More Digestion Notes from Old Notes Flashcards
Ingestion
take food into digestive tract
Mastication
physical breakdown of large clumps into small clumps to increase surface area for digestive enzymes
Digestion
Chemical breakdown of large molecules into small molecules that can be absorbed
Absorption
Movement of molecules into tissues of body across membrane
Egestion
Elimination of materials from GI tract
Defecation
Vomiting
Purpose of Saliva
To create a solution for digestive enzymes to work since they are water soluble
Chyme
Term for material moving through GI tract
Made up of water + food + enzyme + etc.
Amylase
In saliva that digest amylose (a starch)
Where does digestion begin?
Begins in the mouth, but the bulk of digestion occurs downstream
What is peristalsis?
Rhythmic contractions
Used in the movement of food from the esophagus to the stomach
Overall look at the GI tract
Oral cavity Mastication and some carbohydrate digestion Pharynx Transport Esophagus Transport Stomach Storage and protein digestion Small intestine Digestion and absorption Large intestine Salt and water absorption
Name the accessory organs and their function
Salivary Glands - saliva
Pancreas - pancreatic juice containing digestive enzymes
Liver - bile which aids in lipid digestion (it doesn’t digest lipid, only aids in digestion of)
• ^^ These are not part of digestive tract, they add material to GI tract
Teeth
Tongue
T/F: The hypopharyngeal sphincter normally closes off the esophagus when we are not swallowing
T
What is the function of the gastroesophageal sphincter?
A gastroesophageal sphincter near the stomach area of the esophagus at diaphragm keeps material that has entered the stomach from going back up to the esophagus
What is heartburn?
Movement of acid chyme upstream to esophagus and the gastroesophageal sphincter has failed doing its job
Regions & Purpose of the Stomach
There are muscles in the stomach that churn the chyme and allow it to move downstream and enter the small intestines
Portion where esophagus comes in is called the cardiac region
The portion that bulges out is called the Fundus
The central part is called the body
The very end where it meets the intestines is called the pyloris
○ There is a pyloric sphincter there which closes off and keeps material in the stomach
○ We use small intestine to digest and absorb but we don’t want to overwhelm it
○ Therefore, we want to allow food to enter in small portions at a rate that the small intestine can process it
Goblet Cells
Secrete alkaline mucous which will form a barrier on top of the epithelial cells of stomach to help prevent acid contact with cells
There is also constant replacement of stomach lining cells every 4 day or so
Purpose of G cells
Secrete Gastrin
Parietal Cells
Secrete HCl
Lowers pH in chyme
□ More protein you eat in food, the more acid you secrete
□ Low pH needed to maintain shape of pepsin to keep it active
H+ denatures proteins in food
□ This allows easier cleaving of peptide bonds by pepsin
H+ also kill many (but not all) bacteria in food
Helicobacter pylori
Can secrete cytotoxin that will erode epithelial lining of the stomach, leaving the cell exposed to acid causing gastric ulcer
Chief Cells
Secrete Pepsinogen
What is Pepsinogen?
Pepsinogen is an inactive digestive enzyme that is converted into pepsin (active enzyme) in the presence of high acid (H+) produced by parietal cell
What is Pepsin?
Pepsin is a protease that breaks down proteins into protein fragments at specific peptide sites
Where does most protein digestion occur?
Protein digestion begins in stomach, but pepsin does not break down all amino acids
Most protein digestion occurs in small intestines
What is Zymogen?
An inactive form of a protease secreted in the small intestine
Regions of the small intestine
Duodenum - upper region
Jejunum - middle region
Illeum - lower region
Duodenum
Where the bile and pancreatic duct empties into
Acid chyme enters here
What is the role of the small intestine?
Digestion
Absorption
Movement in the small intestines
Peristalsis - moves chyme downstream
Segmentation - mixing the chyme
Amylase
Present in saliva that breaks down amylose (a plant starch)
Glycogen
Animal starch
Cellulose
Most common complex carbohydrate
Major component of all plant cell walls
Broken down by cellulase; humans cannot make cellulase to break it down
Glucose and Galactose are monosaccharides that are taken up by
Secondary Active Transport
Fructose is a monosaccharide taken up by
Facilitated diffusion
T/F: Emulsification is the breaking of chemical bonds among lipid atoms
F
We enhance the digestion of lipids by creating more surface area via the process of emulsification of lipids (breakup of clump of lipid)
Bile Salts
Emulsifying agents
Derived from cholesterol
Created in the liver
Must have a polar region
Purpose of Liver
Makes Bile, a fluid containing bile salts and bilirubin
Does not make digestive enzymes, only aids in breakup of lipids
Used in converting many of the metabolic materials, it is a metabolic interconversion organ
Bile
Fluid of Bile Salts and Bilirubin
Bilirubin
Breakdown product of old heme from hemoglobin, broken down in the spleen/bone marrow
Attached to plasma proteins for transport
Cannot be filtered at kidneys because it is attached
Bacteria convert biliruben into urobilinogen which is
Excreted in feces
Absorbed across walls of large intestine and enters blood
Urobilinogen is water soluble and then filtered out (in kidney) and enters urine
This is how to get rid of heme from the body
Urobilinogen is what makes urine yellow which originally comes form the heme in the red blood cells
The inner sheet that surrounds the gut tube
Visceral Peritoneum
The place where two serous membranes come together and attach to the body wall
Mesenteries
The place where 2 serous membrane connect to each other and connects 2 organs is called
Omentum
Gastric Function
Secrete Pepsinogen and HCl
The Cephalic Phase of Stomach
Brain Control
Sight/smell/taste of food will trigger salivary gland secretion
Vagus nerve stimulates:
a. Parietal cells -> HCl secretion
b. Chief cells -> pepsinogen secretion
c. G cells -> gastrin hormone
Acts on chief and parietal cells to increase HCl and pepsinogen
It starts the process before even eating the food, generates some protein fragments for later positive feedback loop
d. Increased blood flow to the stomach
The Gastric Phase
Protein Fragments trigger:
Gastrin secretion (also HCl and pepsinogen secretion)
Gastric will go into blood and act on chief and parietal cell to increase pepsinogen and HCl
If pepsinogen and HCl secretion is increased, you will break down more proteins, hence make more fragments which will make more gastrin
Positive feedback loop
How does the Gastric Phase end?
Gastrin production is inhibited by very low pH (high acidity) but the pH never falls to very low levels until intact proteins are fragmented
Intact proteins are buffers, pH will be high when digesting and low once we finished
This will end the positive feedback loop to stop gastrin production
GIP
Gastric Inhibitory Protein
Circulates in the blood and act on the stomach to inhibit secretion and the emptying of the chyme by slowing down smooth muscle action
GIP also acts on pancreas to initiate insulin secretion into blood
How to indicate the duodenum is full, thus slow down stomach action to prevent more chyme from entering small intestine
If the walls of the duodenum are stretched that would indicated that the duodenum is full
If there is an increase in the osmotic concentration of chyme in duodenum also indicate duodenum is not done with its job
If there is a high level of lipids in the duodenum
Hormones from the small intestine (and stomach)
Secretin from duodenum in response to low pH of chyme
Act on pancreas to secrete HCO3-
This will neutralize the acidity of the chyme
Cholecystokinin(CCK)secreted from the duodenum in response to high lipid in chyme, acts on pancreas to secrete digestive enzymes
Vitamins
Organic molecules usually coenzymes that are important in regulating certain reactions that we cant make but need in our diet
Anabolism
Synthesis
Building something from smaller units
Catabolism
Breakdown of large units into smaller units
Hypoglycemic
Low blood sugar
If there is too low blood glucose levels what happens to the brain
If glucose concentration is low, the concentration gradient is much weaker so the cells cannot get glucose at the rate they need it
In particular, the brain runs on glucose
Too low [glucose] blood means the brain cant metabolize properly and a person passes out
If there is too high blood glucose levels what happens to the brain?
Too high [glucose] blood is also bad, some cells are damaged by high glucose
In particular, the photoreceptors in the eye
Hyperglycemic
High blood sugar
Insulin
Lowers [glucose] blood and [amino acid] (thereby promoting its uptake)
Glucagon
Raises [glucose]blood(thereby promoting glycogen stores to be used)
After eating a meal high in carbohydrates
Increase in [glucose]blood stimulates insulin secretion and inhibits glucagon secretion
Insulin: Glucagon ratio rises and therefore cell uptake of glucose rises and glycogen breakdown falls
What happens to insulin when we fast
Decrease in [glucose]blood during fasting (we use up our glucose) will stimulate glucagon secretion and inhibit insulin secretion
Insulin: Glucagon ratio falls and cell uptake of glucose will fall as glycogen breakdown increases to return [glucose]blood to normal
What happens when we eat a protein rich meal
Rise in [amino acid]blood stimulates both β and α cells therefore both insulin and glucagon are secreted
Diabetes Mellitus
Kidney cant keep up and glucose gets excreted in the urine
“Sweet Urine”
Type 1 Diabetes
Insulin not being secreted enough after a meal
Early onset usually
Type 2 Diabetes
Insulin not acting on target cells
Late onset
Couch potato disease
Can be reversible by changes in lifestyle
Gluconeogensis
The creation of glucose from non-carbohydrate precursors
Liver converts amino acids to keto acids to glucose
Glucose Sparing
Liver converts fatty acids to ketones which goes to all tissue except for nervous tissue
Glycogenolysis
To maintain blood glucose levels the glycogen in the liver is broken up to glucose and given to the blood
breakdown of glycogen into glucose in the liver to maintain [glucose]blood
Epinephrine
From adrenal medulla
Increases circulating substrates during fight or flight response
Causes glycogenolysis and lipolysis
Cortisol
From cortex
Promotes ketogenesis and lipolysis in the adipose tissues
These will stimulate liver to make enzymes needed for gluconeogenesis
Also stimulate muscle cells to release amino acids so they can be used to make glucose by liver (gluconeogenesis)
ACTH
adrenocorticotrophic hormone from anterior pituitary
Acts on the adrenal cortex
Stimulates the secretion of cortisol and other glucocorticoid
Thyroxine
From thyroid gland
Generally increases metabolism
Needed to grow properly in early years of life
Growth Hormone
From anterior pituitary Works with thyroxine Stimulates Anabolism in tissue-growth Secreted after a meal Helps use of amino acids to convert to protein
