intestines Flashcards
intestines connect ____ to ____
pylorus to anal canal
small intestine consists of
duodenum, jejunum, ileum
large intestine consists of
caecum, colon, rectum
main functions of intestine
- transport
- digestion
- absorption
- concentrate and lubricate residues for excretion
main function of small intetsines
digestion and aborption
main function of large intestine
water and electrolyte transport
small intestine: digestion: intense glandular secretion from:
- enzymes from mucosa
- enzymes and bicarb ions from pancreas
- bile from liver
ingesta are mixed with secretions in small intestine by
muscles
duodenum 3 parts:
- cranial part (become cranial flexure)
- descending duodenum (turns into caudal flexure)
- ascending duodenum
cranial parts of duodenum (first part) runs to ____ of abdomen
RHS, and dorsally along the visceral surface of liver, where it becomes cranial flexure
cranial flexure of duodenum (first flexure) is closely related to
liver and pancreas, and receives bile and pancreatic ducts
how is the cranial flexure of the duodenum attached to the liver
by the hepatoduodenal ligament
the hepatoduodenal ligament attaches
cranial flexure of duodenum to the liver
the descending duodenum runs caudally and is supported by the
mesoduodenum
the descending duodenum is ____ to the right kidney and turns ________ in the caudal flexure
caudal
left and cranially
the ascending duodenum passes ____ to merge with the jejunum
cranially
where does the duodenum merge with the jejunum
at the duodenojejunal flexure
the ascending duodenum is attached to the descending colon by the
duodenocolic fold of mesentery
duodenocolic fold of mesentery attaches
ascending duodenum to descending colon
what is the longest part of the small intestine
jejunum
what mesentery supports the jejunum
mesojejunum
mesojejunum is long and allows
considerable movement of the jejunum
mesenteries originate at the base of
cranial mesenteric artery, where the artery and mesenteries form the “root of the mesenteries”
jejunum large occupies the _____ space in the abdomen (but easily moved but other organs enlarge ie pregnancy)
ventrocaudal
ileum is the
short, last part of the small intestine
length or ileum is indicated by the presence of
an artery (anti-mesenteric ileal branch)
how long is the ileum in the dog roughly
10cm
how is ileum attached to ceacum
iliocaecal fold
ileum is supported by which mesentery
mesoileum
where does ileum end
ileal orifice (iliocolic junction) which is at or near caecocolic junction
what sphincter prevents reflux of large intestine contents
ileocolic sphincter
how is duodenum, jejunum and ileum different histologically
- patterns of folds and villi
- distribution of glands and ducts
- distribution of lymphatic tissue
describe histological change as you move from pylorus –> duodenum
gastric pits –> intestinal villi
pyloric glands –> intestinal glands (crypts of lieberkuhn) and duodenal submucosal glands (brunners glands)
plicae circularis
circular folds in the mucosa and submucosa which increase SA in small intestine for absorption
in small intestine, projections of lamina propria and epithelium are
villi
villi in small intestine are covered by epithelial cells which have ____ of the surface
function?
microvilli
increase SA for absorption
2 main cell types in small intestine epithelium
- enterocytes; absorptive cells (columnar epithelial cells)
- goblet cells
also enteroendocrine cells
in small intestine there is a fast turnover of epithelial cells at the tips of the villi, these cells are replaced in the
crypts of lieberkuhn (intestinal glands)
enterocytes (absorptive cells) in small intestine form what kind of epithelium
simple columnar epithelium with a brush border of microvilli
surface membrane of small intestine has a glycocalyx, which is
jelly-like protective coat of glycoproteins , contains a number of digestive enzymes
goblet cells contribute a mucous coating to glycocalyx in small intestine via
mucopolysaccharides
near apical membrane of the epithelium of the small intestine (made of enterocytes) there is an
unstirred water layer,
Here the liquid flows through the small
intestine at a much slower rate than rest of lumen. In this unstirred water layer,
mucous and the glycocalyx form an important barrier to diffusion. Nutrients must
pass through this before being absorbed.
tight junctions between enterocytes (epithelium of SI) form a band near the apical membrane and are permeable to
but impermeable to
H2O and electrolytes
organic molecules
below tight junctions, enterocytes (which make up epithelium of SI) are unattached creating a
lateral space
how do nutrients exit the enterocytes of SI
through the basolateral membrane and enter the bloodstream
goblet cells secrete (small intestine)
mucin; protein polysaccharide
enteroendocrine cells also present in epithelium of SI, they are
basal, triangular and lie on basement membrane between absorptive cells (enterocytes)
some enteroendocrine cells (SI epithelium) have a process which extends to
free surface of epithelium
enteroendocrine cells (present in SI epithelium) contain dense
basally situated granules w an intranuclear golgi apparatus
enteroendocrine cells (present in SI epithelium) are endocrine cells which mean they secrete
hormones, including secretin, vasoactive intestinal peptide and cholecystokinin
(they also secrete serotonin and bradykinin)
enteroendocrine cells (present in SI epithelium) are endocrine cells which mean they secrete hormones, including secretin, vasoactive intestinal peptide and cholecystokinin
what do these do
regulate motility and secretory activity of the gut, pancreas, liver and gall bladder
crypts of liberkuhn are in which layer of intestines
lamina propria
lamino propria of intestine is
loose connective tissue with elastic fibers; makes up core of villi and fills space between glands
crypts of lieberkuhn
intestinal glands; simple branched tubular glands
lamina propria of intestines contains
lymphatic tissue, glands and blood and lymph vessels
cells in the crypts of lieberkuhn
The outer parts have a cell population similar to that of the
epithelium: absorptive (enterocytes) , goblet and enteroendocrine cells
The bases of the crypts
have less clearly differentiated cells and a high mitotic index.
in crypts of lieberkuhn (intestinal glands) new cells are formed at
base of crypts and move up to replace cells lost at tips of villi
cells have lifespan of about 5 days
lamina propria of each villus contains
lymphocytes, capillaries and central lacteal (which is a central lymph vessel)
what does the central lymph vessel or lacteal do (present in lamina propria of each villus)
drains each villus
into a larger plexus of lymph vessels in the submucosa. The lacteals play an important
role in the transport of absorbed fat. This is synthesized into chylomicrons in the
absorptive cells. These chylomicrons enter lacteals in the villi, and are carried in the
lymph to the bloodstream.
( just FYI By contrast, water‐soluble materials that are absorbed
from the gut enter the blood, and are carried first to the liver in the hepatic portal
vein)
describe the blood vessels in lamina propria of each villus
Each villus has one (or two) arteriole(s)
Form extensive capillary network
Drained by two venules
Drain to larger veins → hepatic portal vein
→ liver
Both blood and lymph pumped through villi via
Contractions of muscularis mucosae
GALT
gut associated lymphoid tissue
lamina propria also contains aggregated lymph nodules while play important role in
protecting animal against invasion of microorganisms
lamina propria also contains aggregated lymph nodules which increase in size and frequency as you move
caudally in small intestine
in the ileum the aggregated lymph nodules are called
Peyer’s patches, extend into submucosa
Epithelial cells overlying the peyer’s patches are
frequently flattened,
with extremely long microvilli, and the surface is often free of villi and glandular
crypts
submucosa of intestines made up of
dense connective tissue (denser than lamina propria) with bundles of collagen and elastic fibers
what kind of glands are present in the submucosa
brunner’s glands (duodenal glands)
submucosa contains an extensive
venous plexus connecting with arteries: arteriovenous anastomoses (AVA’s)
Meissner’s plexus is prominent in which layer
submucosa
brunner’s glands
simple branches tubular- acinar or alveolar glands, (duodenal glands); found in cranial duodenum in carnivores
brunner’s glands open into the
base/ fundus of crypts of lieberkuhn
secretion of brunner’s glands, what and why
alkaline, mucoid and viscous, plays a role in protecting cranial duodenum against acidic gastric secretions
tunica muscularis
structure and function
- circular (inner) & longitudinal (outer) muscle layers
- mix and move contents caudally
where does auerbach’s plexus lie
between layers of tunica muscularis
ileal sphincter is formed from ____ layer of tunica muscularis
circular (inner)
tunica serosa of intestines
loose connective tissue, continuous w mesentery
large intestine; caecum
- blind-ending part of large intestine
- starts at caecocolic orifice (dog)
- in humans, ends in vermiform appendix
how is ceacum joined to the colon
at the ileocaecal orifice
3 main divisions of simple colon
ascending, transverse and descending
ascending colon
from caecum, cranially on right
transverse colon
from right to left, cranial to cranial mesenteric artery (root of mesenteries)
descending colon
on left, caudal to rectum
when you view the colon ventrally it forms a
?
most obvious difference between the small and large intestines is
absence of
villi in the large intestine
flatter, more blocky surface
are there villi in the mucosa of large intestine? are there crypts?
no villi
yes crypts
walls of caecum, colon, and rectum are
v similar
although there is a progressive increase in the number of mucous goblet cells
towards the distal regions
crypts of large intestine are ____ than in small intestine
deeper
in large intestine lymph nodules are present and especially prominent in
in the rectum in the terminal region where the wall is thrown up into longitudinal folds
the tunica serosa of large intestine compared to small intestine
continues as in
the small intestine, except on the terminal portion of the rectum, where it is replaced
by a tunica adventitia of fibrous connective tissue
the jejunal mass lies _______ and is covered by _____
ventral and lateral
greater omentum
when stomach is distended the jejunum mass is displaced
dorsally and to the right
(usually its ventral and lateral)
location of caecum (carnivores)
dogs vs cats
short, on RHS of abdomen
usually located just cranial to caudal duodenal flexure
dogs; points caudal (terminal twist)
cats; v short
in radiographs how do you often see caecum
see small gas caps
colon in carnivores, what is it supported by
short and simple
supported by short mesocolon
does the colon move
no generally fixed in position
descending colon lies close to ______ connected to it by the _______
ascending duodenum
duodenocolic fold
rectum
straight terminal part of large intestine
rectum passes through
pelvic cavity
rectum may have an enlargement caudally called the ____ before the rectum enters the anal canal
ampulla recti
the anal canal is closed by
internal and external sphincters
coccygeus muscle function
fiber type
compresses rectum
striated muscle
levator ani muscle function
fiber type
compresses the rectum and retract anus when it contracts
striated muscle
retractor penis or clitoris muscle function
fiber type
supports the anus
mixed fibers
rectococcygeus muscle function
fiber type
shortens rectum when it contracts
smooth muscle
at the anal canal the epithelium changes from
- mucosa (endoderm) –> skin (ectoderm)
- absorptive –> absorptive
- cuboidal/ columnar –> stratified squamous (keratinized in most species)
- smooth muscle –> striated muscle
the muscularis mucosa and most of the outer longitudinal layer of tunica muscularis ends at the
ano-rectal line
at the anal canal circular muscle forms
internal anal sphincter
columnar zone (at anus area)
- longitudinal folds (anal columns) of rectum
- form pockets; rectal sinuses
- anal mucosa contains lymph tissue and erectile venous tissue
3 zones in mucosa and submucosa or anal area
columnar zone, intermediate zone, cutaneous zone
columnar zone; the submucosa in the anal region contains simple, branched tubular and coiled glands with a fatty or mucous secretion called
anal glands
(different to anal sacs which is what ppl usually call anal glands)
mucosa and submucosa of anal region: intermediate zone
- v short (~1mm)
- it is an irregularly scalloped fold, often referred to as the anocutaneous line
- anal glands continue from columnar zone in submucosa
cutaneous zone of anal region (last zone), what kind of glands, why is one type of gland clinically significant
- epithelium contains sweat glands and modified sebaceous glands called circumanal glands (these grow throughout life in entire male dogs and may become cancerous)
- one duct from the anal sac opens into cutaneous zone on each side (this is what gets squeezed during appts, so its anal sacs NOT anal glands)
internal sphincter, what is it a continuation of, what type of muscle
- continuation of circular muscle of tunica muscularis
- smooth muscle
- does not quite extend to cutaneous zone
external sphincter, type of muscle, location and what muscles is it associated with
- layer of striated muscle
- caudally from anorectal line
- associated w retractor penis and levator ani muscles
anal sacs
- Paired diverticula of anus
- Between internal and external anal sphincters
- Anal sac glands in their wall
- Single duct opens to cutaneous zone
- May become blocked and need manual expression
true anal glands open directly into
columnar and intermediate zones
what zone is circumanal glands found in
cutaneous zone
where are anal sac glands
line wall of anal sac between internal and external anal sphincters
blood supply to intestines
- 3 unpaired arteries from aorta in abdomen
- coeliac
- cranial mesenteric
- caudal mesenteric
coeliac artery (3 branches)
- splenic: spleen, stomach and pancreas
- left gastric; stomach
- hepatic; liver, pancreas, stomach, proximal duodenum
cranial mesenteric artery
- through root of mesentery
- supplies intestine from distal duodenum to transverse colon
- this includes:
- distal duodenum
- jejunum
- proximal ileum
- distal ileum and caecum (ileocaecocolic artery)
- ascending colon (right colic artery)
- transverse colon (middle colic artery)
caudal mesenteric artery
- runs in mesocolon
- supplies descending colon (left colic artery)
- proximal rectum (cranial rectal artery)
internal iliac artery
- major blood.vessel that supplies blood to pelvic organs and lower limbs
- branches into internal pudendal artery (paired)
- further branches into middle rectal artery which supplies distal rectum (paired)
- and the caudal rectal artery and the perineal artery that supplies the anus ( both paired)
Blood from the intestines flows through progressively larger veins to the _____, and then to the ____
hepatic portal vein
liver
branches of hepatic portal vein
gastroduodenal
splenic
cranial mesenteric
caudal mesenteric
Blood leaves the
liver in hepatic veins and is returned to the heart in the
caudal vena cava
Lymph from area supplied by cranial mesenteric artery drains to nodes in
cranial mesenteric lymph centre
order of operations of efferent lymph from area supplied by CRANIAL mesenteric arteries
efferent lymphatics –> intestinal lymph trunk –> cysterna chyli –> thoracic duct
The efferent lymphatics from these nodes lie adjacent to veins, and join
together to form the intestinal lymph trunk. This joins the cysterna chyli, and lymph
then flows through the thoracic duct to the blood stream
Lymph from area supplied by caudal mesenteric artery drains to nodes in
caudal mesenteric lymph centre
order of operations of efferent lymph from area supplied by CAUDAL mesenteric arteries
efferent lymphatics –> intestinal / lumbar lymph trunk –> cysterna chyli –> thoracic duct
Efferent lymphatics drain either to the intestinal or
the lumbar trunks.
Lymphatic drainage of the intestines is extremely important as
fat absorbed in the intestines is transported to the blood stream via this route.
In a dog that has recently eaten a fatty meal the mesenteries of the gut will contain
a lot of milky fluid
Movements of the intestinal smooth muscle are largely inherent in origin (the enteric
nervous system). However, they are modified by the activity of the autonomic
nervous system (both parasympathetic and sympathetic nerves), which terminate in
the myenteric (Auerbach’s) and submucosal (Meissner’s) plexuses
The sympathetic innervation comes via three ganglia located near the proximal part of the major GI arteries, namely the coeliac artery and the cranial and caudal mesenteric arteries. These ganglia are therefore named
the coeliac ganglion, and the cranial and caudal
mesenteric ganglions.
the post ganglionic fibers of the sympathetic nerves (3 ganglia next to 3 main arteries) pass directly to the smooth muscle cells of
blood vessels and muscularis mucosae
sympathetic nerves are primarily
what do they cause
what does this mean
adrenergic, releasing noreadrenaline and cause vasoconstriction
inhibit secretory and motor activity of GI tract
how do sympathetic nerves innervate the pelvic region
- there are no sympathetic nerve fibres leaving the spinal cord in the pelvic
region, sympathetic nerves must run from the abdominal region to innervate the
viscera in the pelvis. - Paired hypogastric nerves (A) leave the caudal mesenteric
ganglion and travel caudally, initially in the mesocolon, then in the lateral ligaments of
the bladder, before forming a plexus on the lateral walls of the rectum. - form the pelvic plexus with the pelvic nerve (sympathetic) before sympathetic and
parasympathetic nerves continue on to their target organs.
parasympathetic nerves origin
- origins in cranial (vagus) nerves and sacral (pelvic nerves)
parasympathetic nerves from cranial origin
Vagus nerve (CN X) to abdominal ganglia
parasympathetic nerves from sacral origin
Pelvic nerve to pelvic ganglia on lateral wall of rectum
Parasympathetic nerves are primarily
what doe they release
what does this cause
what does that mean
cholinergic,
releasing acetylcholine,
and their effects are largely stimulatory in the gut, causing vasodilation,
increased motility and secretory activity
Sensory visceral afferent nerves Run in both
vagal (parasympathetic) and sympathetic nerve trunks back to CNS
Sensory nerve endings and cell bodies are found: (3 places)
- Mucosal epithelium
- Plexuses
- Muscle layers
sensory innervation: Pacinian corpuscles (shaped like an onion)
- Sensitive to stretch
- Common in subserosal connective tissue in mesenteries
- they only respond to changes in pressure, they stop sending action potentials when pressure is consistent.
Sensory nerves monitor two important aspects of the digestive system:
pressure and pain
pressure sensory receptors
- Receptors in gut wall in:
- Oesophagus, stomach to mid colon
- send Impulses to CNS Vagus & pelvic n.
The vagovagal reflex
controls contraction of the
gastrointestinal muscle layers in response to distension of the tract by food. This
reflex also allows for the accommodation of large amounts of food in the
gastrointestinal tract. When food enters the stomach a “vagovagal” reflex goes from
the stomach to the brain, and then back again to the stomach causing active
relaxation of the smooth muscle in the stomach wall, as well as stimulating the
parietal cells to release H+
how sensory nerves sense pain
- Free nerve endings in peritoneum and gut wall
- Very sensitive to stretching and ischaemia (lack of blood)
- Less sensitive to cutting or hot/cold
- Pain impulses pass on small myelinated or unmyelinated fibres
Which of the following is the terminal part of the large intestine?
rectum
Which part of the duodenum runs CAUDALLY in the abdomen?
Descending duodenum
Which is the LONGEST part of the small intestine?
jejunum
The length of the ileum is identified by the presence of an artery on which surface?
Antimesenteric surface
The terminal region of the small intestine is termed the:
Ileum
The large surface area of the small intestine facilitates absorption. Which of the following structures does NOT contribute to this large surface area?
A.
Villi
B.
Microvilli
C.
Glycocalyx
D.
Plicae circularis
Glycocalyx
At the pylorus, there is a change in the mucosa. Which of the following disappears as you move into the duodenum?
Gastric pits
Which of the following cell types in the epithelium of the tunica mucosa secretes mucin?
Goblet cells
Lacteals play a very important role in the transport of:
Absorbed fat
Peyer’s patches are aggregated lymph nodules found in the anti-mesenteric wall of the:
Ileum
The stomach and the small intestine play different roles in the digestive process. This is reflected by a change in the wall of the digestive tract, mainly in the tunica mucosa. As you move aborally (away from the mouth) through the duodenum, which of the following structures disappears
Pyloric glands
Which part of the large intestine is blind-ending?
Caecum
Which of the following is ABSENT in the large intestine?
Villi
When the stomach is distended, the jejunum is displaced in which direction?
Right and dorsal
The descending colon lies close to the ascending duodenum, as they are connected by the:
Duodenocolic fold
Which of the following muscles of the rectum SUPPORTS the anus?
Retractor penis
The anal glands are simple, branched tubular and coiled glands that produce a fatty or mucous secretion. Which zone are they NOT found in?
Cutaneous zone
Where are the circumanal glands located?
Cutaneous zone
Which of the following supplies blood to the ileum?
Cranial mesenteric artery
Which of the following supplies the descending colon?
Caudal mesenteric artery
Branches of the internal pudendal artery supply the distal rectum and anus. The internal pudendal arteries are a branch of the:
Internal iliac artery
Which of the following does NOT contribute to the lymphatic drainage pathway, from the area supplied by the cranial mesenteric artery?
Lumbar lymph trunk
Sympathetic innervation to the pelvic region is supplied through paired hypogastric nerves, which leave which ganglia?
Caudal mesenteric
Parasympathetic innervation to the intestines is largely from branches of which cranial nerve?
CN X
Question 27
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Sensory visceral afferent nerve endings and cells bodies are NOT found in:
A.
Mucosal epithelium
B.
Plexuses
C.
Muscle layers
D.
Serosa
Serosa
