GI Motility + Secretion

Peristaltic Contractions (peristalsis)

Move food/chyme from mouth to anus (contractions)

Segmental Contractions

Mechanical mixing and breakdown; increased surface area (contractions)

Calmodulin, MLCK, cross-bridge

Ca2+ binds ___ and the Ca2+/… complex

• Stimulates __ activity

• Stimulates __-__ formation → Muscle tension

Myosin light chain phosphatase (MLCP)

Dephosphorylates myosin light chain, for muscle relaxation

Sarcomeres

Smooth muscle actin and myosin are NOT organized into…

Electrical, neural, hormonal, paracrine, Ca2+

• GI Contractility is regulated by __, __, __, __ signals

  • Via shifts in intracellular __

Slow Waves

Spontaneous cycles of depolarization for GI smooth muscle depolarization

Cells of Cajal, smooth, plexuses, 3-12, graded

Slow Waves

• Originate in pacemaker cells (__ __ __)

  • Located between __ muscle layers and nerve __

  • Generate about __ waves per minute

  • __ potentials (graded/action)

Slow wave, autonomic, stretch, acetylcholine, and parasympathetics

GI Smooth Muscle Action Potentials

• Triggered when __ __ potentials exceed threshold

• Likelihood modulated by __ signals

  • Also __ (action), __, and __ (2 neuro)

Norepinephrine, sympathetics

GI Smooth Muscle Action Potentials

• Hyperpolarization triggered by: __ (neurot) and or __ (nervous system)

Enteric Nervous System (enteric NS), independently

The __ __ __ senses, integrates, and responds to signals within GI tract

• Can operate __, no extrinsic input

Afferent sensory nerves

Nerves for distension, mucosal irritation, chemical substances

(sensory nerves)

Efferent sensory nerves

Nerves regulating motility and secretions

(sensory nerves)

Submucosal Plexus

Regulates gastrointestinal secretions (plexus)

Submucosa, glands, endocrine, vessels

Submucosal Plexus

• Located in the __

• Innervates __, __ cells, and blood __

Myenteric Plexus

Regulates gastrointestinal motility (plexus)

Circular, longitudinal

Myenteric Plexus

• Located between and innervates __ and __ muscles

Parasympathetic, sympathetic, Ach, VIP

Autonomic NS modulates and receives signals from enteric NS

• __ tone is excitatory to GI whereas __ is inhibitory

• Parasympathetic vagus and pelvic nerves

  • Cholinergic signaling - __

  • Peptidergic signaling - __

Gastrocolic Reflex

Distension of stomach stimulates contraction waves, sending bolus forward thru colon (reflex)

Rectosphincteric Reflex

Movement of fecal material into rectum stimulates stretch Rs → internal anal sphincter relaxes (reflex)

Saliva

Initiates digestion, lubricates food for swallowing, defends against pathogens, buffers acidic food

Salivary Glands

Branching duct system ending in acini

Water, ions, mucus, proteins

Saliva is hyposmotic fluid composed of (4)

ECF, mucus, amylase, lipase, IgA, and lysozymes

Initial acinar/salivary secretions contain: (6)

Na+, Cl-, K+, HCO3-, impermeable, hypoosmotic

Secretions are modified as they pass through ducts

• __ and __ are reabsorbed

• __ and __ are secreted

• Duct cells are __ (permeable/impermeable) to water

  • Net removal of solute leaves __ saliva

Lower, higher

A __ saliva flow rate → __ ductal modification of ions

(higher vs lower)

IgA

Secretory antibody protected against degradation by enzymes in saliva

Parasympathetic, increasing

__ activity > sympathetic activity at __ (increasing/decreasing) saliva secretion

• although both do so

Glycopyrrolate

Anti-muscarinic drug reducing saliva secretions prior to procedures

Glycopyrrolate, neural

__ does NOT cross BBB unlike Atropine

• Atropine with greater __ side effects as can cross BBB

Surface Mucous Cells

Cells produce mucus and HCO3-

Mucous Neck Cells

Cells only produce mucus

Mucus

Glycoproteins forming a physical barrier

Bicarbonate (HCO3-)

Neutralizes acid to maintain pH at cell surface; chemical barrier

Parietal Cells

Cells produce HCl and intrinsic factor

HCl (Stomach Acid)

Denatures proteins and defends against microorganisms

Intrinsic Factor

Protein required for Vitamin B12 absorption

Chief Cells

Cells produce pepsinogen and gastric lipase

Pepsinogen

Precursor of pepsin (protein-digesting enzyme) converting at low pH

Proton Pump

H+ pumped into lumen by H+/K+-ATPase

H+, Cl-, apical, HCO3-, Cl-, basolateral

HCl secretion by parietal cells

• Cl- follows __ to stomach lumen via __ channels on the __ membrane

• __ exits and __ enters via anion exchanger on __ membrane

H+, parietal, HCO3- absorption

How does excessive vomiting of gastric contents lead to metabolic alkalosis?

• Loss of __ from stomach

• Increased __ cell activity

• More __ __ to blood = alkalosis

GERD, PUD, duodenal ulcers

Excessive acid contributes to: (diseases)

• __ if gastric contents reflux

• ____ in stomach if protective factors are compromised

• __ __ in small bowel if too much acid and/or decreased protective factors

Exocrine, HCO3-, chyme

Pancreatic Juices - “__ Pancreas”

• __ (ion) to neutralize incoming acidic __ (substance)

• Many digestive enzymes

Lipids, bile salts, phospholipids, bilirubin

Bile (from liver/gallbladder)

• Helps with digestion and absorption of __

• Major components of bile: __ __ and acids, __, and __ (heme)