breaks down large pieces of food into smaller ones, but does not change chemical composition

uses enzymes to break down food particles, by changing them into simpler chemicals

Organs of the digestive system carry out mechanical and chemical digestion, as well as ingestion, propulsion, absorption, and defecation

The food passageway

Consists of organs that extend from the mouth to the anus

Mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anal canal

Muscular tube, about 8 m long

Consists of organs that empty secretions into alimentary canal

Food does not pass through them

Salivary glands, liver, gallbladder, pancreas

Innermost layer, mucous membrane

Folded in some areas, to increase surface area

Absorbs dietary nutrients, secretes mucus and enzymes

Connective tissue layer

Nourishes cells, transports absorbed food molecules

Outermost layer; serous fluid eliminates friction

Visceral peritoneum of organs within abdominal cavity

Muscle tissue; contains circular and longitudinal layers

Moves tube and food materials

2 types of movement in the alimentary canal

Example: segmentation in small intestine, churning in stomach

Muscle in small sections contracts rhythmically

Does not move materials in one direction

Moves materials in one direction

First part of alimentary canal

Ingests food

Functions as an organ of speech and sensory reception

Surrounded by lips, cheeks, tongue, palate

Includes oral cavity and vestibule

Mechanical breakdown of solid particles, mixes them with saliva

Form the lateral walls of the mouth

Contain muscles for facial expression and chewing

Have an inner lining of stratified squamous epithelium (moist)

Highly mobile structures that surround the mouth opening

Sensory receptors judge temperature and texture of food

Boundary between skin and mucous membrane inside mouth

Thick, muscular organ that occupies the floor of the mouth, and nearly fills the oral cavity when the mouth is closed

Connects tongue to floor of mouth

Projections that move food, contain taste buds

Lymphatic tissue masses on root of tongue

Forms the roof of the oral cavity

Consists of an anterior portion, the hard palate, and a posterior portion, the soft palate

consists of palatine processes of maxillae and palatine bones

Lymphatic masses on sides of tongue

consists of muscular arch, ends in uvula

Masses of lymphatic tissue in posterior wall of pharynx

Hardest structures in the body

Not part of skeletal system

Break food particles down to smaller pieces, beginning mechanical digestion

types of teeth

Moistens food particles and binds them together

Dissolves food so it can be tasted

Largest; secrete serous saliva with amylase

Floor of mouth;

serous + mucous

Under tongue;

mainly mucous

Produce a watery fluid, containing a digestive enzyme

called salivary amylase

Amylase splits starch and glycogen into disaccharides

Secrete mucus

Mucus binds food particles and lubricates food while

swallowing

Cavity posterior to the mouth

Extends from nasal cavity to esophagus

Tubular organ that extends from the pharynx to the

stomach

Parts of pharynx

Posterior to nasal cavity; air

passage; contain openings to auditory tubes

Posterior to oral cavity; air and

food passage

Posterior to larynx;

passageway to esophagus

Swallowing can be divided into 3 stages:

Voluntary stage

Saliva is mixed with chewed food, forming a bolus

Swallowing can be divided into 3 stages:

Starts as food reaches oropharynx, stimulates sensory receptors, and

triggers swallowing reflex

Peristalsis transports food in the esophagus to the stomach

Muscular food passageway from the

pharynx to the stomach (25 cm)

Penetrates the diaphragm through the

esophageal hiatus

J-shaped, pouch-like organ, about 25 to 30

centimeters long

• Inferior to the diaphragm, in the upper-left

portion of the abdominal cavity

• Rugae are folds of mucosa and submucosa

that allow for distention

Receives food from the esophagus

• Mixes food with gastric juice

• Initiates protein digestion

• Has limited absorption

• Moves food into small intestine

Portions of the stomach:

Region near opening to esophagus

Contains lower esophageal sphincter

Rounded area that rises above cardia

Temporary food storage, which sometimes contains swallowed air

Main portion

Lies between fundus and pylorus

Distal portion, closest to small intestine

Funnel-shaped pyloric antrum narrows to become pyloric canal

Pyloric sphincter: Circular smooth muscle, controls gastric emptying

Gastric Secretions

Inactive form of pepsin; secreted by chief cells

Gastric Secretions

Active enzyme that beaks down proteins into polypeptides;

forms from pepsinogen in presence of hydrochloric acid

Gastric Secretions

Fat-splitting enzyme, found in small quantities; action

inhibited by low pH

Gastric Secretions

Produced by parietal cells; converts pepsinogen

into pepsin

Gastric Secretions

Secreted by mucous cells; provides lubrication and protects

stomach lining

Gastric Secretions

Produced by parietal cells; required for absorption of

vitamin B12

Regulation of Gastric Secretion

Neural regulation:

decrease gastric activity

Regulation of Gastric Secretion

Neural regulation:

increase gastric activity; promote release

of histamine, which stimulates gastric secretion

Regulation of Gastric Secretion

Hormonal regulation:

Inhibits hydrochloric acid secretion

Regulation of Gastric Secretion

Hormonal regulation:

Increases gastric juice secretion

Regulation of Gastric Secretion

Hormonal regulation:

Released by small intestine cells when

proteins and fat enter the small intestine; decreases gastric motility

Result of reflex that empties stomach in reverse direction

Causes include certain drugs, toxins from food,

overstretching of stomach, body motion changes, motion

sickness associated with inner ears

Motor response involves deep breath, raising of soft

palate, closing of nasal cavity and glottis, relaxation of

lower esophageal sphincter, contraction of diaphragm and

abdominal wall muscles; forces food out through mouth

Contains enzymes that digest carbohydrates, fats, proteins, and

nucleic acids

Components of pancreatic juice:

Splits starch and glycogen into disaccharides

Components of pancreatic juice:

Breaks down triglycerides

Components of pancreatic juice:

Digests proteins; released as inactive trypsinogen, which is

activated by enterokinase in small intestine

Components of pancreatic juice:

Digest proteins; released as inactive, activated by trypsin

Components of pancreatic juice:

Digests proteins; released as inactive, activated by

trypsin

Components of pancreatic juice:

Digest nucleic acids

Components of pancreatic juice:

Make pancreatic juice alkaline; buffer stomach acid

Largest internal organ

• Located in the upper-right abdominal quadrant, just

beneath the diaphragm

• Reddish-brown organ

• Well-supplied with blood vessels

Liver has 4 lobes

a yellowish-green liquid that hepatic cells continuously secrete

Components of Bile:

Produced from cholesterol

Emulsify fats

Only bile component that have a digestive function (act as fat emulsifying

agents)

Bilirubin and biliverdin, derived from hemoglobin

breakdown

• Cholesterol

• Electrolytes

Yellowing of skin, eye sclerae, mucous membranes

• Caused by blockage of bile ducts, diseases, such as cirrhosis or hepatitis,

or rapid red blood cell destruction

Pear-shaped sac

• Found on inferior surface of liver

• Stores and concentrates bile

• Releases bile into duodenum of small intestine, via common bile

duct at the hepatopancreatic ampulla

____regulates release of bile into the

duodenum

Gallbladder normally concentrates bile salts, bile pigments,

cholesterol

• Sometimes cholesterol precipitates and forms solid crystals

• Crystals can enlarge, forming gallstones

• Causes: Excess bile concentration, too much cholesterol

secretion by liver, or inflammation of the gallbladder

Aid digestive enzymes through emulsification:

Break up of large fat globules into smaller droplets (like soap or detergent)

Aid in fat digestion by increasing surface area accessible to the enzyme lipase

Enhance absorption of fatty acids and cholesterol by forming micelles

Help absorb fat-soluble vitamins A, D, E, and K

Almost all bile salts are recycled

Tubular organ that extends from the pyloric sphincter to the beginning of the large intestine

Fills most of abdominal cavity

Receives chyme from stomach, and liver and pancreatic secretions

Completes digestion of the nutrients in chime

Absorbs products of digestion

Transports the remaining residue to the large intestine

Secretions of the Small Intestine

Secretions of the Small Intestine

Secreted by goblet cells

Also secreted by specialized Brunner’s glands, that secrete a thick, alkaline mucus in response to certain stimuli

Secretions of the Small Intestine

Secreted by intestinal glands

Picks up digestion products, and transports them into villi

Does not contain digestive enzymes

Secretions of the Small Intestine

Breaks down fats into fatty acids and glycerol

Break down peptides into amino acids

Secretions of the Small Intestine

Break down disaccharides into monosaccharides

Absorption in the Small Intestine

Emulsified by bile salts

Digested mainly by enzymes from pancreas and small intestine Digested into glycerol and fatty acids

Fatty acids and glycerol are absorbed by a process involving several steps; absorbed into blood or lymphatic capillaries (lacteals)

Absorption in the Small Intestine

Loose complexes of fatty acids and bile salts, from which fatty acids can migrate to microvilli and be absorbed

Fatty acids + glycerol are resynthesized into triglycerides in smooth ER

New triglyceride clusters are encased in protein, forming_____

______are absorbed by lacteals

Named because diameter is greater than that of small intestine

About 1.5 m long

At distal end, opens to outside of body through the anus

Absorbs some water and electrolytes

Reabsorbs and recycles water and digestive secretions

Forms and stores feces

Parts of the Large Intestine

Pouch, forms beginning of large intestine

Appendix is attached to cecum; lymph nodules in appendix function in the immune response

Parts of the Large Intestine

Ascending, transverse, descending and sigmoid portions

Contains hepatic (right colic) and splenic (left colic) flexures

Parts of the Large Intestine

Extends from sigmoid colon to anal canal

Lies next to sacrum

Parts of the Large Intestine

Last 2.5 to 4 cm of large intestine; opens to outside as anus

Internal and external anal sphincters guard anus

Wall has same 4 layers as other tubular organs of the alimentary canal

Does not have villi and plicae circulares

Functions of the Large Intestine

Has little or no digestive function

Contains tubular glands containing goblet cells; secrete mucus, the only significant secretion of the large intestine

Absorbs water (about 90% of water that enters it) and electrolytes

Houses intestinal flora, bacteria which break down contents such as cellulose, and produce vitamins K, B12, thiamine

Forms feces, and carries out defecation

Functions of the Large Intestine

Mixture of nitrogen, oxygen, methane, carbon dioxide, hydrogen, ammonia, and hydrogen sulfide (causes unpleasant odor)

Similar to those of the small intestine • Slower and less frequent than those of the small intestine

Movements of the Large Intestine

Types of movements:

Mixing movements

Peristaltic waves, 2 to 3 times/day, which usually follow meals

Movements of the Large Intestine

Mixing movements

Eliminates feces from body

Involves holding deep breath, contracting abdominal muscles

Feces move into rectum

Peristaltic waves occur in descending colon

Relaxes internal anal sphincter, and then external anal sphincter

composed of materials not digested or absorbed, and also contain:

Water (~75% of _)

Electrolytes

Mucus

Bacteria

Bile pigments, which provide the color, after bacterial alteration

The pungent odor is produced by bacterial compounds, including: