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28 Cards in this Set
- Front
- Back
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Digestive System
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all the organs, tissues, and cells involved in
Ingesting food and breaking it down into smaller components. Digestion contributes to homeostasis by providing the body with Nutrients needed to sustain the life of cells. A digestive system: 1) Ingests food 2) Breaks down food into small molecules that can cross plasma membranes 3) Absorbs these nutrient molecules 4) Eliminates undigestible remains |
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Digestive tract or gut
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is typically defined as a long tube through which food passes as it is being digested.
While some animals do not have digestive tracts, most do have some sort of digestive tract. |
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Incomplete Digestive tract (incomplete gut)
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has a single opening usually called a mouth.
This single opening can be used for both ingestion of food and elimination of wastes. Example: Planarians |
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Complete Digestive Tract (complete gut)
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has a mouth AND an anus. This separates the functions of
ingestion of food and waste eliminations. They can have many specialized parts as well Examples: Annelids, Arthropods and Vertebrates. |
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Continuous feeders
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are generally filter feeders that rely on water to carry small amounts of food
continuously to them. They do not have a way to temporarily store food for periods of time nor nor do they have much if any long term storage (fat cells for example). Most commonly seen in invertebrates and sponges but there are some large exceptions such as baleen whales that strain tiny crustaceans called krill out of the ocean water |
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Discontinuous feeders
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have evolved the ability to store food temporarily while it is being digested.
This allows them to spend less time feeding and more time engaging in other activities (courtship, nest building, territorial displays, play, video games etc. ) Having a stomach, intestines and in some cases cecums (a blind sac) allow for this. |
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Adaptations to Diet
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Some animals have adapted specializations regarding digestion that go beyond
continuous and discontinuous feeding. • Omnivores • Carnivores • Herbivores These different feeding styles have associated adaptations such as different teeth for different food sources. There are different styles of skulls to accommodate an organism that needs to grind down the tough cellulose of vegetation or the sharp canine teeth found in carnivores. There are even different types of stomachs and mouth parts. |
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The Human Digestive System
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Humans have a complete digestive tract; it begins with a mouth and ends with an anus.
Major structures and organs involved in digestion are: Mouth, pharynx, Esophagus, Stomach, Small intestine, Large intestine, Rectum, Anus. Secondary structures and organs involved in digestion are: Salivary glands, Liver, Gallbladder, Pancreas Digestion in Humans is an extracellular process (takes place outside of cells) and consists of two major stages: • Mechanical digestion • Chemical digestion |
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Mechanical digestion
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is carried out by the physical actions of the mouth (chewing) and the physical
churning and mixing of food in the stomach and small intestine. |
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Chemical digestion
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requires enzymes that are secreted by the digestive tract or by accessory glands
that lie nearby ( salivary glands, pancreas, and gallbladder for example). |
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The Mouth
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Food is chewed in mouth and mixed with saliva from salivary glands. The muscular tongue does this.
Salivary amylase is an enzyme that begins to digest starch (a large polysaccharide carbohydrate). The chewed mass of food is called a bolus. |
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The Pharynx and the Esophagus
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The respiratory and the digestive passages come together in the pharynx (throat region)
and then separate. The esophagus is a tubular structure that takes food to the stomach. Sphincters are muscles that encircle the tubes and act as valves (open and close). When food is swallowed, the epiglottis covers the trachea while the food passes by. The central space of the digestive tract where food passes through as it is digested is called the lumen. From the esophagus to the large intestine, the wall of the digestive tract is composed of four layers: • Mucosa • Submucosa • Muscularis • Serosa The movement of food from the esophagus to the rectum is carried out by peristalsis, a rhythmic contraction that serves to move the contents along in various tubular organs. |
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esophagus
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is a tubular structure that takes food to the stomach
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Sphincters
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are muscles that encircle the tubes and act as valves (open and close)
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lumen
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The central space of the digestive tract where food passes through as it is digested
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peristalsis
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a rhythmic contraction that serves to move the contents along in various tubular organs.
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The Stomach
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Thick walled, J-shaped organ on left side of body underneath the diaphragm
Has deep folds and this allows it to expand. It is Involved in chemical and mechanical digestion. Contains gastric juices consisting of HCL (secreted by gastric glands) and pepsin. Thick mucus protects the stomach lining and tissues from the very acidic conditions. Food mixed with the gastric juices becomes chyme and is passed down into the small intestine. |
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chyme
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Food mixed with the gastric juices
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The Small Intestine
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Small in diameter but about 6 meters long. Has vast surface area due to villi.
First 25 cm is called the duodenum. It is in this region that a small duct brings bile from the liver and gallbladder (where it is made) as well as pancreatic juices from the pancreas, into small intestine. Bile emulsifies fat (acts like a detergent) causing fat droplets to disperse in water. Intestine is slightly basic in pH. Digestion is completed here in the small intestine by enzymes and bacteria. |
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The Large intestine
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Large intestine includes the cecum, the colon the rectum and the anus. It is larger in diameter than the small but shorter in length (1. 5 meters).
It absorbs most of the water, salts and some vitamins in the chyme. It stores undigestible materials until eliminated as feces. The cecum is below the junction between small and large intestine and has the appendix projecting off of the end. |
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The pancreas
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is an elongated and somewhat flattened organ, that acts as both and endocrine and exocrine gland.
Its role in digestion is that of an exocrine gland that secretes its products directly to a location by a duct. Pancreatic juice contains sodium bicarbonate and digestive enzymes for all types of food. Pancreatic juice neutralizes the acidic chyme, pancreatic amylase digests starch, trypsin digests proteins and lipase digests fats. |
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The liver
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is the largest gland in the body. Very large and contains 100,000 lobules that serve as functional and structural units.
Liver acts as the gatekeeper to the blood. As blood in the hepatic portal vein passes through the liver, , it removes many toxic substances and metabolizes them. It also removes and stores iron, vitamins A, B12, D, E, and K. Makes many of the proteins found in blood plasma and helps regulate the quantity of cholesterol in the blood. Maintains blood glucose level. When insulin is present, any excess glucose present in the blood is removed and stored by the liver as glycogen. Makes bile, and stores it in the gallbladder |
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Digestive Enzymes
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The various digestive enzymes present in the digestive juices help break down carbohydrates, proteins, nucleic acids, and fats.
• Salivary amylase • Pepsin • Pancreatic amylase • Maltase • Peptidases |
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Carbohydrates
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sugars, starch and fiber. Glucose and Fructose, sucrose, lactose .
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Lipids
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triglycerides (fats and oils), cholesterol
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Diet and Obesity
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Type 2 diabetes
2. Cardiovascular disease |
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Vitamins and Minerals (about 20 elements needed by the body for functions and regulation)
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1
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Proteins
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1
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