GI system Flashcards
what is the main function of the GI system? What are some of its other functions?
To absorb dietary nutrients. And to store and excrete.
Describe the muscoa layer
Made of Epithelium (single cell layer, the extent of vili and crypts vary with the GI section function), Lamina propria (loose connective tissue made of collagen and elastin fibres, contains sensory nerves, lymphatic and blood vessels and secretory glands) and Muscularis mucosa ( thin layer of smooth muscle, further increases surface area by creating folds and ridges).
Describe the submucosa layer
Thicker layer which has a similar composition to lamina propria. Has blood vessels and nerve bundles that form a submucosal plexus (Meissner plexus), part of the entric nervous system.
Describe the Muscularis externa (ME)
Made of circular and longitudinal muscle and myenteric plexus (Auerbach plexus). Sphincters regulate flow from one compartment to the next.
Describe the Serosa layer
Outermost layer made of connective tissue and a layer of squamous epithelium cells. Some GI tract sections do not have a serosal layer
The GI function is regulated by what?
Three divisions of the autonomic NS (ANSO
- Parasympathetic (PSNS)
- Sympathetic (SNS)
- Enteric (ENS)
Describe some of the features of the PSNS
It has stimulus derived from the vagus (medulla oblongata) and from the pelvic-splanchnic (S2-S4). It has sensory and motor components which respond to strech, pressure, temperature and osmolarity. The primary neurotransmitters used are acetlycholine (ACh), Gastric-releasing peptide and substance p.
Overall how does the PSNS effect the GI system?
It stimulates GI secretions and movement which facilitates digestion and absorption.
Describe some features of the SNS
The nerves originate from the thoracic (T5-T12) and the lumbar (L1-L3) regions. The nerves will synapse in 1 of 3 ganglia; the celiac, superior mesenteric for the upper GI tract and inferior mesenteric for the lower GI system.
Generally how does the SNS affect the GI
It decreases secretions and motility.
How do the nervous systems interact with the ENS
the PSNS and the SNS usually synapse with and modulate the ENS however the ENS can work independently due to intrinsic regulation and sensory reflexes.
how are the ENS nerves organised?
into myenteric and submucosal plexuses.
Describe the Myenteric Plexus
Its primary role is regulating intestinal smooth muscle. It controls rhythmic and tonic contractions.
Describe the submucosal Plexus
Its primary role is to regulate intestinal secretions and local absorptive environment. It can also synapse on blood vessels, circular and longitudinal muscle and muscularis mucosa.
What are ENS neurons supportd by?
Enteric glial cells
Describe the ENS reflexes
Neural circuits involve mechanoreceptors (that pick up movement) or chemoreceptors (pick up changes in chemistry) stimulation in the mucosa, this regulates GI reflex actions.
The signal is transmitted to neurons in the submucosal plexus which can stimulate other neurons in the submucosal or myenteric plexus which regulate endocrine or secretory cells.
Name some ENS neurotransmitters
Enkephalins : constrict circular muscle around sphincters.
VIP, substand p, Acetylcholine (ACh), nitric oxide and serotonin.
Name some non-neural signalling molecules
Hormones; CCK (cholecystokinin), gastrin, motilin and secretin.
Paracrines; Prostaglandins, somatostatin (more widespread) and histamine.
Name the three digestive phases
1) Cephalic phase - triggered by the thought of food or other stimuli, causes ACh and VIP to be released.
2) Gastric phase - when food and oral secretions enter the body, elicits neural, hormonal and paracrine GI responses
3) Intestinal phase - beings when stomach contents reach duodenum. Initiates hormonal, paracrine and neural responses.
Describe the role and structure of the mouth
It transports and prepares food to be absorbed. It mechanically and chemically breaks down food. Teeth cut and tear food, jaw muscles provide force and the tongue repositions food.
Where is saliva produced and what is it controlled by?
In the sublingual, submandibular and parotid glands, controlled by the PSNS and the SNS.
Explain the basics of swallowing
Swallowing which is mostly voluntary but involuntary when initiated. It is a parasympatheic process. Efferent responses through other nuclei so that the muscle is contracted in the correct order. It also coordinates with other functions such as speech and breathing.
What is peristalsis and what’s its role
It is a series of co-ordinated muscle contractions which forces food ahead. It begins after the upper oesopheageal sphincter.
whats the role of the oesophagus?
To transport food to the stomach from the mouth.
Describe the role of the stomach
Accept and store food, mix food with secretions, digest food and deliver to small intestine. The secretions are derived from gastric invaginations. Pits near sphincters have more mucus.
Name the three sections of the small intestine and the role of the small intestine
The duodenum, jejunum, and ileum.
It absorbs macronutrients, vitamins and minerals.
Name the sections of the large intestine and its role.
The caecum, ascending, transverse, descending and sigmoid colon, the rectum ans anus. It absorbs most water and ions and is involved in mixing and propulsion.
