7. Digestive System (part 1) Flashcards
What are the components of the digestive system?
Mouth
Pharynx
Oesophagus
Stomach
Small intestine
Large intestine (including rectum and anal canal)
What are the accessory organs of the digestive system?
Organs that support the functions of the digestive system:
Salivary glands
Pancreas
Liver
Gall bladder and bilary tract
What are some of the reasons why 70% of our immune system is distributed through the digestive system?
- The digestive system is open to the outside world and therefore we need lots of white blood cells to tackle the pathogens that move through the digestive system so they do not cause disease.
- The digestive system is like the nursery school for immune cells to learn from. The white blood cells are exposed to more pathogens here than anywhere else and they learn from what’s around them. They learn for example which bacteria are helpful to us in breaking down food and which are dangerous and need to be eliminated.
Describe the stages of the digestion process
- Ingestion: (into mouth)
- Secretion: DIGESTIVE JUICES released straight away, and saliva even before food hits mouth.
- Mixing and Propulsion: CONTRACTION / RELAXING in walls help mix and propel food and through the GI tract
- Digestion: MECHANICAL and CHEMICAL processes break down ingested food and liquids into absorbable substances
- Absorption: Substances passing through the walls in the alimentary canal into the BLOOD and also LYMPHATIC SYSTEM.
- Elimination: Excretion of waste and indigestible materials
Name the four basic layers of the Gastro Intestinal Tract
The entire GIT has the same basic four-layer arrangement of tissues.
-
Mucosa
* Epithelum (simple and columnar)
* Lamina Propria
* Muscularis Mucosa - Submucosa
- **Muscularis Externa **
- Serosa **(peritoneum) **(only found in the abdomen and pelvis)
How does leaky gut occur?
The inner most layer of tissue in the GIT is the mucosa layer and this layer is itself made up of 3 layers, the innermost layer of which is the epithelium layer.
Epithelial tissue is characterised by tight junctions which make it difficult for pathogens or undigested food to cross the membrane. Leaky gut occurs when this layer is compromised and junctions between cells are not tight, allowing undigested to food to enter.
How often do epithelial cells renew.
Every 3-5 days in the stomach
Every 5-7 days elsewhere
What is the name of the collection of immune cells in the Lamina Propria and where are they especially prevalent in the GIT?
GALT - Gut Associated Lymphoid Tissue. They are like passport control at Heathrow giving clearance before allowing entry in to the blood vessels.
GALT is specific to the GIT and especially prevalent in the oesophagus, small intestine and large intestine.
Elsewhere in the body it is called MALT - Mucosa Associated Lymphoid Tissue.
GALT contains 70% of the body’s immune cells and is the first line of defence against ingested pathogens.
What is the Submucosa layer and what is its structure?
A connective tissue layer below the Mucosa layer of the GIT.
It contains blood vessels and lymph vessels which receive absorbed food molecules. Most nutrients go directly to the blood. Lipids and the fat soluble vitamins A, D, E and K enter the lymphatic system.
Contains part of the nervous system called the submucosa plexus , a bundle of nerve fibres that stimulate the release of digestive juices.
It may contain glands and lymphatic tissue
What is the function of the Muscularis Externa
It comprises skeletal muscle to support voluntary control processes in the digestive system such as chewing, swallowing and defecating. Therefore we find skeletal muscle where these processes take place in the mouth, pharynx, oesophagus and sphincter.
It comprises smooth muscle everywhere else in the GIT for the involuntary processes of
(i) mixing of foods with digestive juices and,
(ii) propelling food (chyme/bolus) through waves of contraction known as peristalsis along the digestive tract..
It contains part of the nervous system called THE MYENTERIC PLEXUS which triggers lots of peristalsis.
What is a serous membrane and what are the three serous membranes in the body
The serous membrane is a smooth tissue membrane of mesothelium lining the contents and inner walls of body cavities, and which secretes a lubricating serous fluid.
Peritoneum (the largest of the 3)
Pericardium
Pleura
All serous membranes have 2 layers:
1. Visceral layer which covers the organs
2. Parietal layer on top of this which cover the walls of the cavity
In between these two layers we have a lubricating serous fluid.
Peritoneum:
What are the two layers of the peritoneum called and what are they for?
What is the name of the substance in between them and what does it do?
The peritoneum is a serous membrane. The largest of the 3 serous membranes of the body,
It has 2 layers
1. Visceral layer which covers the organs
2. Parietal layer on top of this which cover the walls of the abdomen and pelvic cavity
In between these two layers we have the peritoneal cavity with contains a lubricating serous fluid. It helps to deliver lots of blood vessels and lymph vessels AND it provides a physical barrier to the spread of infection
What is the function of the Greater Omentum?
The Greater Omentum is the largest fold of the peritoneum that looks like an apron over the front of the transverse colon and small intestine
Stores lots of fatty (ADIPOSE) tissue. This helps with protection and insulation but too much is a beer belly and can disrupt the endocrine system.
It has many LYMPH NODES CONTAING MACROPHAGES AND PLASMA CELLS to combat infections of the GIT.
What is the function of the Lesser Omentum?
Lesser Omentum is a smaller fold of the peritoneum that suspended from the stomach and duodenum.
It contains the the HEPATIC PORTAL VEIN
It also contains the hepatic artery, common bile duct and lymph nodes.
Explain what is meant by ascites and what causes it.
It is the accumulation of fluid in the peritoneal cavity.
It is caused by liver disease, GIT malignancies including cancer, heart failure, pancreatitis.
The reason you get ascites from heart failure or liver disease is due to portal hypertension. Fluid backflows into the portal vein and then the abdomen.
Shifting dullness is the test. When you tap the stomach lying on your side does it have a different resonance to when standing. If so suggests fluid movement and ascites.
What is the pathology called Peritonitis?
The peritoneum is the serous membrane forming the lining of the abdominal cavity
An acute inflammation of the peritoneum caused by bacterial infection, ruptured appendix, friction. surgical wounds.
What is the Enteric Nervous System
The ‘brain of the gut.
It extends from the oesophagus to the anus and contains 100 million neurons (more than the spinal cord)
Describe the role of the sympathetic and parasympathetic nervous system in the functioning of the ENS.
ENS is regulated by the autonomic (involuntary) nervous system
Parasympathetic - Rest and DIGEST
- INCREASES MUSCULAR ACTIVITY ie: peristalsis
- INCREASES GLANDULAR SECRETION - stomach acid, digestive enzymes, stomach acid, saliva
Sympathetic - fight or flight - STRESS
- DECREASES MUSCULAR ACTIVITY ie: peristalsis
- DECREASES GLANDULAR SECRETION - - stomach acid, digestive enzymes, stomach acid, saliva
What is the impact of chronic stress on digestion
Stress compromises our ability to digest because we are in a sympathetic state rather than a ‘rest and digest’ parasympathetic state. Mechanical digestion and release of digestive juices slows down. This means that food is not digested properly, not broken down to its simplest form and therefore it is not ABSORBED properly.
What is the name of the main nerve in the parasympathetic nervous system?
The vegus nerve.
It runs from the back of the brain and down through the diaphragm
What are the names of two nerve plexus in the enteric nervous systemm, where are they located and what is their function?
Submucosal Plexus located in the submucosal tissue
- controls DIGESTIVE SECERETIONS and detects sensory information
Myenteric Plexus located in the muscularis externa tissue
-Enervates (goes into) the muscle controlling the strength and frequency of muscle contraction - causing peristalsis. GUT MOTILITY
Define gut motility
Refers to the movement of food from the mouth through the pharynx (throat), esophagus, stomach, small and large intestines, and out of the body.
Facilitated by the myenteric plexus.
What are the 3 types of neurons in the Enteric Nervous System
- Motor Neurons: ‘outgoing signal’ in the myentric plexus controls PERISTALSIS and in the SUBMUCOSAL PLEXUS CONTROL SECRTETIONS. (basically sends a message to say to contract muscles and release secretions from glands.
- Sensory Neurons: ‘Incoming signal’ RECEIVE INFORMATION ABOUT THE MUCOSAL ENVIRONMENT. Detest various kinds of sensory information - stretch receptors, chemicals, PH
- Interneurons: connect the Myenteric plexus nd Submucosal Plexus and relay information
What veins drain the lower oesophagus, stomach, pancreas, small and large intestine, upper rectum and spleen? Where does this blood vessel go?
Portal Vein and it goes to the liver.
What vein drains the lower part of the rectum and anal canal (the very last part of the GIT)
Iliac vein
What is the main arteries that give oxygenated blood and nutrients to the digestive tract?
Mesenteric arteries which are branches of the abdominal aorta
GIT Blood Supply:
What is the role of the liver in the GIT blood supply?
The LIVER FILTERS THE BLOOD and processes nutrients when then enter the systemic circulation
What is meant by peristalsis?
A wave of muscular contraction in the digestive tract. (But we get peristalsis in all systems that have smooth muscle)
Oral Cavity:
What is the oral cavity lined with?
Inner surfaces are lined with mucous membranes that are the first part of the mucal membrane that continues through the GIT
Oral Cavity:
What is the main function of the oral cavity?
Break down food mechanically (through chewing) and chemically (through saliva)
Oral Cavity:
Describe the structure of the oral cavity.
Hard Palate: Between oral and nasal cavities and allows us to chew and breathe at the same time
Soft Palate
Uvula: Prevents food from entering the nasal cavity when swallowing
Tongue:
- SKELETAL MUSCLE structure attached to the hyoid bone and mandible
Covered with PAPILLAE which help to grip food and give more surface area for TASTE BUDS to sit on.
Oral Cavity:
What are the functions of the oral cavity?
Mastication
Speech
Taste
Swallowing - Bolus is pushed by the tongue into the pharynx
Teeth:
Describe the structure and function of of teeth.
Function is mastication.
Teeth have a CROWN, NECK and ROOT
DENTIN makes up the bulk of the tooth.
ENAMEL, which is the hardest tissue in the body, covers the tooth giving it the hardness the tooth needs to break down food mechanically
Teeth sit between the gum and the periodontal membrane
Saliva:
What are the functions of saliva?
Digestion - chemical breakdown of polysaccharides (predominantly starch)
Lubrication and dissolving food
Cleansing of oral cavity and teeth
Defence - IgA and Lysosomes break down bacterial cell walls
Taste
Buffer for acidic foods (eg: release of bicarbonate)
Waste removal - urea and uric acid from the body
Saliva:
What is saliva made up of?
99.5 % water
Mineral salts
Enzymes: SALIVARY AMYLASE, LYSOZYMES
Mucus
Immunoglobulins (IgA)
Blood clotting factors
PH - Mildly acidic
Saliva:
Where is saliva produced and when is it deployed?
Saliva is produced by the parotid gland, submandibular gland and sublingual glands.
The autonomic nervous system controls production
- with the parasympathetic nervous system producing 1 to 1.5 litres per day.
- the sympathetic nervous system (STRESS RESPONSE) REDUCES SALIVATION
- TOUCH, TASTE, SMELL and SOUND can stimulate digestive salivation
- During dehydration salivation is stopped contributing to sensation of thirst.
Oesophagus:
What is the oesophagus?
25cm long muscular tube which starts at the larynx and ends at the diaphragm. It is the food pipe that leading from the mouth to the stomach
Oesophagus:
What is it made up of?
Lined with epithelium, lubricated with mucus
The top to middle part where we have control of actions such as swallowing has skeletal muscles. The bottom half where where it is involuntary, peristalsis, is smooth muscle.
Oesophagus:
What is the EPIGLOTTIS?
A flap of elastic cartilage which prevents food from entering the trachea (windpipe)
Oesophagus:
How are the contents of the stomach prevented from rising into the oesophagus?
The LOWER OESOPHAGAL SPHNINCTER acts as a seal on the stomach
Oesophagus:
How does the food travel though the oesophagus?
Via muscular contractions - PERISTALSIS
Stomach:
Name the main regions of the stomach
CARDIA- area of entry
FUNDUS - Top area of stomach
BODY - Main bulk of the stomach
The stomach is a J shaped organ
- Lesser curvature is the inner curve of the J
- and greater curvature the outer curve of the J
PYLORIS - At he bottom where digested food exits. About three fingers width above the belly button
