DIGESTIVE SYSTEM

DIGESTIVE SYSTEM

Two main parts: Gastrointestinal (GI) tract

- mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus.

Accessory digestive organs - teeth, tongue, gallbladder, salivary glands, liver, and pancreas.

Digest. Abdomino-pelvic cavity

is lined by 2 serous membranes = Peritoneal membrane(secretes a watery fluid) 1. Parietal peritoneum -

attached to body wall. 2. Visceral peritoneum -

fused to surface of abdominal organs.

GI – 4 Tunics A. Tunica Mucosa: innermost, 3

parts 1. Epithelial Layer;

Nonkeratinized stratified squamous (oral cavity to stomach) for protection; Simple Columnar (stomach to anus) a. Absorption b. Secretion

i. digestive enzymes ii. mucus from goblet cells

2. Lamina propria - c.t. with lymphatic nodules (groups of WBC's)

3. Muscularis mucosae - thin layer of smooth muscle

GI – 4 Tunics

B. Tunica Submucosa - c.t. 1. Highly vascular 2. May contain mucous

glands 3. Nerve plexus

GI – 4 Tunics

C. Tunica Muscularis most common type is 2 layers of smooth muscle 1. Inner - circular 2. Outer - longitudinal Contract by Peristalsis

(waves of smooth muscle contraction, and are controlled by a nerve plexus)

GI – 4 Tunics

D. Tunica Serosa or Tunica Adventitia:  serosa = simple

squamous epi + c.t.; adventitia = just c.t.

Mouth = Oral or Buccal cavity Functions

1. Receives food 2. Initiates digestion

a. Mastication b. Saliva - has amylase

(an enzyme) which breaks down carbohydrates (long chains of sugars into short chains)

3. Initiates swallowing 

Mouth -Histology

1. Tunica Mucosa; inner epithelial lining = nonkeratinized stratified squamous

2. Tunica Submucosa: c.t.

3. Tunica Muscularis: facial muscles

4. Skin: outer, keratinized stratified squamous

Mouth -Tongue - has Papillae

1. Filiform - most numerous, conical; for tactile sensation (touch, temp., texture, heat, cold, etc.)

2. Fungiform - larger, rounded, taste buds on top

3. Circumvallate - very large, 7-12, taste buds on sides

Palate

1. Hard palate - bone (roof of oral cavity) 

2. Soft palate = muscular arches a. Uvula b. Palatoglossal arch (ant.) c. Palatopharyngeal arch

(post.)   Between the two arches

= palatine tonsils  

Mouth - Teeth

Teeth Mastication

Mouth –Salivary Glands

Salivary glands: 3 pairs 1. Parotid - largest, on

masseter, secretes serous fluid, fluid enters mouth via parotid duct

2. Submandibular - secretes serous & mucous

3. Sublingual - secretes primarily mucus, in floor of mouth

Pharynx - Common to resp. &

digest. systems. Connects oral cavity to esophagus & nasal cavity to larynx.

Parts 1. Nasopharynx - not part

of Dig. Sys. 2. Oropharynx - air & food 3. Laryngopharynx - air

and food

Pharynx –Histo.

1. Tunica Mucosa: contains nonkeratinized stratified squamous

2. Tunica Submucosa: c.t. 3. Tunica Muscularis; composed of 3 bands

of skeletal muscle = constrictors 4. Tunica Adventitia: c.t.

Esophagus

A. Connects pharynx to stomach

B. Passes through diaphragm at esophageal hiatus

C. Ends at stomach; its muscularis layer forms the Gastroesophageal (cardiac) sphincter.

Esophagus – histo.

1. Mucosa - non-keratinized stratified squamous 2. Submucosa - contains mucous glands 3. Muscularis - 3 sections

a. Upper 1/3 = skeletal b. Middle 1/3 = sk. & smooth c. Lower 1/3 = smooth

4. Adventitia - c.t. Function: voluntary & involuntary movement of food

to stomach  

Stomach - General

4 regions: cardiac, fundus, body, & pylorus. Ends at pyloric sphincter

Begins break-down of food

Stomach - histo

1. Mucosa - has Gastric Pits which open up into the Gastric Glands.                 The Gastric Glands are composed primarily of; a. Simple columnar epi.

i. Mucous neck cells - for protection ii. Parietal cells - hydrochloric acid (HCl) iii. Chief cells - pepsinogen (an inactive enzyme that is activated

                         to Pepsin by hydrochloric acid, for protein digestion) 2. Submucosa - c.t. 3. Muscularis - 3 layers of smooth muscle; longitudinal, oblique,

& circular 4. Serosa  

Small Intestine – Major Digest Organ Major digestive organ 8-18 ft long   1. Duodenum: most chemical digestion

occurs here because; Duodenal cells make enzymes to break

down foodstuffs It receives bile from gall bladder It receives enzymes from the pancreas for

the break down of foodstuffs 2. Jejunum - most absorption occurs

here 3. Ileum - very little absorption

  Digestion is completed in Small Intestine.

The small intestine ends at the Ileocecal valve

Sm. Intestine - Histo

1. Mucosa has finger-like folds = Villi a. Epithelium - Simple Columnar with microvilli

(secretion & absorption) and Goblet cells (mucus). b. Lamina propria - contains lacteals Between villi

= intestinal glands 2. Submucosa is in folds 3. Muscularis - 2 layers of smooth muscle;

outer - long., inner - circ. 4. Serosa

Large Intestine – Larger Diameter Regions: Cecum,

Apendix, Colon, Rectum, Anal Canal

Function Re-absorption of digestive fluids