Digestive system

Question 1

What is digestion?

Answer 1

Breakdown of food to a useful form that can be absorbed and used by cells.
This is used for:
- the creation of energy- catabolism which produces ATP.
- repair/ building- anabolism which produces ‘building blocks’

Question 2

Alimentary canal/ GI tract =

Answer 2

The organs that food and liquids travel through when they are swallowed, digested, absorbed, and leave the body as feces. These organs include the mouth, pharynx (throat), esophagus, stomach, small intestine, large intestine, rectum, and anus.

Question 3

Accessory organs=

Answer 3

Accessory organs of digestion are organs that secrete substances needed for the chemical digestion of food but through which food does not actually pass as it is digested.
The main accessory organs are: liver, gallbladder, pancreas and salivary gland.
They are situated outside the GI tract and they empty the secretions into the GI tract

Question 4

What are the digestive system processes?

Answer 4

• Ingestion
• Propulsion
• Digestion (mechanical breakdown, chemical breakdown)
• Absorption
• Defecation

Question 5

What are the four layers of the GI tract wall?

Answer 5

• Serosa
• Muscularis
• Submucosa
• Mucosa

Question 6

Serosa layer =

Answer 6

• Is the outermost layer
• In abdomen
• Barrier to the spread of infection
• Anchors the GI tract

Question 7

Muscularis layer=

Answer 7

• 2 layers of smooth muscle (circular & longitudinal)
• Provides peristalsis and mixing
• Onward movement by sphincters

Question 8

Submucosa layer=

Answer 8

• Loose connective tissue
• Blood vessels
• Nerves
• Lymph vessels
• Lymphoid tissue

Question 9

Mucosa layer=

Answer 9

Has:
1. Mucous membrane (protects, secretes, absorbs)
2. Lamina propria (blood vessels, lymphoid tissue)
3. Muscularis mucosa (provides infoldings)

Question 10

Mesenteries and lymph nodes=

Answer 10

Mesenteries are double layers of a membrane called the peritoneum, which lines the abdominal cavity. They hold the digestive organs in place and provide a pathway for blood vessels, lymph vessels, and nerves.

The digestive system also has lymph nodes and lymph vessels that help with immunity and absorbing fats.

Question 11

Peristalsis=

Answer 11

Peristalsis is a series of wave-like muscle contractions that move food through the digestive tract. Beginning in your throat when you swallow and continuing through your oesophagus, stomach and intestines while you digest.

Question 12

What are the stages of swallowing?

Answer 12

the oral preparatory stage, the oral stage, pharyngeal stage and esophageal stage

Question 13

Oesophagus=

Answer 13

is a tubular, elongated organ of the digestive system which connects the pharynx to the stomach.
Lined with mucosa to reduce friction and has thick protective stratified squamous epithelium.
The passage of food in the oesophagus is facilitated by:
- Flattening of mucosal folds
- Mucous glands
- Loose and elastic submucosa (SM)
It has muscularis externa.

Question 14

The stomach=

Answer 14

• Stores food for 2 hours and the goes through both mechanical and chemical breakdown.
• Has an extra layer in the muscularis: the oblique muscle which are a pair of muscles, one on each side of your rectus abdominis which help rotate the trunk.
• Has highly secretary mucosa essential for digestion and protection: HCL. pepsin, mucus
• Is lined with simple columnar epithelial cells (all mucous gland cells) and millions of gastric pits (leading to gastric glands.

Question 15

Glands of stomach fungus and body=

Answer 15

Gastric glands are found in the mucosa of the funds and body of the stomach.
Gastric glands open into gastric pits. Types of cells in gastric glands:
- Surface mucous cells
- Mucous neck cells: simple columnar, secrete acidic mucus
- Parietal cells: secrete HCL & intrinsic factor
- Chief cells: secrete pepsinogen, lipases
- G-cells: secrete gastrin

Question 16

Small intestine=

Answer 16

Has three parts:
- duodenum
- jejunum
- ileum
The glands secrete intestinal juice, complete chemical digestion and absorbs nutrients.
The small intestine folds many times to fit inside the abdomen, the mucosal folds, villi and microvilli increase surface area for digestion and absorption.

Question 17

What are the cells of the small intestine?

Answer 17

• Absorptive cells
• Goblet cells (mucus)
• Intestinal crypt
• Paneth cells (defensins, lysozyme)
• Secretory cells (intestinal juice)
• Entero endocrine cells (secretin, cholecystokinin)

Question 18

Duodenum specialisations=

Answer 18

Has Brunner’s glands: They produce a special mucus that protects the intestine from stomach acid and helps with digestion.
- Is the first part of your small intestine. Its main job is to break down food into absorbable nutrients.
- Secrete an alkaline mucus that neutralises acidic chyme from stomach and protect the mucosa.
Produces cholecystokinin (CCK) which inhibits gastric emptying.

Question 19

Jejunum specialisations=

Answer 19

• 2nd section of small intestine
  Main absorptive region
  (glucose, vitamins, amino acids, fats)
• Very few Brunner’s glands
• Mucosal folds – large and numerous
  Rapid absorption
• The longest villi is found here

Question 20

Ileum specialisations=

Answer 20

• Is the distal part of small intestine.
• Has peyer’s patches: these are small clusters of immune cells found in the small intestine (mainly in the ileum). They help protect the body by detecting harmful bacteria and triggering an immune response.
• huge domes of lymphoid tissue

Question 21

What is segmentation?

Answer 21

Nonadjacent segments of alimentary tract organs alternatively contract and relax, moving food forward then backward. Food mixing and slow food propulsions occur.

Question 22

The colon=

Answer 22

Also known as the large bowel or large intestine.
It has thick mucosa:
- simple columnar epithelium
Many crypts:
- absorptive cells
- goblet cells (mucus)
No circular folds
No villi
Polypeptide YY- inhibits motility

Question 23

Bacterial flora in the colon=

Answer 23

• There are 10 million types
• They synthesise vitamins B and K
• They metabolise molecules e.g., heparin, mucin
• They ferment indigestible carbohydrates; produce 500ml flatus daily

Question 24

Rectum and anal canal=

Answer 24

Your anal canal continues from your rectum and makes up the last few centimeters of your large intestine. The anus contains important muscles (anal sphincters) that control your bowel movements.

Question 25

Explain the defecation reflex=

Answer 25

The defecation reflex is a physiological process that facilitates the expulsion of feces from the rectum through the anus.
1. Faeces are moved into the rectum by peristaltic contractions of the colon
2. Stretching of rectal walls activates mechanoreceptors in the rectal mucosa, these receptors send afferent signals to the spinal cord via pelvic nerves
3. The spinal cord processes incoming signals and triggers efferent responses: relaxation of internal anal sphincter (smooth muscle, involuntary), increased peristalsis in the sigmoid colon and rectum
4. Signals are also relayed to the brain, particularly the cerebral cortex, creating a conscious sensation of the need to defecate.
5. The external anal sphincter (skeletal muscle, voluntary) remains contracted until defecation is consciously initiated.
Voluntary relaxation of this sphincter allows feces to pass through the anus.
6. If the external anal sphincter is relaxed, coordinated contractions of the rectum and pelvic floor muscles, aided by abdominal muscles (Valsalva maneuver), expel feces.
If defecation is delayed, the rectum accommodates the fecal material, and the urge to defecate subsides until the next reflex is triggered.