Digestive Processes
Secretion
Motility
Digestion
Absorption
Overview: Fig 19.1
Digestive System: Fig 19.2
Gastrointestinal wall structure; Fig 19.3
Review of Smooth Muscle
Chapter 11, pages 360 - 363
Smooth Muscle
Small, discrete cells - 20 ?m
Linked by gap junctions
Membrane invaginations - caveoli
Little SR
Actin & Myosin but no striations
Intermediate filaments
Smooth muscle structure: Fig 11.29
Smooth Muscle
Oscillating Vm
High GNa+ and variable GK+
Responds to stretch
Mysoin regulation of contraction
Smooth muscle slow waves: Fig 19.27
Ca++ for Contraction
Open membrane channels
Voltage gated membrane cannels
Ligand gated membrane channels
SR and ER
Released by IP3
Ca++ Removal
SR, ER, & Membrane Ca++ ATPase
Na+ - Ca++ exchange in membrane
Peristalsis: Fig 19.29a
Segmentation: Fig 19.29b
Innervation of GI Tract
Parasympathetic
Sympathetic
Enteric
local, intrinsic neurons
cell bodies in ganglia in GI walls
Integration (Review Table 10.3 !!!!)
Enteric Nervous System Figs 19.3
Receptors
Mechano
Chemo
Thermo
Interneurons
Reflexes & motor programs
Excitatory and Inhibitory motor neurons
Muscles
Blood vessels
Secretory cells
Enteric Nervous System
Vagus nerve contains afferent and efferent neurons to connect enteric
n.s. with cns
Activity of enteric n.s. influenced by:
chemical composition
volume
Autonomic inputs
Sympathetic Actions
Inhibition:
decrease motility and secretion via ?2 and???2 receptors
decreased blood flow via ?1
decreased NT release by enteric system via ?2 on presynaptic terminals
Parasympathetic
Excitation:
ACh on muscarinic receptors
directly onto muscle and secretory cells
directly onto enteric nerves to cause epsps