anatomy chapter 23

digestion breaks larger food particles into

nutrients that are small enough to be absorbed into the bloodstream

main part of the digestive system - alimentary canal, aka gastrointestinal (go) tract (or digestive tract)

a long (""30ish" foot) tube that food passes through, from the mouth to the anal opening

the are many extra (accessory) organs that assist in the digestive process

such as the pancreas and liver, that produce secretions that dump into the gi tract to help with digestion

two kinds of digestion

mechanical and chemical

mechanical digestion

breaks particles into smaller pieces of the same chemical consistency ex. tearing a piece of bread in half

chemical digestion

changing the chemistry ex. enzymes changing polysaccharides [starch] into monosaccharides [glucose]

4 tissue layers to the "tube"

innermost mucosa, then submucosa, muscularis, and outer serosa

mucosa

epithelium (but type of epithelium varies depending on where it is along the canal)

submucosa

includes blood and lymphatic vessels

muscularis

double layer (circularis and longitudinal) of smooth muscle

serosa

connective tissue (also called adventitia) - visceral peritoneum

mesentery

holds digestive organs in place

parietal peritoneum

touches abdominal wall

visceral peritoneum

touches the organ

there is a fluid in the

space between the peritoneum

serosa is the

visceral peritoneum

chemical digestion starts in

the mouth

proteins into

amino acids

carbohydrates into

monosaccharides

lipids into

glycerol and fatty acids

nucleotides into

nitrogen bases

absorption

mainly from the small intestine (nutrients enter the bloodstream)

defecation

removal of undigested materials (shitting)

ingestion

entry of food

teeth, cheeks, lips, and the tongue are used to move food around in the mouth in the process of mechanic digestion

we call chewing (mastication)

propulsion

the action of driving or pushing forward.

swallowing (deglutition)

voluntary - occurs when the individual deems that the food is sufficiently shewed and pushes in from the mouth into the pharynx

peristalsis

involuntary- wavelike contractions that propel food along the digestive tract - using the two muscularis muscles (circularis and longitudinal) (also what pushes urine through ureters)

food is mechanically broken down in the mouth, but then reformed into a ball

called bolus - using mucus from salivary gland secretions

besides forming the bolus, mucus also

makes it slippery to aid in moving it through the pharynx, esophagus, and large intestines

longitudinal muscles in

front of the bolus contract (while circularis muscles in front of the bolus relax) which tends to open up the tube

circularis muscles behind

the bolus contract (while longitudinal muscles relax), pushing the food along

mouth structures 6

oral cavity, labia, palate, tongue, teeth, salivary glands

labia

lips

palate

hard (anterior) and soft (posterior)

tongue

muscular

tongue papillae

bumps with tastes buds

not all tongue papillae

are the same

tongue functions -facilitating ingestion

mechanical digestion (chewing/mastication & swallowing/deglutiton), sensation, vocalization

sensation

taste

three pairs of salivary glands

parotid, submandibular, sublingual

all three salivary glands

secrete salvia, though each has unique differences in secretory

sublingual gland

just below the tongue (thickest secretion with least amount of saliva amylase)

parotid gland

in upper jaw (watery secretion)

Submandubular gland

in lower jaw (watery secretion)

saliva

95.5% water, enzyme salivary amylase (used to break polysaccharides into disaccharides)

20

deciduous teeth (baby or milk teeth)

deciduous teeth

appear at about 6 months, fall out/ replaced by permanent teeth

32

permanent teeth

types of permanent teeth

incisors, cuspids, premolars, molars

incisors

sharp, used to bite into food

cuspids

pointed edge, tear up food

premolars

flatter shape, mash food

molars

several pointed cusps, crush food

crown

portion above the gum line (gingiva)

gum line

gingiva

enamel

protective (harder than bone) covering

dentin

bone like material under enamel

neck of the tooth

transition from crown (enamel not covering toward the bottom)

Root is embedded within

maxilla and mandible

the root of the tooth is held in place by

cementum & periodontal ligament

the root has no

enamel

pulp cavity

loose connective tissue, has blood vessels and nerves, and is surrounded by dentin

the pharynx is involved in

digestion and respiration

the pharynx run from posterior oral and nasal cavities to the

opening of the esophagus and larynx

Pharynx three subdivisions

nasopharynx, oropharynx, laryngopharynx

Esophagus

muscular tube, 10 inches in length, posterior to trachea

Esophagus is a passage of food

upper esophageal sphincter, lower esphageal sphincter

lower esophageal (aka cardiac - near heart) sphincter

prevents reflux of food/acid from the stomach

the esophagus is made up of

stratified squamous epithelium

esophagus's mucosa

secretes mucus to make food slide through

esophagus's muscularis

consists of circularis and longitudinal muscles for peristalsis

the stomach is not

THE major digestive organ (that would be the small intestine)

the stomach is

really mostly a storage "bladder" for ingested food (limited chemical digestion)

the stomach has four regions

cardia, fundus, body, pylorus

cardia

entry area from the esophagus

fundus

pouch above cardia

body

main area

pylorus

exit area (into the small intestine/duodenum)

curves of the stomach

greater curve - outer, lesser curve - inner

the muscularis layer of the stomach lining gains an extra layer of muscle

(oblique) besides the circularis and longitudinal layers

the three muscularis muscles in the stomach are used for propulsion as well as for

mixing up food in the stomach

the pyloric sphincter only slightly relaxes so that only a small amounts of

stomach contents empty (most gets "retropulsed"/swished back into the stomach - "mixing")

the churning of the stomach contents is important for

mechanical (and chemical) digestion, sort of like blending up the food

the stomach has ridges called

rugae

rug allows

for expansion (stretch) of the stomach (after big meals)

the mucosa lining in the stomach has small holes in it called

gastric pits

mucosa (neck) cells

lining in the stomach touching food and upper portion (neck) of the pits

mucus secretion in the stomach is VERY important to prevent

digestion of the stomach wal

mucosa creates a protective layer in the stomach and if it is compromised

ulcers may result

the food and secretions in the stomach are collectively called

chyme

the acid and enzymes in chyme could

break down digestive linings

the mucosal barrier protects from

self- digestion/ulcers

alkaline

rich (neutralizes acid) mucus

the mucosal barrier has

tight junctions between epithelial cells

in the mucosal barrier stem cells

quickly replace damaged cells

parietal cells

secrete HCl ("activates" pepsinogen) and intrinsic factor (necessary for absorption of Vitamin B12)

chief cells

secrete pepsinogen (enzyme that will chemically break down when activated)

Enertoendocrine cells

secrete hormones that control digestion

there are 3 regions of the small intestines

duodenum, jejunum, ileum