Anatomy Flashcards
What are the components of the GI tract?
Oral cavity Pharynx Oesophagus Stomach Small intestine Large intestin Rectum Anal canal Anus
What are the functions of the upper GI tract?
Mastication
Taste
Salivation
Deglutition (swallowing)
What is mastication?
The process of chewing which is conducted by movement of the jaw and tongue to breakdown food. Mastication facilitates taste and digestion by mixing food with saliva
What is the buccinator?
A muscle inside the cheek that pushed food from side to side innervated by cranial nerve 7
What are the oestology features of the TMJ?
Temporal bone has a mandibular fossa where the condylar process (of mandible) can fit in. The articular tubercle is a bump in the zygomatic arch and lies anteriorly to the TMJ
What are the muscles of mastication innervated by?
CN V3 (mandibular division of the trigeminal nerve)
Which muscles facilitate closing of the jaw?
Temporalis (temple fossa to the coronoid process)
Masseter (angle of the mandible to the zygomatic arch)
Medial pterygoid (mimics masseter on the internal surface)
Which muscle facilitates the opening of the jaw?
Lateral pterygoid (condyle of mandible to the pterygoid plates of sphenoid bone)
What does the articuar disc in the TMJ separate?
Two cavities - superior caivty for translation and inferior cavity for rotation
What is the course of the trigeminal nerve?
From pons through the foramen ovale to the muscles of mastication and sensory area
What is the sulcus terminalus?
Divides the tongue into the anterior and posterior tongue
What is the function of the vertical part of the tongue?
Taste and sensation innervated by glosopharyngeal nerve
What is the function of the horizontal part of the tongue?
Taste - innervated by the facial nerve
General sensory - innervated by the V3
What are the papillae with taste buds?
Foliate papillae
Vallate papillae
Fungiform papillae
What is the papillae that detects touch and temperature?
Filiform papillae
What is the course of the facial nerve?
From pontomedullary junction travels through the temporal bone via interal acoustic meatus and then through the stlomastoid foramen to supply taste to the anteroir 2/3rds of tongue, muscles of facial expression and glands in the floor of the mouth
What innervates the superior half of the oral cavity?
Maxillary division of the trigeminal nerve
What innervates the inferoir half of the oral cavity?
Mandibular division of the trigeminal nerve
What is the gag reflex?
A protective reflex that prevents foreign bodies from entering the pharynx or larynx
What innervates the sensory part of the gag reflex?
Nerve fibres within the glossopharyngeal nerve
What carries out the motor part of the gag reflex?
Nerve fibres within the glossopharyngeal nerve and vagus nerve
What does the gag reflex do to the pharynx?
When the posterior wall of the oropharynx is touched the pharynx constricts
What is the course of the maxillary division of the trigeminal nerve?
From pons through the formaen rotundum to the sensory area (mid-face)
What is the course of the glossopharyngeal nerve?
From medulla through the jugular foramen to the posterior wall of the oropharynx (sensory), parotid gland (secretomotor) and posterior 1/3rd of the tongue (sensation and taste)
Where does the parotid gland secrete saliva?
Parotid duct secretes into mouth by upper 2nd molar (upper 7th)
Where does the submandibular gland secrete saliva?
The submandibular duct enters the floor of the mouth and secretes via lingual caruncle
Where does the sublingual gland secrete saliva?
Lays in the floor of mouth and secretes via several ducts superiorly
What is the function of the extrinsic muscles of the tongue?
Change the position of the tongue during mastication, swallowing and speech
What is the function of the 4 pairs of intrinsic muscles of the tongue?
Located mainly dorsally to modify the shape of the tongue during function
What are the 4 intrinsic muscles of the tongue?
Palatoglossus - palate to tongue
Styloglossus - styloid process to the tongue
Genioglossus - chin to tongue
Hyoglossus - hyoid bone to tongue
What innervates all of the tongue muscles (except the palatoglossus)?
Hypoglossal nerve
What is the course of the hypoglossal nerve?
Medulla through the hypoglossal canal to the extrinsic and intrinsic muscles of the tongue
What innervates the constrictor muscles pharynx?
Vagus nerve
What is the function of the upper oesophageal sphincter?
To prevent reflux at level of C6 as it attaches to cricoid cartilage
What is the midline raphe?
Where all of the 3 circular constrictor muscles insert into
What innervates the longitudinal muscles of the pharynx?
Vagus and glossopharyngeal
What is the function of the longitudinal muscles?
Attach to pharynx and larynx to shorten the pharynx and raise the larynx to close over the laryngeal inlet
What is the anatomy of swallowing?
Close lips to prevent drooling (orbicularis and facial nerve
Tongue pushes bolus posteriorly towards oropharynx
Sequentially contract pharyngeal contrictor muscles to push the bolus inferiorly towards oesophagus
Inner longitudinal muscles contract to raise larynx, shorten the pharynx and close the laryngeal inlet
Bolus reaches oesophagus
Where does the oesophagus start?
At the inferior edge of criopharyngeus muscle (vertebral level C6)
What are the sphincters present in the oesophagus?
Anatomical upper sphincter (cricopharyngeus) and a physiological lower oesophageal sphincter which aids in controlling food movement
What is the oesophageal plexus?
Runs on the surface to supply smooth muscle within its walls (distally)
What does the oesophageal plexus contain?
Parasympathetic nerve fibres (vagal trunks) and sympathetic nerve fibres
What do these autonomic nerve fibres of the oesophageal plexus do?
They influence the enteric nervous system to speed up (P) or slow down (S) peristalsis
Terminates by entering the cardia of the stomach
Where does the oesophagus pass through the diaphragm?
At T10
What heart ventricle does the oesphagus pass under?
The left atrium
What factors influence the lower oesophgeal sphincter effect?
Contraction of diaphragm
Intrabdominal pressure if it is slightly higher that intragastric pressure
Oblique angle at which oesophagus enters the cardia of the stomach
What does the lower oesohpageal sphincter help to reduce?
The occurrence of reflux `
What is the z-line?
An abrupt change in the type of mucosa lining of the wall
What are the different parts of the large intestine?
Colon Caecum Appendix Ascending colon Transverse colon Descending colon Sigmoid colon Rectum Anal canal Anus
What makes up the foregut?
Oesophagus to mid-duodenum
Liver and gall bladder
Spleen
1/2 of pancreas
What supplies the foregut?
Celiac trunk
What makes up the midgut?
Mid-duodenum to proximal 2/3rds of transverse colon
1/2 of pancreas
What makes up the hindgut?
Distal 1/3rd of transverse colon to proximal 1/2 of anal canal
What supplies the midgut?`
Superior mesenteric artery
What supplies the hindgut?
Inferior mesenteric artery
What organs make up the RUQ?
Liver Gallbladder Duodenum Head of pancreas Right kidney and adrenal gland Hepatic flexure of colon
What organs make up the LUQ?
Stomach Spleen Left lobe of liver Body of pancreas Left kidney and adrenal gland Splenic flexure of colon Parts of transverse and descending colon
What organs make up the RLQ?`
Cecum Appendix Ascending colon Right ovary and fallopian tube Right ureter
What organs make up the LLQ?
Small bowel (ileum) Transverse colon Descending colon Sigmoid colon Rectum Left ureter Left ovary and fallopian tube
What are the muscles of the anterolateral abdominal wall?
Rectus abdominus External oblique Interal oblique Transversus abdominus Parietal peritoneum
What is peritoneum?
A thin, transparent, semi-permeable, serous membrane
What does the peritoneum line?
The walls of the abdominopelvic cavity and organs
What is peritonitis?
Blood, pus or faces in the peritoneal cavity will cause severe and painful inflammation of the peritoneum (peritonitis)
What are intraperitoneal cavities?
Almost completely covered in visceral peritoneum
Minimally mobile
What are organs with a mesentery (intraperitoneal)?
Covered in visceral peritoneum
Visceral peritoneum wraps behind the organ to form a double layer - mesentery
Mesentery suspends the organ from the posterior abdominal wall - very mobile
What is a retroperitoneal organ?
Only has visceral peritoneum on its anterior surface in the retroperitoneum
What are intraperitoneal organs?
Liver and gall bladder Stomach Spleen Parts of small intestine Transverse colon
What are retroperitoneal organs?
Kidneys Adrenal gland Pancreas Ascending colon Descending colon
What are the different types of peritoneum?
Mesentery - usually connects organ to posterior body wall
Omentum (greater and lesser) - double layer of peritoneum that passes from stomach to adjacent organs
Peritoneal ligaments - double layer of peritoneum connects organs to one another or body wall
What makes up the mesentery?
Have a core of connective tissue with blood and lymph vessels, nerve, lymph nodes and fat
What are the 3 types of mesentery?
Mesentery proper (small intestine)
Transverse and sigmoid mesocolon
Mesoappendix
What is the function of the greater omentum?
Four layered
Hangs like an apron
Attaches the greater curvature of stomach to the transverse colon
What is the function of the lesser omentum?
Double-layered
Runs between lesser curvature of stomach and duodenum to the liver
Has a free edge
What are the sacs in the peritoneum?
The omenta divide the peritoneal cavity into the greater and lesser sacs
What is the omental foramen?
How the greater and lesser sacs communicate
What is the portal trial?
Hepatic portal vein, hepatic vein proper and common bile duct
Where is portal triad?
It lies in the free edge of the lesser omentum in the hepatoduodenal ligament
What are the pouches that are formed by the peritoneum in the female?
Recto-uterine pouch known as the pouch of douglas
Vesico-uterine pouch
What is ascites?
Collection of fluid in the peritoneal cavity
What commonly causes ascites?
Cirrosis
Portal hypertension
How can ascitic fluid be drained?
Via paracentesis
Where is the needle inserted in abdominocentesis?
Placed lateral to the rectus sheath to avoid the inferior epigastric artery
Where does the inferior epigastric artery arise from?
The external iliac medial to the deep inguinal ring
What does organ pain tend to present as?
Dull, achy and nauseating
What does somatic pain present as?
Sharp and stabbing
What is the enteric nervous system?
A network of nerves found only within the walls of the GI tract which can act independently of other part of the the nervous system to bring about peristalsis but can also be influenced by autonomic motor nerves
Where do sympathetics that innervate the abdomen leave the spinal cord?
Between T5 and L2
Where do the sympathetic nerves synapse?
They synpase at the prevertberal ganglia which are located anterior to the aorta at the exit points of the major branches of the abdominal aorta
What are the 3 different ganglion within the abdomen?
Celiac ganglion
Superior mesenteric ganglion
Inferior mesenteric ganglion
Where do sympathetic fibers for the adrenal gland leave the spinal cord and where do they synpase?
T10-L1 and enter the abdominopelvic splanchnic nerves but do not synapse at prevertebral ganglia but instead are carried with the periarterial plexuses to the adrenal gland and synapse directly onto cells
What is the course of the vagus nerve when innervating the abdomen?
Presynaptic nerve fibres enter abdominal cavity on the surface of the oesophagus and travel into the periarterial plexuses around the abdominal aorta. Here they are carried to the walls of the organs where they synapse and supply to GI tract and abdominal organs up to the dital end of the trasnverse colon
What do the pelvic splanchinic nerves supply?
S2,3,4 supply smooth muscle/glands of the descending colon to anal canal
What does foregut pain present as?
Epigastric pain
What does midgut pain present as?
Umbilical pain
What does hindgut pain present as?
Pubic region
Where doe foregut structures enter the spinal cord?
T6-T9
Where do midgut structures enter the spinal cord at?
T8-T12
Where do hindgut structures enter the spinal cord at?
T10-L2
Why does liver or galllbladder pain tend to radiate to the shoulder/upper back?
It will often irritate the diaphragm which is supplied by C3,4,5 whose dermatomes are in that region
Where is the appendix located?
Midgut- right ilia fossa
Why does the presentation of appendicitis change?
Pain from midgut is umbilical but as spendicitis worsens, the appendix will start to irritate the paritetal periotoneum in the right iliac fossa which lies anterior to it
What causes jaundice?
An increase in the blood levels of bilirubin
How does jaundice present?
Yellowing of the sclera (white of eyes) and the skin
What is bilirubin?
A normal by-product of the break down of red blood cells
Where does the breakdown of RBCs usually occur?
In the spleen
What is bilirubin used for?
To form bile
Where does bile travel to?
It travels from the liver thourgh the biliary tree which is a set of tubes that connects the liver to the 2nd part of the duodenum
What is the function of the gallbladder?
Storage and concentration of bile
What is the function of bile?
Important for the normal absoprtion of fats from the small intestine
What are the functions of the liver?
Glycogen storage
Bile secretion
Other metabolic functions
What is the surface anatomy of the liver?
Located mainly in the RUQ
Protected by ribs 7-11
The location changes during breathing as it is so closely related to the diaphragm
What are the anatomical relations of the liver?
Inferior to the right hemi-diaphragm Gallbladder - posterior and inferior Hepatic flexure - inferior Right kidney, right adrenal gland, IVC, abdominal aorta - posterior Stomach - posterior at mid/left side
How many anatomical lobes are there in the liver?
4 - right, left, caudate and quadrate
How many functional lobes are there in the liver?
8 - related to vasculature and bile drainage
What separates the right and left lobe?
The falciform ligament that ends with the round ligament (remnant of the umbilical vein)
What does each segement of the liver have?
A brach of a hepatic artery
Branch of a hepatic portal vein
Bile drainage (to bile duct)
Venous drainage
What is the portal triad?
Contains main structures that enter or leave the liver parenchyma:
Hepatic portal vein
Hepatic artery proper
Bile duct
Where does the portal triad run?
Within the hepatoduodenal ligament within the lesser omentum
Where can the coeliac trunk be found?
First of three midline branches of the aorta, retroperitoneal, leaves the aorta at T12 vertebral level
What does the coeliac trunk supply?
The organs of the foregut
What are the branches of the coeliac trunk?
Splenic artery
Left gastric artery
Common hepatic artery
When does the common hepatic artery become the hepatic artery proper?
When the common gives of the gastroduodenal artery it becomes the hepatic artery proper
What is the course of the splenic artery?
Very tortous course that runs along the superior border of the pancreas
Where does the spleen sit?
It is an intraperitoneal organ within the left hypochondrium
What are the anatomical relations fo the spleen?
Posteriorly - diaphragm Anteriorly - stomach Inferiorly - splenic flexure Medially - left kidney Protected by ribs 9-11
What is the function of the spleen?
Functions within the haematologicla system to break down red blood cells to produce bilirubin
What supplies the stomach with a blood supply?
Right and left gastric arteries (lesser curvature and lesser omentum)
Right and left gastro-omental arteries (greater curvature and greater omentum)
All anastomose
What is the blood supply to the liver?
Right and left hepatic arteries
Branches of the hepatic artery proper
Hepatic portal vein
What are the 2 clinically important areas of the peritoneal cavity related to the liver?
Hepatorenal recess (morison’s pouch)
Sub-phrenic recess
Both within the greater sac
What is the lowest part of the peritoneal cavity?
When lying down, the hepatorenal recess is lowest. Pus from an abscess in the sub-phrenic recess can drain into the hepatorenal recess
What does the hepatic portan vein (HPV) drain blood from?
The foregut, midgut and hindgut to the liver for first pass metabolism (cleaning)
What veins form the HPV?
Splenic vein (drains foregut) Superior mesenteric vein (midgut) Inferior mesenteric vein drains blood from hindgut into spenic vein
Where is the IVC found?
Retroperitoneal
Drains the cleaned blood from the hepatic veins into the RA
Where is the gallbadder in relation to the liver?
Lies on the posterior aspect of the liver (often firmly attached)
Lies anterior to the duodenum
Where does bile flow into and out of the gallbladder?
Cystic duct
What is the blood supply to the gallbladder?
Cystic artery which is a branch of the right hepatic artery
What is the cystohepatic triangle of calot?
Cystic duct, common hepatic duct and cystic artery
What is a cholecystectomy?
Surgical removal of the gallbladder
What is the biliary tree?
A set of tubes connecting the liver to the second part of the duodenum
What makes up the common hepatic duct?
Right and left heaptic ducts
What makes up the common bile duct?
Common hepatic duct and common bile duct
What are the 4 parts to the duodenum?
Supeior
Descending
Horizontal
Ascending
What parts ot the duodenum are intraperitoneal?
Superior part which contains the duodenal cap
What is the function of the pyloric sphincter?
Anatomical sphincter that controlls the flow of chyme from the stomach to the duodenum via smooth muscle (symp contraction, parasymp relaxation)
Where does the duodenum begin and end?
Begins at the pyloric sphincter
Ends at the duodenojejunal flexure
What hormones does the duodenum secrete?
Peptide hormones gastrin and CCK
Where does the pancreas lie
Within the retroperitoneum and lies transversly across the posterior abdomen
What are the parts to the pancreas?
Head (with uncinate process)
Neck
Body
Tail
What surrounds the head of the pancreas?
Duodenum
What structures lie posterior to the pancreas?
Right kidney and adrenal gland IVC Bile duct Abdominal aorta SMA Left kidney and adrenal gland Part of the portal venous system
What structure lies anterior to the pancreas?
Stomach
What lies superoposterior to the pancreas?
The splenic vessels
What is the exocrine function of the pancreas?
Acinar cells release pancreatic enzymes into the pain pancreatic duct. They are stimulated by parasymp activity
What is the endocrine function of the pancreas?
Islets of langerhans release insulin and glucagon into the blood stream
Where does the ampulla of vater enter the duodenum?
Enters the 2nd part of the duodenum via the major duodenal papilla
What makes up the ampulla of vater?
The common bile duct and the main pancreatic duct (of Wirsung)
What is between the hepatopancreatic ampulla of vater and the duodenum?
The sphincter of oddi
What can cause obstruction of the biliary tree?
Gallstones
Carcinoma at the head of the pancreas
What can this obstruction cause?
Flow of bile back up to the liver that causes overspill into the blood including bilirubin
What are the 3 branches to the coeliac trunk?
Common hepatic duct, splenic artery and left gastric artery
What does the superior panacreticoduodenal artery anastomose with?
The inferoir pancreaticoduodenal artery
What is the origin of the superior pancreaticoduodenal artery?
Gastroduodenal artery which originates from the common hepatic artery
What is the origin of the inferoir pancreaticoduodenal artery?
The SMA
Where does the SMA leave the aorta?
At L1
What can cause pancreatitis?
Blockage of the ampulla by a gallstone diverting bile into the pancreas leading to irritation and inflammation
What type of pain does the pancreas produce?
Foregut and midgut so pain can be epigastric and/or umblical with radiation to the back
What can occur in more advanced cases of pancreatitis?
Vascular haemorrhage leading to blood/fluid accumulation in the retoperitoneal space. Grey-turner’s sign or cullen’s sign
Where does the jejunum begin?
The duodenaljejunal flexure
Where does the ileum end?
At the ilecaecal junction
What are the differences between the jejunum and ileum?
Jejunum is deep red. Ileum is light pink
Jejunum is thick and heavy. Ileum is thin and light
Jejunum ismore vascular
Jejunum has less mesenteric fat
Jejunum has large, tall and closely packed folds. Ileum has low and sparce folds
Where are peyer’s patches found?
In the ileum
Where is fat (within chylomicrons absorbed)?
From intestinal cells into specialised lymphatic vessels of the small intstine called lacteals where they will travel via the lymphatic system to drain into the venous system at the left venous angle
Where are the lymphatics of the abdomen found?
Lie alongside arteries - main ones are celiac, SMA, IMA and lumnar (kidneys, posterior abdo wall, pelvis and lower limbs)
What is the cisterna chyli?
Dilated sac at the lower end of the thoracic duct into which lymph from the intestinal trunk and two lumbar lymphatic trunks flow
What is the function of the larrge intestine?
Defence - commensal bacteria
Absorbtion - water and electolytes
Excretion of formed stool
Where is the appendix, caecum and ascending colon found?
Intraperitoneal and secondarily retroperitoneal
Where is the hepatic flexure found?
Inferior to the liver
Where is the transverse colon found?
Intraperitoneal - highly mobile, has own mesentery
Where is the splenic flexure found?
Inferior to the spleen
Where is the descending colon douns?
Secondary retroperitoneal
Where is the sigmoid colon found?
Intraperitoenal - has own mesentery
Where are the paracolic gutters found?
Between the lateral edge of ascending and descending colon and abdominal wall
Part of the greater sac of peritoneal cavity
What is the function of paracolic gutters?
Potential sites for pus collection
Similar to subphrenic or hepatoprenal recesses
What are the distinguishing features of the colon?
Omental appendices
Tania coli
Haustra
What is the omental apendices?
Small, fatty projections
What is the tenaie coli?
3 distinct longitudinal bands of thickened, smooth muslce running from the caecum to the distal end of the sigmoid. Come together at the appendix
What is haustra?
Fromed by tonic contractionf of the teniae coli
What is higher, the splenic of hepatic flexure?
Splenic flexure
Where doe the ceacum and appendix lie?
Within the right iliac fossa
What is the appendiceal orifice?
Lies on the posteromedial wall of the caecum. Corresponds to McBurney’s point on the abdo wall which is 1/3 of the way between the right ASIS to ubmilicus
Where does the sigmoid colon lie?
Left iliac fossa
What is ths sigmoid mesocolon?
Long mesentery that gives the sigmoid a considerable degree of movement
What is the downside to the sigmoid mesocolon?
Sigmoid at risk of twisting around itslef - sigmoid volvulus which results in bowel obstruction
What are the 3 midline branches of the abdominal aorta?
Celiac trunk (T12)
SMA (L1)
IMA (L3)
Where can the abdominal aorta be found?
Midline, retroperitoneal structure that lies anterior to the vertbral bodies and to left of the IVC
What do the lateral branches of the abdominal aorta supply?
Renal (L1)
Gonadal (L2)
Lumbar arteries
What does the abdominal aorta bifurcate into?
The common iliac arteries (L4) which further bifurcate into the interal and external iliacs
What are the branches of the SMA?
Inferior pancraticoduodenal artery Middle colic artery Right colic artery Ileocolic branches Appendicular jejunal and ileal arteries
What is the difference between the jejunual and ileal arteries?
Jejunum has a longer vasa rectae and larger and fewer arcades
What are the branches of the IMA?
Left colic artery
Sigmoid arteries
Superior rectal artery
What is the martinal artery of drummond?
Arterial anastomose between the branchs of the SMA and IMA that can help to prevent intestinal ischaemia by providing an alternative route by which blood can travel
What supplies the rectum and anal canal?
Superior rectal artery - branch of IMA. Supplies up the the pectinate line and the remainder of the GI tract is supplies by the interal iliac artery
What is the function of the hepatic portal venous system?
Drains venous blood from absorptive parts of the GI tract and associated organs to the liver for cleaning
What is the function of the systemic venous system?
Drains venous blood from all other organs and tissues into the superior or inferior vena cava
What is the function of the IVC?
Drains cleaned blood from the hepatic veins into the RA
Waht is the function of the hepatic portal vein?
Drains blood from foregut, midgut and hindgut to the liver for first pass metabolism
What is the functino of the splenic vein?
Drains blood from the foregut structures to hepatic portan vein
What is the function of the SMV?
Drains blood from midgut to hepatic portal
Wha is the function of IMV?
Drains blood from hindgut to splenic vein
What are the portal-systemic anastomoses?
Anastomosis between systemic and portal venous system that allows blood to flow both ways into either system
What are the sites of the portal-systemic anastomosis?
Skin around umbilicus
Distal end of oesophagus
Rectum/anal canal
What does the skin around umbilicus anastomosis connect?
Para-umbilical veins and small epigastric veins
Para-umbilica veins to hepatic portal vein along round ligament of liver
Epigastric veins to caval system
What does the dital end of oesophagus anastomosis connect?
Inferior part drains to the hepatic portal vein
Superior part drains into azygoud
What does the rectum/anal canal anastomosis connect?
Rectum and supeiror anal canal drains to IMV
Inferior part of GI tract drains into internal iliac vein
What is portal hypertension?
Elevation of BP in portal system caused by liver pathology (cirrhosis) or tumour compressing HPV
What does portal hypertension result in?
Reversal of blood flow that means a larger volume of blood flow to the anastomotic areas causes them to become varicosed
What can haematemsis be caused by?
Peptic ulcer which erodes through mucosa and fills stomach or duodenum with blood
Bleeding from oesophagel varices
What is the purpose fo the rectum?
To hold faeces until it is appropriate to defacate
What can affect faecal continence?
Neurological pathology
Medications
Natural age-related degenration of nerve innervation of muscle
Affected by constiency of stool
Where does the pelvic cavity lie?
Within the bony pelvis
Continous with abdominal cavity above
Lies between pelvic inlet and pelvic floor
Contains pelvic organs and supporting tissues
What muscle is known as the pelvic floor?
Levator ani muscle, forms the muscolofacial inferior part of the pelvic cavity
Where does the sigmoid colon become the rectum?
Anterior to S3, at the recto-sigmoid junction
Where does the rectum become the anal canal?
Anterior to the tip fo the coccyx just prior to passing through the levator ani muscl
Where is the anus?
Distal end of the anal canal and is the orifice through which faeces pass
Where does the rectal ampulla lie?
Immediately superior to the levator ani muscle
What can the rectal ampulla do?
Relax to accomodate faecal material
What is the levator ani muscle?
Forms most of pelvic diaphragm together with fascial coverings, made up of a number of smaller muscles, forms most of floor of pelvis and roms most of roof of perineum
What type of muscle makes up the levator ani muscle?
Skeletal muscle
What are the 3 muslces that makes up the levator ani?
Pubococcygeus
Puborectalis
Illiococcygeus
What nerve innervates the levator ani?
Pudendal (S2,3,4 keeps the guts off the floor)
Why must the levator ani muscle relax?
To allow for defacation and urination
What is the importance of the puborectalis muscle?
Maintaining faecal continence, contraction of this decreases the anorectal angle, acting like a sphincter
What type of muscle in the puborectalis muscle?
Skeletal muscle
What are the characteristics of the interal anal sphincter?
Smooth muscle
Superior 2/3rds of anal canal
Contraction is stimulated by sympathetic nerves
Contraction is inhibited by parasymp nerves
Contracted all the time, relaxes relexively in response to distension of the rectal ampulla
What are the characterisics of the external anal sphincter?
Skeletal muscle
Inferior 2/3rds of the anal canal
Contraction is stimulated by the pudendal nerve
Voluntarily contracted in response to rectal ampulla distension and internal sphincter relaxation
What are the 2 important spinal cord levels for nerve supply to the rectum/anal canal?
T12-L2
S2-S4
What is the function of the sympathetic fibres on the rectum/anal canal?
Travel to inferior mesenteric ganglia where they synapse then travel via periarterial plexuses around branches of IMA
Contraction of interal anal sphincter and inhibits peristalsis
What is the function of the visceral afferents from S2-4?
Run with parasymps to sense stretch and ischaema
What is the function of the parasym fibres from S2-4?
Travel via pelvic splanchinc and synapse in walls of rectum to inhibit interal anal sphincter and stimualte peristalsis
What is the function of the somatic motor pudendal nerve?
Contraction of external anal sphincter and puborectalis
What is the pectinate line?
Marks the junction between the part of the embry which formed the GI tract (endoderm( and the part that formed the skin (ectoderm)
Superior to line = visceral
Inferior to line = parietal
What are the characterics of nerve supply, arterial supply, venous and lymphatic drainage above the line?
Autonomic
IMA
Hepatic portal system
Inferior mesenteric nodes (interal iliac nodes)
What are the characterics of nerve supply, arterial supply, venous and lymphatic drainage below the line?
Somatic and pudendal
Interal iliac artery
Drains to system venous system via interal iliac
Lymph drains to superficial inguinal nodes
