ZOOL-LAB 103

Functions of Digestive System

1. Takes in food
2. Break down food
3. Absorbs digested materials
4. Provide nutrients
5. Eliminate waste

Digestive system

is one large tube from mouth to anus plus the accessory organs

Layers of Digestive System

Mucosa, Submucosa, Muscularis Externa, Serosa/adventitia:

Mucosa

- Epithelial layer or innermost layer absorbs
and secretes mucus and enzymes
- Lamina propia or middle layer contains
blood and lymph vessels
- Muscularis interna or outermost layer
contains smooth muscle

Submucosa

-contains blood vessels, nerves, small
glands
- contains the submucous plexus (Meissner's plexus) -responsible in secretion of
digestive juices

Muscularis Externa

- contracts automatically; contains myenteric
plexus (Auerbach' s plexus) for muscle
relaxation
- longitudinal, circular, and oblique muscles
- where peristalsis occurs

Serosa/adventitia:

- peritoneum is present called serosa
- no peritoneum called adventitia (Ex.
Esophagus)

Peritoneum

Layer of smooth epithelial tissue

Types of Mesenteries

Lesser omentum
Greater omentum

Mesenteries

connective tissue of organs in abdominal cavity

Lesser omentum:

mesentery connecting lesser curvature of stomach
to liver and diaphragm

Greater omentum

mesentery connecting greater curvature of stomach
to transverse colon and posterior body wall

Oral Cavity

First part of digestive system
Contains stratified squamous epithelia

Salivary glands

produce saliva which contains enzymes to
breakdown carbohydrates into glucose
cleanse mouth
dissolve and moisten food

Bolus

Initially digested food while inside the oral
cavity

Amylase

salivary enzyme that breaks down carbohydrates
into sugars

Lysozyme

salivary enzymes that are active against
bacteria

Tongue

houses taste buds and mucus

Teeth

Used to masticate/chew food into small
fragments.
• 32 teeth in normal adult
• Incisors, canine, premolars, molars, wisdom
• 20 primary teeth (baby teeth)
• Each tooth has crown, cusp, neck, root
• Center of tooth is pulp cavity
• Enamel is hard covering protects against
abrasions
• Cavities are breakdown of enamel by acids
from bacteria

Teeth

It is used to masticate/chew food into small
fragments.

32

How many teeth in normal adult ?

20

The number of primary teeth in babies ?

Incisors, canine, premolars, molars, wisdom

Different Types of Teeth?

crown, cusp, neck, root

Each Tooth has

Pulp cavity

What is the center of the tooth?

Enamel

It is hard covering protects against
abrasions

Cavities

Are breakdown of enamel by acids
from bacteria

Palate

Roof of oral cavity

Hard palate

Anterior part

Soft palate

Posterior part

Salivary Glands

- includes submandibular,
- sublingual,
- parotid
- produce saliva that contains
- enzymes to
- breakdown food
- mumps is inflammation of parotid gland

Salivary Glands

It includes submandibular, sublingual, and parotid to produce saliva that contains enzymes to break down foods.

Mumps

Inflammation of parotid gland

Pharynx

Throat
Connects mouth to the Espohagus

Esophagus

It is the tube that connects pharynx to stomach, transport food to stomach, joints stomach at cardiac opening.

Peristalsis

Wave-like contractions moves food
through digestive tract

Heartburn

occurs when gastric juices regurgitate into
esophagus
caused by caffeine, smoking, or eating or
drinking in excess

Pharyngeal phase, Voluntary phase, Esophageal phase:

Phases of Swallowing

Voluntary phase

Bolus (mass of food) formed in mouth and pushed
into oropharynx

Pharyngeal phase

swallowing reflex initiated when bolus stimulates
receptors in oropharynx

Esophageal phase

moves food from pharynx to stomach

Stomach

Located in abdomen
Storage tank for food
Can hold up to 2 liters of food
Produces mucus, hydrochloric acid, protein
digesting enzymes
Contains a thick mucus layer that lubricates
and protects epithelial cells on stomach wall
form acidic pH (3)

Abdomen

Where is stomach located?

Stomach

It is the storage tank for food.

Stomach

It can hold up to 2 liters of food

Mucus, hydrochloric acid, protein,
digesting enzymes

The stomach produces

Cardia, Fundus, Body, Pyloric Antrum

What are the four regions of stomach?

Outer longitudinal, Middle circular, and Inner oblique

The 3 muscular layers of stomach to produce churning action

Rugae of stomach

Large folds that allow stomach to stretch
Pylon ping-End

Gastric Pits

Dive down to gastric glands which produces
gastric secretions: Hydrochloric acid-destroys
pathogen from the food

Pepsin
Mucus
Water

Types of Gastric Pits

Pepsin

breakdown proteins

Mucus

protects the stomach

Water

makes the bolus liquid called chyme

Chyme

paste-like substance that forms when food begins to
breakdown

Pyloric opening

Opening between stomach and small intestine

Pyloric sphincter

thick, ring of smooth muscle around pyloric opening

Regulation of Stomach Secretions

Parasympathetic system, gastrin, histamine
increase stomach secretions

Cephalic Phase, Gastric Phase, Intestinal Phase

What are the phases of stomach digestion?

Cephalic Phase

The taste, smell, or thought of food or
tactile sensations of food in the mouth
stimulate the medulla oblongata (green
arrows).

Cephalic Phase

Vagus nerves carry parasympathetic
action potentials to the stomach (pink
arrow), where enteric plexus neurons are
activated.

Cephalic Phase

Postganglionic neurons stimulate secretion
byparietal and chief cells and stimulate
gastrin and histamine secretion by
endocrine cells.

Cephalic Phase

Gastrin is carried through the circulation
back to the stomach (purple arrow), where,
along with histamine, it stimulates
secretion.

Gastric Phase

Distention of the stomach stimulates
mechanoreceptors (stretch receptors) and
activates a parasympathetic reflex. Action
potentials generated by the mechanoreceptors
are carried by the vagus nerves to the medulla
oblongata (green arrow).

Gastric Phase

The medulla oblongata increases action
potentials in the vagus nerves that stimulate
secretions by parietal and chief cells and
stimulate gastrin and histamine secretion by
endocrine cells (pink arrow).

Gastric Phase

Gastrin is carried through the circulation back
to the stomach (purple arrow), where, along
with histamine, it stimulates secretion. (The fourth step of the second phase)

Intestinal Phase

Chyme in the duodenum with a pH less than 2
or containing fat digestion products (lipids)
inhibits gastric secretions by three mechanisms
(2-4).

Intestinal Phase

Chemoreceptors in the duodenum are
stimulated by H (low pH) or lipids. Action
potentials generated by the chemoreceptors
are carried by the vagus nerves to the medulla
oblongata (green arrow). where they inhibit
parasympathetic action potentials (pink arrow),
thereby decreasing gastric secretions.

Intestinal Phase

Local reflexes activated by H or lipids also
inhibit gastric secretion (orange arrows).

Intestinal Phase

Secretin and cholecystokinin produced by the
duodenum (brown arrows) decrease gastric
secretions in the stomach.

Mixing waves, Peristaltic waves, Hormonal and neural mechanisms stimulate stomach secretions, Stomach empties every 4 hours after
regular meal, and 6-8 hours after high fatty meal

Movement in Stomach

Hormonal and neural mechanisms

What stimulate stomach secretions

4 hours

When does stomach empties after a regular meal?

6-8 hours

When does stomach empties after a high-fatty meal?

Small Intestine

• Measures 6-10 meters in length
• Major absorptive organ
• Chyme takes 3-5 hours to pass through
• Contains enzymes to further breakdown food
• Contains secretions for protection against chime' s acidity

6-10 meters

What is the measurement of small intestine?

Small Intestine

It is the major absorptive organ

Chyme

It takes 3-5 hours to pass through

Small intestine

Contains enzymes to further breakdown food

Small Intestine

Contains secretions for protection against chime' s acidity

duodenum, jejunum, ileum

Wh are the three Parts of Small Intestine?

Duodenum

It contains absorptive cells, goblet cells,
granular cells, endocrine cells.
It contains microvilli and many folds contains
bile and pancreatic ducts

Jejunum

2.5 meters long and absorbs nutrients

Ileum

3.5 meters long and also helps to further
digest food and also absorbs other
nutrients.

Bile-secreted, Cholecystokinin, Proteases/Peptidases, Pancreatic lipase, Pancreatic amylase, Secretin-hormone, Bicarbonate

Enzymes and Hormones

Bile

Secreted by the gallbladder; emulsifies fat

Cholecystokinin

signals the gallbladder to secrete
bile in the small intestine

Proteases/Peptidases

breaks down protein into
smaller peptides or amino acids.

Pancreatic lipase

breaks down triglycerides into
fatty acids and glycerol.

Pancreatic amylase

breaks down carbohydrates
into disaccharides.

Secretin-hormone

secreted by enteroendocrine
cells which stimulates pancreatic duct cells to
secrete water and bicarbonate.

Bicarbonate

Helps neutralize acidic chyme
increasing the pH of the intestinal lumen; alsosecreted by glands in the submucosa of duodenal
wall. It also helps digestive enzyme work more efficiently.

Large Intestine

Function is to absorb water from indigestible food
Contains cecum, colon, rectum, anal canal

Cecum

- joins small intestine at ileocecal junction
- where appendix is attached

Appendix

9 cm structure that is often removed during
appendectomy

Colon

1.5 meters long
contains ascending, transverse, descending,
sigmoid regions

Rectum

straight tube that begins at sigmoid and ends at
anal canal

Anal Canal

last 2-3 cm of the digestive tract
Food takes 18-24 hours to pass through
Feces is product of water, indigestible food, and
microbes

Anal canal

What is the last 2-3 cm of digestive tract?

18-24

How many hours does food takes to pass through?