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The Digestive System
Transcript of The Digestive System
the blood steam, heart then back
to the digestive system where they
stimulate secretion of digestive juices
and organ movement. Gastrin causes the stomach to produce acid for dissolving and digesting some foods. Secretin causes the pancreas to send out a digestive juice that is rich in bicarbonate. It stimulates the stomach to produce pepsin, an enzyme that digests protein, and it also stimulates the liver to produce bile. CCK causes the pancreas to grow and to produce the enzymes of pancreatic juice, and it causes the gallbladder to empty. Nerves that Control the Digestive System Cell Types in Digestive Organs Taste Bulb Sensory Cells: neuroepithelial cells Salvary Glands Serous cells: Protein Secretion
Myoepithelial cells: move secretory products through contraction
Mucous cells: Mutin secretion
Simple Cubodial cells: Reabsorb sodium Esophagus Connective tissue/blood vessels/ lymphatic vessels
Muscular for Peristalsis Stomach Small Intestine Duodenum, Jejunum, Ileum
Plicaecircularis (valves of Kerckring) - transverse semilunar folds that contain a core of submucosa.
Intestinal glands (krypts of Lieberkuhn) - simple tubular glands that extend from the muscularis mucosae and open to the luminal surface at the base of villi.
Colon Enetrocyte cells: Transport electrolytes and water from lumen to the circulatory system
Muscularis Externa: Segmentation - local contractions of circular muscle layer for moving contents into contact with the mucosa for absorption. Peristalsis - largely involves the longitudinal muscle layer and moves the intestinal contents distally. Liver Lipoprotein synthesis, bile
organized cell plates. Extended protein synthesis in Rough ER. Many mitochondria for energy generation and urea is created from the Ammonium ion excreted. Peroxisomes for gluconeogenesis.
Hepatic cells: Receive blood Gallbladder Creates/stores bile. Located on postinferior surface of liver
Has electrolytes to maintain bile as an isotonic fluid Pancreas Exocrine pancreas
Secretion of enzymes
Synthesizes and secretes, into the blood, insulin and glucagon, hormones that regulate glucose, lipid, and protein metabolism in the whole body.
Ob/Db Genes Certain hormones regulate long-term and short-term appetite which affects a “satiety center” of the brain. Hormone release-endocrine system. Mutations in ob or db genes cause voracious eating: Was found that ob genes produce the satiety factor and db gene responds to the factor. Ob genes clone for the hormone leptin and the db gene encodes the leptin receptor. Leptin receptors regulate appetite. Loss of fat decreases leptin levels, signals brain to increase appetite. Overview of Digestion:
Oral Cavity contains amylase (breaks down carbs) tongue and teeth crush food into bolis.
Esophagus uses peristalsis
Past Esophageal sphincter, a “trap door” to the stomach
Into Stomach which contains pepsin (breaks down proteins)
Past Pyloric Sphincter
Into Small Intestine that has villi. Most digestion occurs here.
-brush border-microvilli to increase surface area
Sent to the liver
Pancreatic duct expels enzymes and bile (stored in gallbladder) to aid in digestion
Enters the Colon that reabsorbs water and exits the body through the rectum . Microvilli / Villi The inner surface of the small intestine contains numerous fingerlike projections called villi that extend into the intestinal lumen. Each villus has projections of cells called microvilli to increase the surface area.Microvilli form the striated border and provide the major amplification of the luminal surface. (structure/function)
The products of digestion enter cells of the villi, move across the cells, and enter blood vessels Extrinsic (outside) nerves come to the digestive organs from the unconscious part of the brain or from the spinal cord. They release a chemical called acetylcholine and another called adrenaline. Acetylcholine causes the muscle of the digestive organs to squeeze with more force and increase the "push" of food and juice through the digestive tract. Acetylcholine also causes the stomach and pancreas to produce more digestive juice. Adrenaline relaxes the muscle of the stomach and intestine and decreases the flow of blood to these organs. The intrinsic nerves are triggered to act when the walls of the hollow organs are stretched by food. They release many different substances that speed up or delay the movement of food and the production of juices by the digestive organs. Carbohydrates broken down by salivary amylase starting in the mouth
o Also broken down in the duodenum due to pancreatic amylase- hydrolyzes starch, glycogen, and smaller polysaccharides into disaccharides.
o The the enzyme maltase compleates the digestion of maltose, which completes the digeston of maltose into glucose.
§ Sucrose- hydrolyzes sucrose
§ Lactase digests lactose
o Monomers are then absorbed into the blood Proteins Break down begins in the stomach with the presence of Pepsin.
o Enzymes in the duodenum breakdown the polypeptides into amino acids
§ Trypsin and chymotrypsin
o Dipeptidases (enzymes)- attached to intestinal lining split small peptides
o Carboxypeptidase and aminopeptidase work together to break down protein
§ Both break off one at a time,
§ c from the end
§ A from the beginning
o Intestinal enzymes triggers activation of these enzymes Lipids Starts in small intestine
o Bile salts from the gallbladder emulsify the lipids- which keeps them from coalescing
o Lipases from the pancreas hydrolyzes Nucleic Acids A Team of enzymes called nucleases hydrolyze DNA and RNA into nucleotides.
o Then other hydrolytic enzymes break nucleotides into nucleosides, nitrogenous bases, sugars and phosphate. Cephalic Phase Regulated by vagus nerve which is activated by sight, smell, and taste of food. The vagus nerve indirectly causes parietal cells to secrete HCl and directly stimulates chief cells to secrete pepsinogen to digestion proteins Gastric Phase Stimulated by amount of chyme and chemical nature of the chyme in the stomach which is controlled by peptides, pepsinogen, and acid secretion. The Gastric Phase uses feedback loops to regulate the system during this time. The positive feedback loops cause acid and pepsinogen to be released which causes more peptides to come into stomach. The negative feedback loops kick in when the stomach has a low pH which then inhibits gastrin secretion by G cells and causes there to be less acid secretion. Stimulation of HCl secretion The vagus nerve and amino acids in the stomach lumen stimulate G-cells to release gastrin. Gastrin in turn then stimulates histamine to be released from ECL cells. The released histamine then stimulates parietal cells to begin secretion of HCl. Intestinal Phase Inhibits gastric activity due to a neural reflex of stretching of the duodenum and a secretion of an inhibitory hormone. The hormone is called Gastric Inhibitory Polypeptide or GIP. Enteric division of the nervous system regulates digestive organs and peristalsis
Endocrine hormones such as gastrin, secretin, and cholecystokinin (CCK), which travel in the bloodstream, ensure secretions are only present when needed. As the diets of organisms change, so do their digestive tracts.
The tongue has become more prominent in the process of digestion by becoming more mobile and muscular. It can now be used to manipulate food as well as used for other activities. In cats, the development of papillae on the tongue allows the tongue to be used for grooming as well as stripping away surfaces of food. Teeth have also evolved depending on the diets of the organisms. Carnivores, such as dogs and cats, have large pointed incisors, jagged premolars and molars, and large canines. Herbivores, horses and deer, have developed premolars and molars with broad ridged surfaces and small incisors and canines for biting of pieces of vegetation. Omnivores, for example humans, have blade-like incisors for biting, pointed canine for tearing, and premolars and molars for grinding and crushing. Also in some organisms, such as cows, the saliva produced in the oral cavity act as a buffer system. The saliva is used to neutralize the acidity of the rumen produced as a result of fermentation. The "Thrifty Genotype" Hypothesis
Some scientists think that our bodies have adapted when there were a lot of famines to survive by eating lots of fatty foods. They believe that this adaption has carried over and that it is the reason that we have a taste for fatty foods. The secondary palate in the mouth has evolved to allow for dual mastication and breathing. As another result of evolution, the length of the small intestine and the cecum can change because of an organism's diet. For example, koalas have a very long cecum because of their diet of eucalyptus leaves. Another theory is that the small intestine and cecum were actually parts of a larger functional organ in human descendants. the anticipation of eating stimulates nerves within the brain which signal to the stomach and stimulate the release of gastrin. Gastrin release is also stimulated by the stretch of the stomach walls Stomach Chief Cells Chief Cells: secrete pepsinogen. Pepsinogen is converted to the enzyme pepsin in the presence of hydrochloric acid
Proton Pumps HCl in stomach lining. Parietal Cells The hydrogen ion concentration in parietal cell secretions is roughly 3 million fold higher than in blood, and chloride is secreted against both a concentration and electric gradient. Thus, the ability of the partietal cell to secrete acid is dependent on active transport.
This ATPase is magnesium-dependent
Histamine's effect on the parietal cell is to activate adenylatecyclase, leading to elevation of intracellular cyclic AMP concentrations and activation of protein kinase A (PKA). Enetrocyte Cells transport of substances from lumen of the intestine to the circulatory system, synthesis of the glycoprotein enzymes needed for terminal digestion and absorption. Paneth Cells their secretory granules contain the antibacterial enzyme lysozyme, other glycoproteins and zinc, play a role in regulating the normal bacterial flora of small intestine. Cells in Pancreas B Cells: Secrete insulin
A Cells: Secrete glucagon
D Cells: Secrete somatostatin which inhibits insulin and glucagon secretion Rugae: longitudinal folds (structure/function surface area)
Made of Mucosa: Secretes mucous and is a barrier that provides protection from gastric juices
Produce digestive juices