Lecture 16 - Digestive System
GI tract has its own nervous system, referred to as
enteric nervous system - Also called "gut brain" -Contains more neurons than spinal cord
Enteric Nervous System made up of
enteric neurons that communicate extensively w/each other -Major nerve supply to GI tract wall that controls motility
What alters the tongues position?
extrinsic muscles
Lips (labia) composed of
fleshy orbicularis oris muscle
Mouth is where
food is chewed and mixed with enzyme-containing saliva that begins process of digestion, and swallowing process is initiated
splanchnic circulation
includes arteries that branch off aorta to serve digestive organs and the hepatic portal circulation
lamina propria of mucosa
Made up of loose areolar connective tissue Rich supply of capillaries located here -Needed for nourishment and absorption Also contains lymphoid follicles that help defend against microorganisms -Follicles are part of MALT (mucosa-associated lymphoid tissue)
mucosal epithelium
- Simple columnar epithelium and mucus-secreting cells in most of tract - Mouth, esophagus, and anus are made up of stratified squamous epithelium - Secretes mucus - Protects digestive organs from enzymes - Eases food passage - May secrete enzymes and hormones (e.g., in stomach and small intestine)
Functions of the tongue
-Gripping, repositioning, and mixing of food during chewing -Formation of bolus, mixture of food and saliva -Initiation of swallowing, speech, and taste
Digestive activity is provoked by a range of mechanical and chemical stimuli
-Receptors located in walls of GI tract organs -Respond to stretch, changes in osmolarity and pH, and presence of substrate and end products of digestion
Organs of digestive system fall into two groups:
1. Alimentary canal (gastrointestinal or GI tract or gut) 2. Accessory digestive organs
Three key concepts regulate GI activity
1. Digestive activity is provoked by a range of mechanical and chemical stimuli 2. Effectors of digestive activity are smooth muscle and glands 3. Neurons (intrinsic and extrinsic) and hormones control digestive activity
Processing of food involves six essential activities
1. Ingestion: eating 2. Propulsion: movement of food through alimentary canal, which includes: - Swallowing - Peristalsis: major means of propulsion of food that involves alternating waves of contraction and relaxation 3. Mechanical breakdown: includes chewing, mixing food with saliva, churning food in stomach, and segmentation 4. Digestion: series of catabolic steps that involves enzymes that break down complex food molecules into chemical building blocks 5. Absorption: passage of digested fragments from lumen of GI tract into blood or lymph 6. Defecation: elimination of indigestible substances via anus in form of feces
All digestive organs have the same four basic layers, or tunics
1. Mucosa 2. Submucosa 3. Muscularis externa 4. Serosa
Neurons (intrinsic and extrinsic) and hormones control digestive activity
1. Nervous system control 2. Hormonal controls
Major salivary glands include:
1. Parotid 2. Submandibular 3. Sublingual
oral cavity is
Bounded by lips anteriorly, cheeks laterally, palate superiorly, and tongue inferiorly
functions of saliva
Cleanses mouth Dissolves food chemicals for taste Moistens food; compacts into bolus Begins breakdown of starch with enzyme amylase
Submucosa
Consists of areolar connective tissue Contains blood and lymphatic vessels, lymphoid follicles, and submucosal nerve plexus that supply surrounding GI tract tissues Has abundant amount of elastic tissues that help organs to regain shape after storing large meal
Alimentary canal (gastrointestinal or GI tract or gut)
Continuous muscular tube that runs from the mouth to anus -Digests food: breaks down into smaller fragments -Absorbs fragments through lining into blood -Organs: mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus
hepatic portal circulation
Drains nutrient-rich blood from digestive organs Delivers it to the liver for processing
mucosa made up of three sublayers
Epithelium Lamina propria Muscularis mucosae
peritoneal cavity
Fluid-filled space between two peritoneums Fluid lubricates mobile organs
Arteries that branch off aorta to serve digestive organs include
Hepatic, splenic, and left gastric arteries Inferior and superior mesenteric arteries
Hormonal controls
Hormones from cells in stomach and small intestine stimulate target cells in same or different organs to secrete or contract
Nervous system control - intrinsic + extrinsic controls
Intrinsic controls: involve short reflexes (ENS) Extrinsic controls: involve long reflexes (ANS)
whats changes the shape of the tongue?
Intrinsic muscles
submandibular gland
Medial to body of mandible Duct opens at base of lingual frenulum
Walls of mouth lined with stratified squamous epithelium
Tough cells that resist abrasion Cells of gums, hard palate, and part of tongue are keratinized for extra protection
muscularis externa
Responsible for segmentation and peristalsis Contains inner CIRCULAR MUSCLE LAYER and outer LONGITUDINAL LAYERS Circular layer thickens in some areas to form sphincters
minor salivary glands
Scattered throughout oral cavity; augment slightly
salivary glands composed of 2 types of secretory cells
Serous cells + Mucous cells
Main functions of digestive system
Take in food Break it down into nutrient molecules Absorb molecules into the bloodstream Rid body of any indigestible remains
Effectors of digestive activity are smooth muscle and glands
When stimulated, receptors initiate reflexes that stimulate smooth muscle to mix and move lumen contents Reflexes can also activate or inhibit digestive glands that secrete digestive juices or hormones
oral orifice
anterior opening of the mouth
parotid gland
anterior to ear and external to masseter muscle Duct opens into oral vestibule next to second upper molar
sublingual gland
anterior to submandibular gland under tongue Opens via 10-12 ducts into floor of mouth
oral cavity proper
area that lies within the teeth and gums
lingual frenulum
attachment of tongue to floor of mouth
cheeks composed of
buccinator muscles
mechanical breakdown of food
chewing, mixing food with saliva, churning food in stomach, and segmentation
Ankyloglossia
congenital condition in wh. children are born with extremely short lingual frenulum -Often referred to as "tongue-tied" or "fused tongue" -Restricted tongue movement distorts speech Treatment: surgical snipping of frenulum
myenteric nerve plexus
controls GI tract motility
mucosa function
different layers perform one or all three -SECRETES mucus, digestive enzymes, and hormones -ABSORBS end products of digestion -PROTECTS against infectious disease
sympathetic system inhibits
digestion
Parasympathetic system enhances
digestive process
mesentary peritoneum
double layer of peritoneum; layers are fused back to back Extends from body wall to digestive organs Provides routes for blood vessels, lymphatics, and nerves Holds organs in place + stores fat
ingestion
eating
Mumps
inflammation of parotid glands caused by the mumps virus (myxovirus) -Common children's disease -Can spread from person to person via saliva -Symptoms: pain upon trying to open mouth or chew, moderate fever and pain when swallowing acidic foods, such as pickles, grapefruit, or juice -Mumps in adult males carries a 25% risk of infecting testes too, which could lead to sterility
Peritonitis
inflammation of the peritoneum Can be caused by piercing abdominal wound, perforating ulcer, or ruptured appendix Peritoneal coverings stick together, which helps localize infection Dangerous and lethal if it becomes widespread Treatment: debris removal and megadoses of antibiotics
Enteric neurons make up bulk of two main interconnecting
intrinsic nerve plexuses: -Submucosal nerve plexus -Myenteric nerve plexus
parietal peritoneum
lines the body wall
Segmentation
local constriction of intestine that mixes food with digestive juices
retroperitoneal organs
located outside, or posterior to, the peritoneum Includes most of pancreas, duodenum, and parts of large intestine
Most saliva produced by ______________ located outside the oral cavity
major (extrinsic) salivary glands
peristalsis
major means of propulsion of food that involves alternating waves of contraction and relaxation
labial frenulum
median attachment of each lip to gum
Short reflexes:
mediated by enteric nerve plexuses (gut brain); respond to stimuli in GI tract
organs of the alimentary canal
mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus
Associated organs include:
mouth, tongue, salivary glands, teeth
propulsion
movement of food through alimentary canal
MALT
mucosa-associated lymphoid tissue
but sublingual gland consists mostly of
mucous cells
tongue
occupies floor of mouth Composed of interlacing bundles of skeletal muscle
The mouth is also called the
oral or buccal cavity
Intraperitoneal (peritoneal) organs
organs that are located within the peritoneum
serosa
outermost layer, made up of the visceral peritoneum - Formed from areolar connective tissue covered with mesothelium (single layer of squamous epithelium) in most organs - Replaced by fibrous adventitia in esophagus (Dense connective tissue that holds esophagus to surrounding structures)
Mucous cells
produce mucus
Digestive glands
produce secretions that help break down foodstuffs
Serous cells
produce watery secretion, enzymes, ions, bit of mucin
oral vestibule
recess internal to lips and cheeks, external to teeth and gums
submucosal nerve plexus
regulates glands and smooth muscle in the mucosa
Long reflexes:
respond to stimuli arising inside or outside of gut, such as from autonomic nervous system -Parasympathetic system enhances digestive process -Sympathetic system inhibits digestion
Parotid and submandibular glands contain mostly
serous cells
peritoneum
serous membranes of abdominal cavity that consists of: -Visceral peritoneum: membrane on external surface of most digestive organs -Parietal peritoneum: membrane that lines body wall
Enteric nervous system participates in both
short and long reflex arcs
muscularis mucosae of mucosa
smooth muscle that produces local movements of mucosa
accessory digestive organs
teeth, tongue, gallbladder, digestive glands (salivary glands, liver, pancreas)
visceral peritoneum
the inner layer of the peritoneum that surrounds the organs of the abdominal cavity
mucosa
tunic layer that lines lumen Functions: different layers perform one or all three Secretes mucus, digestive enzymes, and hormones Absorbs end products of digestion Protects against infectious disease