The Digestive System Part I Flashcards
Refer to Course Notes (46 cards)
Functions of Digestive System:
Absorb molecules into bloodstream
Produce hormones, neurotransmitters, hormone-like compounds, nutrient synthesis,
Remove toxins
Take in food
Digest
What major processes occur
during digestive system activity?
Ingestion: eating
propulsion: food through the alimentary canal, includes swallowing - oropharynx (voluntary),
- Peristalsis: contraction & relaxation of muscles (squeeze food along the tract, some mixing. It’s powerful even standing on your head, won’t stop it. Swallowing (oropharynx)
* Peristalsis (esophagus, stomach, small intestine, large intestine)
Mechanical breakdown/digestion:
increase surface area of food increase before digestion by enzymes.
Chewing (mouth)
* Churning (stomach) * Segmentation
(small intestine) - Segmentation, a type of mixing wave, mixes food with digestive juices against the intestinal wall.
Digestion: series of steps in which enzymes secreted into the lumen (cavity) of the alimentary canal, break down complex food molecules to their chemical building blocks.
- How does a cell synthesize and store these enzymes without digesting itself? The answer is that the cell makes proenzymes, or zymogens. These are inactive forms of the enzymes that are only activated once they are released.
Absorption:
Defecation
Components of alimentary canal (gastrointestinal tract) vs. accessory digestive organ:
Major Organs of Digestive Tract:
Oral Cavity (Mouth)
Pharynx
Esophagus
Stomach
Small Intestine
Large intestine (dehydration & indigestible materials accumulate)
Accessory Organs of Digestive System:
Teeth
Tongue
Salivary Glands
Liver (secrete bile for lipid digestion)
Gallbladder
Pancreas (exocrine cells - buffers & digestive enzymes) (endocrine cells - secrete hormones)
Pancreas - also secret pancreatic juice.
Peristalsis vs. Segmentation
P.: adjacent segments of Alimentary canals contract and relax. Distally, primarily propulsion
S.: non-adjacent. Moves fwd. then bkw. some propulsion, mainly mixing.
Most digestive system organs reside in the abdominopelvic cavity.
ventral body cavities contain slippery serous membranes or peritoneum:
Two types of p. membranes:
- Visceral p.: covers external surface of digestive organs
- Parietal p.: lines the body wall
Btw. them is the parietal cavity - contains slippery fluid (serous) secreted by both membranes
- allows mobile digestive organs to glide easily.
Mesentery: double layer of
peritoneum. Both dorsal and ventral.
Function:
- routes for blood vessels, lymphatic, & nerves to reach digestive viscera.
- Hold organs in place
- Store fat
Peritoneum: Serous membranes (double membrane lines visceral and abdominal wall)
Types:
Visceral p. external surface of digestive organs
Parietal p.: lines body wall
q
Most digestive organs are intraperitoneal and are suspended from the body wall by a dorsal mesentery.
a
Some digestive organ mesenteries have specific names (such as the omenta)
Not all alimentary canal organs are suspended by a mesen- tery.
9
q
during development, some regions of the small intestine, pancreas, large intestine, duodenum, adhere to the dorsal abdominal wall, so they lose their mesentery and lie posterior to peritoneum
a
Retroperitoneal organs
10
q
Digestive organs (like the stomach) that keep their mesentery and are completely surrounded by the peritoneum are called intraperitoneal or peritoneal organs.
a
Peritonitis is inflammation of the peritoneum. From leaking juice, burst appendix (sprays bacteria-contained feces). often lethal.
11
q
Some intraperitoneal digestive organs are also suspended from the body wall by ventral mesenteries.
a
Some digestive organs are retroperitoneal because they have lost their mesentery during development
12
q
The walls of the alimen-tary canal have the same four basic layers, or tunics—mucosa, submucosa, muscularis externa, and serosa
a
The mucosa: Innermost layer, moist epithelial membrane mouth to anus.
Functions:
- secret mucus, digestive enzymes, hormones (lining epithelium)
- absorb end products of digestion into blood
- Protection from infection
Sublayers:
1) a lining epithelium,
(2) a lamina propria (areolar connective tissue) - underlies the epith. nourish epith. and absorb nutrients, part of MALT (protection)
(3) a muscularis mucosae (smooth muscle cells): external to LP, local movements of mucosa (absorption & secretion)
Not sure this is right - probably taken from online: The epithelium is usually a single layer of tall, column-shaped cells (simple columnar) in most places, but in areas with more mechanical stress (like the mouth and esophagus), the epithelium is tougher and stratified squamous (multiple flat cell layers, secretes mucus, protect digestive organs from being digested by organs.
Submucosa:
13
q
Particularly large collections of lymphoid follicles occur within the pharynx (as the tonsils) and in the appendix.
Except for that of the mouth, parts of the pharynx, the esophagus, and the anus where it is stratified squamous, the epithelium of the mucosa is a simple columnar epithelium rich in mucus-secreting cells
Fluid-filled space btw. two peritoneum
Lubricates mobile organs
Peritoneal cavity
The digestive system’s organs are related to the peritoneum in the following ways:
Intraperitoneal organs: These are located within the peritoneum, suspended by the mesentery. Examples include the stomach, liver, and small intestine.
Retroperitoneal organs: These are located outside or behind the peritoneum. No mesentery. Examples include parts of the pancreas, duodenum, and large intestine.
Mesentery: A double layer of peritoneum that supports and anchors organs to the posterior body wall. It provides structural support, holds vessels and nerves, and stores fat.
Most digestive organs are intraperitoneal
The alimentary canal has four basic histological layers:
Mucosa: Lines the lumen; made of epithelium (secretes mucus, enzymes, hormones), lamina propria (supports absorption and immunity), and muscularis mucosae (local movements).
Submucosa: Areolar tissue with blood/lymph vessels, lymphoid follicles, and elastic fibers for shape recovery.
Muscularis Externa: Controls segmentation and peristalsis with circular/longitudinal muscle layers and sphincters. nerve plexus.
Serosa: Outermost layer of areolar tissue and mesothelium; replaced by fibrous adventitia in the esophagus.
Retroperitoneal Organs: Have both serosa (peritoneal side) and adventitia (dorsal side).
Blood Flow to Digestive Organs:
Oxygen-rich blood comes from the aorta.
It travels through specific arteries:
Hepatic artery: Supplies the liver.
Celiac artery: Branches into three main arteries:
Splenic artery: Supplies the spleen and pancreas.
Left gastric artery: Supplies the stomach.
Hepatic artery: same
Superior mesenteric artery: Supplies the pancreas, small intestines, and colon.
Inferior mesenteric artery: Also supplies the colon.
Blood Flow from Digestive Organs:
Blood from the digestive organs is drained via veins
.
The blood collects in the hepatic portal vein:
This carries nutrient-rich blood from the digestive organs (such as intestines) to the liver.
From the liver, blood is sent to the hepatic veins, then into the inferior vena cava, returning to the heart.
Why the Hepatic Portal Circulation?
The hepatic portal circulation allows the liver to process and filter nutrients, toxins, and other substances absorbed from the digestive system before they enter the general circulation. This ensures proper nutrient management and detoxification.
The digestive system receives 20-25% of cardiac output, which increases after a meal and decreases during exercise.
Peristalsis and segmentation both occur throughout the GI tract, with peristalsis primarily moving food forward in a wave-like motion, while segmentation mainly mixes food and digestive enzymes, especially in the small intestine.
In the GI tract, peristalsis propels food forward by contracting circular muscles behind the bolus and relaxing longitudinal muscles ahead, while segmentation mainly mixes food with digestive juices by contracting circular muscles at intervals. Peristalsis moves food along, while segmentation ensures thorough digestion through mixing.
3-5 pounds of food daily per each person but may differ from one person to another.
Bloodstream - major transportation system in the body. Need oxygen as well.
Nutrient molecules are small enough to be absorbed by the body, though fiber, which is not digestible, cannot be processed. The gut microbiome plays a significant role in health, influencing functions such as regulating blood sugar in diabetes, supporting the nervous system, and aiding in weight management, according to research. Additionally, gut bacteria produce certain vitamins, like Vitamin K, which is crucial for the formation of clotting factors. Nutrients are absorbed both from the food we eat and the byproducts produced by gut bacteria.
Peritonitis
Inflammation of peritoneum
Four types of tissues: epithelial, connective, nervous, and muscle tissues.
Mucosa (lines the lumen of the GI tract) has 3 layers:
Epithelial: Avascular (relies on underlying connective tissue for blood supply).
Lamina propria: Contains blood vessels, glands, and immune cells.
Muscularis mucosa: Responsible for local movements within the mucosa.
Muscularis externa: Controls global movements in the GI tract.
Villi and microvilli: Increase surface area for nutrient absorption.
Mucosa-associated lymphoid tissue (MALT): Traps harmful substances and provides immune defense.
The Enteric Nervous System (ENS), or “gut brain,” is a network of neurons that controls GI motility and is connected to the central nervous system via the autonomic nervous system.
Study diagram
The Enteric Nervous System has two main plexuses (or intrinsic nerve plexuses):
Submucosal plexus: Regulates glands and smooth muscle in the mucosa.
Myenteric plexus: Controls GI motility through pacemaker cells and local reflex arcs.
Neurons (intrinsic and extrinsic) and hormones control digestive activity. The nervous system controls digestive activity via both intrinsic controls (involving short reflexes entirely within the enteric nervous system as described above) and extrinsic controls (involving long reflexes).
External stimuli - CNS - local intrinsic plexus -effectors - response
Internal stimuli chemo, osmo, mechano receptors - CNS (short reflexes)
or instead of CNS - local intrinsic plexus - effectors - response
(long reflexes)
Digestive activity is regulated by both the nervous system and hormones.
Nervous system:
Intrinsic controls (short reflexes): Managed by the Enteric Nervous System (ENS) alone.
Extrinsic controls (long reflexes): Involve the central nervous system.
Hormonal controls: Hormones from the stomach and small intestine regulate muscles and glands to affect secretion and contraction.
Digestive activity is triggered by mechanical and chemical stimuli (e.g., stretch, pH, and substrate presence), which activate reflexes that stimulate smooth muscles (SM) and digestive glands to mix food, move contents, and secrete digestive juices or hormones.
Oral Cavity: Bounded by lips, cheeks, palate, and tongue; lined with stratified squamous epithelium; where digestion begins with chewing and saliva.
Lips and Cheeks: Lips (orbicularis oris muscle); cheeks (buccinator muscles); oral vestibule (space inside lips and cheeks); oral cavity proper (between teeth and gums).
Tongue: Repositions and mixes food; aids in swallowing, speech, and taste; divided into anterior 2/3 (oral cavity) and posterior 1/3 (oropharynx); has papillae with taste buds (filiform (this), fungiform (this), circumvallate, foliate (this)). The tongue has intrinsic and intrinsic muscles (change shape of tongue), extrinsic m. (alter tongue’s position.
Palate: Hard palate (palatine bones) for friction; soft palate (skeletal muscle) with uvula to close nasopharynx during swallowing.
Ankyloglossia: Condition where the lingual frenulum is short, causing “tongue-tied.”
See diagrams
The uvula extends out from and past the soft palate area of the palatopharyngeal arch.
Salivary Glands:
Function: Secrete saliva for mouth cleaning, taste, food moistening, and starch breakdown.
Types:
Serous cells (submandibular, parotid): Produce watery secretion with enzymes.
Mucous cells (in sublingual): Produce mucus.
Major Glands: Sublingual, submandibular, parotid (main saliva producers).
Saliva: Contains water, electrolytes, enzymes (amylase, lipase), proteins (IgA, lysozyme, mucin), and wastes (urea).
Protection: Defends against microbes with IgA, lysozyme, defensins.
Xerostomia: Dry mouth due to low saliva production.
Teeth:
Location: In sockets of the mandible and maxilla.
Types:
Deciduous: 20 baby teeth, lost by age 12.
Permanent: 32 adult teeth.
Structure: Crown (above gum) and root (in jawbone).
Classification:
Incisors: Cutting.
Canines: Tearing.
Premolars: Grinding.
Molars: Best for grinding.
Mumps - viral infection affects salivary glands
Salivation Control:
1500 ml/day of saliva produced.
Minor glands/intrinsic: Continuously moistens mouth.
Major glands/extrinsic: Activated by PNS.
Chemo- & mechanoreceptors: In mouth detect food.
Signals sent to salivatory nuclei in brainstem.
Cranial nerves VII (facial) & IX (glossopharyngeal): Stimulate salivary glands.
Salivation is controlled primarily by the parasympathetic division of the autonomic nervous system.
Crown: Enamel-covered, exposed part.
Root: Embedded in jawbone, with cement and periodontal ligament.
Dentin: Shock-absorbing material beneath enamel.
Pulp: Contains nerves, blood vessels.
Enamel: Hardest body substance, cannot regenerate.
Digestive Processes of the Mouth:
Ingestion: Food enters the mouth.
Mechanical Breakdown: Teeth and tongue grind food into a bolus.
Propulsion: Swallowing moves food down.
Chemical Breakdown: Salivary amylase starts starch digestion (polysaccharides), and lingual lipase starts fat digestion.
Mastication:
Mechanical: Teeth grind, tongue mixes food with saliva.
Chemical: Enzymes begin breaking down starches and fats.
Only polysaccharides are digested in the mouth, the rest in the stomach.
