Lecture 3 - Digestion, Absorption and Transport Flashcards
What are the 3 processes that food undergo when we eat it?
Digestion
Absorption
Elimination
What is the GI tract?
Series of organs arranged as a long tube
-from the mouth to the anus
What are the 2 components that make up the GI tract?
Organs (stomach, intestines)
Sphincters (muscles that control the passage if material from one organ to the next)
What are challenges of the digestion process?
Multi-taskis of the mouth Diaphragm Steady movement Lubrication of food Digestive Enzyme functions Management of waste
What is digestion?
The process of breaking large food molecules down to smaller molecules
What are the 2 ways in which we can digest food?
Mechanical via chewing and peristalsis
Chemical via enzymes and acids
What re the 3 phases of digestion?
- Cephalic Phase- mouth (the thought of food, smell taste, chewing and swallowing)
- Gastric - Stomach
- Intestinal - Intestines
How does digestion start in the mouth?
Chewing and grinding of food.
Saliva moistens food
Salivary amylase starts comical digestion of carbs
What are the 2 phases of swallowing you do voluntarily?
Oral preparatory phase ( formation of the bolus)
Oral transit phase ( bolus moves from the front to the back of your mouth for passage to the pharynx)
What is the Pharyngeal Phase?
Involuntary process that closes the nasal passage, tongue base to posterior pharyngeal wall contact, contraction of muscles, closure of epiglottis and opening of upper esophageal sphincter
How does the bolus move to the esophagus?
Through the upper esophageal sphincter
How does the bolus move down the esophagus?
Peristalsis moves the bolus down the esophagus to the stomach
-movement is also aided by gravity
What is peristalsis?
Waves of squeezing and pushing contractions by muscles that move food through the GI tract
What separates the stomach from the esophagus?
The lower esophageal sphincter
cardiac sphincter, where people feel heartburn
Why do people get heartburn?
When stomach juices get past the lower esophageal sphincter. The pH is so low i hurts and can cause damage to the tissue
Does chemical or mechanical digestion occur in the stomach?
Both
Chemical digestion of proteins and fats
Mechanical digestion to mix food with gastric juices
Where does gastric juices come from?
Secreted by the gastric glands
What is gastric juice composed of?
HCl- denature proteins and activate pepsin
Pepsin- digest protein
Gastric lipase- digest fat
Mucus-protect stomach lining
What is Chyme?
Semi-solid product of mechanical and chemical digestion in the stomach
How does food from the top of the stomach get to the small intestine?
Peristalsis breaks down the food, mixing it with the gastric juices. When it breaks down it starts to drop to the bottom.
Why doesn’t chyme burn the small intestine?
When chyme enters the small intestines, the pancreas releases bicarbonate to neutralize the acidic chyme
How does food get out of the stomach?
Slowly through the pyloric sphincter
What are the 2 different movements of peristalsis?
P: continuous steady movement 9sneak eating food)
S: starting of the mechanical squeezing of the food products to become available for digestion
-combination of the 2 breaks down the chyme into small pieces
What are the 3 accessory organs to digestion?
Liver - makes bile
Gall bladder - stores bile
Pancreas - makes digestive enzymes and bicarbonate
Why is liver bile important for digestion?
Bile acts as an emulsifier which helps digest fat
What happens when people don’t have a gall bladder?
You are unable to digest higher quantities of fat
What is to note about the enzymes in the pancreas?
Pacrease produces enzymes but in the inactive form, they are only the precursors. When the enzymes hit the right pH in the intestine they are released
What are the 4 sphincters, where are they and what are they meant to do?
Upper esophageal: opens in response to swallowing
Lower esophageal: prevents reflux of stomach contents
Pyloric Sphincter: holds chyme in stomach to be mixed and prevents intestinal contents from coming back up
Ileocecal Sphincter: Allows emptying of small intestine contents into large intestine
What is absorption?
The process of taking molecules across a cell membrane and into cells of the body
Where does most absorption take place in the body?
Small intestines
-a little in the stomach (water, alcohol)
How long does it take the body to absorb nutrients after you have eaten?
3-4 hours
Why does absorption require a constant supply of blood?
To transport all the nutrients out of the small intestine and into the blood for it to be taken to all parts of the body
What are villi?
Folds in the lining that are in close contact with nutrient molecules
What is the brush border?
Composed of microvilli which greatly increase the surface area
Where does the absorption of iron and folate take place?
Duodenum
Where does the absorption of B12 and bile salts tale place?
ileum
Where does the absorption of carbs, fats, proteins, Ca, Mg, Vitamins and trace elements take place?
Small intestine as a whole
Where does the absorption of short chain fatty acids take place?
Large intestines
Where does water and electrolyte absorption take place?
All throughout the small and large intestines
What produces the short chain fatty acids in the large intestines?
Bacteria in the colon
After nutrient absorption into the blood, where does it go?
Liver which detoxifies the blood, then moves through to the heart, blood stream, tissue than organ
What is different about fatty acid absorption?
Large fatty acids bypass the liver via the lymphatic system and first goes to the heart
What is the vascular system?
Closed system of vessels filled with blood
- heart is the pump for continuous flow
- delivers O2 and nutrients
- removes CO2 and waste from tissues
What is the order of blood circulation via the vascular system?
Heart –> Arteries –> Capillaries intestines –> Helatic portal vein –> capillaries in liver –> hepatic vein –> heart
What is the body most metabolically active organ?
Liver
How are nutrients delivered to the liver?
- Water soluble nutrients are absorbed through the vessels
- Vessels merge into the hepatic portal vein. brings all absorbed material to liver
- Hepatic artery bring oxygenated blood for liver cells
- Capillaries within the entire liver brand out to deliver O2 and nutrients to cells
- Hepatic vein gathers blood from liver and returns it to the heart
What is the lymphatic system?
A one way rout that circulates between cells and collects into tiny vessels
Where do lymphs collect?
In the thoracic duct
How do lymph contents enter the bloodstream?
Via the left subclavian vein
In the final stages, what happens to the undigested residues?
Continue through the GI tract, help exercise the GI muscles and are able to retain water
What is normally found within the large intestine?
Bacteria (ferments fibre) Recyclable materials (water, salts)
What is the difference between pre and probiotic
Prebiotic is the bacteria food
Probiotic is the actual strain of the bacteria
How does undigested food move from the SI to the LI?
via the ileocecal valve (another sphincter)
How long it material stored in the large intestine before it is eliminated?
Material is stored 12-24 hours prior to elimination
-water and some nutrients are absorbed (short chain fatty acids, Na, K)
What are the 4 sections of the large intestine?
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
What is the other excretion organ?
Kidney, filters passing blood, waste materials are concentrated and exerted as urine
-Na and K reabsorbed to help control blood pressure
How is the GI tract kept healthy and regulated?
Gastrointestinal bacteria (flora) - # depends on diet, pH, peristalsis and other microorganisms
Probiotics
Ferment fibre and complex proteins
What are the 2 GI hormone pathways?
Endocrine - releases hormones to make you feel satisfied
Nervous - sphincter opening and closing
What is gastrin and how does it work?
Is a GI hormone that is secreted from stomach wall cells which responds to food in the stomach, which stimulates stomach glands to secrete HCl into the stomach
What is secretin and how does it work?
Is a GI hormones that is secreted from the duodenal wall which responds acidic chyme in the SI which stimulates the pancreas to release bicarbonate juices into the SI
What is Cholecystokinin and how does it work?
GI hormone that is secreted from the intestinal wall which responds to fat or protein in the SI, which stimulates the gall bladder to release bile into the duodenum and the pancreas to release bicarbonate and enzyme rich juices into the SI
What does CCK do on the length of absorption?
Slows down the transit time int eh SI so we have more time to absorb nutrients and allow for the reactions to be completed
At its best, what can the digestive system do?
Sensitive and responsive to environmental conditions
- provides immunity
- protection against invaders
in order for the digestive system to be at its best, what does this depend on?
Healthy Blood supply
Lifestyle factors
Diet
How does choking occur?
Food is stuck in the trachea and is blocking air.
-Epiglottis is open allowing the larynx to be open
What is vomiting
Mechanism to get rid of unwanted things/ make you feel better
What is diarrhea
Mechanism to rid the body of something that is upsetting it
-Frequent loose and watery stools
What do vomiting and diarrhea have in common?
Both result in dehydration and elimination of foreign substance
What is constipation?
Hard infrequent bowl movements
Which foods produce gas?
Most common are foods rich in carbs (sugar, starches and fibre)
-foods must be determined individually to see if they actually cause gas
Partially digested carbs reach the LI then bacteria ferment them, producing gas as a byproduct
What is heartburn?
Gastroesophageal refulx
-stomach acid into the esophagus
What are ulcers?
Lesions or sores that lead to compromised cells
What are the causes of ulcers?
Bacterial infections
NSAIDs: Non Steroidal Anti-Inflammatory Drugs
Excess acid production
How to prevent choking?
Small bites
Chew thoroughly
How to prevent belching?
Eat slowly
Relax
Chew thoroughly
How to prevent intestinal gas?
Eat bothersome foods in moderation
How to prevent Heartburn?
Eat small meals Drink liquids between meals Sit up while eating Wait 3 hours before lying down Don't wear tight clothes Lose weight
How to prevent ulcers?
Medicine
Avoid coffee and alcohol containing beverages
Minimize aspirin, ibuprofen and naproxen intake
How to prevent diarrhea?
Rest
replace lost fluids
How to prevent constipation
Fibre
Hydration
Exercise
Poop regularly
