Digestive system1

Question 1

Functions of digestion:

Answer 1

Absorb water, vitamins and minerals and eliminate waste

Question 2

Name the 2 basic digestive processes

Answer 2

Mechanical: the process of physically breaking down the food e.g. through chewing, churning and peristalsis.

Chemical: the process of chemically splitting large molecules into smaller molecules using enzymes, acids and bile.

Question 3

Name the two groups of organs in the digestive system:

Answer 3

Gastrointestinal (GI) tract: A continuous tube that extends from the mouth to the anus, through the thoracic and abdominopelvic cavities. Includes mouth, most of the pharynx, oesophagus, stomach, small intestine and large intestine.

Accessory digestive organs: Organs that help or feed liquids into the GI tract; teeth, tongue, salivary glands, liver, gallbladder and pancreas

Question 4

What are the 4 major layers of the GI tract?

Answer 4

Mucosa (innermost)
Submucosa
Muscularis
Serosa (which is visceral peritoneum)

Question 5

Structure and function of the mucosa layer

Answer 5

A mucous membrane that forms the inner lining of the GI tract. Consists of:

-A layer of epithelium: in direct contact with the contents of the GI tract (cells are non-keratinised stratified squamous, simple columnar, exocrine and enteroendocrine cells)

-Lamina propria: a layer or connective tissue
(loose areola CT, blood and lymph vessels, Mucosa associated lymph tissue (MALT))

-Muscularis mucosa: a thin layer of smooth muscle
The section throws the mucous membrane of the stomach and small intestine into many small folds which increases the surface area for digestion and absorption.

Question 6

Structure and function of the submucosa layer:

Answer 6

Blood and lymphatic vessels: Receives absorbed food and molecules.

Submucous Plexus: An extensive network of neurons from the autonomic nervous system that innervates mucosa, blood vessels and secretory cells of mucosal glands.

Glands and lymphatic tissue

Question 7

Structure and function of the muscularis layer

Answer 7

Skeletal muscle: In mouth, pharynx, upper oesophagus and anus; voluntary control over swallowing and defecation.

Smooth muscle: Rest of the GI tract; involuntary control that mixes, crushes and propels food along by peristalsis. This process is controlled by our enteric and autonomic nervous systems.

Myenteric plexus: Innervates circular and longitudinal smooth muscle layers.

Question 8

structure and function of serosa

Answer 8

This layer is a serous membrane that is superficial to the GI tract organs suspended in the abdominopelvic cavity.

This is the visceral peritoneum layer that secretes a slippery fluid which allows the GI tract to sit in the right orientation within the body.

The oesophagus lacks a serosa and instead, a single layer of areolar connective tissue called the adventitia form the superficial layer of this organ.

Question 9

what is known as the ‘gut brain’?

Answer 9

the enteric nervous system (ENS);

an intrinsic set of nerves forming the myenteric plexus and submucosal plexus

Question 10

the GL tract is regulated by what (3)?

Answer 10

Enteric nervous system “gut brain”: an intrinsic set of nerves forming the myenteric plexus and submucosal plexus.

Autonomic nervous system: an extrinsic set of sympathetic and parasympathetic nerves that form neural connections with the enteric nerves.

Gastrointestinal reflex pathways: short reflexes are mediated by local enteric plexuses and long reflexes involve extrinsic autonomic nerves and CNS centres.

Question 11

local (short) reflex innervation from start to finish:

Answer 11

1- internal stimuli
2- chemo/osmo/mechanoreceptors register signal
3- local nerve plexus sends message
4- effectors receive message
5- response occurs

Question 12

What is the extra step in a long reflex, often following external stimuli like sight, smell, taste or thought of food?

Answer 12

Central nervous system

Question 13

what is the peritoneum and its divisions?

Answer 13

The largest serous membrane of the body, the peritoneum consists of two divisions:

Parietal peritoneum: lines the wall of the abdominal cavity
Visceral peritoneum: covers some of the organs and constitutes their serosa

The peritoneal cavity is the potential space between the parietal and visceral portions of the peritoneum, which contains serous fluid.

Question 14

what are peritoneal folds and the 5 major ones?

Answer 14

The weave between the viscera is known as the peritoneal folds, which bind the organs to one another and to the walls of the abdominal cavity. They contain blood vessels, lymphatic vessels and nerves of the abdominal organs. There are five main peritoneal folds:

Greater omentum​
Falciform ligament​
Lesser omentum​
Mesentery​
Mesocolon

Question 15

structure and function of the greater omentum?

Answer 15

the greater omentum acts as a fold that hangs down over the inner abdominal viscera.
These peritoneal folds provide the gastrointestinal tract with the blood and nerves while the mesentery ties all this of the viscera together.

Question 16

list the salivary glands

Answer 16

Small glands: Labial, buccal, palatal, lingual

Major glands:
Parotid (inferior and anterior to ears)
Submandibular (medial and partly inferior or mandible)
Sublingual glands (beneath tongue; superior to submandibular)
They secrete fluid into the mouth vis canals

Question 17

structure and function of saliva

Answer 17

Saliva helps to remove waste molecules from the body, protects the mouth from infection with its rinsing action and keeps the mucous membranes of the mouth and pharynx moist. It is composed of:

Water: Dissolves foods to be tasted by gustatory receptors and begin digestive reactions.
Mucus: Lubricates food to facilitate bolus formation and swallowing.
Bicarbonate and phosphate ions: Buffer acidic foods that enter the mouth.
Chloride ions: Activate salivary amylase.
Salivary amylase: Starts the breakdown of starch in the mouth.
Lysozyme: Enzymes that kill bacteria.
Immunoglobulin A (IgA): Prevents attachment of microbes to the epithelium.

Question 18

2 types of chemical digestion:

Answer 18

Salivary amylase​: Begins starch digestion at pH of 6.5 or 7.0 found in mouth​. When bolus and enzyme hit the pH 2.5 gastric juices hydrolysis ceases​.

Lingual lipase​: Secreted by glands in tongue​ and activated in stomach and breakdown triglycerides into fatty acids and diglycerides.

Question 19

pathway of food

Answer 19

mouth, pharynx, oesophagus, stomach, through pyloric sphincter into small intestine, large intestine (colon), rectum, anus

Question 20

the 3 stages of swallowing?

Answer 20

voluntary, pharyngeal (involuntary) and oesophageal (involuntary)

Question 21

describe the pharyngeal stage of swallowing

Answer 21

The bolus in the oropharynx stimulates receptors which send impulses to the deglutition centre in the medulla oblongata and lower pons of the brainstem.

• The soft palate and uvula move upward to close off the nasopharynx
• The epiglottis closes off the opening to the larynx
• The bolus moves through the oropharynx and the laryngopharynx
• The upper oesophageal sphincter relaxes and the bolus moves into the oesophagus

Question 22

describe the oesophageal stage of swallowing

Answer 22

This stage beings when the bolus enters the oesophagus.

Peristalsis: A progression of coordinated contractions and relaxations of the circular and longitudinal layers of the muscularis; pushes the bolus further down the tract​.

Lower oesophageal sphincter: Relaxes as the bolus approaches the end of the oesophagus, and the bolus moves into the stomach.​

Oesophageal glands: Secret mucus to lubricate the bolus and reduce friction.

Question 23

function and structure of the stomach

Answer 23

Starting at the bottom of the oesophagus and ending at the pyloric sphincter, the stomach is a j-shaped structure that has the following functions:

Mixes saliva, food and gastric juices to form chyme
Serves as a reservoir for food before release into the small intestine
Secretes gastric juices
Secretes gastrin into blood

Question 24

subdivisions of the stomach:

Answer 24

The gross anatomical subdivisions of the stomach are the cardia, fundus, body and pylorus. We can also see:

Rugae: the mucosal folds, when the stomach is empty. It allows the stomach to stretch to accommodate a meal.

Pyloric sphincter: A smooth muscle sphincter through which the pylorus communicates with the duodenum of the small intestine

Lesser curvature: Concave medial border of the stomach.

Greater curvature: Convex lateral border of the stomach, increases in size when the stomach fills.

Question 25

function of the gastrin hormone (from G cell)

Answer 25

The Gastrin hormone acts as a local endocrine hormone. It also:

Stimulates parietal cells to secrete HCl and chief cells to secrete pepsinogen​
Contracts lower oesophageal sphincter
Increases motility of the stomach
Relaxes pyloric sphincter​

Question 26

describe gastric emptying

Answer 26

Gastric emptying occurs as food reaches the pylorus, each mixing wave periodically forces about three millilitres of chyme into the duodenum through the pyloric sphincter. This will create neural reflexes that determine how long that food will stay in the stomach.

Foods rich in carbohydrates spend the least amount of time in the stomach; high protein foods remain slightly longer and gastric emptying is slowest after fat-rich meals containing large amounts of triglycerides.