Gastrointestinal system
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Gastrointestinal system Roger Watson Twitter: @rwatson1955
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Transcript of Gastrointestinal system
Gastrointestinal system
Roger WatsonTwitter: @rwatson1955
Gastrointestinal system
The gastrointestinal system runs from the mouth to the anus.
It is responsible for the ingestion and digestion of food and the excretion of waste products.
Topologically, it lies ‘outside’ the body.
Peritoneum
Organs of the gastrointestinal system are contained in the:• peritoneal cavity
Peritoneum:
• a transparent membrane that lines the abdominal cavity in mammals and covers most of the viscera
Mesentery
Fold of peritoneum that supports the intestines
Also provides blood and nervous supply
Gastrointestinal system
General structure:
• Composed of smooth muscle
• Under control of autonomic nervous system
Gastrointestinal system
General structure:
• Composed of smooth muscle
Arranged in two planes:• longitudinal• circular
lumen
Gastrointestinal system
General structure:
• Composed of smooth muscle
Arranged in two planes:• longitudinal• Circular
Muscle arrangement allows PERISTALSIS• Waves of contraction and relaxation which propel food
along the GI tract
Gastrointestinal system
General structure:
• Composed of smooth muscle
Arranged in two planes:• longitudinal• Circular
Contains:• Lumen (space)• Mucosa
Mucosa
Both secretory and absorbtive.
Tends to be:
Secretory at the topAbsorbtive at the bottom
secretory
absorbtive
Gastrointestinal tract
• Mouth• Oesophagus• Stomach• Small intestine• Large intestine• Rectum• Anus
AND:• Pancreas• Gall bladder• Liver
Mouth
Contains:
• Teeth• Tongue• Salivary glands
Mouth
Contains:
• Teeth• For breaking food into smaller particles
• Tongue• Organ of taste but also helps in chewing and swallowing
• Salivary glands• Lubricate food in the mouth and begin carbohydrate digestion
Process know as MASTICATION
Mastication (chewing)
Enabled by the muscles of mastication:
• Temporalis• Masseter
Temporalis
Masseter
Mastication (chewing)
Enabled by the muscles of mastication:
• Temporalis• Masseter
And the temperomandibular joint:
• Allows movement in three planes
Mastication (chewing)
Enabled by the muscles of mastication:
• Temporalis• Masseter
And the temperomandibular joint:
• Allows movement in three planes
Chewing is a prelude to swallowing
Epiglotiss
trachea
Oesophagus
Food is propelled down the oesophagus by peristalsis
The trachea (windpipe) is protected by the EPIGLOTTIS
The stomach
The stomach is a food reservoir:
• It completes the mechanical breakdown of food
• It initiates protein digestion
• It produces CHYME
Note US spelling!
Convoluted surface (rugae) allows for expansion
The stomach
The stomach has three muscle layers:
• Longitudinal• Circular• Oblique
longitudinal
circular
oblique
The stomach
The stomach is lined with gastric pits from which is secreted:
• Mucus• Hydrochloric acid• Pepsin• Gastrin• Intrinsic factor
The intestines
• Small intestine• Large intestine
Small intestine
Large intestine
Liver Stomach
Small intestine
• Propels food along by peristalsis
Small intestine
• Propels food along by peristalsis• Mixes food by segmentation
Small intestine
• Propels food along by peristalsis• Mixes food by segmentation• Large surface area enabled by:
• VILLI
Small intestine
• Propels food along by peristalsis• Mixes food by segmentation• Large surface area enabled by:
• VILLI• Secretions include:
• Sodium bicarbonate• Protein digesting enzymes:
• Peptidase• Trypsin*
• Fat digesting enzymes:• Lipase*
• Carbohydrate digesting enzymes:• Amylase*• Maltase • Sucrase • Lactase
Pancreas
Lies below the stomach and is linked to the small intestine (duodenum) via the:
• pancreatic duct• ampulla of Vater (controlled by the sphincter of Oddi)
Ampulla of Vater
Pancreas
Lies below the stomach and is linked to the small intestine (duodenum) via the:
• pancreatic duct• ampulla of Vater (controlled by the sphincter of Oddi)
Pancreatic secretions:• Trypsin• Amylase• Lipase
Gall bladder
• Stores bile which is produced in the liver
• Bile is released via the ampulla of Vater
• Bile is an emulsifying agent
Ampulla of Vater
LIVER
Digestion
Breaks large molecules down into smaller ones which can be absorbed in the intestines and used by the body in metabolism
The proteins involved in digestion (eg amlyase, lipase, pepsin) are called ENZYMES.
Digestion
Breaks large molecules down into smaller ones which can be absorbed in the intestines and used by the body in metabolism
The proteins involved in digestion (eg amlyase, lipase, pepsin) are called ENZYMES.
Digestion is controlled in three phases:• Cephalic • Gastric • Intestinal
Cephalic phase
Prepares the stomach for incoming food and lasts very briefly. Sight, smell, taste, or thought can stimulate secretions. This stage is directed by the CNS and, under the control of the vagus nerve, parasympathetic fibers innervate the cells which secrete the gastric juices.
Gastric phase
Begins with the arrival of food, causing the secretion of the hormone gastrin, which is released along with stomach acid and enzymes. This phase may last for several hours.
Intestinal phase
Begins with the entrance of chyme into the small intestine, causing the secretion of many hormones including secretin, CCK (cholecystokinin), and GIP (gastric inhibitory peptide).
Large intestine
Acts as a reservoir and as an area for reabsorbtion of water
Linked to small intestine by ileo-caecal valve
Large intestine
Acts as a reservoir and as an area for reabsorbtion of water
Linked to small intestine by ileo-caecal valve
Movement in large intestine:
• Peristalsis• Haustral churning• Mass movement
Intestinal bacteria:• E.coli• Play an important role in digestion of residual products
Large intestine
Produces waste product: faeces
Defaecation:• Process of expelling faeces
Gastrointestinal system
The gastrointestinal system runs from the mouth to the anus.
It is responsible for the ingestion and digestion of food and the excretion of waste products.
Topologically, it lies ‘outside’ the body.
Questions
1. Describe the GI system.
2. What are the four main regions of the GI tract between mouth and anus?
3. Name four organs/structures that are linked to the GI tract.
4. Describe the peritoneum and what is the space that it encloses called?
5. What kind of muscle is found in the GI tract, how is it arranged and how is it controlled?
6. What is the process that moves food along the GI tract? Describe this process.
Questions
7. What is the space in the GI tract called and what is the lining of the GI tract called? What are the two functions of the lining?
8. Name the three pairs of salivary glands. What is the MAIN function of saliva?
9. What is mastication? In addition to saliva what other parts of the mouth are involved? What is the end product of mastication?
10. What are the muscles of mastication? Which joint is involved and what is unique about it?
11. In the process of swallowing, which tube does the bolus of food enter on its way to the stomach? Which tube is protected by the epiglottis and what is the epiglottis? How is the bolus of food moved to the stomach?
Questions
12. What are the functions of the stomach?
13. What are the three muscle layers of the stomach and what are the convolutions on the inner surface of the stomach called?
14. State the three regions of the small intestine in the correct order.
15. What are the functions of the small intestine?
Questions
16. What features of the lining of the small intestine provide it with a large surface area? What are the three groups of enzymes (ie in terms of what they digest) that are secreted into the small intestine?
17. Where do pancreatic secretions enter the duodenum? In addition to sodium bicarbonate what digestive enzymes are produced by the pancreas?
18. Where is bile made? What does the gall bladder do? Where is bile released into the duodenum? What does bile do?
19. Describe digestion.
20. What do enzymes do? What are the three phases of digestion?
Questions
21. What is mainly reabsorbed in the large intestine and what are the three major regions of the large intestine?
22. What are the three types of movement in the large intestine and which bacterium is mainly found here?
23. Describe the structure and function of the internal and external anal sphincters.
Four things about…(a simple approach to anatomy and physiology)
Special Senses
Four things about…(a simple approach to anatomy and physiology)
The gastrointestinal system
