The Digestive System

Question 1

What organs does the alimentary canal consist of?

Answer 1

Mouth, Pharynx, oesophagus, stomach, small intestine, large intestine and anus

Question 2

Name the accessory organs of digestion.

Answer 2

The Teeth, Tongue, gall bladder, and a large number of glands, namely the salivary glands, liver and pancreas.

Question 3

What are the 6 basic digestive processes?

Answer 3

Ingestion
Propulsion 
Mechanical breakdown 
Chemical digestion 
Absorption 
Dedication

Question 4

What are the four tissue layers of the GIT wall?

Answer 4

Adventitia or serosa 
Muscle layer
Submucosa 
Mucosa 
(Lumen)

Question 5

Describe the structure and composition of the Adventitia.

Answer 5

Outermost layer of the GIT.
In the Thorax it is made up of loose fibrous tissue
In the Abdomen the organs are covered with a serous membrane (serosa) called peritoneum

Question 6

Describe the structure of the peritoneum.

Answer 6

Largest serous membrane in the body
It is a closed sac containing a small amount of serous fluid within the abdominal cavity
It is richly supplied with blood and lymph vessels, and contains many lymph nodes.
Has 2 layers

Question 7

What is the function of the peritoneum?

Answer 7

Provides a physical barrier to local spread of infection

Can isolate infective focus such as appendicitis, preventing involvement of other abdominal structures.

Question 8

What are the two layers of the peritoneum?

Answer 8

The parietal peritoneum, lines the abdominal wall.

The Visceral peritoneum covers the organs (viscera) within the abdominal and pelvic cavities.

Question 9

What is the function of the serous fluid in the peritoneal cavity?

Answer 9

The serous fluid prevents friction between the peritoneal layers.
The fluid is produced by peritoneal cells thus creating the cavity.

Question 10

Describe the structure of the peritoneal cavity.

Answer 10

In males it is completely closed
In females the uterine tubes open into it and the ovaries are the only structures inside it.
The arrangement of the peritoneum is such that the organs are invaginated (forming a pouch) into the closed sac from below, behind and above.
The pelvic organs are only covered on their superior surface.
The stomach and intestines are deploy invaginated from behind and are almost completely surrounded by peritoneum

Question 11

Describe the structure location and function of the greater omentum

Answer 11

The greater Omentum is the peritoneal fold that encloses the stomach and extends down in-front of the abdominal organs like an apron.
It’s function is to store fat that provides both insulation and an energy store.

Question 12

Describe the structure and function of the Mesentery

Answer 12

The Mesentery is a broad fan shaped fold that suspends coils of intestine from the posterior abdominal wall

Question 13

What are the retroperitoneal organs and why are the given this name?

Answer 13

The Pancreas, Kidneys, Adrenal glands, Duodenum and ascending and descending colons are known as retroperitoneal organs as they lie on the posterior abdominal wall and only their anterior surface is covered by peritoneum

Question 14

Describe the muscle layer of the GIT.

Answer 14

With some exceptions this layer consists of two layers of involuntary smooth muscle.
Outer muscle fibers are arranged longitudinally
Inner muscle fibers are arranged to encircle the walls of the tube
Between these two layers there are blood vessels, lymph vessels and a plexus (network) of sympathetic and parasympathetic nerves.

Question 15

Describe how the muscle layer of the mouth, Pharynx and superior and middle parts of the oesophagus differs slightly from everywhere else.

Answer 15

The muscle layer of the mouth, Pharynx and superior and middle parts of the oesophagus contains skeletal muscle that produces voluntary swallowing.
Skeletal muscle also forms the external sphincter, which permits voluntary control of deification

Question 16

Describe the structure of the submucosa

Answer 16

This layer consists of areolar connective tissue containing collagen and some elastic fibers, which bind the muscle layer to the mucosa.
Within the submucosa, there are blood vessels, lymph vessels and a plexus of sympathetic and parasympathetic nerves.

Question 17

What are the three layers of the mucosa and what are there functions

Answer 17

The mucosa membrane is the innermost membrane and has three main functions; protection, secretion and absorption
The Lamina Properia is the middle layer consisting of loose connective tissue that supports the blood vessels, and lymphoid tissues that protect against microbial invaders
The Muscularis mucosa is a thin layer of smooth muscle that increases the surface area for digestion and absorption.

Question 18

Describe the parasympathetic nerve supply of the GI tract and their effects.

Answer 18

Supplied by one pair of the vagus nerves and their effects are,

Increased muscular activity (especially peristalsis)

Increased glandular secretion .

The activity of the parasympathetic nervous system is increased when digestion is required. (Rest and digest)

Question 19

Describe the sympathetic nerve supply of the GI tract and there effects

Answer 19

Supplied by numerous nerves from the spinal cord from the thoracic and lumbar regions, there effects are,

Decreased muscular activity (especially peristalsis)

Decreased glandular secretion

Question 20

Describe the components of the oral or buccal cavity and their location in relationship to each other

Answer 20

Formed by cheeks, hard and soft palate and the tongue
The cheeks are the lateral walls of the mouth, anteriorly they are continuous with the lips. The lips are fleshy folds surrounding the opening of the mouth, they contain a muscle that is covered externally by skin and internally by a mucous membrane. The hard and soft palate provides the roof of the oral cavity.
The hard palate is the anterior part of the roof, formed by bones and covered by a mucous membrane.
The soft palate is the posterior muscular arch shaped part. The uvula is a comical muscular process, hanging from the free border of the soft palate. During swallowing the soft palate and uvula are drawn superiorly , preventing the food and liquid from entering g the nasal cavity.

Question 21

What bones make up the hard palate

Answer 21

The two bones that make up the hard palate are,

The palatine process of the maxilla
And
The palatine bone

Question 22

What is important about both the vestibule and the fauces when managing an airway?

Answer 22

The vestibule is a part of the the oral cavity that includes the space between the cheeks, lips and teeth. This part needs to be considered during suctioning of the mouth as part of airway management.
The fauces is the opening between the oral cavity And the pharynx, this opening needs to be considered during the insertion of a supraglottic airway device

Question 23

What are the main functions of the mouth?

Answer 23

It analyses material before swallowing
It mechanically processes material through the action of teeth, tongue, and palates
It lubricates material by mixing it with mucus and saliva.
It begins the digestion of carbohydrates with the help of salivary enzymes (amylase)

Question 24

Describe the structure and location of the oesophagus?

Answer 24

The oesophagus is a muscular tube that starts at the Pharynx and ends at the stomach.
It is about 25 cm long with a diameter of about 2cm
The oesophagus lies posterior to the trachea in the neck, passes through the mediastinum in the thoracic cavity.
It then enters the peritoneal cavity through an opening in the diaphragm, at the level of the 10th thoracic vertebra, to join the stomach.

Question 25

Describe the structure of the stomach

Answer 25

The stomach is a j-shaped organ of the GIT located in the left upper quadrant of the abdominal cavity The stomach divided into three main regions, the fundus, body and pylorus It is continuous with the oesophagus at the cardiac sphincter and with the duodenum at the pyloric sphincter The lesser curvature is the left border of the stomach, concave in shape it provides attachment to the lesser omentum. The greater curvature is the right border of the stomach, convex in shape and provides attachment to the greater omentum

Question 26

Describe the structure of the stomach wall and the function of it

Answer 26

Unlike the two layered muscularis externa of the other portions of the GIT, that of the stomach contains three layers allowing the churning motion of the gastric activity. These layers are; The outer layer of longItudinal fibers The middle layer of circular fibers The inner layer of oblique fibers When the stomach is empty the mucous membrane lining is thrown into prominent ridges and folds called rugae When the stomach is full it’s smooth muscle and mucous membrane stretch, the rugae disappear giving the surface a smooth appearance.

Question 27

What is the function of the stomach

Answer 27

Temporary storage , allowing time for enzymes to act Chemical digestion including pepsin breaking down protein to polypeptides Mechanical breakdown, helped by gastric juice, turns food into Chyme Limited absorption, e.g. water, alcohol and some lipid soluble drugs Non specific defense by HCL acid against microbes Preparation for absorption. HCL solubilizes iron salts for absorption in S-intestine Production of intrinsic factors needed for B12 absorption in S-intestine Secretion of Hormone gastrin from the g cells which stimulates increased gastric juice production from gastric cells during digestion.

Question 28

What is the function of Gastrin and where is it produced?

Answer 28

Gastrin is produced by the G cells in the pylorus. It stimulates the gastric glands to produce more gastric juice during digestion This is controlled by the parasympathetic nervous system (rest and digest)

Question 29

What are the three parts of the Small intestine? And How is the small intestine adapted for absorption

Answer 29

``` The small intestine consists of, The duodenum The jejunum The ileum The surface area of the intestine is increased by villi and microvilli to aid absorption. ```

Question 30

Describe the structure of the duodenum

Answer 30

About 25cm long, begins at the pyloric sphincter of the stomach and curves around the head of the pancreas. Secretions from the gall bladder (via the common bile duct) and pancreas (via the pancreatic duct) enter the duodenum via the hepatopancreatic ampulla (ampulla of Vater)through an opening that is guided by a ring of smooth muscle called the sphincter of the hepatopancreatic ampulla (sphincter of oddi) Most people just have one pancreatic duct however some have another accessory pancreatic duct (duct of Santorini) this opens 2.5cm above the ampulla of vater.

Question 31

What is the name of the duct that enters the duodenum via the sphincter of oddi? Also What is the name of the additional duct that some people can have?

Answer 31

``` Hepatopancreatic ampulla (ampulla of Vater) The duct of santorini (additional accessory pancreatic duct) ```

Question 32

Describe the structure of the jejunum and the ileum

Answer 32

The jejunum is the middle section of the small intestine and is about 2m long The ileum is the terminal section and is around 3m long. It ends at the ileocaecal valve, which controls the flow of material from the ileum to the caecum, and prevents back flow.

Question 33

What are payer’s patches and where would you find them?

Answer 33

Peyer’s patches are small masses of lymphatic tissue found throughout the ileum region of the small intestine. They are also known as Aggregated lymphatic follicles. The form an important part of the immune system by monitoring intestinal bacteria populations and preventing growth of pathogenic bacteria in the intestines.

Question 34

Describe the structure and function of villi

Answer 34

Villi are finger like protections covered by columnar epithelial cells (enterocytes)

Question 35

What are the overall functions of the small intestine

Answer 35

Onward movement of its contents by peristalsis Secretion of intestinal juice, which is an alkaline mucous secretion that helps in buffering the acids in the chyme. Complete too of chemical digestion of carbohydrates, proteins and fats in the enterocytes. Protection against infection by microbes that have survived the HCL in the stomach, by both solitary or aggregated lymph follicles Secretion of hormones that help in the digestion process Absorption of nutrients

Question 36

Describe the general structure of the large intestine

Answer 36

The large intestine is about 1.5m beginning at the

Question 37

Describe the structure and function of the caecum

Answer 37

First par of the large intestine It is a dilated region that has a blind end inferiorly and is continuous with the ascending colon superiorly It opens to the ileum through the ileocaecal valve

Question 38

Describe the structure and function of the vermiform appendix

Answer 38

The vermiform appendix is a blind ended tube connected to the caecum It is about 8-9cm and has the structure of the walls of the large intestine but contains more lymphoid tissue It is no digestive function. It’s function primarily is an organ of the lymphatic system

Question 39

What are the 4 parts of the colon and what are there location?

Answer 39

The ascending colon, passes upwards from the caecum to the level of the liver where it curves to the left at the hepatic flexure The traverse colon that extends across the abdomen from right to left to the area of the spleen where it curves inferiorly at the splenic flexure The descending colon that passes down the left side of the abdomen The sigmoid colon, which has an s shaped curve in the pelvic cavity

Question 40

Describe the structure and function of the rectum and anal cavity

Answer 40

The rectum is about 13cm long and is slightly dilated The anal canal is a short passage that opens to the exterior It is under control of two sphincters. The internal sphincter, consists of smooth muscle and is under control of the autonomic nervous system The external sphincter consists of skeletal muscle and is Nader voluntary control

Question 41

What are the overall functions of the large intestine

Answer 41

Absorption of water, salts, vitamins and some drugs Synthesis of vitamin K and folic acid by the bacterial flora of the large intestine Mass peristalsis Storage of faecal material prior to defecation

Question 42

What is mass peristalsis

Answer 42

Is a wave of strong peristalsis along the transverse colon that forces its contents into the descending colon and sigmoid colon. This type of peristalsis is stimulated by the entry of food into the stomach. Mass peristalsis occurs at fairly long intervals (about twice an hour) Usually the rectum is empty, but when mass movement pushes the contents from the sigmoid into the rectum, the nerve endings in its walls are stimulated by stretching leading to defecation.

Question 43

Describe the structure of the pancreas

Answer 43

It is a pale grey gland weighing around 60g and is about 12-15cm long It extends laterally from the duodenum towards the spleen. The pancreatic surface is knobby in texture. The tissue is soft and easily torn The pancreas consists of a broad head, a body and a narrow tail. It is both an exocrine and endocrine gland The exocrine gland consists of a large number of lobules made up of small acini (groups of cells that secrete pancreatic juice containing digestive enzymes) the walls of which contain secretory cells.

Question 44

What is the overall function of the exocrine pancreas? | What what is the nervous control of it?

Answer 44

The function of the exocrine pancreas is to produce pancreatic juice. This juice is Alkaline (ph8) and contains water, mineral salts, enzymes (amylase, lipase and nucleases and some inactive precursors (trypsinogen and chymotripsinogen ) these enzymes digest carbohydrates, proteins and fat. As in the GIT parasympathetic stimulation increases the secretion of pancreatic juice and sympathetic stimulation depresses it

Question 45

Describe the external structure of the liver

Answer 45

Largest gland in the body 1.5kg Large, firm , reddish brown organ is situated in then upper part of the abdominal cavity The liver is divided into four lobes

Question 46

Describe the maternal structure and function of the liver

Answer 46

The liver contains 100,000 lobules Liver elks called hepatocytes within a lobule are arranged into a series of irregular plates like the spokes of a wheel Sinusoids specialized and highly permeable capillaries, form passageways between the adjacent plates to empty into the central vein Kupffer cells that engulf pathogens , cell Debra and damaged blood cells are also present in the sinusoidal lining

Question 47

Describe the blood flow in the lobule

Answer 47

The blood enters the sinusoid from the branches of the hepatic portal vein and the hepatic artery and as blood flows past the liver Ella absorb andsecrete minerals into the bloodstream. Blood the leaves the sinusoids and enters the central vein of the lobule. The central veins of all the lobules merge to form the hepatic vein which drains into the inferior vena cava

Question 48

Describe how bile is produced in the liver

Answer 48

Bile is s secretory produc released into a network of bile canaliculi between adjacent liver cells These canaliculi carry bile toward the left and right hepatic bile ducts which unite to form the common hepatic duct Bile then enters either the duodenum by the common bile duct or the gall bladder by the cystic duct

Question 49

What is the difference between the cystic duct and the common bile duct

Answer 49

The common bile duct takes bile to the duodenum and the cystic duct takes bile to the gall bladder

Question 50

What the the three main functions of the liver

Answer 50

Metabolic regulation Hematological regulation Bile production

Question 51

What are the metabolic functions of the liver

Answer 51

all blood leaving the absorptive areas of the digestive tract flows through the liver before reaching the circulation. Thus liver cells can extract absorbed nutrients or toxins from the blood before they reach the rest of the body They can also monitor + adjust levels of organic nutrients, excess is removed and stored and using stored reserves or producing necessary compounds corrects deficiencies Functions include Storage of glycogen and lipid reserves Maintenance of normal blood levels of glucose, amino acids and fatty acids Synthesis and interconversion of nutrient types Synthesis and release of cholesterol bound to transport proteins Inactivation of toxins Storage of iron Storage of fat soluble vitamins A D K and E

Question 52

What are the hematological functions of the liver

Answer 52

The liver is the largest blood reservoir in the body Phagocytic cells in the liver remove damaged red blood cells, debris and pathogens from the circulation Liver cells produce plasma proteins and clotting factors Bile is synthesized and secreted by the liver Bile is made up of water, ion, bilirubin (a pigment derived from hemoglobin), cholesterol and a group of lips collectively known as bile salts. Bile is important in digestion and the absorption function nutrients Other functions include Synthesis of inactive hormones angiotensinogen Absorption + breakdown of circulating hormones and immunoglobulins Inactivation of fat soluble drugs

Question 53

Describe the structure and function of the gall bladder

Answer 53

A muscular organ shaped like a pear Two main functions Bile storage and bile modification As bile remains in the gall bladder it’s composition gradually changes. Water is absorbed and the bile salts and other components become more concentrated Sometimes if the become too concentrated they form gallstones which can cause clinical problems