GI: Control, Blood Circulation, Motility, Secretion- Mahmoud

Conditions in what part of the GI are controlled by stimuli

Lumen

What controls the control mechanisms of the GI

Luminal content and composition

What are some luminal stimuli

Distension
Osmolarity
Acidity
Concentration of digestive products

What are some types of receptors in the GI and where are they located

Mechao, osmo, and chemoreceptors located in the wall of the tract.

What are the effectors of the GI

Muscles in the wall of the tract and exocrine glands

What are two types of broad control mechanisms

Neural and GI Peptide Control

Name 7 layers of the GI tract, Outside--> Lumen

Serosa, Longitudinal Muscle, submucosa, muscosal muscle, mucosa, epithelial

Three types of neural control of the GI

Enteric System (myenteric/Submucosal), ANS, Sensory Nerves

Define Enteric System

Lies in the the GI Wall, controls movement and secretion, can fxn on its own or under ANS

What are the two divisions of the enteric system

Myenteric Plexus Submucosal Plexus

Myenteric Plexus

GI full length control of movement, b/w longitudinal and circular muscle layers, excitatory and inhibitory

Submucosal Plexus

Locally controls secretion and blood flow

What are neurotransmitters of the Enteric System

ACh: Excitatory, N.E.: Inhibitory

What are four basic neuron types of the enteric system

Sensory
Secretory
Motor
Interneurons

sensory afferent neurons of the enteric system send signals from these two types of receptors in the GI tract.

Mechano or chemo receptors respond to stretch or food stimuli within the mucosal epithelium

Secretory neurons of the enteric system

innervate secretory cells and regulate endocrine and exocrine fxns

Motor neurons of the enteric system

Control gut motility, mucosa surface area, and blood vessel diameter

interneurons of the enteric system

Allows for communication between sensory and motor neurons in/out and up/down the GI tract. Also communication between two plexus (myenteric and submucosal)

What are the two nerves involved in parasympathetic control of the GI tract enteric system; inhibitory or excitatory

Vagus and Pelvic Nerves; excitatory control

How is sympathetic ANS connected to the enteric system; inhibitory or excitatory

Through sympathetic nerves originating b/w T5 and L2; inhibitory

What do to the afferent neurons of the GI do

They allow the brain to know the conditions of the GI

What do the motor nerves of the GI do

They allow for some voluntary control like swallowing and defecation

Where do the sensory nerves in the GI send afferent fibers to (3)

Enteric Plexus
Sympathetic system
Parasympathetic system

What kind of control is carried out by GI peptides

Non neural control of the GI tract

What are three types of GI peptides

paracrine, endocrine (hormone), and neurocrine

What is an example of a paracrine hormone

Histamine

What are three examples of neurocrine peptides in the GI

Vasoactive Intestinal Peptide (VIP)
Gastrin Releasing Peptide (GRP)
Enkephalins

Where are endocrine GI peptides realeased from and how are endocrine peptide hormones of the GI utilized

Released into the blood from APUD cells, into portal circulation, then systemic circulation, then target cell and slow to act

What are some examples of endocrine GI peptides

Cholycystokinein CCK (maybe in ileum)
Gastrin
Motilin
Secretin

Where are paracrine GI peptides released from and how are paracrine peptide hormones of the GI utilized

Released from paracrine APUD cells not into the circulation, delivered by diffusion to neighboring cells.

Where are most APUD cells

in the duodenum and jejunum, none in the colon

What is the only hormones secreted by the stomach

Gastrin

What are the two types of GI peptides released by APUD cells

endocrine and paracrine

Neurocrines

Produced in neurons realeased via AP and act on target cell

What type of mechanism controls the affect of hormones on their target cell, give an example

Feedback mechanism: FAs and AAs trigger CCK release from the small int. CCK stimulate pancreas and gall bladder, CCK is removed upon absorption of FAs and AAs

What is special about an effector cell

Receptors for more than one hormone
Receptors for more than one NT
Receptors for more than one paracrine agent

What is hormone potentiation

when one hormone affects amplifies the response of another

What is the portal circulation

Blood coming from the GI with nutrients and toxins to the liver

What do the sinusoids in the liver do

Blood flows through them and they remove bacteria and particulates

Where does blood in the Portal Vein come from and where does it end up

GI, spleen and pancreas. Ends up in the liver and systemic circulation

What is the hepatic vein

Blood from the GI that leaves the liver into the systemic circulation, travels through here

What is splanchnic circulation, from where and what three parts of the GI does it go through, what organs are supplied blood

Blood flow from the AORTA through the GI; celiac artery(stomach/spleen), superior mesenteric artery(pancreas/sm. int/lg. int.), inf. mesenteric artery(only lg. int.)

What is the flow of blood in the villi of the small int.

They flow in the opposite direction of the veins. exchange happens at the very bottom of the villi

Through what blood vessel does blood from the GI enter the liver

Portal vein

What are the branches of the portal vein in the liver called

Sinusoids

Through what vein does the blood in the liver leave

Hepatic Vein

What is the portal triad

Consists of portal vein, bile duct, and hepatic artery.

What are two types of GI motility movements

Propulsive and mixing movements

What is peristalsis

Propulsive movements caused by a series of alternating contractions and relaxationsof smooth muscle in the wall of GI tract.

What are three mehanisms that stimulate peristalsis

Distension, chemical and physical

Perisitalsis is only effective with the aid of what plexus and what type of muscle

Myenteric plexus and contractile ring in circular muscles behind the point of distenstion

disorder of peristalsis of distal bowel caused by absence of parasympathetic ganglion cells

Congenital megacolon

How is peristalsis initiated

Spreading contraction of the the circular muscle

What is happening to the longitudinal muscle and the circular muscle during peristalsis

Longitudinal muscle is contracting and the circular muscle ahead of the bolus is relaxing.

What is segmentation movement in the GI

It is the mixing movement. Circular layer contraction of the lumen an compress GI contents at that site. Not for propulsion of food.

What is the transit time of food through the GI tract

about 36-48 hours

What two types of muscles is the myenteric plexus composed of

Circular(inner) and longitudinal (outter)

Contraction of the myenteric plexus results in what

Increased GI motility

Relaxtion of the myenteric plexus results in what

Decreased GI motility

What are some GI smooth muscle sphincters, and where are they located (7)

1)UES: Oral cavity and esophagus
2)LES: Esophagus and stomach
3)Pyloric: Stomach and duodenum
4)Ileocecal: Ileum and Colon
5)Colorectal: colon and rectum
6)Int. Anal: Rectum and anal canal
7)Ext. Anal: Anal canal and external.

Relaxation of the sphincters results in what

Increased GI propulsion

Contraction of the GI sphincters results in what

Decreased GI propulsion

What has dominant control over GI motility

Neural control
Parasympathetic: increase propulsion and mixing
Sympathetic: Decrease propulsion and mixing

What is intrinsic myogenenic control or intrisic basal tone

Smooth muscle of GI under constant tonic contraction, without extrinsic input from nerves or hormones

What does enteric autonomic control contribute

Controls myenteric plexus, integrates with extrinsic controls for fine local control and coordinates propulsion/mixing

What can modulate basal tone

Extrinsic factors such as neural and hormonal

Define GI secretion

Production and release of fluids and substances into the lumen of the GI tract by mucosal cells and accessory organs

What is the total volume of secretions by the GI

7200 ml

What is usually the composition of secreted fluid in the GI; what does it depend on

Water, mucus and ions, enzymes and hormones; depends on the type of cell it is secreted from

Goblet cells

Single celled glads in the mucosa secrete mucus to lubricate and protect the surface from abrasion and chemical digestion

Brunner's glands

Compound glands near the proximal duodenum, secrete alkaline mucus to neutralize the gastric acid entering from the stomach

Tubular glands

Located in the stomach and duodenum. Acid secreting parietal cells and pepsinogen secreting chief cells for protein digestion and GI immunity

Crypts of Lieberkuhn

Deep pits formed by mucosal folds in the small int. that secrete digestive enzymes, H2O and ions to facilitate digestion and absorbtion

APUD cells

single cell mucosal endocrine glands mainly in the small int. Secrete various hormones

Accessory glands

Salivary glands, pancreas, liver. secrete saliva Bicarb, enzymes and bile for lubrication acid neutralization, digestion and absorption