GI tract

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Functions of the digestive system

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Functions of the digestive system

motility, secretion, absorption, storage and elimination

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function 1: motility=

movement of food thru GI tract

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mechanisms that allow motility

  1. ingestion

  2. mastication

  3. deglutition

  4. peristalsis

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ingestion=

taking food into oral cavity

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mastication=

chewing

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degultition=

swallowing

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peristalsis=

rhythmic contraction of smooth muscle cells thru GI tract

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lots of GI pathology comes from :

motility issues

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dysphasia=

difficulty swallowing (example of GI pathology)

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function 2: secretion=

release of chemicals or hormones to allow digestion to occur

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endocrine secretions=

made in one place, acts in another place

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exocrine secretion=

released and acts locally

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function 3: absorption=

transfer of nutrients out of GI tract and into blood

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function 4: storage and elimination=

-temporary storage of food -elimination of waste

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GI tracts AKA:

"alimentary canal"

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GI tract organ list=

  1. mouth

  2. esophagus

  3. stomach

  4. SI

  5. LI

  6. rectum

  7. anus

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T/F GI tract is open on both ends

true, and continuous

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esophagus goes from ___ cavity to ___ cavity by passing thru _____

thoracic abdominal diaphragm

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what separates the thoracic cavity from abdominal cavity?

diaphragm

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the hole that the esophagus passes thru from thoracic cavity to abdominal cavity, in the diaphragm=

esophageal hiatus

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accessory organs=

liver, pancreas, salivary glands, teeth, gallbladder

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4 major layers of tissues of GI tract= inner most --> outer most

  1. mucosa (inner most)

  2. submucosa

  3. muscularis

  4. serosa (outer most)

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2 major functions of mucosa layer=

  1. absorption: transfer of nutrients

  2. secretion: or chemicals to help with digestion

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anatomy of mucosa layer=

highly convoluted -peaks and troughs, ridges

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convolutions of mucosa layer are called:

Villi

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vili does what for GI tract:

increases surface area available for absorption of nutrients

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anatomy of submucosa:

relatively thick layer

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submucosa contains:

-blood vessels -capillaries -nerve endings -lymphatic vessels -connective tissue

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nutrients in the GI tract are pulled in by ___ of the ____ layer and absorbed into the ____ of the ____ layer

villi in the mucosa layer capillaries/bood vessels in the submucosa layer

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nerve endings in the submucosa are under what control?

autonomic N.S control

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muscularis layer anatomy:

layer of smooth muscle cells that allow for motility/peristalsis to occur (muscles that allow the movement)

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serosa anatomy:

outermost, protective layer, made of connective tissue

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what nervous systemcontrols GI activity?

autonomic (parasymp. and sympathetic nervous systems)

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parasympathetic nervous system is GI ______

excititory

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sympathetic nervous system is GI _____

inhibitory

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GI excitatory (PsNS)=

increase peristalsis increase motility increase secretion of hormones/chemicals

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GI inhibitory (SNS)=

decrease peristalsis decrease motility decrease secretion of hormones/chemicals

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what occurs at the 1. mouth?

mastication

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mastication @ the mouth=

chewing + mixing of food with saliva

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important enzyme in saliva=

salivary amylase

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What does salivary amylase do?

breaks down complex carbohydrates (polysaccharides)

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polysaccharides are first broken down where?

in the mouth (bc of salivary amylase)

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initial digestion of carbohydrates begins _______

in the mouth (bc of salivary amylase)

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  1. pharynx=

common passageway of air and food

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important function of the 3. esophagus

peristalsis= mov't of food from oral cavity --> stomach

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upper 1/3 of esphagus muscle

ONLY skeletal muscle helps with swallowing

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middle 1/3 of esophagus muscle

skeletal AND smooth muscle

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lower 1/3 of esophagus muscle

ONLY smooth muscle

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at the distal end of the esophagus, sphincter b/t esophagus and stomach=

lower esophageal sphincter = LES

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lower esophageal sphincter is a __ way valve

one

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LES opens when you ___

swallow, to allow food IN the stomach

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LES closes ___

after you swallow, to prevent food from getting back into esophagus

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problems with LES closing=

GERD/ acid reflux/ food regurgitation

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esophageal hiatus

where the esophagus passes through the diaphragm

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the stomach is the most ____ in the GI tract

descendable (can stretch out the most)

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contents of stomach drain into...

duodenum of small intestine

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functions of the stomach:

  1. storage of food

  2. initial digestion of PROTEINS

  3. helps kill bacteria (b/c acidic)

  4. assists with the creation of chyme

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chyme=

mixture of food with hydrochloric acid

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initial digestion of proteins occurs in the:

stomach

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initial digestion of carbs occurs in the:

The mouth (by the enzyme salivary amylase)

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sphincter at the proximal end of the stomach=

LES (esophagus --> stomach)

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sphincter at the distal end of stomach=

pyloric sphincter (stomach --> small intestine)

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top region of the stomach=

fundus

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main portion/middle of stomach=

body

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bottom region of stomach=

antrum

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inner lining of stomach is highly convoluted: the folds=

rugae

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groves between the rugae/folds =

gastric pits

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function of rugae/folds=

secrete a variety of chemicals/exocrine hormones (act locally within stomach)

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rugae/folds AKA (because the secrete hormones)

gastric glands

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6 different types of cells within the folds that act as gastric glands=

  1. goblet cells

  2. parietal cells

  3. chief cells

  4. ECL cells

  5. G cells

  6. D cells

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goblet cells secrete

mucus (also found in nose and airway, etc.)

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what is the function of muscus?

invade / capture foreign bodies

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parietal cells produce:

hydrochloric acid (HCL)

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What is HCl used for?

digestion- breaks down food

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parietal cells also make:

Intrinsic Factor (a protein)

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what's the role of intrinsic factor?

allows absorption of B12 to blood

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B12 helps with

making RBCs in the bone marrow

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what happens if you don't have B12

PERNICIOUS ANEMIA

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what is the cause of pernicious anemia?

no intrinsic factor ---> B12 cannot make RBCs in bone marrow

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pathology of parietal cells @ level of GI tract leads to-->

no intrinsic factor, B12 deficiency -->pernicious anemia! (or no HCL)

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pernicious anemia is a pathology @ the level of:

GI tract

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chiefs cells AKA

zygogenic cells

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chief cells secrete:

PEPSINOGEN

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pepsinogen is an inactive form of -->

PEPSIN

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pepsin =

enzyme that breaks down proteins!

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initial digestion of protein occurs at stomach b/c....

chief cells ---> pepsinogne --> pepsin --> breaks down proteins

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ECL cells AKA

enterochromolin cells

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ECL cells release

HISTAMINE

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Histamine causes

more gastric acids to be produced (acts as a regulator)

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G cells secrete

GASTRIN

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gastrin is a precursor that

increases release of gastric acids

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G cells controls release of

gastric acids thru gastrin

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G cells --> gastrin --> ___ --> ____

parietal cells ---> HCL acid

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D cells "delta cells" secrete:

SOMATOSTATIN

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What does somatostatin do?

REDUCES gastric acid secretion

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how to increase release of gastric acids?

ECL cells --> histamine --> parietal cells --> more HCL or G cells --> gastrin --> parietal cells --> more HCL

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how to decrease release of gastric acids?

D cells --> somatostatin --> parietal cells --> less HCL

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structure of small intestine

-the largest part of GI tract -highly convoluted

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folds of small intestine are called:

villi

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why is the small intestine highly convoluted?

increases surface area for more absorption, so nutrients can go from SI to blood

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