Digestive System: Mouth to Stomach

alimentary canal

breakdown of food and absorption of digested fragments through lining

• GI tract

alimentary canal

The following organs make up the _____ ______

• mouth, pharynx, esophogus, stomach, small intestine, large intestine, anus

accessory digestive organs

organs not part of GI tract, but contribute to digestion

• produce a variety of secretion that contribute to food breakdown

accessory digestive organs

these organs are part of this:

• teeth, tongue, gallbladder, salivary glands, liver, pancreas

ingestion

first part of digestive process

• taking food into the GI tract (occurs at mouth)

propulsion

moving through alimentary canal

• second part of digestive process

• swallowing

• peristalsis

peristalsis

involuntary, alternating contractions and relaxation to mix food up

mechanical digestion

Third part of digestive process that physically prepares food for digestion via enzymes

• chewing and mixing food with saliva by tongue

• churning by stomach

• segmentation

segmentation

local constriction of small intestine that mixes food with juices and increases efficiency of absorption by repeadetly moving food over intestinal walls

• part of mechanical digestion

chemical digestion

4th step in digestion

• series of catabolic steps that food molecules are broken down by enzymes in the lumen.

• begins at mouth, and complete in small intestine

absorption

5th step in digestion

• passage of digested foodstuff from lumen of GI tract through mucosal cells by active or passive transport into blood or lymph

defecation

6th step in digestion

• excretion of indigestible substance from the body via the anus in form of feces

peritoneum

serous membrane of the abdominopelvic cavity made up of

• visceral peritoneum

• parietal peritoneum

• peritoneal cavity

• mesentery

visceral peritoneum

covers external surface of most digestive organs - continuous with parietal

parietal peritoneum

covers body wall of peritoneum

peritoneal cavity

in between the visceral and parietal peritoneum

• responsible for lubricating mobile digestive organs so they can move across one another

mesentery

double layer of peritoneum that extends from digestive organ to the body wall

contains:

• retroperitoneal organs

• intraperitoneal organs

mesentery

functions of this

1. anchor organ in place

2. route for blood vessels, nerves to reach digestive tract

3. stores fat

retropreitoneal organs

organs that don’t retain mesenteries

• pancreas, parts of large intestine

intraperitoneal organs

organs that do keep mesenteries

• stomach

peritonitis

inflammation of the periteneum

• treatment is removing infectious debris and megadoses of antibiotics

peritonitis

caused by: abdominal wound, perforating ulcer, poor sterile technique during abdominal surgery, burst appendix

peritonitis

results in: peritoneal covering sticking together at infection site

• if infection becomes widespread: can be lethal

alimentary canal

these four layers make up this:

• mucosa

• submucosa

• muscularis externa

• serosa

mucosa

layer of alimentary canal that is responsible for secreting, absorbing, and protecting

• three sublayers

  • lining epithelium

  • lamina propria

  • muscularis mucosae

lining epithelium

mucus-secreting cells

lamina propria

loose areolar tissue; contain lymphoid follicles (MALT - mucosa associated lymph tissue)

muscularis mucosae

smooth muscle cells

submucosa

areolar tissue with rich blood and nerve supply

• abundant elastic fibers so stomach and stretch and retain shape

muscularis externa

responsible to peristalsis and segmentation

• circular layer and longitudinal layers of smooth muscle

• sphincters

sphincters

ring-shaped muscles that control the opening and closing of body passages, regulating the flow of substances like food, liquid, and waste

serosa

protective outermost layer of alimentary canal; visceral peritoneum

• retroperitoneal organs: have ___ and adventitia

• esophagus: only adventitia

enteric neurons

in-house nerve supply

• made of:

  • submucosal nerve plexus

  • myenteric nerve plexus

submucosal nerve plexus

submucosa

• sensory and motor neurons

• regulates activity of smooth muscle and glands

myenteric nerve plexus

lies between circular and longitudinal layers

• supply GI wall and GI tract mobility

enteric neurons

these are linked to the CNS by viscera afferent neurons and branches of sympathetic and parasympathetic nervous system

mouth

• only part of alimentary canal associated with ingestion

• continuous with oropharynx

• palate

• tongue

palate

roof of mouth

tongue

• during chewing, grips food and repositions

• forms bolus with saliva

• initates swallowing

• important for speech

salivary glands

secrete saliva

saliva

purpose of this

• cleanse mouth

• dissolves food chemicals for tase

• moistens food and aids in bolus formation

• contains enzymes for breakdown of starch

saliva

composition of ____

• water

• slight acidity

• electrolytes

• amylase and lingual lipase

• mucin, lysozyme, IgA antibodies

• urea and urea acid

parotid gland

anterior to ear, between masseter muscle and skin

• salivary gland

sublingual gland

salivary gland under tongue

submandibular gland

medial aspect of mandibular body

• salivary gland

saliva secretion

diseases that inhibit ___ ____ can cause:

• cavities

• difficulty talking, swallowing, eating

• Halitosis: bad breath

oropharynx, laryngopharynx, esophagus

food passes from mouth into _____ to the _____ and then to _____

esophagus

muscular tube that is ~25 cm long

esophagus hiatus

where esophagus pierces diaphragm and enters abdomen

cardiac orifice

where the esophagus joins stomach

• gastroesophageal or cardiac sphincter here

heartburn

• first symptom of gastroesophageal reflux disease

  • radiating substernal pain

  • caused by gastrojuices going back into esophagus

  • common in those with hiatal hernia

hiatal hernia

occurs when the stomach bulges up into the chest cavity through an opening in the diaphragm called the hiatus

esophagus

these are the four layers that make up ____

• mucosa and submucosa

• mucosa

• muscularis externa

• fibrous adventitia

mucosa and submucosa

form longitudinal folds when food isn’t present

• esophagus

submucosa

contain mucus secreting glands

• esophagus

muscularis externa

varies in composition: skeletal and smooth muscle

• esophagus

adventitia

what esophagus has instead of serosa

mastication

chewing

deglutition

swallowing

• buccal phase

• pharyngeal-esophageal phase

buccal phase

voluntary process where the tongue pushes the food bolus to the back of the oral cavity and into the pharynx.

pharyngeal-esophageal phase

the coordinated movement of food from the pharynx (throat) into the esophagus and then down into the stomach

amylase

enzyme in saliva that digests starch and glycogen

lingual lipase

fat digesting enzyme

stomach

temporary storage for food

• chemical breakdown of protein begins here

• food converted to chyme

50 mL, 4

stomach empty = ___, collapses inward formin

distended = up to __ L

cardiac/cardia

region of stomach near heart

fundus

dome-shaped part of stomach

pyloric region

wide, superior part of pyloris in stomach

lesser omentum

liver to lesser curvature of stomach

greater omentum

in stomach, hangs inferiorly from greater part of stomach to cover small intestine

ANS

innervation of stomach is done via __ ___ __

modified muscularis externa

layer of alimentary canal

• additional layer of smooth muscle that runs obliquely

  • allows stomach to churn and mix food

modified mucosa

layer of alimentary canal:

• goblet cells that produce a 2-layer mucus; gastric pits that lead to gastric glands that product gastric juices

mucus neck cells

acidic mucus

parietal cells

hydrochloric acid and intrinsic factor

• hydrochloric acid activates pepsin; HCl is why stomach is so acidic

chief cells

are pepsinogen or an inactive form of pepsin

• is a protein digesting enzyme

enteroendocrine cells

variety of hormone/hormone-like substances

• ex. gastin, histamine, endorphins, serotonin, cholecystokinin, somatostatin

mucosal barrier

factors that create ____ _____

• thick coating of bicarbonate mucus

• epithelial cells of mucosa joined by tight junctions (nothing can seep through)

mucosal barrier

factors that create ____ ____

• deep to gastric glands, which are external faces of PM of glandar cells are impermeable to HCl

• damaged epithelial mucosal cells are replaced rapidly

gastritis

DEF: inflammation of stomach wall

CAUSE: H pylori, breeches mucosal barrier

RESULT: damages tissue to promote gastric ulcers

RISK: too much secretion of HCl and mucus

stomach

location of protein digestion:

• denatured by HCl

• Pepsin

• Rennin: acts on milk protein in baby

stomach

secretion of intrinsic factor occurs here

• vitamin B12 absorption

gastric secretions

• controlled via neural and hormonal mechanisms

• stimuli from head, stomach, small intestines can promote or inhibit

cephalic phase

phase of gastric srecretion BEFORE food enters stomach

• lasts only a few minutes

• triggered via smell, taste, sight, or thought of food

gastric phase

phase of gastric secretion once food reaches stomach

• 2-4 hours long

• 2/3 of gastric juices released

• stimulated by distension, peptides, and low acidity

• gastrin

gastrin

hormone that stimulates stomach gland

intestinal phase

phase of gastric secretion made up of excitatory and inhibitory components

excitatory component

partially digested food fills duodenum

• stimulates intestinal mucosa cells to secrete intestinal gastrin

inhibitory component

as duodenum distends to accommodate the chyme

• prevents further food entry and reduces secretory activity

emesis (vomiting)

stomach emptying through oral cavity

• extreme stretching of stomach or small intestine, irritants

• diaphragm and abdominal walls contract, cardiac sphincter relaxes

• LOCATED IN MEDULLA OBLONGATA

1

stomach stretches but pressure remains unchanged until ___ L of food has been

reflex-mediated relaxation

the unchanged pressure during stomach filling is related to____ ____ ____

• made of two components

  • receptive and adaptive relaxation

receptive relaxation

coordinated relaxation of stomach as food moves down esophagus

adaptive relaxation

how stomach reflexively dilates in response to gastric filling

cardiac sphinster

• perstalsis during gastric contractile activity begins near ___ ____

pyloris

during gastric contractile activity contractions become stronger around ____

• food here is mixed and broken down

pyloric region

during gastric contractile activity, this region only allows liquids and small particles through barely open pyloric valve to the small intenstine

• rest sent back to stomach

peristalsis

intensity of ____ can be modified, but rate is constant

interstitial cells of cigal

rate of peristalsis is set by pacemaker cells called ____ ___ ___ ___

• depolarize/repolarize 3 times

• pacemakers are electrically couples to the rest of smooth muscle cells

basic electrical rhythm (BER)

the depolarization and repolarization 3 times/minute produces the stomach’s ___ ___ ___