general histology

GENERAL HISTOLOGY

DR SAMINA SHAHEENASSISTANT PROFESSOR OF ANATOMY

KEMU

BASIC TISSUES

Epithelium

Connective tissue

Muscular tissue

Nervous tissue

Organs divided into:

Parenchyma –cells

Stroma –supporting tissue

SIMPLE SQUAMOUS EPITHELIUM

Composed of very thin flat

irregular shaped cell that form

a continuous surface

Also called pavement

epithelium

Found in:

Lining of blood & lymph vessels

Alveoli of lungs

Parietal layer of Bowman’s

capsule

Loop of Henle in kidney

SIMPLE CUBOIDAL EPITHELIUM

Cells appear cube or box like

Nucleus is rounded & placed in

centre of cell

cells rest on basement

membrane

Present in:

Follicles of thyroid gland

Distal convoluted tubules of kidney

FUNCTION

Absorption

excretion

SIMPLE COLUMNAR NON CILIATED EPITHELUIUM

Composed of tall columnar cells

Rests on basement membrane

Nucleus in elongated & lies in basal half of cell

Apical surface of cells may have microvilli which give apperance of brush border

Found in: Lining of GIT FUNCTIONS: Absorption Excretion

SIMPLE COLUMNAR CILIATED EPITHELIUM

CILIA present on surface of

simple columnar epithelium

Present in:

Small intrapulmonary bronchi

Simple columnar non-ciliated

cells may be present between

ciliated cells

Example :

Uterine tube

Efferent ductules of testis

PSEUDOSTRATIEIED EPITHELIUM

NON-CILIATED

Variant of simple columnar

epithelium

Tall & short cells are present

All cells rest on basement

membrane

Nuclei disposed at different

levels

Present in;

Parts of male urethra

PSEUDOSTRATIEIED EPITHELIUM

CILIATED

This epithelium

may be ciliate

with goblet cells

Example:

Trachea

Larger bronchi

STRATIFIED EPITHELIASTRATIFIED SQUAMOUS NON

KERATINIZEXEPITHELIUM Multi-layered Basal layer low columnar or high

cuboidal This layer divides Subsequent layers polygonal Surface layers flattened Underlying connective tissue

raised into ridges Examples : Oesophagus Anal canal Cervix Vagina

STRATIFIED SQUAMOUS KERATINIZED EPITHELIUM

Features same as

non-keratinized

epithelium except

Surface layer

composed of non-

nucleated cells

They acquire

protein keratin

Example :

Skin

TRANSITIONAL EPITHELIUM

IN RELAXED STATE Is 4-5 cell layer thick Basal layer is cuboidal Intermediate layer is

polyhedral surface layer is cuboidal

with binucleate cells

IN STRETCHED STATE Is 2-3 cell thick Surface layer is

squamous Example : urinary tract

STRATIFIED CUBOIDAL

Consists of two

layers of cuboidal

cells

Cells of superficial

layer are smaller

Examples :

Ducts of salivary

glands

Ducts of sweat

glands

STRATIFIED COLUMNAR EPITHELIUM Basal layer consists of low columnar or cuboidal cells

Surface layer is of tall columnar cells

Examples :

Conjunctiva

Parts of male urethra

ENDOTHELIUM Lines all blood & lymph channels

MESOTHELIUM Lining of pleura, pericardium & peritoneum

CONNECTIVE TISSUE

Characterized by the presence of relatively few cells & abundant

intercellular substance

FUNCTIONS

STRUCTURE

Cells

Fibres

Ground substance

Develops from MESENCHYME

CELLS OF CONNECTIVE TISSUE

Fibroblasts

Mast cells

Plasma cells

Macrophages (histiocytes)

Leukocytes

Adipocytes

MESENCHYMAL CELLS

FIBROBLASTS

MACROPHAGES

PLASMA CELLS

MAST CELLS

ADIPOCYTES

FIBERS OF CONNECTIVE TISSUE

Collagen

Elastic

Reticular

COLLAGEN FIBERS

ELASTIC FIBERS

RETICULAR FIBRES

GROUND SUBSTANCE

Glycosaminoglycans (mucopolysaccharides)

Proteoglycans

Multiadhesive glycoproteins

TYPES OF CONNECTIVE TISSUE

Embryonic connective tissue Mesenchyme Mucous

Adult connective tissue Connective tissue proper

Loose Dense

Irregular Regular

Specialized Reticular Adipose

Bone Cartilage

LOOSE CONNECTIVE TISSUE & DENSE IRREGULAR CONNECTIVE

TISSUE

DENSE REGULAR CONNECTIVE TISSUE

RETICULAR TISSUE

EMBRYONIC CONNECTIVE TISSUE

MESENCHYME MUCOUS

CARTILAGE

Cells (chondrocytes)

Extra-cellular matrix

Fibrils

Ground substance

Proterglycan

Glycosaminoglycanp (mucopolysaccharide)

TYPES OF CARTILAGE

Hyaline

Elastic

Fiibrocartilage

HYALINE CARTILAGE

ELASTIC CARTILAGE

FIBROCARTILAGE

BONE

Cells Osteocytes Osteoblasts Osteoclasts

Bone matrix Organic

Collagen type 1 Ground substance

Proteoglycans Glycoproteins

Inorganic Hydroxyapatite Ca Po4, magnesium, bicarbonate, citrate, sodium & potassium

TYPES OF BONE(GROSS OBSERVATION)

TYPES OF BONE(MICROSCOPIC EXAMINATION)

PRIMARY/IMMATURE BONE SECONDARY/ MATURE

MUSCLE

Skeletal muscle

Smooth muscle

Cardiac muscle

ORGANIAZATION OF SKELETAL MUSCLE

Endomysium – muscle fiber

Perimysium – fascile

Epimysium – entire muscle

ORGANIZATION OF SKELETAL MUSCLE

SKELETAL MUSCLE

CARDIAC MUSCLE

CARDIAC MUSCLE

SMOOTH MUSCLE

SMOOTH MUSCLE

COMPARISON BETWEEN THE THREE TYPES OF MUSCLES

NERVE TISSUE & NERVOUS SYSTEM

Central nervous system Brain & spinal cord

Peripheral nervous system Spinal, cranial & peripheral nerves ganglia

Nerve cells (neuron) Glial cell (supporting cells)

STRUCTURE OF NEURON

Cell body

Axon

dendrite

GLIAL CELLS

CNS

Oligodendrocytes

Ependymal cells

Astrocytes

Microglial cells

PNS

Neurolemmocytes

(Schwann cells)

Saltellite cells

PERIPHERAL NERVOUS SYSTEMCOMPONENTS OF PNS• Nerves• Ganglia• Nerve endings.CONNECTIVE TISSUE COMPONENTS OF A

PERIPHERAL NERVE:• Endoneurium: constitues the loose c.t

associated with individual nerve fiber. It merges with an external lamina of IV collagen ,laminin and other proteins produced by schwann cells. Other cells are fibroblasts and mast cells.

• Perineurium is a specialized c.tissue surrounding a nerve fascicle. It serves as a metabolically active diffusion barrier that contribute to the formation of blood –nerve barrier. It may be one or two cell thick depending on the nerve diameter .It is formed by layers of flattened epithelial cells. The cells of each layer of the perineurium are joined at their edges by tight junctions

• Epineurium consists of dense irregular c .tissue that surround and binds nerve fascicles into a common bundle. Blood vessels that supply the nerve travel in epineurium.

GANGLIA• It is an ovoid structures

contain neuronal cell bodies and glial cells supported by c.tissue.

• Serves as relay stations to transmit nerve impulses.

Types of ganglia:• Sensory ganglia: They

receive afferent impulses that go to the CNS. They are associated with cranial nerves called cranial ganglia, and the dorsal root of spinal nerves called spinal ganglia

continued….• Connective tissue capsule which is continuous

with the epineurium of nerve on which ganglion is situated Ganglion cells are neurons of pseudounipolar type. Each neuron gives rise to a single process which makes several irregular turns around the cell body and bifurcate in a T- shaped manner. One branch acts as dendrite and pass in a spinal or cranial nerve to periphery and terminate at a receptor and other branch act as functional axon and passes to CNS. Size of nerve cell body varies. Small cell bodies give rise to unmyelinated processes, large perikarya give origin to myelinated processes. Nerve cell bodies are arranged as groups in peripheral zone of ganglion and surrounded by a single layer of low cuboidal cells called satellite cells. The central zone is devoid of nerve cell bodies and contain nerve fibers.

AUTONOMIC GANGLIA• They are associated with

sympathetic and parasympathetic division of autonomic nervous system.

• Arranged as small bulbous dilatations in autonomic nerves.

• Located in certain organs especially in the wall of GIT called intrameural ganglia.

• Covered by less well developed c. tissue capsule.

• Multipolar neuron which are evenly distributed.

• Covered by a layer of satellite cells.

• Parasympathetic ganglia lacks distinct capsule, perikarya and associated satellite cells form a loosely organized plexus within the surrounding c .tissue.

STRUCTURE OF THE CEREBRAL CORTEX The cerebral cortex forms a

complete covering of the cerebral hemisphere. It is composed of gray matter and contains approx. 10 million neurons. The gray matter contains nerve cells, neuroglia and blood vessels. The following types of nerve cells are present in the cerebral cortex: Pyramidal cells Nonpyramidal cells

PYRAMIDAL CELLS

Contains a large vesicular nucleus

Abundant nissl granules One main dendrite arises from

the apex and ends in the most superficial layer of the cortex.

Four or more branching dendrite pass outward from the base of the perikaryon.

Axon emerges from the center of the base and runs into the underlying white matter.

Classified into small, medium and large varieties.

Nonpyramidal cells Stellate/granule cells: small polygonal

perikaryon; each cell gives off a number of small dendrites passing in various direction and a short axon which ramifies close to the cell body; most of the extrinsic inputs to the cerebral cortex terminate on the dendrites of the stellate cells.

Horizontal cells of cajal: small, fusiformed, horizontally oriented; found in the most superficial cortical layer; has many short dendrites and a long axon which runs parallel to the surface of the cortex making contact with the dendrites of the pyramidal cells.

CONTINUED Martinotti cells: small, multipolar cells found in the

deeper layers of the cerebral cortex; has a short dendrite but the long axon ascends towards the cortical surface to end in a more superficial layer.

Fusiform cells. They have long axis vertical to the surface and concentrated mainly in the deeper cortical layers.Dendrites arise from each pole of the cell body and ascend toward the surface of the surface of the cortex and branch in the superfical layers. The axon arises from the inferior pole of cell body and enter the white matter as a projection ,association or commissural fiber.

LAYERS OF THE CEREBRAL CORTEX Molecular or Plexiform Layer:

composed chiefly of cell processes (of the cells lying in the deeper layers). Some horizontal cells are also present.

External Granular Layer: contains large number of small pyramidal cells and numerous closely packed stellate cells.

Pyramidal Cell Layer: also known as external pyramidal layer and is composed mainly of large pyramidal cells. some granule cells are also present.

Internal Granular Layer: consists of closely packed stellate cells. There is a high concentration of horizontally arranged nerve fibers known as outer band of Baillarger.

Ganglionic Layer: also known as internal pyramidal layer contains large pyramidal cells. Scattered among the pyramidal cells are stellate and martinotti cells. This layer also contains a large number of nerve fibers which forms the inner band of Baillarger.

Multiform Layer: composed of neurons of many shapes. Also contains pyramidal cells, stellate cells and martinotti cells.Many nerve fibers are also present that are entering or are leaving the underlying white matter.

All areas of cerebral cortex do not possess six layers.

They are called as heterotypical as compared to majority which are homotypical and possess six layers.

Two heterotypical areas are the granular type and the agranular type.

In the granular type layer 2 and 4 are well developed and layer 3 and 5 are poorly developed. It is found in postcentral gyrus.

In agranular type layer 2 and 4 are absent, pyramidal cells in layer 3 and 5 are densely packed and are very large . It is found in precentral gyrus. These areas are associated with motor functions.

CEREBELLUM Cerebellum is

composed of an outer covering of gray matter called cortex and inner white matter. Embedded in the white matter of each hemisphere are three masses of gray matter forming intracerebellar nuclei.

STRUCTURE OF CEREBELLIUM The cerebellar cortex on section shows

three layers from within outwards. Molecular layer: This layer contains

two types of neurons, the outer stellate cells and inner basket cells. These neurons are scattered among dendritic arborizations and numerous thin axons that run parallel to the long axis of the folia. Neuroglial cells are found between these structures.

The Stellate cells have small star- shaped perikarya.Each cell has many short thin dendrites and a fini unmyelinated axon.The dendrites ramify near the cell body,while the axon extends tranversely to make synapses with the dendrites of Purkinje cells.

The Basket cells have small perikarya which give rise to numerous branching dendrites that ascends towards the surface. The unmyelinated axons of the basket cell runs horizontally,along its course it gives off many descending branches which form basket like terminal arborization around the bodies of the Purkinje cells.

PURKINJE CELL LAYER The Purkinje cells are large Golgi type l

neurons they are flask shaped and are arranged in a single layer. In a plane transverse to the folium ,the dendrites pass into the molecular layer, where they undergo profuse branching. The primary and secondary branches are smooth and subsequent branches are covered by short thick dendritic spines.Spine form synaptic contacts with the parallel fibers derived from the granule cell axons.

At the base of thePurkinje cells, the axons arises and passes through the granular layer to enter the white matter. On entering the white matter, the axons acquires a myelin sheath, and it terminates by synapsing with cells of one of the intracerebellar nuclei .Collateral branches make synaptic contact with the dendrites of basket and stellate cells of the granular layer in the same area or in distal folia. A few Purkinje cell axons pass directly to end in the vestibular nuclei of the brainstem.

GRANULAR LAYER

Small granule cells with dark staining nucleous with very little cytoplasm.

Also present in this layer are Golgi type II cells with vesicular nucleous and abundant cytoplasm

Clear spaces called glomeruli are present in this layerEach granule cell give rise to four to five short

dendrites .The unmyelinated axon of agranule cell ascend to the molecular layer where it bifurcate into two branches and called parallel fibers .Thesefibers make synapses with dendrites of purkinje cells. .

AFFERENT FIBERS OF CEREBELLUM Climbing fibers .They originate from inferior

olivery nucleus of m.oblongata.Asthey enter in cerebllum they run in white matter and then synapse with dendrites of purkinje cell in molecular layer.

Mossy fibers .They originates in spinal cord and terminate in glomeruli of cerebellar cortex where they synapse with dendrites of granule cells and axons of golgi type11 cells

CEREBELLUM

CEREBELLUM

SENSORY NERVE ENDINGS OR RECEPTORS• Morphologically divided into:• Non –encapsulated or free nerve endings• Encapsulated nerve endings• Free nerve endings• Afferent fibers are myelinated or unmyelinated• Specialized to respond to sensation of pain,

temperature or light touch.• In epidermis of skin they form disc like endings

with modified epithelial cells called Merkel corpuscle.

• Function as mechanoreceptors, detecting mechanical displacement of skin.

ENCAPSULATED NERVE ENDINGSTactile corpuscles of meissner:• Located in non hairy skin especially finger

tips, palm and soles, lips and nipples.• Oval bodies covered by c.t capsule

continuous with epineurim of nerve supplying the corpuscle which contain multilayered flattened cells.

• Myelinated nerve fibers supply each corpuscle.

• They are concerned with perception of touch sensation.

RUFFINIS ENDINGS

Fusiform struture 1-2mmin length and present in skin in joint capsule.

Consist of thin c.tissue capsule containing a fluid filled space.

A single myelinated nerve supply it .

Function as mechanoreceptor.

END BULB OF KRAUSE

They are spherical bodies covered by a c.tissue capsule and contain a central cavity.

A myelinated nerve supply it. Concerned with perception of cold

sensation Present in skin.

MUSCLE SPINDLES• Present in skeletal

muscle.• Fusiform structure,0.5-

5mm in length.• Consist of intrafusal

fibers and covered by a capsule.

• Supplied by both afferent and efferent fibers.

• Concerned with regulation of reflex muscle tone.

TENDON ORGANS OF GOLGI

Located in tendons close to muscle tendon junction.

Consist of small bundle of collagen fibers covered by a c.tissue capsule.

A large myelinated nerve enter the organ.

They respond to an increase in muscle tension.

NERVE FIBERS

PERIPHERAL NERVE

Endoneurium

Perineurium

epineurium

CIRCULATORY SYSTEM

Heart

Arteries

capillaries

Veins

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Blood Vessel Tunics Tunica Intima, or Tunica Interna

innermost layer composed of:

an endothelium (simple squamous epithelium) subendothelial layer (areolar CT)

Tunica Media middle layer of the vessel wall composed of:

circularly arranged smooth muscle cells Sympathetic innervation:

Increase: vasoconstriction (narrowing of the blood vessel lumen)

Decrease: vasodilation (widening of the blood vessel lumen)

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Blood Vessel TunicsTunica Externa, or Tunica Adventitia

outermost layer composed of:

areolar connective tissue that contains elastic and collagen fibers helps anchor the vessel to other tissues Term adventitia is used to specify outer layer in blood

vessels that are buried in CT Vasa vasorum : blood vessels that supply large blood

vessels In the externa

Arteries vs Veins: Media largest in arteries, externa largest in veins Lumen is smallest in arteries Artery wall have more elastic and collagen fibers

Capillaries: only the Interna

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Arteries In the systemic circulation, carry

oxygenated blood to the body tissues. Pulmonary arteries carry deoxygenated

blood to the lungs. Three basic types of arteries:

elastic arteries, muscular arteries, and arterioles

as an artery’s diameter decreases corresponding decrease in the amount of elastic fibers relative increase in the amount of smooth muscle

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Capillaries Contain only the tunica intima, but this layer

consists of a basement membrane and endothelium only.

Allow gas and nutrient exchange between the blood and the body tissues to occur rapidly.

Smallest blood vessels, connect arterioles to venules.

Are called the functional units of the cardiovascular system.

A group of capillaries (10–100) functions together

and forms a capillary bed.

STRUCTURE OF BLOOD VESSELS

Endothelium Smooth muscle Connective

tissue Collagen fibers Elastic fibres

Tunica intima Tunica media Tunica

adventitia

ARTERIES

Elastic artery

Muscular aryery

Arterioles

Capillaries

ELASTIC ARTERY

MUSCULAR ARTERY

ARTERIOLE

CAPILLARIES

STRUCTURE OF VEINS

VEINS

Venules

Medium sized veins

Large sized veins

SMALL VEIN

MEDIUM SIZED VEIN

LARGE VEIN

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