Transcript Digestive System

Digestive System
Introduction
1. Ingest food
2. Transport ingested material
3. Secrete substances needed for digestion
•
Enzymes, etc
4. Digest material into smaller usable components
5. Absorb digested nutrients into bloodstream
6. Expel waste products from body
Introduction
1. Digestive organs
– gastrointestinal (GI)
tract
2. Accessory organs
– secrete substances
into GI tract
Oral Cavity
•
Site of mechanical and chemical digestion
1. Cheeks, lips and palate
2. Tongue
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•
Manipulates and mixes food
Compresses food into bolus
3. Salivary glands
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Produce and secrete saliva
4. Teeth
•
Mechanically digest food
–
Break into smaller pieces
Permanent Teeth
• 32 total – each quadrant has:
– Incisors (2) – shaped like chisel, for gnawing
– Canines (1) – pointed tips for puncturing and tearing
– Premolars (2) – flat crowns with prominent ridges for
crushing and grinding
– Molars (3) – also adapted for crushing and grinding
Salivary Glands
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Saliva serves the following functions:
1.
2.
3.
4.
5.
Moistens ingested materials
Moistens, cleanses and lubricates oral structures
Chemical digestion
Antibacterial action
Dissolves materials to stimulate taste receptors
Parotid Salivary Glands
• Secrete 25-30% of total saliva
• Via parotid duct
• Also secretes amylase
– Begins chemical digestion of starch
• Innervated by which CN?
Submandibular and Sublingual Salivary
Glands
• Submandibular salivary glands
– Produce the majority of saliva (60-70%)
• Sublingual salivary glands
– Contribute only 3-5% of total saliva
• Innervated by which CN?
Pharynx
• Shared by respiratory and digestive systems
• Which two CN innervate?
Peritoneum
•
Serous membrane of abdominal cavity:
1. Parietal peritoneum
2. Visceral peritoneum
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Organs may be:
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Intraperitoneal
Retroperitoneal
•
Lie against posterior cavity wall
Mesenteries
• Folds of peritoneum
– support and stabilize intraperitoneal GI tract organs
– Contain blood vessels, lymphatic vessels and nerves
• Include:
– Greater omentum – hangs from stomach
– Lesser omentum – connects stomach to liver
– Mesentery proper – suspends SI from posterior wall
– Mesocolon – attaches LI to posterior wall
The Wall of the Abdominal GI Tract
•
Composed of four tunics:
1.
2.
3.
4.
Mucosa
Submucosa
Muscularis
Serosa
Mucosa
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Three components:
1. Simple columnar ET
–
Except esophagus
2. Lamina propria (CT)
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Contains lymph nodules
MALT – mucosa-associated
lymphatic tissue
–
T cells, B cells, plasma cells,
and macrophages
3. Smooth muscle layer called
muscularis mucosa
• May have villi
– Increase surface area
– Contains lacteal
• Lymph capillary
Submucosa
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Components include:
1.
2.
3.
4.
Lymphatic ducts
Mucin-secreting glands
Blood vessels
Nerves
Muscularis
•
Two layers of smooth
muscle:
1. Inner circular layer –
constricts lumen and forms
sphincters
•
Involved with peristalsis
2. Outer longitudinal layer –
shortens tube
•
Involved with segmentation
Esophagus
• Tubular, muscular
passageway
• Passes through
esophageal hiatus of
diaphragm
• At junction of esophagus
and stomach =
gastroesophageal (cardiac)
sphincter
–
Prevents regurgitation
into esophagus
Stomach
• Continues mechanical and chemical digestion of
bolus
– processed into paste-like soup called chyme
• Three layers of muscle
– Additional oblique layer
Regions of the Stomach
•
Four regions:
1.
2.
3.
4.
Cardiac region
Fundus
Body
Pylorus
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•
Pyloric sphincter regulates movement of chyme into SI
internal surface folded – rugae (gastric folds)
Wall of the Stomach
• Little absorption occurs in stomach
• Stomach mucosa contains gastric pits
Gastric Secretions
• Along gastric pits are gastric
glands
• Mucous neck cells - Mucus
• Parietal cells:
• HCl - Protein breakdown
• Intrinsic factor - Vit B12 absorption
• Chief cells – Pepsinogen
• Precursor of pepsin - enzyme for
protein digestion
• G cells –Gastrin
• Hormone that stimulates other
gastric glands
Small Intestine
• About 22 feet long
• Finishes chemical digestion process
– Carbs, proteins, and lipids
• Absorbs majority of nutrients
• Takes ~ 12 hrs to digest and absorb food
Small Intestine
• Duodenum
– Brunner’s glands in submucosa secrete alkaline mucus
– Contains hepatopancreatic ampulla and sphincter
• Opening of ducts from liver, gallbladder, and pancreas
• Jejunum
– Primary region of digestion and absorption
• Ileum
– Contains Peyer’s patches (MALT)
– Ileocecal valve regulates passage into LI
– Secretions of the SI
– CCK – stimulates release of bile from gall bladder
– Sucrase, lactase, maltase – digest disaccharides
Histology of the Small Intestine
• Mucosa and submucosa have circular folds (plicae
circularis)
• Folds have villi
• Villi have microvilli
• All serve to increase surface area for absorption
Large Intestine
• Shorter than SI, but larger diameter
• Functions:
– Absorbs fluids and ions
– Compacts indigestible wastes into feces
– Stores feces until defecation
• Intestinal flora
– Over 700 species of bacteria
– Produce vitamins (K, B12)
– Facilitate water absorption
– Digest plant matter
• Creates gas!
Large Intestine
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Comprised of:
1. Cecum
•
appendix
2. Colon
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•
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Ascending colon
Transverse colon
Descending colon
Sigmoid colon
3. Rectum
4. Anal canal
Rectum
• Expands to store fecal material
• Rectal valves ensure fecal material retained during
passage of gas
Anal Canal
• Anal sinuses secrete mucin for lubrication during
defecation
• Internal and external anal sphincters control
defecation
– Internal – smooth muscle
– External – skeletal muscle
Liver
• Produces bile
• Detoxifies
• Processes nutrients
Gall Bladder
• On inferior surface of liver
• Collects and concentrates bile from liver
• Stimulated to contract by CCK from SI after eating
fatty meal
Biliary Apparatus
• Ducts transport bile from liver and gall bladder to
duodenum
Liver
R. Hepatic duct
Gall Bladder
L. Hepatic duct
Common hepatic duct
Cystic duct
Common bile duct
Duodenum
Pancreas
• Located inferior to stomach in curve of duodenum
• Exocrine functions involve secreting pancreatic
juices into duodenum via pancreatic ducts
Pancreatic Juice
• Contains digestive enzymes
– Trypsin – protein digestion
• Many other proteases too
– Lipase – lipid digestion
– Amylase – starch digestion
• Contains bicarbonate
– Buffer
– Neutralizes acidity from stomach