Lecture 21 - GI system intro Flashcards
What is the GI tract?
A network of organs and specialised cells that enables you to transform the food you eat into the energy and nutrients required for life.
The Gi system contains the GI tract. What organs make up the tract?
Mouth, oesophagus, stomach, small intestine, large intestine, anus
The GI system contains accessory organs. What are these? What is their role?
salivary glands, liver, gallbladder, pancreas
not part of the GI tract but secrete substances into the tract via ducts
The GI system contains mesentery. What is this?
the membranous tissue surrounding the organs of the GI system. Holds intestines in place. It contains lots of blood vessels involved in the absorption of nutrients. It also contains lots of lymphatics, part of the immune system and also absorbs fats.
Mouth:
- what does it contains?
- what is the main function?
- Teeth, tongue, mucous membranes
- Main function = to chew food
What are the pharynx and epiglotis?
- Contains pharynx and epiglottis which are muscular flaps in the back of the mouth. These prevent food travelling into the lungs.
What is the oesophageal sphincter?
in stomach - prevents anything from passing back into the oesophagus.
The stomach is made up of three different layers of smooth muscle…
outer, middle and inner layer
What is the role of the stomach?
Involved in the storage of food and also digestion of food- mechanical digestion and not really enzymatic digestion. This involves mixing, protein digestions, HCl/pepsin digestion and fat emulsification.
There are four layers of the stomach wall. What are they?
= mucosa, submucosa, smooth muscle layer and serosa
Cell types found in the stomach
- mucous neck cell- secrete mucus which protects the lining
- parietal cells- secrete gastric acid/HCl
- enterochromaffin like cell- secrete histamine which stimulates acid chief cells- secrete enzymes
- D cells- produce hormone called somatostatin which inhibits production of gastric acid
- G cells- secrete gastrin hormone which stimulates acid.
The longest part of the GI tract is…
the small intestine
The small intestine is the main site for…
absorption
The small intestine is divided into three main sections. What are these?
the duodenum at end of stomach, jejunum and the ileum
What are the different layers of the wall of the small intestine?
mucosa, submucosa, thick muscle layers and serosa
The small intestine is the primary site of what molecules?
- Primary site of breakdown of carbs, proteins and fats
Give the cells in the small intestine
microvilli which are absorptive cells, goblet cells which secrete mucus, enteroendocrine cell which secretes hormones and the Paneth cell which secrete lysozymes and is capable of phagocytosis.
How is the small intestine adapted for better absorption?
Has a large surface area- the surface of the small intestine folds, these folds are covered in villi which are covered with epithelial cells covered in microvilli. The increase in surface area increases rate of absorption
Role of the crypts of Lieberkuhn
Paneth cells- secrete lysosomes and are phagocytic and antimicrobial, stem cells- regeneration and goblet cells- secrete mucous.
What is the large intestine divided into?
ascending colon, transverse colon and descending colon
Large intestine role
- Water and ion conservation
- Bulk movement of faeces
Like the small intestine, the large intestine also has crypts of Lieberkühn involved in…
immune function
Give three different salivary glands
parotid glands, sublingual gland and submandibular gland
What is the role of the salivary gland?
- Lubrication – mucus
- Protection – lysozymes and thiocyanate
- Digestion – saliva contains amylase and lipase enzymes
- Solubilise chemicals in food which are what produces taste
The liver is one of the largest organs in the body. What is the role of the liver?
- Bile production – bile is needed for emulsification of fats, needed for fat digestion
- Excretion of bile into the gall bladder
Describe the role of the gall bladder.
- Storage vesicle for bile
- Concentrates bile into a thick viscous substance
- Delivers bile to the duodenum in response to meals
What is the role of pancreas?
- Makes enzymes involved in digestion – needed to digest proteins, fats and carbs
- Produces the hormones insulin and glucagon
What are the functions of the Gi system?
- Ingestion
- Secretion
- Movement
- Digestion
- Absorption
- Excretion
What is ingestion?
The process of taking food or drink through the mouth
The Gi system works before we even take a bite of food. Explain.
The GI system secretes saliva, mucus, HCl, enzymes and bile
The sight of food, thought of food triggers the release of substances that contribute to digestion. Eg. saliva.
The food we eat must move through our system. What are the two main types of movement?
- segmentation - non-adjacent segments of the small intestine alternatively contract and relax moving food forwards and backwards
- peristalsis - muscular movements travelling in a wavelike fashion in one direction
What movement of food in the GI system is voluntary? And what is involuntary?
Initial movement of food into the oesophagus occurs through swallowing, which is a voluntary process. Then food moves through the remainder of the gastrointestinal system by peristalsis- involuntary
What is digestion?
The breakdown of larger portions of food and breaking them down into smaller components- micronutrients- small enough to be that can be absorbed by cells
Name the two types of digestion?
Mechanical and chemical
What is mechanical digestion? Give the two stages of mechanical digestion.
- Physically breaking down food substances into small particles
1. Mastication – food is initially broken down in the mouth by the grinding action of teeth
2. Peristaltic contractions – stomach lining contains muscles which physically squeeze and mix the food with strong gastric acids – eg. HCl. This process is called churning
What is chemical digestion?
- Use of enzymes to breakdown food- chemical digestion breaks down different nutrients such as proteins, carbs, fats into smaller parts…
- Fats into fatty acids and monoglycerides
- Nucleic acids into nucleotides
- Polysaccharides or carbs into monosaccharides
- Proteins into amino acids
The enzymes for chemical digestion are released by….
accessory organs
What is absorption?
Once food is broken down, absorption occurs….
Absorption – the process through which nutrients, water and electrolytes move from the lumen of the small intestine into the cell, then into the blood. This occurs through passive or active transport. Once nutrients are absorbed, they can generate energy or provide the building blocks to the cells
What is excretion? Describe the process
- The process by which metabolic waste is eliminated from the body - excreted
- Waste left over from the digestive process is referred to as stool. As stool passes through the colon excess water is removed leaving a solid mass of mostly food debris and bacteria.
- Takes about 36 hours for stool to pass through the colon.
- Stool is then stored in the rectum before exiting the body through the anus.
The GI tract plays an important role in immune function. it is said to be the first…
line of defence against pathogens
How does the GI system play a part in immune function?
Stomach acid stops most of the germs that enter the body in the food we eat.
Contains its own bacteria/microbiome to prevent overgrowth of harmful bacteria. Cells secrete mucus and antimicrobial peptides
Gut contains resident immune cells
Many pathogens enter the body via the intestinal mucosa so it is vital the gut-associated lymphoid tissues can provide effective immune responses when needed
The gut associated lymphoid tissue represents…
almost 70% of the entire immune system
