Ch. 25- Digestive System

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Digestive System

The organ system that processes food, extract nutrients from it and eliminates the residue.
Also can be called "disassembly line".

Ingestion

Selective intake of food.

Digestion

The mechanical and chemical breakdown of food into a form usable by the body.

Absorption

The uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood or lymph.

Compaction

Absorbing water and consolidating the indigestible residue into feces.

Defecation

Elimination of feces.

Mechanical digestion

The physical breakdown of food into smaller particles.

Chemical digestion

a series of hydrolysis reactions that break dietary macromolecules into their monomers (residues): polysaccharide into monosaccharides, proteins into amino acids, fats into monoglycerides and fatty acids and nucleic acids into nucleotides.

Gastroenterology

The study of the digestive tract and the diagnosis of its disorder.

Digestive tract

a muscular tube extending from mouth to anus, measuring about 9m (30 ft) long in the cadaver.
Also known as "alimentary canal".

Accessory organs

teeth, tounge, salivary glands, liver, gallbladder and pancreas.

Mucosa (mucous membrane)

lining the lumen consists if an inner epithelium, loose connective tissue and a thin layer of smooth muscle.

lamina propria

a loose connective tissue.

muscularis mucosae

a thin layer of smooth muscle.

Submucosa

think layer of loose CT containing blood vessels, lymphatic vessels, a nerve plexus, and in some places, glands that secrete lubricating mucus into the lumen.

muscularis externa

two layers of smooth muscle near the outer surface of the digestive tract; the inner layer encircles the tract and the outer layer runs longitudinally.

serosa

composed of a thin layer of areolar tissue topped by a simple squamous mesothelium.

adventitia

a fibrous connective tissue layer surrounding the pharynx, esophagus and the rectum.

enteric nervous system

a nervous network in the esophagus, stomach, and intestines that regulated digestive tract motility, secretion, and blood flow. Composed of 2 network: submucosal plexus and myenteric plexus.

submucosal (Meissner) plexus

in submucosa. it controls glandular secretion of mucosa and the movements of muscularis mucosae.

myenteric (Auerbach) plexus

parasympathetic ganglia and nerve fibers between the two layers of the muscularis interna. It controls peristalsis and other contractions of muscularis externa.

mesenteries

connective tissue sheets that loosely suspend the stomach and intestines from the abdominal wall.

parietal peritoneum

a serous membrane that lines the wall of the abdominal cavity.

dorsal mesentery

a translucent two-layered membrane extending to the digestive tract.

ventral mesentery

sheet of tissue that continues beyond the digestive organs. it hangs freely in the abdominal cavity or it may attach to the ventral abdominal wall.

lesser omentum

a ventral mesentery that extends from the lesser curvature of the stomach to the liver.

greater omentum

hangs from the left inferior margin (greater curvature) of the stomach and loosely covers the small intestine like an apron.

mesocolon

the mesentery (folds of peritoneum) that attach the colon to the posterior wall of the abdominal cavity.

intraperitoneal

when an organ is enclosed by mesentery on both sides.

retroperitoneal

when an organ lies against the posterior body wall and is covered by peritoneum on the anterior side only.

What control the motility and secretion of the digestive tract?

motility and secretion of the digestive tract are controlled by neural, hormonal, and paracrine mechanisms.

Short ( myenteric) reflexes

stretch or chemical stimulation acts through myenteric plexus.

Long (vagovagal) reflexes

parasympathetic stimulation of digestive motility and secretion.

What hormone does the digestive tract produce?

the digestive tract produce gastrin and secretin and paracrine secretion such as histamine and prostaglandins.

Mouth (oral or buccal cavity)

Its function include ingestion, taste and other sensory responses to food, chewing, chemical digestion, swallowing, speech and respiration.

oral fissure

the anterior opening between the lips.

fauces

the posterior opening into the throat.

labial frenulum

the median fold that attaches each lip ot the gum, between the anterior incisors.

vestibule

the space between the cheeks or lips and the teeth.

Lips are divided into 3 areas:

1. Cutaneous area, 2. red area (vermilion) and 3. labial mucosa.

hormones

chemical messengers secreted into bloodstream, and stimulate distant parts of the digestive tract.

Tongue

muscular, bulky, but remarkably agile and sensitive organ. it manipulates food between teeth while it avoids being bitten, it can extract food particles from the teeth after a meal and it sensitive enough to feel a stray hair in a bite of food.

lingual papillae

bumps and projections on the tongue that are the sites of the taste buds.

body

anterior two-thirds of the tongue occupies oral cavity.

root

posterior one-third of the tongue occupies the oropharynx.

vallate papillae

a V-shaped row of papillae that mark the boundary between the body and root of the tongue.

terminal sulcus

groove behind the V-shaped vallate papillae.

lingual frenulum

median fold that attaches the body to the floor of the mouth.

intrinsic musclea

contained entirely within the tounge, produce the relatively subtle tongue movements of speech.

extrinsic muscles

with origins elsewhere and insertions in the tounge, produce the stronger movements of food manipulation. Includes genioglossus, hyoglossus, palatoglossus and styloglossus.

lingual glands

secrete a portion of the saliva. The lingual tonsils are contained in the root.

Palate

separating the oral cavity from the nasal cavity, making it possible to breath while chewing food.

Hard palate

supported by the palatine processes of the maxillae and by the smaller palatine bones.

soft palate

a spongy texture and is composed mainly of skeletal muscle and glandular tissue, but no bone.

uvula

small projection hanging from the back middle edge of the soft palate.

palatoglossal arch

anterior membrane to the palatine tonsils.

palatopharyngeal arch

posterior membrane to the palatine tonsils.

Teeth (dentition)

serve to masticate the food, breaking it into smaller pieces.

incisors

chisel-like cutting teeth used to bite off a piece of food.

canines

are more pointed and act to puncture and shred the food.

premolars and molars

for crushing and grinding.

alveolus

a bony socket in the alveolar ridge that holds a tooth. form a joint called a gomphosis between the tooth and bone.

periodontal ligament

lined by alveolus. A modified periosteum whose collagen fibers penetrate into the bone on one side and into the tooth on the other.

Gum (gingiva)

covers the alveolar bone.

crown

portion above the gum.

root

the portion below the gum, embedded in alveolar bone.

neck

where the crown, root and gum meet.

gingival sulcus

space between the tooth and gum.

dentin

hard yellowish tissue that makes up most of the tooth.

enamel

covers crown and neck.

cementum

covers root.

cells of the cementum (cementocytes)

are scattered more or less randomly and occupy tiny cavities similar to the lacunae of bone.

Cells of the dentin (odontoblasts)

line the pulp cavity and have slender processes that travel through tiny parallel tunnels in the dentin.

pulp cavity

the central cavity of a tooth containing the pulp (including the root canal).

root canal

the passage in the root of a tooth through which its nerve and blood vessels enter the pulp cavity.

pulp

a mass of loose connective tissue, blood and lymphatic vessels and nerve.

apical foramen

pore at the basal end of each root canal.

occlusion

meeting of the teeth with the mouth closed.

occlusal surface

the surface where occlusion happen and this has two rounded bumps called cusps.

deciduous teeth(milk teeth)

ages 6-30 months. Has 20 teeth.

permanent teeth

between 6-25 yrs of age, they replace the deciduous teeth by 32 teeth.

wisdom teeth

erupt around ages 17-25.

impacted

so crowded against neighboring teeth and bone that they cannot erupt.

plaque

sticky residue on the teeth made up of bacteria and sugars.

calculus

calcified plaque.

mastication (chewing)

breaks food into smaller pieces to be swallowed and exposes more surface to the action of digestive enzymes.

saliva

moistens the mouth, digests a little starch and fat, cleanses the teeth, inhibits bacterial growth, dissolves molecules so they can stimulate the taste buds, and mostens food and binds particles together to aid in swallowing.

salivary amylase

enzyme that begins starch digestion in the mouth.

lingual lipase

enzyme that is activated by stomach acid and digests fat after the food is swallowed.

mucus

binds and lubricates the mass of food and aids in swallowing.

lysozyme

enzyme that kills bacteria.

immunoglobulin A (IgA)

an antibody that inhibits bacterial growth.

electrolytes

Na+, K+, Cl-, phosphate and bicarbonate.

intrinsic salivary glands

small glands dispersed amid other oral tissues.

lingual glands

in the tongue - produce lingual lipase.

labial glands

inside of the lips.

buccal glands

inside of the cheek.

extrinsic salivary glands

three pair connected to oral cavity by ducts.

parotid gland

located beneath the skin anterior to the earlobe.

mumps

an inflammation and swelling of the parotid gland caused by a virus.

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