Digestive System Flashcards
What are the 8 compartments of the digestive tract?
1) Mouth
2) Pharynx
3) Oesophagus
4) Stomach
5) Small Intestine
6) Large Intestine
7) Rectum
8) Anus
What are the 3 accessory glands?
1) Salivary glands
2) Liver
3) Pancreas
2 types of digestion that occur in the mouth?
1) Mechanical
2) Chemical (salivary glands)
What are the 3 pairs of salivary glands called?
1) Parotid gland
2) Sublingual gland
3) Submandibular gland
How much saliva is produced in a day?
1 - 1.5 L
What does the PNS stimulate the salivary glands to do?
Stimulates the salivary gland to produce saliva normally
What does the SNS stimulate the salivary gland to do?
Stimulates the salivary gland to produce thick saliva in order for the mouth to become dry and encourage the person to drink
What are the 7 components of saliva?
1) Salivary amylase - initiates carbohydrate digestion
2) Lingual lipase - initiates lipid digestion
3) Mucin - lubricates the bolus
4) Serous fluid - washes the oral cavity so the taste doesn’t lingur
5) Lysozyme - antibacterial
6) Immunoglobulin A - protection against pathogens
7) Bicarbonates - neutralise the oral cavity (prevention against tooth decay)
Where is the oesophagus located?
Extends from the pharynx to the stomach. Sits behind the trachea.
What kind of epithelium lines the oesophagus?
Stratified squamous epithelium
What muscles are in the walls of the oesophagus?
1) Smooth
2) Mixed
3) Skeletal
Where is the stomach located (in terms of abdominal regions)?
In the epigastrium and extends into the left hypocondrium
What are the 6 functions of the stomach?
1) Stores food
2) Mechanical digestion
3) Chemical digestion
4) Absorption (e.g. alcohol)
5) Hydrochloric acid (to kill micro-organisms)
6) Production of an intrinsic factor (allows Vitamin B12 to be absorbed as it will bind to this intrinsic factor)
Can we live without our stomach?
Yes - as long as we are given B12 injections
Anatomy of the stomach contains:
1) Abdominal oesophagus
2) Cardia
3) Fundus
4) Body
5) Lesser Curvature
6) Greater Curvature
7) Antrum
8) Pyloric canal
9) Pyloric Sphincter - thick & strong
10) Duodenum
What are the special features of the stomach?
Rugae (folds) - in the mucosa & submucosa layer
3 types of muscle (oblique, circular, longitudinal) - in the muscularis externa layer
The cells of the mucosa layer are split into 2 regions that form:
1) Gastric Pit
2) Gastric Glands
What cells are contained within the gastric pit and their function?
Mucous cells and mucous neck cells - both secrete mucous in order to:
1) Form a mucous layer which allows cells to be protected from the acid secretions in the stomach
2) They are in tight junction with each other so that acid in the stomach does not pass through to tissue layers underneath.
What cells are contained within the gastric glands and their functions?
1) Parietal cells - secrete hydrochloric acid and intrinsic factor
2) Chief cells - secrete pepsinogen (which is converted to pepsin by hydrochloric acid and pepsin breaks down proteins into amino acids)
3) Enteroendocrine cells - secrete gastrin (hormone)
Why doesn’t the chief cells (in the mucosa layer of the stomach) secrete pepsin?
As if it was to secrete pepsin, it would break down the chief cells as they are made of protein. Therefore, it secretes the inactive form of pepsin - pepsinogen.
Collectively, what do the secretions from the cells making up the gastric gland produce?
Gastric juice
How much gastric juice do the gastric glands produce, in a day?
1.5-2L
What 4 things stimulate the secretion of gastric juice?
1) Low pH
2) Gastrin
3) Histamine
4) Acetylcholine
What 3 things are contained in gastric juice?
1) Hydrochloric acid
2) Intrinsic factor
3) Gastrin
Where is hydrochloric acid secreted from and its function?
Parietal cells. Function: 1) Kills microbes 2) Breaks down connective tissue (meat) and cell walls (plants) 3) Activates pepsinogen into pepsin
Where is intrinsic factor secreted from and its function?
Parietal cells:
Function: Bind to Vitamin B12 so that is can be absorbed
Where is gastrin secreted from and its function?
Enteroendocrine cells (will secrete gastrin when food is present in the stomach):
Function:
1) Stimulates the secretion of gastric juice
2) Stimulates contraction of the muscle layers in the muscular externa layer of the stomahc walls
3) Works on the pyloric sphincter
Do the parietal cells produce hydrochloric acid directly?
No - they will produce hydrogen (which will then bind to chloride - to produce hydrochloric acid)
What are the 3 stages of gastric activity?
1) Cephalic stage - sight, smell and taste senses food which results in the secretion of saliva
2) Gastric stage - gastrin is secreted from the enteroendocrine cells as food enters the stomach
3) Intestinal stage - Less gastric juice is secreted into the stomach as food goes into the intestines
Where is the peritoneum by the pancreas?
The peritoneum is only infront of the pancreas (therefore the pancreas is = retroperitoneum)
Where is the pancreas located?
Behind the stomach. And sits in the curve of the duodenum
Where does the pancreatic duct (contained in the pancreas) open up?
The pancreatic duct will open up into the duodenum (via the sphincter of Oddi)
What are the 2 types of glands in the pancreas gland?
1) Exocrine gland - 99%
2) Endocrine gland - 1%
What are the 2 types of cells that make up the exocrine gland in the pancreas and their functions?
1) Acini cells = contain Zymogen granules - which produce and secrete
- Propeptidase (breaks down protein)
- Lipase
- amylase
- ribonuclease and deoxyribonuclease
2) Duct cells = secrete water and sodium bicarbonate (which will increase the pH of the chime in the duodenum from the low pH - produced from the gastric acid)
Which 2 cells make up the endocrine gland of the pancreas gland?
Islet of Langerhans:
a cells - secrete glucagon
b cells - secrete insulin
Where is the liver located?
Liver is located in the right hypocondrium and extends into the epigastrium
What are the 4 lobes of the liver?
Anterior - right (bigger side) and left lobe
Posterior - caudate lobe and quadrate lobe
Where is the gall bladder located in the liver?
Posterior - sits on top of the quadrate lobe
What are the 3 functions of the liver?
1) Bile production
2) Blood clotting
3) Blood cell production
When does the liver produce bile?
ALL THE TIME
What is the function of bile?
To break down the fats in the duodenum
What is the function of the gall bladder?
To store and concentrate the bile that is being produced by the liver but isn’t being used to break down the fats in the duodenum.
How much concentrate bile can the gall bladder store (and what helps the gall bladder to store this much)?
40 - 70 ml (rugae allows the walls of the gall bladder to expand)
What is the biliary tree?
A collection of ducts which connects the liver with the gall bladder and the duodenum.
What ducts are contained in the biliary tree?
1) Right and left hepatic duct
2) Common hepatic duct
3) Cystic duct (comes from the common hepatic duct and joins to the gall bladder)
4) Common bile duct
If you have eaten a fatty meal - where does the bile go?
1) Bile is produced in the liver
2) It is transports down the right and left hepatic duct and common hepatic duct
3) Travel down the common bile duct
4) The common bile duct will meet the pancreatic duct and this forms the sphincter of Oddi.
5) The bile will travel through the sphincter of Oddi, the duodenal ampulla and the duodenal papilla - in order to get to the duodenum.
6) The bile will break down fats in the duodenum
Why is the sphincter of Oddi also known as the hepatopancreatic sphincter?
Because this is where the common bile duct and the pancreatic duct meet.
If you have not eaten a fatty meal - where does the bile go?
1) The bile is produced in the liver
2) travel down the right and left hepatic duct
3) Travel down the common hepatic duct
4) Travels down the cystic duct to the gall bladder
5) The bile is stores and concentrated in the gall bladder
6) The sphincter of Oddi closes up
How long is the small intestine?
6 m long
What are the 3 parts of the small intestine and what occurs there?
1) Duodenum - majority of digestion and starts absorption
2) Jejunum - majority of absorption
3) Ileum (continuous with the large intestine) - only substance absorbed at the ileum is Vitamin B12
What are the 3 functions of small intestine?
1) Chemical digestion
2) Mechanical digestion
3) absorption
What are the special features of the small intestine (modified to increase the SA:V for absorption)?
1) Plicae circulares (circular folds in the walls)
2) Vili
3) Micro-vili
What stimulates the 2 hormones for chemical digestion in the duodenum to be released?
1) Food in the stomach is churned and stored.
2) Chime is released into the duodenum as the pyloric sphincter opens.
3) Proteins and fats in the duodenum cause the secretion of CCK.
4) Low pH (caused by the chime coated in the gastric juice - contains hydrochloric acid) stimulates secretin to be secreted into the duodenum.
What are the functions of CCK?
1) Stimulates the Acini cells (1 out of the 2 pancreatic exocrine cells) - in order to release the enzymes from their Zymogen granules.
2) Stimulates the gall bladder to contract and the Sphincter of Oddi to relax - in order for the bile to be released down the cystic duct and common bile duct and enter he duodenum in order to break down fats.
3) Acts on stomach - Reduces gastric motility and gastric juice secretion
What are the functions of secretin?
1) Stimulates the duct cells (1 out of the 2 pancreatic exocrine cells) - in order to release water and sodium bicarbonate.
2) Stimulates the liver to produce more bile so that the bile in the gall bladder can be restored.
3) Acts on the stomach - Reduce gastric motility and gastric juice secretion
Why is it important that secretion stimulates the pancreatic exocrine duct cells to release sodium bicarbonate?
Because sodium bicarbonate will increase the pH (which is currently low due to the chime covered in gastric juice - that contains hydrochloric acid) to 8/9 - which is the pH in which the duodenum enzymes work best at.
What is the most important propeptidase (released from the pancreatic Acini cells) into the duodenum & why?
Trypsin. Trypsingon is activated to Trypsin by enterokinase (loacted in the microvili of the duodenum walls). Trypsin activates all the other propeptidases into their active forms so that they can no break down proteins into amino acids.
How are amino acids absorbed into the duodenum walls?
1) Facilitated diffusion
2) Co- transport
When does carbohydrate digestion start?
It will start in the mouth as the saliva contains salivay amylase. But, the carbohydrates will not be digested to monosaccharides until in the duodenum. Because, the microvili of the duodenum contains the enzymes that will break the disaccharides into the monosaccharides.
How does carbohydrate digestion occur in the duodenum?
1) The pancreatic acini cells release pancreatic amylase, when stimulates by CCK.
2) The pancreatic amylase will break down the carbohydrate to disaccharides.
3) The enzymes contained in the microvili of the duodenum walls will secrete enzymes that break down the disaccharides into monosaccarides.
What 3 enzymes are secreted from cells in the microvili of the duodenum that will break down the disacharides?
1) Maltase (maltose - glucose and glucose)
2) Sucrase (sucrose - glucose and fructose)
3) Lactase (lactose - glucose and galactose)
How are the monosaccarides absorbed into the duodenum walls?
1) Facilitated diffusion
2) Co-transport
What are the stages of fat digestion and absorption in the duodenum?
1) Fats will enter the duodenum as large lipid droplets.
2) Bile enters the duodenum (when CCK stimulates the gall bladder) and bile will break down the large lipid droplets into small emulsion droplets.
3) The small emulsion droplets have a larger SA:V ratio for pancreatic lipase (secreted from the pancreatic acini cells, when stimulates by CCK) to break down the triglycerides into 3 fatty acids and glycerol.
4) The fatty acids and glycerol will associate with the bile salts in order to become MICELLES (with an outer coating).
5) The micelles can now enter the duodenum wall via diffusion.
6) In the duodenum walls the fatty acids and glycerol in the micelles will re-synthesis back into tryglycerides.
7) Tryglycerides are then covered in a protein coat and becomes CHYLOMICRONS.
8) The Chylomicrons will enter the interstitual fluid via exocytosis.
9) In the interstitual fluid the chylomicrons will enter LACTEALS.
10) As they enter lacteals they will be transported to the Lymphatic system, before entering the blood stream.
What are the parts of the large intestine?
1) Caecum
2) Ascending colon
3) Hepatic flexure
4) Transverse colon
5) Splenic flexure
6) Descending colon
7) Sigmoid colon
8) Rectum
9) Anus
What part of the large intestine doesn’t do anything in humans and what is the problem with it?
Caecum (at the start of the large intestine). As it is narrow - it can get blocked and infected quickly
How long is the large intestine?
1.5m long
What are the 5 special features of the large intestine?
1) Taenia Coli - the arrangement of the 3 bands of longitudinal muscle, that meet at the appendix.
2) Haustra - bumps in the large intestine formed by the taenia coli to increase the surface area.
3) Epiploic appendages - fat-filled (the amount will vary between people)
4) Crypts - instead of vili
5) Many goblet cells - secrete mucus so faeces can pass through.
What is absorbed in the large intestine?
1) Water
2) Electrolytes
What is stored in the large intestine?
1) Undigested materials (inc: cellulose and fibre)
2) Fats
3) Good Bacteria
4) Mucus (secreted from the goblet cells)
5) Epithelial cells (lost due to abrasion in the digestive tract)
What is the role of the good bacteria stored in the large intestine?
1) Ferments the undigested carbohydrates
2) Synthesis Vitamin B and K
How long does it take for the faeces to travel through the large intestine? (from caecum to the rectum)
12-24 hours
What is the function of the digestion system?
Food will provide cells with energy for:
1) Biological Processes
2) To replace and repair damaged cells
What are the 4 surface landmarks of the abdomen?
1) Xiphisternum
2) Costal margin
3) ilia crest
4) Inguinal ligament
What are the 4 planes which divde the abdomen into the abdominal regions?
1) 2 Midclavicular lines
2) Subcostal plane
3) Transtubercular plane
What are the names of the 9 abdominal regions?
1) Right hypocondrium
2) Epigastrium
3) Left hypocondrium
4) Right Lumbar
5) Umbilical
6) Left Lumbar
7) Right iliac
8) Hypogastrium/suprapubic
9) Left iliac
What are the 2 planes that seperate the abdomen into the abdomen quadrants?
1) Median plane
2) Transumbilical plane
What are the names of the abdomen quadrants?
1) Right upper quadrant
2) Left upper quadrant
3) Right lower quadrant
4) Left lower quadrant
What is the peritoneum?
A double layered membrane that lines the cavities in the abdomen and pelvic regions
What are the 2 layers of the peritoneum?
Visceral - lines organs
Parietal - underneath walls
What is the space called inbetween the 2 layers and its importance?
The parietal cavity which contains parietal fluid. The fluid allows the organs to move without friction.
What organs are retroperitoneum (behind the peritoneum so only covered at the front)?
1) Pancreas
2) Part of the duodenum
What organs are intraperitoneum (covered completely by the peritoneum)?
1) Stomach
2) Most of the small intestine
What makes parts of the peritoneum specialised?
The specialised parts of the peritoneum are those that have a double layer of visceral peritoneum
What are the 2 names given for the the specialised parts of the peritoneum and their definition?
1) Mesentery - connects organ to the body wall
2) Omentum - connects organ to organ
What is an important feature of the mesentery?
It allows the blood vessels to reach the small intestine without getting tangled up.
Blood vessels will travel through the mesentery to organs.
What are the names of the 2 kinds of omentum and what organs do they join together?
Lesser Omentum - (liver to stomach)
Greater Omentum - (stomach to the transverse colon of the large intestine)
What are the 4 basic layers of the walls of the digestive tract?
1) Mucosa
2) Submucosa
3) Muscularis externa
4) Serosa or adventia
What happens if an ulcer occurs in the mucosa layer and travels through to the serosa or adventia layer?
There will be an opening the digestive tract wall and food will leak out into the parietal cavity (as the viseral layer lines the serosa or adventa layer)
What are the 3 layers of the mucosa layer and their function?
1) Epithelium (either protection or absorption)
2) Lamina propria (connective tissue that supports the epithelium layer - contains: blood vessels, lympatic vessels and glands)
3) Muscularis mucosa (circular then longitudial muscle - which controls the movement of the mucosa layer)
What is the submucosa layer and what does it contain?
Dense, irregular connective tissue. Contains: 1) Blood vessles 2) Lymphathic vessels 3) Glands 4) Submucosal plexus
What are the 3 layers of the muscularis externa and its function?
1) Circular smooth muscle
2) Myenteric plexis
3) Longitudinal smooth muscle
FunctionL Peristalsis
What is serosa and adventia & what is the difference between the 2?
Both connective tissue.
Serosa = covers the organs intraperitoneum.
Adventia = covers the organs retroperitoneum and those above the abomen (including the oesophagus and pharynx)
Describe the arterial supply to the digestive tract:
Supplied by the arteries extending from the abdominal aorta:
1) Celiac trunk
2) Superior Mesenteric artery
3) Inferior Mesenteric artery
Why can’t the venous drainage from the digestive tract go straight to the heart?
The blood will need to go through the hepatic portal system (so nutrients in the blood can be dropped off at the liver) - before returning to the heart
What are the 2 types of nervous systems that control the digestive system and what is each responsible for?
1) Autonoic NS - controls long-term reflexes (e.g. long-term peristalsis
2) Enteric NS - controls short-term reflexes (e.g. local peristalsis and glandular secretions)
What is special about the divisions of the autonomic NS that control the digestive tract?
The divisions have opposite roles to that they normally have.
Sympathic = slows down activity
Parasympathic = speeds up activity
Where are the post-ganglonic neurones of the enteric NS found?
1) Submucosal plexus - in the submucosa layer
2) Myenteric plexus - in the muscularis externa layer
What kinds of cells make up the endocrine system of the digestive tract?
Enteroendocrine glands (like the ones in the gastric gland) which secrete:
1) gastrin
2) CCK
3) Secretin
The 2 types of motility of the functional processes of the digestive tract?
1) Mechanical digestion - breaking food down into bolus
2) Propulsion - moving the bolus down the digestive tract
What are the 3 types of mechanical digestion and where do they occur?
1) Chewing (mouth)
2) Churning (stomach and small intestine)
3) Segmentaion (small intestine only)
What 5 parts of the mouth are involved in chewing?
1) Teeth
2) Tongue
3) Muscles of mastication
4) Temporal mandibular joint
5) Salivary glands
What happens in the process of segmentation?
1) Cycles of relaxation and contraction in the small intestine walls
2) Pushes the bollus outwards in each direction
3) So that the enzymes can reach it more easily
What are the 4 types of propulsion and where do they occur?
1) Swallowing (mouth, pharynx and oesophagus)
2) Peristalsis (oesophagus and small intestine)
3) Mass movement (large intestine)
4) Elimination of waste
What are the 3 stages of swallowing?
1) Oral stage
2) Pharyngeal stage
3) Oesophageal stage
Which layer out of the 4 layers of the digestive tract is involved in peristalsis?
Muscularis externa
Describe the process of peristalsis?
(AT THE SAME TIME)
1) The circular smooth muscles contract in front of the bolus - pushing it along the tract
2) The longitudinal smooth muscle contract behind the bolus - shortens the distance it has to travel
What occurs in mass movements?
Very strong peristalsis contractions that will push the bolus along the large intestine and to the rectum.
What are mass movements stimulated by?
Distension of the stomach and the duodenum
How many times a day do mass movements occur?
2-3 times a day
What occurs during the elimination of waste?
1) After mass movement, faeces will enter the rectum.
2) This stimulates the defication reflex.
3) Faeces will enter the anal canal.
4) Internal anal sphincter relaxes and faeces moves into the anorectal canal.
5) The external anal sphincter contracts in order to stop the elimination of waste at an inappropriate time.
6) Once the cerebral cortex is stimulates, the external anal sphincter will relax and the elimination of faeces will occur.
