Color Atlas A17
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.
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Fig. A10.1: Spleen
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A18 Textbook of Human Histology
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.
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Fig. A11.1: Thymus
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.
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Fig. A12.1: Palatine tonsil
Color Atlas A19
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 (keratinized). The epidermis rests on a thick layer of connective tissue which is called the dermis.
Thick Skin
Thick or glabrous skin is characterized byPresence 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 dermisThick skin is found in palm of hand and
sole of foot.
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Fig. A13.1:
Thin Skin
Thin skin or hairy skin is characterized byPresence 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.
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A20 Textbook of Human Histology
TONGUE
The tongue is another structure covered on both surfaces by stratified squamous epithelium (non-keratinized)
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
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Fig. A14.1: Tongue |
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ESOPHAGUS |
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Fig. A15.1: Esophagus (Low power) |
Fig. A15.2: Esophagus (High power) |
In transverse section the esophagus shows the following layers (from within outwards):
Lining of non-keratinised stratified squamous epitheliumThe underlying connective tissue of the lamina propria
The muscularis mucosae in which the muscle fibers are cut transversely.The lining epithelium, lamina propria and muscularis mucosa collectively
constitute the mucosa
The submucosa having esophageal 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 esophagus, mixed in the middle one-third, and smooth in the lower one-third.
Color Atlas A21
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-keratini- sed 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 esophagus.
Muscular layer consists of smooth muscle fibers.
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Fig. A22.1: Vagina
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CORNEA
The cornea is made up of five layers
The outermost layer is of non-keratinized stratified squamous epithelium (corneal epithelium)
The corneal epithelium rests on the structureless anterior limiting lamina
Most of the thickness of the cornea is formed by the substantia propria (or corneal stroma) made up of collagen fibers 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.
Fig. A16.1: Cornea
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A22 Textbook of Human Histology
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 esophagus, has already been seen in Fig. A15.1. The vermiform appendix (Fig. A5.1) also has a similar structure.
STOMACH
The basic structure of stomach is similar to esophagus, i.e. it is composed of (from within outwards):
Mucosa
Submucosa
Muscularis externaSerosa
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
Fig. A17.1: Stomach muscle—inner oblique, middle circular, and outer longitudinal
Serosa is visceral peritoneum (Simple squamous epithelium) over a layer of loose connective tissue.
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SMALL INTESTINE
The basic structure of small intestine is similar to esophagus 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 fibers. 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.
Color Atlas A23
JEJUNUM
The structure of jejunum should be regarded as typical for small intestine.
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Fig. A18.1: Small intestine
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.
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Fig. A18.2: Duodenum
Note: Intestinal crypts lie “above” the muscularis mucosae while the glands of Brunner lie ‘below’ it. The presence of the glands of
Brunner is a distinctive feature of the duodenum.
A24 Textbook of Human Histology
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.
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Fig. A18.3: Ileum
Presence of Peyer's patches is the most distinguishing feature of ileum.
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.
Fig. A19.1: Large intestine
Note: The mucosa is cut obliquely so that the deeper parts of the crypts appear circular.
A section of the large intestine is easily distinguished from that of the small intestine because of the absence of villi; and from the stomach because of the presence of goblet cells (which are absent in the stomach).
Color Atlas A25
GALLBLADDER
Fig. A20.1: Gall Bladder
GallBladder can be differentiated from small intestine by:Absence of villi
Absence of goblet cellsAbsence of submucosa
Absence of proper muscularis externa
It is characterized by the following features:
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 propriaSubmucosa is absent
The muscle coat is poorly developed there being numerous connective tissue fibers amongst the muscle fibers. This is called fibromuscular coat
A serous covering lined by flattened mesothelium is
present.
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URINARY BLADDER
The organ is easily recognized 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 fibers. The distinct muscle layers may not be distinguishable.
The outer surface is lined in parts by peritoneum (not seen in slide).
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Fig. A21.1: Urinary Bladder
A26 Textbook of Human Histology
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.
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Fig. A23.1: Uterus
You might confuse this appearance with that of the large intestine. To distinguish between the two remember that in the uterine
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TRACHEA
