Digestive system Flashcards
What is digestion?
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’
Alimentary canal/ GI tract =
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.
Accessory organs=
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
What are the digestive system processes?
- Ingestion
- Propulsion
- Digestion (mechanical breakdown, chemical breakdown)
- Absorption
- Defecation
What are the four layers of the GI tract wall?
- Serosa
- Muscularis
- Submucosa
- Mucosa
Serosa layer =
- Is the outermost layer
- In abdomen
- Barrier to the spread of infection
- Anchors the GI tract
Muscularis layer=
- 2 layers of smooth muscle (circular & longitudinal)
- Provides peristalsis and mixing
- Onward movement by sphincters
Submucosa layer=
- Loose connective tissue
- Blood vessels
- Nerves
- Lymph vessels
- Lymphoid tissue
Mucosa layer=
Has:
1. Mucous membrane (protects, secretes, absorbs)
2. Lamina propria (blood vessels, lymphoid tissue)
3. Muscularis mucosa (provides infoldings)
Mesenteries and lymph nodes=
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.
Peristalsis=
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.
What are the stages of swallowing?
the oral preparatory stage, the oral stage, pharyngeal stage and esophageal stage
Oesophagus=
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.
The stomach=
- 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.
Glands of stomach fungus and body=
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
Small intestine=
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.
What are the cells of the small intestine?
- Absorptive cells
- Goblet cells (mucus)
- Intestinal crypt
- Paneth cells (defensins, lysozyme)
- Secretory cells (intestinal juice)
- Entero endocrine cells (secretin, cholecystokinin)
Duodenum specialisations=
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.
Jejunum specialisations=
- 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
Ileum specialisations=
- 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
What is segmentation?
Nonadjacent segments of alimentary tract organs alternatively contract and relax, moving food forward then backward. Food mixing and slow food propulsions occur.
The colon=
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
Bacterial flora in the colon=
- 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
Rectum and anal canal=
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.
