Seventh Edition
Revised and Edited by Neelam Vasudeva MBBS MD
Director Professor and Head, Department of Anatomy Maulana Azad Medical College, New Delhi
Sabita Mishra MBBS DNB PhD (AIIMS)
Professor, Department of Anatomy Maulana Azad Medical College, New Delhi
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Inderbir Singh's Textbook of Human Histology
First Edition | : 1987 | Fifth Edition | : 2006 |
Second Edition | : 1992 | Reprint | : 2008 |
Third Edition | : 1992 | Reprint | : 2009 |
Fourth Edition | : 2002 | Sixth Edition | : 2011 |
Reprint | : 2005 | Seventh Edition | : 2014 |
9789351523222
Printed at
5Preface
Textbook of Human Histology by Professor Inderbir Singh has remained an authoritative and standard textbook for the past many decades and it is our proud privilege to revise this book and bring out the 7th edition. The strength and popularity of this textbook has been its simple language and comprehensiveness that has essentially remained unchanged since its inception. Professor Singh's eye for details and his meticulous writing style has always been popular amongst the generations of medical students. Although all the chapters have been revisited and thoroughly revised, we have taken special care to retain the basic essence of the book.
To make this standard textbook fulfill the needs of today's generation of students, some new features have been introduced in this edition. A new chapter on Light Microscopy and Tissue Preparation has been added to acquaint the students with the basics of histology. Every student of histology is expected to identify the slides and differentiate amongst them in a perfect manner. To make the students familiar with the various slides, Histological Plates have been added in each chapter that include a photomicrograph, line drawing, and salient features that are visible while examining under the microscope.
Each chapter has been rearranged to provide sequential learning to the students. All the diagrams have been redrawn and many new illustrations have been added for easy comprehension of the basic concepts. Clinical and Pathological Correlations have been added at relevant places for creating an interest of the students in the understanding of pathologies associated with various tissues.
For providing an overview of histology to the student and for quick recall, an atlas has been provided at the beginning of the book. The atlas includes more than 80 slides of histological importance along with their important features.
As envisioned by Professor Inderbir Singh, this textbook is of utmost utility not only for the undergraduate students but also for the students pursuing postgraduation in Anatomy. Keeping this in mind, advanced information on various topics has been included as Added Information to cater to the needs of postgraduate students.
The revision of this book was a team effort. We are thankful to our colleagues for their constant encouragement throughout our venture. We extend our heartfelt thanks to our staff in the Histology laboratory for preparing the slides for photography. We are thankful to Dr Sawti Tiwari for her important contribution in drawing some of the figures.
We are grateful to Professor Ivan Damjanov, an esteemed teacher and expert in the field of pathology well known across the globe, for allowing us to use some of the slides from his collection. We gratefully acknowledge Professor Harsh Mohan, a well known surgical pathologist of India, for providing pathological correlations in the book. We are thankful to Dr Sunayna Misra [M.D (Path.), PGI Chandigarh] for her valuable suggestions and inputs especially in the pathological correlations.6
We extend our heartfelt thanks to Shri Jitendar P Vij (Group Chairman) and Mr Ankit Vij (Group President) for providing us the opportunity to revise Text of Human Histology and for their persistent support in publication of this book.
Dr Sakshi Arora (Chief Development Editor), the driving force of this endeavour, deserves a special thanks for her tireless efforts. She has perservered throughout this venture with a smile on her face. We are thankful to her entire development team comprising Dr Mrinalini Bakshi, Dr Swati Sinha, and Ms Nitasha Arora (Editors), and Mr Prabhat Ranjan, Mr Neeraj Choudhary, Mr Ankush Sharma, Mr Phool Kumar, Mr Deep Dogra and Mr Sachin Dhawan (Designers and Operators) for providing insights and creative ideas that helped in polishing this book to best meet the needs of students and faculty alike.
We present the 7th edition of this most popular textbook to the medical fraternity as our tribute to a legendary anatomist, Professor Inderbir Singh for being a pillar in the education of generations of doctors throughout the world.
Neelam Vasudeva
Sabita Mishra
7Colour Atlas
HISTOLOGY & ITS STUDY
The study of histology is very important for the understanding of the normal functioning of the human body. It also forms the essential basis for the study of the changes in various tissues and organs in disease. (This is the science of pathology). From these points of view the study of histology is best done taking one organ system at a time. That is the approach most teachers prefer to take in practical classes of histology. It is also the basis on which the chapters of this book have been organised.
However, in practical examinations, the emphasis is on the ability of the student to recognise a tissue or organ that is being viewed through a microscope. Here it becomes necessary to know how to distinguish between similar looking tissues or organs belonging to different systems. This atlas has been organised to serve this objective. Tissues and organs that have a similar appearance are considered in one lot. For example, if a slide presents something that looks like a tube, whether it be an artery or the ureter or the ductus deferens, these are considered together. This makes the grouping unusual, but this is exactly what the student needs at the time of an examination.
At the same time it is true that an organ can be composed of several tissues, (or layers), and the ability to recognise them can go a long way is arriving at a correct diagnosis of the organ being seen. We will, therefore, first try to study and identify the various tissues that make up different organs. We will then have a good basis for identifying any organ that we are required to recognise.
BASIC TISSUES THAT CAN BE RECOGNISED IN HISTOLOGICAL SECTIONS
EPITHELIA
The outer surface of the body, and the luminal surfaces of cavities (big or small) lying within the body are lined by one or more layers of cells that completely cover them. Such layers of cells are called epithelia. Epithelial tissue forms the lining of the general body surfaces, passages and cavities within the body. Basement membrane connects the epithelium to the underline subepithelial tissues.
Classification of epithelial tissue is based on shape of the cells, number of cell layers and special modifications seen on the cells. Epithelia may be simple, when they consist of only one layer of cells, or stratified when there are several layers of cells. Epithelial cells may be flat (or squamous), cuboidal, columnar etc.
Several types of epithelia can be recognised. Learning to identify an epithelium can be of considerable help in finding out what organ you are seeing.8
Simple Squamous Epithelium
- ❑ The cells of this epithelium are flattened.
- ❑ In sections they appear so thin that bulgings are produced on the surface by nuclei.
- ❑ In surface view () the cells have polygonal outlines that interlock with those of adjoining cells.
- ❑ A simple squamous epithelium lines the alveoli of the lungs, the free surfaces of peritoneum, pleura and pericardium. Here it is given the name mesothelium. It also lines the inside of blood vessels, where it is called endothelium, and of the heart where it is called endocardium.
Simple Cuboidal Epithelium
- ❑ The epithelium is made up of cells that look like squares (in which the length and breadth is equal).
- ❑ Nuclei are rounded.
- ❑ A typical cuboidal epithelium lines follicles of the thyroid gland, kidney tubules, germinal layer of ovary and ducts of various glands.
Simple Columnar Epithelium
- ❑ In this epithelium the height of the cells is much greater than their width.
- ❑ The nuclei are oval being elongated in the same direction as the cells. They lie near the bases of the cells. Because of this we see a zone of clear cytoplasm above the nuclei.
- ❑ A simple columnar epithelium lines the mucous membrane of the stomach and of the large intestine.
Columnar Epithelium showing Striated Border
- ❑ In some regions the free surfaces of the cells of columnar epithelium show a thickening with vertical striations in it: this is called a striated border.
- ❑ This is seen typically in the small intestine
Pseudostratified Ciliated Columnar Epithelium
- ❑ Pseudostratified epithelium differs from simple columnar epithelium in that it appears to be multi-layered. However, there is actually only one layer of cells. The multi-layered appearance is due to the fact that the nuclei lie at different levels in different cells. Such an epithelium is seen in the ductus deferens.
- ❑ In some situations, pseudostratified columnar epithelium bears hair-like projections called cilia.
- ❑ Pseudostratified ciliated columnar epithelium is seen in trachea and in large bronchi.
Pseudostratified Columnar Epithelium with Stereocilia
- ❑ In some situations, the pseudostratified columnar epithelium bears stereocilia as seen in epididymis.
- ❑ Stereocilia are actually long microvilli and not cilia.
Transitional Epithelium
- ❑ In this type of epithelium we see several layers of cells with round nuclei.
- ❑ The deepest cells are columnar or cuboidal. The middle layers are made up of polyhedral or pear-shaped cells.
- ❑ The cells of the surface layer are large and often shaped like an umbrella
- ❑ This epithelium lines many parts of the urinary tract.
Stratified Squamous Epithelium (Non-keratinised)
- ❑ The stratified epithelium is made up of several layers of cells.
- ❑ Although this is called stratified squamous epithelium, only the most superficial cells are squamous (flattened).
- ❑ The cells in the deepest (or basal) layer are columnar. In the middle layers they are polyhedral, while the more superficial layers show increasing degrees of flattening.
- ❑ The nuclei are oval in the basal layer, rounded in the middle layer, and transversely elongated in the superficial layers.
- ❑ There is no superficial keratinized zone; flattened nuclei are seen in the topmost layer.
- ❑ This kind of epithelium is seen lining some internal organs like the oesophagus and the vagina.
Stratified Squamous Epithelium (Keratinised)
- ❑ Here the deeper layer are covered by additional layers that represent stages in the conversion of cells into non-living fibres. This process is called keratinisation (or cornification).
- ❑ The surface layer is made up of keratin which appears as fibres. No cellular outline or nuclei can be seen.
- ❑ It is seen typically in epidermis of the skin.
Key
- Keratin
- Stratified squamous epithelium
CONNECTIVE TISSUE
In most organs there are areas filled in by fibres that are described as connective tissue. The main constituent of connective tissue is collagen fibres that stain pink. In stretch preparations they are seen as wavy bundles. Other fibres present (elastic, reticular) can be seen with special stains. Connective tissue also contains many cells but only their nuclei can be made out.
Irregular Connective Tissue
- ❑ Irregular connective tissue is typically seen in dermis of skin.
- ❑ It consists of compactly packed bundles of collagen fibres that are not arranged in orderly fashion.
- ❑ Thin elastic fibres are present, but are not seen with H & E stain.
Regular Connective Tissue
- ❑ Tendons are also made up of collagen fibres, but here the fibres (or fibre bundles) are arranged in orderly fashion parallel to each other.
- ❑ Nuclei of some cells (mainly fibroblasts) are seen between the bundles of collagen. They are elongated (elliptical).
Key
- Collagen fibres
- Nuclei of fibroblasts
Adipose Tissue
- ❑ Adipose tissue is made up mainly of compactly arranged fat cells.
- ❑ In routine sections the cells appear empty as the fat gets dissolved during preparation of the section.
- ❑ The cytoplasm of each cell is seen as a pink ‘rim’.
- ❑ The nucleus is flat and lies to one side.
Key
- Nuclei of adipocyte
- Thin rim of cytoplasm
SPECIALISED CONNECTIVE TISSUE
CARTILAGE
Unlike connective tissue, that can be deformed easily, cartilage is a special form of connective tissue that is firm, and retains its shape.
Hyaline Cartilage
- ❑ It is characterised by groups of cartilage cells (chondrocytes) surrounded by a homo-geneous matrix which separates the cells widely.
- ❑ Near the surface of the cartilage the cells are flattened and merge with the cells of the overlying connective tissue. This connective tissue forms the perichondrium.
- ❑ Costal cartilage and articular cartilage of synovial joint are example of hyaline cartilage.
Key
- Chondrocytes
- Homogenous matrix
- Perichondrium
Elastic Cartilage
- ❑ In elastic cartilage chondrocytes are surrounded by matrix containing many elastic fibres
- ❑ Perichondrium covering is present over the cartilage
- ❑ It is seen typically in auricle and epiglottis
Key
- Chondrocytes
- Elastic fibres
- Perichondrium
Fibrocartilage
- ❑ Fibrocartilage is characterized by presence of collagen fibresarranged in bundles with rows of chondrocytes interveningbetween the bundles
- ❑ Perichondrium is absent
- ❑ Fibrocartilage is seen typically in pubic symphysis and manubrio sternal joint
Key
- Chondrocytes
- Bundles of collagen fibres
BONE
Compact Bone
- ❑ A transverse section through the compact bone shows ring-like osteons (or Haversian systems).
- ❑ Haversian canal is seen at the centre of each osteon.
- ❑ Around the canal there are concentric lamellae of bone amongst which there are small spaces called lacunae in which osteocytes are present.
- ❑ Delicate canaliculi radiate from the lacunae containing processes of osteocytes.
- ❑ Interstitial lamellae fill intervals between Haversian systems.
- ❑ Volkmanns canal interconnecting the adjacent haversian canal may be seen
Note: The appearance of compact bone is so characteristic that you are not likely to confuse it with any other tissue.
Key
- Haversian system (osteon)
- Haversian canal
- Concentric lamellae
- Interstitial lamellae
- Volkmann's canal
Spongy (Cancellous) Bone
- ❑ It is made up of a network of bony trabeculae (pink) in which the nuclei of some osteocytes can be seen.
- ❑ The spaces of the network are filled in by bone marrow in which numerous fat cells are present.
- ❑ The spaces between the fat cells are occupied by numerous blood forming cells (only nuclei of which are seen).
Key
- Trabeculae
- Osteocytes
- Fat cells
MUSCLE
Skeletal Muscle
- ❑ In a longitudinal section through skeletal muscle the fibres are easily distinguished as they show characteristic transverse striations.
- ❑ The fibres are long and parallel without branching.
- ❑ Many flat nuclei are placed at the periphery.
- ❑ The muscle fibres are separated by some connective tissue.
Key
- Muscle fibres with transverse striations
- Peripherally placed nuclei
Smooth Muscle
- ❑ In a longitudinal section through smooth muscle elongated spindle shaped cells without straitions are seen.
- ❑ A single elongated (oval) centrally placed nucleus can be identified.
- ❑ Smooth muscle is present in the walls of parts of the alimentary canal, in the urogenital tract etc.
Key
- Oval centrally placed nuclei
Cardiac Muscle
- ❑ The fibres are made up of ‘cells’ each of which has a centrally placed nucleus and transverse striations.
- ❑ Adjacent ‘cells’ are separated from one another by transverse lines called intercalated discs.
- ❑ Fibres show branching.
Key
- Centrally placed nuclei
- Branching and anastomosing of fibres
Nervous Tissue
- ❑ Grey matter contains cell bodies of neurons and neuroglia
- ❑ White matter contains axons of neurons and neuroglia
Key
- White matter
- Grey matter
STRUCTURES THAT ARE USUALLY SEEN AS SINGLE TUBES
ARTERIES
The structure of an artery varies greatly with its size. Each artery shows three layers, the tunica intima, tunica media and the tunica adventitia (in internal to external order). The lumen is lined by endothelium (flattened cells).
Elastic Artery
Elastic artery is characterised by presence of
- ❑ Tunica intima consisting of endothelium, subendothelial connective tissue and internal elastic lamina.
- ❑ The first layer of elastic fibres of tunica media is considered the internal elastic lamina.
- ❑ Thick tunica media with many elastic fibres and some smooth muscle fibres.
- ❑ Tunica adventitia containing collagen fibres and vasa vasorum.
Key
- Tunica media
- Tunica adventitia
Muscular Artery
- ❑ In muscular arteries, the tunica intima is made of endothelium and internal elastic lamina (arrow) which is thrown into wavy folds due to contraction of smooth muscle in the media.
- ❑ Tunica media–is composed mainly of smooth muscle fibres arranged circularly.
- ❑ Tunica adventitia–contains collagen fibres.
Key
- Tunica intima
- Tunica media
- Tunica adventitia
Vein
Key
- Tunica intima
- Tunica media
- Tunica adventitia
VERMIFORM APPENDIX
- ❑ The vermiform appendix is the narrowest part of the gastrointestinal canal and is seen as a tubular structure.
- ❑ The innermost layer of the mucosa, is lined by simple columnar epithelium with goblet cells and lymphocytes.
- ❑ Crypts are seen in lamina propria.
- ❑ The next layer, the submucosa may show a variable number of lymphatic nodules.
- ❑ The submucosa is surrounded by smooth muscle layer (muscularis externa) followed by serosa.
- ❑ The longitudinal muscle coat is complete and equally thick all round. Taenia coli as seen in colon are not present.
Key
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
URETER
- ❑ The ureter can be recognised because it is tubular and its mucous membrane is lined by transitional epithelium.
- ❑ The epithelium rests on a layer of connective tissue (lamina propria).
- ❑ The mucosa shows folds that give the lumen a star shaped appearance.
- ❑ The muscle coat has an inner layer of longitudinal fibres and an outer layer of circular fibres. This arrangement is the reverse of that in the gut.
- ❑ The muscle coat is surrounded by adventitia made of fibroelastic connective tissue in which blood vessels and fat cells are present.
Key
- Mucosa comprising of transitional epithelium and lamina propria
- Muscle coat
- Adventitia
DUCTUS DEFERENS
- ❑ This is a tube that is distinguished from the ureter as its mucous membrane is lined by pseudostratified columnar epithelium.
- ❑ The muscle coat is very thick. Three layers, inner longitudinal, middle circular and outer longitudinal are seen.
- ❑ The muscle coat is surrounded by adventitia containing blood vessels and nerves.
Key
- Small lumen lined by pseudostratified columnar epithelium
- Submucosa
- Muscle layer
- Adventitia
UTERINE TUBE
- ❑ The uterine tube is characterized by presence of numerous branching mucosal folds that almost fill the lumen of the tube.
- ❑ The mucosa is lined by ciliated columnar epithelium.
- ❑ The uterine tube has a muscular wall with an inner circular and outer longitudinal muscle layer.
Key
- Mucous membrane with numerous branching folds
- Inner circular muscle layer
- Outer longitudinal muscle layer
STRUCTURES MADE UP MAINLY OF LYMPHOID TISSUE
LYMPHOID TISSUE
Lymphocytes are one variety of cells of blood. Collections of them are frequently seen in many tissues. Such aggregations constitute lymphoid tissue. Such tissue is seen in the form of aggregations of dark staining nuclei. Some organs (lymph nodes, spleen) are made up almost entirely of such tissue. At some sites lymphoid tissue shows nodules where the lymphocytes are more densely packed than elsewhere. The nodule may show a central area that is lighter staining (because the cells are less densely packed)
LYMPH NODE
- ❑ A lymph node has an outer cortex and an inner medulla.
- ❑ The cortex is packed with lymphocytes. A number of rounded lymphatic follicles (or nodules) are present. Each nodule has a pale staining germinal centre surrounded by a zone of densely packed lymphocytes.
- ❑ Within the medulla the lymphocytes are arranged in the form of anastomosing cords. Several blood vessels can be seen in the medulla.
- ❑ A thin capsule surrounds the lymph node, sending trabeculae into the cortex.
- ❑ Beneath the capsule is a clear space called subcapsular sinus.
Note: All lymphoid tissue are easily recognised due to presence of aggregation of dark staining nuclei. The nuclei belong to lymphocytes.
Key
- Lymphatic nodule
- Germinal centre
- Zone of dense lymphocytes
C. Cortex
M. Medulla
Ca. Capsule
SPLEEN
It is characterized by–
- ❑ A thick capsule with trabecula extending from it into the organ (not shown in photomicrograph)
- ❑ The substance of the organ is divisible into the red pulp in which there are diffusely distributed lymphocytes and numerous sinusoids; and the white pulp in which dense aggregations of lymphocytes are present. The latter are in the form of nodules surrounding arterioles.
Key
- Red pulp
- White pulp
- Germinal centre
- Arteriole present in an eccentric position
THYMUS
In the slide it can be seen that
- ❑ The thymus is made up of lymphoid tissue arranged in the form of distinct lobules. The presence of this lobulation enables easy distinction of the thymus from all other lymphoid organs.
- ❑ The lobules are partially separated from each other by connective tissue.
- ❑ In each lobule an outer darkly stained cortex (in which lymphocytes are densely packed); and an inner lightly stained medulla (in which the cells are diffuse) are present.
- ❑ The medulla contains pink staining rounded masses called the corpuscles of Hassall.
Key
- Cortex
- Medulla
- Corpuscle of Hassall
PALATINE TONSIL
- ❑ Palatine tonsil is an aggregation of lymphoid tissue that is readily recognized by the fact that it is covered by a stratified squamous epithelium on its oral surface.
- ❑ At places the epithelium dips into the tonsil in the form of deep crypts.
- ❑ Deep to the epithelium there is diffuse lymphoid tissue in which typical lymphatic nodules can be seen.
Key
C. Crypt
- Stratified squamous epithelium
- Lymphatic nodule
SOME STRUCTURES COVERED BY STRATIFIED SQUAMOUS EPITHELIUM
SKIN
The skin consists of two layers. The most superficial layer is the epidermis which consists of stratified squamous epithelium (keratinised). The epidermis rests on a thick layer of connective tissue which is called the dermis.
Thick Skin
Thick or glabrous skin is characterized by
- ❑ Presence of thick epidermis made up of keratinized stratified squamous epithelium (stratum corneum is very thick)
- ❑ Absence of hair follicles and sebaceous glands
- ❑ Presence of sweat glands in the dermis.
- ❑ Thick skin is found in palm of hand and sole of foot.
Key
- Keratin
- Epidermis (stratified squamous epithelium)
- Dermis
- Sweat glands
Thin Skin
Thin skin or hairy skin is characterized by
- ❑ Presence of thin epidermis made up of keratinized stratified squamous epithelium (stratum corneum is thin)
- ❑ Presence of hair follicles, sebaceous glands and sweat glands in the dermis.
- ❑ Thin skin is found in all parts of body except palm of hand and sole of foot.
Key
- Epidermis
- Dermis
- Hair follicle
- Sebaceous gland
TONGUE
- ❑ The tongue is another structure covered on both surfaces by stratified squamous epithelium (non-keratinised).
- ❑ The undersurface of the tongue is smooth, but on the dorsum the surface shows numerous projections or papillae.
- ❑ Each papilla has a core of connective tissue (lamina propria) covered by epithelium. Some papillae are pointed (filiform), while others are broad at the top (fungiform). A third type of papilla is circumvallate, the top of this papilla is broad and lies at the same level as the surrounding mucosa.
- ❑ The main mass of the tongue is formed by skeletal muscle seen below the lamina propria. Muscle fibres run in various directions so that some are cut longitudinally and some transversely. Numerous serous glands and mucous glands are present amongst the muscle fibres.
Key
P. Papillae
- Stratified squamous epithelium
- Lamina propria
- Skeletal muscle
OESOPHAGUS
In transverse section the oesophagus shows the following layers (from within outwards):
- ❑ Lining of non-keratinised stratified squamous epithelium.
- ❑ The underlying connective tissue of the lamina propria.
- ❑ The muscularis mucosae in which the muscle fibres are cut transversely.
- ❑ The lining epithelium, lamina propria and muscularis mucosa collectively constitute the mucosa.
- ❑ The submucosa having oesophageal glands (mucous secreting).
- ❑ The layer of circular muscle, and the layer of longitudinal muscle constituting the muscularis externa.
Note: In muscularis externa the muscle is of the striated variety in the upper one third of the oesophagus, mixed in the middle one third, and smooth in the lower one third.
Key
- Muscosa lined by stratified squamous epithelium
- Lamina propria
- Submucosa
- Muscularis externa
- Submucous glands
VAGINA
- ❑ The vagina is a fibromuscular structure consisting of an inner mucosa, a middle muscular layer and an outer adventitia.
- ❑ The mucosa consists of Stratified squamous non-keratinised epithelium.
- ❑ Loose fibroelastic connective tissue (lamina propria) with many blood vessels and no glands.
- ❑ The mucosa of vagina is rich in glycogen and hence stains palely which distinguishes it from oesophagus.
- ❑ Muscular layer consists of smooth muscle fibres.
Key
- Stratified squamous non-keratinised epithelium
- Lamina propria
CORNEA
The cornea is made up of five layers
- ❑ The outermost layer is of non-keratinised stratified squamous epithelium (corneal epithelium).
- ❑ The corneal epithelium rests on the structureless anterior limiting lamina (also called Bowman's membrane)
- ❑ Most of the thickness of the cornea is formed by the substantia propria (or corneal stroma) made up of collagen fibres embedded in a ground substance.
- ❑ Deep to the substantia propria there is a thin homogeneous layer called the posterior limiting lamina.
- ❑ The posterior surface of the cornea is lined by a single layer of flattened or cuboidal cells.
Note: The structure of the cornea is fairly distinctive and its recognition should not be a problem.
Key
- Stratified sqaumous corneal epithelium
- Anterior limiting membrane (Bowman's)
- Substantia propria
- Posterior limiting membrane (Descemet's)
- Posterior cuboidal epithelium
SOME ORGANS IN WHICH TISSUES ARE ARRANGED IN PROMINENT LAYERS
In this group we will consider organs that have a thick wall and a fairly large lumen. Some of these are tubular, but as the tube has a large diameter, only part of it is seen in a section. The wall in most of these organs is made up of an inner mucosa, a submucosa and layers of muscle. One such organ, the oesophagus, has already been seen in . The vermiform appendix () also has a similar structure.
STOMACH
The basic structure of stomach is similar to oesophagus i.e. it is composed of (from within outwards):
- ❍ Mucosa
- ❍ Submucosa
- ❍ Muscularis externa
- ❍ Serosa
- ❑ Mucosa is lined by simple tall columnar epithelium. It shows invaginations called gastric pits.
- ❍ Lamina propria contains gastric glands.
- ❍ Muscularis mucosa is made of layers of smooth muscle.
- ❑ Submucosa consists of fibroelastic connective tissue, blood vessels and meissner's nerve plexus.
- ❑ Muscularis externa is composed of three layers of smooth muscle–inner oblique, middle circular and outer longitudinal.
- ❑ Serosa is visceral peritoneum (Simple squamous epithelium) over a layer of loose connective tissue.
Key
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
SMALL INTESTINE
The basic structure of small intestine is similar to oesophagus and stomach i.e. it is composed of:
- Mucosa
- Submucosa
- Muscularis externa
- Serosa
- ❑ Mucosa is made of simple columnar absorptive epithelium with goblet cells. The epithelium and the underlying lamina propria shows finger-like evaginations called intestinal villi. Epithelium also shows tubular invagination from the base of the villi into the lamina propria known as crypts of Lieberkuhn (intestinal glands). These crypts are lined by columnar and goblet cells.
- Lamina propria consisting of connective tissue
- Muscularis mucosa is made of smooth muscle fibres. This layer is responsible for movement and folding of mucosa
- ❑ Submucosa shows presence of Brunner's gland in duodenum and Peyer's patches in ileum
- ❑ Muscularis externa and serosa corresponds exactly with stomach.
JEJUNUM
The structure of jejunum should be regarded as typical for small intestine.
Key
- Submucosa
V. Villi
Cl. Crypts of Lieberkuhn
Duodenum
- ❑ The general structure of the duodenum is the same as that described for the small intestine, except that the submucosa is packed with mucous secreting glands of Brunner.
Key
- Lamina propria
- Muscularis mucosa
- Submucosa
- Muscularis externa
Bg. Brunner's gland present in submucosa
Cl. Crypts of Lieberkuhn present in lamina propria
Ileum
The general structure of the ileum is similar to that of the jejunum except for
- ❑ The entire thickness of the lamina propria is infiltrated with lymphocytes amongst which typical lymphatic follicles can be seen which extend into the submucosa. These lymphatic follicles are called as Peyer's patches.
- ❑ In the region overlying the Peyer's patch villi may be rudimentary or absent.
Key
P. Peyer's patches
Cl. Crypts of Lieberkuhn
Large Intestine
- ❑ The most important feature to note in large intestine is the absence of villi.
- ❑ The lamina propria shows numerous uniformly arranged crypts of Lieberkuhn in the entire thickness.
- ❑ The surface of the mucosa, and the crypts, are lined by columnar cells amongst which there are numerous goblet cells.
- ❑ The muscularis mucosae, submucosa and circular muscle coat are similar to those in the small intestine. However, the longitudinal muscle coat is gathered into three thick bands called taenia coli.
- ❑ The longitudinal muscle is thin in the intervals between the taenia.
Note: The mucosa is cut obliquely so that the deeper parts of the crypts appear circular.
Key
Cl. Crypts of Lieberkuhn
- Lamina propria
- Muscularis mucosa
- Submucosa
GALL BLADDER
It is characterised by
- ❑ The mucous membrane is lined by tall columnar cells with brush border. The mucosa is highly folded and some of the folds might look like villi.
- ❑ Crypts may be found in lamina propria.
- ❑ Submucosa is absent.
- ❑ The muscle coat is poorly developed there being numerous connective tissue fibres amongst the muscle fibres. This is called fibromuscular coat.
- ❑ A serous covering lined by flattened mesothelium is present.
Key
- Mucous membrane lined by tall columnar cells with brush border
- Lamina propria
- Fibromuscular coat
- Serosa
C. Crypt in lamina propria
URINARY BLADDER
- ❑ The organ is easily recognised because the mucous membrane is lined by transitional epithelium (Observe that the nuclei are distributed in the entire thickness of the epithelium and the appearance is uniform).
- ❑ The epithelium rests on a layer of lamina propria.
- ❑ The muscle layer is thick. It has inner and outer longitudinal layers between which there is a layer of circular or oblique fibres. The distinct muscle layers may not be distinguishable.
- ❑ The outer surface is lined in parts by peritoneum (not seen in slide).
Key
- Transitional epithelium
- Lamina propria
- Interstitial connective tissue
- Smooth muscle bundles
UTERUS
- ❑ The wall of the uterus consists of a mucous membrane (called the endometrium) and a very thick layer of smooth muscle (the myometrium). The thickness of the muscle layer helps to identify the uterus easily.
- ❑ The endometrium has a lining of columnar epithelium that rests on a stroma of connective tissue. Blood vessels are present in the lower portion of endometrium.
- ❑ Numerous tubular uterine glands dip into the stroma.
- ❑ The appearance of the endometrium varies considerably depending upon the phase of the menstrual cycle.
Key
- Columnar epithelium
- Connective tissue
- Uterine glands
- Blood vessels
E. Endometrium
M. Myometrium
TRACHEA
- ❑ The wall of the trachea is made up of layers but these are quite different from other tissues described above.
- ❑ Mucosa is formed by pseudostratified ciliated columnar epithelium with goblet cells and the underlying lamina propria.
- ❑ Submucosa is found deep to mucosa and is made up of loose connective tissue containing mucous and serous glands, blood vessels and ducts of the glands.
- ❑ The next layer is made up of hyaline cartilage. Chondrocytes increase in size from periphery to centre. They may appear as isogenous groups surrounded by darkly stained territorial matrix.
- ❑ External to the cartilage is the outer covering of collagen fibres called adventitia (not seen in slide).
Key
- Pseudostratified ciliated columnar epithelium
- Lamina propria
- Submucosa
- Hyaline cartilage
EYEBALL
The wall of the eyeball is made up of several layers as follows (from without inwards):
- Sclera, made up of collagen fibres.
- Choroid, containing blood vessels and pigment cells.The remaining layers are subdivisions of the retina.
- Pigment cell layer.
- Layer of rods and cones.
- Outer nuclear layer.
- Outer plexiform layer.
- Inner nuclear layer.
- Inner plexiform layer.
- Layer of ganglion cells.
- Layer of optic nerve fibres.
SOME ORGANS CONSISTING PREDOMINANTLY OF ACINI OR ALVEOLI
Acini are rounded structures found in glands. Each acinus appears as a rounded or oval mass. It is made up of cells but their boundaries are often not distinct. Each cell is more or less triangular, its base lying near the periphery of the acinus and its apex near the centre of the acinus. Each acinus has a small lumen that is often not seen. Acini are of two types. Some of them are dark staining (and usually bluish) and are termed serous acini. Others are very light staining. These are mucous acini. In the mammary gland, the secretory unit is termed alveolus, not acinus. Please do not confuse the alveoli of mammary gland with the alveoli of lung!
MIXED SALIVARY GLAND (SUBMANDIBULAR GLAND)
- ❑ The submandibular gland is characterised by the presence of both serous and mucous acini. In some cases serous cells are present in relation to mucous acini forming demilunes (or crescents).
Key
- Serous acini
- Mucous acinus
- Mucous acinus with serous demilune
- Duct
PANCREAS
- ❑ This gland is made up of serous acini.
- ❑ The cells forming the acini of the pancreas are highly basophilic (bluish staining). The lumen of the acinus is seldom seen.
- ❑ Amongst the acini some ducts are present.
- ❑ Some acini may show pale staining ‘centro-acinar cells’.
- ❑ At some places the acini are separated by areas where aggregations of cells is quite different from those of the acini. These aggregations form the pancreatic islets: these islets have an endocrine function.
Key
- Serous acini
- Pancreatic islets
MAMMARY GLAND
- ❑ Mammary gland consists of lobules of glandular tissue separated by considerable quantity of connective tissue and fat.
- ❑ Non lactating mammary glands contain more connective tissue and less glandular tissue.
- ❑ The glandular elements or alveoli are distinctly tubular. They are lined by cuboidal epithelium and have a large lumen so that they look like ducts. Some of them may be in form of solid cords of cells.
- ❑ Extensive branching of duct system seen.
Key
- Lobule
- Connective tissue
- Alveoli
- Duct
- Adipose tissue
SOME ORGANS SHOWING MULTIPLE TUBULAR ELEMENTS
KIDNEY
When we look at a section of the kidney we see that most of the area is filled with a very large number of tubules. These are of various shapes and have different types of epithelial lining. This fact by itself suggests that the tissue is the kidney.
- ❑ The kidney is covered by a capsule.
- ❑ Deep to the capsule there is the cortex.
- ❑ Deep to the cortex there is the medulla of the kidney.
- ❑ In the cortex circular structures called renal corpuscles are present surrounding which there are tubules.
- ❑ The lumen of proximal convoluted tubules is small and indistinct. It is lined by cuboidal epithelium with brush border. The distal convoluted tubule has a simple cuboidal epithelium and presents a distinct lumen.
- ❑ The medulla shows cut sections of collecting ducts and loop of Henle. Collecting ducts are lined by simple cuboidal epithelium and loops of Henle are lined by simple squamous epithelium.
- ❑ Cut sections of blood vessels are seen both in the cortex and medulla.
Key
- Renal corpuscle
- Proximal convoluted tubules
- Distal convoluted tubules
EPIDIDYMIS
- ❑ The body of the epididymis is a long convoluted duct.
- ❑ It shows cut sections of tubules lined by pseudostratified columnar epithelium in which there are tall columnar cells and shorter basal cells that do not reach the lumen. The columnar cells bear stereocilia.
- ❑ Smooth muscles are present around each tubule.
- ❑ Clumps of spermatozoa are present in the lumen of the tubule.
Key
- Pseudostratified columnar epithelium with stereocilia
- Spermatozoa clumps
- Smooth muscle fibres
SEMINAL VESICLE
- ❑ The seminal vesicle shows highly convoluted tubule and irregular lumen.
- ❑ It has an outer covering of connective tissue, a thin layer of smooth muscle and an inner mucosa.
- ❑ The mucosal lining is thrown into numerous folds that branch and anastomose to form a network.
- ❑ The lining epithelium is usually simple columnar or pseudostratified.
Key
- Folds of mucosa
- Muscle wall
SOME ORGANS THAT ARE SEEN IN THE FORM OF ROUNDED ELEMENTS THAT ARE NOT CLEARLY TUBULAR
TESTIS
- ❑ The testis has an outer fibrous layer, the tunica albuginea deep to which are seen a number of seminiferous tubules cut in various directions.
- ❑ The tubules are separated by connective tissue, containing blood vessels and groups of interstitial cells.
- ❑ Each seminiferous tubule is lined by several layers of germinal cells which will eventually form the spermatozoa.
Key
- Seminiferous tubule
- Interstitial cells of Leydig
PROSTATE
- ❑ The prostate consists of glandular tissue embedded in prominent fibromuscular tissue.
- ❑ The glandular tissue is in the form of follicles with serrated edges. They are lined by columnar epithelium.
- ❑ The lumen may contain amyloid bodies called corpora amylacea (pink stained).
- ❑ The follicles are separated by broad bands of fibromuscular stroma.
Key
- Follicles lined by columnar epithelium
- Corpora amylacea
- Fibromuscular tissue
THYROID GLAND
- ❑ The thyroid gland is made up of follicles lined by cuboidal epithelium.
- ❑ The follicles contain pink staining colloid. In the intervals between the follicles, there is some connective tissue.
- ❑ Parafollicular cells are present in relation to the follicles and also as groups in the connective tissue.
Key
Bv. Blood vessel
- Follicles lined by cuboidal epithelium
- Pink stained colloidal material
SOME TISSUES THAT APPEAR AS COLLECTIONS OF CELLS
LIVER
- ❑ Many hexagonal areas called hepatic lobules are present. The lobules are partially separated by connective tissue.
- ❑ Each lobule has a small round space in the centre. This is the central vein.
- ❑ A number of broad irregular cords seem to pass from this vein to the periphery of the lobule.
- ❑ These cords are made up of polygonal liver cells (hepatocytes).
- ❑ Along the periphery of the lobules there are angular intervals filled by connective tissue. Each such area contains a branch of the portal vein, a branch of the hepatic arter, and an interlobular bile duct. These three constitute a portal triad. The identification of hepatic lobules and of portal triads is enough to recognize liver tissue.
Key
- Central vein
- Radiating cords of hepatocytes
SUPRARENAL GLAND
The suprarenal gland is made up a large number of cells arranged in layers.
- ❑ It consists of an outer cortex and an inner medulla.
- ❑ The cortex is divisible into three zones.
- The zona glomerulosa is most superficial. Here the cells are arranged in the form of inverted U-shaped structures or acinus-like groups.
- In the zona fasciculata the cells are arranged in straight columns (typically two cell thick). Sinusoids intervene between the columns. The cells of this zone appear pale.
- The zona reticularis is made up of cords of cells that branch and form a network.
- ❑ The medulla is made up of groups of cells separated by wide sinusoids. Some sympathetic neurons are also present.
Key
- Capsule
- Zona glomerulosa
- Zona fasciculata
- Zona reticularis
C. Cortex
HYPOPHYSIS CEREBRI
- ❑ The hypophysis cerebri consists of three main parts.
- The pars anterior is cellular. It consists of groups or cords of cells with numerous sinusoids between them.
- The pars intermedia is variable in structure.
- The pars posterior consists of fibres, and is lightly stained
Key
- Pars anterior
- Pars intermedia
- Pars posterior
PARATHYROID GLANDS
- ❑ These glands are made up of masses of cells with numerous capillaries in between.
- ❑ Most of the cells (of which only nuclei are seen) are the chief cells (small basophilic cells).
- ❑ Oxyphilic cells and adipose cells are also seen. The number of oxyphilic cells is very less as compared to chief cells.
Key
- Chief cells
- Oxyphillic cells
- Adipose cells
CEREBRAL CORTEX
- ❑ The cerebral cortex consists of many cells having varied shapes. Nerve fibres, myelinated and unmyelinated, are also present. Blood vessels are seen. The nerve fibres are arranged in several layers as follows (from without inwards).
- Molecular layer consisting mostly of nerve fibres.
- External granular layer with densely packed nuclei.
- Pyramidal cell layer with large triangular cells.
- Internal granular layer.
- Ganglionic layer with large cells.
- Multiform layer with cells of varied shapes.
Key
- Molecular layer
- External granular
- Pyramidal cell layer
- Internal granular layer
- Ganglionic layer
- Multiform layer
P. Piamater
SENSORY GANGLIA
- ❑ Ganglia are of two types, sensory and autonomic.
- ❑ In sensory ganglion large pseudounipolar neurons are arranged in groups that are separated by bundles of nerve fibres.
- ❑ Each neuron has a vesicular nucleus with a prominent nucleolus. The neuron is surrounded by a ring of satellite cells.
Key
- Pseudounipolar neurons
- Nerve fibres
- Satellite cells
E–Epineurium
AUTONOMIC GANGLIA
- ❑ Autonomic ganglion consists of multipolar neurons which are not arranged in groups, but are scattered amongst nerve fibres.
- ❑ Satellite cells are present, but are less prominent than in sensory ganglia.
Key
- Multipolar neurons
- Nerve fibres
MISCELLANEOUS STRUCTURES THAT DO NOT FIT IN ANY OF THE GROUPS
LUNG
- ❑ The lung substance is made up of numerous alveoli.
- ❑ Alveoli are thin-walled spaces lined by simple squamous epithelium.
- ❑ The structure of large bronchus is similar to that of the trachea. Smooth muscle, cartilage and glands are present in its wall; and it is lined by pseudostratified ciliated columnar epithelium with goblet cells.
- ❑ Small bronchioles are lined by a simple columnar epithelium, and have a wall of smooth muscle. There is no cartilage in their walls.
- ❑ Bronchioles subdivide and when their diameters are approximately 1 mm or less, they are called terminal bronchioles.
- ❑ Arteries are seen near the bronchioles.
- ❑ Respiratory bronchiole and alveolar duct are also present.
- ❑ The lung surface is covered by pleura. It consists of a lining of mesothelium resting on a layer of connective tissue.
- ❑ This slide shows a medium-sized bronchiole surrounded by alveoli.
Key
- Alveoli
- Bronchiole
OVARY
Key
- Ovarian follicles
C. Cortex
M. Medulla
- ❑ The surface is covered by a cuboidal epithelium. Deep to the epithelium there is a layer of connective tissue that constitutes the tunica albuginea.
- ❑ The substance of the ovary has an outer cortex in which follicles of various sizes are present; and an inner medulla consisting of connective tissue containing numerous blood vessels.
- ❑ Just deep to the tunica albuginea many primordial follicles each of which contains a developing ovum surrounded by flattened follicular cells are present. Large follicles have a follicular cavity surrounded by several layers of follicular cells, membrana granulosa.
- ❑ The cells surrounding the ovum constitute the cumulus oophoricus.
- ❑ The follicle is surrounded by a condensation of connective tissue which forms a capsule for it.
- ❑ The capsule consists of an inner cellular part (the theca interna), and an outer fibrous part (the theca externa). The theca interna and externa are collectively called theca folliculi.
- ❑ The follicle is surrounded by a stroma made up of reticular fibres and fusiform cells.
Key
- Maturing oocyte
- Zona pellucida
- Cumulus oophoricus
- Discus proligerus
- Antrum folliculi
- Membrana granulosa
- Capsule
- Stroma
SPINAL CORD
- ❑ The spinal cord has a characteristic oval shape. It is made up of white matter (made up mainly of myelinated fibres), and grey matter (containing neurons and unmyelinated fibres). The grey matter lies towards the centre and is surrounded all round by white matter. The grey matter consists of a centrally placed mass and projections (horns) that pass forwards and backwards.
Note: The stain used for the slide is Luxol Fast Blue.
Key
- Posterior median septum
- Posterior white column
- Posterior grey column
- Lateral white column
- Anterior grey column
- Anterior white column
- Central canal lying in grey commissure. The fibres in front of the grey commissure form the anterior white commissure
- Anterior median sulcus.
AT. Anterior motor tracts
LT. Lateral motor tracts
CEREBELLUM
- ❑ The cerebellum contains leaf like folia. The core of each folium is formed by pink staining fibres of the white matter.
- ❑ The layers overlying the white matter form the cerebellar cortex which consists of (from without inwards):
- Molecular layer
- Purkinje cells
- Granule cell layer
- ❑ The cortex is covered by piamater.
Key
- Molecular layer
- Purkinje cells
- Granule cell layer
- White matter
P. Piamater
PERIPHERAL NERVE
- ❑ The nerve has been fixed in osmic acid that stains the myelin sheaths (around nerve fibres) black. The myelin sheaths, therefore, appear as black rings.
- ❑ The nerve fibres are arranged in bundles that are held by connective tissue (called perineurium).
- ❑ The connective tissue around individual nerve fibres is called endoneurium.
Key
- Perineurium
- Endoneurium