The Digestive System Overview of the Digestive System Organs are - - PowerPoint PPT Presentation

The Digestive System

Overview of the Digestive System

• Organs are divided into two

groups – The alimentary canal

• Mouth, pharynx, and

esophagus

• Stomach, small

intestine, and large intestine (colon)

• Accessory digestive organs

– Teeth and tongue – Gallbladder, salivary glands, liver, and pancreas

Overview of Digestive Processes

• 1. Motility
• 2. Digestion
• a. Mechanical
• b. Chemical
• 3. Absorption
• 4. Secretion

GI Tract Composition

• 1. Serosa

Thin loose connective tissue, and epithelium which is continuous with the visceral peritoneum

• 2. Muscularis externa

Responsible for motility in GI tract Longitudinal and circular muscles (exceptions in stomach and colon). Contains nerves (myenteric plexus) for local control

• 3. Submucosal

Contains vessels, glands, nerves (submucosal plexus)

• 4. Mucosal

Composed of three layers:

• a. Epithelium – highly variable depending on region
• b. Lamina propria, contains GALT (gut associated lymphatic

tissue)

• c. Muscularis mucosae

GI Tract Layers

The Peritoneal Cavity and Peritoneum

Peritoneum – a serous membrane

Visceral peritoneum – surrounds digestive

• rgans

Parietal peritoneum – lines the body wall

Peritoneal cavity – the thin sandwiched space between the visceral and parietal peritoneum.

Figure 22.5a

Mesentery Structure

• Mesentery – a double

layer of peritoneum

– Suspend & holds

• rgans in place

– Sites of fat storage – Provides a route for circulatory vessels and nerves

Mesenteries

Superficial view of the abdominal organs

Figure 22.6b

Mesenteries

Mesenteries

• Greater omentum and

transverse colon reflected

• Visible Mesenteries:

– Greater omentum – Transverse mesocolon – Mesentery – Sigmoid mesocolon

Figure 22.6c

Mesenteries

• Sagittal section through

the abdominopelvic cavity

• Visible Mesenteries:

– Lesser omentum – Falciform ligament – Transverse mesocolon – Mesentery – Greater omentum

Figure 22.26d

Organ Location with respect to the Peritoneum & Mesenteries

• Retroperitoneal organs

– Behind the peritoneum

• Pancreas
• Duodenum
• Portions of colon
• Peritoneal organs

– Digestive organs that keep their mesentery

Figure 22.5b

The Mouth and Associated Organs

• The mouth – oral cavity

– Mucosal layer composed of . . .

• Stratified squamous epithelium
• Lamina propria
• The lips and cheeks

– Formed from orbicularis oris and buccinator muscles, respectively

• Site of start of chemical digestion!

– Salivary amylase & lingual lipase

Anatomy of the Mouth

Figure 22.8a

Anatomy of the Mouth

• The labial frenulum

anchors the tongue

• The palate – forms the

roof of the mouth

• The palatoglossal arch

and uvula form the fauces (the arches that

• pen into the
• ropharynx)

Figure 22.8b

The Tongue

• Muscular structure of tongue:

– Interlacing fascicles of skeletal muscle

• Tongue functions:

– Motility ‐ grips food and repositions it – Communication ‐ helps form some consonants – Taste

• on the surface of the tongue and adjacent areas of

the pharynx and larynx.

• Taste buds lie at the sides of epithelial projections

called papillae. There are three types of papillae:

– Filiform – Fungiform – Circumvallate

Gustatory Receptors

The Teeth ‐ dentition and dental formula

• Deciduous teeth – 20 teeth

– First appear at 6 months of age

• Permanent teeth – 32 teeth

– Most erupt by the end of adolescence

• Dental formula – shorthand

– Way to indicate number and type of teeth. For Example: I 2/2, C 1/1, P 2/2, M 3/3), where I= incisors, C = canines, P = Premolars, M= Molar and the numbers represent the numbers of teeth in the upper and lower quadrant. To get the total number of teeth in a mouth, add all numbers and multiply by 2 = 32 teeth!

• Functions in mastication!

The Teeth

Figure 22.10

Deciduous (Baby) Teeth Permanent (Adult) Teeth

Tooth Structure

• Longitudinal section
• f tooth in alveolus

Figure 22.11

The Salivary Glands

• Produce saliva
• Compound tubuloalveolar glands

– Parotid, submandibular, and sublingual glands

Figure 22.12

The Pharynx

• Oropharynx and laryngopharynx – passages

for air and food

– Lined with stratified squamous epithelium – External muscle layer

• Consists of superior, middle, and inferior pharyngeal

constrictors – What about the nasopharynx?

The Esophagus

• Gross anatomy

– A 25 cm long simple muscular tube – Begins as a continuation of the pharynx at the upper esophageal sphincter – Travels through the posterior mediastinum – Joins the stomach inferior to the diaphragm – Ends at the lower esophageal sphincter (cardiac sphincter)

• Microscopic anatomy

– Epithelium is stratified squamous epithelium – When empty

• mucosa and submucosa in longitudinal folds

– Mucous glands

• primarily compound tubuloalveolar glands

– Muscularis externa

• skeletal muscle first third of length, then smooth

– Most external layer – adventitia

Esophagus

Note the thick stratified squamous epithelium as well as the submucosoal and muscularis layers. Muscularis Submucosa Mucosa

The Stomach

• Starts at the end of the esophagus

(esophageal‐stomach junction)

The Stomach

• Site where food is churned into chyme

– Due to churning action created by the additional

• blique muscle layer (in addition to the

longitudinal and circular muscles)

• Carbohydrate digestion continues until salivary

amylase is denatured in acidic lumen

• Protein digestion begins

– Secretes pepsin – Functions under acidic conditions

• Absorption limited

– Water, alcohol, salts, aspirin

The Stomach

• Capacity:

~ 1 qt. (slightly less than 1 liter)

• Size: ~12

inches long, by 6 inches wide

• Start:

junction of esophagus

• End:

pyloric sphincter

The Stomach – Gross Anatomy

Figure 22.14b

The Stomach

Microscopic Anatomy

Histology of Stomach