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What are the 6 processes related to digestive function?
- Mechanical Processing
What is ingestion?
Occur when foods enter the digestive tract
What is the mechanical processing of food?
Physical manipulation of food by mouth and digestive tract ( swirling and mixing)
Chemical breakdown of food into organic fragments that can be absorbed by the digestive epitheleum
Release of water, acids, enzymes and buffers by digestive tract and digestive organs
Movement of small organic molecules, electrolytes, vitamins and water across the digestive epithelium & into interstitial fluid of the digestive tract
Removal of waste products from body fluids
Describe the defensive role of the digestive tract.
Protects surrounding tissues fr corrosive effects of digestive acids & enzymes and fr bacteria swallowed w food or that resides in the there
Four major layers of the digestive tract are. . . . .
- Muscularis Externa
The mucosa is . . . .
Inner lining of digestive tract consisting of mucosal epithalium and the lamina propria, an underlying layer of loose connective tissua
The submucosa is . . . . .
Second layer of loose connective tissue containing lg blood vessels, lmyphatic vessels, nerve fibers, sensory neurons and parasympathetic motor neurons
What is the submucosal plexus?
Controls & coordinates contractions of smooth muscle layers and regulating secretion of digestive glands
The muscularis externa is. . . .
Band of smooth muscle cells arranged in an inner circular layer and an outer longitudinal layer. Contractions both agitate materials & propel them along the digestive tract
What is the Serosa?
Serous membrane that covers muscularis externa along most porttions of the digestive tract within the peritoneal cavity
Pacesetter cells do what?
Trigger waves of motion within the smooth muscle of the digestive tract resulting in rhythmic cycles of activity
What is Peristalsis?
Waves of muscular contraction that move along digestive tract propelling digestive contents
What happens to dead areas in digestive tissue? 27 minutes digestive part 1
They often must be removed b/c w/o movement of that muscle they could become necrotic fr something sitting in there and rotting
What are four activities of the oral cavity?
- Sensing & analyzing material b/f it is swallowed
- Mechanically processing material thru actions of teeth, tongue & surfaces of palate
- Lubricates material by mixing it w/ mucus & salivary secretions
- Begins digestion w/ salivary enzymes
The oral cavity is aka?
What does the tongue do?
- Mechanical processing by compression, abrasion & distortion
- Manipulation to assist in chewing & to prepare material for swallowing
- Sensory analysis by touch, temp & taste
What do salivary glands produce?
1.0 - 1.5 liters of saliva/day consisting of 99.4% water plus mucins & assorted ions, buffers, waste products, metabolites & enzymes
What does the pharynx do for digestion?
Pharyngeal muscles cooperate w/ oral muscles & esophagus to initiate process of swallowing
The esophagus is. . . .
muscular tube that conveys food & liquids to stomach. Begins @ pharynx, passes thru mediastinum & enters peritoneal cavity thru the esophageal hiatus (opening in the diaphragm) before emptying into the stomach
The stomach is located where?
Within L upper quadrant of the abdominopelvic cavity
What are the four primary functions of the stomach?
- Temporary storage of ingested food
- Mechanical breakdown of ingested food
- Breakdown of chemical bonds in food using acids and enzymes
- Production of intrinsic factor, compound necessary for absorption of vitamin B12
What is intrinsic factor?
Compound produced in the stomach that is necessary for the absorption of Vitamin B12
What is chyme?
Viscous, acidic, soupy mixture of ingested materials & secretions of the glands of the stomach
What is the cardia?
Smallest part of the stomach where the esophagus connects
The fundus is . . .
The bulge of the stomach superior to the cardia
Where is the body of the stomach located?
Lg area between the fundus and the curve of the J
The pylorus . . . .
is the distal part of the J and connects the stomach w/ the small intestine thru the pyloric sphincter
Rugae are . . . .
Folds or ridges within the mucosa of the stomach when it is empty
What are gastric pits?
Openings onto the gastric surface containing gastric glands that actively divide and replace superficial cells of the mucus epithelium shed into chyme
Each day the cells of the gastric glands secrete about ____ mL of ____ ____.
1500 mL of gastric juice
What do parietal cells do?
Secrete intrinsic factor and hydrochloric acid
Chief Cells. . . .
Secrete protein called pepsinogen into stomach lumen.
What happens when pepsinogen meets hydrochloric fr parietal cells?
It is converted to pepsin which is a proteolytic (protein digesting) enzyme
What are renin and gastric lipase used for in newborns?
- Renin coagulates milk slowing passage thru stomach & allowing more time for digestion
- Gastric lipase initiates digestion of milk fats
What are the three phases gastric secretion & where do they begin?
- Cephalic Phase - Begins w/ senses fr your brain
- Gastric Phase - Begins in stomach
- Intestinal Phase - Begins when chyme starts to enter the small intestine
Describe the cephalic phase.
- Begins in ur head
- Under ctrl of vagus nerves, parasympathetic fibers innervate mucous, parietal, chief & endocrine cells of stomach
- Lasts only a few minutes
Describe the gastric phase.
- Begins in the stomach w/ arrival of food
- Gastrin stimulates stomach contractions which begin to swirl & churn stomach contents creating chyme
Describe the Intestinal Phase
- Begins when chyme enters the sm intestine
- Inhibitory function that controls rate of gastric emptying to ensure secretory, digestive & absorptive functions proceed efficiently.
- Release of intestinal hormones Secretin, Cholecystokinin (CCK) & Gastric Inhibitory Peptide (GIP)
Two things that effect rate of movement of chyme
- Stomach is distended & meal contains little protein
- Addition of caffeine or alcohol
Four reasons nutrients are NOT stored in the stomach are?
- Epithelial cells covered w/ alkaline mucus & not directly exposed to chyme
- Epithelial cells lack specialized transport mechanisms
- Gastric lining is impermeable to H2O
- Chyme is not completely broken down when it leaves the stomach
Describe the small intestine size & 3 sections.
- About 20' long w/ diameter ranging 1 1/2" - 1"
- Broken into Duodenum, Jejunum, Ileum
Describe the duodenum
- Closest segment to the stomach
- Curves in a C that encloses that pancreas
- Receives chyme fr the stomach & digestive secretions fr pancreas & liver
Describe the Jejunum
- Supported by sheet of mesentary & is about 8' long
- Bulk of chem digestion & nutrient absorption occurs here
Describe the Ileum
- Third segment and longest @ about 12'
- Ends @ ileocecal valve that ctrls flow fr ileum into cecum (1st section of lg intestine)
What are plicae?
Series of transverse folds in the intestinal lining
Describe the Lacteal
Transport materials that cannot enter blood capillaries such as protein lipid packages that are too lg to diffuse into blood stream
When and where is gastrin secreted?
Secreted by duodenal cells in response to lg quantities of incompletely digested proteins
- Released when pH falls in the duodenum as acidic chyme arrives
- Increases secretion of bile and buffers by liver and pancreas
Describe Cholecystokinin (CCK)
Secreted when chyme arrives in the duodenum especially when chyme contains lipids & partially digested proteins
Describe Gastric Inhibitory Peptide (GIP)
- Released when fats & carbs enter sm intestine
- Inhibits gastric activity & causes release of insulin fr pancreatic islets
What do pancreatic islets do?
Secrete hormones insulin and glucagon
Describe the pancreas
- A primarily exocrine organ that produces pancreatic juice, mixture of digestive enzymes and buffers
- Made up of ducts & end @ sac like pouches called pancreatic acini
- Pancreatic Ducts carry secretions to the duodenum
- Pancreatic enzymes do most of the digestive work in the sm intestine
Explain the Ctrl of pancreatic secretion
Acidic chyme arrives in the duodenum, secretin is released triggering the pancreas to secrete a watery, alkaline fluid w/ a pH between 7.5 & 8.8
Location of the Liver
In the R hypochondriac and epigastric abdominopelvic regions
The liver is divided into 4 unequal lobes called?
- Left and Right lobes
- Caudate Lobe
- Quadrate Lobe
Where is the Gall Bladder located & what is it?
- Within the recess under the R lobe
- Muscular sac that stores & concentrates bile b/f it is excreted into sm intestine
Liver cells are called
The neurons that innervate the smooth muscle of the muscularis externa are not under voluntary ctrl.
T or F
The 4 functions of the oral cavity are
- Sensory analysis of potential foods
- Mechanical processing using teeth, tongue & palatal surfaces
- Lubrication of food using mucus & salivary secretions
- Digestion by salivary enzymes
The pharynx serves as a . . . .
common passageway for food, liquids and air
The four major functions of the stomach are
- Temporary storage of ingested food
- Mechanical breakdown of food
- Breakage of chemical bonds by acids & enzymes
- Production of intrinsic factor
What does the pancreatic duct do?
Delivers pancreatic secretions to the sm intestine thru the wall of the duodenum
The endocrine function of the pancreas secretes what?
Insulin and glucagon into the blood
The exocrine function of the pancreas secretes what?
Water, ions & digestive enzymes into the sm intestine
Enzymes secreted by the pancreas include?
Pancreatic exocrine cells produce ____ ____ in response to hormonal instructions fr the ____
When chyme arrives in the sm intestine ____ & ____ are released
secretin & CCK
Secritin triggers the pancreas to produce?
Fluid containing buffer (primarily Na bicarb) that brings the pH of chyme under ctrl
CCK stimulates the pancreas to produce and secrete?
- pancreatic amylase
- pancreatic lipase
- proteolytic enzymes- trypsin, chymotrypsin, carboxypeptidase
The bile ducts fr each lobule of the liver follow what path
Common hypatic duct meets the cystic duct to form common bile duct which empties into the duodenum
What does the gall bladder do?
Stores and concentrates bile for release into the duodenum
The 3 main functions of the lg intestine are?
- Reabsorb H2O & compact feces
- Absorb vitamins made by bacteria
- Store fecal matter prior to defacation
Bacteria living in the lg intestine can cause?
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