digestion - lecture 1

Question 1

what is the gastrointestinal tract

Answer 1

alimentary canal
continuous tube from mouth to anus

Question 2

what makes up digestive system

Answer 2

gastrointestinal tract and accessory digestive organs

Question 3

what are accessory digestive organs

Answer 3

salivary glands
pancreas
liver
gallbladder
secretions into tract to help with digestion

Question 4

what are git functions

Answer 4

conveys food along git
allows it be broken down into small molecules which can be absorbed into circulation
while moving down tract - used for energy needed by all cells of body

Question 5

name the 6 activities of digestive system

Answer 5

1. ingestion - chew
2. secretion
3. motility
4. digestion - muscular and secretory
5. absorption
6. defecation

Question 6

describe secretion

Answer 6

glandular activity - exocrine and endocrine
leads to chemical breakdown

Question 7

describe motility

Answer 7

propulsion and physical breakdown - muscular activity of git
moves through

Question 8

describe absorption

Answer 8

transfer to blood circulation and to all cells of body

Question 9

what are most important git functions

Answer 9

secretion
motility
absorption

Question 10

describe homeostasis

Answer 10

git is an important contributor
fundamental principle in physiology
at all levels of organization, body activities are directed at maintaining optimal and relatively constant internal conditions - in nutrient concentrations in body

Question 11

what is gits role in homeostasis

Answer 11

provide nutrients to body
from external environment = food, git breaks food down into absorbable molecules and then processed to all cells = energy and raw materials for growth and repair, function and regulation

Question 12

describe git capacity

Answer 12

digestive and absorptive capacity
git is exquisitely efficient = digest and absorb almost all the food we eat
carbs = 99%
fat = 95%
protein = 92%

Question 13

name activities for git and integration

Answer 13

propulsive, secretory and absorptive activities highly coordinated and integrated for high functional efficiency by neural and hormonal mechanisms
the efficiency of git is due to this

Question 14

describe git structure

Answer 14

tubular structure
communicates with external environment at both ends = lumen contacts, central lumenal cavity = considered as extracellular space
good for function - if toxins or bacteria = wont get into blood stream, but also must be able to absorb nutrients and molecules we need

Question 15

name parts of git

Answer 15

mouth –> stomach –> si –> li –> anus

Question 16

what is git length

Answer 16

4.5 m in living adult = longer than human (1.5 meters)
in cadaver = 10 m since humans have lots of muscle tone = always contracts while alive

Question 17

describe growth of git - sa

Answer 17

increase in total internal sa
adult = 200-250 m^2
600x larger than external sa due to = invaginations and fingerlike projections - in and out pushings
FORM FOLLOWS FUNCTION

Question 18

describe differentiation of git

Answer 18

tube into alimentary canal and all accessory organs near canal

Question 19

describe wall of gi tract

Answer 19

4 main layers =
mucosa (secretory and absorptive cells)
submucosa (lymphatics and circulation = absorb nutrients and provide nutrients to cells in git)
muscularis externa
serosa

Question 20

describe mucosa of git

Answer 20

3 layers =
epithelial layer = epithelial and glandular cells - exocrine and endocrine secretory cells and absorptive cells
lamina propria = loose ct
Muscularis mucosae = smooth muscle

Question 21

describe submucosa of git

Answer 21

loose ct with lymphatics and bvs and neuronal networks

Question 22

describe muscularis externa of git

Answer 22

2 diff layers of muscle =
Inner layer circular fibers - decrease aperture of lumen when contracts
outer layer longitudinal fibers - along lenght of git = if contract it shortens
striated muscle at beginning of git (oral cavity, pharynx and upper 1/3 eso and external anal sphincter) then majority smooth (involuntary) and then striated at anus again

Question 23

describe serosa of git

Answer 23

thin tough layer of ct
in some places = serosa acc continuous with peritoneum (abdominal mesentery) (lining of abdominal cavity) (holds git in place)

Question 24

what is ens

Answer 24

Enteric nervous system
controls secretion and motility
neurons reside within wall of git
Billions of neuron’s

Question 25

describe ens

Answer 25

independent (of cns/other nervous systems) and integrative nervous system
can extend processes and control diff parts of git, integrate functions over long distances
initiates, programs, regulates and coordinates activities of muscular and secretory and absorptive elements of git

Question 26

describe git wall innervation

Answer 26

submucosal plexus = between muscularis mucosae and circular muscle
myenteric plexus = between circular and longitudinal muscle of muscularis externa
though anatomicall distinct - the 2 plexuses behave as one functional unit

Question 27

define plexus

Answer 27

collection of nerve cell bodies
contain all elements needed for reflex arcs

Question 28

describe sensory neurons

Answer 28

sense parameters
with receptors in mucosa or muscle
respond to stretch receptors (moving of gut), chemoreceptors and osmoreceptors (sample contents = ph, concentrations or osmolarities)

Question 29

describe motor/effector neurons

Answer 29

activate secretory and muscle cells
secretory = synapse on muscles and leads to contraction or relaxation result

Question 30

describe interneurons

Answer 30

expand responses to stimuli in git and allow integration over longer distances = connect sensory and interneurons

Question 31

describe ex of git wall innervation

Answer 31

spring like ending = type of neuron that responds to stretch or distension
sensory neuron in mucosa
signals to interneurons to effector neurons
effector neurons may lead ti excitation of secretory elements = increase secretion
could also activate inhibitory neurons and relax musculature
precise and graded activity of git due to circuitry = many types of neurons and connections

Question 32

describe enteric neurons

Answer 32

excitatory = release ach on muscarinic receptors, blocked by atropine
inhibitory = release non adrenergic and non cholinergic = transmitter like nitric oxide
ultimate activity = algebraic sum of influences (five excite and one inhibits = effect excitatory)

Question 33

describe intramural reflexes

Answer 33

short enteric
all things happens in gut gall
stimulus sensed by chemo, osmo and mechano receptors and sends to nerve plexus then effect at smooth muscle or gland cell and leads to motility and secretion and response
Independent and integrative innervation = regulates git

Question 34

what does ens consist of - plexuses

Answer 34

myenteric plexus = between longitudinal and circular muscle layers
and submucosal plexus
each = Anatomically distinct but behave as one functional unit = all elements required for reflex arcs (sensory, motor and inter neurons)

Question 35

what does ens consist of - cells

Answer 35

ganglion cells and their processes that synapse with sm cells, endocrine and exocrine cells and other ganglion cells

Question 36

describe enteric neurons - specifics

Answer 36

may be excitatory = release ach on muscarinic receptors
or
inhibitory = release nanc (non adrenergic non cholinergic transmitters like NO)

Question 37

describe sensory fibers ens

Answer 37

have cell bodies in plexuses
get info from gut chemo and mechano receptors

Question 38

describe ans innervation of git enteric neurons

Answer 38

cns –> parasympathetic preganglionic nicotinic excitatory release ach and synapse on ens
cns –> excitatory nicotinic ach receptor activation to sympathetic chain of ganglia, sympathetic = postganglionic noradrenaline inhibitory - synapse on ens neurons and inhibit
ans gives modulatory input, never synapses directly on muscles or glandular cells = always impinges on enteric neurons

Question 39

describe parasympathetic innervation of git

Answer 39

preganglionic
excitatory
vagus X - most of input
pelvic nerves - mostly for distal part of git - colon

Question 40

describe sympathetic innervation of git

Answer 40

postganglionic
inhibitory
celiac ganglion
superior mesenteric ganglion
inferior mesenteric ganglion

Question 41

how can ans influence git

Answer 41

via the ens only
parasymp = excitatory = release ach
symp = inhibitory = release noradrenaline
long reflexes from ans to modulate git

Question 42

what does ans do

Answer 42

modulates ens
via long extrinsic reflexes = synaptic connections with ens neurons

Question 43

describe ans parasympa

Answer 43

neurons reach wall of git as preganlionic fibers, synapse via nicotinic ach receptors, with enteric neurons (excitatory and inhibitory), exert excitatory effect
Parasympathetic input → dilation of blood vessels

Question 44

describe ans sympa

Answer 44

reach wall of git as postganglionic fibers, synapse via NA receptors with enteric neurons (excitatory and inhibitory) exert inhibitory effect
neurons also innervate smooth muscle in bvs =
Sympathetic input → constriction of blood vessels

Question 45

describe overview of git - gen

Answer 45

sensory neurons allow for long reflexes
v specialized and highly developed alimentary canal
at each level of git = diff specializations - motility, absorption or both
all secretory and muscular functions controlled by enteric nervous system and ans impinging on ens neurons = motility and secretion