Anatomy Flashcards
Large intestine components (proximal to distal)
Colon (caecum, appendix, ascending, transverse, descending, sigmoid)
Rectum
Anal Canal
Anus
Large intestine functions
Defence = Commensal bacteria Absorption = H2O and electrolytes Excretion = Formed stool
Where are the Paracolic Gutters?
Between the lateral edge of the ascending and descending colon, and abdominal wall.
Potential for pus/fluid collection
What are haustra and why do they occur?
Small “pouches” along the colon
Formed by tonic contraction of the teniae coli
What are teniae coli?
Three distinct longitudinal bands of thickened smooth muscle. Run from caecum to distal end of sigmoid colon.
What is the most common position of the appendix?
Retrocaecal
Variation in appendix position causes…..?
Variation in pain felt with appendicitis
Where is the appendiceal orifice found?
Posteromedial wall of caecum (below the ileocaecal orifice)
What is McBurney’s point?
Point 1/3rd of the way between the right ASIS and umbilicus. Should correspond to appendiceal orifice. Should be point of maximum tenderness.
Where does the sigmoid colon lie?
Left iliac fossa
What do you call the long mesentery specific to the sigmoid colon?
Sigmoid Mesocolon
Due to it’s degree of movement, what is a particular risk to the sigmoid colon?
Twisting around itself (sigmoid volvulus). Causes obstruction, ishaemia, infarction and rupture
Where does the abdominal aorta sit?
Midline, retroperitoneal, anterior to vertebral bodies, left of IVC
Three midline branches of the abdominal aorta
Celiac trunk (forgeut)
Superior mesenteric artery (midgut)
Inferior mesenteric artery (hindgut)
Lateral branches of the abdominal aorta supply…?
Kidneys/adrenal glands
Gonads
Body wall (posterolateral)
Abdominal aorta bifurcates into…?
Common iliacs (then to internal and external iliac)
Superior mesenteric branches (Superior to Inferior)
Inferior pancreaticoduodenal Middle colic Right colic Ileocolic Jejunal and Ileal Appendicular
Inferior mesenteric branches (Superior to Inferior)
Left colic
Sigmoid colic
Superior rectal
What is the marginal artery of Drummond?
An anastomoses between the superior and inferior mesenteric artery branches
Why is the marginal artery of Drummond important?
Helps to prevent ischaemia by providing collateral route for blood flow
Describe the blood supply of the rectum and anal canal
Inferior mesenteric artery = proximal half of anal canal (to pectinate line)
Internal iliac artery = Rest of anal canal
Anastomoses between
How could peptic ulcers cause haematemesis?
Peptic ulcer erodes mucosa of stomach/duodenum, through to blood supply, which then fills stomach/duodenum
What is an oesophageal varice?
Abnormal, dilated veins. Thin-walled, so rupture easily, causing bleeding into oesophagus
What could cause haematemesis?
Peptic/Duodenal Ulcers
Oesophageal Varices
Venous drainage - Inferior Vena Cava
Drains cleaned blood from hepatic veins into right atrium
Venous drainage - Hepatic Portal Vein
Drains from forget, midgut and hindgut to the liver for first pass metabolism
Venous drainage - Splenic Vein
Drains from foregut to hepatic portal vein
Venous drainage - Superior Mesenteric Vein
Drains from midgut to hepatic portal vein
Venous drainage - Inferior Mesenteric Vein
Drains hindgut to splenic vein
Where are the three “portal systemic anastomoses”?
Distal end of the oesophagus
Skin around the umbilicus
Rectum/anal canal
Describe veins involved in the oesophageal anastomoses
Inferior part drains to hepatic portal vein
Superior part drains to azygous vein
Describe the veins involved in the anastomoses around the umbilicus
Inferior epigastric vein
Usually) closed ligamentum teres (round ligament
How could the three anatomical anastomoses become varicosed?
Portal hypertension causes blood to be diverted through the collateral veins back to the systemic venous circulation. Increased blood volume = dilation (varicosed)
Muscles of Mastication
Masseter
Temporalis
Medial Pterygoid
Lateral Pterygoid
At which joint does jaw opening and closing occur?
Temporomandibular Joints
Synovial joint between mandibular fossa and articular tubercle of temporal bone AND head of condylar process of mandible
Four Types of Papillae on the Tongue
With tastebuds =
Foliate
Vallate
Fungiform
Without tastebuds =
Filiform
Components of the Distal GI Tract
Rectum
Anal Canal
Anus
Components Necessary for Faecal Continence
Holding area = rectum
Visceral afferent nerve fibres = fullness
Functioning muscle sphincters = contract and relax to prevent and allow defecation
Normal cerebral function = control time of defecation
Factors Affecting Faecal Continence
Neurological pathology
Medications
Age-related degeneration muscle nerve innervation
Consistency of stool
Pelvic Cavity
Between pelvic inlet and pelvic floor
Contains pelvic organs and supporting tissues
Rectum located here
Anatomical Locations of Distal GI Tract
Rectosigmoid junction = S3 Rectum becomes anal canal = anterior to tip of the coccyx Anus = orifice through which faeces pass Pelvis = rectum Perineum = anal canal, anus
Rectum
Rectal ampulla = superior to levator ani muscle
Walls relax to accomodate faeces
Anatomical Relationships of Rectum
Male = Prostate lies anterior Female = Vagina and cervix lie anterior
Components of Levator Ani
Iliococcygeus Pubococcygeus Puborectalis All skeletal muscle Supplied by nerve to levator ani Forms floor of pelvis/roof of peritoneum
Levator Ani Function
All skeletal muscle
Forms floor of pelvis/roof of peritoneum
Tonic contraction provides support for pelvis organs
Relax to allow defecation and urination
Puborectalis
Forms a sling around the rectum
Contraction decreases anorectal angle, acting like a sphincter
Skeletal muscle
Voluntary contraction helps to maintain continence
Anal Sphincters
One internal = smooth muscle
One external = skeletal muscle
Overlap between the two
Internal Anal Sphincter
Superior two thirds of anal canal
Contraction = Sympathetic
Relaxation = Parasympathetic
Tonic contraction, reflexive relaxation due to distension of rectal ampulla
External Anal Sphincter
Inferior two thirds of anal canal
Contraction = pudendal nerve
Voluntarily contracted due to rectal ampulla distension and internal anal sphincter relaxation
Nerve Supply to Pelvic Structures
Body cavity
Sympathetic, parasympathetic, visceral afferent
Nerve Supply to Perineum Structures
Body Wall
Somatic motor and somatic sensory
Somatic Motor Supply to Anal Canal
Via pudendal nerve and nerve to levator ani
Leave SC from S2-S4
Contraction of external anal sphincter and puborectalis
Parasympathetic Supply to Rectum
Via pelvic splanchnic nerves, synapsing in rectum wall
Leave SC from S2-S4
Inhibit internal anal sphincter
Stimulate peristalsis
Visceral Afferent Supply to Rectum
Run with parasympathetics
Enter SC by S2-S4
Sense stretch, ischaemia etc.
Sympathetic Supply to Rectum
Via inferior mesenteric ganglia, synapsing, then via periarterial plexuses around branches of IMA
Leave SC from T12-L2
Contraction of internal anal sphincter
Inhibit peristalsis
Pudendal Nerve
Branch of sacra plexus S2, S3, S4 anterior rami Supplies external anal sphincter Exits pelvis via greater sciatic foramen Enters perineum via lesser sciatic foramen Branches to supply perineum structures
Pudendal Nerve or Sphincter Damage
Can occur during pregnancy
Stretching of nerve fibres or tearing of muscle fibres
= Weakened muscle
Faecal incontinence
Pectinate Line
Marks junction between visceral and parietal parts
Different arterial, venous, lymphatic and nerve supply at either side
Superior to Pectinate Line
Nerve = autonomic Arterial = inferior mesenteric artery Venous = portal venous system (IMV) Lymphatics = inferior mesenteric nodes (internal iliac nodes)
Inferior to Pectinate Line
Nerve = somatic and pudendal Arterial = internal iliac artery Venous = systemic venous system (internal iliac) Lymphatics = superficial inguinal nodes
Lymphatics of Pelvis
Tend to lie alongside arteries
Internal iliac = drains inferior pelvis structures
External iliac = drains lower limb, and more superior pelvic structures
Common iliac = drains external and internal iliac
Lymph then drains to lumbar nodes, thoracic duct then left sternal angle
Haemorrhoids
Prolapses of the rectal venous plexuses
Not related to portal hypertension
Due to raised pressure e.g. chronic constipation, straining, pregnancy
Ischioanal Fossae
Right and left, but communicate posteriorly
Form a “U” shape around the anal canal
Filled with fat and connective tissue
Infection here is called an ischioanal abscess
