A&P - Digestive System

6 functions of the digestive system/tract

6 functions of the digestive system/tract

• ingestion

• digestion

• secretion

• motility

• absorption

• defecation

structures of digestive tract from superior to inferior

• mouth/oral cavity

• oropharynx

• laryngopharynx

• esophagus

• stomach

• small intestine

• large intestine/colon

• rectum

• colon

digestive regulation sphincters/muscles from superior to inferior

• orbicularis oris

• upper esophageal sphincter

• lower esophageal sphincter

• pyloric sphincter

• ileocecal valve

• internal anal sphincter

• external anal sphincter

what does the upper esophageal sphincter separate

laryngopharynx and esophagus

what does the lower esophageal sphincter separate

esophagus and stomach

what does the pyloric sphincter separate

stomach and small intestine

what does the ileocecal valve separate

small intestine and large intestine

what does the internal anal sphincter separate

rectum and anus

what does the external anal sphincter separate

anus and external environment

ingestion definition

ingestion of macronutrients (carbs, proteins, and fats/lipids)

digestion definition

breakdown of macronutrients into micronutrients (can be chemical or mechanical)

secretion definition

secretions of enzymes, bile, H2O, acid, etc. are emptied into lumen of GI tract from accessory organs or cells lining organs/mucosa to perform CHEMICAL DIGESTION

motility definition

movement via smooth muscle contraction/relaxation

absorption definition

movement of micronutrients from GI tract into blood/lymph

defecation definition

elimination of waste products (feces)

4 main tissues of the digestive system

• nonkeratinized stratified squamous epithelium

• simple columnar epithelium

  • skeletal muscle

• smooth muscle

locations of nonkeratinized stratified squamous epithelium

• mouth/oral cavity

• oropharynx

• laryngopharynx

• esophagus

• anus (more external region)

function of nonkeratinized stratified squamous epithelium

protection against abrasion

locations of simple columnar epithelium

• stomach

• small intestine

• large intestine/colon

• rectum

• anus (more internal region)

function of simple columnar epithelium

secretion and absorption

2 specific structures of simple columnar epithelium

goblet cells → mucus (protects against acidity)

microvilli → increase surface area and therefore absorption

locations of skeletal muscle

• orbicularis oris

• upper esophageal sphincter

• external anal sphincter

what branch of nervous system is skeletal muscle innervated by

somatic NS

what branch of nervous system is smooth muscle innervated by

autonomic NS

locations of smooth muscle

• lower esophageal sphincter

• pyloric sphincter

• ileocecal valve

• internal anal sphincter

sympathetic NS effects on digestion

innervate smooth muscle and halts digestion, tonic contraction

parasympathetic NS effects on digestion

helps promote digestion, relax smooth muscles via vagus nerve (CN X)

locations of ingestion

mouth/oral cavity

locations of digestion

• mouth/oral cavity

• stomach

• small intestine

• large intestine (if leftovers)

locations of secretion

• mouth/oral cavity → salivary glands

• stomach → cells in mucosa

• small intestine → liver, gall bladder, pancreas

• large intestine → H2O

locations of motility

• oropharynx/laryngopharynx (peristalsis)

• esophagus (peristalsis)

• stomach (peristalsis and segmentation)

• small intestine (peristalsis and segmentation)

• large intestine (peristalsis)

peristalsis

propulsion of contents along length of GI tract (→)

segmentation

mixing/churning movement for mechanical digestion (

locations of absorption

• mouth/oral cavity

• stomach

• small intestine (majority)

• large intestine (water balance)

4 layers of GI wall

• mucosa

• submucosa

• muscular layer

• serosa

mucosa

• linine of the lumen

• has epithelial cells

• specific secretory/absorptive cells

• capillary beds that receive absorbed nutrients (blood/lymph)

submucosa

• connection b/w layers

• areolar CT

• continuation of blood and lymphatic vessels

• submucosal plexus of enteric NS

what plexus innervates the submucosa

submucosal plexus of enteric NS

muscular layer

• 2 layers of muscle

  • inner: circular layer → contraction and decrease diameter of lumen (segmentation)

  • outer: longitudinal layer → contraction is key for peristalisis

• myenteric plexus of enteric NS

what plexus innervates the muscular layer

myenteric plexus of enteric NS

what type of motility is the inner/circular layer of muscular layer responsible for

• segmentation

• reduces diameter of lumen

what type of motility is the outer/longitudinal layer of the muscular layer responsible for

peristalsis

what serous membrane lines the surface of digestive organs

visceral peritoneum

what serous membrane lines the abdominal cavity

parietal peritoneum

function of peritoneal folds

anchor organs and serve as a pathway for nerves and vessels

what are the 3 types of peritoneal folds

• greater omentum

• lesser omentum

• mesentery

what is ingestion controlled by in the oral cavity/mouth

orbicularis oris and temporomandibular joint

what is the goal of mechanical digestion in the oral cavity/mouth

physically break down macronutrients to form a bolus that can be swallowed

absorbable nutrients of the 3 macronutrients

carbs → monosaccharides (ex. glucose)

proteins → amino acids

fats → fatty acids

what structures and muscles are involved in mechanical digestion in the mouth/oral cavity

• palate/cheeks

  • lips, teeth, tongue/genioglossus (skl. muscle)

• muscle of mastication/chewing

  • temporalis

  • masseter

goal of chemical digestion in the oral cavity/mouth

salivary glands secrete saliva through ducts into oral cavity to begin breakdown of macronutrients to micronutrients via enzymes

components of saliva

• H2O, ions, mucus, lysozymes

• salivary amylase

• lingual lipase

what are lysozymes

enzymes that break down

what is the function of mucus and H20 in saliva

to moisten the food

where is salivary amylase secreted

oral cavity

where does salivary amylase act

oral cavity

where is lingual lipase secreted

oral cavity

where does salivary amylase act

stomach

what does salivary amylase do

• acts on carbs

• breaks starches/polysaccharides down into disaccharides

what is salivary amylase regulated by

• Cl- stimulates salivary amylase

• stomach acid stops it from acting

what does lingual lipase do

• acts on fats

• breaks triglycerides down into fatty acids and glycerol

what is lingual lipase regulated by

stomach acid stimulates lingual lipase

overall main goal of oral cavity

• start carb digestion (enzymatic)

• mechanical formation of bolus

tissue type of mucosal lining of hard palate

nonkeratinized stratified squamous epi

what two bones form the hard palate

maxilla (anterior) & palatine (posterior)

location of esophagus

• in thoracic cavity

• posterior to trachea

tissue type of mucosal lining of esophagus

nonkeratinized stratified squamous epi (protect)

tissue type of submucosal lining of esophagus

areolar CT

tissue type of muscular layer of esophagus

superiorly in upper e. sphincter → skeletal muscle

inferiorly in lower e. sphincter → smooth muscle

along length of esophagus for peristalsis → smooth muscle

what layer is in the esophagus differs from normal structure

there is no serosa, instead it is the adventitia

what is the tissue type in the adventitia of the esophagus

only areolar CT (no simple squamous like in other serosa layers)

main overall goal/function of esophagus

no digestion or absorption only motility/conduction

when the bolus is pushed to the ------- region of the oral cavity by the tongue, it causes ------- of the oropharynx (voluntary)

posterior; distension

receptors in the ------- detect the distention of the oropharynx

oropharynx

what is the control center for the “bolus reflex arc”

pons and medulla

5 responses of the “bolus reflex arc”

• tongue and soft palate elevate

• epiglottis depresses

• upper esophageal sphincter

• peristalsis

• lower esophageal sphincter

why does the tongue and soft palate elevate in “bolus reflex arc”

• closes off nasopharynx and nasal cavity

• allows bolus to move through oropharynx

why does the epiglottis depress in “bolus reflex arc”

• closes off larynx and airway

• bolus moves into laryngopharynx

why does the upper esophageal sphincter relax in “bolus reflex arc”

bolus moves into esophagus (decrease somatic innervation)

in order for the upper esophageal to relax we have to decrease

somatic innervation

why does peristalsis occur in in “bolus reflex arc”

allow bolus to move down the esophagus

smooth muscle for peristalsis is innervated by what nervous system

parasympathetic NS

in order to increase peristalsis we would increase innervation from (sympathetic/parasympathetic)

parasympathetic

why does the lower esophageal sphincter relax in the “bolus reflex arc”

allows bolus to enter stomach

to relax the esophageal sphincter we have to

increase parasympathetic NS

decrease sympathetic NS

5 functions of the stomach

• reservoir for food/liquids

• mechanical digestion

• chemical digestion

• secretion of hormone gastrin in blood

• absorption of H2O, ions, fatty acids, aspirin, and alcohol

what do surface and neck mucous cells secrete

secrete mucus

function of mucus secreted by surface and neck mucous cells

coat surface of mucosa for added protection

what do parietal cells secrete

• intrinsic factor

• Hydrochloric acid (HCl)

function of intrinsic factor secreted by parietal cells

helps with vitamin B12 absorption in the small intestine

function of HCl secreted by parietal cells

protein digestion and kill microbes

what do chief cells secrete

• pepsinogen (inactive form of pepsin)

• gastric lipase

what is the function of pepsinogen secreted by chief cells

once active as pepsin it helps with protein digestion

what is the function of gastric lipase secreted by chief cells

fat digestion

what do G-cells secrete

gastrin

what is the function of gastrin secreted by G-cells

stimulate stomach activity

• contract lower esophageal sphincter

• increase motility

• stimulate parietal and chief cells

• relax pyloric sphincter

chemical digestion overview in the stomach: carbs

no chemical digestion of carbs in stomach

chemical digestion overview in the stomach: proteins

• proteins begin being broken down into peptides

• pepsinogen (inactive) → pepsin (active) → +protein digestion

• needs HCl to activate pepsinogen

chemical digestion overview in the stomach: fats

• fats broken down into monoglycerides and free fatty acids

• lingual lipase (HCl is needed to stimulate)

• gastric lipase

what structures are on the apical surface of a parietal cell

• H-K ATPase’s (proton pumps)

• K+ channels

• Cl- channels