GI system

Question 1

what is the main function of the GI system? What are some of its other functions?

Answer 1

To absorb dietary nutrients. And to store and excrete.

Question 2

Describe the muscoa layer

Answer 2

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).

Question 3

Describe the submucosa layer

Answer 3

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.

Question 4

Describe the Muscularis externa (ME)

Answer 4

Made of circular and longitudinal muscle and myenteric plexus (Auerbach plexus). Sphincters regulate flow from one compartment to the next.

Question 5

Describe the Serosa layer

Answer 5

Outermost layer made of connective tissue and a layer of squamous epithelium cells. Some GI tract sections do not have a serosal layer

Question 6

The GI function is regulated by what?

Answer 6

Three divisions of the autonomic NS (ANSO

• Parasympathetic (PSNS)
• Sympathetic (SNS)
• Enteric (ENS)

Question 7

Describe some of the features of the PSNS

Answer 7

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.

Question 8

Overall how does the PSNS effect the GI system?

Answer 8

It stimulates GI secretions and movement which facilitates digestion and absorption.

Question 9

Describe some features of the SNS

Answer 9

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.

Question 10

Generally how does the SNS affect the GI

Answer 10

It decreases secretions and motility.

Question 11

How do the nervous systems interact with the ENS

Answer 11

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.

Question 12

how are the ENS nerves organised?

Answer 12

into myenteric and submucosal plexuses.

Question 13

Describe the Myenteric Plexus

Answer 13

Its primary role is regulating intestinal smooth muscle. It controls rhythmic and tonic contractions.

Question 14

Describe the submucosal Plexus

Answer 14

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.

Question 15

What are ENS neurons supportd by?

Answer 15

Enteric glial cells

Question 16

Describe the ENS reflexes

Answer 16

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.

Question 17

Name some ENS neurotransmitters

Answer 17

Enkephalins : constrict circular muscle around sphincters.

VIP, substand p, Acetylcholine (ACh), nitric oxide and serotonin.

Question 18

Name some non-neural signalling molecules

Answer 18

Hormones; CCK (cholecystokinin), gastrin, motilin and secretin.
Paracrines; Prostaglandins, somatostatin (more widespread) and histamine.

Question 19

Name the three digestive phases

Answer 19

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.

Question 20

Describe the role and structure of the mouth

Answer 20

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.

Question 21

Where is saliva produced and what is it controlled by?

Answer 21

In the sublingual, submandibular and parotid glands, controlled by the PSNS and the SNS.

Question 22

Explain the basics of swallowing

Answer 22

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.

Question 23

What is peristalsis and what’s its role

Answer 23

It is a series of co-ordinated muscle contractions which forces food ahead. It begins after the upper oesopheageal sphincter.

Question 24

whats the role of the oesophagus?

Answer 24

To transport food to the stomach from the mouth.

Question 25

Describe the role of the stomach

Answer 25

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.

Question 26

Name the three sections of the small intestine and the role of the small intestine

Answer 26

The duodenum, jejunum, and ileum.

It absorbs macronutrients, vitamins and minerals.

Question 27

Name the sections of the large intestine and its role.

Answer 27

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.