the function of the medial pterygoid?
Elevation and side to side movements
How does our soft palate relate to our nasopharynx?
The soft palate is skeletal muscle/tissue that helps to close off our nasopharynx during vomiting or coughing or something similar
What are the parts of the mouth?
Notice the hard palate, palatine raphe, superior labial frenulum, inguinal frenulum and the gingivae (gums)
The palatine raphe is mostly the bone that goes on the midline of the roof of the mouth. The superior labial frenulum is the portion of skin surrounding the uvula “lips ties”. The inguinal frenulum is the skin that “ties the tongue down” aka “tongue ties” and is common in breastfeeding babies. Affects movement of tongue, which affects speech. Sometimes the inguinal frenulum can extend so far forward that it can cause gaps in the teeth.
What are the structures of the tooth?
Notice the crown, enamel, root, and root canal
Dental abscesses and infections
What are the different types of teeth?
Describe dentition
Primary dentition consists of 20 deciduous teeth, or milk or baby teeth that erupt between 6 and 24 months of age,
Around 6-12 years of age, 32 deep lying permanent teeth enlarge and develop while roots of milk teeth are absorbed from below, causing them to loosen and fall out.
How are teeth classified into shapes?
Incisors: chisel shaped for cutting
Canines: fang like teeth that tear or pierce.
Premolars: (bicuspids): broad crowns with rounded cusps used to grind or crush
What are the layers of the lumen of the GI tract?
Mucosa, Submucosa, Muscularis externa, and serosa.
The surface is convoluted to increase surface area to help with absorption. This is often referred to as the apical surface of the cells. The mucosa is frequently replaced, because food is constantly scraping it.
Because the mucosa is frequently replaced and they are rapidly dividing cells, what also attacks it?
chemotherapy
Describe the mucosa of the GI tract
Innermost layer is the epithelial cells which secrete acid, HCO3, digestive enzymes, hormones (enteroendocrine cells), mucus.
Lamina propria: loose connective tissue, still considered part of the mucosa. Small amounts of blood vessels and lymphatics
Muscularis mucosa
Describe the submucosa of the GI tract
Submucosal plexus which regulates the secretions and local functions (rest and digest, parasympathetic)
Describe the muscularis externa of the GI tract
Myenteric plexus (PS, S innervation) helps with the motor functions of the smooth muscles, coordinating peristalsis
What are the 3 phases of digestion?
What is the serosa?
Serious outermost layer. It faces the abdominal cavity and is made up of visceral peritoneum.
What are the stimulatory and inhibitory effects of the cephalic phase?
The cephalic phase is initiated in the presence of food, by stimulating our senses in our brain. It signals the vagus nerve to start secreting more HCl in the stomach.
What are the stimulatory and inhibitory effects of the gastric phase?
The gastric phase is stimulated by stomach stretch, by the presence, chemicals, and nutrients of food to release G cells and gastrin. It helps prep the rest of the GI system.
What are the stimulatory and inhibitory effects of the intestinal phase?
The intestinal phase occurs when the digested chyme enters into the duodenum. The presence of acidity of the HCl and stretch in the duodenum stimulates the intestinal phase. Many hormones are released around this phase as well.
What is the site of production, stimuli for release and target organ or response of secretin?
Produced in the small interest and the stimuli for release is the acid in the small intestine. The target organ/response is that it inhibits acid secretion and motility in the stomach, stimulates HCO3 secretion from the pancreas to neutralize stomach acid.
What is the site of production, stimuli for release and target organ or response of Cholecystokinin (CCK)?
-SI
- amino acids and fatty acids - digestive enzymes from the pancreas causes gallbladder to contract, relaxes the sphincter of Oddi to allow liver secretions to flow into the small intestine.
What is the site of production, stimuli for release and target organ or response of gastrin?
Produced in the antrum of the stomach and the stimuli for release are amino acids, peptides in stomach, and PS nerves. The target organ/response is that it inhibits acid secretion in the stomach and slows stomach motility
What is the site of production, stimuli for release and target organ or response of Glucose-dependent insulinotropic peptide (GIP)?
-SI
-glucose, fat in the small intestine
-inhibits acid production in the stomach and stimulates insulin release from the pancreas
What is the site of production, stimuli for release and target organ or response of Ghrelin “hunger hormone”?
Produced in the stomach and the stimuli for release are an empty stomach, low blood glucose, circadian rhythm. The target organ and response is that it stimulates hunger signals from the stomach.
What is the site of production, stimuli for release and target organ or response of leptin?
Produced in the fat cells and adipocytes. The stimulus for release is that it is increased in fat stores in the body. The target organ and response is that it regulates energy balance and signals satiety.
What is the site of production, stimuli for release and target organ or response of acetylcholine?
Produced by the vagus nerve, The stimulus for release is the PS nervous system. The target organ and response is the enteric neurons to coordinate peristalsis.
What are the cranial nerve involvements in salivation?
VII (facial) and IX (glossopharyngeal) to glands. These CN can even be stimulated by smell, sight, senses, etc and stimulate GI upset.
What are the components of saliva?
Water, mucus, HCO3-, Lysozyme, Amylase, Lipase
That helps to break down the food in our mouth and create what is called a bolus. A food bolus so that it can be safely swallowed and when it hits the GI, it is known as chyme.
What is the function of water in saliva?
Moistens food and dissolves molecules to facilitate chemoreception
What is the function of mucus in saliva?
Lubricates food and facilitates formation of a bolus for swallowing
What is the function of Lysozyme in saliva?
Kills bacteria to maintain health of gums and teeth
What is the function of HCO3- in saliva?
Neutralizes acids in foods and bacterial metabolism
What is the function of amylase in saliva?
Begins the digestion of polysaccharides. May be referred to as salivary amylase
What is the function of lipase in saliva?
Begins the digestion of triglycerides. May be referred to as salivary lipase
How does swallowing occur?
After we have chewed mechaniclaly and enzymatically, we have broken down food into a bolus and it moves in the pharynx. The soft will elevate and close off the nasopharynx to prevent the food form entering back into the nasal cavity. During this time, impulses from the swallowing center in the medulla inhibit respiration, simultaneously we will close off the epiglotis to inhibit repsiration. These impulses and signals to do this come from the medulla and prevent food from enetrign the trachea and prevent food from enterign the esophagus. The upper esophageal sphincter coordinates peristalsis to push the bolus down.
When food enters our stomach, what structure does it enter thrrugh?
The stomach lumen
How is HCL produced in the stomach?
Stimulated by gastrin and inhibited by somatostatin (HCl also inhibits gastrin)
What is chyme?
When chyme enters the stomach, mechanical and chemical digestion starts to take place. The parietal cells immediately secrete HCl and there is a thorough mixing with it and the food bolus and furthers digestion by breaking food down and killing some bacteria as well. Parietal cell also stimulate intrinsic factor for B12 to aid in chemical digestion by promoting B12 uptake.
chief cells secrete pepsinogen for protein digestion
Limited absorption of water, ETOH, certain meds
What is rugae?
This is kind of the inside if you take the stomach and reflect it open.
Where does the majority of reabsorbation actually occur?
The duodenum
Patients with poor diabetes, neuropathy, blood supply, or gastroporesis, have issues with what process?
Peristalsis
How is HCl made in the stomach?
Via the enzyme carbonic anhydrase in the stomach which are secreted by the parietal cells.
Carbonic acid mmediately disscociates into Bicarb and a H ion. Bicarb is secreted to float freely in the body as a buffer and is exchanged for Cl, while the H ion is secreted into the lumen to form an acidic environment, but we want to keep the cell charged as neutral so the lumen will reabsorb the K ion. Some Cl will make it into the lumen form the bicarb exchange to bind with H+ to form HCl
What is pepsinogen?
This is the inactive form of pepsin that is secreted by chief cells and once it enters into the lumen and acidic environment, it is activated to become pepsin which is a protein for digestion that is active in HCl and inactive in HCO3
What is peristalsis?
Coordinated wave-like contractions and relaxation of smooth muscle in the GI tract
What are the stages of peristalsis?
Initiation, Contraction, Mixing, and Emptying
What is the initiation phase of peristalsis?
Stretching sensed by mechanoreceptros in the stomach wall and stimulates the enteric NS activation
What is the contraction phase of peristalsis?
Contraction of muscularis externa. Starts close to fundus and then propogates or moves down toward the pylorus. It moves behind the bolus
What is the mixing phase of peristalsis?
Retropulsion (muscles push the food forwards and backwards) of food for further breakdown and mixing with gastric acid and enzymes for digestion
What is the emptying phase of peristalsis?
Movement of food to pyloric sphincter to allow small amts of chyme to enter duodenum to regulate gastric emptying. Heavily hormone mediated.
What is gastroparesis?
Delayed gastric emptying
Food/Chyme is basically done being digested by the time it gets where?
After the duodenum and then a little bit of a wasy into the jejunum. But the ielum is our back up and body guard and can work just as hard.
It is common to have delayed gastric emptying in what patient population?
Diabetics, because they are unable to move things forward, especially T1 with poorly controlled diabetes
Describe the structure of the small intestine
microvilli/brush border
Goblet cells
Lymphatic vessels/lacteals
What is the function of lymphatic vessels/lacteals?
fat absorption
What is the function of the microvilli and brush border?
used to increase surface area (has the same surface area of a tennis court)
What is the function of goblet cells?
mucus production
What are the functions and cells of the pancreas?
Endocrine (insulin and glucagon)
Exocrine function
Acinar cells
Duct cells
What are the functions of ductal cells?
produce HCO3 in response to secretin so the SI is not damaged by acid
What does CFTR stand for?
cystic fibrosis transmembrane conductance regulator
What is the function of acinar cells?
produce digestive enzymes in response to CCK
What is the exocrine function of the pancreas in regards to ions?
The CFTR channel.
Bicarb and H ions are formed and H ion flows out into systemic circulation, which starts an exchange cascade that eventually leads to K+ getting excreted out. There is a Cl and bicarb exchange in the cell in the duct lumen that facilitates the entire process. At the same time, the H ion is reabsorbed back into the blood in exchange for sodium. Na+/K+ ATP pump in relation to systemic circulation. In exchange for bicarb, we have chloride and Cl i brought in to keep the net charge neutral, but it also usually flows put pretty fast, because of the CFTR pump
How does the CFTR pump relate to patients with cystic fibrosis?
They have a decrease in bicarb, which can decrease the acidity and water movement within the body. It also effects pancreatic secretions, causing scarring of the pancreas.
What are the specific exocrine functions of acinar cells?
Proteases
Peptidases
These are inactive, which prevents them from being broken down. The only active enzymes are amylase, lipase and nucleases
What are the functions of proteases?
trypsin, chymotrypsin, elastase. They are the substrates of proteins and work to break peptide bonds in proteins to form peptide fragments.
What are peptidases?
carboxypeptidases. They are the substrates of proteins and they split off terminal amino acid from carboxyl end of protein
How are the inactive proteases and peptidases activated?
The membrane-bound eneterkinase is proteolytic and is secreted from the epithelial cells of the lumen of the pancrease to cleave trypsinogen to turn it into trypsin, so trypsin can act on the inactive enzymes to become active
How does an increase in acid from the stomach form a feedback loop within the GI system?
Increase in plasma secretion, increases bicarbonate secretion from the ductal cells of the pancreas and therefore increasing the flow of bicarb into the small intestine and therefore the neutralization of acid, negatively inhbits the cycle from starting over.
How does the increase of intestinal fatty acids and amino acids stimulate a feedback loop in the GI system?
The increase in CCK secretion and in plasma CCK stimulates the pancreas to secrete CCK from the acinar cells of the pancreas, therefore increasing the flow of enzymes into the SI and therefore increasing digestion and absorption of fats and proteins to negatively inhibit the cycle from starting over.
What is the functional unit of the liver?
Lobule
Within the lobules of the liver are these structures called portal triads, what are they and what do they do?
They contain branches of the bile duct, hepatic portal arteries and veins
Substances absorbed from the small intestine, actually end up in these little openings that are present, that you can see as the Hepatic sinusoid.
What is a hepatic sinusoid?
The substances end up in the hepatic sinusoid and they will eneter the venous system and will be taken into the haptocytes, so the small cells of the liver, where things are modified and broken down.
What is the function and significance of the alanine aminotransferase (ALT)?
The function is amino acid breakdown and it is significant in increased in liver damage
What are the enzymes of the liver?
alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), Gamma-Glutamyl Transferase (GGT)
What is the function and significance of the aspartate aminotransferase (AST)?
The function is amino acid breakdown (also found in heart and muscles) and it is significant in increased in liver damage and in heart/muscle problems
What is the function and significance of the alkaline phosphatase (ALP)?
The function is breakdown of molecules and important for bone health and bile flow and it is significant in increased in liver problems, bile duct issues, or bone disease
What is the function and significance of the Gamma-Glutamyl Transferase (GGT)?
The function is amino acid transport and antioxidant in cells and it is significant in increased in liver or bile duct problems and in ETOH use (alcoholics)
What are the components of bile in the liver?
HCO3, cholesterol, phospholipids, bile salts (made by cholesterol and are responsible for fat emulsification and are reabsorbed), organic wastes, bilirubin/bile pigments (erythrocyte breakdown). Bilirubin is further modified by some bacterial enzymes in our intestinal tract and the presence of bilirubin is what gives our feces that characteristic brown color
Why do we like to see brown feces in newborns?
to make sure they have good bilirubin function
How is bile regulated?
by CCK and presence of fatty acids in duodenum
What is the process of carbohydrate digestion and absorption in the small intestine?
Brush border enzymes and amylase, occur in the mouth, but the rest occur in the SI.
Polysaccharides into monosaccharides to then become the monosaccharides glucose, fructose, and galactose
Monosaccharides: glucose, fructose, and galactose are transported by what?
Transported via glucose transporters (GLUT) or NA-glucose cotransporter (SGLT)
What is the process of protein digestion and absorption in the small intestine?
Most proteins are broken down into di and triacids and amino acids
Partially broken down in stomach by pepsin
Proteases and peptidases in the intestinal lumen and in brush border help break down proteins into amino acids which are then reabsorbed in the interstitial fluid
What is the process of fat/triglyceride and absorption in the small intestine?
Partially broken down in the mouth and stomach by gastric lipase
Fat is not soluble in water, so it kind of floats on top of the chyme and aggregates, which forms and fills these fat globules, so balls of fat, that make it really hard to digest. The fat globules will stimaulte the release of bile salts, to form fat droplets, which increaes the surface area for our enzymes to take action, which starts the process of emulsification.
Undergoes emulsification → enzymatic digestion (pancreatic lipase) → micelle formation → absorption/reassembly/package into chylomicrons.
Once we have a fat emulsion droplet, what happens?
Our pancreatic lipases come in to start to bring up the emulsion droplet to be broken down into fatty acids and triglycerides into monglycerides and fatty acids. The fatty acids can be reabsorbed via division, but the monoglycerides usually need more processing and the bile salts will form something called micelles which transport them into the intestinal lining for absorption.
Define chylomicrons
large triglyceride-rich lipoproteins produced in enterocytes from dietary lipids
After micelles are used and have transported the ions, what happens to them?
Micelles will be reabsorbed and then packaged into something called chlymicrons and then the chlyomicrons can be transported via the lacteals of the lymphatic system
What is the main function of the large intestine?
To store and concentrate our feces. Fecal matter sits in our large intestine for 12-24 hours.
What are the main functions of the large intestine?
K and HCO3 secretion
Na, Cl, and water reabsorption
What are the metabolic functions of bacterial flora of the large intestine?
Fermentation of indigestible carbs and proteins and the byproduct of this occurring is the elease of irritant acids and gases
Vitamin synthesis: Vitamin K needed by the liver for clotting, biotin, folic acid
Beneficial bacteria outnumber and suppress pathogenic bacteria
Immune system destroys any bacteria that try to breach mucosal barrier
Defecation is assisted by what maneuver?
Assisted by Valsalva’s maneuver: closing of glottis, contraction of diaphragm and abdominal wall muscles cause increased intraabdominal pressure
How does the parasympathetic and sympathetic signals stimulate the defecation process?
Parasympathetic signals: stimulate contraction of sigmoid colon and rectum to relax internal anal sphincter
Voluntary muscles of external and sphincter contract to expel feces.
