HUMAN ANATOMY: Digestive System

digestive system

function is to break down food/drink into smaller units of absorbable nutrients which are used by your own body to generate energy

alimentary canal

structures form long tube that break down food (usually 24 hours: mouth, pharynx, esophagus, stomach, small intestine, and large intestine

accessory digestive organs

participate in digestive process but food does not pass through these structures; tongue, salivary glands, liver, gallbladder, and pancreas

ingestion

put food into mouth; extracellular process

propulsion

movement of food through canal; extracellular process

peristalsis

an organized contraction and relaxation of smooth muscle layers that propels food through the alimentary canal in one direction

mechanical digestion

physical break down of food particles; extracellular process

segmentation

contractions of smooth muscle move chyme back and forth within canal to allow mixing and further break down

chemical digestion

enzymes break down food particles; extracellular process

absorption

particles (sugars, fatty acids, etc) transported from canal into blood and lymph capillaries

defecation

indigestible products eliminated from body as feces; extracellular process

lumen

inside space of tubular structure

mucosa

innermost layer of alimentary canal and lines the lumen; has three sublayers

submucosa

second innermost layer of alimentary canal; higher concentration of collagen fibers for more support, highly vascularized, glands, submucosal nerve plexus

muscularis externa

second outermost layer of alimentary canal; two layers of smooth muscle (circular and longitudinal) and myenteric nerve plexus

serosa (visceral peritoneum)

outer surface of alimentary canal

epithelium

sublayer of mucosa; continuous with many digestive glands and functions include mucus production, absorption, protection, etc.

lamina propria

sublayer of mucosa; loose areolar connective tissue, capillary rich (absorption), MALT

MALT

mucosa associate lymphoid tissue; provides defense against bacteria

muscularis mucosa

sublayer of mucosa; thin layer of smooth muscle specializes in localized movements

submucosal nerve plexus

control of muscle cells, glandular secretions, etc

circular musclaris externa

inner layer, typically squeezes tube

longitudinal musclaris externa

outer layer, typically shortens tube; peristalsis and segmentation

serous membrane

simple squamous epithelium within a loose areolar connective tissue

adventita

fibrous CT that forms outer layer of esophagus (does not have serosa)

myenteric nerve plexus

controls peristalsis and segmentation; within muscularis externa

nerve plexuses

allow for localized response within visceral organs

oral cavity

chemical and physical digestion; stratified squamous epithelium and no muscularis externa or serosa/adventita

lips

margin between skin and oral cavity; not as keratinized as skin

teeth

accessory digestive organs

heterodont dentition

different shapes of teeth for different jobs

deciduous teeth

20 total erupt typically between ages 6 months to 6 years

permanent teeth

32 total that gradually deciduous

mandible

jaw

incisors

four pairs with one root; surface good for cutting and shearing food

canines

two pairs with one root; surface good for holding and tearing

premolars

four pairs with at least two cusps and 1 or 2 roots; rounded broad surface for grinding

molars

six pairs with four to five cusps and two to three roots; grinding surface

crown

portion of tooth above the gumline

neck

portion of tooth contained within gum tissue

root

portion of tooth contained within bone

pulp

layer of tooth composed of loose areolar CT, provides nutrients and sensation, odontoblasts

odontoblasts

create dentin

dentin

largest layer of tooth; collagen and minerals, no cells or blood vessels, harder than bone

enamel

layer of tooth that is 99% calcium; no cells or blood vessels, ameloblasts

ameloblasts

create enamel

cementum

layer of tooth that anchors tooth into place; calcified connective tissue similar to bone

cementoblasts

continually replace cementum

periodontal ligaments

dense connective tissues that attaches cementum of tooth to bony socket

cavity

enamel and dentin erode when plaques made of sugars and and bacteria form on teeth; bacteria feed on sugars and produce acids that demineralize tooth surface

root canal

when pulp of canal is infected nerves and blood vessels are removed; pulp is removed and filled

tongue

skeletal muscle covered in keratinized stratified squamous epithelium; moves food, helps mix with saliva to form bolus

filiform papilla

rough surface of tongue

fungiform and circumvallate papilla

contain taste buds

lingual frenulum

fold of mucosa layer that connects tongue to floor of mouth

tongue tied

lingual frenulum extends too far forward, tip of tongue can’t move and speech is difficult

salivary glands

accessory digestive organs; exocrine glands, produce saliva (cleans teeth, taste, digestive enzymes, mucus), serous and mucous cells

mucous cells

secrete mucus, lubricant

serous cells

secrete digestive enzymes

parotid gland and duct

largest contains serous cells, furthest away (longer ducts) more of a watery secretion

submandibular gland

approximately 50/50 serous to mucus cells; ducts open lateral to lingual frenulum

sublingual gland and duct

mucous cells with several shorter ducts that empty below tongue

pharynx

connects oral cavity to esophagus and nasal cavity

oropharynx

stratified squamous epithelium

laryngopharynx

stratified squamous epithelium

esophagus

stratified squamous epithelium; connects pharynx to stomach, mucous glands in submucosa and mucosa secrete mucus to lubricate as bolus of food passes through

upper muscularis externa of esophagus

skeletal muscle

middle muscularis externa of esophagus

mix of skeletal and smooth muscle

lower muscularis externa of esophagus

smooth muscle

stomach

mechanic and chemical digestion takes four hours to turn food into chyme, absorbs primarily water and drugs; simple columnar epithelium, abundant mucous cells

rugae

folds of mucosa that increase surface area and allow stomach to expand

sphincters

thickened regions of muscularis externa

cardiac sphincter

prevents food from moving back to esophagus

pyloric sphincter

controls release of chyme into duodenum

oblique muscularis externa

innermost; exists only in the stomach

gastric pits

regions where epithelium pushes dow into gastric gland

gastric gland

connected to lumen through gastric pit; specialized cells

mucous neck cells

parietal cells

produce/secrete HCl which destroys bacteria and gastric intrinsic factor which helps with absorption

gastric intrinsic factor

absorption and transportation of vitamin B12

chief cells

produce/secrete pepsinogen

enteroendocrine gland

releases hormones; ex. gastrin signals both parietal and chief cells

pepsin

breaks down proteins in food; created when pepsinogen (chief cells) and HCl (parietal cell) mix which is stimulated by gastrin

undifferentiated stem cells

found at junction between gastric pits and gastric glands

gastric fistula

abnormal connection between stomach and skin that left open hole into stomach

small intestine

simple columnar epithelium; 9 to 15 ft long where most absorption and chemical digestion occurs, chyme moves through peristalsis and segmentation

duodenum

shortest (5%) and busiest part of small intestine; receives chyme from stomach, digestive enzymes from pancreas and bile from liver/gallbladderj

jejunum

where majority of absorption occurs; 40%

ileum

longest portion (55%); absorption also occurs here and drains into large intestine

gallbladder

stores bile and breaks down fat; sphincters relax to let bile in; right below the right lobe of the liver

pancreas

empties directly into duodenum and adds digestive enzymes; pancreatic juices neutralize chyme

hepatopancreatic sphincter

the final control ‘valve’; controls bile and pancreatic juices

plicae circulares

easily visible folds of mucosa and submucosa in the small intestine

villi

folds of mucosa in small intestine and muscularis mucosa is responsible for localized movements; lamina propria, capillaries, lacteals

lacteals

transports fats that are too large to enter capillaries

enterocytes (absorptive cells)

transports nutrients across, majority of epithelial cells; protein pumps and endocytosis

protein pumps

move sugars, amino acids, etc

endocytosis

moves macromolecules

goblet cells

secrete mucus on to lumen to protect epithelium