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Lecture

PHGY 210 Lecture Notes - External Anal Sphincter, Muscularis Mucosae, Loose Connective Tissue


Department
Physiology
Course Code
PHGY 210
Professor
K.Andrew White

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Digestive System
Gastrointestinal Tract
Provides nutrients to maintain homeostasis
Site of nutrient processing providing raw materials for growth, repair,
function & regulation
Anatomy
Earthworm
o Hollow tube with lumen (central cavity)
Mammals
o Hollow tube with lumen
o Communication with external environment @ both ends
o 3X longer then height of person
Extreme folding
Up to 9X longer in cadaver
o Interior lining 600X > exterior lining
200-250m2 (1/2 tennis court)
o Sequence of specialized organs that are interconnected
Serosa
o Thin tough layer of connective tissue
o Surrounds tube
Muscularis externa
o Muscular layer
Straited
Oral cavity
Pharynx
Upper 1/3 esophagus
External anal sphincter
Smooth
Between upper 1/3 of esophagus & external anal
sphincter
Outer layer
Longitudinal fibers
Inner layer
Circular fibers
Submucosa
o Loose connective tissue
Nerce cell bodies
Ganglia
Blood vessels
Lymphatics

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Mucosa
o 3 distinct smaller layers
Muscularis mucosae
Smooth muscle
Lamina propria
Loose connective tissue
Epithelial layer
Absorption
Endocrine secretion
Exocrine secretion
Functions
Motility/Propulsion
Pressure gradient
-
Variations in
resistance
-
Segmentation
Myogenic response to distension
ENS organizes
Parasympathetic
Sympathetic
Alternating relaxation &
contraction
Peristalsis
Propagated wave
Ring moves along
Narrowing lumen
8-10 seconds
Smooth
Frequency of swallowing
Flow under normal
conditions
Slow
Aboral
Little to no resistance
Absorption
Regulation
Local enteric reflexes
Vagal-vagal interactions
Hormones
Quantities of
exchange
50% ions circulate daily
80g proteins released in lumen daily
Secretion
How
Glandular activity
Result
Chemical breakdown via enzymes
& fluids
Where
In mucosa

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9L fluids absorbed daily
7L absorbed by small intestine
2L absorbed in colon
Mal-absorption
Dehydration & electrolyte imbalance
Where
Sites of exchange need abundant blood supply
Colon
Water & ions
Small intestine
Duodenum
o Fe, Ca, CHO, proteins, lipids, water,
Na
Jejunum
o CHO, proteins, lipids, water, Na
Ileum
o Vitamin B12 & bile acids (not fat!)
How
Simple diffusion
Facilitated diffusion
Active transport
Pinocytosis
Osmosis
Requirements
Adequate digestion
Enzymes activated by enterokinases for
proteases
pH level
Ion
Sufficient breakdown
Adequate size
<50% surface area
Distal ileum for bile salt absorption &
intrinsic factor
Adequate transport time
2-6 hours
Adequate co-factors
Intrinsic factor for B12
Co-lipase for pancreatic lipase
Specific transporters
Results
99% carbs = absorbed
95% fats = absorbed
92% proteins = absorbed
Highly efficient system
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