Lecture 2 - Digestion System [1]

Question 1

What are the 6 processes of the digestion system?

Answer 1

1. Ingestion
2. Propulsion (motility)
3. Mechanical Digestion
4. Chemical Digestion
5. Absorption
6. Defecation

Question 2

What happens during ingestion?

Answer 2

process of placing food into the mouth

Question 3

What happens during Propulsion?

Answer 3

movement of foods from one region of the digestive system another Muscle contractions, mixes contents, and moves them along the GI tract. (Aids digestion and abosrption)

Peristalsis and Segementation

Question 4

What happens Peristalsis?

Answer 4

Alternating waves of contraction and relaxation that squeezes food along the GI tract

Question 5

What happens during Segmentation?

Answer 5

movement of materials back and forth to allow mixing in the small intestine.

Question 6

What happens during the mechanical digestion?

Answer 6

Mechanical digestion prepares food for further degradation by enzymes.

Examples: Mixing of food in the mouth by the tongue. Churning of the food in the stomach, segmentation in the small intestine.

Question 7

What happens during Chemical digestion?

Answer 7

1. Digestion occurs when enzymes chemically bark down large molecules into their building blocks
2. Each major food group uses different enzymes
3. Carbohydrates are broken to monosaccharides (simple sugars).
4. Proteins are broken to amino acids
5. Fats are broken to fatty acids and glycerol

Question 8

What happens during absorption?

Answer 8

1. The active and passive transfer of the products of digestion from the limen of the GI tract to the extracellular fluid
2. End products of digestion are absorbed in the blood or lymph
3. Nutrients must enter mucosal cells and then into blood or lymph capillaries

Question 9

What happens during Defecation?

Answer 9

1. Elimination of indigestible substances from the GI tract the form of feces.

Question 10

What are properties of the GI tract?

Answer 10

1. It is a hollow convoluted tube that opens to the external environment at the both ends (mouth and anus)
2. Lumen of the tube therefore is considered an extension of the external environment

Question 11

What is the pathway of the GI tract?

Answer 11

1. Mouth (oral cavity)
2. Pharnyx
3. Esopagus
4. Stomach
5. Small intestine
6. Large intestine (colon)
7. anus

Question 12

What are the divisions of the digestive system?

Answer 12

1. GI tract - gastro intestinal tract

2. Accessory organs

Question 13

What is the structure of the GI tract?

Answer 13

made up of four distinct tissue layers. 
[Inner most layer] 
1. Mucosa
2. Submucosa
3. Muscularis externa
4. Serosa
[Outer most layer]
Adventitia - Outermost layer of the GI tract, does not lie within peritoneal cavity i.e esophagus .

Question 14

What is the Mucosa?

Answer 14

Innermost layer of the GI tract: Lines the lumen and separates GI lumen from internal envrionment

Question 15

What is the function of the Mucosa?

Answer 15

1. Secretion of mucus
2. Absorption of end products of digestion (small intestine)
3. Immune protection

Question 16

What are the cell types that line the lumen of the GI tract and their functions?

Answer 16

1. Enterocytes
2. Absorptive cells - absorb nutrients - in the small intestine
3. Exocrine cells - Produce digestive enzymes in the small intestine
4. Endocrine cells - Produce hormones that regulate the function of the GI tract

Question 17

What are the three layers of Mucosa

Answer 17

1. Surface columnar epithelium that is made up of the enterocytes
2. Connective tissue: ‘Lamina Popria’: Small blood vessels, lymphatic vessels, Nerves, Lymphatic tissue
3. Muscularis mucosae: Thin smooth muscle.

Question 18

What do the modification in the Mucosa allow?

Answer 18

Increase in surface area

Question 19

What is the role of the epithelium?

Answer 19

1. secretes mucus which lubricates the passage of food

2. secretes digestive enzymes of the stomach and small intestine

Question 20

What are the properties of the Lamina propria?

Answer 20

1. Lymph nodules that contain lymphocytes to produce antibodies and macrophages.
   - > which phagocytise bacteria and other foreign material that gets through the epithelium

Question 21

What are the properties of the muscularis

Answer 21

1. Thin layers of the smooth muscle creates folds in the mucosa and ripples so that all epithelial cells are in touch with the contents of the organ and to increase the surface area.

Question 22

What is the small intestine important for?

Answer 22

absorption

Question 23

What is the submucosa?

Answer 23

thick layer of connective tissue which contains collagen and elastin fibrils and blood vessels, lymphatics and some regions also contain submucosal glands

Question 24

What is the function of the submucosa?

Answer 24

Distensibility and Elasticity

Question 25

What is the submucosa plexus?

Answer 25

part of the enteric nervous system

• Nerve networks innervate the mucosa to regulate secretion.
• Parasympathetic impulses increase secretions, where as sympathetic impulses decrease secretion.
  Sensory neurones are also present to the smooth muscle as are motor neurones to blood vessels to regulate vessel diameter and blood flow

Question 26

What are the two layers the Muscularis external is made of?

Answer 26

1. Inner layer of circular muscle
2. Outer layer of longitudinal muscle
   * except from the stomach which there is a 3rd smooth layer the oblique muscle

Question 27

What is the function of the Muscularis external (the external muscle layer)

Answer 27

1. Motility (propulsion) of the GI tract
   - Peristalsis: Coordinated contractions –> propels the lumen contents through the GI tract towards the anus (one-way movement)

• Segmentation: Coordinated contractions that mix the content with secretion that contain digestive enzymes to help digest food.

Question 28

What is the the Sphincter and what is the role of it?

Answer 28

1. Circular muscle layers is modified to form a ring of tissue called sphincter throughout the GI tract.

Role: Control movement from one organ of the GI tract to the other

Where are they found?

• Between PHARNYX and ESOPHAGUS
• ESOPHAGUS AND STOMACH
• STOMACH AND SMALL INTESTINE
• ILEUM (small intestine) and CAECUM (large intestine)

Question 29

What is the role of myentric plexus with muscularis externa

Answer 29

1. Sympathetic impulses decrease contractions and peristalsis wheres parasympathetic impulses increase contractions and peristalsis promoting normal digestion.

Question 30

What happens during Motility?

Answer 30

1. Propulsion: the movement of foods from one region of the digestive system to another
2. Peristalsis:
   - waves of contraction and relaxation
   - Requires circular and longitudinal muscle contractions
   - propels contents forward
3. Segmentation
   - a type of motility of the small intestine
   - requires circular muscle layer
   - alternating contractions between intestinal segments
   - movement of chyme back and forth to facilitate mixing with digestive enzymes

Question 31

What is the Serosa and function of

Answer 31

• the outermost layer of the GI tract wall
• made of two layers
• -> inner layer of loose connective tissue
• -> outer layer of an epithelial tissue (mesothelium)

Function: acts as a protective layer maintains correct positions of the GI organs but allows them to move about

Question 32

What happens during chemical Digestion?

Answer 32

• Carbohydrates are broken to monosaccharides
• Proteins are broken down to amino acids
• Lipids are broken down to fatty acids and glycerols

Each digestive enzyme is produced by a specific digestive organ and functions at a specific site