Digestive System

Chapter 14

Digestive system

Divided into two parts: 1. Alimentary canal (aka GI tract)

– Path that the food takes through the body– Performs all digestion functions (ingest,

digest, absorb, defecate)– In a cadaver the length is about 9-10m

• Shorter when living….Why?

– Organs included?

Digestive System

2nd part = Accessory organs– Assist in the digestive system process in

various ways– Organs included: Teeth, Tongue, Salivary

Glands, Liver, Gallbladder, Pancreas, Spleen

Mouth

aka Oral Cavity Where food enters the body and digestion

begins here.– How?

Teeth (mechanical) and saliva (chemical) What role do the following play in the

mouth?– Lips, cheeks, uvula

Tongue Mostly muscle tissue

– What type of muscle would it be? Frenulum – connects the tongue to the bottom

of the mouth– What could be a problem if this is too short or

long? What is the purpose of the tongue? Taste and move food around Papillae – rough projections that contain

taste buds– Why would these be rough?

Four types of taste buds – sweet, sour, salt, bitter

Palate 2 sections Hard Palate

– What bone would make this up?– Anterior Portion

Soft Palate– Posterior Portion – mostly a muscular arch– This and the uvula are drawn up during

swallowing• Why is this important?

Blocks off the nasal passage during swallowing

Tonsils

Play a role in the defenses of the body Two types: Lingual – at the base of the tongue

– Used as anchor, covered by lymphatic tissue

Palatine – Located on the posterior sides of the tongue– These are the ones removed when you

have tonsilitis

Teeth

Used to mechanically breakdown food– aka masticate, aka chewing

2 sets Primary (baby) – 10 on each jaw

– What happens to these? They are lost

– The roots are resorbed and teeth are pushed out by secondary teeth

Secondary (permanent) – 16 on each jaw– Begin to appear around age six

Secondary Teeth Incisors – 8, front teeth

– Function? Cuspids (Canine) – 4, sharper teeth (fangs)

– Function? Bicuspids (premolar) – 8, behind cuspids, a

bit flatter– Function?

Molars – total of 12, back teeth, much flatter (4 first, 4 Second, 4 Third)– Third also known as wisdom teeth– Function?

Tooth Structure Crown – above gums Root – below gums Enamel –

– Hardest substance in the body (but brittle) and cannot be replaced

– What problem does this pose? Pulp cavity – Blood supply and nerves Dentin – deep to the enamel and

surrounds the pulp cavity

Salivary Glands

Main Secretions– Amylase – breaks down large starch

and glycogen molecules– Mucus –

• What is its purpose? Bind food particles and lubricate

alimentary canal What triggers secretions? Autonomic nervous system

Salivary Glands – 3 different glands

Parotid – Located anterior and inferior to the ear– Secretes saliva rich in amylase

Submandibular – Located where?– Secretes thicker saliva than parotid.

• Why thicker? Sublingual – Located where?

– Secretes primarily mucus

Pharynx

Connects nasal and oral cavities with the esophagus

Contains the epiglottis– What is this?

Flaplike structure used to seal off trachea during swallowing.

Performs the swallowing reflex

Oral Cavity ?’s

In comparison to bone, why is enamel stronger and more brittle?

Differentiate between the parotid, submandibular, and sublingual salivary glands.

Why would it be a problem if the tongue was not skeletal muscle tissue?

Why is the uvula important? (2 reasons) Describe the teeth of a 12 year old girl.

Steps of Swallowing Soft palate raises Hyoid and larynx raise causing the epiglottis to

close off larynx Tongue compresses against the soft palate, sealing

the oral cavity from the pharynx Longitudinal muscles pull the pharynx up toward the

food Muscles of the lower pharynx relax to open the

esophagus Peristaltic wave forces food into the esophagus

Peristalsis

Wall Structure The rest of the alimentary canal is really just a long

coiled tube with 4 layers. Mucosa –inner most layer

– Secretes mucus and enzymes Submucosa – contains blood vessels

– Carries nutrients to surrounding tissues but also nutrients away during absorption.

Muscular layer – contains circular and longitudinal muscles– Moves food through the system

Serosa – outer layer, secretes serous fluid – Why is this important?

Esophagus

Connects pharynx to stomach– Function?

Found posterior to the trachea Ends at cardioesophageal sphincter

– What is a sphincter? Ring of muscle that is contracted unless

opened for physiological function– This one connects the stomach and the

esophagus, what will its function be?– What will happen if it is not functioning all

the way?

Stomach

Found on the upper left side of the abdominal cavity

What happens in the stomach?– Food is mixed with gastric juices to promote chemical

digestion, very little absorption Size is small when empty, yet it can hold up to 4

liters of food. – How?

Interior of stomach is lined with large folds called rugae– These unfold and the stomach has more area

Stomach Regions of the stomach

• Cardiac – near cardioesophageal sphincter• Fundic – anterior portion (curvature above

ces)• Body – Main region• Pyloric – posterior portion, near pyloric

sphincter

Stomach ends at Pyloric Sphincter– What does this control?

Gastric Juice

4 Components– Pepsin – main component – digests protein– Pepsinogen – inactive form of pepsin– Hydrochloric Acid – converts pepsinogen to

pepsin– Mucus – lubrication and protection

Regulated by autonomic nervous system When this is mixed with food it is called chyme

Small Intestine

The largest part of the alimentary canal– Anywhere from 2.5m to 7m in length

4 major functions: Receives secretions from the pancreas

and liver Completes digestion of chyme Absorbs products Transports residues to large intestine

Small Intestine

3 subdivisions– Duodenum - smallest section, comes just after

stomach• Receives food from stomach, and secretions from

pancreas and and liver/gallbladder

– Jejunum – middle section• Continues digestion, most absorption takes place

here

– Ileum – last and largest section• Prepares residue for large intestine

Small Intestine Walls are well suited for absorption Have folds, villi, and microvilli

– What are these going to do? Greatly increase surface area

Pancreas Located near posterior abdominal wall inferior to

stomach 3 important functions Secretes pancreatic juice into the duodenum.

(where is this?)– PJ contains amylase, lipase and nuclease

• What are these and what will these do?

– PJ is also very basic (high pH)• Why is this important?

What other important function?

Liver

Located in superior medial part of abdominal cavity

Very large and lobed (largest gland in body) One of the most important glands in the body Multiple Functions (thought to have over 500)

– Many having to do with the filtering and regulation of many compounds in the blood

Digestive functions Produce and secrete bile (huge in digestion of fats) Secretes it into the duodenum

Bile

Consists of: 1. Water 2. Bile pigments

Two types biliverdin (green) and bilirubin (yellow) Which one is bad?

3. Bile salts Only part of the bile that has digestive function Emulsification

4. small amounts of other compounds (electrolytes, cholesterol, phospholipids)

Storage area– What do you think it stores?

Bile (between meals)– Reabsorbs water to concentrate it

If stored too long, gall stones may form

Gallbladder

Large Intestine Shorter than the small intestine (~1.5m) Begins at cecum, ends at anus (has two sphincters)

– Why would it have two? Divided into four sections: ascending, transverse,

descending, sigmoid colon Lacks villi Little digestive function

– absorbs water and electrolytes– Eliminates food residue as feces

Questions If a person had a condition which limited their ability

to produce hydrochloric acid in the stomach, how might this affect digestion and why?

Why would it be a problem if a person’s intestinal walls were completely flat?

Why would storing bile for too long in the gall bladder cause gallstones?

What would result if a person did not produce much mucus in the stomach?

Thinking about the contents of the stomach, what might happen to a person with a cardioesophageal sphincter that does not close completely?

Disorders of the Digestive system What are these disorders and what causes

them?– Diarrhea

– Peptic Ulcers

– Emesis

– Constipation

– Pancreatitis

– Heartburn

– Diverticulosis

– Jaundice