digestive system Flashcards
What is the primary function of the digestive system?
To bring essential nutrients into the internal environment for each cell of the body.
List the three main processes of the digestive system.
- Ingestion
- Digestion
- Absorption
- Defecation
What are the two main groups of organs in the digestive system?
- Alimentary canal / gastrointestinal (GI) tract
- Accessory digestive organs
Name the organs of the GI tract.
- Mouth
- Pharynx
- Oesophagus
- Stomach
- Small intestine
- Large intestine
- Anus
Identify the accessory digestive organs.
- Salivary glands
- Teeth
- Pancreas
- Liver
- Gall bladder
What is mechanical digestion?
Mixing of food in the mouth by the tongue, churning of food in the stomach, and segmentation in the small intestine.
What is chemical digestion?
Large molecules such as carbohydrates, lipids, and proteins are broken down into smaller absorbable molecules.
Define defecation.
Elimination of indigestible substances, dead cells, and bacteria as faeces.
What is the innermost layer of the GI tract called?
Mucosa.
What does the lamina propria contain?
- Areolar connective tissue
- Blood and lymphatic vessels
- Immune cells
- Mucosa-associated lymphoid tissue (MALT)
What type of epithelium is found in the oral cavity?
Stratified squamous epithelium, partially keratinized.
What are gastric pits?
Depressions in gastric epithelium that lead into gastric glands.
What is the function of parietal cells in the stomach?
Produce hydrochloric acid that activates pepsin and intrinsic factor needed for vitamin B12 absorption.
What is the role of chief cells in the stomach?
Produce inactive protein-digesting enzymes called pepsinogens and gastric lipase.
What are the functions of saliva?
- Lubricates and cleanses the mouth
- Moistens food to form a food bolus
- Begins breakdown of starch to maltose
- Buffers acidic foods
- Dissolves chemicals in food for taste
What triggers increased salivation?
Entry of food into the mouth, as well as the sight and smell of food.
What is the function of the pharynx?
Serves as a passageway for air and food.
What is the oesophagus primarily composed of?
Striated muscle (first 2/3) and smooth muscle (last 1/3).
What does peristalsis refer to?
The involuntary muscle contractions that move food through the digestive tract.
What is the role of the enteric nervous system?
Regulates gastrointestinal motility and local conditions such as secretion and absorption.
What are the two types of muscle in the muscularis of the GI tract?
- Inner circular layer
- Outer longitudinal layer
What is the main function of the stomach?
Acts as a storage organ for food and secretes gastric juice.
What is the significance of intrinsic factor produced by the stomach?
Necessary for the absorption of vitamin B12.
What are the components of gastric juice?
- Hydrochloric acid
- Pepsin
- Intrinsic factor
- Gastric lipase
Fill in the blank: The _______ is a muscular tube connecting the laryngopharynx and stomach.
oesophagus
True or False: The stomach has a simple-columnar epithelium.
True
What are the three major salivary glands?
- Parotid glands
- Submandibular glands
- Sublingual glands
What do the muscularis mucosae in the mucosa layer consist of?
A thin layer of smooth muscle fibres.
What is the main role of the submucosal plexus?
Regulating local conditions such as secretion, absorption, and blood flow within the gut.
What is Pepsinogen converted into in the presence of HCl?
Pepsin
Pepsinogen is an inactive precursor of pepsin, activated by hydrochloric acid.
What enzyme cleaves triacylglycerols found in the fat of milk?
Gastric Lipase
Gastric lipase’s action is limited in adults and has an optimum pH of 5-6.
What is the function of Rennin in infants?
Turns casein in milk into curd
This action slows the progression of milk into the intestine.
What stimulates the production of Pepsinogen?
Gastrin
Gastrin is produced by G cells in response to various stimuli.
What do Peptic (Chief) Cells secrete?
HCl and intrinsic factor
Intrinsic factor is necessary for the absorption of vitamin B12.
What enhances the effects of gastrin and acetylcholine in driving HCl secretion?
Histamine
What hormone is released by G cells?
Gastrin
G cells are enteroendocrine cells that respond to stomach distension and other factors.
Which phase of gastric digestion is triggered by the sight, smell, or taste of food?
Cephalic Phase
What reflex occurs when food reaches the duodenum?
Enterogastric reflex
This reflex inhibits gastric motility and decreases gastric emptying.
What does cholecystokinin (CCK) stimulate?
Production of pancreatic juice and release of bile
CCK is secreted by I cells in the small intestine.
What is the primary digestive organ of the body?
Small intestine
What are the three subdivisions of the small intestine?
Duodenum, Jejunum, Ileum
What is the role of enterocytes in the small intestine?
Production of digestive enzymes and absorption of nutrients
Which enzymes are responsible for carbohydrate digestion in the small intestine?
Pancreatic amylase and brush border carbohydrases
Brush border enzymes include glucoamylase and lactase.
What are the products of protein digestion?
Free amino acids, dipeptides, and tripeptides
Approximately 40% are free amino acids and 60% are dipeptides and tripeptides.
What is the primary enzyme for lipid digestion produced by the pancreas?
Pancreatic Lipase
What is the function of bile salts?
Emulsification and absorption of lipids
Bile acids are synthesized from cholesterol.
What is the absorption mechanism for glucose and galactose in the intestine?
Secondary active transport via SGLT-1
This mechanism utilizes the sodium gradient created by the Na+/K+ ATPase pump.
What type of movement primarily propels food through the GI tract?
Peristalsis
What is the primary function of the large intestine?
Fluid balance and production of feces
What triggers the defecation reflex?
Distension of the rectum
What is the role of hepatocytes?
Secretion of bile
Hepatocytes synthesize bile acids and other components of bile.
What is the composition of bile?
Bilirubin, bile salts, lecithin, cholesterol
Bile plays a crucial role in digestion and excretion.
What is the purpose of segmentation in the intestine?
Mixing and breaking apart food
Segmentation involves back-and-forth action in the GI tract.
What type of enzymes are produced by the pancreas for protein digestion?
Proteases
Includes trypsinogen, chymotrypsinogen, and procarboxypeptidase.
What is the order of the GI tract?
