W3 - Digestive System Flashcards
What are the processes involved in the human digestive system?
Ingestion
Initial processing
Storage
Digestion
Absorption
Elimination
What happens at the mouth, pharynx, larynx + salivary glands?
Ingestion + chewing of food
Initiation of swallowing reflex
Moistens food
Partial digestion of food by amylase enzyme
What happens at the oesophagus?
Peristalsis
Lubrication
What happens at the liver
Secretes bile for the small intestine.
Describe the pancreas
Elongated gland behind stomach
What does the pancreas do?
Secreted digestive enzymes into small intestine
Where is the stomach located?
Between oesophagus + small intestine.
What does the stomach do?
Stores, dissolves + mixes food.
Partial digestion
Regulates emptying of dissolved food into small intestine.
What does the large intestine do?
Temporary storage of undigested material
Absorbs some salt + H20
Defecation
Describe the small intestine
Long tube leading from stomach to large intestine.
What do the tongue + cheeks do?
Keep food particles between surfaces of grinding teeth as lower jaw moves up + down.
Where are buccal glands situated?
Inner surfaces of cheeks as serous + mucous glands.
What do the salivary + buccal glands do?
Secrete fluids into oral cavity
Where are the taste buds found?
On tongue + back of oral cavity
What holds food particles together as bolus?
Mucus in saliva
Define mastication
Food particles broken down into smaller pieces to ⬆️ SA.
Define satiation
Feeling of being well fed
What controls the degree of hunger or satiation?
Hypothalamus
Process of swallowing
Bolus is moved posteriorly OUT of oral cavity –> pharynx.
Down oesophagus –> stomach
Adaptations of the stomach for the storage function
Stretchable wall
Mucosal linings of stomach are longitudinal folds called rugae which flatten as stomach capacity ⬆️
Valves
What are the valves in the stomach
Gastroesophageal valve
Pylorus or pyloric valve
Where can the Gastroesophageal valve be found?
Where oesophagus enters stomach
Where can the Pylorus or pyloric valve be found?
Between stomach + small intestine.
Adaptations of the stomach for additional food processing
Mucosal lining contains gastric glands producing gastric digestive juices.
Some prod HCL, making chyme more acidic.
What are the accessory organs of the digestive system?
Salivary glands
Pancreas
Gall bladder
Liver
Why are the accessory organs of the digestive system called that?
Not directly involved in food passing through them but are still involved in digestion.
What muscle is involved in mastication + is the strongest muscle in your body?
Masseter
What does the epiglottis do when chewing?
Close pathway to trachea.
What % of saliva comes from the 3 pairs of salivary glands?
95%
What % of saliva comes from the buccal glands?
5%
List the 3 pairs of salivary glands
Parotid
Submandibular / submaxillary
Sublingual
Which of the 3 pairs of salivary glands does most the saliva come from?
Parotid gland in the cheek
60% of the total 95% coming from the salivary glands.
Where can the submandibular gland be found?
Under chin
Where can the sublingual gland be found?
Under tongue
What in the saliva protects you from the acid you may have consumed?
Potassium + bicarbonate
What in the salivary gland has the ability to make saliva?
Acinar units (mucous cells)
What type of solution do we want saliva to be when it enters the mouth?
Hypotonic
What type of solution is saliva when in the salivary gland?
Isotonic
How is the saliva converted from an isotonic solution to a hypotonic one upon entering the mouth from the salivary gland?
Cells lining the ducts of the salivary glands actively reabsorbs sodium + some chloride.
Then secrete bit of potassium + bicarbonate.
Actively transporting the sodium + some chloride makes solution more hypotonic.
Are the cell walls of the ducts of the salivary glands permeable to water?
NO
Means the H20 can’t follow sodium when its being actively pumped out.
What are the 3 stages of deglutition (swallowing)
Buccal / voluntary / oral phase
Pharyngeal phase
Oesophageal phase
What happens in the buccal / voluntary / oral phase
Bolus is forces to back of throat voluntarily
What happens in the pharyngeal phase
Respiratory passageway has been closed off.
Bolus enters oesophagus
What happens in the oesophageal phase?
Bolus moves down oesophagus by peristalsis.
What are the layers of the oesophagus?
OUTER –> INNER
Adventitia
Muscularis (Longitudinal then circular)
Submucosa
Mucosa
How long roughly does it take to get food from the mouth down to the stomach?
4-8 sec
What are the 2 ways to get food down the oesophagus?
Pressure of swallowing
Peristalsis
How does peristalsis occur?
When circular muscle constricts + longitudinal muscle relaxes.
– Behind the bolus
Whats found at the end of the oesophagus?
Oesophageal sphincter
– Regulates food entering stomach
How many parts are there to the stomach?
4
What are the parts of the stomach?
Cardia
Fundus
Body
Pylorus
Where is the cardia part of the stomach?
Top
Where is the fundus part of the stomach?
Above + left to cardia
Where in the stomach is your food storage?
Fundus
What are the 3 functions of the stomach?
Storage
Chyme prod
Regulation of emptying chyme to duodenum
What is chyme
Semifluid mass of partially digested food + digestive secretions.
Passage of chyme when being secreted
Pyloric antrum
Pyloric canal
Pyloric sphincter
Duodenum
How much chyme can the stomach usually hold?
About 1.5L
But after a big meal about 6L
Where is HCL acid released from in the stomach?
Parietal cells
Where are lipases released from in the stomach?
Chief cells
Where are ions + mucus released from in the stomach?
Mucous cells
Where is pepsinogen released from in the stomach?
Chief cells
How many layers of tissues does the gut wall have?
Name them.
4
INNER
- Mucosa
- Sub-mucosa
- Circular then longitudinal muscle
- Serosa
OUTER
Describe the serosa + relate to function
Tough connective tissue = protection
⬇️ friction w/ other abdominal organs esp. during movement of gut
Covered in squamous epithelium tissue
What’s the difference between the longitudinal and circular muscles?
Circular - Thins the gut lumen when contracts
Longitudinal - Shortens gut wall when contracts
Describe the sub-mucosa + its function
Connective tissue containing:
- Blood + lymph vessels that remove absorbed products of digestion
- Nerves that co-ordinate peristalsis
Describe the mucosa + its function
Single layer of epithelial cells
Goblet cells to secrete mucus.
Secretes digestive juices + absorbs digested food
What is the function of the muscularis mucosa
Smooth muscle that moves villi to contact the digested food
What are the 3 phases for gastric secretion
Cephalic phase
Gastric phase
Intestinal phase
What % of the response to a meal for gastric secretion does the cephalic phase account for?
30%
When does the cephalic phase of gastric secretion happen?
Prior to food arrival
What happens in the cephalic phase of gastric secretion?
Gastrin is released
hormone that ⬆️ gastric juice secretion
What % of the response to a meal for gastric secretion does the gastric phase account for?
60%
When does the gastric phase of gastric secretion happen?
When food enters stomach.
What happens in the gastric phase of the gastric secretion?
Fundus of stomach stretch = stimulating gastric juice + gastrin release.
Intestinal phase of gastric secretion
Chyme entering duodenum ⬇️ gastric secretion + motility
Stomach vol. ⬇️ = cessation of stretch mechanism
Removal of peptide fragments = no gastrin released
What pH inhibits gastrin release?
Very low pH - around 2.
– Happens when all food has been removed from stomach
A pH less than 2 inhibits gastrin release.
What happens to the duodenum + what’s a consequence of this?
Stretches
CCK released
What does CCK do?
Further inhibits gastrin release
What is used to neutralise the acidic chyme?
Bicarbonate secretions
Where are all secretions released from from the gall bladder + pancreas?
Sphincter of oddi
What are the 2 types of cells in the pancreas?
Exocrine
Endocrine
Which of the 2 cells of the pancreas does hormone secretion happen from?
Endocrine
What do exocrine cells have?
Acinar + duct cells
What do the acinar cells of the pancreas do?
Release digestive juice + enzymes
Rich chlorine solution to help take H20 with it.
Why is secretin released?
Due to acidic env.
To what pH does the bicarbonate increase the pH to?
about 7
What does the portal vein / hepatic portal vein do?
Carries blood from GI tract, gall bladder, pancreas + spleen TO the liver.
What is the only form in which you can absorb CHO?
In monosaccharide form
What does salivary a-amylase break down and at which point?
1-4 glycosidic bonds in amylose + amylose pectin.
In mouth + oesophagus
What enzymes are there in the duodenum for CHO digestion?
Pancreatic a-amylase
Breaks 1-4 glycosidic bonds
Then need the de-branching enzyme to break the 1-6 glycosidic bonds.
Give an example of a de-branching enzyme
a-dextrinase (found on microvilli)
What other enzymes besides a-dextrinase can be found on the microvilli of the duodenum?
Disaccharidases (i.e lactase, sucrase, maltase…)
What is glucose + galactose transported with when being absorbed across the interstitial wall from the interstitial lumen into the blood?
Sodium (going ⬇️ its conc. gradient)
How is glucose + galactose absorbed in the epithelial cells of the ileum?
Na+ are AT OUT of epithelial cells == ⬇️ NA+ conc in cell.
Na+ from lumen of ileum moves into epithelial cells down con grad by co-transport w/ glucose.
Glucose + galactose moves by FD from high con inside epithelial cell through Na+ glucose transporter.
What transporter does the glucose + galactose go through after the Na+ glucose transporter?
GLUT-2 to get into blood
Through what transporter can fructose enter the intestinal wall and then get into the blood?
GLUT-5 to get into intestinal wall.
GLUT-2 to get into blood.
What happens to the fructose + galactose once in blood?
Taken to liver + converted to:
- Glucose
- Derivatives of glucose
- Glucose metabolites
What helps the break down of proteins in the stomach?
Acidity from gastrin
What happens to pepsinogen once it reaches the stomach?
Activated into pepsin to hydrolyse peptide bonds.
Why is the action of the pepsin stopped in the duodenum?
Because it only works in an acidic env.
What are the 2 forms of proteases?
Endopeptidases
Exopeptidases
Endopeptidases
Cleave the interior bonds of the pop
Exopeptidases
Cleave the external peptide bonds
What 2 hormones help with protein digestion in the small intestine?
How?
CCK
Secretin
They ⬆️ release of proteases.
How are amino acids absorbed in the epithelial cells of the ileum?
Na+ are AT OUT of epithelial cells == ⬇️ NA+ conc in cell.
Na+ from lumen of ileum moves into epithelial cells down con grad by co-transport w/ aa.
aa move by FD from high con inside epithelial cell to a low con in the capillaries (blood)
Where does most fat digestion occur?
Small intestine
Some fat digestion happens in the mouth, by what?
Lingual lipase
Where is lingual lipase released from?
Serous gland
What enzyme digests fat in the stomach?
Gastric lipase
Where is gastric lipase produced?
Chief cells
What emulsifies fats?
Bile
How many L of water are absorbed each day?
8
How many L of water are secreted into the GI tract?
6
What % of water is absorbed in the small intestine?
90%
What % of water is absorbed in the large intestine?
10%
Where is the ileocecal valve located?
Sphincter muscle
Between ileum + colon
Functions of the gall bladder
Stores + concentrates bile made by the liver
What enzyme breaks down alcohol to acetaldehyde?
alcohol dehydrogenase (ADH)
What are the major hormones involved in digestion?
Gastrin ( stomach )
Secretin ( small intestine )
Cholecytokinin (small intestine)
Gastric inhibitory peptide (small intestine)
Motilin (small intestine).
Briefly describe fat absorption
Bile salts emulsify FAs + monoglycerides to form micelles
FAs enter epithelial cells + link to form TG
TG combine w. proteins in Golgi body to form chylomicrons.
Chylomicrons enter lacteal + transported away from intestine.
When will less alcohol be absorbed?
The longer its in the stomach
Acetaldehyde vs alcohol
Acetaldehyde = less intoxicating
What % less of alcohol dehydrogenase do females activate than men?
60%
Fat soluble vitamins
A
D
E
K
How are fat soluble vitamins absorbed?
Emulsified + incorporporated into mixed micelles containing cholesterol, PL + FAs.
Enter chylomicrons + lymph system.
What does the absorption of fat soluble vitamins require?
Bile + pancreatic enzymes
How are water soluble vitamins absorbed?
Diffusion or AT
Can water soluble vitamins be stored in the body?
NO
