1. Length of Vas deferens or ductus deferens
2. Length of thoracic duct
3. Length of Spinal cord
4. Femur (for 6 feet person)
5. Length of transverse colon
6. Distance from the incisor teeth to the cardiac end of the stomach
7. Umbilical cord at birth
8. Length of sartorius muscle

All are about 25 cms or 10 inches:

1. Length of Esophagus
2. Length of Ureter
3. Length of Duodenum
4. Length of Descending colon

All are about 10 cms or 4 inches:

1. Length of Trachea
2. Length of Fallopian or Uterine tube
3. Length of Common bile duct
4. Length of 3rd part of Duodenum (Transverse Duodenum)
5. Length of Posterior wall of Vagina
6. Anteroposterior measurement of Inlet of Pelvis
7. Transverse measurement of Outlet of Pelvis

All are about 4 cms or 1.5 inches:

1. Length of Auditory tube
2. Length of Anal canal
3. Length of Female urethra
4. Length of Cystic duct
5. Length of Common hepatic duct
6. Length of External acoustic/auditory meatus when measured from tragus
7. Length of Optic nerve
8. Length of Ovary
9. Length of Inguinal canal
10. Length of Femoral sheath
11. Thickness of Kidney
12. Width of Pons

All are about 1 inch or 2.5 cm

1. Length of Medulla
2. Length of Midbrain
3. Length of Pons
4. Length of 4th part of Duodenum (Ascending Duodenum)
5. Length of Ducts of Bartholin’s gland (Greater vestibular glands)
6. Diameter of Trachea
7. Diameter of Right main bronchus
8. Distance between Ureteric orifice in Empty bladder

Structures whose width is greater than length:

1. Pons varioli
2. Cecum
3. Prostate

Descent of Testis:

1. 3rd month: Reaches Iliac fossa
2. 6th month: Rests at Deep Inguinal ring
3. 7th month: Traverses Inguinal canal
4. 8th month: Reaches Superficial Inguinal ring
5. 9th month: Descneds into Scrotum

Rule of 2s for Meckel’s Diverticulum:

Meckel’s Diverticulum is a congenital outpouching of the ileum that is a normal variant and is the remnant of omphalomesenteric (vitellointestinal) duct. It is a true diverticulum, that consists of all the layers of the intestinal wall (mucosa, submucosa and muscularis).

1. Occurs in 2% population
2. 2 times more common in male
3. 2 feet proximal to ileocecal valve
4. 2 inches in length
5. 2 years of age is typical for onset of symptoms
6. 2 % are symptomatic
7. 2 types of mucosa possible (Small intestine and Gastric)

Rule of 2s: 2nd week of Development (Embryology)

1. Trophoblast differentiates into 2 layers: Cytotrophoblast and Sycytiotrophoblast
2. Embryoblast forms 2 layers: Epiblast and Hypoblast
3. Extraembryonic mesoderm splits in 2 layers: Somatopleure and Splanchnopleure
4. 2 cavities are formed: Amniotic cavity and Yolk sac cavity

Rule of 3s: Thoracic spine levelling

1. T1-3 (and T12) transverse processes are at the level of the corresponding thoracic spine.
2. T4-6 (and T11) transverse processes lie superiorly between its level’s spine and the spine of the thoracic segment above it.
3. T7-9 (and T10) transverse processes lie superiorly at the level of the superior segment’s spine.

Rule of 3s: 3rd week of Development

1. Bilaminar germ disc changes into trilaminar germ disc with 3 layers ectoderm, mesoderm and endoderm
2. Formation of 3 important structures: Notochord, Neural plate and Primitive streak
3. 3 layered chorionic villi
4. 3 carnegie stages

Dalley/Voss Rule of 3s of 2s: Sacral Plexus

For 3 sets of 3 nerves:

• 1st set of 3 nerves will all have 3 spinal contributions (3,3,3)
• 2nd set of will have 2 nerves with 3 spinal contributions and 1 nerve with 2 spinal contributions (3,3,2)
• 3rd set will have 1 nerve with 3 spinal contributions and 2 nerves with 1 spinal contribution (3,2,2)

1st set of nerves (3,3,3):

1. Superior gluteal nerve: 3 spinal contributions beginning from L4 (L4,L5,S1)
2. Inferior gluteal nerve: 3 spinal contributions beginning from L5 (L5,S1,S2)
3. Posterior femoral cutaneous nerve: 3 spinal contributions beginning from S1 (S1,S2,S3)

2nd set of nerves (3,3,2):

1. Nerve to Quadratus femoris: 3 spinal contributions beginning from L4 (L4,L5,S1)
2. Nerve to Obturator internus: 3 spinal contributions beginning from L5 (L5,S1,S2)
3. Nerve to Piriformis: 2 spinal contributions beginning from S1 (S1,S2)

3rd set of nerves (3,2,2):

1. Pudendal nerve: 3 spinal contributions beginning from S2 i.e. where you left off with pyriformis (S2,S3,S4)
2. Nerve to levator ani: 2 spinal contributions beginning from S3 (S3,S4)
3. Nerve to coccygeus:2 spinal contributions beginning from S4 (S4,S5)

Gate’s Rule of 4s: For Detecting Brainstem Lesion

There are 4 rules in Rules of 4s:

1. 4 structures in the “M“idline begins with “M“: Motor pathway (Corticospinal Tract), Medial Lemniscus, Medial longitudinal fasciculus, Motor nucleus and nerves (CN 3,4,6,12)
2. 4 structures to the “S“ide begins with “S“: Spinothalamic, Spinocerebellar tract, Sensory nucleus of CN V, Sympathetic pathway
3. 4 Cranial nerves in Each of:
• Medulla: 9,10,11,12
• Pons: 5,6,7,8
• Above Pons: 1,2,3,4
4. The 4 midline motor nuclei can exactly divide 12 (excluding 1 and 2 which are purely sensory) – 3, 4, 6 and12 (Remaining 4 motor nuclei are on sides/laterally i.e 5, 7, 9 and 11).

Associated deficits of 4 Midline “M” structures:

1. Motor pathway (or corticospinal tract): contralateral weakness of the arm and leg.
2. Medial Lemniscus: contralateral loss of vibration and proprioception in the arm and leg.
3. Medial longitudinal fasciculus: ipsilateral internuclear ophthalmoplegia (failure of adduction of the ipsilateral eye towards the nose and nystagmus in the opposite eye as it looks laterally).
4. Motor nucleus and nerve: Ipsilateral loss of affected cranial nerve function (3, 4, 6 or 12).

Associated deficits of 4 Side “S” structures:

1. Spinocerebellar pathways: ipsilateral ataxia of the arm and leg.
2. Spinothalamic pathway: contralateral alteration of pain and temperature affecting the arm, leg and rarely the trunk.
3. Sensory nucleus of 5th Cranial nerve: ipsilateral alteration of pain and temperature on the face in the distribution of the 5th cranial nerve (this nucleus is a long vertical structure that extends in the lateral aspect of the pons down into the medulla).
4. Sympathetic pathway: Ipsilateral Horner’s syndrome i.e ptosis, miosis, anhydrosis.

Associated deficits of 4 Cranial nerves in Medulla:

1. 9th or Glossopharyngeal: ipsilateral loss of pharyngeal sensation
2. 10th or Vagus: ipsilateral palatal weakness
3. 11th or Spinal accessory: ipsilateral weakness of the trapezius and sternocleidomastoid muscles
4. 12th or Hypoglossal: ipsilateral weakness of the tongue

Associated deficits of 4 cranial nerves in Pons:

1. 5th or Trigeminal: ipsilateral alteration of pain, temperature and light touch on the face back as far as the anterior two-thirds of the scalp and sparing the angle of the jaw
2. 6th or Abducens: ipsilateral eye abduction weakness
3. 7th or Facial: ipsilateral facial weakness
4. 8th or Auditory: ipsilateral deafness

Associated deficits of 4 cranial nerves above Pons:

1. 1st or Olfactory: not in midbrain.
2. 2nd or Optic: not in midbrain.
3. 3rd or Occulomotor: impaired adduction, supraduction and infraduction of the ipsilateral eye (eye is turned out and slightly down)
4. 4th or Trochlear: eye unable to look down when the eye is looking in towards the nose

Applying the knowledge:

Pathways and tracts pass through the entire length of brainstem and can be likened  to “meridians of longitude” whereas the cranial nerves can be likened to “parallels of latitude”. To establish the site of brainstem lesion, you need to detect the point of intersection of the meridians of longitude and parallels of latitude. Thus a medial brainstem syndrome will consist of the deficits of 4 “M”s and the relevant motor cranial nerve, and a lateral brainstem syndrome will consist of the deficits of 4 “S”s and either the 9–11th cranial nerve if in the medulla, or the 5th, 7th and 8th cranial nerve if in the pons.

Example:

58 years old lady with left hemiparesis, Left side loss of proprioception and right sided tongue deviation.

1. Left hemiparesis is associated with deficit of Motor or corticospinal pathway of Right side which lies medially
2. Left sided loss of proprioception is associated with deficit of medial lemniscus of Right side which lies medially
3. Right sided tongue deviation is associated with deficit of Cranial nerve 12 on Right side which lies medially in medulla

Diagnosis: Medial medullary syndrome due to lesion in right vertebral artery

Rule of 7s: For Orbit

There are 7 bones, 7 intraorbital muscles and 7 nerves in orbit

• 7 Bones: Frontal, Ethmoid, Lacrimal, Sphenoid, Zygomatic, Palatine, Maxilla
• 7 intraorbital muscles: Levator palpebrae, 4 recti (Superior, Inferior, Medial and Lateral), 2 oblique (Superior and Inferior)
• 7 orbital nerves: Optic (CN II), Occulomotor (CN III), 3 branches of Opthalmic nerve (CN V1) – Frontal, Nasociliary, Lacrimal, Abducens nerve (CN VI)

Definition:

Size and Extent:

• Length: About 25 cm (10 inches)
• Diameter: About 3 mm
• Extent: Pelviureteric junction to urinary bladder

Location:
Retroperitoneal structure in the posterior abdominal wall (upper part) and lateral pelvic wall (lower part)

Parts, Courses and Relations:

A) Pelvis of Ureter:

• Arises from the renal pelvis (leaves kidney from hilum situated medially) formed by calyces encircling the renal papillae
• Descends along the medial margin of the kidney
• At the lower end of kidney, it becomes continuous with the abdominal ureter

B) Abdominal ureter:

• Passes downwards and medially to lie on the medial edge of psoas major
• Then enters into the pelvis at the bifurcation of the common iliac artery in front of the sacroiliac joint.
• Anteriorly, the right ureter is covered at its origin by the 2nd part of the duodenum and then lies lateral to the inferior vena cava and behind the posterior peritoneum
• Right ureter is crossed by the testicular (or ovarian), right colic, and ileocolic vessels. The left ureter is crossed by the testicular (or ovarian) and left colic vessels
• Then passes above the pelvic brim, behind the mesosigmoid and sigmoid colon to cross the common iliac artery immediately above its bifurcation and enter the true (lesser) pelvis

C) Pelvic ureter:

• Runs downwards and backwards on the lateral pelvic wall in front of the internal iliac artery to reach just in front of the ischial spine
• Then turns forwads and medially to enter the urinary bladder
• In the male it lies above the seminal vesicle near its termination and is crossed superficially by the vas deferens
• In the female, the ureter passes above the lateral fornix of the vagina lateral to the supravaginal portion of the cervix and lies below the broad ligament and uterine vessels

D) Intravesical ureter:

• Passes obliquely through the wall of the bladder and open into it at the lateral angle of trigone

Normal Ureteric Contrictions:

A) 3 Anatomical Constrictions:

1. Pelviureteric junction
2. Pelvic brim (Crossing of iliac vessels)
3. Ureterovesical junction

B) 5 Surgical Constrictions:

1. Pelviureteric junction
2. Pelvic brim (Crossing of iliac vessels)
3. Crossing of Vas deferens(♂) / Broad ligament(♀)
4. Ureterovesical junction
5. Ureteric orifice (Intravesical)

These sites of ureteral narrowing are clinically significant because they are common locations for urinary calculi to lodge during passage.

Comparison with Esophageal constrictions:

Esophagus has 4 constrictions but ureter as 5 constrictions (surgical).

1. Cricopharyngeal = Pelviureteric
2. Crossing of aorta = Crossing of iliac artery
3. Crossing of left main bronchus = Crossing of vas deferens/broad ligament
4. Diaphragmatic hiatus = Ureterovesical junction

Blood Supply:

1. Abdominal part: Branches from Renal artery, Abdominal aorta and Gonadal artery
2. Pelvic part:

• As it crosses pelvic brim: Branches from Common Iliac and Internal Iliac arteries
• Inside the pelvis: Inferior vesical artery (Male) and Uterine artery (Female)

Veins correspond to the arteries

Nerve Supply:

• Sympathetic: T10-L1 spinal segments
• Parasympathetic: S2-S4 nerves

Histology:

From inside to outside

1) Mucosa:

• Presents a few longitudinal folds giving its lumen a star shaped appearance
• Epithelial lining: Transitional epithelium
• Lamina propria: Fibrous tissue containing many elastic fibers, blood vessels and nerves

2) Muscularis:

• Smooth muscles
• Upper 2/3 of ureter: Inner longitudinal and Outer circular fibers
• Lower 1/3 of ureter: Inner longitudinal, Middle circular and Outer Longitudinal fibers

3) Adventitia:

• Fibrous connective tissue
• A portion of the ureter has serosa (mesothelium/simple squamous epithelium) covering it

Development of Ureter:

1. Mesodermal in origin
2. Metanephric duct (Ureteric bud) appears as a diverticulum at the lower end of the mesonephric duct
3. The metanephric duct (Ureteric bud) develops into the ureter, pelvis, calyces and collecting tubules
4. On top of metanephric duct, later a cap of tissue differentiates to form the definitive kidney or metanephros which develops into the glomeruli and the proximal part of the renal duct system.

Congenital anomalies:

1. Ureteral duplication: The mesonephric duct may give off a double metanephric bud so that 2 ureters may develop on one side (Double ureter) or both sides (Bifid ureter). These ureters may fuse into a single duct anywhere along their course or open separately into the bladder

2. Ectopic ureter: Extra ureter may open ectopically into the vagina or urethra resulting in urinary incontinence.

3. Retrocaval ureter: Ureter deviates medially and passes behind the inferior vena cava, winding about and crossing in front of it from medial to lateral side. It may lead to right lumbar pain, recurrent urinary tact infections or episodes of acute pyelonephritis.

Detecting Ureteric Calculi:

Calculi in left ureter lateral to spine

In searching for a ureteric stone on a plain radiograph of the abdomen, one must imagine the course of the ureter in relation to the bony skeleton. It lies along the tips of the transverse processes, crosses in front of the sacroiliac joint, swings out to the ischial spine and then passes medially to the bladder.

An opaque shadow along this line is suspicious of calculus. This course of the ureter is readily studied by examining a radiograph showing a radio-opaque ureteric catheter in situ.

Summary:

Transpyloric plane passes through:

1. L1 (1st lumbar) vertebra
2. Pylorus of stomach
3. Neck of pancreas
4. Duodenojejunal flexure
5. Fundus of gall bladder
6. Tip of 9th costal cartilage
7. Hila of kidneys
8. Origin of portal vein from superior mesenteric and splenic vein
9. Root of transverse mesocolon
10. 2nd part of duodenum
11. Origin of superior mesenteric artery
12. Hilum of spleen
13. Termination of spinal cord

Although the appendix serves no digestive function, it is thought to be a vestigial remnant of an organ that was functional in human ancestors.

The length varies from 2 to 20 cm with an average of 9 cm with diameter of about 5mm. It is longer in children compared to adults. In the fetus it is a direct outpouching of the caecum, but differential overgrowth of the lateral caecal wall results in its medial displacement.

The appendix is suspended by a small traignular fold of peritoneum, called the mesoappendix.

Clinical

• Inflammation of the appendix is known as the appendicitis. Acute appendicitis is a common cause of abdominal pain requiring surgery, particularly in the West where there is low roughage diet. Appendicitis usually follows obstruction of the lumen with distal infection and ulceration. The usual causes are: fecolith, calculi, foreign body, tumor, worms (Oxyuriasis vermicularis), diffuse lymphoid hyperplasia, vascular occlusion, inadequate dietary fiber intake, etc.

• The lumen of the appendix is relatively wide in the infant and is frequently completely obliterated in the elderly. Since obstruction of the lumen is the usual precipitating cause of acute appendicitis it is not unnatural,therefore, that appendicitis should be uncommon at the two extremes of life. It is seen more commonly in older children and young adults.

Location of Appendix:

• Right lower quadrant of abdomen and more specifically right iliac fossa.
• McBurney’s point lying at the junction of lateral one-third and the medial two-thirds of the line joining the umbilicus to the right anterior superior iliac spine roughly corresponds to the position of the base of the appendix.
• McBurney’s point is the site of maximum tenderness in appendicits.

Clinical

• Examination of a case of acute appendicitis reveals following physical signs:
  1. Hyperaesthesia in the right iliac fossa
  2. Tenderness at McBurney’s point
  3. Muscle guard and rebound tenderness over the appendix

• Appendicectomy is usually performed through a muscle-splitting incision in the right iliac fossa. The caecum is delivered into the wound and, if the appendix is not immediately visible, it is located by tracing the taeniae coli along the caecum—they fuse at the base of the appendix. When the caecum is extraperitoneal it may be difficult to bring the appendix up into the incision; this is facilitated by first mobilizing the caecum by incising the almost avascular peritoneum along its lateral and inferior borders.

Variations in Appendix position:

Although the base of the appendix is fixed, the tip can point in any direction. Hence, the position of the appendix is extremely variable. The appendix is the only organ in the body which is said to have no anatomy. When compared to the hour hand of a clock, the positions would be:

1. 12 o clock: Retrocolic or retrocecal (behind the cecum or colon)
2. 2 o clock: Splenic (upwards and to the left – Preileal and Postileal)
3. 3 o clock: Promonteric (horizontally to the left pointing the sacral promontory)
4. 4 o clock: Pelvic (descend into the pelvis)
5. 6 o clock: Subcecal (below the cecum pointing towards inguinal canal)
6. 11 o clcok: Paracolic (upwards and to the right)

Most common position of appendix (75% of cases): Retrocecal
Second most common position of appendix (20% of cases): Subcecal
If the appendix is very long, it may actually extend behind the ascending colon and abut against the right kidney or the duodenum; in these cases its distal portion lies extraperitoneally.

Clinical

The location of the tip of the appendix determines early signs and symptoms of appendicitis.

• Retrocecal: Extension of the hip joint may cause pain because the appendix is disturbed by stretching of the psoas major muscle. Pain usually localizes in the right flank.
• Pelvic: Pain may be felt when the thigh is flexed and medially rotated, because the obturator internus is stretched. Pelvic appendix may irritate the bladder or rectum causing suprapubic pain, pain with urination, or feeling the need to defecate.
• Retroileal: In some males, it can irritate the ureter and cause testicular pain.
• Pregnancy: the appendix can be shifted and patients can present with RUQ (Right upper quadrant) pain.

Arterial Supply:

1. Appendicular artery: The mesoappendix, containing the appendicular branch of the ileocolic artery (branch of superior mesenteric artery), descends behind the ileum.
2. Accessory appendicular artery: An accessory appendicular artery can branch from the posterior cecal artery which is also a branch of ileocolic artery.

Clinical

• Acute infection of the appendix may result in thrombosis of the appendicular artery with rapid development of gangrene and subsequent perforation.
• The accessory appendicular artery can lead to significant intraoperative and postoperative hemorrhage and should be searched for carefully and ligated once the main appendicular artery is controlled.

Venous drainage:
Appendicular vein –> Ileocolic vein –> Superior mesenteric vein –> Portal vein

Lymphatic drainage:

• There is abundant lymphoid tissue in its walls.
• From the body and apex of the appendix 8-15 vessels ascend in the mesoappendix and are ocasionally interrupted by one or more nodes –> unite to form 3 or 4 larger vessels –> inferior and superior ileocolic nodes
• A few of them pass indirectly through the appendicular nodes situated in the mesoappendix.

Clinical

Appendicular dyspepsia: Chronic appendicits produces dyspepsia resembling disease of stomach, duodenum or gall bladder. It is due to passage of infected lymph to the subpyloric lymph nodes which causes irritation of pylorus.

Nerve supply:

1. Sympathetic nerves: T9 and T10 spinal segments through the celiac plexus
2. Parasympathetic nerves: Vagus

Clinical

Both the appendix and the umbilicus are innervated by segment T10 of the spinal cord and hence the pain caused by appendicitis is first felt in the region of umbilicus (referred pain). With increasing inflammation pain is felt in the right iliac fossa due to involvement of the parietal peritoneum of the region which is sensitive to pain in contrast to pain insensitive visceral peritoneum.

Histology: Inside to outside

1. Mucosa:

• No villi
• Epithelium invaginates to form crypts of Liberkuhn but the crypts do not occur as frequently as in the colon
• Muscularis mucosae is ill defined

2. Submucosa:

• Large accumulations of lymphoid tissue in the lamina propria and submucosa. Hence appendix is also called abdominal tonsil.
• There is often fatty tissue in the submucosa.

3. Muscularis externa:

• Thinner than in the remainder of the large intestine
• Comprises 2 layers: Inner circular muscle layer and Outer longitudinal muscle layer
• Outer longitudinal smooth muscle layer does not aggregate into taenia coli

4. Serosa and peritoneum

Clincial:

The submucosal lymphoid follicles enlarge, peak from 12-20 years, and then decrease. This correlates with the incidence of appendicitis. Enlarged or hyperplastic lymhoid follicles contribute to the obstruction of small lumen of appendix.

Pathology:

In acute appendicitis, the microscopy of cross section of appendix reveals:

1. Fibrin on peritoneal surface
2. Neutrophil exudate in lumen
3. Neutrohpil exudate spreads in submucosa and soon affects all layers