Chapter 24: The Digestive System Flashcards
What are the 6 essential functions of the digestive system?
- Ingestion
- Secretion
- Mixing and propulsion
- Digestion (mechanical & chemical)
- Absorption
- Defecation
What are the 4 layers throughout the digestive tract walls?
- Mucosa (innermost; lining lumen)
- Submucosa
- Muscularis
- Serosa (outermost)
Mesentery
Connects the small intestine to the posterior body wall
Falciform ligament
Attaches the liver to the anterior body wall and diaphragm
Mesocolon
Connects the large intestine to the posterior body wall
Which organ lacks a serosa layer? What is the layer called instead?
The esophagus
The layer is called adventitia
(i.e. mucosa, submucosa, muscularis, adventitia)
What are the 2 layers of the muscular portion of the digestive tract calls? What organ has a 3rd layer and what is it called?
- Inner circular muscle
- Outer longitudinal muscle
The stomach has a 3rd layer called the oblique smooth muscle layer which comes before the other 2.
What is the difference between an omentums and mesenteries?
Omentums bind organs to eachother.
Mesenteries bind organs to the abdominal wall.
What are the 2 control mechanisms involved in regulating the digestive functions of muscle motility and secretions ?
- Endocrine control - involves various hormones (gastrin, secretin, CCK)
- Neural control - uses chemoreceptors and stretch receptors to send sensory input to the enteric NS and autonomic NS (both systems will control gut motility and GIT secretions)
What is the myenteric plexus?
Part of the enteric NS located in the gut wall between the circular and longitudinal muscle layers.
It controls gut motility
What is the submucosal plexus?
Part of the enteric NS located within the submucosa layer.
Controls GIT secretions
Which nervous system increases GIT activity and which one decreases it?
Parasympathetic - increases GIT activity
Sympathetic - decreases GIT activity
What secretion is made in the mouth and what does it do?
Salivary glands near the mouth will secrete salivary amylase into the mouth to begin carbohydrate digestion to turn starch into sugar.
What are the steps of swallowing?
- Tongue pushed food against hard palate and stimulates receptors for swallow initiation in pons/medulla
- The soft palate and uvula rise to close nasopharynx and allow food to pass through
- Epiglottis covers glottis and food passes through upper esophagus
- Peristalsis propels food (bolus) down
What is the main action of the esophagus?
Peristalsis
Occurs by circular muscle layer contracting to squeeze bolus downwards, and longitudinal muscle layer contracting to expand and receive the bolus.
What are the 4 regions of the stomach?
- Cardiac
- Fundic
- Body
- Pyloric
Parietal cells of the stomach
Produce HCL to maintain an acidic pH environment within the stomach.
Chief cells of the stomach
Make pepsinogen that will be activated into pepsin by HCL, and then will be able to digest proteins
Enteroendocrine cells of the stomach
Produce G cells that will secrete gastrin
Mucus neck cells of stomach
Produce mucus to protect the lining of the lumen from the acidic HCL and pepsin
How much gastric juice is secreted per day?
About 2-3 litres
Absorptive cells of small intestine
Absorb and digest nutrients, and produce brush border enzymes (ex. Sucrose, Maltase)
Goblet cells of small intestine
Make mucus to protect from HCL that traveled down from stomach
Secretory cells of small intestine
Secret alkaline (basic pH) intestinal juice
This is water + mucus (includes NO enzymes)
Paneth cells of small intestine
Secrete lysozyme
Enterenocrine cells of the small intestine
S cells which secrete secretin
How much nutrient absorbsion takes place in the small intestine?
90%
What is the difference between peristalsis and segmentation?
Peristalsis involves adjacent segments alternatively contracting and relaxing to push food down
Segmentation involves non-adjacent segments alternatively contracting and relaxing to mix food together in the small intestine
What is the difference between and exocrine and endocrine gland? What percentages of the pancreas are these glands?
Exocrine - make secretions into a duct system (99% of the pancreas)
Ex. Secrete pancreatic juice into ducts before it goes into the duodenum
Endocrine - make secretions directly into the bloodstream (1% of the pancreas)
What is pancreatic juice made up of
- Pancreatic amylase (to break down carbohydrates)
- Pancreatic lipase (to break down lipids
- Tripsinogen (to break down proteins)
Others: water, salts, various enzymes
Which lobe of the liver is bigger?
The right lobe is bigger than the left lobe
What is a portal system?
Allows the transportation of something from one capillary bed to another capillary bed through a vein
Ex. Hepatic portal vein
What are liver cells called and what do they do?
Hepatocytes
Functions to process nutrients arriving from the GIT through the hepatic portal vein (which gives the liver capillaries nutrient rich blood from the stomach-intestines capillaries )
They also produce 1L of bile per day
What are kupffer cells in the liver?
Phagocytic cells able to destroy any worn out red or white blood cells, bacteria, and other foreign matter from venous blood coming from the GIT.
What is bile made of? Does it have enzymes?
- mostly water and ions
- bile salts (to emulsify lipids)
- cholesterol
- bile pigments (bilirubin)
NO ENZYMES (makes sure to know for exam)
Does bile use chemical or physical breakdown? Why is this the case?
Physical breakdown
This is due to the fact that bile contains no enzymes so there is no chemical breakdown occurring
Define amphipathic. What have we studied that relates to this?
Molecules that have both polar and non polar parts to it (therefore they can dissolve in water)
Bile salts are an example of this
What is emulsification?
The breakdown of large lipids into smaller lipids using bile salts
What hormone stimulates the gall bladder to release bile into the duodenum?
CCK hormone
Which hormone stimulates the liver to produce bile?
Secretin hormone
Where is water absorbed? How is it absorbed
90% is absorbed in the small intestine
10% is absorbed in the large intestine
Both through the process of osmosis
What are the 3 phases of digestion?
- Cephalic - smell, sight, thought of food will activate neural centres and increase salivary/gastric activity
- Gastric - food arrives in stomach, increase of motility and gastric gland activity
- Intestinal - exit of food out of the stomach into the duodenum to be absorbed
Are enzymes secreted in the large intestine?
No
