Flashcards in Digestive System Deck (47):
What is a Batch Reactor?
Found in some hydra and herbivores; Coelenterates. There is one hole that is used for the input and the output of matter; all the matter is added at the same time (discontinuous), and one batch is processed and eliminated before the second batch is brought in. Pulsed, uniform composition.
What is a Continuous-flow Stirred-tank Reactor?
Found in Herbivores, allowing them to digest cellulose. It's a ruminant fore-stomach. Has a hollow, tubular cavity that allows for the continuous flow and processing of the material. The mixture is well mixed; homogenous and uniform. Overflow passes on.
What is a Plug-flow Reactor?
Example: Small Intestine
The bolus of food moves through a continuous tubular vessel. There is a gradient throughout the tube, therefore the composition of the mixture changed according to the position of the tube.
What does extracellular digestion permit?
An animal to store and break down larger varieties and quantities of food items. This is very cost effective. The food in the gut is not stored in the body, it has to be absorbed.
What type of extracellular digestion do Cnidarian pages have?
A blind-end sac lined by gastrodermis.
What do advanced organisms with extracellular digestion have?
A tube with an entrance (mouth) and exit (anus).
The lumen (space inside the gastrointestinal track) is technically part of the external environment.
What four regions is the gut tube divided into?
Headgut, foregut, midgut, and hindgut.
What are the accessory organs of the digestive track of vertebrates?
Salivary glands, exocrine pancreas, and biliary system (liver and gallbladder).
What is the stomach called in ruminants?
What is the stomach called in bird?
What alimentary canals are found in vertebrates?
Mouth, pharynx, esophagus, stomach, small and large intestine, anus.
Basic summary of the Alimentary Canal.
Materials in the canal move in one direction, through regions with specialized tasks. In these regions they are subjected to mechanical, chemical, and bacterial treatments before being absorbed or excreted.
What are the functions of the Headgut?
The head gut is involved in feeding and swallowing, with associations like teeth, salivary glands, and the tongue. In many species this is a common pathway for both digestion and respiratory gases, so there is a valve-like structure involved.
What are Salivary Glands for?
To produce saliva, which helps for lubrication during swallowing and provides mucin, enzymes, and anticoagulants.
What is the Tongue for?
The tongue in chordates helps with mechanical digestion and swallowing, and contains chemoreceptors (taste buds).
What is the process of Swallowing (deglutition)?
Process of moving food from the mouth, through the esophagus, and into the stomach. It starts with the bolus of food being forced (by the tongue) into the pharynx. The pharyngeal pressure receptors send afferent impulses to the medulla oblongata, where the swallowing centre activates a programmed all-or-none sequence of highly coordinated activites.
What are the two phases of the swallowing reflex?
Oropharyngeal phase and esophageal phase.
What is the Oropharyngeal Phase of the swallowing reflex?
The uvula is elevated, sealing off the nasal passage. The glottis is closed, and covered by the epiglottis to ensure food does not enter the respiratory pathways. Pharyngeal muscles contract to force the bolus into the esophagus.
What is the Esophageal Phase of the swallowing reflex?
The bolus enters the esophagus and peristaltic waves (ringlike contraction of circular smooth muscle, progressively moving forward) sweeps it through the esophagus. The gastroesophageal sphincter relaxes, allowing the bolus into the stomach.
What causes heartburn?
Inappropriate opening of the gastroesophageal sphincter.
What allows people to eat/drink while upside down?
The ringlike peristaltic contraction of the esophagus.
What are the functions of the Foregut?
It contains the esophagus. It works in conducting food from the headgut to the stomach.
What types of foregut functions are found in leeches and birds?
Some leeches have a crop (storage area); birds will regurgitate food for nestlings.
What are the functions of the Midgut?
It contains the stomach and small intestine and is used for the mechanical mixing. In the vertebrates it deals with protein digestion (pepsinogen -> pepsin, HCl), the and the chemical digestion of proteins, fats, and carbohydrates. There is some absorption of products.
Carnivores have a shorter midgut.
The midgut has receiving ducts from the liver and pancreas.
What comes from the Liver and what does it do?
[Midgut] Bile from the liver emulsifies fats and neutralizes acids.
What comes from the Pancreas and what does it do?
[Midgut] pancreatic juice, brings alkaline and important enzymes.
What is the basics of stomachs in monogastric mammals?
The human stomach is divided into three regions (Fundus, body [corpus], and antrum [more muscular, a lot of contraction]).
The pyloric sphincter separates the stomach from the duodenum (upper small intestine).
Mechanical mixing pushes food in the pyloric sphincter into the small intestine.
The functions of the stomach include the storage of food, the digestion of proteins, and the formation of chyme.
What is Chyme?
A thick, liquid mixture of food and gastric secretions.
What is Gastric Emptying?
A peristaltic contraction of the stomach, starting in the upper fundus and that becomes more vigorous as it reaches the antrum. The strong antral peristaltic contraction propels the chyme forward, causing a small portion of chyme to move through the partially open pyloric sphincter.
What is Gastric Mixing?
Occurs when the pyloric sphincter is closed; the peristaltic contraction still occurs but chyme can not flow into the duodenum.. The chyme is still propelled forward, but it is tossed back into the antrum and mixed.
What is important about the layer of mucus coating the gut?
The stomach mucosa has mucous cells that protect the mucosa against the acidity in the stomach. It has a much higher pH value than the gut, making it so the gut does not 'eat' itself.
What is the Small Intestine?
Part of the midgut; it has a large surface area for absorption. This is done through folding of the inner surface with villi (finger like projections; each villus has a capillary network and a terminal lymphatic vessel (central lacteal)). Microvilli are smaller hair-like projections arising from the luminal surface of epithelial cells (form the brush border). These features increase the surface area by about 600 fold.
Where does absorption take place in the small intestine?
In the duodenum and jejunum. Fats, monosaccharides, proteins, and vitamins are absorbed here.
7000 mL of secreted digestive juices must be absorbed daily.
[Small Intestine] How does Fat absorb?
Through diffusion across the luminal membrane.
[Small Intestine] How does Carbohydrate absorb?
As monosaccharides, they are absorbed by a secondary active transport with Sodium as a cotransporter.
[Small Intestine] How does Protein absorb?
Amino acids are absorbed by secondary active transport, similar to glucose transport.
What are the functions of the hindgut?
Storage and absorption of water and ions.
What does the hindgut do in herbivores?
In some herbivores, there is hindgut fermentation. Larger animals who utilize this have plug-flow reactors (horses, elephants), and smaller animals who utilize this have enlarged cecum (outpocket) acting as a continuous-flow reactor (rodents).
What does the Vertebrate Hindgut consist of?
Colon, cecum, and rectum/cloaca.
What does the Vermiform Appendix do in the Vertebrate Hindgut?
In humans and some apes it stores lymphocytes, but has no digestive function.
What is the Colon of the Vertebrate Hindgut made up of?
Three regions: ascending, transverse, and descending.
What is the difference between Carnivore and Omnivore/Herbivore Colons?
Carnivores have short, simple colons.
Omnivores/herbivores have longer colons with expandable side sacs called haustra.
Where does the Hindgut terminate in amphibians, reptiles, birds, and some mammals?
A cloaca, shared by the renal and reproductive systems. Excretes both urine and feces.
What is the motility of the esophagus regulated by?
The Central Nervous System.
What is the motility of the GI tract (excluding esophagus) regulated by?
Intrinsic control of motility:
Smooth muscle in the GI tract is myogenic (does not rely on nerve innervation or outside stimulus); has a Basic Electric Rhythm (BER) that is modulated by local stimulations. These stimulations include mechanical, such as stretching, and chemical stimulation in the lumen by chyme.
Extrinsic control of motility:
Through hormones and the Autonomic Nervous System. Local stimuli, such as locally released gastrointestinal peptide hormones in response to the composition of chyme, cause the sympathetic (inhibitory) and parasympathetic (stimulatory) nervous system to react.
Enteric Nervous System:
Intrinsic of the gastrointestinal tract, it's the only part of the peripheral nervous system capable of local autonomous function due to extensive, interconnected, neural circuits.
What is Peristalsis?
The coordinated muscle contraction. Seen in the stomach and intestines.