Showing posts with label Anatomy. Show all posts
Showing posts with label Anatomy. Show all posts

Tuesday, June 3, 2014

Visceral and parietal layer of serous pericardium

The pericardium is a fibroserous sac surrounding the heart and the roots of the great vessels. It consists of two components, 
1) the fibrous pericardium and 
2) the serous pericardium.

The fibrous pericardium is a tough connective tissue outer layer that defines the boundaries of the middle mediastinum. 

The serous pericardium is thin and consists of two parts:
1) The parietal layer lines the inner surface of the fibrous.
2) The visceral layer adheres to the heart and forms its outer covering.

The parietal and visceral layers of serous pericardium are continuous at the roots of the great vessels. The narrow space created between the two layers of serous pericardium, containing a small amount of fluid, is the pericardial cavity. This is pictured in the diagram above as a fist in a filled balloon. This potential space allows for the relatively uninhibited movement of the heart.

Fibrous pericardium
The fibrous pericardium is a cone-shaped bag with its base attached to the central tendon of the diaphragm
and a small muscular area on the left side of the diaphragm and its apex continuous with the adventitia of the great vessels. Anteriorly, it is attached to the posterior surface of the sternum by sternopericardial ligaments. 
These attachments help to retain the heart in its position in the thoracic cavity. The sac also limits cardiac 

Serous pericardium
The parietal layer of serous pericardium is continuous with the visceral layers of serous pericardium around the roots of the great vessels. These reflections of serous pericardium occur in two locations:
1) one superiorly, surrounding the arteries, the aorta and pulmonary trunk;
2) the second more posteriorly, surrounding the veins, the superior and inferior vena cava and the pulmonary veins.

Monday, February 11, 2013

, ,

May-Thurner syndrome

As seen in the diagram above, the left common iliac vein is predisposed to be compressed by the right common iliac artery. This can lead to stasis and eventually causing thrombosis. Another effect is that the pulsatile nature of the artery over the vein leads to turbulence in the blood flow, thereby favouring thrombosis. 
Because of this anatomical predisposition, most Deep Vein Thrombosis (DVT) seen during pregnancy occur in the left iliac vein system. All the classic investigations done for cases of DVT should be performed here also.

Friday, January 20, 2012

Shoulder joint / Glenohumeral joints

The shoulder joint is a synovial multi-axial spheroidal joint. It occurs between the roughly hemispherical head of the humerus and the shallow glenoid fossa of the scapula. Since there is no major bony constraint, the joint has 3 degrees of freedom. It is the most mobile joint of the body and allows all the movements shown above. The stability of the joint depends on the surrounding muscular and soft tissue envelope. It is one of the most frequently dislocated joints in the body.

Neck compartments

The neck has 4 major compartments.
1) Vertebral compartment which is contains the cervical vertebrae and associated muscles of posture,
2) Visceral compartment which contains the thyroid, thymus and parathyroid as well as the esophagus and larynx,
3) 2 vascular compartments on both sides and these contain the major blood vessels and vagus nerve.

Saturday, December 24, 2011


Skin - structure

The skin is sometimes called the cutaneous membrane or the integument. It has 2 regions notably the epidermis and the dermis. The hypodermis is a subcutaneous tissue and is found between the dermis and any underlying structure like muscles. 

It is the outer and thinner layer of the skin. It is made up of stratified squamous epithelium divided into several layers; the deepest layer is the stratum basale, and the most superficial layer is the stratum corneum. The deepest layer is constantly producing new cells and pushing them to the surface. The stratum corneum, on the other hand, gets keratinised to form a waterproof layer and also acts as a mechanical barrier. 

It is a thicker and denser region than the epidermis. It is composed of dense and irregular connective tissues. Its upper layer has structures called as dermal papillae that project into the epidermis to cause ridges. These form unique patterns and give the characteristic fingerprint to all individuals, though its primary function was to increase friction and give a better grip. 
It is also a highly vascular region. It is here that blood increases when you blush.

It is composed of loose connective tissues including adipose tissue (fat). This layer helps to give insulation to the body. Excess of adipose tissue in this layer leads to obesity. It is in this layer that subcutaneous injections are given.

Thursday, September 8, 2011

Axilla / Cubital fossa / Carpal tunnel

The axilla is an irregularly shaped pyramidal area formed by muscles and bones of the shoulder and the lateral surface of the thoracic wall. The apex or inlet opens directly into the lower portion of the neck. The skin of the 'armpit' forms the floor. All major structures that pass between the neck and arm pass through the axilla.

The cubital fossa is a triangularly shaped depression formed by muscles anterior to the elbow joint. The brachial artery and the median nerve pass from the arm to the forearm through this fossa.

The carpal tunnel is the gateway to the palm of the hand. Its posterior, lateral, and medial walls form an arch, which is made up of small carpal bones in the proximal region of the hand. A thick band of connective tissue, the flexor retinaculum, spans the distance between each side of the arch and forms the anterior wall of the tunnel. The median nerve and all the long flexor tendons passing from the forearm to the digits of the hand pass through the carpal tunnel.

Friday, July 15, 2011


Carpal bones arrangement - anatomy and mnemonic

A simple mnemonic to remember how the carpal bones are arranged is:

"She Looks Too Pretty; Try TCatch Her"


Last reviewed on: 1 September 2015

Wednesday, June 29, 2011

, ,

cardiac muscles properties - morphology

Cardiac muscle is striated same as a typical skeletal muscle. The muscle fibrils are surrounded by numerous and elongated mitochondria since the heart needs energy supply continously. The muscle fibres branch and interdigitate. They lie parallel to one another but at the end of each muscle fibres there are extensive folds of the cell membrane that are called as intercalated disks/discs.

The intercalated discs act as gap junctions that is very permeable and allow almost free diffusion of ions. They always occur at the Z lines i.e. the dark middle section of the light (I) band of the muscle. They provide a strong union between fibers, maintaining cell-to-cell cohesion, so that the pull of one contractile cell can be transmitted along its axis to the next.

The heart muscle thus acts as a syncytium. i.e. a multinucleated mass. Therefore when one of the cells is excited, the action potential spreads from cell to cell through the latticework interconnections fast and the syncytium as a whole contracts.

The heart is divided into the atrial and ventricular syncytium separated by the fibrous annulus at the A-V juntion. The action potential has to travel through the specialised conducting system that pierces the fibrous tissue. This division of the heart into 2 functional syncytiums allow the atria to contract a short time before the ventricles, which is important for the effectiveness of the heart as a pump.

The T system in cardiac muscle is located at the Z lines rather than at the A–I junction, where it is located in mammalian skeletal muscle. The T system of transverse tubules, which is continuous with the sarcolemma of the muscle fiber, forms a grid perforated by the individual muscle fibrils. It provides a path for the rapid transmission of the action potential from the cell membrane to all the fibrils in the muscle. The sarcoplasmic reticulum is an important store of Ca2+ and also participates in muscle metabolism.
, ,

Conducting system of the heart - SAN, AVN, Bundle of His, Purkinje fibres

The conducting system of the heart consists of:
1) Sino-Atrial Node (SAN),
2) Internodal tract,
3) Atrio-Ventricular Node (AVN),
4) Bundle of His or A-V Bundle,
5) Right and left Bundle branches,
6) Fascicles and 
7) Purkinje fibres.

In the human heart, the SA node is located at the junction of the superior vena cava with the right atrium. 

The AV node is located in the right posterior portion of the interatrial septum. 

There are three bundles of atrial fibers that contain Purkinje-type fibers and connect the SA node to the AV node: 
a) the anterior internodal tract of Bachman, 
b) the middle internodal tract of Wenckebach, and 
c) the posterior internodal tract of Thorel. 
Conduction also occurs through atrial myocytes, but it is more rapid in these bundles. 

The AV node is continuous with the bundle of His, which gives off a left bundle branch at the top of the interventricular septum and continues as the right bundle branch. 
The left bundle branch divides into an anterior fascicle and a posterior fascicle. 
The branches and fascicles run subendocardially down either side of the septum and come into contact with the Purkinje system, whose fibers spread to all parts of the ventricular myocardium.

Saturday, June 18, 2011

Pleura - parietal, visceral and mediastinum

Each pleural cavity is completely lined by a mesothelial membrane called the pleura. The latter is a serous membrane arranged as a closed invaginated surface.

During development, the lungs grow out of the mediastinum, becoming surrounded by the pleural cavities. As a result, the outer surface of each organ is covered by pleura.

The pleura lining the walls of the cavity is the parietal pleura, whereas that reflected from the mediastinum at the roots and onto the surfaces of the lungs and interlobar fissures is the visceral pleura or pulmonary pleura. The space formed between the two is called pleural cavity.

The parietal and visceral layer are continuous at the hilar structures.

The lung does not completely fill the potential space of the pleural cavity, resulting in recesses, which do not contain lung and are important for accommodating changes in lung volume during breathing. The costodiaphragmatic recess, which is the largest and clinically most important recess, lies inferiorly between the thoracic wall and diaphragm.

Wednesday, June 8, 2011

Vertebra - diagram of a typical vertebra

The function of the vertebral body is mostly weight bearing. As we go caudally, the size of the body increases. Other structures are well illustrated in the diagrams above. 

Sunday, June 5, 2011


The mediastinum is divided into superior and inferior, the plane of division being a line from the manubriosternal joint to the lower surface of the fourth thoracic vertebra.
The inferior mediastinum is further divided into anterior, middle and posterior mediastinum.
Anterior boundary includes the sternum, posterior one being the thoracic vertebral column. Superiorly it starts at the thoracic inlet and ends at the diaphragm.

Tuesday, April 12, 2011


The peritoneum is a thin membrane that lines the walls of the abdominal cavity and covers much of the viscera. The parietal peritoneum lines the walls of the cavity and the visceral peritoneum covers the viscera. Between the parietal and visceral layers of peritoneum is a potential space called as the peritoneal cavity.

Abdominal viscera are either suspended in the peritoneal cavity by folds of peritoneum called as mesenteries or are outside the peritoneal cavity. Organs suspended in the cavity are referred to as intraperitoneal and organs outside the peritoneal cavity, with only one surface or part of one surface covered by peritoneum, are retroperitoneal.

The peritoneal cavity is subdivided further into the greater sac and the omental bursa:
  • the greater sac accounts for most of the space in the peritoneal cavity, beginning superiorly at the diaphragm and continuing inferiorly into the pelvic cavity-it is entered once the parietal peritoneum has been penetrated;
  • the omental bursa is a smaller subdivision of the peritoneal cavity posterior to the stomach and liver and is continuous with the greater sac through an opening, the omental foramen.

Tuesday, May 4, 2010


Hesselbach's triangle

A direct hernia passes through the Hesselbach's triangle while an indirect one passes lateral to it.

This area is the weakest because the abdominal here consists only of the transversalis fascia covered by the external oblique aponeurosis.

As shown by the figure below:

Inferiorly : Inguinal ligament
Laterally : Inferior epigastric artery
Medially : Lateral border of rectus abdominis.

To confirm this we can do a ring occlusion test whereby the deep inguinal ring is occluded at 1.25cm above the midpoint of the inguinal ligament after reducing the hernia. Now we can ask the patient to cough or stand up. If the hernia is seen even though the deep ring is occluded it means that the hernia is of the direct type.

First published on : 4 May 2010
Last reviewed on : 2 May 2020