git Flashcards
accessory glands of GIT?
teeth, tongue, salivary
glands, liver, gallbladder, pancreas
Digestive tract
Open at both ends and continuous with the environment – Considered “outside” the body – Materials that cannot be digested (cellulose) never actually “enter” the body
Structure of the Gastrointestinal Tract Wall
it has four layers; 1.Mucosa lamina propia muscularis mucosa epithelium(with exocrine, endocrine and mucous cells)
2.submusosa major blood and lymphatics vessels submucosal plexus 3.muscularis externa circular muscle myenteric pexus longitudinal muscles serosa
GI Tract Layers
• Also called tunics
• There are four tunics:
1. Mucosa: inner secretory and absorptive
layer; may be folded to increase surface area
- Submucosa: very vascular, to pick up
nutrients; also has some glands - Muscularis: smooth muscle; responsible for
peristalsis and segmentation - Serosa: outer binding and protective layer
primary fubction of digestive tract
From food, humans must get basic organic
molecules to make ATP, build tissues, and
serve as cofactors (Zn, Mg) and
coenzymes (NADH, FADH).
– Digestion breaks polymers (carbohydrates,
fats, and proteins) into monomer building
blocks.
– Absorption takes these monomers into the
bloodstream to be allocated
digestive tract motility function
Motility
– Ingestion: taking food into the mouth
– Mastication: chewing
– Swallowing: food moves from mouth into
stomach
– Peristalsis: one-way movement through tract
– Segmentation: churning/mixing
volume of secretions of fluids
salivary secretion=pancreatic secretion=intestinal secretion- 1500 mL
2000mL gastric secretion
amount of bile produced
500mL
how much is absorbed in small intestine
6700mL
how much is absorbed in large intestine
1400mL
regulation food intake(feeding behaviour)
it involves 3 hypothalamic nuclei(is a portion of of the brain that contains number of small nuclei with variety of function)
1. Lateral hypothalamus nuclei-regulates feeding
which means it can increase/decrease food intake
if this nuclei is removed you will have no desire to eat
once you are full your GIT will sense chemical being released, blood nutrient which have increased in your blood and distention which will stimulate the satiety center
2.Ventromedial nucleus(satiety center)
This center has inhibitory effect on lateral hypothalamus and prevent food intake(it makes you feel like you have taken enough amount of food)
- Arcuate nuclei(it controls ventromedial nucleus)
Primary Peristalsis
contraction of pharyngeal muscles; wave of
contraction, followed by the wave of relaxation of muscle fibers of
GI tract which travel away from the mouth.
Secondary peristalsis
induced by distention of esophagus
• Swallowing occurs in three stages:
• I. Oral stage, when food moves from mouth to pharynx • II. Pharyngeal stage, when food moves from pharynx to esophagus • III. Esophageal stage, when food moves from esophagus to stomach, regulated by Upper and lower esophageal sphincters
Oral phase: 1 sec
Initiates swallowing process tongue pushes the bolus of
food to the back of the hard palate, pharynx/throat to
stimulate the sensory (oropharyngeal) receptors in
pharynx - initiate the swallowing reflex- this result in
peristalsis.
These receptors send afferent impulses (via vagus,
glossophyrangeal, trigeminal nerves) to the swallowing
center in the medulla oblongata. This center then elicits
swallowing via efferent impulses to the muscles in the
pharynx (glossophyrangeal nerve) and esophagus (vagus
nerve)
Pharyngeal phase: 1-2 sec
• Tongue against soft palate prevent return of bolus back
into mouth
• Soft palate move upward prevent bolus into nasal
cavity/ nasopharynx
• Stimulates larynx movements, cause epiglottis to closed
airways and upper esophageal sphincter (UES) to
open ONE WAY
• Peristalsis is produced by pharyngeal muscles and move
bolus into esophagus
• Swallowing apnea: All these movements arrest
respiration for a few seconds
Esophageal phase:
• Begins with relaxation of the UES and continuation of
peristalsis (primary) produced in the pharyngeal stage to
propel bolus into the stomach.
• The lower esophageal sphincter (LES) opens and remains
relaxed throughout the period of swallowing, allowing the
arriving food to enter the stomach.
• Secondary peristalsis: induced by distention of esophagus
• LES closes/constricts after food passes into stomach,
resealing the junction between the esophagus and the
stomach
Secretion
– Exocrine: digestive enzymes, acid, mucus
– Endocrine: hormones to regulate digestion
Digestion
– Breaking food down into smaller units
Absorption
– Passing broken-down food into blood or lymph
Saliva functions
Lubrication and binding
• Initiates carbohydrate digestion
• Oral hygiene: Flow of saliva decreases during sleep
allowing bacteria to build up in mouth
functions of Saliva
Washes mouth - secretion rate 0.5 ml/min
• Destroys bacteria - proteolytic enzymes (lysozyme)
- thiocyanate
- antibodies
• Xerostomia (dry mouth) - (absence of saliva)
Storage and elimination
Temporary storage and elimination of
undigested food
Immune barrier
Simple columnar epithelium with tight
junctions prevents swallowed pathogens
from entering body
regulation of the GIT
- Autonomic system:
• Sympathetic division:
– Inhibits peristalsis and secretion
– Stimulates contraction of sphincters
• Parasympathetic nerves:
– Stimulates motility and secretions via vagus
nerve in esophagus, stomach, small intestine,
pancreas, gallbladder, and upper portion of
large intestine
2.Hormones:
– digestive organs
- Intrinsic regulation:
– Intrinsic sensory neurons in gut wall help in
intrinsic regulation via separate enteric
nervous system (ENS)
– ENS: Myenteric plexus (Auerbach’s plexus)
Submucosal plexus (Meissner’s plexus)
How are Gastrointestinal Processes
Regulated?
Control mechanisms of the gastrointestinal
system are governed by the volume and
composition of the luminal contents, rather
than by the nutritional state of the body.
• This means that the body is designed to absorb
all the nutrients that are ingested, whether or
not the body really needs them to function
