Файл: Kaplan USMLE-1 (2013) - Anatomy.pdf

Section Ill • Gross Anatomy

Figure 111-3-39. Abdomen: CT, L4

ChapterSummary

•The abdominal wall consists primarily of 3 flat muscles (external oblique, internal oblique, and transversus abdominis muscles), rectus abdominis muscle, and the transversalis fascia.

•The inguinal canal contains the round ligament in the female and the spermatic cord in the male. The inguinal canal is an oblique canal through the lower abdominal wall beginning with the deep inguinal ring laterally and the superficial inguinal ring medially. Weakness ofthe walls ofthe canal can result in 2 types of inguinal hernias: direct and indirect.

•A direct hernia emerges through the posterior wall ofthe inguinal canal medial to the inferior epigastric vessels.

•An indirect hernia passes through the deep inguinal ring lateral to the inferior epigastria vessels and courses through the inguinal canal to reach the superficial inguinal ring.

•A persistent processus vaginalis often results in a congenital indirect inguinal hernia.

•The gastrointestinal (GI) system develops from the primitive gut tube formed by the incorporation ofthe yolk sac into the embryo during body foldings.

The gut tube is divided in the foregut, midgut, and hindgut.

•Defects in the development of the GI tract include annular pancreas, duodenal atresia, Meckel diverticulum, and Hirschsprung disease.

(Continued)

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Chapter 3 • Abdomen, Pelvis, and Perineum

ChapterSummary (Cont'd)

•The foregut, midgut, and hindgut are supplied by the celiac trunk, superior mesenteric artery, and inferior mesenteric artery, respectively. These arteries and their branches reach the viscera mainly by coursing in different parts of the visceral peritoneum. Venous return from the abdomen is provided by the tributaries of the inferior vena cava, exceptfor the GI tract. Blood flow from the GI tract is carried by the hepatic portal system to the liver before returning to the inferior vena cava by the hepatic veins.

•Diseases ofthe liver result in obstruction offlow in the portal system and portal hypertension. Four collateral portal-caval anastomoses develop to provide retrograde venous flow back to the heart: esophageal, rectal, umbilical, and retroperitoneal.

•The viscera ofthe GI system are covered by the peritoneum, which is divided into the parietal layer lining the body wall and the visceral layer extending from the bodywall and covering the surface ofthe viscera. Between these layers is the potential space called the peritoneal cavity.

•The peritoneal cavity is divided into the greater peritoneal sac and the lesser peritoneal sac (omental bursa). Entrance into the omental bursa from the greater sac is the epiploic foramen that is bound anteriorly by the lesser omentum and posteriorly by the inferior vena cava.

•The kidneys develop from intermediate mesoderm by 3 successive renal systems: pronephros, mesonephros, and metanephros. The mesonephric kidney is the first functional kidney that develops during the first trimester.

The final or metanephric kidney develops from 2 sources: the ureteric bud that forms the drainage part of the kidney and the metanephric mass thatforms the nephron ofthe adult kidney.

•The urinary bladder develops from the urogenital sinus, which is formed after division of the cloaca by the urorectal septum.

•The kidneys are located against the posteriorabdominal wall between the T12 and L3 vertebrae. Posterior to the kidneys lie the diaphragm and the psoas major and quadratus lumborum muscles. The superior pole of the kidney

lies against the parietal pleura posteriorly. The ureters descend the posterior abdominal wall on the ventral surface ofthe psoas major muscle and cross the

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Section Ill • Gross Anatomy

ChapterSummary(Cont,d)

Pelvis

•The pelvic cavity contains the inferior portions ofthe GI and urinary systems along with the reproductive viscera. The pelvic viscera and their relationships are shown for the male and female pelvis in Figures 111-3-26 and 111-3-27, respectively.

•There are 2 important muscular diaphragms related to the floor of the pelvis and the perineum: the pelvic diaphragm and the urogenital diaphragm, respectively. Both of these consist of 2 skeletal muscle components under voluntary control and are innervated by somatic fibers ofthe lumbosacral plexus.

•The pelvic diaphragm forms the floor of the pelvis where it supports the weight ofthe pelvic viscera and forms a sphincter for the anal canal. The urogenital diaphragm is located in the perineum (deep perineal space) and forms a sphincter for the urethra. Both diaphragms are affected by an epidural injection.

•The broad ligament ofthe female is formed by 3 parts: the mesosalpinx, which is attached to the uterine tube; the mesovarium attached to the ovary; and the largest component, the mesometrium, attached to the lateral surface ofthe uterus. In the base of the broad ligament, the ureter passes inferior to the uterine artery just lateral to the cervix.

•The suspensory ligament of the ovary is a lateral extension of the broad ligament extending upward to the lateral pelvic wall. This ligament contains , the ovarian vessels, lymphatics, and autonomic nerves.

Perineum

•The perineum is the area between the thighs bounded by the pubic symphysis, ischial tuberosity, and coccyx. The area is divided into 2 triangles. Posteriorly, the anal triangle contains the anal canal, external anal sphincter, and the pudenda! canal that contains the pudenda! nerve and internal pudenda! vessels. Anteriorly is the urogenital triangle, containing the external and deep structures ofthe external genitalia.

•The urogenital triangle is divided into 2 spaces. The superficial perinea[ space contains the root structures ofthe penis and clitoris, associated muscles, and the greatervestibular gland in the female. The deep perineal space is formed by the urogenital diaphragm and contains the bulbourethral gland in the male.

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Section Ill • Gross Anatomy

MUSCLE INNERVATION

Terminal Nerves of Upper Limbs

The motor innervation by the 5 terminal nerves of the arm muscles is summa­ rized in Table III-4-1 .

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ChapterIf • Upper Limb

Collateral Nerves

In addition to the S terminal nerves, there are several collateral nerves that arise from the brachia! plexus proximal to the terminal nerves (i.e., from the rami, trunks, or cords). These nerves innervate proximal limb muscles (shoulder girdle muscles). Table III-4-2 summarizes the collateral nerves.

Table 111-4-2. The Collateral Nerves ofthe Brachial Plexus

Segmental Innervation to Muscles of Upper Limbs

The segmental innervation to the muscles ofthe upper limbs has a proximal­ distal gradient, i.e., the more proximal muscles are innervated by the higher segments (CS and C6) and the more distal muscles are innervated by the lower

segmendtsprtwimal(C8 and Tl)forearm. Therefore,musclestheareintrinsicinnervatedshoulderby C6musclesand C7,areandinnervatedthe more by CS and C6, the intrinsic hand muscles are rvated by C8 and Tl, distal

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distal forearm muscles are innervated by C7 and C8.

SENSORY INNERVATION

The skin of the palm is supplied by the median and ulnar nerves. The median supplies the later.,µ 3¥2 digits and the adjacent area of the lateral palm and the thenar eminence. The ulnar supplies the medial 1Yz digits and skin of the hypo­ thenar eminence. The radial nerve supplies skin ofthe dorsum ofthehand in the area of the first dorsal web space, including the skin over the anatomic snuffbox.

The sensory innervation of the hand is summarized in Figure III-4-2.

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