Week 7 Flashcards
What is the digestive system?
The digestive system is essential for converting food into energy and materials for body cells.
What are the functions of the digestive system?
- takes in food
- breaks food down into nutrient molecules
- absorbs nutrient molecules into the bloodstream
- eliminates indigestible remains from the body
What are the two main components of the digestive system?
· Alimentary Canal (Gastrointestinal or GI Tract):
- Continuous muscular tube running from the mouth to the anus
- Includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine
- The inside of the GI tract is technically considered outside the body, as it is open to the external environment at both ends
· Main functions:
- Digests food by breaking it down into smaller fragments
- Absorbs the digested fragments into the bloodstream
· Accessory Digestive Organs:
- Help in the process of digestion
- Include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas
- Involved in mechanical processing and secretion of digestive enzymes and fluids
What is the digestive tract?
a food disassembly line, in which food becomes less complex at each step of processing.
What are the six activities involved with the processing of food?
Ingestion, propulsion, mechanical digestion, chemical digestion, absorption, defecation
What is ingestion?
· the process of taking food or substances into the mouth to begin the digestive process.
· This initial step involves chewing (mastication) and swallowing (deglutition), leading to the passage of food into the digestive tract, where further breakdown and absorption occur.
What is propulsion?
Propulsion refers to the movement of food and other substances through the digestive tract. It is primarily driven by peristalsis, which involves rhythmic, wave-like contractions of smooth muscles in the GI tract walls. These contractions:
- Propel contents forward
- Mix and churn food
- Are most prominent in the esophagus and stomach
- Work like squeezing toothpaste from a tub
What is mechanical digestion?
Mechanical digestion is the physical breakdown of food into smaller particles, making it easier for enzymes to act and aiding nutrient absorption. It:
- Increases surface area for digestive enzymes
- Supports efficient digestion and absorption
Where it occurs: - Mouth:
Begins with mastication (chewing)
Teeth break food into smaller fragments - Stomach:
Muscular contractions churn and mix food with gastric juices
Forms chyme, a semi-liquid mixture - Small intestine:
Peristalsis moves and mixes chyme
Segmentation contractions slosh contents back and forth
Enhances mixing in the small and large intestines
What is chemical digestion
Chemical digestion is the breakdown of complex food molecules into simpler molecules using enzymes and digestive substances. It:
Complements mechanical digestion
Breaks food into molecules small enough for absorption
Allows nutrients to be used for energy, growth, and repair
Where it occurs:
Mouth:
Begins with enzymes like amylase
Starts digestion of carbohydrates into simple sugars
Stomach:
Hydrochloric acid and pepsin break down proteins into amino acids
Small intestine (main site):
Enzymes from pancreas and bile from liver aid digestion
Carbohydrates → simple sugars
Proteins → amino acids
Fats → fatty acids and glycerol
Nutrients are absorbed through intestinal lining into the bloodstream
What is absorption?
Absorption is the process of taking up digested nutrients, water, and electrolytes from the GI tract into the bloodstream or lymph for distribution throughout the body.
Where it occurs:
Small intestine (main site – ~90%):
Villi and microvilli increase surface area
Nutrients absorbed by:
→ Diffusion
→ Facilitated diffusion
→ Active transport
Absorbed nutrients include:
→ Glucose
→ Amino acids
→ Fatty acids and glycerol
Large intestine:
Absorbs remaining water and electrolytes
Helps maintain fluid and electrolyte balance
Purpose:
Nutrients are transported to body cells for
→ Energy production
→ Growth
→ Repair
Indigestible material continues and is excreted as feces
What is defecation?
Defecation is the process of expelling waste from the body through the anus. It removes indigestible materials, bacteria, cellular waste, and excess water, helping maintain digestive health.
How it works:
After digestion and absorption in the small intestine, leftovers enter the large intestine
Water is absorbed, and material is formed into faeces
Faeces include:
→ Undigested food
→ Bacteria
→ Cellular debris
→ Water
In the rectum:
Faeces accumulate, triggering nerve signals
Internal anal sphincter relaxes (involuntary)
Faeces move into the anal canal
External anal sphincter (voluntary) controls release
Muscles of rectum and abdomen contract to assist expulsion
Purpose:
Removes waste
Supports digestive system balance and health
What are the digestive reflexes and how do they work?
Digestive reflexes are responses triggered by specialized receptors in the GI tract that detect:
- Stretching of the walls
- Chemical composition
- Presence of nutrients or irritants
These reflexes can:
- Activate/inhibit digestive glands (release juices or hormones)
- Stimulate smooth muscle to mix and move contents through the tract
How are hormones secreted in the digestive system?
Hormones are secreted by endocrine cells in the stomach and small intestine lining.
- Stimuli cause these cells to release hormones into the interstitial fluid
- Hormones enter the bloodstream and travel to target cells
- They regulate digestive processes like secretion and motility
What are key digestive hormones and their functions?
Several hormones regulate digestion:
Gastrin – stimulates gastric acid secretion
CCK (Cholecystokinin) – stimulates bile release and pancreatic enzyme secretion
They help regulate:
Enzyme and fluid secretion
GI tract motility
Coordination of digestion and nutrient absorption
What is the mouth (oral cavity) and its function?
The oral cavity is lined with squamous epithelium, which helps it withstand friction from eating.
- The gums, hard palate, and back of the tongue are slightly keratinized for extra protection.
- Function: Receives food, begins mechanical digestion (chewing), and starts chemical digestion (salivary enzymes).
What role do the lips and cheeks play in digestion?
The lips and cheeks help keep food between the teeth during chewing, facilitating, proper mastication and making it easier to break down food.
What is the role of the tongue in digestion?
The tongue:
- Is an accessory organ of digestion.
- Contains taste buds in papillae.
- Grips and repositions food during chewing.
- Mixes food with saliva to form a bolus.
- Initiates swallowing by pushing the bolus into the pharynx.
- Composed of skeletal muscle and assists in speech, especially in the formation of consonants.
What are the functions of teeth in digestion?
Teeth:
- Embedded in the gums.
- Used for mastication (chewing), grinding food to break it into smaller pieces.
- Help process food for easier swallowing and digestion.
What is the structure and function of the palate?
The palate forms the roof of the mouth and consists of two parts:
- Hard palate: Provides a rigid surface for food to be forced against while chewing. Slightly corrugated to create friction with the tongue.
- Soft palate: Closes off the nasopharynx during swallowing to prevent food from entering the nasal cavity.
What is deglutination (swallowing)?
Deglutination refers to swallowing. It takes:
- About 8 seconds for solid food to reach the stomach.
- 1 to 2 seconds for liquids to reach the stomach.
What is ingestion in the digestive process?
Ingestion is the intake of food.
- It involves mechanical digestion (chewing) by the teeth and chemical digestion via enzymes like salivary amylase and lingual lipase.
- Ingestion is partly voluntary and partly reflexive.
What is the buccal phase of swallowing?
The buccal phase is the propulsion of the bolus into the oropharynx and then the laryngopharynx.
- It involves multi-layered epithelial cells that protect the pharynx and skeletal muscles that contract to propel food.
- The nasopharynx has no digestive role.
What occurs during the pharyngeal phase of swallowing?
During the pharyngeal phase:
The food moves through the laryngopharynx, and the epiglottis closes the larynx to prevent food from entering the respiratory system.
Peristalsis moves the bolus from the pharynx to the esophagus involuntarily.
What happens during the esophageal phase of swallowing?
In the esophageal phase:
- The lower esophageal sphincter opens to allow the bolus into the stomach.
- The bolus is moved down the esophagus by peristalsis, which is involuntary.
