Download Renal system

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Digestion
I. Overview
A. Organs
1. Alimentary canal
a. Function
i. Digests
ii. Absorbs
b. Organs
i. Mouth
ii. Pharynx
iii. Esophagus
iv. Stomach
v. Small intestine
vi. Large intestine
2. Accessory digestive
a. Organs
i. Teeth
ii. Tongue
iii. Gallbladder
b. Glands
i. Salivary
ii. Liver
iii. Pancreas
II. Digestive Process
A. Essential activities
1. Ingestion
a. Taking food into the digestive system via the mouth
2. Propulsion
a. Movement of food through the digestive tract
b. Swallowing
i. Voluntary
c. Peristalsis
i. Involuntary
3. Mechanical digestion
a. Chewing
b. Mixing
i. Saliva
c. Churning
d. Segmentation
i. Local constriction of the small intestine
4. Chemical digestion
a. Mouth through small intestine (see below)
5. Absorption
a. Movement of digested end products from lumen of the GI tract into blood and lymph
6. Defecation
a. Elimination of undigested materials
III. Histology of the Alimentary Canal
A. Four basic layers
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1. Mucosa
a. Innermost layer
b. Functions
i. Secretion
ii. Absorption
iii. Protection
c. Sub-layers
i. Lining epithelium
ii. Lamina propria
iii. Muscularis mucosae
d. Epithelium
i. Simple columnar with goblet cells
e. Lamina propria
i. Loose areolar connective tissue
ii. Capillary beds
iii. Lymph nodules
f. Muscularis mucosae
i. Thin layer of smooth muscle
2. Submucosa
a. Dense connective tissue
i. Blood vessels
ii. Lymphatic vessels
b. Elastic fibers
3. Muscularis externa
a. Segmentation and peristalsis
b. Inner circular and outer longitudinal layer of smooth muscle
c. Sphincters
i. Thickened areas of smooth muscle
4. Serosa
a. Areolar connective tissue covered with mesothelium
i. Single layer of squamous epithelium
IV. Functional Anatomy
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A. Mouth (oral cavity or buccal cavity)
1. Boundaries
a. Lips
b. Cheeks
c. Tongue
d. Palate
2. Palate
a. Hard palate
i. Underlain by bone
ii. Rigid
b. Soft palate
i. Formed from muscle
B. Tongue
1. Bundles of skeletal muscle
2. Function
a. Mix food with saliva
i. Bolus
b. Position bolus for swallowing
C. Salivary glands
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1. Function of saliva
a. Cleanses mouth
b. Dissolves tastants
c. Moistens
d. Initiates chemical breakdown
2. Types
a. Extrinsic
i. Three pairs
ii. Parotid
iii. Submandibular
iv. Sublingual
b. Intrinsic
i. Buccal glands
3. Secretory cells
a. Serous cells
i. Watery secretion with enzymes
b. Mucous cells
i. Viscous
D. Teeth
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1. Classification
a. Incisors
b. Canines
c. Premolars
d. Molars
2. Dental formula:
(2I, 1C, 2PM, 3M/2I, 1C, 2PM, 3M) X 2 = 32
E. Pharynx
1. Oropharynx to Laryngopharynx (see Respiration Lecture)
F. Esophagus
1. Laryngopharynx into esophagus
2. Pierces diaphragm
3. Joins stomach
a. Cardiac orifice
b. Cardiac sphincter
4. Four layers
a. Mucosa
b. Submucosa
c. Muscularis
i. Skeletal and smooth
ii. Distribution is regionalized
d. Adventia (not serosa)
i. Entirely connective tissue
G. Digestive processes in mouth, pharynx and esophagus
1. Mastication
a. Mechanical breakdown by teeth and tongue
2. Deglutition
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a. Complicated process of swallowing
i. Two phases
ii. Involves 22 muscles
H. Stomach
1. Expansion of the GI tract
2. Sack for storage and chemical breakdown
a. Food converted to chyme
V. Stomach
A. Gross anatomy
1. Regions
a. Cardiac
i. Region where food enters
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b. Fundus
c. Body
d. Pyloric
i. Terminates at the pylorus
ii. Connects with small intestine
iii. Pyloric sphincter
2. Greater curvature
a. Lateral convex surface
3. Lesser curvature
a. Medial concave surface
B. Microscopic anatomy
1. Four tunics
2. Lining epithelium
a. Simple columnar
i. Entirely goblet cells
b. Gastric pits
i. Gastric glands
ii. Produce gastric juice
3. Secretory cells of gastric glands
a. Mucous neck cells
i. Produce acidic mucus
b. Parietal cells
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i. Secrete HCl and intrinsic factor
c. Chief (zymogenic) cells
i. Produce pepsinogen
ii. Converted initially by HCl into pepsin
iii. Pepsin will catalyze conversion thereafter
d. Enteroendocrine cells
i. Produce hormones that regulate digestive function (see below)
C. Digestive processes occurring in stomach
1. Enzymatic digestion
a. Protein digestion is initiated in stomach
i. Pepsin
2. Lipid soluble substances can pass through stomach mucosa
a. Alcohol and aspirin
3. Production of intrinsic factor
a. Required for absorption of B12
D. Regulation of gastric secretion
1. Three phases
a. Cephalic
b. Gastric
c. Intestinal
2. Cephalic phase
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a. Occurs prior to food entering stomach
i. Brain response to food
b. Hypothalamic stimulation of the vagus nerve
i. Parasympathetic enteric ganglionic neurons stimulate the stomach glands
3. Gastric phase
a. Local signaling within stomach due to the presence of food
i. Distension
ii. Peptides
iii. Low acidity
b. Lead to HCl release
i. Gastrin is released in response to chemical stimuli
ii. Gastrin stimulates the release of HCl by parietal cells
4. Intestinal phase
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a. Excitatory phase
i. Duodenum releases a gastrin-like substance that promotes additional activity of gastric
glands
b. Inhibitory phase—enterogastric reflex
i. Inhibit vagal nuclei
ii. Inhibit local reflexes
iii. Activate sympathetic fibers that tighten pyloric sphincter
iv. Cause the release of enterogastrones
5. Enterogastrones
a. Secretin
b. Cholecystokinin (CCK)
c. Vasoactive intestinal peptide (VIP)
d. Gastric inhibitory peptide (GIP)
VI. Small Intestine
A. Gross anatomy
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1. Pyloric sphincter to ileocecal valve
2. Subdivisions
a. Duodenum
b. Jejunum
c. Ileum
B. Microscopic anatomy
1. Expanded surface area for absorption
2. Structural modifications
a. Circular folds
i. Deep folds of the mucosa and submucosa
b. Villi
i. Fingerlike projections of the mucosa
c. Microvilli (brush border)
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i. Projections of plasma membranes
C. Histology
1. Simple columnar epithelium
2. Submucosa include lymphatic tissue
a. Peyer’s patches
D. Liver and gallbladder
1. Accessory organs associated with small intestine
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2. Liver has a role in digestion in addition to its other functions
a. Bile production and export
i. Emulsification of fat
3. Gallbladder
a. Stores bile
4. Bile
a. Only bile salts and phospolipids aid in digestion
b. Other components that do not contribute to digestion (not discussed)
c. Emulsify fat
5. Regulation of bile release
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a. CCK from small intestine is released into blood in response to fatty chyme entering small
intestine
b. CCK stimulates secretion of pancreatic juice
c. CCK relaxes hepatopancreatic sphincter
i. Controls entry of pancreatic juice and bile entering duodenum
E. Pancreas
1. Accessory digestive organ
2. Produces digestive enzymes
a. Exocrine product—pancreatic juice
3. Acini
a. Secretory cells surrounding ducts
4. Composition of pancreatic juice
a. Proteases
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b. Amylase
c. Lipases
d. Nucleases
5. Regulation of pancreatic secretion
a. Local hormones
i. CCK
ii. Secretin
b. Parasympathetic nervous system
VII. Large Intestine
A. Gross anatomy
1. Ileocecal valve to the anus
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2. Absorbs water from indigestible food residues
3. Unique features
a. Teniae coli
i. Three bands of longitudinal smooth muscle
b. Haustra
i. Pocketlike sacs
c. Epiploic appendages
i. Fat-filled pouches
4. Subdivisions
a. Cecum
i. Saclike
ii. First segment
b. Appendix
i. Lymphatic
ii. Dead end
c. Colon
i. Several regions
ii. Ascending colon
iii. Transverse colon
iv. Descending colon
v. Sigmoid colon
d. Rectum
i. Rectal valves
ii. Internal transverse folds
e. Anal canal
i. Two sphincters
ii. Internal and external
iii. Internal is involuntary
iv. External is voluntary
5. Digestive processes
a. No breakdown
b. Water and vitamin absorption
c. Major function is the peristaltic movement of fecal material
6. Defecation
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a. Rectal walls stretch
i. Defecation reflex
b. Spinal-parasympathetic reflex
i. Causes colon and rectum to contract
ii. Anal sphincters relax
VIII. Chemical Digestion
A. Background
1. Hydrolysis
a. Catabolic process
b. Large molecules into monomers
c. Enzymes into lumen of alimentary canal
i. Intrinsic and accessory glands
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B. Carbohydrates (starch)
1. Carbohydrates are broken down into glucose, fructose and galactose
2. Process
a. Salivary amylase
b. Pancreatic amylase
C. Proteins
1. Begins in stomach
a. Pepsinogen to pepsin
2. Continues in small intestine
a. Trypsin and chymotrypsin
i. Pancreatic enzymes
b. Carboxypepsidase
i. Pancreatic enzymes
D. Lipids
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1. Digestion occurs solely in small intestine
a. Lipases from pancreas
2. Bile emulsifies fats so they are soluble
a. Only increases area that enzymes can contact
E. Nucleic acids
1. Pancreatic nucleosides
IX. Absorption
A. Active transport through the intestinal villi
1. Lipids can pass through cell membranes
a. Active transpost is not requires
2. Carbohydrates
a. Protein carriers
i. Metabolic energy is required
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