GI tract

Functions of the digestive system

motility, secretion, absorption, storage and elimination

function 1: motility\=

*movement* of food thru GI tract

mechanisms that allow motility

1. ingestion
2. mastication
3. deglutition
4. peristalsis

ingestion\=

taking food into oral cavity

mastication\=

chewing

degultition\=

swallowing

peristalsis\=

rhythmic contraction of smooth muscle cells thru GI tract

lots of GI pathology comes from :

*motility* issues

dysphasia\=

difficulty swallowing
(example of GI pathology)

function 2: secretion\=

release of chemicals or hormones to allow digestion to occur

endocrine secretions\=

made in one place, acts in *another place*

exocrine secretion\=

released and acts *locally*

function 3: absorption\=

transfer of nutrients out of GI tract and into blood

function 4: storage and elimination\=

-temporary storage of food
-elimination of waste

GI tracts AKA:

"*alimentary* canal"

GI tract organ list\=

1. mouth
2. esophagus
3. stomach
4. SI
5. LI
6. rectum
7. anus

T/F GI tract is open on both ends

true, and continuous

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

thoracic
abdominal
*diaphragm*

what separates the thoracic cavity from abdominal cavity?

diaphragm

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

*esophageal hiatus*

accessory organs\=

liver, pancreas, salivary glands, teeth, gallbladder

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

1. mucosa (inner most)
2. submucosa
3. muscularis
4. serosa (outer most)

2 major functions of mucosa layer\=

1. absorption: transfer of nutrients
2. secretion: or chemicals to help with digestion

anatomy of mucosa layer\=

highly convoluted
-peaks and troughs, ridges

convolutions of mucosa layer are called:

*Villi*

vili does what for GI tract:

increases surface area available for absorption of nutrients

anatomy of submucosa:

relatively thick layer

submucosa contains:

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

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

*nerve endings* in the submucosa are under what control?

*autonomic N.S* control

muscularis layer anatomy:

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

serosa anatomy:

outermost, *protective layer*, made of *connective tissue*

what nervous systemcontrols GI activity?

*autonomic* (parasymp. and sympathetic nervous systems)

parasympathetic nervous system is GI \______

excititory

sympathetic nervous system is GI \_____

inhibitory

GI excitatory (PsNS)\=

increase peristalsis
increase motility
increase secretion of hormones/chemicals

GI inhibitory (SNS)\=

decrease peristalsis
decrease motility
decrease secretion of hormones/chemicals

what occurs at the 1. mouth?

mastication

mastication @ the mouth\=

chewing + mixing of food with saliva

important enzyme in saliva\=

*salivary amylase*

What does salivary amylase do?

breaks down complex carbohydrates (polysaccharides)

polysaccharides are first broken down where?

*in the mouth* (bc of salivary amylase)

initial digestion of carbohydrates begins \_______

*in the mouth* (bc of salivary amylase)

2. pharynx\=

common passageway of air and food

important function of the 3. esophagus

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

upper 1/3 of esphagus muscle

ONLY *skeletal* muscle
*helps with swallowing*

middle 1/3 of esophagus muscle

skeletal AND smooth muscle

lower 1/3 of esophagus muscle

ONLY *smooth* muscle

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

*lower esophageal sphincter* \= LES

lower esophageal sphincter is a \__ way valve

one

LES opens when you \___

swallow, to allow food IN the stomach

LES closes \___

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

problems with LES closing\=

GERD/ acid reflux/ food regurgitation

esophageal hiatus

where the esophagus passes through the diaphragm

the stomach is the most \____ in the GI tract

descendable (can stretch out the most)

contents of stomach drain into...

duodenum of small intestine

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

chyme\=

mixture of *food with hydrochloric acid*

initial digestion of proteins occurs in the:

stomach

initial digestion of carbs occurs in the:

The mouth
(by the enzyme salivary amylase)

sphincter at the proximal end of the stomach\=

LES (esophagus --\> stomach)

sphincter at the distal end of stomach\=

pyloric sphincter
(stomach --\> small intestine)

top region of the stomach\=

fundus

main portion/middle of stomach\=

body

bottom region of stomach\=

antrum

inner lining of stomach is highly convoluted: the folds\=

*rugae*

groves between the rugae/folds \=

*gastric pits*

function of rugae/folds\=

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

rugae/folds AKA (because the secrete hormones)

*gastric glands*

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

goblet cells secrete

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

what is the function of muscus?

invade / capture foreign bodies

parietal cells produce:

hydrochloric acid (HCL)

What is HCl used for?

digestion- breaks down food

parietal cells also make:

*Intrinsic Factor* (a protein)

what's the role of intrinsic factor?

allows absorption of B12 to blood

B12 helps with

making RBCs in the bone marrow

what happens if you don't have B12

*PERNICIOUS ANEMIA*

what is the cause of pernicious anemia?

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

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

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

pernicious anemia is a pathology @ the level of:

GI tract

chiefs cells AKA

zygogenic cells

chief cells secrete:

*PEPSINOGEN*

pepsinogen is an inactive form of --\>

*PEPSIN*

pepsin \=

enzyme that breaks down *proteins*!

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

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

ECL cells AKA

enterochromolin cells

ECL cells release

*HISTAMINE*

Histamine causes

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

G cells secrete

*GASTRIN*

gastrin is a precursor that

increases release of gastric acids

G cells controls release of

gastric acids thru gastrin

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

parietal cells \---\> HCL acid

D cells "delta cells" secrete:

*SOMATOSTATIN*

What does somatostatin do?

REDUCES gastric acid secretion

how to increase release of gastric acids?

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

how to decrease release of gastric acids?

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

structure of small intestine

-the largest part of GI tract
-highly convoluted

folds of small intestine are called:

villi

why is the small intestine highly convoluted?

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