2.Digestion and Absorption Flashcards
If a persons estimated energy requirement is 8000kJ per day, how many grames of fat would you recommend they consume to be within the AMDR?
43-76g
What is the difference between digestion and absorption?
Digestion is the process by which food is broken down into absorbable units, absorption is the uptake of nutrients by the walls of the small intestine for transport into either the blood or the lymph.
What are the 2 main functions of the GI tract?
- To convert food into nutrients that the body needs 2. to rid the body of waste
What is the GI tract?
A flexible muscular tube that runs from the mouth to the anus.
What are the roles of the mouth in digestion?
Digestion begins in the mouth, with mastication, stimulation of taste buds and swallowing.
What is food called after is is swallowed?
A bolus
What does the epiglottis do?
Protects the airway during swallowing
What is the role of the oesophagus in digestion?
It transfers the bolus from the mouth to the stomach.
Which enzymes are present in the mouth?
Primary: salivary amylase, which starts the digestion of carbohydrate. Secondary: salivary lipase, initiates minimal digestion of fats.
How is a bolus formed?
Through mastication, addition of saliva and action of the tongue, which transforms food into a coarse mash.
How much saliva do you make per day?
~1L
Can you swallow if you are upside down?
Yes
How is a sphincter muscle formed?
Tube form with circular muscles around the hollow inside, and longitudunal muscles around the outside.
What condition can result from weakened lower esophogeal sphincter?
Reflux
Why is reflux potentially harmful?
Acid from the stomach can damage tissue of the oesophagus.
What are 4 symptoms of reflux?
heartburn, chest pain, nausea and regurgitation
What are the main functions of the stomach?
Collecting and churning, and some digestion. Adds juices and converts bolus to chyme.
What determines the activation of the pyloric sphicter, and how ofter does it occur?
The pyloric sphincter stays closed until chyme is completely liquified, ~3 times per minute.
What happens with respect to digestion of each of the macronutrients in the stomach?
Carbohydrate - digestion by salivary amylase continues until the enzyme is deactivated by HCl in the stomach, Protein- proteins are denatured by stomach acid and pepsin is activated by the acid. Lipids- triacylglycerols start to break down (~20% of lipid digestion).
What main processes occur in the small intestine?
Digestion and absorption
Which organ(s) provide digestive juices to the small intestine?
The gallbladder and the pancreas.
What are the 3 segments of the small intestine called?
- duodenum, 2. jejunum, 3. ileum
What is the approximate length of the duodenum?
30cm
What is the approximate length of the jejunum?
2.5m
What is the approximate length of the ileum?
4m
What is the structure of the epithelial lining designed to do?
Maximize suface area of the small intestine, increasing the ability to absorb nutrients.
What compounds are broken down by enzymes from the small intestine and pancreas?
proteins (peptides) triglyceride, starch, oligossacharides and disaccarides
With all of the folds in the lining, the surface area of the small intestine is comparable to a) a parking spot, b) a tennis court, c) a football field.
b.
What structures carpet the wall of the small intestine?
villi
What structures cover the surface of the vili in the small intestine?
microvilli
What do microvilli do?
Provide the absorptive surfaces that allow nutrients to pass through to the body.
What is the name of the process that moves food through the small intestine?
peristalsis
How does peristalsis work?
The inner circular muscles contract, tightening the tube and pushing food forward. When the circular muscles relax, the outer longitudinal muscles contract and the intestinal tube is loose. As the circular and longitudinal muscles tighten and relax, the chyme moves ahead of the constriction.
How does segmentation occur?
Circular muscles contract, creating segments in the small intestine. As each set of circular muscles expand and contract, the chyme is broken up and mixes with digestive juices.
What is the purpose of segmentation in the small intestine?
to mix chyme, increase surface area to enzyme action and bring nutrients in contact with the intestinal lining for absorption.
How often do the muscle contractions that control segmentation in the small intestine occur?
12-16 times per minute
What main processes occur in the large intestine?
Reabsorbing and eliminating - absorbs, water, vitamins and any remaining absorbable nutrients (not much) and collects waste material for storage in the rectum.
What is the name of the valve at the beginning of the large intestine?
ileocaecal valve
What happens to fibre in the large intestine?
fermentation
What happens to energy yielding nutrients during digestion?
They are disassembled for absorption
What happens to vitamins and minerals during digestion?
They are absorbed but do not require disassembling.
What happens to undigestable material, including some fibres, during digestion?
They continue through the digestive tract and form the stool.
What substance is secreted by the salivary glands, and what does it do?
saliva - eases swallowing and contains amylase to begin the break down of carbohydrate
What substances are secreted by the gastric glands in the stomach, and what do they do?
gastric juice - contains HCL to denature proteins, and peptides break down proteins. Mucus protects the lining of the stomach.
What organ receives secretion from the pancreas?
The stomach
What is secreted by the pancreas and what does it do?
They are absorbed but do not require disassembling.
What happens to undigestable material, including some fibres, during digestion?
They continue through the digestive tract and form the stool.
What substance is secreted by the salivary glands, and what does it do?
saliva - eases swallowing and contains amylase to begin the break down of carbohydrate
What substances are secreted by the gastric glands in the stomach, and what do they do?
gastric juice - contains HCL to denature proteins, and peptides break down proteins. Mucus protects the lining of the stomach.
What organ receives secretion from the pancreas?
The stomach
What is secreted by the pancreas and what does it do?
pancreatic juice - includes pancreatic enzymes for the breakdown of carbohydrates, fats and proteins, and bicarbonate to neutralize acidic gastric juices.
What substance does the liver produce?
bile
What does the gallbladder do?
stores bile from the liver
What does bile do?
emulsifies fat so it can be broked down by enzymes
Which organs contribute secretions to the small intestine?
Liver and gallbladder, as well as intestinal glands in the small intestine
Where does digestion of fat take place in the body?
Saliva and gastric uices contain lipases, but most of the breakdown of fats occurs in the small intestine.
Arrange in order of increasing pH: Bile, pancreatic juice, saliva, gastric juice
Gastric juice ~2, saliva ~7, Pancreatic juice ~8, bile ~9.
Which macronutrients are not digested?
minerals, vitamins and water
Why are minerals, vitamins and water not digested?
they are small enough to be absorbed by the body without being broken down.
Is fibre digested?
No.
By which 3 processes are nutrients absorbed into the body?
- simple diffusion, 2. facilitated diffusion, 3. active transport
Do all cells in the lining of the small intestine absorb the same nutrients?
No, cells are specialized to absorb different nutrients.
What substances are released to the bloodstream during absorption?
water soluble nutrients and small products of fat digestion.
What substances are released to the lymphaic system during absorption?
Fat soluble vitamins and larger fats form chlyomicrons and are released intot the lymphatic system.
How does simple diffusion occur in the small intestine?
Nutrient cross intestinal walls freely. Incl water and small lipids.
Which nutrients are absorbed in the small intestine by simple diffusion?
water and small lipids
How does facilitated diffusion occur in the small intestine?
requires a carrier protein to transport nutrient across membrane or to form a channel. Incl. water soluble vitamins and fructose
Which nutrients are absorbed in the small intestine by facilitated diffusion?
water soluble vitamins and fructose
How does active transport work to absorb nutrients in the small intestine?
requires a carrier protein and energy to move the nutrient across the concentration gradient. Incl glucose and amino acids.
Which nutrients are absorbed in the small intestine via active transport?
glucose, amino acids
Where does blood leaving the digestive system go, and via which route?
goes to the liver via the hepatic portal vein
Which nutrients go to the liver via the bloodstream after absorption?
water soluble nutrients and small products of fat digestion.
Where does blood go after it leaves the liver?
To the heart
What is the role of the vascular circulatory system in digestion?
To transport blood containing nutrients to the liver.
What is the role of the liver after absorption?
It prepares nutrients that have been absorbed for use in the body.
What is the role of the lymphatic circulartory system in digestion?
provides a one-way route for fluid from the tissue spaces to enter the blood.
What drives circulation within the lymphatic system?
It has no pump: lymph circulates between cells and collects into tiny vessels.
Where does lymph collect before it enters the blood stream?
in the thoracic duct behind the heart.
Do large fats and fat soluble vitamins go via the liver into thte bloodstream?
No, they go tot the heart and are pumped into al the body’s cells from there, bypassing the liver.
What is the role of the hepatic vein?
gathers blood from the liver and takes it to the heart.
How do the cells of the liver access the nutrients and oxygen in the blood?
From capillaries, which branch all over the surface of the liver
What is the role of the hepatic artery?
brings a supply of freshly oxygenated blood from the lungs (not loaded with nutrients) to supply oxygen to the liver.
How do nutrients from the digestive system get to the liver via the vascular circulatory system?
Blood vessels within the villi gather up the nutrients, these vessels merge into the hepatic vein, which take all nutrients to the liver.
What factors can influence the health and regulation of the GI tract?
diet and good absorption of nutrients, sleep patterns, physical activity, relaxed mealtimes
Where do the bacteria of the GI tract reside?
Primarily in the small and large intestines.
What do gut macrobiota do?
digest fibres and some complex proteins. When thriving, prevent infectious bacteria from establishing themselves.
What is the pH of the large and small intestines?
neutral.