Human Phys chapter 8

Serosa

Outermost protective covering

Longitudinal muscle

Shortens the GI tract when it contracts

Circular muscle

Squeezes the GI tract inward

Submucosa

Contains blood vessels, nerves, and supporting tissue

Mucosa

Innermost lining involved in secretion and absorption

Example: Instead of each intestinal muscle cell contracting independently, electrical signals spread between cells to coordinate contractions that move food.

syncytium

Increasing excitability

stretching muscle, ACh, Certain Gi Hormones

Decreases excitability

NE, Epinephrine, Sympathetic stimulation

Depolarization of GI smooth muscle

less negative membrane, less excitable, NO contraction

Hyperpolarization of GI smooth muscle

more negative membrane, less excitable, decreased likelihood of contraction

Tonic Contractions

can form repeated spikes, partial depolarization, and continuous ca+ entry

ENS enteric nervous system

myenteric plexus

Myenteric plexus (Auerbach's)

the movement of food.

Submucosal plexus (Meissner's)

Mainly controls GI secretion and local blood flow

Parasympathetic

increase GI motility

Sympathetic (autonomic NS)

decreases GI motility

during a stressful situation, _ activation can slow digestive movements because your body is prioritizing other functions.

sympathetic

Gastrocolic

Stomach activity increases colon movements, often causing the urge to defecate after eating

Gastroileal

Stomach activity increases ileal motility and movement into the colon

Enterogastric

Duodenum signals stomach to slow emptying

Ileogastric

Distended ileum inhibits stomach motility

Colonoileal

Colon inhibits emptying from ileum into colon

Vagovagal

Signals travel through the vagus nerves to the brainstem and back to regulate stomach activity

You eat breakfast and suddenly need to use the bathroom.

gastrocolic reflex

Gastrin

Increases stomach acid secretion and gastric mucosal growth

Gastrin triggered by

Food, stomach distention, protein products

CCK triggered by

Fatty acids and fat digestion products

Secretin triggered by

acid entering duodenum

GIP triggered by

Nutrients in upper small intestine

Motilin triggered by

fasting

You eat something fatty. CCK tells your gallbladder to contract and release bile to help digest fats.

CCK

Acidic chyme enters your duodenum. Secretin tells the pancreas to release bicarbonate to neutralize that acid.

Secretin

Nutrients enter your small intestine, and GIP helps stimulate insulin secretion.

GIP

You haven't eaten for a while. Motilin stimulates waves of movement that help clear the stomach and small intestine between meals.

Motilin ( migrating motor complex )

Law of the gut

When the intestine stretches:

The intestinal muscle contracts behind the food.

atropine can..

greatly reduce peristalsis by blocking cholinergic activity

The law of the gut ( when the gut stretches ) requires

myenteric plexus

splanchnic circulation

supplies blood to the GI organs, spleen, pancreas, and liver

what is a key pathway in gastrointestinal blood circulation

intestines,spleen, pancreas→ hepatic portal vein→ liver sinusoids→ hepatic veins to the vena cava

blood flow to the intestines increases during this time because the gut needs more oxygen and and nutrients to support digestion and absorption

after eating

Countercurrent oxygen exchange

Some oxygen moves directly from villus arterioles to venules, leaving villus tips vulnerable when blood flow decreases.

Autoregulatory escape:

ympathetic vasoconstriction initially reduces gut blood flow, but local metabolic vasodilators can restore it toward normal.

The muscles of mastication are controlled by

cranial nerve V (trigeminal nerve), mandibular division.

Three stages of swallowing

oral

which stages of swallowing is voluntary

oral

which stages of swallowing are not voluntary

Pharyngeal

“the soft palate closes off the nasal cavity, the vocal cords close, the epiglottis helps protect the airway, and the upper esophageal sphincter relaxes.” is an example of which stage of swallowing

pharyngeal stage

where is the swallowing center

medulla and lower pons

Primary peristalsis

Triggered by swallowing.

secondary peristalsis

Triggered by esophageal distention from retained food

tertiary peristalsis

Irregular, nonpropulsive contractions.

lower esophageal sphincter (LES)

normally contracted to prevent acid reflux, but relaxes during swallowing to let food enter the stomach

Retropulsion

When stomach contractions push chyme toward the pylorus, only a small amount passes into the duodenum. Most is pushed backward into the stomach.

Retropulsion helps…

mix food thoroughly

The enterogastric reflex and CCK help…

slow emptying so the small intestine has time to digest and absorb nutrients

The small intestine uses:

Segmentation: Mixing chyme with digestive secretions.

Peristaltic rush:

Intense intestinal irritation, such as severe infectious diarrhea, can trigger very strong, rapid peristalsis to move irritating contents into the colon.

The ileocecal valve helps prevent backflow of colonic contents into the

small intestine

Large intestine and defecation

The colon has two main functions:

Absorb water and electrolytes to form solid feces.

Haustrations

pouchlike segments created by contractions of circular muscle and the longitudinal muscle bands called the teniae coli. They help mix colonic contents

an example of defecation reflex

voluntary relaxation of the external anal sphincter allows defecation

what is the difference between internal anal sphincter and external anal sphincter

internal relaxes involuntarily, external is voluntarily controlled