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