Anatomy: digestive system

digestive system function

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

your digestive tract is approximately 15-20 feet long. on average, how long do you think it takes for the sandwich you ate at lunch to completely pass through your digestive tract?

24 hours

alimentary canal

structures form long tube that breaks down food

- approximately 24 hours from ingestion to defecation

alimentary canal structures

1. mouth (oral cavity)

2. pharynx

3. esophagus

4. stomach

5. small intestine

6. large intestine

what makes up small intestine

duodenum, jejunum, ileum

accessory digestive organs

participate in digestive process but food does not pass through these structures

- tongue

- salivary glands

- liver

- gallbladder

- pancreas

ingestion

put food into mouth

propulsion

movement of food through canal

- swallowing -> voluntary

- peristalsis -> involuntary

peristalsis happens where

- esophagus

- stomach

- small intestine

peristalsis

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

mechanical digestion

- physical breakdown of food particles

- chewing, churning, segmentation

segmentation

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

chyme

food product being digested

chemical digestion

enzymes break down food particles

absorption

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

defecation

ingestible products eliminated from body as feces

anything passing through _______ is considered to be OUTSIDE the body and extracellular

the lumen of the alimentary canal

which processes are extracellular

- ingestion

- propulsion

- mechanical digestion

- chemical digestion

- defecation

which processes are intracellular

absorption

layers of organs of alimentary canal

1. mucosa

2. lines the lumen

3. muscularis externa

4. serosa

mucosa

- lines the lumen

- innermost layer

- 3 sublayers

- contains a stratified squamous epithelium

submucosa

support layer

- similar to loose areolar CT but higher concentration of collagen fibers provides more support

- highly vascularized

- glands connecting to lumen may project into submucosa

- submucosal nerve plexus

- areolar connective tissue

muscularis externa

muscle layer (red on diagram)

- 2 layers of smooth muscle

- myenteric nerve plexus

serosa

outer surface

- found around organs within abdominal cavity

- simple squamous epithelium with a thin loose areolar CT -> serous membrane

- visceral peritoneum

in which of the 4 main layers of the ailmentary canal would you expect to find an epithelium?

mucosa and serosa

3 sublayers of mucosa

1. epithelium

2. lamina propria

3. muscularis mucosa

epithelium

type varies by location

- mucus production, absorption, protection, etc

- continuous with many digestive glands

lamina propria

loose areolar CT

- MALT: Mucosa Associate Lymphoid Tissue provides defense against bacteria

muscularis mucosa

thin layer of smooth muscle

- localized movements

submucosa is highly vascularized

blood supply to mucosa for nutrient absorption

submucosal nerve plexus

control of muscle cells, glandular secretions, etc

- secretions of glands

- muscularis mucosa contractions

- within submucosa

2 layers of smooth muscle in muscularis externa

- circular layer

- longitudinal layer

circular layer of muscularis externa

inner layer, typically squeezes tube

longitudinal layer of muscularis externa

outer layer, typically shortens tube

- peristalsis and segmentation

the serosa is a simple squamous epithelium around organs that are within the abdominal cavity. another name for a serosa is:

visceral peritoneum

adventitia

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

- the esophagus is not contained within a body cavity lined by a serous membrane

nerve plexuses

- allow for localized response within visceral organs

- partly independent of CNS

intrinsic nerve plexuses

1. myenteric nerve plexus

2. submucosal nerve plexus

myenteric nerve plexus

- controls peristalsis and segmentation

- within muscularis externa

oral cavity

mouth

- ingestion of food

- mechanical digestion

- chemical digestion

oral cavity mechanical digestion

chewing

oral cavity chemical digestion

mixed with saliva which starts the breakdown of carbohydrates

which type of epithelium would you expect to find lining the oral cavity?

stratified squamous

why would you expect to see a stratified squamous epithelium in the oral cavity?

- the oral cavity is a continuation of the skin

- food is abrasive

- food and drink temperatures vary considerably

anatomy of the mouth

- stratified squamous epithelium

- thin submucosa layer anchored directly to underlying bone

- NO muscularis externa or serosa/adventitia

- lips: margin between skin and oral cavity

lips

margin between skin and oral cavity

- keratinized like skin

- no suderiferous or sebaceous glands

teeth

- accessory digestive organs

- heterodont dentition

- deciduous teeth

- permanent teeth

heterodont dentition

different shapes of teeth for different jobs

deciduous teeth

20 total erupt typically between ages 6 mo -> 6 yr

permanent teeth

32 total gradually replace deciduous

4 types of teeth (permanent dentition)

1. incisors

2. canines

3. premolars

4. molars

incisors

4 pairs

- surface good for cutting and shearing food

- 1 root

canines

2 pairs

- surface good for holding and tearing

- 1 root

premolars

4 pairs

- rounded, broad surface good for grinding

- at least 2 cusps

- 1 or 2 roots

molars

6 pairs

- grinding surface

- 4-5 cusps

- 2-3 roots

regions of a tooth

- crown

- neck

- root

crown of tooth

portion above gumline

neck of tooth

narrow portion contained within gum tissue

root of tooth

contained within bone

layers of a tooth

- pulp

- dentin

- enamel

- cementum

- periodontal ligaments

pulp layer of tooth

- loose areolar CT

- provides nutrients and sensation to tooth

- odontoblasts

loose areolar CT in pulp layer of tooth

blood vessels and nerves

odontoblasts

create dentin

dentin layer of tooth

- collagen (from odontoblasts) and minerals

- no cells or blood vessels

- harder than bone

enamel layer of tooth

- 99% calcium

- no cells or blood vessels

- layer is added during tooth development by ameloblasts

cementum layer of tooth

- calcified connective tissue similar to bone

- cementoblasts continually replace

periodontal ligaments

dense CT that attaches cementum of tooth to bony socket

the periodontal ligaments are part of what type of joint?

gomphosis

cavities

enamel and eventually dentin erode when plaques formed of sugars and bacteria form on teeth. bacteria feed on the sugars and produce acids that demineralize the tooth surface

root canal procedure

- procedure may be required when pulp within the canal becomes infected

- pulp is drilled out -> tooth is now "dead"

- cavity is sterilized and filled

- tooth is capped off to help strengthen it

permanent teeth in children who suffer from Celiac Disease may lack enamel, a condition known as hypoplastic dentition. This is not a symptom found in individuals who develop Celiac Disease as adults. Why?

- after all the permanent teeth have erupted, adults no longer have the cells needed to create enamel

- malabsorption of calcium could only impact tooth enamel levels while the enamel is being added to the tooth during its formation within the bone

- permanent teeth develop within the bone during childhood, so any abnormalities of the tooth would form at this time

tongue

- accessory digestive organ

- primarily skeletal muscle

- covered in keratinized stratified squamous epithelium

- moves food, helps mix with saliva to form bolus

- fusiform papilla

- fungiform and circumvallate papilla

fusiform papilla

rough surface

fungiform and circumvallate papilla

contain taste buds

lingual frenulum

- fold of mucosa layer

- connects tongue to floor of mouth

"tongue tied"

if lingual frenulum extends too far forward, the tip of the tongue cannot move and speech is difficult

which layer of the alimentary canal lines the lumen of a digestive organ?

mucosa

salivary glands

- accessory digestive organs

- exocrine glands

- produce saliva

saliva

- solvent

- dissolve food

- contains digestive enzymes

- contains mucus

- two types of cells: serous and mucous

saliva as a solvent

cleanse teeth

saliva for dissolving food

taste

saliva contains mucus

helps swallowing

salivary gland cell types

serous cells and mucous cells

serous cells of the salivary glands

secrete digestive enzymes

mucous cells of the salivary glands

secrete mucus

primary salivary glands

- parotid gland and duct

- submandibular gland and duct

- sublingual gland and duct

parotid gland and duct

- largest

- contains serous cells -> watery enzyme rich secretion

- ducts open lateral to lingual frenulum

submandibular gland and duct

- approximately 50/50 serous to mucous cells

- ducts open lateral to lingual frenulum

sublingual gland and duct

- mucous cells -> mucus secretion

- several ducts empty below tongue

which process of digestion does not typically take place in the oral cavity?

absorption of nutrients

pharynx

connects oral cavity to esophagus and nasal cavity

- muscularis externa has skeletal muscle for swallowing

parts of pharynx that are considered part of the digestive system

- oropharynx

- laryngopharynx

oropharynx

stratified squamous epithelium

laryngopharynx

stratified squamous epithelium

esophagus

- connects pharynx to stomach

- stratified squamous epithelium

- mucous glands in submucosa and mucosa secrete mucus to lubricate as bolus of food passes through

upper 1/3 of muscularis externa of esophagus is what kind of muscle

skeletal muscle

middle 1/3 of muscularis externa of esophagus is what kind of muscle

mix of skeletal and smooth

lower 1/3 of muscularis externa of esophagus is what kind of muscle

smooth muscle

the outer layer of the esophagus is called the _____

stomach

- food spends ~4 hours in stomach being turned into chyme

- simple columnar epithelium

- absorption