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BIOL 252: TEST 3-FINAL DIGESTIVE SYSTEM
Steps of Digestive System (6) |
Ingestion
Digestions Propulsion Absorption Removal Excretion
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Ingestion |
Taking food and water into the mouth
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Digestion |
Mechanical (mouth) and chemical (stomach) breaking down of food into small components.
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Propulsion |
Swallowing- propels food down esophagus
Continues down intestines
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Absorption |
Absorption |
Removal |
Defecation
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Excretion |
Movement opposite from absorption (from body to digestive tract)
Takes place in liver.
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Stimuli to the GI tract to change its activity |
Mechanical: stretching
Chemical: smell and taste Maybe mental activity- thinking of food
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2 Types of responses from the GI tract |
Extrinsic (long reflexes) and Intrinsic (short reflexes)
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Extrinsic Reflex |
Long reflexes
Nervous system takes a sensory neuron from stomach/intestines that goes up to the CNS, sends impulses down to the medulla and causess a reflex
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Intrinsic Reflex |
Short Reflex/Enteric Nervous System
Neurons which rakes a stimulus and response w/o involving the CNS at all
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Enteric Nervous System |
The enteric nervous system (ENS), also referred to as the efferent nervous system, is a subdivision of the peripheral nervous system (PNS), that directly controls the gastrointestinal system.
Surrounds the digestive tract to SECRETE (glands) and CONTRACT (musculeris externa)
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Histology of the GI Tract |
Serosa (visceral peritoneum)
Muscularis externa Submucosa Lumen
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Serosa (Visceral peritoneum) |
Peritoneal cavity- visceral membrane that covers the organ
* Internal parietal peritoneum is what lines the body wall Comes together in the back-posterior side of the body to the vertebrae. When it reaches the wall, it turns outward to the parietal peritoneum
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Muscularis externa |
Smooth muscle responsible for mechanical digestion/propulsion
2 layers in GI tract: Circular and Longitudinal muscle Circular: decreases in diameter to contract GI tract Longitudinal: Shortens GI tract and Widens diameter when contracted
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Submucosa |
Where a lot of blood vessels and nerves reside; supplying blood to body
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Mucosa |
Lining the cavity; mucous secreting epithelium
Passes through lumen; has an epithelium continuous with mouth and anus epithelium. It's a barrier where food passes through during absorption
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Lumen |
The cavity itself
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Accessory organs |
Liver, gall bladder, pancreas
Function: secrete/excrete things into the small intestines (in duodenum)
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Digestive Organs |
Mouth/Salivary Glands
Esophagus Stomach Small Intestines Large Intestines
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Ingestion (Mouth) |
Teeth: chew/break up food (mechanical digestion)
Salivary glands (Submandibular, Sublingual, and Parotid) are exocrine glands (chemical digestion) * Intrinsic salivary glands- part of mucosa behind the mouth still secretes some more saliva * Slaviary glands can be inhibited during fight/flight (sympathetic) Salivary centers in the brain stem respond to chemo- and mechano- receptors
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Saliva (Compontents) |
Mostly water, electrolytes, ions, Amylase and Lingual Lipase Enzyme - neutral in osmality; slightly acidic
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Amylase |
Starch digesting enzyme to simple sugars
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Lingual Lipase |
Breaks fats to lipids
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Propulsion: Pharynx and Esophagus |
Esophagus: responsible of propulsion from mouth to stomach (peristalsis)
* contracts rhythmically * NO visceral peritoneum - but all other layers are there * Mucous: helps lubricate food so it wont get stuck * Muscularia Externa- inner circular and longitudinal * Mucosa - stratified squamous epithelium Food/saliva is mixed into a Bolus
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Stomach |
Site of liquidation of food
Layers of the stomach is much thinner * Different mucosa! 3 layers instead of 2 layers of smooth muscle: circular, longitudinal and OBLIQUE- for better mixing Ridges: Rugae- folds of mucosa and allows stomach expansion * can hold 2 L of fluid
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Peritoneal Cavity |
Location: Just under the diaphragm
* Visceral Peritonium * Mesentery
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Visceral Peritoneum |
(4th Layer) Serous membrane that covers organs
Under that is the Parietal Peritoneum
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Mesentery |
Ssuspending 2-layer group of peritoneum that contains blood vessels and nerves
Function: Keeps organs in place (from posterior wall) and from twisting around; transmits blood vessels and nerves
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Pyloric Sphincter |
Valve that keeps food in the stomach to churn food with secretions into chyme- liquefied food
Chyme is released a little at a time into the duodenum
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Stomach Secretions |
Come from the epithelium glands from the mucosa epithelium layer
Glands secrete into the lumen of the stomach to mix with the fuid
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Cells of Gastric Glands |
Mucous neck cells
Parietal Cells Chief Cells Enteroendocrine Cells Located: inside gastric pits in the inner wall of stomach
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Mucous Neck Cells |
Function: Secrete Mucous
Location: Closest to pits, form connective region
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Parietal Cells |
Function: secretes HCL and intrinsic factor (needed for B12 absorption) - important in intestines for cell division and RBC.
Protects cells along the surface
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Chief Cells |
Function: Secrete pepsinogen- 3rd enzyme that the food has encountered (after amylase and lipase)
Pepsinogen --> Pepsin (smaller pieces): a protein/enzyme that breaks down other proteins * Not active in the pH 7 in mouth. Only in pH 2 in stomach
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Enteroendocrine Cells |
Paracrine factors and hormone secreting cells into the BLOOD
* Hormones leave the lower layer to diffuse into the extracellular space * Gastrin is released by the stomach
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Phases of Gastric Secretion Regulation |
1) Cephalic Phase
2) Gastric Phase 3) Intestinal Phase
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Cephalic Phase |
Stimulated by: sight, smell, taste, and/or thought of food
Effect: Sends signals to the stomach by the Parasympathetic Nervous System through the Vagus nerve (X) --> Stimulation of Gastric Secretion Lack of stimulation stops secretion
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Gastric Phase |
When: when food has arrived in the stomach
Input: Stretching of stomach Output: Stimulates mechanoreceptors * long reflexes: stretch -> brain -> Vagus nerve -> stomach (chemical signal) Releases gastrin to release pepsinogen and HCl through blood back to stomach * short reflex: nerve from stomach to stomach (mechanical stimuli) Lack of stimulation stops secretion
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Intestinal Phase |
Function: Primarily inhibitory to long AND short reflexes gastric secretion because intestines can only receive a little bit of chyme at a time
Duodenum senses stretch/acidic chyme --> releases "intestinal hormones" --> stomach stops secreting
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Interogastric Reflex |
Intestines instructing the stomach to stop secreting
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Gastric Motility and Emptying: Receptive Relaxation |
Stomach expands as it is stretched; mediated by long reflexes
Bolus of food is covered with substances, and surface area is maximzed
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Gastric Motility and Emptying: Plasticity |
Smooth muscle expands when stretched
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Contractile Activity |
Peristaltic waves increase in intensity near pylorus
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Regulation by emptying |
By stomach: large liquidy meals are passed through quicker
* Liquid portion goes to the pyloric sphincter By duodenum: enterogastric reflex and hormonal response inhibits emptying; fatty chyme inhibits emptying * Chyme in the duodenum triggers closing of pyloric sphincter * Acidity is neutralized by enzymes and is processed in intestines
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Jejunum |
* Cradles the pancreas
* Pancreas has ducts that lead out of liver (where bile comes from) * Gall bladder contracts and releases bile into jejunum after a fatty meal
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Pancreas |
Produces digestive enzymes to digest micromolecules when released into the intestines
* Neutralizes acidity so that enzymes can work (pH 7)
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Ilium |
Function: Absorbing molecules from micromolecules from lumen and passes through blood
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plica |
Ridges in the intestinal wall to absorb nutrients.
With each ridge, there are tons of villi- each contained capillaries * blood vessels pick up food through diffusion
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Lymphatic vessel |
aka Lacteal
* Where fats are picked up to be emulsified * Molecules from chyme -> epithelial layer -> blood or lymphatic system -> blood
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Liver |
Major functions: Processes nutrients, Filters toxins, Produces Bile
Liver filters/detoxifies the blood from stomach to the heart Liver stores glycogen, excess proteins and vitamins, process hemoglobin Has 2 blood supplies
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Blood in Liver |
Hexagonal dimensions of sinusoids capillaries with big holes in walls to remove nutrients and toxins
Toxins are collected in the center of the unit that leads to the hepatic portal vein *Unique because of interrupting vein in the middle Artery -> capillary bed -> portal vein -> capillary bed -> hepatic vein
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Hepatic Portal Vein |
a vein in the abdominal cavity that drains blood from the intestines and spleen to the liver.
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Hepatocytes |
Main liver cells
Characteristics: require oxygen Produces: bile salts Function: filters blood in liver
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Bile |
Composition: Cholesterol, Bile Pigments, and Bile Salts
Function: to get rid of cholesterol (excess) and bilirubin (hemoglobin breakdown) through excretion, emulsifies fat (bile salts)
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Gallbladder |
Function: stores and concentrates bile
When: muscular wall ejects bile to duodenum when stimulated
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Regulation of Bile Release |
Stimuli: Fatty chyme -> CCK from intestines to duodenum to gall bladder -> gallbladder contracts
Amt of bile into intestines is proportional to the amt of fat present Inhibition: Emulsifying fat reduces the signal coming from duodenum and CCK levels return back to normal
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Pancreas |
Function: exocrine gland that secretes enzymes into the duodenum (only 1% is endocrine releasing)
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Composition of Pancreatic Juice |
Bicarbonate ions, Proteases, Amylase, Lipases, and Nucleases
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Regulation of Pancreatic Secretion |
Pancreatic enzymes: released in response to presence of CCK
Bicarbonate enzymes: released in response to presence of secretin (stimulated by acidic chyme) * to neutralize the pH of food in intestines
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Digestive Process of the Small Intestines |
Chemical digestion- pancreatic enzymes break down macromolecules
Absorption- absorptive cells move substnaces into blood by diffusion and active transport (leaves behind fibers) Motility- peristalsis, segmentation (sphincters holds chyme in specific regions exposing it to the surface are of the intestines)
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Large Intestines |
Function: Moving waste products along the pathway to the rectum, peristalsis, absorbs water, bacterial activity breaks things down that our enzymes can't so that we can use the released nutrients
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Cells of Large Intestines |
Large goblet cells- mucous secreting cells
* to move dehydrated fibrous stuff that is left over
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Bacteria in the Large Intestines |
Different types of bacteria colonize different parts of the large intestines
~700 species of bacteria chemically digest otherwise undigestible molecules Produces B vitamins (cell metabolism) and vitamin K (for clotting factors)
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Digestive Process of the Large Intestines |
Absorption- water electrolytes, and bacterial metabolies
Motility- peristalsis Defectation- spinal reflex, under voluntary control, assisted by Valsalva's maneuver?
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