Module 3 - Digestion and Absorption Flashcards
Digestive system supplies fuel and building blocks by…
- taking in food
- breaking it down into nutrient molecules
- absorbing nutrient molecules into the bloodstream
- ridding the body of indigestible remains
What is anabolism?
process of building up complex macromolecules (nucleic acids, proteins, lipids)
What is catabolism?
process of breaking down complex macromolecules into simple molecules
What subdivisions is the GI tract made up of? (OPESSL)
Oral cavity, pharynx, esophagus, stomach, small intestine, large intestine
Old pirates eagerly search sandy lands
What are the general functions of accessory organs?
produce saliva, bile, digestive enzymes to breakdown food
What are the 6 accessory organs?
- teeth
- tongue
- salivary glands
- liver
- gallbladder
- pancreas
The oral cavity works with what accessory organs?
teeth, tongue, salivary glands
The small intestine works with what accessory glands?
gallbladder, liver, pancreas
In the case of the digestive system, what is “transit time”?
amount of time it takes food to pass the length of GI tract
Digestive activity provoked by a range of ___ and ___ stimuli
chemical and mechanical
What is the function of chemical stimuli in digestive system?
activates glands that secret digestive juices into tract or hormones into blood
How are mechanical stimuli present in digestive system?
smooth muscles of GI tract walls are stimulated and mixes food
What is the purpose of food disassembly?
use food for energy and to build/repair/maintain new cells
Food is broken down by mechanical and chemical processes into ___ and then ___
polymers (Carbs, lipids, protein, nucleic acids) and then monomers (sugars, fatty acids, amino acids, nucleotides)
What are the 6 steps in which the GI tract and accessory organs work together to disassemble food and use it? (IPMCAE)
- ingestion
- propulsion
- mechanical breakdown
- chemical digestion
- absorption
- elimination
incredible processes make chewing anyhting enjoyable
What is the function of the Plica circulares layer of the GI tract?
folds increase SA for absorption
Where does mechanical breakdown of food happen?
stomach and oral cavity
Where does most of nutrient absorption happen?
small intestine
where does elimination of food occur?
large intestine
What are the 5 main layers of GI tract? (PMSMS)
- Plica circulares
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
What is the function of Plica circulares layer in absorption in the GI tract?
it’s folds increase surface area for absorption
What is the function of Mucosa layer in absorption in the GI tract?
secretion of mucus, enzymes, hormones and it also absorbs nutrients
What type of epithelial tissue lines GI tract in Oral Cavity, Pharynx, Esophagus and Anus?
Stratified squamous (because of mechanical stresses)
What type of epithelial tissue lines GI tract in stomach, small and large intestine?
Simple columnar epithelium (rich in mucus secreting cells, lots of absorption)
What does the Submucosa layer contain?
large blood vessels, lymphatic vessels, and elastic fibers
What is the use of the elastic fibers in the Submucosa layer of GI tract, specifically stomach ?
enable stomach to regain normal shape after storing large meal
Submucosa binds ___ to ___
Mucosa to Muscularis Externa
What type of cell is Muscularis externa?
smooth muscle cell
What is function of Serosa layer of GI tract?
protective covering of muscularis externa
Where is the Serosa (visceral peritoneum) not present?
oral cavity, pharynx, esophagus, rectum
What accessory organs does the oral cavity include?
tongue, teeth, salivary glands
4 Functions of oral cavity?
- sensory analysis of food before swallowing
- mechanical processing
- lubrication
- some digestion of carbs and lipids
What is Mastication?
process of breaking down food in oral cavity and covering it with enzymes (salivary excretions)
What is saliva composed of?
99.4% water and 0.6% electrolytes, enzymes, antibodies
What is role of buffers in saliva?
keep it at around PH of 7 and prevent acid build up
What is role of Mucins in saliva?
give saliva it’s lubricating effect
What is the role of Antibodies in saliva?
control oral bacteria
What is role of enzymes (like salivary amylase) in Saliva?
initiate breakdown of carbohydrates
What is the functions of saliva?
it moistens and lubricates food in mouth before swallowing and initiates digestion of carbohydrates (via salivary amylase) and initiates breakdown of lipids (via lingual lipase)
What is the role of Lingual Lipase in oral cavity?
breakdown of lipids
Does absorption occur in oral cavity?
NO
What is the pharynx?
passage way for food, liquid, air from oral cavity into esophagus
What does the pharynx do?
muscular propulsion of materials into esophagus
What is the function of Esophageal sphincter (end of esophagus)?
prevents heart burn
What is the role of Esophagus in digestion?
transports solid food and liquid to stomach
What is ingestion?
taking food into digestive tract via mouth
What is propulsion?
moving food through GI tract
Name and describe two forms of propulsion in digestion
- Swallowing - voluntary
- Peristalsis - involuntary waves of contraction/relaxation to squeeze food from one organ to another
What is the role of the Stomach in digestion?
chemical breakdown of materials by acid and enzymes and mechanical processing through contractions
What is the empty volume of stomach?
50ml
What is the capacity of stomach?
2-4L of food storage
What is the name for ingested substances mixed with secretions of glands of stomach?
Chyme
What is the role of Intrinsic Factor that is made in stomach?
required for small intestine to absorb vitamin B12
Without B12, what illness will develop?
anemia
How long does it take food to go through stomach?
about 4 hours
Does the stomach have an extra layer in the GI tract? and if so, where?
Yes, in the muscularis externa
Does the stomach store ingested foods?
YEA
What are the 4 regions of the stomach?
Fundus, Body, Pylorus, Cardia
Fundus and Body secrete what cells?
mucus, parietal cells (secrete intrinsic factor and HCl), chief cells (secrete pepsin which digests proteins when combined with HCl)
What is the function of HCL in stomach? Also what cells is it secreted from?
Breaks down food and allows pepsinogen to become active form of pepsin to break down proteins. Is secreted from parietal cells.
What cells does the Pylorus secrete?
Mucus, G-cells (secretes gastrin), D-cells (secretes somatostatin)
What cell secretes gastrin? What is the role of gastrin?
Secreted by G-cells - Gastrin stimulates secretion of HCL
What cell secretes somatostatin? What is the role of somatostatin?
Secreted by D-cells - Somatostatin stops release of gastrin
HCl secretions done by parietal cells keep stomach PH at…
1.5-2.0
What is the purpose of the acidic environment of the stomach?
- kill many microorganisms
- denatures proteins
- breaks down plant cell walls and connective tissue in meat
- activates pepsin (protein digesting enzyme secreted by chief cells)
pH 7 is __
pH less than 7 is __
pH more than 7 is __
neutral
acidic
basic
What is the function of Parietal Cells?
secrete intrinsic factor and HCl
What is the function of Chief Cells?
secretion of pepsinogen (digestive enzyme) which combines with HCl and turns into pepsin which breaks down proteins
Stomach protects itself from self digestion with a ___
mucosal barrier
A stomach ulcer is…
an injured area of the mucosa caused by gastric juice
What is Heart Burn?
Acid reflux from stomach backs up into esophagus
What part of esophagus usually prevents acid reflux?
esophageal sphincter
What is Receptive Relaxation done by Fundus and Body (parts of stomach)?
stomach muscles relax in anticipation of and to response to food entry
What is Adaptive Relaxation?
stomach relaxes in response to gastric filling; stretch receptors activated
What passes through the stomach quicker, solids or liquids?
liquids, solids linger until they are mixed with gastric juice and converted to liquid state
What takes longer to pass through duodenum, fats or carbs? and why?
fats, they form an oily layer on the top of chyme which is digested more slowly by intestinal enzymes
What are the 3 regions of the small intestine?
Duodenum, Jejunum and Ileum
What accessory organs help the small intestine in breaking down food?
Liver and Gallbladder (production and storage of bile), Pancreas (digestive enzymes)
Chemical digestion happens in what part of the small intestine?
Duodenum
Nutrient absorption happens in what part of the small intestine?
Jejunum
Viatmin absoprtion happens in what part of the small intestine?
Ileum
Duodenum is the shortest subdivision of the small intestine and often referred to as a “Mixing Bowl”, what is “mixed” in the Duodenum?
Chyme from the stomach, digestive enzymes and buffers from the pancreas, Bile from liver and gallbladder
What is the function of bile?
digests fats into fatty acids
What is the major stimulus for intestinal juice production by glands?
arrival of chyme
What is the purpose of intestinal juice (secretions from glands on walls of small intestine)?
moisten chyme, buffer acids, keep digestive enzymes and products of digestion together
The liver produces…
bile
The gallbladder stores…
bile
The pancreas produces…
digestive enzymes and buffers
What is the process of emulsification done by bile?
breaking down of large fat globules into millions of small fatty droplets
Bile release is increased when GI tract contains ____
fatty chyme
If Bile becomes too concentrated in the gallbladder it can lead to ___
gallstones (made up of mostly cholesterol)
Endocrine cells secrete __ and __ to control blood sugar
insulin and glucagon
Exocrine cells secrete ___
pancreatic juice
In the small intestine, there are two forms of movement for chyme?
Peristalsis: alternate waves of contraction/relaxation
Segmentation: division and mixing of chyme by smooth muscles, moving bile back and forth
What percent of nutrient absorption happens in small intestine?
90%
What structural modifications of small intestine increase SA of absorption?
Plicae circulares: deep circular folds that remain even when food is present (unlike stomach)
Villi: fingerlike extensions of mucosa on plicae circulares
Microvilli: tiny projections of plasma membrane of absorptive mucosal cells on the villi
What is the function of brush border enzymes in microvilli?
complete final stages of digestion of carbs and proteins in small intestine
Specially what part of the small intestine aids in most of nutrient absorption?
Jejunum
What does the Jejunum look like?
2.5 M long circular folds which twists back and forth within abdominal cavity
What is the longest section of small intestine?
Ileum (3.5M long)
What are the major roles of Ileum?
vitamin absorption and it controls flow of material from ileum into cecum of large intestine through the ileocecal valve
What is the role of large intestine?
enzymatic digestion and reabsorption of water, also absorbs vitamins, ions
What are the dimensions (length and width) of the large intestine?
1.5 m long and 1.7 cm wide
What does large intestine do with fecal matter?
reabsorbs water from matter and turns liquid into stool and moves towards anus for elimination
What are the sections of large intestine?
Cecum
Colon
Rectum
The majority of the large intestine is the colon, what are the 4 parts of the colon?
ascending
transverse
descending
sigmoid
What is the role of the rectum (last 15cm) of the large intestine?
temporarily stores feces
As most bacteria entering cecum (first part of large intestine) from small intestine is dead (killed by enzymes, HCl), the surviving bacteria make up…
the bacterial flora of large intestine
intestinal bacterial flora is capable of…
fermenting indigestible carbohydrates (like cellulose) which releases mixture of gases and also synthesizes B complex vitamins and Vitamin K
In a healthy gut microbiota, how many bacterial species would you want?
> 1000 bacterial species, high abundance of “good” bacteria and low amount of “bad bacteria”
Probiotics are…
alive and aid in digestion (usually are in the form of yeast and bacteria)
Prebiotics are …
a form of fiber and serve as food for probiotics
When is Cholecystokinin (CCK) released?
in response to chyme arrival, especially when high in lipid
What is the function of Cholecystokinin (CCK)?
causes secretion of bile by gall bladder and pancreatic juice by pancreas
What is the role of Secretin hormone?
increases secretion of bile by the liver and buffers by the pancreas
When is Secretin released in small intestine?
upon arrival of chyme
What is the role of Gastrin hormone (produced in stomach as well as small intestine)?
stimulates production of gastric acid/enzymes when proteins are not fully digested
What happens to amino acids after they are absorbed?
transported to the liver
What happens to triglycerides after they are absorbed?
they are taken into lacteals of the lymphatic system
