Basic Medical Sciences Epithlia

7/29/2019 Basic Medical Sciences Epithlia

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Basic medical sciences

Tissues

There are four main tissue types

Epithelial tissues

Connective tissues Muscle tissues and nervous tissues

Nervous Tissue,

Epithelial tissues

Epithelial tissues are sheets of cells witch cover or line the body surface and form secretory

glands they have a variety of functions which include

1. Crating a barrier which aid or prevents movement of substances into or out of the

structure

2. Release secretory products i.e. the goblet cells excrete mucus in the respiratory tract.

3. Protect surfaces, lubrication prevent abrasion and damage to organs.

The apical free surface faces the body surface, cavity lumen

space. The apical surfaces may contain cilia or microvillus.

The basal layer of an epithelial cell is the opposite of apical it is the

part that is closes to the basement membrane

The basemant membrane is a thin extracellular layer that commonly exist in two layers the basal

lamina (lamina = thin layer) this layer contain proteins such as collogen, laminin and

glycolprotiens the second part of the basement membrane is the recticular lamina this is closer

to the underlying connective tissue and contains proteins.

Apical = most superficial

Basal most deepest


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Classification

The classification of the epithelial cells depends on three things the:

How the sheets are made up. Epithelial sheets may be made up of either a single layer of

cells, a simple epithelium, or from several layers, called stratified epithelium.

The cell shape. The cells may have different shapes: cuboidal, squamous (flattened),columnar, or transitional (where the cells vary in shape across the different layers of thestratified epithelial sheet).

The type of surface specialisation, for example cilia or keratin

Glandular epithelial cells

Glandular epithelial cells store and secrete many compounds such as hormones and enzymes. Themost simple type of glandular epithelium are the unicellular goblet cells, which secrete mucus into theintestinal lumen. Epithelial cells are also organised into glands. Glandular epithelia form eitherexocrine glands, which are continuous with the body surfaces and secrete either to the outside ofthe body or into luminal spaces via an excretory duct, orendocrine glands, which are ductless andwhere the secretions pass directly into the bloodstream. For example, the sweat glands arecontinuous with the skin surfaces. In contrast, endocrine glands, such as the adrenal gland, surroundblood vessels and secrete hormones into the blood.

Exocrine secretion

Exocrine glands have a secretory portion, where the secretory product is released into the lumen ofthe gland, and an excretory portion consisting of a duct, by which the secretory product is transportedto the outside. Exocrine glands are classified as eithersimple (such as the sweat glands), where theduct is unbranched, orcompound where the secretory duct is branched and the gland is divided into

units called lobes, which themselves are further subdivided into lobules. A compound gland, such asthe salivary gland, contains many different types of epithelial cells in different parts of the gland.


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There are three types of secretion:

Merocrine, where the release is by exocytosis

e.g. salivary gland - secretion passes from cells without damage to plasma membrane Most glands secrete in this way

Apocrine, where part of the apical surface is pinched off with the secretions inside it

e.g. mammary gland

Holocrine, where the entire cell disintegrates to release the stored product.

e.g. sebaceous glandcellular debris part of secretion (sebum)

involves death of the cell


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In the mammary glands, milk proteins are secreted by merocrine secretion (exocytosis) and milk lipidsare secreted by apocrine secretion. An example of holocrine secretion occurs in the sebaceous

glands where sebum stored in the cytoplasm is released when the entire cell disintegrates.


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Cell junctions

Desmosome: binding spots between cells with proteins called cadherins

Tight junctions: impermeable

E.g. gut tube, doesnt let enzymes from gut into blood stream

Gap junctions: tubes that let small molecules pass between cells


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CONNECTIVE TISSUE

White fibrous connective tissue (tendon)

White fibrous tissue connects structures that require a mechanically strong bond.

The main functions of white fibrous tissue involve supporting and protecting the surrounding

structures

Contain collagen white coloured protein

Type 1 collagen found in tendons loosely/densely arranged depending on specimen

Arranged in Parallel fibres

X1 a stripy smear

x400


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MUSCLE

6 smooth non striated muscles

Smooth muscle is so named because, unlike other forms of muscle, the arrangement ofcontractile proteins does not give the histological appearance of cross-striations. This type ofmuscle forms the muscular component of visceral structures such as blood vessels, thegastrointestinal tract, the uterus and the urinary bladder, giving rise to the alternative name ofvisceral muscle. Since smooth muscle is under inherent autonomic and hormonal control, it

is also described as involuntary muscle. Structure:

Unlike Skeletal and Cardiac muscle tissue,Smooth muscle is not striated. Smoothmuscle fibres are small and tapered - withthe ends reducing in size, in contrast to thecylindrical shape of skeletal muscle. Eachsmooth muscle fibre has a single centrallylocated nucleus.

Function:Contractions of smooth muscleconstrict (i.e. narrow = reduce the

diameter of) the vessels they surround.This is particularly important in thedigestive system in which the action of smooth muscle helps to move food along thegastrointestinal tract as well as breaking the food down further. Smooth muscle alsocontributes to moving fluids through the body and to the elimination of indigestiblematter from the gastrointestinal system

Visualsmooth muscle fibres are elongated, spindle-shaped cells with tapered ends which mayoccasionally be bifurcated. Smooth muscle fibres are generally much shorter than skeletalmuscle fibres and contain only one nucleus which is elongated and centrally located in thecytoplasm at the widest part of the cell; however, depending on the contractile state of thefibres at fixation, the nuclei may sometimes appear to be spiral-shaped.


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Note thin fibers, with diameter not much greater than that of the nucleus

(about 5 m).

Each fiber is an individual cell, with length ranging from 20 to half a

millimeter (depending on location in the body).

Individual fibers are often not readily distinguishable (unlike skeletal muscle,

where individual fibers are huge and distinct).

Nuclei are normally long and cigar-shaped (they may appear wiggly in

contracted muscle).


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7 Striated (skeletal) muscle

Skeletal muscle is responsible for the movement of the skeleton and organs such as theglobe of the eye and the tongue. Skeletal muscle is often referred to as voluntary muscle

since it is capable of voluntary (conscious) control. The arrangement of the contractileproteins gives rise to the appearance of prominent cross-striations in some histologicalpreparations and so the name striated muscle is often applied to skeletal muscle. The highlydeveloped functions of the cytoplasmic organelles of muscle cells has led to the use of aspecial terminology for some muscle cell components: plasma membrane or plasmalemma =sarcolemma; cytoplasm = sarcoplasm; endoplasmic reticulum = sarcoplasmic reticulum.

This diagram illustrates the arrangement of the basic components which make up a typical skeletalmuscle.

The individual muscle cells (muscle fibres) are grouped together into elongated bundles calledfasciculi with delicate supporting tissue called endomysium occupying the spaces betweenindividual muscle fibres.

Each fascicle is surrounded by loose collagenous tissue called perimysium. Most muscles are madeup of many fasciculi and the whole muscle mass is invested in a dense collagenous sheath called theepimysium. Large blood vessels and nerves enter the epimysium and divide to ramify throughout themuscle in the perimysium and endomysium.

The size of the fasciculi reflects the function of the particular muscle concerned. Muscles responsiblefor fine, highly controlled movements, e.g. the external muscles of the eye, have small fasciculi and arelatively greater proportion of perimysial supporting tissue.


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Note large diameter (10-100 m) and extreme length of skeletal muscle

fibers.

Nuclei (many per fiber) are usually located along the margin of the fibers.

Striations may or may not be conspicuous, depending on staining and section

plane.

Sarcomere length (distance from one striation to the next) varies with state of

contraction. It is about 2 m for contracted muscle.


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8 Cardiac muscleCardiac muscle has many structural and functional characteristics intermediate between those ofskeletal and smooth muscle and provides for the continuous, rhythmic contractility of the heart.

Although striated in appearance, cardiac muscle is readily distinguishable from skeletal muscle andshould not be referred to by the term 'striated muscle'.Between the ends of adjacent cardiac muscle cells are specialised intercellular junctions, calledintercalated discs, which not only provide points of anchorage for the myofibrils but also permitextremely rapid spread of contractile stimuli from one cell to another. Thus, adjacent fibres aretriggered to contract almost simultaneously, thereby acting as a functional syncytium. In addition, a

system of highly modified cardiac muscle cells constitutes the pacemaker regions of the heart andramifies throughout the organ as the Purkinje system, thus coordinating contraction of themyocardium as a whole in each cardiac cycle

Note that fibers branch and interconnect.

Fibers consist of individual cells attached end-to-end.

Nuclei (one per cell) are centrally located within each cell.

Intercalated discs are sites of attachment between cells.

Striations may or may not be conspicuous (not here), depending on stain and

plane of section


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INTEGUMENT

Skin

Skin structure

The skin has three main layers:

Epidermis - a self-regenerating stratified squamous epithelium which produces a surfacelayer of the protein, keratin, which is the component of skin in direct contact with externalenvironment.

Dermis - a layer of fibrocollagenous and elastic tissue which contains blood vessels, nervesand sensory receptors.

Subcutis or hypodermis - the deepest layer of skin which is mainly adipose tissue, but also

contains the larger vessels which supply and drain the dermal blood vasculature.

In addition there are the skin appendages, specialised structures such as hair follicles, sweat glandsand sebaceous glands which arise as downgrowths into the dermis from the epidermis duringembryological development. These skin appendages mainly occupy the dermis and, occasionally, theupper subcutis.


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E= epidermis D=DERMIS EG=ENDOCRINE GLAND SC= SUBCUTIS ED= ENDOCRINE DUCT

K= KERATIN BV = BLOOD VESSEL

BV


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The skin appendages include:

Hair follicles which produce long thin cylindrical structures (hair shafts) composed largely ofkeratin arranged in an organised manner. In normal coarse hair, each hair shaft is composedof a central medulla surrounded by a cortex, with a surface cuticle composed of a singlelayer of flattened scales. In the animal kingdom the function of hair is thermoregulation(particularly heat conservation) and display; only the latter function can be ascribed to hair inhumans. The structure of the hair follicle is complex (Fig. 9.8), and hair growth is cyclical, withthree phases - a phase of active growth (anagen), a phase of involution (catagen) and a

resting phase (telogen). In the scalp, most hairs are in the anagen phase with their baseslocated in subcutis; telogen hairs have their bases in mid-dermis.

Sebaceous glands occur in two forms. The majority are associated with hair follicles, anddevelop as lateral protrusions from the hair follicle at about the junction between its upperthird and lower two thirds. Sebaceous glands secrete a mixture of lipids called sebum, whichmay provide some waterproofing of the skin surface and hair shafts; the sebum is secretedinto the hair follicle (seeFig. 9.9c). At some sites in the skin (areolae and nipples, labiaminora of vulva, eyelids) and in the buccal and labial mucosa, the sebaceous glands areindependent of hair follicles and open directly onto the skin or mucosal surface.

Eccrine sweat glands are widespread throughout the skin. They are located around thejunction between dermis and subcutis and synthesise a thin watery liquid (sweat) which ispassed along eccrine ducts and deposited onto the skin surface. Evaporation of this sweatreduces body temperature.

Apocrine glands are confined to a few localised areas, mainly in the axillary and groinregions. Like eccrine sweat glands, the secretory component is located in lower reticulardermis or subcutis, and a duct system carries the secretion to be discharged into the upperpart of the hair follicle above the sebaceous duct. Apocrine gland secretions in humans haveno definite function, but in animals they are responsible for scent production, used in territorymarking and as a sexual attractant.

HAIR FOLICLE

CT =connective tissue sheath Cu= cuticle Cx= cortex IRS= internal root sheath ERS= external root

sheath HP= hair papilla GM= glassy membrane

Ref =pg 177 LIYDF
http://www.studentconsult.com/content/bookcontent.cfm?ID=HC009011&channel=tochttp://www.studentconsult.com/content/bookcontent.cfm?ID=HC009011&channel=tochttp://www.studentconsult.com/content/bookcontent.cfm?ID=HC009011&channel=tochttp://www.studentconsult.com/content/bookcontent.cfm?ID=HC009011&channel=tochttp://www.studentconsult.com/content/bookcontent.cfm?ID=HC009011&channel=tochttp://www.studentconsult.com/content/bookcontent.cfm?ID=HC009011&channel=tochttp://www.studentconsult.com/content/bookcontent.cfm?ID=HC009011&channel=tochttp://www.studentconsult.com/content/bookcontent.cfm?ID=HC009011&channel=toc


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Sebaceous glands

F= hair follicle G= sebaceous gland M= erector Pilli muscle

http://www.siumed.edu/~dking2/index.htm

http://students.auamed.net/histology/histobase.htm
http://www.siumed.edu/~dking2/index.htmhttp://www.siumed.edu/~dking2/index.htmhttp://students.auamed.net/histology/histobase.htmhttp://students.auamed.net/histology/histobase.htmhttp://students.auamed.net/histology/histobase.htmhttp://www.siumed.edu/~dking2/index.htm

Basic Medical Sciences Epithlia

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