Gross Anatomy of The Abdomen, Abdominal Cavity & Its Contents PDF

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Gross Anatomy of The Abdomen, Abdominal Cavity & Its Contents...

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22/11/2020

The Abdominal Cavity, Its Contents & Major Viscera Regional Anatomy 1 - MBChB 1 2020-21

The Abdominal Cavity • It is the largest anatomical cavity of the body by volume • It lies under the cover of •

• Lower Ribs & • Dome of the Diaphragm

• Some of the abdominal cavity projects backwards into the pelvis just in front of the buttocks • It is continuous with the pelvic cavity. They are known together as the Abdomino pelvic cavity. • It is the cavity for:

• The Digestive Tract • Late Pregnancy (Primarily in the Pelvis)

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Gross Anatomical Features of The Abdominal Cavity • Its boundaries are: • Diaphragm (Superior) • Pelvic Brim (Inferior- Imaginary) • Anterolateral Abdomino-pelvic Wall (Ant-Lat) • Posterior Abdominal Wall (Posterior) • Note: Psoas complex muscle. • Behind the psoas major muscle there is a nerve complex which supplies the lower limb. This is known as the lumbar plexus.

Tissue Layers of Lateral Abdominal Wall            

Skin Subcutaneous layer of fat (camper fascia) Scarpa fascia - tethers the skin to the rest of the body Superficial (investing) layer of deep fascia External oblique Intermediate layer of deep fascia Internal oblique Deep layer of deep fascia Transversus abdominis Endoabdominal fascia o Deepest layer of anterior abdominal wall is the Endoabdominal fascia (endothoracic fascia equivalent) Extraperitoneal fat Parietal peritoneum, one cell thick.

Anterolateral Abdominal Wall in X-Section

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Linea alba defines the midline of the body (follow the sternum down) Then tendons of the external, internal oblique and Transversus abdominis blend together forming the rectus sheath which then envelopes the rectus abdominis muscle. o The rectus abdominis muscle are the abs

Surface Map of The Anterior Abdominal Wall 2 Systems Abdomino Pelvic Quadrant • The Abdomino Pelvic Quadrant system is based on physically palpable anatomical structures • It standardises the mapping surface of the body between patients • It is useful in surface palpation of major abdominal organs e.g. liver and kidneys • Point of reference are: – The Linea Alba  vertical line (runs from the xyphoid process to the pubic symphysis) – The Umbilicus  horizontal line (bisects the Linea alba) – This divides the region in RUQ, LUQ, RLQ, LLQ  The following Viscera lie in each quadrant:  URQ: liver and gall bladder  LUQ: Stomach, Pancreas, spleen  LLQ: Descending colon and part of ilium  RLQ: Ascending colon, appendix

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9 Compartments Abdominopelvic regions The 9 Compartments Abdominopelvic region system is more precise, it uses: 2 Vertical planes  One on each side of the midline  They are lines that join the mid-clavicular point to the mid-inguinal point.  It passes just lateral to the tip of the ninth costal cartilage, which is palpable as a distinct step along the costal margin 2 Horizontal planes  Based on lines drawn between easily palpable bony points: o Subcostal plane  A line drawn joining the lowermost bony point of the rib cage - usually 10th costal cartilage  The body of the L3 vertebra; the origin of the inferior mesenteric artery and 3rd part of the duodenum lie on this plane o Trans-tubercular plane  A line uniting the two tubercles of the iliac crests  Upper border of the L5 vertebra and the confluence of the common iliac veins (i.e. IVC origin) lie on this plane

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Gross Anatomical Features of The Abdominal Cavity • White space in the middle in the

abdominal cavity. • Its boundary is created by the parietal

peritoneum.

• Parietal Peritoneum: The deepest tissue envelope which houses the viscera of the abdomen & pelvis.

What is Peritoneum?    

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It is a one-cell thick tissue membrane It is classified histologically as simple squamous epithelium It is also known as the pavement epithelium There are two variants of peritoneum. o Parietal peritoneum (red), lines the interior surfaces of the abdominal wall, the diaphragm and pelvis. o Visceral peritoneum (blue) lines the surfaces of all viscera of the abdomen (except Bare area of the liver)  The bare area of the liver is a small area between the superior surface of the liver and the inferior surface of the diaphragm.  There is no nervous innervation is this region. The parietal and visceral peritoneum are the same membrane, they are continuous. They have different names as they cover different surfaces

The Bare Area of The Liver • The bare area of the liver is that part of the liver whose surface is not covered by visceral peritoneum • It occurs when parietal peritoneum on the inferior surface of the diaphragm dives inferiorly to cover the surface of the liver • This then is known as the coronary ligament • In 3D this forms somewhat of a crown over the liver • It is important clinically because it has no sensory or nervous innervation. So, if there is pathological development in the bare area the patient will not be aware of it.

Innervation of the Peritoneum 

Parietal peritoneum o Innervated by sensory division of the somatic nervous system o It allows for pain sensations which are sharp & localised

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Visceral peritoneum o Innervated by the sensory division of the autonomic nervous system o Its allows for pain sensations which are not ‘localised‘ but perceived as ‘non-defined’ discomfort e.g. indigestion is an example of visceral pain

What is The Peritoneal Cavity?  

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Peritoneal cavity (abdominal cavity): The cavity created between parietal and visceral peritoneum. It is one of the spaces derived from the coelomic cavity of the embryo, others being the: o Pleural cavities around the lungs o & o Pericardial cavity around the heart. The peritoneal cavity is: o The largest fluid-filled cavity in the body o It secretes approximately 50 mL of fluid per day o Its fluid acts as a lubricant and has anti- inflammatory properties

Gross Anatomical Features of Viscera of The Abdomen & Pelvis 

Structures are said to be either o Within the compartment created by boundaries of the peritoneum  Green line forms the boundary  These are Peritoneal Organs o Outside the compartment created by boundaries of the peritoneum  These are Extraperitoneal Organs

Extra Peritoneal Cavity

Peritoneal Cavity

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The Peritoneal Cavity: Area Shaded Blue Extraperitoneal Cavity: Rest of the cavity not shaded Blue

Sub-classification of Peritoneal Organs • Intraperitoneal organs: when the entire surface of a peritoneal organ is covered with visceral peritoneum

Sub-classification of Extra-Peritoneal Organs 

Extraperitoneal organs are further divisible into those that are: o Lying in front of the peritoneal sac  Pre-peritoneal structures  Exists only conceptually  Normally, no structure is found in this area  This space can be invaded pathologically at the level of the pelvis o Lying behind the peritoneal sac  Retro-peritoneal structures

Gross Anatomy of Retroperitoneal Organs  

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The retroperitoneal organs of the abdomen are found lying in relation to the posterior abdominal wall Retroperitoneal organs lie outside the compartment created by the peritoneum. They lie behind the peritoneal sac. The parietal peritoneum will only line one side of these organs, usually the anterior surface. Retroperitoneal organs include kidneys & Great Vessels

Kidneys are Retroperitoneal Structures: What Does This Mean?     

Kidneys are located within the abdomen They are attached to the posterior abdominal wall They lie posteriorly to the posterior surface of the parietal peritoneum Only their anterior surfaces enjoy covering of the parietal peritoneum They are thus, said to be retroperitoneal structures

Examples of Retroperitoneal Organs • One easy way to remember which abdominopelvic organs are retroperitoneal, is to use a mnemonic such as SAD PUCKER: • • • • • • • •

S = Suprarenal (adrenal) glands A = Aorta/Inferior Vena Cava D = Duodenum (second and third segments) P = Pancreas U = Ureters (Proximal 50%) C = Colon (ascending and descending only) K = Kidneys E = Oesophagus

CT of the Abdomen (Remember looking up from the feet) • • • • • • • • • • • • • •

1 Left lobe of liver 2 Right lobe of liver 3 Gallbladder 4 Stomach 5 Portal vein origin 6 Inferior vena cava 7 Splenic vein 8 Body of pancreas 9 Tail of pancreas 10 Spleen 11 Right adrenal gland 12 Left adrenal gland 13 Left kidney 14 Aorta

Laparoscopic Access to The Peritoneal Cavity • The abdominal cavity is also known as

the peritoneal cavity

• When using the laparoscopic approach it is formally divisible into: o The Greater Sac o The Lesser Sac (lies behind the stomach). Its size gets smaller as the stomach gets fuller. o The omental foramen (epiploic foramen of Winslow) is the window that allows for communication between the greater and lesser sac

Epiploic Foramen of Winslow

Gross Anatomy of The Abdominal Cavity Peritoneum • Double folds of peritoneum can be referred to as either an: – Abdominal Ligament (not normal ligament) – Omentum – Mesentery

• What is an Abdominal Ligament • It is: – Any double fold of visceral peritoneum ans

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• It is:

– A double fold of visceral peritoneum that starts on the greater curvature of the stomach and connects it to the transverse colon • Also known as the Abdominal Apron • It is also known as the ‘Policeman or Policewoman’ of the abdomen as it moves to a site of infection and pours its fluid to neutralise the infection. – It is chemotactic (moves in response to a chemical stimulus) and capable of moving

• What is The Lesser Omentum? • It is: – A double fold of visceral peritoneum that starts on the lesser curvatures of the stomach and connects the stomach to the liver.

What is A Mesentery? • It is: – Any double fold of visceral peritoneum starting and ending on the intestines and containing neurovascular structures (BV and nerves) between the two layers of peritoneum. They supply blood and nervous supply.

Some Ligaments of The Abdominal Viscera

Colic Compartments • The abdomen is divided into – Supracolic Compartment: contains the liver, gall bladder and the stomach – Infracolic Compartment: contains most the intestines  The dividing line is determined by the attachments of the transverse mesocolon

Paracolic Gutters       

Paracolic gutters join the supra colic compartment to the infra colic compartment. You have right and left paracolic gutters. Bleeds in the supra colic compartments will move into the infra colic compartments via the gutters If a patient is lying in a supine position fluid move infrasupra This can mean finding the source of bleeds can be difficult. On the right gutter the flow of fluid between compartments is uninterrupted. However of the left side the Phrenicocolic ligament blocks the flow of fluids between compartments.

Supracolic Compartment (sagittal) 

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Also known as the: o Sub-diaphragmatic space or o Sub-phrenic Space Divided into 4 sub-spaces as follows: o The Coronary Ligament divides the subphrenic spaces into  the left Sub-phrenic space  the right Sub-phrenic space  The subphrenic space lies immediately inferior to the diaphragm and superior to the liver. o Falciform Ligament divides subhepatic space into the  Left Sub-hepatic Space  Right Sub-hepatic Space (A.K.A. Hepatorenal Pouch of Rutherford Morrison)  The hepatic space is located below the liver, but above the transverse mesocolon

The Infra-Colic Compartment • It is that part of the Abdominal Cavity that is: – Inferior to Transverse mesocolon – Superior to The Pelvic Inlet • Its Visceral Organs Include

Small intestine Ascending and descending colon • Its Anatomical Spaces of Importance are: – Recto-uterine Pouch of Douglas and utero-vesical pouch (females) • Recto-uterine pouch of Douglas is the lowest point where fluid collects – Recto-Vesical Pouch (males) (as males have no uterus see below) – –

Divisions of The Stomach (Learn all parts)

Musculature of The Stomach

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Longitudinal muscles are on the outside, next is the circular muscle then the oblique muscle layer Inside of stomach has the Rugae End of the stomach has the pylorus sphincter (smooth muscle)

The Coealiac Trunk   

The Coealiac trunk is formed from Branches of the Abdominal Aorta at Vertebral Level L1 It supplies most of the blood to the stomach It gives rise to the o left gastric artery o splenic artery o common hepatic artery

The Portal Triad The portal triad consists of the  portal vein  hepatic artery  bile duct

The Intestines           

The small intestine starts of at the duodenum (first part) then we move through the Duodenojejunal junction into the jejunum. The jejunum is second of the three sections that make up the small intestine From the jejunum we move into the ileum and then progress into large intestine. The ileum is the final section of the small intestine. The large intestine starts at the Ileocecal junction. This is the start of the ascending colon. The ascending colon, starts on the right side of the body, then progresses into the transverse colon and then to the descending colon on the left side of the body. The descending colon  the rectum at the anal sphincter. The Linea alba line passes through the Duodenojejunal junction. The superior mesenteric artery supplies the whole small intestine. Neuronal innervation of the intestines is provided by the vagus nerve (CN X).

Large Intestines 

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Blood supply o Blood supply to the large intestine on a person’s left side is provided by the branches of the inferior mesenteric artery.  This includes the descending colon, the sigmoid colon and the rectum. o The ascending colon and the transverse colon are largely supplied by the branches of the superior mesenteric artery. Tenia coli is a longitudinal muscle runs through the middle of the colon. Epiploic appendages are pockets of fat storage and have some immune function Small intestine is smooth whereas large intestine is sacculated. The individual sacculations are known as haustra....