Transcript Large Intestine - Peoria Public Schools

Chapter 17 - Digestive System
• Digestion - process by which food is
changed into forms that can be absorbed
through cell membranes.
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Major Organs
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General Characteristics of the
Alimentary Canal (GI Tract)
• Extends from mouth to anus (about 9m
long)
• Organs include: mouth, pharynx,
esophagus, stomach, small intestine, and
large intestine
• Accessory organs: salivary glands, liver,
gall bladder, pancreas
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Structure of the wall- 4 layers
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1. Mucosa
2.Submucosa
3. Muscularis
4. Serosa
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Mucosa
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innermost layer
made of epithelial and connective tissue
and some smooth muscle
has glands that secrete mucus for
lubrication and protection from digestive
enzymes
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Submucosa
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beneath mucosa
contains connective tissue, glands, blood
vessels lymph vessels, and nerves
nourishes mucosa and carries absorbed
nutrients away
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Muscularis
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2 layers of muscle (smooth)
circular muscle layer around submucosa
longitudinal layer around circular layer
function is to move food through the canal
(mixing & peristalsis
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Serosa
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outermost layer
protects underlying tissues
secretes serous fluid to lubricate outer tube
so organs slide freely against each other
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Alimentary Canal
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Alimentary Canal Wall
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. Movements of the tube
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1. Mixing
Smooth muscles contract rhythmically
Mix food, digestive juices, and mucus
2. Peristalsis
Wavelike motion of longitudinal muscle layer to
move food along
• Begins when food expands the tube
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Movements of the Tube
• mixing movements
• peristalsis
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Innervention of the Tube
1. Parasympathetic NS (autonomic NS)
• Increases digestive activities
• In control under normal, restful conditions
2. Sympathetic NS (autonomic NS)
• In control in stressful situations
• Contract sphincter muscles (blocks movement of
food) - found between organs of GI tract
• Inhibits digestive activities
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Digestive Organs
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Mouth (Fig 17.7 page 650)
• Receives food and starts digestion by
chewing and mixing with saliva
• Cheeks and lips
Tongue
• Muscular organ that mixes and moves food
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Palate
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roof of mouth
Hard palate - anterior portion
Soft palate - posterior portion
Uvula - extension of soft palate
Tonsils - masses of lymphatic tissue
- Palatine tonsils (lateral to palate)
- Pharyngeal tonsils = adenoids (posterior
pharynx)
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Mouth
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Tongue
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Palate
• roof of oral cavity
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Teeth
• 2 sets develop in sockets in mandibular and
maxillary bones
• 20 primary (deciduous) lost between 6-12
years
• 32 secondary (permanent)
• function is to break food into smaller pieces
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Primary Teeth
• 8 incisors
• 4 cuspids
• 8 molars
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• 4 types of teeth - incisors, cuspid, bicuspids,
molars (fig 17.9 page 656)
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Secondary Teeth
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tooth structure (fig 1 7.10 page 657)
• crown = exposed area of tooth
• root = area below gum (gingiva)
• enamel = covering on crown made ofCa+
salts (hardest substance in body)
• dentin = bulk of tooth under enamel
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• pulp = central cavity that contains blood
• vessels, nerves, and connective tissue cementum = encloses root
• periodontal ligament = attaches tooth to
jaw
• See Clinical application 17.1 page 657 effects of bacteria on teeth
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Section of a Tooth
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Salivary Glands
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Secretes saliva to moisten and bind food
and begins digestion of carbohydrates
Helps cleanse mouth and regulate pH (6.5
- 7.5)
Makes taste possible
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Salivary secretions
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Serous cells secrete amylase (enzyme) to
start carbohydrate digestion
Mucus cells secrete mucus for lubrication
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Major Salivary Glands (fig 17.11
page 658)
Parotid
• Anterior to ear
• largest
• secrete saliva rich in amylase
Submandibular
• located on floor of mouth
• secrete viscous saliva
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Sublingual
• located inferior to tongue
• secretes mostly mucus
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Salivary Glands
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Pharynx (throat)
• divided into 3 parts
Nasopharynx
• superior to soft palate
• passageway for air during breathing
Oropharynx
• posterior to mouth
• passageway for food and air moving to and from
nasal cavity
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Laryngopharynx
• inferior to oropharynx
• passageway to esophagus
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Pharynx
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Esophagus
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Straight collapsible tube about 25cm long
Passageway for food from pharynx to stomach
Posterior to trachea (tube to lungs)
See hiatal hernia page 661
Lower esophageal sphincter muscles usually
remains contracted to prevent regurgitation of
stomach contents
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Esophagus
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Stomach
• J shaped pouchlike organ 25-30cm long
• Inner has thick mucosal folds called rugae - pg
662 fig 17.17
• Pyloric sphincter muscle found at entrance to
small intestine (duodenum)
• Mixes food with gastric juice, initiates digestion of
proteins, carries on a limited amount of
absorption, and moves food to small intestines.
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Stomach
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Radiograph of Stomach
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Lining of Stomach
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Gastric secretions
• Mucosa of stomach has gastric pits that are
the openings of gastric glands. Page 664 fig
17.19
• Gastric juice contains: see page 665 table
17.5
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Gastric Secretions
• pepsinogen
• from chief cells
• inactive form of pepsin
• pepsin
• from pepsinogen in presence of
HCl
• protein splitting enzyme
• hydrochloric acid
• from parietal cells
• needed to convert
pepsinogen to pepsin
• mucus
• from goblet cells and mucous
glands
• protective to stomach wall
• intrinsic factor
• from parietal cells
• required for vitamin B12
absorption
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Regulation of Gastric Secretions
Parasympathetic NS (normal conditions)
- stimulates release of the hormone gastrin
which increases the activity of gastric
glands
- hormone somatostatin inhibits acid
secretion
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Gastric Absorption
• Stomach wall not well adapted to absorb
digestive products
• Only small quantities of water, certain salts,
alcohol and some lipid soluble drugs are
absorbed
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Mixing and emptying actions
• Mixing of food + gastric juice = chyme
• Peristalsis moves chyme toward small intestine
• Pyloric sphincter relaxes (opens) & chyme is
pushed a little at a time into small intestine
• Enterogastric reflex inhibits peristalsis in stomach
as small intestine fills
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Mixing and Emptying Actions
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Enterogastric Reflex
regulates the rate at which chyme leaves the stomach
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Vomiting
• Caused by irritation or distension in stomach or
intestines
• Can be stimulated by drugs, toxins in foods, rapid
changes in body motion, sights, sounds, odors,
tastes, emotions and mechanical stimulation of
back of pharynx
• Vomit center is in medulla oblongata
• Stomach is squeezed from all sides forcing
contents upward
• Nausea caused by activity in or near vomit center
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Pancreas (accessory organ)
• Secretes digestive juice called pancreatic juice
Structure
• Its head is found in C-shaped curve of duodenum
and tail against the spleen
• Page 668 Fig 17.23
• Pancreatic duct connects to small intestine at the
same place as the bile duct from the liver and
gallbladder
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Pancreas
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Pancreatic Juice
• Contains 4 classes of enzymes that break
down:
- carbohydrates: amylase
- fats/tryglycerides: lipases
- proteins:proteinases
- nucleic acids: nucleases
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Regulation of Pancreatic Secretion
• Hormone called secretin stimulates
pancreas to release fluid when chyme enters
duodenum
• Proteins and fats in chyme stimulate release
of cholecystokinin from intestinal wall that
then stimulates pancreatic juice secretion
• Impulses regulated by parasympathetic NS
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Liver (accessory)
Structure - See Page 671
• Largest internal organ
• Enclosed in fibrous capsule
• Connective tissue divides organ into larger right
lobe and smaller left lobe
• 2 smaller lobes (within right lobe): caudate (by
vena cava) and quadrate (by gallbladder)
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• functional units = hepatic lobules that
contain hepatic cells
• hepatic sinusoids separate groups of cells
from each other
• kupffer cells - remove bacteria from blood
(fig17.28 pg672)
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Liver
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Hepatic Lobule
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Liver Functions
• metabolism of carbohydrates, lipids, and
proteins (most important)
• stores glycogen, vitamin A, B12, D, and
iron
• removes toxic substances from blood
• removes damaged RBC' s and foreign
substances by phagocytosis from blood
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• production/secretion of bile
• Liver Inflammation = hepatitis (Page 673
Clinical App 17.3)
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Clinical Application
Hepatitis
• inflammation of the liver
• most commonly caused by viral infection
• can be caused by reactions to drug, alcoholism or autoimmunity
Signs and Symptoms
• headache
• low fever
• fatigue
• vomiting
• rash
• foamy urine
• pale feces
• jaundice
• pain
Hepatitis A – not washing hands or
eating raw shellfish
Hepatitis B – chronic; serum
Hepatitis C – serum
Hepatitis D – very severe; only produces
symptoms if infected with B; serum
Hepatitis E, F, G – more rare
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Composition of Bile
• Yellowish-green liquid secreted by hepatic
cells(liver)
• Contains: water, bile salts, bile pigments,
cholesterol, and electrolytes
• Only bile salts have a digestive function to
emulsify fats (break into smaller droplets) - allows
fatty acids, cholesterol, and fat soluble vitamins to
be absorbed
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Gallbladder
• Pear-shaped sac in a depression on inferior
(underside)
• surface of liver
• Connected to liver via cystic duct (Fig 17.26 pg
671)
• Stores bile between meals (30 - 50 ml)
• Connected to small intestine (duodenum) via the
common bile duct
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Gallbladder
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• Common hepatic duct connects liver to
common bile duct (Fig 17.26 pg 671)
• Gallstones may form if bile is too
concentrated, hepatic cells secrete too much
cholesterol or gallbladder is inflamed. (See
Clinical App 17.4 pg 674)
• Bile release controlled by cholecystokinin
(hormone)
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Small Intestine
• Receives secretions from liver and
pancreas, completes digestion of nutrients,
absorbs products of digestion (90% of all).
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Parts of small intestine
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Duodenum - nearest stomach
Jejunum - mid region
Ileum - near large intestine (ileocecal
sphincter separates)
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Three Parts of Small Intestine
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Structure of small intestine wall
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Lined with villi to increase surface area (greater
absorption)
Passageway called the lumen
Glands located between villi (fig 17.35 pg 678)
Each villi have many blood and lymph capillaries
to carry away absorbed nutrients
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Intestinal Villus
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Secretions of small intestine
• Mucus
Digestive enzymes:
• Peptidases: peptides
• Sucrase, maltase, lactase: carbohydrates
• Lipases: triglycerides
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Absorption in small intestine
• Villi absorb water, electrolytes,
monosaccharides, amino acids, fatty acids,
and glycerol
• Fat (larger molecules) enters lacteals of villi
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Movements of small intestine
• Mixing of chyme + intestinal juices
• Peristalsis moves chyme toward large
intestine (3 -10 hours)
• Diarrhea - chyme passes through too
quickly
- water, chyme & electrolytes are not
absorbed
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Large Intestine
• Parts of the large intestine (Fig 17.43 pg 683)
Cecum - nearest ilium of small intestine
• Colon - majority of length (ascending, transverse,
descending)
• Rectum - distal end of colon
• Anal canal - narrowing of rectum & opening to
outside
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Large Intestine
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Structure of Large Intestine Wall
• Lacks villi
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Large Intestinal Wall
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Functions of large intestine
• Secretes mucus
• Absorbs water & electrolytes
• Has bacteria (intestinal flora) that break
down some undigestible material (cellulose)
and synthesize some vitamins (K, B12,
thiamine & riboflavin)
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Movements of large intestines
• Peristaltic waves 2-3/day usually following
a meal
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Feces
• Undigested and unabsorbed material
• Color due to bile pigments
• Odor due to compounds produced by
intestinal bacteria
• 75% water
Disorders of the Large Intestine
• Clinical Application 17.5 page 687
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Life-Span Changes
• teeth become sensitive
• gums recede
• teeth may loosen or fall out
• heartburn more frequent
• constipation more frequent
• nutrient absorption decreases
• accessory organs age but the effects are less
noticeable
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