digestive system Flashcards
What are the major valves in the digestive system?
cardiac sphincter
pyloric sphincter
illeocaecal valve
What does the pyloric sphincter do?
Controls emptying rate of stomach
What does the cardiac sphincter do?
Prevents reflux of stomach contents into eosphagus
What does the illeocaecal valve do?
Prevents reflux of large intestine contents into the small intestine
What does the celiac trunk supple blood to?
lower oesophagus
stomach
duodenum
pancreas
liver
spleen
What does the superior mesenteric artery supply blood to?
most of the small intestine
proximal half of the large intestine
What does the inferior mesenteric artery supply blood to?
distal half of large intestine
rectum
Define ingestion
The selective intake of food
Define digestion
Mechanical and chemical breakdown of food
Define absorption
Uptake of nutrient molecules into epithelial cells of the digestive tract and then to blood and lymph
Define compaction
Absorption of water and consolidation of the indigestible residue
Define defamation
Elimination of waste
What is peristalsis?
Waves of contraction of circular muscle behind the food bolus and relaxation of muscle in front of the bolus
What does peristalsis do?
Moves food along the gut
What is segmentation?
Alternate contraction of rings of smooth muscle
What does segmentation do?
Divides and squeezes back and forth, mixes food within the gut
What epithelium are the lips and cheeks lined with?
Non keratinised stratified squamous epithelium
What is mastication?
Chewing, mechanical digestion
What are the purposes of mastication?
Makes food easier to swallow, exposes more surface area of food for the action of digestive enzymes which increases the rate of chemical digestion
What are the two phases of swallowing?
buccal - voluntary
pharyngoesophagal - involuntary
Why is the pyloric sphincter so important?
It limits the flow of highly acidic stomach contents into the duodenum so that the submucosal glands and pancreatic secretions can neutralise the contents
Epithelium of the digestive tract
oral cavity: non-keratinised stratified squamous
esophagus: non-keratinised stratified squamous
stomach: simple columnar
small intestine: simple columnar
large intestine: simple columnar
Embryological development of the digestive system
Endoderm forms lining of gut
Mesoderm forms Ct and surrounding muscle
What cells are found in the stomach?
mucous cells & mucous neck cells
chief cells
parietal cells
What do chief cells secrete?
pepsinogen
What do parietal cells secrete?
hydrochloric acid
How does the production and action of pepsin work?
- Pepsin breaks down proteins that are found in foods into smaller pieces (polypeptides).
- It breaks down proteins only at certain points, so the protein is not digested completely to the amino acid level
How is pepsin autocatalytic?
Pepsin is autocatalytic because it can activate itself.
Why does the stomach have 3 layers of muscular is externa?
the three layers of the muscularis externa in the stomach provide the framework that enables mechanical digestion, mixing of food with gastric secretions, and controlled passage of chyme into the small intestine
What do tight junctions in the stomach epithelium do?
prevent gastric juice from reaching the underlying tissue layers
What are the three ways that the small intestine increases surface area?
plicae circulares, villi, and microvilli.
Characteristics of plica circulares
circular folds of the mucosa and submucosa. They force chyme to move spirally through the lumen.
What is the function of plica circulares?
increasing Surface Area
Enhancing Absorption
Slowing Down Chyme Flow
What primary tissues types is the digestive tract derived from?
Endoderm: This innermost layer gives rise to the epithelial lining of most of the digestive tract
Mesoderm: The mesoderm forms the connective tissues, smooth muscle, and blood vessels of the digestive tract.
Ectoderm: The ectoderm contributes to the lining of the mouth and anus.
What are the layers of the digestive tract?
mucosa, submucosa, muscularis mucosa, and serosa
Mucosa
Epithelium: This is the innermost layer of the mucosa
Lamina Propria: This is a layer of loose connective tissue under the epithelium
Muscularis Mucosae: This thin layer of smooth muscle helps create gentle movements of the mucosa,
Submucosa
Dense Connective Tissue: The submucosa is primarily made of dense irregular connective tissue
Blood Vessels and Lymphatics: This layer contains large blood vessels and lymphatic vessels
Nerve Plexus (Submucosal or Meissner’s Plexus): The submucosa contains a network of nerves
Muscularis externa
Inner Circular Layer: This layer has muscle fibers that are oriented circularly around the digestive tract
Outer Longitudinal Layer: This layer has muscle fibers arranged lengthwise along the tract.
serosa
Protection
Lubrication
Lubrication
Adventitia
Support and Protection ( anchor the digestive organs to nearby structures, providing stability )
Integration with Surrounding Tissues ( The loose connective tissue allows for the integration )
Vascularization ( contains blood vessels and nerves that supply the outer layers of the digestive tract )
What are the 2 neural networks in the digestive tract?
Myenteric Plexus (Auerbach’s Plexus
Submucosal Plexus (Meissner’s Plexus)
Myocentric plexus
myenteric plexus primarily regulates gastrointestinal motility
controls the muscle contractions that facilitate peristalsis
Submucosal plexus
Regulation of Digestive Secretions
Control of Blood Flow
Sensory Functions:
Coordination with Myenteric Plexus:
Intrinsic salivary glands
Lingual glands: Located in the tongue, these glands produce saliva
Labial glands: Found in the lips, they contribute to saliva production as well.
Buccal glands: Located in the inner lining of the cheeks, these glands also secrete saliva.
lubrication of food, initiation of digestion, facilitation of taste,
Extrinsic salivary glands
Parotid Glands located near the ear
Submandibular Glands located beneath the floor of the mouth
Sublingual Glands located under the tongue
essential for saliva production, contributing to digestion, lubrication of food
What are the parts of the small intestine?
duodenum, involved in the initial digestion and neutralization of chyme
jejunum, responsible for nutrient absorption
ileum, completes nutrient absorption and is crucial for absorbing specific vitamins and bile salts
What is the function of saliva?
aiding in digestion
lubricating food for easier swallowing maintaining oral hygiene
regulating pH
Where does most of the digestion and nutrient absorption occur?
the small intestine is the primary site for digestion and nutrient absorption
Digestion of carbohydrates
Carbohydrate digestion starts in the mouth with salivary amylase, continues in the small intestine with pancreatic amylase, and finishes with brush border enzymes that break down disaccharides into monosaccharides.
monosaccharides are then absorbed into the bloodstream and sent to the liver for processing and distribution to cells for energy.
Digestion of proteins
Protein digestion starts in the stomach with pepsin and continues in the small intestine with pancreatic enzymes. These enzymes break down proteins into smaller peptides and then into amino acids. The amino acids are absorbed into the bloodstream and used by the body for tissue repair, hormone production, and enzyme synthesis.
Digestion of fats
digestion of fats involves a combination of mechanical processes (chewing and churning) and chemical processes (enzyme action and emulsification).
Muscularis externa of the large intestine
- Aids in moving waste through the colon
Gastro-esophageal junction
is where your food pipe (oesophagus) joins your stomach.
- 3-4cm
Mostly intra-abdominal
Pepsinogen
Pepsin is produced in an inactive form called pepsinogen, so it doesn’t damage cells.
Acid Activation
When pepsinogen reaches the acidic environment of the stomach, part of it is cut off, creating a small amount of active pepsin.
Self-Activation
This initial pepsin can then activate more pepsinogen by cutting it, creating even more pepsin.
Pancreas
Regulates the level of sugar in the blood, insulin and glucagon
liver
produces bile
gallbladder
gallbladder stored bile
relationship between liver, gallbladder, and the pancreas to the duodenum
liver makes bile, gallbladder stores bile, pancreases produces digestive enzymes to the duodenum
Inner circular layer
- circularly arranged muscle fibers.
- forms a continuous ring around the intestine
- helping to control the diameter of the colon and contributing to segmental contractions.
Outer Longitudinal Layer (Teniae Coli)
- the large intestine’s outer layer is concentrated into three thick bands called the teniae coli.
- These bands run along the length of the colon and create sac-like pouches called haustra, which give the large intestine its segmented appearance
