Download Functions of the digestive system

Chapter 25-1
The Digestive System
Functions of the digestive system
LaPointe Spring ‘12
Slide # 2
• Ingestion
• Mechanical processing (mastication, propulsion, mixing)
• Digestion (Chemical digestion)
• Secretion
• Absorption
• Elimination (defecation)
The Digestive system includes (but not limited to):
• The muscular digestive tract (alimentary tract)
• esophagus
• stomach
• small intestine
• large intestine
• Various accessory organs (e.g.)
• salivary glands
• exocrine pancreas
• liver
• gall bladder
LaPointe Spring ‘12
Slide # 3
Components of the Digestive System
LaPointe Spring ‘12
Slide # 4
Peritoneum
LaPointe Spring ‘12
Slide # 5
• Serous membrane that lines the peritoneal cavity
• parietal peritoneum
• visceral peritoneum
• develops into the mesentery that holds and supports
the digestive organs
Mesentery and the peritoneum
LaPointe Spring ‘12
Slide # 6
• Mesenteries
• Sheets of serous membranes that support portions of
the digestive tract
• Greater omentum lies anterior to abdominal viscera
• Provides padding, protection, insulation, and
energy reserves
• Lesser omentum lies between the stomach and the
liver.
• Stabilizes the stomach and provides support for
blood vessels entering and leaving the stomach
Mesentery
LaPointe Spring ‘12
Slide # 7
• Falciform ligament supports and stabilizes the liver.
• Mesocolon - mesentery associated with the large
intestine.
• transverse mesocolon
• sigmoid mesocolon
• Retroperitoneal organs
• duodenum
• pancreas
• rectum
Mesenteries
LaPointe Spring ‘12
Slide # 8
Mesenteries
LaPointe Spring ‘12
Slide # 9
Histology of the digestive tract
LaPointe Spring ‘12
Slide # 10
I. Mucosa lines the inside of the digestive tract
• mucous epithelium
• Lamina propria - areolar tissue, nerves, blood vessels,
lymphatics, MALT system, etc,
• muscularis mucosae - thin layer of smooth muscle
cells
Mucous Epithelium
1. Stratified squamous epithelium
• (mouth, oral pharynx, esophagus, anus)
2. Simple columnar epithelium
• (most of the tract)
3. Enteroendocrine cells
4. Goblet cells
Moistened by glandular secretions
LaPointe Spring ‘12
Slide # 11
Histology of the digestive tract
LaPointe Spring ‘12
Slide # 12
II. Submucosa
• Layer of irregular connective tissue
• exocrine glands
• large blood vessels and lymphatic vessels
• Meissner’s plexus - (submucosa plexus) network of
sensory neurons, parasympathetic ganglionic neurons,
sympathetic nerves
• mainly controls secretions, mucosa muscle
contraction
Histology of the digestive tract
LaPointe Spring ‘12
Slide # 13
III. Muscularis externa
• Two layers of smooth muscle arranged in a circular
and a longitudinal layer (in most parts of the tract)
• myenteric plexus - a second nerve plexus
• mainly coordinates smooth muscle contraction of
the muscularis externa
IV. Serosa (visceral peritoneum)
• Serous membrane covering most of the muscularis
externa
• Adventitia- oral cavity, pharynx, esophagus, rectum
Structure of the Digestive Tract
LaPointe Spring ‘12
Slide # 14
Also see fig 25.2
Marieb Figure 23.6
G.I. Reflexes
• Short reflexes
• stay within the GI tract
• myenteric and submucossal networks
• Long reflexes
• go to and from the CNS
• mainly vagovagal reflexes
LaPointe Spring ‘12
Slide # 15
Movement of material in the digestive tract
LaPointe Spring ‘12
Slide # 16
• Visceral smooth muscle show rhythmic cycles of activity
• Pacemaker cells
• Peristalsis
• Waves that move a bolus
• Segmentation (mixing)
• Churn and fragment a bolus
Peristalsis
LaPointe Spring ‘12
Slide # 17
1. Contraction of circular muscle behind bolus / relaxation in front of
bolus.
2. Contraction of longitudnal muscle. (shortens the segment)
3. Series of contractions of circular muscle (pushes bolus forward)
Figure 23.3
Peristalsis
LaPointe Spring ‘12
Slide # 18
Mixing: Segmental contraction
LaPointe Spring ‘12
Slide # 19
Control of the digestive system
LaPointe Spring ‘12
Slide # 20
• Movement and digestion of materials are controlled by:
• Neural mechanisms
• Parasympathetic and local reflexes
• short or enteric reflexes
• Long reflexes - CNS control
• Hormonal mechanisms
• Enhance or inhibit smooth muscle contraction and
gland secretion
• Local mechanisms
• Coordinate response to changes in pH or chemical
stimuli
• activate both neural and hormonal responses
Regulation of Digestive Activities
endocrine
LaPointe Spring ‘12
Slide # 21
b
l
o
o
d
Figure 23.4
Oral or buccal cavity
LaPointe Spring ‘12
Slide # 22
• Functions include:
• Ingestion
• Analysis of material before swallowing
• Mechanical processing by the teeth, tongue, and
palatal surfaces
• Lubrication
• Limited digestion
Oral cavity
• Lined by oral mucosa
• Roof of cavity = hard and soft palates
• Floor of cavity = tongue
• Cheeks form the lateral walls
• Uvula guards opening to pharynx (Fauces)
LaPointe Spring ‘12
Slide # 23
The Oral Cavity
LaPointe Spring ‘12
Slide # 24
The tongue
LaPointe Spring ‘12
Slide # 25
• Primary functions include:
• Mechanical processing
• Assistance in chewing and swallowing
• Sensory analysis by touch, temperature, and taste
receptors
• Papillae
• fungiform
• cicumvallate
• foliate
Tongue movements
LaPointe Spring ‘12
Slide # 26
• Skeletal muscle
• intrinsic muscles
• extrinsic muscles
• lingual frenulum - mucous membrane attachment
• Innervated by the hypoglossal nerve
Salivary glands (three pairs)
LaPointe Spring ‘12
Slide # 27
• Parotid glands
• parotid ducts empty at level of 2nd upper molar
• salivary amylase
• serous gland - watery saliva
• Sublingual glands
• numerous ducts along the lingual frenulum
• mucous and serous secretions (see fig 25.10)
• salivary lipase
• Submandibular glands
• ducts along the lingual frenulum posterior to the teeth
• salivary amylase
Saliva
LaPointe Spring ‘12
Slide # 28
• Functions include:
• Lubrication, moistening, and dissolving
• Initiation of digestion of complex carbohydrates
• Watery solution containing electrolytes, buffers, enzymes
glycoproteins, and antibodies (IgA)
• salivary amylase, (ptyalin or alpha amylase)
• salivary lipase
• lysozyme - weak antibacteria substance
• IgA
The Salivary Glands
LaPointe Spring ‘12
Slide # 29
Marieb Figure 23.9
Eruption of teeth
LaPointe Spring ‘12
Slide # 30
• 20 primary teeth - deciduous teeth
• 32 teeth of secondary dentition - permanent teeth
• incisors (8)
• cuspids (canine teeth) (4)
• bicuspids (premolars) (8)
• molars (8-12)
• (depending on how many wisdom teeth come in)
Primary and Secondary Dentation
LaPointe Spring ‘12
Slide # 31
Numbering of Teeth
LaPointe Spring ‘12
Slide # 32
Teeth
• Function in mastication of bolus
• Contact of occlusal surfaces
• Contain three layers
• Enamel covering crown
• Dentin forms basic structure
• pulp cavity
• contains blood vessels and nerves
• Root coated with cementum
• Periodontal ligaments hold teeth in alveoli
LaPointe Spring ‘12
Slide # 33
Teeth
LaPointe Spring ‘12
Slide # 34
The pharynx
LaPointe Spring ‘12
Slide # 35
• Common passageway for food, liquids, and air
• nasopharynx, oropharynx, and laryngopharynx
• Lined with stratified squamous epithelium
• Pharyngeal muscles assist in swallowing
• Pharyngeal constrictor muscles- push food toward
the esophagus
• Palatal muscles - elevate the soft palate, move the
uvula
Read book for swallowing (deglutition) (see fig 25.11)
The esophagus
LaPointe Spring ‘12
Slide # 36
• Carries solids and liquids from the pharynx to the
stomach
• Begins at C6
• Passes through esophageal hiatus in diaphragm
• The wall of the esophagus contains 4 layers - mucosal,
submucosal, muscularis layers, & adventitia
• upper esophageal sphincter (skeletal muscle)
• lower esophageal sphincter (smooth muscle)
• not true sphincter muscles but regions that function
in that capacity
Histology of the esophagus
LaPointe Spring ‘12
Slide # 37
• Nonkeratinized, stratified squamous epithelium
• Folded mucosa and submucosa
• mucosa muscularis has irregular layer of smooth
muscle
• Submucosa contains esophageal glands
• mucous glands
• thick mucous
Histology of the esophagus
• Muscularis externa
• top 1/3 skeletal muscle
• middle 1/3 mixed skeletal and smooth muscle
• bottom 1/3 smooth muscle
• Lacks serosa
• Anchored by an adventitia
LaPointe Spring ‘12
Slide # 38