W27 Digestive System Flashcards
What are some examples of macronutrients in the digestive system?
- Carbohydrates/Sugars
- Fats/Lipids
- Proteins
What are the key functions of the digestive system? (4)
- Ingestion- food intake
- Digestion (mechanical and chemical)
- Absorption
- Elimination
What are the two major anatomical components of the Digestive System?
- Gastrointestinal tract
(Mouth, Oral Cavity, Orapharynx, Oesophagus, Stomach, Small & Large intestines, Rectum, Anus) - Accessories components (Teeth, Tongue, Salivary glands, Liver, Gall bladder, Pancreas)
What is the gastrointestinal tract?
One long tube (also known as alimentary canal/tract)
~30 feet (~ 9 meter) long
Consists of: (Mouth, Oral Cavity, Orapharynx, Oesophagus, Stomach, Small & Large intestines, Rectum, Anus)
What are the different layers of the gastrointestinal tract? (5)
Lumen
Mucosa
Submucosa
Circular muscular layer
Longitudinal muscle layer
Serosa
What is the Lumen?
Epithelial tissue; food move from mouth to anus
What is the Mucosa layer?
What is its function?
-Thin layers of epithelium, lamina propria (connective tissue) and muscularis mucosa (smooth muscle).
-Secretes mucus, digestive enzymes, and hormones
What is the Submucosa layer?
What does it contain?
-Thick layer of loose connective tissue.
-Contains blood vessels, lymphatic vessels, and nerves.
-Glands may be embedded in this layer. Enables peristalsis
What is the muscular layer composed of?
The circular and longitudinal muscle layers.
What is the circular muscle layer?
Smooth muscle layers, blood vessels and plexus nerves and innervation
What is the Longitudinal muscle layer?
Peristalsis- Involuntary contraction and
relaxation- movement of food
What is the Serosa layer?
A thin sheet of connective tissue that contains blood and lymphatic vessels, and is covered by the peritoneum, Secretes serous fluid to allow lubricated sliding movements between opposing surfaces
GI Motility: How do peristaltic waves work?
- Moves the bolus forward movement/Propulsive
- Coordinated involuntary contraction and relaxation of circular and longitudinal muscles
- Adjacent segments alternatively contract and relax
- Sphincters prevent the back flow
Epiglottis opens, when food is swallowed it shuts to prevent food going into airway
(Hiccups- food goes into airway)
Epiglottis sphincter contracts involuntary, food moves from mouth to stomach
GI Motility: How does segmentation occur?
Moves the bolus first forward and then backword
Primarily mixing, some propulsive movement as well
Blending of bolus with digestive enzymes and secretions
Non-adjacent segments alternatively contract and relax
What is Mastication?
- Chopping and grinding of food in the mouth
(physical digestion) - Teeth (bone) and tongue (skeletal muscle) aid the
physical breakdown of food - Salivary glands in the mouth secrete amylase
enzyme (amylase digest the carbohydrates-
chemical digestion, breaks down into simple/smaller molecule) - Water in the saliva helps to make the food moist
and bolus for easy swallowing and passage into propharynx
What is the Saliva composed of?
What is the pH of saliva?
99.5% of water
0.5% amylase, bicarbonate ion and other electrolytes
pH of saliva at 6.5-7.5
What is the Oesophagus?
What is the structure like?
Swallowed food passes into the oesophagus, a narrow tube that travels through the thorax to the abdomen (~ 8 inch long in adult)
The walls are skeletal muscle initially but transition to smooth muscle about two-thirds of the way down the length.
The muscles are under conscious control, used when breathing, eating, belching, and vomiting.
Stomach:
What is the cardiac sphincter?
-A thin ring-like muscle helps to prevent
stomach contents from going back up into the oesophagus.
-Also, vents air out (burping)
Stomach:
What are the three regions of the stomach?
What is the function?
Fundus
Body
Antrum
-mixing of food bolus with acid & enzyme
- largely digestion but some absorption (like alcohol,
aspirin, some lipid-soluble’s
J-shaped- Size~12x6 inches, capacity: 1-4 L
(food stays 2-4 hrs; pH: 1-3, Strongly acidic
Chyme (Stomach acids + enzymes + food) moves to the intestine after being formed in the stomach
Stomach:
What is the Rugae?
Series of ridges by folding of the stomach walls; contains secretory pits (acid and others); provides large surface area and expansion to full capacity
Stomach:
What is the Pylorus sphincter?
-A valve/sphincter that connects the stomach to the small intestine.
-Prevents the backflow of contents from the small
intestine to the stomach
Small intestine:
What occurs in the duodenum?
Mixing of chyme and secretions (digestive acids and
enzymes) from gall bladder & pancreas ducts (Oddi-tonically controlled sphincter).
Absorption of minerals, vitamins and other micronutrients begins here.
What occurs in the small intestine?
How long is it?
What are its 3 parts?
What does its cross-section look like?
Most digestion and absorption
3 m to 5 m long (~10 feet to 20 feet)
Duodenum- Jejunum- Ileum
Cross section of SI: Intestinal mucosa has finger-like projections, Villi.
Multi-folded (plicae), the invaginations are known as crypt
After SI, Waste/unabsorbed moves to the large intestine (caecum
What occurs in the jejunum?
Further (segmentation) mixing of chyme and secretions(digestive acids and enzymes).
Absorption of minerals, vitamins and other micronutrients, digested carbs, fats and proteins.
What occurs in the ileum?
Last part (largest part) of the small intestine,
several folds-thin walls; mixing of digested, and non-digested (segmentation) and secretions (digestive acids and enzymes). Absorption of leftover
digested carbs, fats and proteins from the jejunum
What occurs in the large intestine?
How long is it?
What do the bacteria in the LI produce? (4)
water & electrolytes absorption
1.5 metres, or 5 feet (20-30 hrs holding)
Completion of absorption of nutrients. 2-3 times a
day of gastrocolic reflux (bowel movement).
The bacteria in the LI produce vitamins
(B12, thiamin, and riboflavin) as well as vitamin K.
Large intestine:
What is the Caecum?
First part of the LI/colon
Water and electrolyte absorption starts and the mixing of mucus to lubricate the faeces
(churning and kneading motion)
What is the Rectum?
Last part of the large intestine, a storage place for faeces
What is the Anal sphincter?
A group of muscles at the end of the rectum that surrounds the anus and controls the release of stool
In which order does food pass along the:
Small intestine
Large intestine
Duodenum, Jejunum, Ileum
Caecum, ascending, transverse, descending, sigmoid, rectum, anal sphincter