4 digestive system
TRANSCRIPT
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