USMLE First Aid Organ Systems GI

Primitive GI begins to form around which week in embryological development?
4th week

In the 4th week, the endoderm gives rise to
intestinal epithelium and glands

In the 4th week, mesoderm gives rise to
connective tissue, muscle, and wall of intestine

5th Week of Embryological Development
intestine elongates and midgut loop herniates through umbilicus.

Names of limbs of midgut loop and what each limb gives rise to
cranial limb becomes distal duodenum and proximal ileum
caudal limb becomes distal ileum to proximal 2/3rds of transverse colon

What is a key event in the 10th week of development?
midgut loop returns to abdominal cavity in its final fixed position after rotating a total of 270 degrees counterclockwise around axis of the superior mesenteric artery

Failure of bowel to return to the abdomen following herniation of abdominal contents into base of umbilical cord during 5th week of embryonic life. Herniated intestine is covered by peritoneal membrane. Most commonly affects children of mothers of extremes of reproductive age.

Presentation of Omphalocele
2nd trimester ultrasound (95% of cases) or herniated sac found at birth

Associated anomalies of Omphalocele
Beckwith-Wiedemann syndrome: Gigantis, macroglossia, umbilical defect, and hypoclycemia
Pentalogy of Cantrell: Omphalocele, diaphragmatic hernia, cleft sternum, absent pericardium, and intracardiac defects

Diagnosis of Omphalocele
alpha-Fetoprotein (AFP) serum values are elevated in 70% of cases

Full-thickness abdominal wall defect caused by vascular injury during development allowing small or large bowel to escape abdominal cavity. No protective peritoneal membrane covers herniated intestine. Most common in children born to women younger than 20.

Presentation of Gastroschisis
Similar to omphalocele. Extruded abdominal contents are usually right of the abdominal midline

Treatment of Gastroschisis
Artificial covering may be used to minimize heatfluid loss and assist with temperature regulation (exposed bowel causes increased heat loss)

Ladd’s Bands
Aberrant peritoneal attachments that causes partial or complete obstruction of the duodenum due to malrotation during development

Midgut Volvulus
Malrotated intestine twists on axis of SMA, compromising intestinal blood flow

Presentation of Midgut Volvulus
May occur at any time during 1st year of life and presents with sudden onset of severe bilious emesis, abdominal pain and distention, and rectal bleeding

Bilious Emesis
presumed to be midgut volvulus until proven otherwise

Treatment of Malrotation
Ladd’s procedure

Duodenal Atresia
In weeks 6 and 7 of development, duodenum becomes completely obstructed by proliferating endoderm. Failure of duodenum to recanalize by week 10 results in duodenal atresia.

Presentation of Duodenal Atresia
Newborn may be small for gestational age. Vomiting (often bilious) and abdominal distention within 48 hours after birth.

Pyloric Stenosis
Idiopathic congenital elongation and thickening of pylorus, resulting in obstruction of gastric outlet.

Presentation of Pyloric Stenosis
Nonbiliious projectile vomiting at 3-6 weeks but notable absence of other signs of illness (fever, diarrhea)

Diagnosis of Pyloric Stenosis
Palpable mass size of an olive in epigastric region

Margins of Abdomen
Diaphragm superiorly, inlet of pelvis inferiorly

Surface Landmarks of Abdominal Wall
Surface Landmarks of Abdominal Wall

Linea Alba
Vertical fibrous band that extends from symphysis pubis to xiphoid process and lies in midline. Formed by fusion of aponeuroses of muscles of anterior abdominal wall that is represented by a median groove.

Linea Seminlunaris
Lateral edge of rectus abdominis muscle and crosses costal margin at tip of 9th costal cartilage

Inguinal Groove
Formed by rolled-under margin of aponeurosis of external oblique muscle

Transpyloric Plane
Cuts through pylorus horizontally and passes through tips of 9th costal cartilages on each side. Lies at L1.

What does the transpyloric plane identify?
Pylorus of stomach, duodenojejunal junction, neck of pancreas, and hila of kidneys

Subcostal Plane
Horizontal plane joining lowest point of costal margin on each side. Lies at level L3.

Intertubercular Plane
Horizontal plane joining tubercles on iliac crests. Lies at level L5.

McBurney’s Point
RLQ at 2/3rds distance from umbilicus to anterior superior iliac spine. Pain in this location indicates appendicitis.

Abdominal Regions and Contents
Abdominal Regions and Contents

Right Hypochondriac Region
Liver and gallbladder
(Kidney) and suprarenal gland
Colon, hepatic flexure

Epigastric Region
(Transverse colon)
Abdominal aorta and vena cava
Pylorus and duodenum (first part)

Left Hypochondriac Region
(Kidney) and suprarenal gland
Colon, splenic flexure

Right Lumbar Region
Colon, ascending
Small intestine
Duodenum (first part)

Umbilical Region
(Transverse colon)
Duodenum and pancreas
Abdominal aorta and vena cava
Small intestine
Iliac vessels

Left Lumbar Region
Colon, descending
Small intestine (jejunum)

Right Iliac region
Small intestine (ileum)

Hypocastric Region
Distensible organs of pelvis (bladder/uterus)
Small intestine
Iliac vessels
Spermatic cords

Left Iliac Region
Sigmoid colon
Small intestine

Layers of Anterolateral Abdominal Wall
Superficial fascia (fatty Camper’s and membraneous Scarpa’s)
Deep fascia
External oblique muscle – lateral wall
Internal oblique muscle – lateral wall
Transversus abdominis muscle – lateral wall
Transversalis fascia
Extraperitoneal fat
Parietal peritoneum

Abdominal Quadrants and Contents
Abdominal Quadrants and Contents

Inguinal Canal
Site of inguinal hernias

Boundaries of inguinal canal
Deep inguinal ring
Superficial inguinal ring
Anterior wall
Posterior wall

Patent communication between abdominal cavity and scrotal sac
Failure of processus vaginalis to obliterate

Boundaries of Femoral Triangle
Superiorly: Inguinal ligament
Laterally: Sartorius muscle
Medially: Adductor longus muscle

Femoral Canal
Femoral Canal

Third Spacing
Non-intravascular space where fluid and edema can accumulate

Common causes of ascites
Liver failure, right heart failure, ovarian cancer

air or other gas in peritoneal cavity (intestinal/stomach perforation, or intentional insufflation for laparoscopy)

Parietal Peritoneum
Outer membranes that lines deep surface of abdominal walls and inferior surface of diaphragm

Nerve Supply of Parietal Peritoneum
Nerves of surrounding abdominal muscles and skin
Intercostal and phrenic nerves in abdominal region
Obturator nerve in pelvic region

Visceral Peritoneum
Membrane that directly covers abdominal organs. No somatic nerve supply.

Intraperitoneal Viscera
First part of duodenum
Jejunum, ileum, cecum, and appendix
Transverse and sigmoid colon
Proximal rectum
Liver and gallbladder
Tail of pancreas

Extraperitoneal Viscera
Parts 2, 3, and 4 of duodenum
Ascending and descending colon
Distal rectum
Head, neck, and body of pancreas
Abdominal aorta
Inferior vena cava
Kidneys, ureters, and adrenal glands

Lesser Sac (Omental Bursa) of Peritoneal Cavity
Posterior to stomach, liver, and lesser omentum

Epiploic Foramen (Winslow’s Foramen)
Enables communication between greater and lesser sac of peritoneal cavity

Greater Sac
Subdivided by transverse mesocolon into supracolic compartment and infracolic/pelvic compartments below mesocolon

Supracolic Compartment
Divided by falciform ligament

Subphrenic Recess
Area to right of falciform ligament between liver and kidney

Double layer of peritoneum that wraps around abdominal organs, includes blood vessels, and attaches organ to its major blood supply

Gradual occlusion of abdominal aorta can result in
Claudication and impotence

3 Main Branches of Celiac Trunk
Supply structures derived from foregut:
Left gastric
Common hepatic

Abdominal Aorta and Its Branches
Abdominal Aorta and Its Branches

Celiac Trunk
Celiac Trunk

Superior Mesenteric Artery
Supplies derivatives of midgut

Inferior Mesenteric Artery
Supplies hindgut derivatives, distal 3rd of transverse colon, descending colon, sigmoid colon, superior portion of rectum

Should Organ Donation After Death Be Automatic or Not? Essay Sample

Should Organ Donation After Death Be Automatic or Not? Essay Sample

Organ donation seems to be the only hope for many desperate patients with major diseases. A donor may help several people enjoy a healthy life because there are different organs in his body. Also because of the success in transplantation surgeries, organ donation changed to be a solution for those patients. For this reason, many people around the world demand that organ donation should be automatic especially after death. Many other people who find the matter so offensive, both for the dead body and the whole family as well reject this demand. It became a big debate between those who want organ donation after death to be automatic and those who refuse it.

On the first side, rejecting automatic organ donation after death lies behind many reasons. These people find that the idea looks insulting and humiliating to the dead bodies. They have their religious, personal and even cultural reasons to refuse it, too. Automatic donation after death destroys the inalienable right to deal with the dead bodies. Hospitals will be turned to be donors and patients will be put under great pressures. The evidence shows a big problem that the donated organs are removed while the person is dying not after death. Former transplant doctors confess that organs for transplant are workable if the donor is still alive, so they abandoned the practice. These people believe that removing organs of the dead body adds more sorrow to his family. Therefore automatic organ donation will be the most alarming violation of human rights and a decline into oppression.

On the other side, those who demand organ donation to be automatic have their own reasons and evidence. They depend on statistics and researches. They believe that through donating organs after death, they can bring a person back from the brink. They say that with providing more organs, more sick patients can be rescued. They want to make organ donation automatic since the body should belong to the government after death. Statistics show that every ten minutes a new patient needs organ transplantation. The number of patients is increasing so fast which implies a quick decision on this issue. In fact, organ donation is important and that we have to educate all the people on the great gift and favor that they can do at the end of their lives.

The idea of automatic organ donation looks so argumentative as not all the people can accept it or agree to carry it out. Those who reject feel more passionate about the dead bodies. They deal with respect to their dead persons. They refuse to let the dead humiliated and buried in bad shape. They also believe that a human body should be dealt with more respect even after death. On the other hand, we find the others demand to apply an implementation to make organ donation automatic for more practical reasons. They added that a dead body doesn’t feel pain and can create a life from tragedy. They want to lessen the cost of these organs when they are available.

In brief, organ donation is a gift of life and a solution to many desperate patients. Thus making it automatic became a most for many people. It also seems to be offensive and oppressive for others. Despite both have their own reasons, still the idea so complicated and need to be settled down with more realistic thinking. We have to give hope to patients and watch out the whole process.