Structure, function and control of the gastrointestinal system

1. Gastrointestinal system
Roger Watson
Twitter: @rwatson1955

2. 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.

3. Bozeman biology You Tube link
The digestive system

6. 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

8. Mesentery
Fold of peritoneum that supports the intestines
Also provides blood and nervous supply

10. Gastrointestinal system
General structure:
•Composed of smooth muscle
•Under control of autonomic nervous system

12. Gastrointestinal system
General structure:
•Composed of smooth muscle
Arranged in two planes:
• longitudinal
• circular

14. lumen

15. 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

18. Gastrointestinal system
General structure:
•Composed of smooth muscle
Arranged in two planes:
• longitudinal
• Circular
Contains:
• Lumen (space)
• Mucosa

19. Mucosa
Both secretory and absorbtive.
Tends to be:
Secretory at the top
Absorbtive at the bottom
secretory
absorbtive

20. Gastrointestinal tract
•Mouth
•Oesophagus
•Stomach
•Small intestine
•Large intestine
•Rectum
•Anus
AND:
•Pancreas
•Gall bladder
•Liver

21. Mouth
Contains:
•Teeth
•Tongue
•Salivary glands

24. 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

26. Mastication (chewing)
Enabled by the muscles of mastication:
•Temporalis
•Masseter

27. Temporalis
Masseter

28. Mastication (chewing)
Enabled by the muscles of mastication:
•Temporalis
•Masseter
And the temperomandibular joint:
•Allows movement in three planes

31. 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

32. Epiglotiss
trachea

33. Oesophagus
Food is propelled down the oesophagus by peristalsis
The trachea (windpipe) is protected by the EPIGLOTTIS

35. The stomach
The stomach is a food reservoir:
•It completes the mechanical breakdown of food
•It initiates protein digestion
•It produces CHYME

36. Note US
spelling!

37. Convoluted surface (rugae)
allows for expansion

38. The stomach
The stomach has three muscle layers:
•Longitudinal
•Circular
•Oblique

39. longitudinal
circular
oblique

40. The stomach
The stomach is lined with gastric pits from which is secreted:
•Mucus
•Hydrochloric acid
•Pepsin
•Gastrin
•Intrinsic factor

42. The intestines
•Small intestine
•Large intestine

43. Small intestine
Large
intestine
Liver Stomach

45. Small intestine
•Propels food along by peristalsis

47. Small intestine
•Propels food along by peristalsis
•Mixes food by segmentation

49. Small intestine
•Propels food along by peristalsis
•Mixes food by segmentation
•Large surface area enabled by:
• VILLI

54. 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

55. 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)

56. Ampulla of
Vater

57. 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

58. Gall bladder
•Stores bile which is produced in the liver
•Bile is released via the ampulla of Vater
•Bile is an emulsifying agent

59. Ampulla of
Vater
LIVER

61. 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.

63. 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

64. 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.

65. 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.

66. 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).

67. Large intestine
Acts as a reservoir and as an area for reabsorbtion of water
Linked to small intestine by ileo-caecal valve

71. 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

72. Large intestine
Produces waste product: faeces
Defaecation:
• Process of expelling faeces

75. 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.

76. 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.

77. 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?

78. 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?

79. 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?

80. 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.

81. r.watson@hull.ac.uk
Four things about…(a simple approach to
anatomy and physiology)
Special Senses
r.watson@hull.ac.uk
Four things about…(a simple approach to
anatomy and physiology)
The gastrointestinal system