Lecture 28 - GI Organization and Function Flashcards
What are the 3 basic types of digestive tract systems?
-Simple stomached
-Forestomach (foregut) fermenters
-Hindgut fermenters
What are the main functions of the GI tract?
-Ingestion
-Mechanical breakdown
-Chemical breakdown
-Nutrient absorption
-Defecation
What are some common signs of GI problems?
-Vomiting
-Diarrhea
-Constipation
-Gas
-Lack of appetite
-Weight loss
-Fever
-Dehydration
-Abdominal pain
-Abdominal distension
What 2 parts make up the digestive system?
-Alimentary canal organs
-Accessory digestive organs
What makes up the alimentary canal organs?
-Pharynx
-Esophagus
-Stomach
-Small intestines
-Large intestines
What makes up the accessory digestive organs?
-Salivary glands
-Liver
-Gall bladder
-Pancreas
What are the 3 parts of the small intestine?
Duodenum
Jejunum
Ileum
What are the 4 parts of the large intestine?
Caecum (hindgut fermenters)
Colon
Rectum
Anus
What are the functions of the oral cavity?
-Prehension of food
-Mastication of food material
-Swallowing and protecting the animal from inhaling food
-Beginning stages of digestion
What kind of senses does the tongue have?
-Taste
-Temperature
-Pain
-Touch
What are there taste receptors for?
Salty
Sour
Sweet
Bitter
Umami
What is the function of incisors?
Cutting food into smaller pieces that fit in the mouth
What is the function of premolars and molars?
Reducing the ingested material into finer particles for easier swallowing and to aid in digestion (more surface area)
Why are premolars and molars important in herbivores?
They are used to break down cell walls
What are brachydont teeth?
Teeth that erupt and are worn down. They do not get replaced
What are hypsodont teeth?
Teeth that erupt and grow continuously throughout the animals life
What are the layers of the wall of the GI tract from inside to outside?
Lumen
Mucosa
Muscularis mucosae
Submucosa
Circular smooth muscle
Longitudinal smooth muscle
Serosa
What does the mucosa contain?
Specialized epithelial cells for digestion and absorption
What does the submucosa contain?
-Loose connective tissue
-Larger nerve trunks, blood vessels, lymph vessels
What does contraction of the circular smooth muscle cause?
Segmentation
What does contraction of the longitudinal smooth muscle cause?
Wave-like contractions
What is the function of the serosa?
Suspends the GI organs within the abdominal cavity
What are the two plexus of the enteric nervous system (ENS)?
-Submucosal plexus
-Myenteric plexus
Where do the cells bodies of the submucosal plexus lie?
In the submucosa
Where do the cells bodies of the myenteric plexus lie?
Between the circular muscle and longitudinal muscle layers
What can the nerve fibers in the GI tract detect?
Changes in pH, distension, osmolarity, certain toxins
What does the myenteric plexus control?
Movement of GI tract
What does the submucosal plexus control?
Secretion and blood flow
What is important about the ENS?
It functions autonomously and integrates motor and secretory activities of the GI tract
What would happen to the gut if sympathetic and parasympathetic nerves are cut?
Many motor and secretory activities would continue
Where are the parasympathetic efferent fibers that can control functions of the esophagus and part of the colon
Vagus nerve in the medulla oblongata (dorsal vagal complex)
Where are the parasympathetic efferent fibers that can control functions of the colon and rectum?
Sacral region of the spinal cord
What do parasympathetic preganglionic neurons release and onto what kind of receptor?
Releases Acetylcholine (Ach) onto Nicotinic receptors of the postganglionic neuron
What do parasympathetic postganglionic neurons release and onto what kind of receptor of the target tissue?
Releases Acetylcholine (Ach) onto Muscarinic receptors of the target tissue
What does the parasympathetic system primarily control in the GI tract?
Motility, secretion, digestion
How does the parasympathetic system control GI functions?
By acting directly on the target tissue or by indirectly modulating the activity of the ENS
What do sympathetic preganglionic neurons release and onto what kind of receptor?
Releases Acetylcholine (Ach) onto Nicotinic receptors of postganglionic fiber
What do sympathetic postganglionic neurons release and onto what kind of receptor?
Releases Norepinephrine onto adrenergic receptors of target tissues
Which nervous system has the most effect on the GI tract (not including the ENS)?
The parasympathetic nervous system
What happens to the GI tract during the fight or flight response?
Blood gets shunted away from the GI tract and to other body systems (ex muscles)
What are the two functions blood vessels serve for the GI tract?
- Transport nutrients that have been absorbed by the mucosal cells
- Supply the organs with oxygen and nutrients
What are lipids absorbed through in the GI tract and what system are these structures part of?
Absorbed through lacteals, which are part of the lymphatic system
About how much blood is pumped to the intestines with each heartbeat during the rest and digest phase?
25% of the blood from each pump of the heart is sent to the intestines
What are portal veins?
Veins that divert blood to the liver for processing before being returned to the heart
What is the peritoneum?
A broad, membranous sac made of squamous epithelial tissue surrounded by connective tissue that hold digestive organs in place
What are the two regions of the peritoneum?
-Visceral peritoneum (lines organs)
-Parietal peritoneum (lines abdominal wall)
What is between the visceral peritoneum and the parietal peritoneum? What is it filled with?
The peritoneal cavity, which is filled with serous fluid for lubrication
What do the large folds of the visceral peritoneum contain?
Blood vessels, lymphatic vessels, and nerves
What is peritonitis?
Inflammation or the peritoneum
What is chemical peritonitis?
Occurs when gastric juices spill into the peritoneal cavity (ex ulcers)
What is hemorrhagic peritonitis?
Occurs when trauma to the liver or spleen fills the peritoneal cavity with blood.
How does the cardiovascular system contribute to the digestive system?
Blood supplies digestive organs with oxygen and processed nutrients
How does the endocrine system contribute to the digestive system?
Endocrine hormones help regulate secretion in digestive glands and accessory organs
How does the integumentary system contribute to the digestive system?
Skin helps protect digestive organs and synthesizes vitamin D for calcium absorption
How does the lymphatic system contribute to the digestive system?
Mucosa-associated lymphoid tissue and other lymphatic tissue defend against entry of pathogens
Lacteals absorb lipids
Lymphatic vessels transport lipids to bloodstream
How does the muscular system contribute to the digestive system?
Skeletal muscles support and protect abdominal organs
(Masticatory muscles for chewing and smooth muscle in the intestines as well)
How does the nervous system contribute to the digestive system?
Sensory and motor neurons help regulate secretions and muscle contractions
How does the respiratory system contribute to the digestive system?
Respiratory organs provide oxygen and remove CO2
How does the skeletal system contribute to the digestive system?
Bones protect and support digestive organs
How does the urinary system contribute to the digestive system?
Kidneys convert vitamin D into its active form, allowing calcium absorption in the small intestine.
