1. Digestive System
Chapter 14

2. 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?

3. 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

5. 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

6. 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

7. Palate 2 sections Hard Palate Soft 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

8. 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

10. Teeth Used to mechanically breakdown food 2 sets
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

11. Secondary Teeth Incisors – 8, front teeth
Function?
Cuspids (Canine) – 4, sharper teeth (fangs)
Bicuspids (premolar) – 8, behind cuspids, a bit flatter
Molars – total of 12, back teeth, much flatter (4 first, 4 Second, 4 Third)
Third also known as wisdom teeth

13. 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

15. 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

16. 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

17. 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

19. 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.

20. 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

22. Peristalsis

23. 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?

25. Esophagus Connects pharynx to stomach Found posterior to the trachea
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?

26. 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

27. Stomach Regions of the stomach Stomach ends at Pyloric Sphincter
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?

29. Gastric Juice 4 Components Regulated by autonomic nervous system
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

30. 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

31. 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

32. Small Intestine Walls are well suited for absorption
Have folds, villi, and microvilli
What are these going to do?
Greatly increase surface area

33. 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?

34. 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

35. Bile Consists of: 1. Water 2. Bile pigments 3. Bile salts
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)

36. Gallbladder Storage area Bile (between meals)
What do you think it stores?
Bile (between meals)
Reabsorbs water to concentrate it
If stored too long, gall stones may form

39. 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

41. 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?

42. Disorders of the Digestive system
What are these disorders and what causes them?
Diarrhea
Peptic Ulcers
Emesis
Constipation
Pancreatitis
Heartburn
Diverticulosis
Jaundice