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The Digestive System
Transcript of The Digestive System
The Main Stages of Food Processing
Foods engulfed through phagocytosis or pinocytosis are surrounded by a food vacuole.
Mammalian Digestive System
The act of eating
breaks down macromolecules into component monomers which the animal then uses to make its own molecules or as fuel for ATP production.
Animals eat organic material in food which largely consists of proteins, fats, and carbohydrates.
Animals can not readily use these macromolecules because
1) too large to pass through membrane and enter cell
2) macromolecules of food and body not identical
THUS LEADING TO ...
the process of breaking down food into molecules the body can absorb
Starts with enzyme hydrolysis which splits macromolecules from food by the enzymatic addition of water.
breaking material into smaller parts increases surface area digestive juices containing hydrolytic enzymes (saliva)
Polysaccharides and disaccharides are split into simple sugars
fats are digested to glycerol and fatty acids
proteins are split into amino acids
nucleic acids are cleaved into nucleotides
The uptake of small nutrient molecules by an organism’s own body
undigested materials are expelled from body
Problems and Diseases
The enzymes break down food safely within a compartment that is enclosed by a protective membrane, thus not digesting cytoplasm
The vacuole fuse with lysosomes, which are organelles containing hydrolytic enzymes.
Ex: Sponges, humans, and most mammals
the breakdown of food outside cells
digestion occurs within compartments that are continuous with the outside of the animal’s body
organisms devour much larger prey
Ex: fruit flies and grasshoppers
They spit up stomach acid and then digest thus easy consumption
An extensive pouch that serves as the site of extracellular digestion and a passageway to disperse materials throughout most of an animal's body. Only one opening.
Ex: cnidarians and flatworms
Complete Digestive Tract
digestive tube extending between two openings, a mouth and an anus
food moves along the canal in a single direction, entering into specialized regions that carry out digestion and nutrient absorption
nematodes, annelids, molluscs, arthropods, echinoderms, and chordates
animals with alimentary canals have ability to ingest additional food before earlier meals are completely digested unlike animals with gastrovascular cavities.
Digestion in a hydra.
Common bile duct
aka Poop aka Shit
Food enters the oral cavity
Food present in mouth triggers nervous reflex allowing saliva secretion through ducts to mouth
increase in SA of food - easier to swallow
Conditioning to food can cause preliminary salivation
Saliva contains a slippery glycoprotein called mucin: protects the lining of the mouth and lubricates food.
an enzyme that hydrolyzes starch and glycogen, producing smaller polysaccharides and the disaccharide maltose.
tongue tastes food shape the food into a ball called a bolus
tongue pushes a bolus to the back of the oral cavity and into the pharynx.
Bolus Enters the Esophagus
Esophagus conducts food from the pharynx down to the stomach by peristalsis - rhythmic waves of contraction by smooth muscles in the wall of the canal, pushes the food along the tract
muscles at top of esophagus striated -swallowing voluntary then the involuntary peristalsis happens
Prevents food from reentering esophagus
stores food and performs preliminary steps of digestion
accordionlike folds, very elastic wall, can stretch to accommodate about 2 L of food and fluid
stomach can store an entire meal so we don't need to eat constantly
secretes a digestive fluid called gastric juice
action of the smooth muscles in the stomach wall mixes food with gastric juice - acid chyme
Abigail Cajayon - Sara Rodriguez - Christian Shramek - Elom Essamaa-Ayi
Gastric juice is secreted by the epithelium lining numerous deep pits in the stomach wall.
high concentration of hydrochloric acid, has a pH of 2
disrupt the extracellular matrix that binds cells together in meat and plant material
acid also kills most bacteria that are swallowed with food
begins the hydrolysis of proteins
low pH of gastric juice denatures (unfolds) proteins in food, increasing exposure of their peptide bonds to pepsin
Pepsin breaks peptide bonds
cleaving proteins into smaller polypeptides
works best in a strongly acidic environment
What prevents pepsin from destroying the cells of the stomach wall?
regulate the passage of chyme into the intestine
normally dilates only when a bolus arrives
occasional backflow of acid chyme from the stomach into the lower end of the esophagus causes heartburn.
backflow is a persistent problem, an ulcer may develop in the esophagus.
Contracts if epiglottis is up, relaxes when down
defense against self-digestion
pepsin is secreted in an inactive form called pepsinogen by chief cells in gastric pits
parietal cells, also in the pits, secrete hydrochloric acid
acid converts pepsinogen to active pepsin but not until they enter the lumen (cavity) of the stomach
coating of mucus, secreted by the epithelial cells of the stomach lining
mitosis generates enough cells to completely replace the stomach lining every three days
The Small Intestine
Most of the enzymatic hydrolysis of food macromolecules and most of the absorption of nutrients into the blood occur in the small intestine
Duodenum of small intestine
acid chyme mixes with digestive juices from the pancreas, liver, gallbladder, and gland cells of the intestinal wall itself
hydrolytic enzymes and an alkaline solution rich in bicarbonate
bicarbonate acts as a buffer, offsetting the acidity of chyme from the stomach
pancreatic proteases are activated once in the the duodenum
mixture of substances, bile, is stored in the gallbladder until needed
Bile contains no digestive enzymes, contain bile salts
act as detergents (emulsifiers) that aid in the digestion and absorption of fats
contains pigments that are by-products of red blood cell destruction in the liver; these bile pigments are eliminated from the body with the feces.
epithelial lining of the duodenum source of several digestive enzymes
enzymatic digestion is completed as peristalsis moves the mixture of chyme and digestive juices along the small intestine
Most digestion is completed early in this journey, while the chyme is still in the duodenum
Jejunum and Ileum of Small Intestine
function mainly in the absorption of nutrients and water
Hormones of Digestion
At stage 0, normal replacement of lining cells goes awry
At stage 1, grown into the wall of the intestine but have not spread beyond its muscular coat
At stage 2, penetrated beyond the muscular layers of the large intestine and spreads into adjacent tissue
At stage 3, disease has spread to the lymph nodes
At stage 4, spreads to distant organs such as the liver, lungs, or ovaries
Malignant tumor arising from the inner wall of the large intestine
Change in a person bowel habits
Tumor grows within the colon, thus obstructing the stool’s flow through the colon
Tumor growth within a small rectal space results to partial and complete blockage of the stool passage
Deficiency of the enzyme lactose, produced by the cells lining the small intestine
Improperly digested is digested lactose in the colon leads to uncomfortable symptoms
Symptoms occur because the unabsorbed lactose passes through the small intestine sand into the colon
Causes inflammation, or swelling, and irritation of any part of the digestive tract
Inflammation extends deep into the lining of the affected part of the digestive tract
Swelling can cause pain and can make the intestine, the bowel, empty frequently, resulting in diarrhea
Long lasting inflammation may produce scar tissue that builds up inside the intestine to create a stricture
A stricture is a narrowed passageway that can slow the movement of food through the intestine, causing pain or cramps.
Crohn’s disease is an inflammatory bowel disease (IBD), the general name for diseases that cause inflammation and irritation in the intestines.
Crohn's disease is most often found in a section of the small intestine called the ileum, but Crohn's can happen anywhere in your GI tract from the mouth to the anus.
A person with a fistula (abnormal passageway between various organs or tissues) in the rectal area may have pain and leaking discharge around the rectum.
Early Digestive System
In Invertebrates: 2 types
1) Some invertebrates, such as cnidarians, have a gastrovascular cavity in which there is a single opening that acts as the mouth and the anus, food is ingested and waste is excreted from one opening. Intercellular digestion in which cells lining the cavity secrete enzymes to break down food
2) Other invertebrates, such as arthropods and annelids, have an alimentary canal, a tube that begins with a mouth and ends with an anus. The food goes through structures such as the crop, the gizzard where it is digested, and the intestine where nutrients are extracted before it reaches the anus. (Extracellular digestion)
The digestive system is similar in most vertebrates; they all follow the general pattern of Mouth - Esophagus - Stomach Small intestine - Large intestine - Excretion
The fish takes in food through the mouth, varying types of teeth and mouths for different diets, it goes through the esophagus to the stomach, exits and goes through the liver and pancreas which breaks it down, goes through the intestines (very long in herbivores) which allow it to absorb nutrients into the bloodstream, exits through cloaca
Reptiles, Birds, Mammals
Use of saliva, more advanced kidneys and nephrons (functional unit of the kidney) that filter urine from the blood, reabsorbs nutrients, and secretes waste, exits through cloaca
Herbivores vs. Carnivores
Large and expandable stomachs so they can eat as much as possible when they catch prey
Sharp incisors and canines used for tearing away flesh and molars used for crushing food
Longer alimentary canals than carnivores because vegetation takes longer to digest than meat; a longer tract allows for more digestion time and a bigger surface area for the absorption of nutrients.
Much of the energy in diets comes from cellulose (in plant cell walls), but animals don’t make enzymes that break it down, so they house large populations of microorganism that can digest cellulose into sugars that the animal can use; most of the time, the microorganisms are in the cecum or in the large intestine; animals such as sheep and cattle have 4 chambers in their stomach dedicated to these microbes
Teeth with rigid surfaces designed for grinding vegetation, modified incisors for biting vegetation
Hormonal Control of Digestion
Digestive System Function
But if you really want to, zoom in.
Absorption of nutrients
has a huge surface area
most absorption occurs in the small intestine
Villus: A fingerlike projection of the chorion of the mammalian placenta. Large numbers of villi increase the surface areas of these organs.
Microvillus: One of many fine, fingerlike projections of the epithelial cells in the lumen of the small intestine that increase its surface area.
Lacteal: A tiny lymph vessel extending into the core of an intestinal villus and serving as the destination for absorbed chylomicrons.
Nutrients are absorbed across the intestinal epithelium and then across the unicellular epithelium of the capillaries or lacteals. Only these two single layers of epithelial cells separate nutrients in the lumen of the intestine from the bloodstream.
Amino acids and sugars pass through the epithelium, enter capillaries, and are carried away from the intestine by the bloodstream.
Digestion and absorption of fats.
Fats are then mixed with cholesterol and coated with proteins, forming small globules called chylomicrons
transported by exocytosis out of the epithelial cells and into lacteals
Muscular Valve (Sphincter)
controls the movement of material
cecum has a fingerlike extension, the appendix, which is dispensable. (Lymphoid tissue in the appendix makes a minor contribution to body defense.)
contains a mass of white blood cells that contribute to immunity.
A major function is to recover water that has entered the alimentary canal as the solvent of the various digestive juices.
The colon reclaims much of the remaining water that was not absorbed in the small intestine
Large Intestine Continued
The wastes of the digestive tract, the feces, become more solid as they are moved along the colon by peristalsis
If the lining of the colon is infected less water than normal may be reabsorbed, resulting in diarrhea.
constipation, occurs when peristalsis moves the feces along the colon too slowly. An excess of water is reabsorbed, and the feces become compacted.
Large Intestine Cont'd
rich flora of mostly harmless bacteria such as E. Coli
Intestinal bacteria live on unabsorbed organic material. As by-products of their metabolism, many colon bacteria generate gases, including methane and hydrogen sulfide
Some of the bacteria produce vitamins, including biotin, folic acid, vitamin K, and several B vitamins. These vitamins, absorbed into the blood, supplement our dietary intake of vitamins.
contain masses of bacteria, as well as cellulose and other undigested materials. Although cellulose fibers have no caloric value to humans, their presence in the diet helps move food along the digestive tract.
feces are stored until they can be eliminated
strong contractions of the colon create an urge to defecate.