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Zoology, lecture 17
Vertebrates: Digestive system
| Question | Answer |
|---|---|
| Digestive system qualities | Its a very conservative system. That is, it barely changes from fish to mammals through evolution. |
| How does the digestive system start during embryonic development? | In the gastrula stage the formation of the archenteron (with a mesodermal roof) seals off from the mesodermal tissue giving a gut lined entirely with endoderm. |
| What is the name of the mesodermal tissue that makes up the muscles that function in the digestive system? | Splanchnopleura. |
| What is the germ tissue structure of the digestive tissue? | The digestive system is only lined with endoderm. All of the muscles, etc are made of a thick layer of mesoderm. |
| Functions of the digestive system | Breaking apart food particles to increase surface area for chemical digestion. Chemical digestion by enzymes to simpler units, transfer of food during its digestion through peristaltic contractions and absorption of nutrients/release of waste. |
| Chemical digestion of food particles | Performed by enzymes that break down proteins and polysaccharides into simpler units so that they might be used by our systems to produce our own proteins. |
| Amphioxus digestive system | Simple digestive system starting with a mouth (no jaws) into the pharynx which has gill slits that filter out food particles that then continue through the tube with a simple cecum that might be a digestive gland. |
| Fish (all vertebrates) digestive system | They have a skull with jaws lined with teeth (cyclostoma have no jaws) |
| Teeth | Appear to be derived from the exoskeleton of primitive vertebrates. |
| Placoid | Teeth as in sharks that are derived from their skin scales (remainder from a primitive exoskeleton. |
| Homodont | Teeth that have the same shape used for tearing food but not for chewing. All groups except mammals and birds. |
| Salivary glands | Used for moistening food and pre-digestion. They do not exist in fish. |
| Mammal teeth | The only vertebrates with different shaped teeth (heterodonts) that are buried in craters in the jaw (thecodont) |
| Bird teeth | Birds don't have teeth |
| Heterodonts | Teeth of different shapes/sizes. Found only in mammals. |
| Thecodont | Teeth that are buried inside craters in the jaw (found only in mammals) |
| Pharynx | The tube that follows the mouth and is lined with pharyngeal slits in all chordates. |
| Pharyngeal slits | Found in the pharynx of all chordates. In lower chordates there are a whole bunch of them. In higher groups the basic number is 7 with reduction as a result of evolutionary advance. |
| What is the purpose of the pharyngeal slits in fish? | They are the first to use them for respiration. |
| Esophagus | Very wide among sharks vs the narrow esophagus in humans because we chew our food whereas sharks do not--they swallow prey whole. |
| Thecodont | Teeth that are buried inside craters in the jaw (found only in mammals) |
| Pharynx | The tube that follows the mouth and is lined with pharyngeal slits in all chordates. |
| Pharyngeal slits | Found in the pharynx of all chordates. In lower chordates there are a whole bunch of them. In higher groups the basic number is 7 with reduction as a result of evolutionary advance. |
| What is the purpose of the pharyngeal slits in fish? | They are the first to use them for respiration. |
| Esophagus | Very wide among sharks vs the narrow esophagus in humans because we chew our food whereas sharks do not--they swallow prey whole. |
| What comes after the esophagus? | A large J shaped stomach. |
| What are the parts of the stomach? | The top has two parts: the fundus and the cariac and the after the bend in the J of the stomach there is a more narrow area called the pyloric. |
| What is the benefit of stomach development in chordates? | It allowed them to eat large amounts and spend the rest of their time doing other things (rest etc) as opposed to filter feeders that must eat constantly in order to sustain the amount of energy that they need. |
| How does the stomach preserve food? (keep it from going bad?) | It secretes hydrochloric acid תיחלמ הצמוח that kills all kinds of living organisms, bacteria and viruses, preserving the food. |
| HCl function in digestion | Both for killing bacteria, etc and also functions in hydrolysis of substances. |
| What is the downside of the preservative HCl in the stomach? | The HCl can also kill the stomach cells. |
| How does the stomach prevent itself from being damaged by the HCl it secretes for preservation and hydrolysis of the food? | Some cells in the stomach secrete mucopolysaccharides that cover the wall of the stomach and separation between the stomach and the food. Because it can be removed with the HCl the gastric epithelial cells regrow really fast. |
| What are the two mechanisms of protection for the stomach wall from HCl damage? | Mucopolysaccharide secretion on the stomach wall and high rate of division of stomach epithelial cells to replace those destroyed. |
| Where in the digestive system can you find these solutions to the given HCl problems? | Along the entire digestive tract. |
| What makes up the digestive tract wall | Three types of muscles with splanchnopleura origin. There is row of longitudinal and a row of circular muscles whose contraction results in breaking down of the food particles. |
| Which germ layer secretes enzymes into the food? | Endodermal cells |
| Pepsin | An enzyme secreted at the end of the digestive system that starts to break down proteins within the food. |
| Sphincter | Musclular ring that closes the hole between the stomach and the continuation of the digestive system--important cause it prevents food from being forced out of the gut before you want it to. |
| Duodenum | The first section of the small intestine. When the food passes through it digestion gets more significant. The epithelial cells of the duodenum have two large glands that participate in digestion. |
| Two large glands that grow out of the duodenum | Liver (larger) and pancreas (smaller) |
| Pancreas | Two protrusions from the epithelial cells of the duodenum that remain separate in sharks (with 2 separate openings) but fuse in higher vertebrates. |
| Pancreatic function | Secretion of enzymes for high level digestion of food. Stuff that breaks down lipids, carbs, etc. |
| Where does most of the digestion take place? | Along the digestive tract |
| Pancreatic enzymes | As opposed to the stomach enzymes (2.5 pH, 1.5 in sharks) they only work in a basic environment (7-8 pH). To solve this problem the pancreas secretes enzymes like bicarbonate to neutralize the acidity. |
| Bicarbonate enzyme secretion by the pancreas | Responsible for increasing the pH of the food that comes out of the stomach to allow for function of the digestive enzymes secreted by the pancreas. |
| Exocrine secretion | Secretion of enzymes into the digestive system (like pancreas secreting bicarbonate) which has an entrance from outside of the body and an exit outside of the body. |
| What are the exocrine secretions of the pancreas? | Digestive enzymes and pH neutralizing (pH raising) enzymes |
| What are the endocrine secretions of the pancreas? | Secretion of hormones into the blood stream like insulin etc. |
| Liver functions | An outpouching of the primitive gut made of 3 lobes (two large, one small central). The primary job was for the digestive system to produce bile, (in some organisms to store it in the gallbladder) responsible for emulsifying the lipids and fats. |
| Emulsification of lipids and fats | Done by the bile (and gallbladder) a growth from the liver that breaks the fats down into smaller particles with a greater surface area for better digestion. |
| Special liver function in sharks | While in most vertebrates the stored material is glycogen (for energy) in sharks its fat. Their livers are enormous so they can store a lot of energy (fat has more energy than sugar) and it also helps them float. |
| Mechanisms for increase in surface area of the digestive system | 1. A long digestive system (very long in vegetarians, shorter in predators), 2. folding the walls of the digestive system |
| Plicae | Folds in the wall of the digestive system that function in increasing its surface area. |
Created by:
YaelNoa
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