Digestive system Flashcards
Label the digestive system
What is the function of the GI system?
- To break down food into a form that can be utilised by the human body
- To absorb water from food and drinks
What is the GI system comprised of?
- The alimentary canal
- The accessory digestive organs (teeth, tongue, salivary glands, liver, gallbladder and pancreas)
What Structures Comprise the Accessory Organs?
- Teeth
- Tongue
- Salivary glands
- Liver
- Gallbladder
- Pancreas
What are the 3 parts of your teeth?
- The crown – visible above the gums
- The neck – connects the crown and the roots
- The roots – teeth have between one and three roots which ‘slot’ into sockets within the mandible (fibrous gomphoses joints)
Label the parts of the mouth (oral cavity)
Label the Longitudinal Section
through a Tooth
Describe the composition of a tooth?
- Composed primarily of dentine (calcified connective tissue)
- Enclosed within the dentine is the pulp cavity which contains connective tissue, blood vessels, nerves and lymph vessels
- The root canal is an opening which runs through the root to open at the base of the tooth and is the means by which vessels and nerves enter and leave the tooth
- The crown is covered with enamel (calcium phosphate and calcium carbonate)
- Enamel is the hardest substance within the human body and protects the tooth from mechanical wear and tear
What is the function of teeth?
•The function of the teeth is to cut, tear and grind food in order to reduce solid material into smaller particles that can be more readily swallowed
When do deciduous teeth start to erupt?
Begin to erupt age 6/12 m
Appear at rate of one pair a month until all 20 are present
How many teeth are in an adults full set?
32
Label the cross section of a tongue
The Tongue
- Skeletal muscle covered with mucous membrane
- Is anchored to the floor of the oral cavity by the lingual frenulum (a fold of mucous membrane on the inferior surface of the tongue)
- The extrinsic muscles of the tongue manoeuvre food around the mouth for mastication
- The intrinsic muscles of the tongue enable swallowing and speech
What are the 3 taste buds?
Fungiform papillae
- Most contain taste buds
Vallate papillae
- All contain taste buds
Filiform papillae
- Do not contain taste buds
- Receptive to touch
- Increase friction
Where are papillae found?
What are papillae?
- The superior and lateral surfaces of the tongue are covered with raised projections called papillae
- These papillae are projections of the lamina propria and are covered with keratinized epithelium
- The majority of the papillae contain taste buds
Fungiform papillae- where are they found?
Found mainly on the sides and tips of the tongue – deep red in colour (most contain taste buds)
Vallate papillae- where are they found and how many are there?
•Found on the posterior surface of the tongue, about 8 – 12 in number (all contain taste buds)
Filiform papillae- where are they found?
•Found in parallel rows on the anterior 2/3 of the dorsum of the tongue (lack taste buds but are receptive to touch and increase friction between the tongue and food enabling the tongue to manoeuvre food)
Label the taste cell
Label the taste senses on the tongue
eg. sweet, sour
Label the types of cell on this tongue
Label the 3 salivary glands
Composition of saliva
- 99.5% water
- 0.5% solutes including salivary amylase, lysozyme (antibacterial enzyme), ions, dissolved gases and organic compounds including urea
- The salivary glands each produce saliva that has a slightly different composition (e.g. with a varying amount of mucous depending on how many mucal cells line the gland)
Salivary glands:
Sublingual gland
Mostly mucous alveoli
Produces a thick saliva with only a small amount of salivary amylase
Salivary glands:
Submandibular gland
Some mucous alveoli
Produces a saliva partially thickened by mucous
Salivary glands:
Parotid gland
Some mucous alveoli
Produces a saliva partially thickened by mucous
Label the salivary glands
Explain the functions of saliva?
- Under basal conditions the saliva is mostly the mucous type, and during sleep very little saliva is secreted. The flow of saliva helps to wash away some of the bacteria on food particles not completely broken down after a meal. Saliva contains thiocyanates and lysozymes that will attack and destroy bacteria in the mouth. Saliva can contain antibodies that destroy oral bacteria.
- The more common functions include the following: moistening and lubricating of mouth and food, aiding in tasting, swallowing, and speaking, and early metabolism of carbohydrate due to -amylase action. Finally, saliva helps to maintain the calcium phosphate matrix of the teeth
Interesting facts about the liver?
- Heaviest organ in body
- 2nd largest organ
- Almost completely covered by the peritoneum
- Completely covered by dense irregular connective tissue
- Divided into two principal lobes (right and left) by the falciform ligament which is an extension of the peritoneum
Histology of the liver
The lobes of the liver are made of functional units called lobules
A lobule is typically hexagonal in cross section
Hepatocytes are specialised epithelial cells that are arranged around a central vein
Instead of capillaries, the liver contains larger sinusoids that are lined with endothelium
Reticuloendothelial (Kuppfer) cells are fixed phagocytes that are scattered along the blood sinusoids
What do hepatocytes secrete?
Hepatocytes secrete bile
Describe the route of bile from the hepatocytes to the common hepatic duct
Hepatocytes secrete bilec
Bile enters bile canaliculi which are small canals running through the lobules of the liver
The bile canaliculi drain into bile ductules which drain into bile ducts at the edges of the lobules
These bile ducts merge to form the right and left hepatic ducts which merge before leaving the liver as the common hepatic duct
What is this?
Cross section through a liver lobule
Label the cross section though a liver lobule
What are stellate reticuloendothelial (Kupffer) cells?
FIXED phagocytes,
These are able to destroy worn out blood cells bacteria and other foreign matter that is bought in on the venous blood draining from the gastrointestinal tract.
What’s wrong with this liver?
Advanced Cirrhosis
alcoholic liver disease
Label this image
Describe the blood supply to the liver
- The liver receives blood from two arteries
- The hepatic artery supplies oxygenated blood
- The hepatic portal vein supplies deoxygenated blood that contains newly absorbed nutrients
- Branches of both vessels carry blood along the sinusoids of the liver where oxygen and nutrients are extracted by the hepatic cells
- The blood then drains into the central vein and into the hepatic vein and back to the venous circulation
Label this diagram
Explain the bile ducts chain
•Bile is a substance secreted by the hepatocytes, as it is secreted it enters the narrow canals (bile canaliculi) which run between the cells, the canaliculi enter into small ducts at the edges of the lobules.
The bile ducts merge to form the right and left hepatic ducts which unite to form the common hepatic duct.
The common hepatic duct joins the cystic duct from the gall bladder to form the common bile duct.
How much bile do your hepatocytes produce each day?
Your hepatocytes produce ~ 800-1000 mL of bile a day.
What colour is bile?
Is it acidic or alkaline?
Bile is a yellow/olive green coloured fluid with a slightly alkaline pH.
What are the constituents of bile?
The constituents of bile are water, bile salts, cholesterol, lecithin, bile pigments and several ions.
What is the function of bile?
- Bile is an excretory product of liver metabolism, it is however used by the body to help digest fats.
- Bile emulsifies and breaks up large lipid globules into smaller globules, this allows the digestive lipases (enzymes) to break the fat down further.
Bile salts also help the absorption of lipids (fats) following digestion.
(bile salts are mainly the Na+ and K+ salts of cholic acids)
Complete the diagram
Complete the diagram
Complete the diagram
Complete the diagram
List the three main metabolism functions of the liver
Carbohydrate metabolism
Lipid metabolism
Protein metabolism
Functions of the liver:
Describe carbohydrate metabolism
The liver is vital in maintaining the normal glucose levels in the blood.
When blood glucose levels are low, the liver can breakdown glycogen to be release into the blood stream. The liver can also convert some amino acids and lactic acid to glucose, as well as being able to convert other sugars to glucose.
When glucose levels are high the liver converts glucose to glycogen and triglycerides for storage.
Functions of the liver:
Describe lipid metabolism
- Hepatocytes store some triglycerides. They can breakdown fatty acids to from ATP
- They can synthesise lipoproteins- these act as transporters of fatty acids etc. to and from body cells
- They synthesise cholesterol and bile salts
Functions of the liver:
Describe protein metabolism
- Hepatocytes deaminate (remove NH2 groups) amino acids so that they can be used for ATP production or be converted into carbohydrates or fats.
- The toxic NH3 produced is converted into urea for excretion by the kidney
- Hepatocytes also synthesise most of the plasma proteins
List the livers functions other than metabolism
- Processing of drugs and hormones
- Excretion of bilirubin and synthesis of bile salts
- Storage of glycogen and vitamins A, B12, D, E, and K
- Phagocytosis by Kupffer cells
- Activation of vitamin D (note: this also occurs in the kidney)
List the 3 layers of the gall bladder
- The outer serous layer is the visceral peritoneum
- The middle smooth muscle layer
- The inner mucous membrane, arranged in folds called rugae (similar arrangement to the lining of the stomach
How big is the gall bladder?
Where is it?
The gall bladder is an 8cm sac that lays on the under surface of the liver.
What is the gall bladder’s function?
It’s function is to store and concentrate the bile produced by the liver and to deliver it to the gut (duodenum and small intestine) when you eat.
Label the pancreas
What is the composition of the pacreas’ cells?
1% cells
- Islets of Langerhans (endocrine)
99% cells
- Acini cells (exocrine)
- Secrete pancreatic juice
Where does the pancrease lie relative to the stomach?
•Lies posterior to the greater curvature of the stomach
How is the pancreas connected to the small intestine?
•Connected to the duodenum by the larger pancreatic duct (through the hepatopancreatic ampulla) and the smaller accessory duct (through the duct of Santorini)
What hormones do the Islets of Langerhans secrete?
They secrete the hormones:
- Insulin
- Glucogen
- Stomatostatin
- Pancreatic polypeptide.
What do insulin and glucagon do?
Insulin acts to lower blood glucose levels and glucagon raises blood glucose levels.
What does somatostatin do?
Somatostatin can act to inhibit insulin and glucagon release
What does pancreatic polypeptide do?
Pancreatic polypeptide inhibits somatostatin secretion, gall bladder contraction and secretion of digestive enzymes from the pancreas.
How much pancreatic juice does the pancreas secrete and what is it made of?
The pancreas secretes between 1200 and 1500 mL of clear colourless liquid (pancreatic juice), this contains mostly water, some salts sodium bicarbonate and several important enzymes.
What does the bicarbonate in pancreatic juice do?
The bicarbonate buffers the acidic gastric juice as well as inactivating pepsin from the stomach, this provides the correct pH for the pancreatic enzymes to function.
List the pancreatic enzymes
Pancreatic amylase – starch digestion
Trypsin and Chymotrypsin – protein digestion
Carboxypeptidase and Elastase – protein digestion
Pancreatic lipase – triglyceride digestion
Ribonuclease and Deoxyribonuclease – nucleic acid digestion
What organ secretes bile?
Liver
What is the basic overarching function of the biliary system?
The function of the biliary system is to store and concentrate bile until it is needed
If bile is not needed for digestion, what stops the bile from reaching the stomach?
If bile is not needed for digestion the sphincter of Oddi (sphincter of the hepatopancreatic ampulla) which is around the ampulla of Vater (hepatopancreatic ampulla) closes
If bile is not needed and gets blocked up, where does it go?
Bile backs up and overflows along the cystic duct into the gallbladder for storage
Label the Pancreas and Biliary tree
What is enamel composed of?
Calcium phosphate and calcium carbonate
