Digestive System

Digestive system

Organ system that process food, extracts nutrients and eliminates residue

Five stages if digestion

1. Ingestion

2. digestion

3. Absorption

4. Compilation

5. Defecation

Ingestion

Selective intake of food

• what do you want to eat

Digestion

Mechanical and chemical breakdown of food into a form usable by the body

• catabolic

Absorption

Uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood and lymph

• inside of you

Compication

Absorbing water and consolidating the indigestible residue into feces

Defecation

elimination of feces

Mechanical digestion

the physical breakdown of food into smaller particles

• cuttign and grinding action of the teeth

• Chruning action of stomach and small intestines

• Increases surface area of food

Increasing surface area of food exposes…

more food surface to digestive enzyme

Chemical digestions

a series of hydrolysis reactions that breaks dietary macromolecule into their monomers (residues)

Chemical digestion is carried out by..

digestive enzymes produced by salivary glands, stomach, pancreas and small intestines

Results of chemical digestion

Polysaccharides into monosaccharides

Proteins into amino acids

Fats into monoglycerdies and fatty acids

nucleic acids into nucleotides

Some nuteirnts are present in a usable form in ingestied food and can be ….. and Ex:

directly absorbed

• Vitamens, amino acids, minerals, cholesterol and water

Digestive system has two subdivisions

Digestive tract and accessory organs

Digestive tract

Alimentary canal

• 30 ft long muscular tube extending from mouth to anus

• Includes Mouth, pharynx, esophagus, stomach, small intestine, and large intestine

Gastrointestinal tract (GI tract)

the stomach and intestines

Accessory organs

Aren’t tube but help process

• Teeth

• tongue

• salivary glands

• liver

• gallbladder

• pancreas

Digestive wall consisting layers of…

mucosa

submucosa

muscularis externa

serosa

Mucosa

• epithelium

• Lamina propia

  • Muscularis mucosae

Submucosa

very vascular

Muscularis externa

inner circular layer

outer longitudinal layer

Serosa

Areolar tissue

Mesothelium

Enteric nervous system

nervous network in esophagus, stomach and intestines that regulates digestive tract motility, secretion and blood flow

• have 1 million neurons

• Can function independently of CNS

but CNS usually exerts influence on its action

enteric nervous system is often considered part of …

autonomic nervous system

Enteric nervous system is composed of

two networks of neurons

• submucosal plexus

• Myenteric plexus

Submucosal plexus is in..

In submucosa

submucosal controls ..

Controls glandular secretions of mucosa

Controls movements of muscularis mucosae

Submucosal plexus = controls the inside lining.

• Glands → controls secretions (fluids).

• Muscularis mucosae → controls small movements of the lining.

Myenteric plexus

parasympathetic ganglia and nerve fibers between the two layers of the muscularis externa

Myenteric plexus controls …

Controls peristalsis and other contraction of musclaris externa

• push food through

Mesenteries

Connective tissue sheets that suspend stomach and intestines from abdominal wall

Losseness of Mesenteries allows…

Stomach and intestines to undergo strenuous contraction with free of movement in the abdominal cavity

Mesenteries holds..

abdominal viscera in proper relationship to each other

Mesenteries prevents intestines from becoming …

twisted and tangled by changes in body position and. by its own contractions

Mesenteries provides passage of,…

blood vessels and nerves that uspple digestive tract

Mesenteries contain many ….

lymph nodes and lymphatic vessels

Parietal peritoneum

a serous membrane that lines the wall of the abdominal cavity

Parietal peritoneum turns ..

inward along persterior midline

Parietal peritoneum froms …

dorsal mesentery

• a translucent two-layered membrane extending to digestive tract

the two layers of the mesentery separate pass around…

opposite sides of the organ forming the serosa

the two layers of the mesentery then come together on the…

far side of the organ and continue as another sheet of tissue, called the anterior (ventral) mesentery

• may hang freely in abdominal cavity

• May attach to the anterior abdominal wall or other organs

Lesser omentum

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

greater omentum

Hangs fromt he freater curvature of the stomach ( its left inferior margin)

• covers small intestine like an apron

• The inferior margin turns back on itself and passes upward

• Forms a deep pouch between its deep and superficial layers

Inner superior margin forms …

serous membranes around the spleen and transverse colon - mesencolon

Mesencolon

Extensio of the mesentery that anchors the colon to the abdominal wall

Intraperitoneal

when an organ is enclosed by mesentery on both sides

• considered within the peritoneal cavity

• Stomach, liver and parts of small and large intestine

Retroperitoneal

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

• considered to be outside the peritoneal cavity

• Duodenum, pancreas, and parts of the large intestine

Motility and secretion of the digestive tract are controlled by…

neural, hormonal and paracrine mechanisms

Neural control

short (myenteric ) reflexes

Long ( vagovagal) reflexes

short (myenteric ) reflexes

stretch or chemical stimulation acts through myenteric plexus

Long ( vagovagal) reflexes

parasympathetic stimulation of digestive motility and secretion

hormones

regulate digestive tract

• Chemical messengers secreted into bloodstream that stimulate distant parts of digestive tract

• Gastrin and secretin

Paracrine secretions

regulate digestive tract

• chemical messengers that diffuse through the tissue fluids to stimulate nearby target cells

the mouth is known as the

oral or buccal cavity

Functions of mouth

Ingestion (food intake )

taste and other sensory responses to food

chewing and chemical digestion

swalloing, speech and respiration

mouth is enclosed by..

cheeks

lips

palate

tongue

what epithelium line mouth

stratified squamous epithelium

keratinized in areas …

that are subject to food abrasion

• gums

• hard palate

non keratinized in areas like…

floor of mouth

soft palate

insides of cheeks

lips

Tongue

muscular, bulky, but remarkable agile and sensitive organ

• manipulates food in between teeth

• senses tase and texture of food

• can excrete food particles from the teeth after a meal

what epithelium covers surface of tongue

nonkeritinzed stratified squamous epithelium

Lingual papillae

bumps and projections that are the sites of most taste buds

Body of tongue

anterior two-thirds of tongue

• occupies oral cavity

Root of tongue

posterior one -third of the tongue

• it occupies the oropharynx

Palate

separates oral cavity from nasal cavity

• make it possible to breath while chewing food

hard palate

anterior portion that is supported by the palatine process of the macialle and the palatine bones

Soft palate

posterior with more spongy texture

• composed of skeletal muscle and glandular tissue

• no bone

uvula

conical medical projection visible at the rear of the mouth

• helps retain food in the mouth until one is ready to swallow

Regions of a tooth

Crown

Root

Neck

Gingival sulcus

Crown

portion about the gum

Root

the portion below the gum

• embedded in alveolar bone

Neck

the point wher crown, root and gum meet

Gingival sulcus

space between the tooth and the gum

• hygiene in the sulcus in important to dental health

Dentin

hard yellowish tissue that makes up most of the tooth

Enamel

Coverscrown and enck

• a non cellular secretion that cannot regenerate

Cement

Covers root

cementum and dentin are…

• are living tissue and can regenerate

Root canal

space in a root leading to pulp cavity in the crown

• nerves and blood vessels

Apical foramen

pore at the base end of each root canal

Occlusion

meeting of the teeth with the mouth closed

The human tooth is home to more than ___ species of microorganisms, especially ___

700

especially bacteria

plaque

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

calculus

cacified plaque

bacteria on teeth do what

metabolize sugars and release acids that dissolve the minerals of enamel and dentin to form dental caries

Root canal therapy is necessary if …

cavity reaches pulp

Mastication

Chewing

• breaks food into smaller pieces to be swallowed and exposes more surface to digestive enzymes

What is the first step in mechancil digestion

mastication

Food stimulates …

oral receptors that trigger an involuntary chewing reflex

Saliva

• moistens mouth

• begins starch and fat digestion

• cleanses teeth

• inhibits bacterial growth

saliva Dissolves molecules so they can

stimulate the taste buds

Saliva moistens food and …

binds it together into bolus to aid in swallowing

Bolus

a mass swallowed as a result of saliva binding food particles into a soft, slippery , easily swallowed mass

Pharynx

Muscular funnel connecting oral cavity to esophagus and nasal cavity to larynx

Pharynx is where what intersect

Digestive and respiratory tracts intersect

Pharynx has dep layer of

longitudianal skeletal msucle

Pharynx has superficial layer of

circular skeletal muscles that form pharyngeal constrictors that force food downward during swallowing

when not swallowing

the inferior constrictor ( upper esophageal sphincter ) remains contracted to exclude air from the esophagus

Disappears at the time of death when the muscles relax, so it it a physical sphincter and not an anatomical structure

Esophagus

Straight muscular tube 25-30 cm long

Extends from Pharynx to cardial orifice of stomach

nonkaretinized stratified squamous epithelium

Lower esophageal sphincter

food pauses here because of constriction

• prevents stomach contents from regurgitating into the esophagus

• Protects esophageal mucosa from erosive stomach acid

Heart burn

Burning sensation produced by acid reflux into the esophagus

Swallowing ( deglutition )

a complex action involving over 22 muscles in the mouth, Pharynx and esophagus