TISSUES

Tissues are communities of cells working together to perform a function for the organism.

Remember at all times that we are still talking about CELLS!

Even though commonly we think of organs as heart, lungs, kidney etc. that other tissues are also called organs such as muscles, bones etc.

Four Basic Tissue Types and Basic Functions

Epithelial tissue – covering - ectoderm Connective tissue – support –

mesoderm/endoderm Muscle tissue – movement - mesoderm Nervous tissue – control - ectoderm

Epithelial Tissue

Covers the body surface and lines body cavities Forms parts of most glands (organs are mainly epithial

and connective tissues with nerves and blood vessels serving the cells)

Functions of epithelium Protection – part of immune system Absorption (intestine), secretion (glands), and ion transport

(nephron tubules) Filtration (capillaries) Forms slippery surfaces (mucus membranes) Glandular Epithelium (sweat, oil, wax, hormones, mucus) Greatest capacity for regeneration (therefore is the origin of

most cancers)

Classifications of Epithelia First name of tissue indicates number of cell layers

Simple – one layer of cells Stratified – more than one layer of cells

Last name of tissue describes shape of cells Squamous –

cells are wider than tall (plate-like)

Cuboidal – cells are as wide as tall, like cubes

Columnar – cells are taller than they are wide, like columns

EPITHELIUM AS GLANDS

EXOCRINE GLANDS –with ducts ENDOCRINE GLANDS – without ducts

Exocrine Glands

Ducts carry products of exocrine glands to epithelial surface

Include the following diverse glands Mucus-secreting glands Sweat and oil glands Salivary glands Liver and pancreas

Goblet cells produce mucin Mucin + water mucus Protects and lubricates many internal body surfaces Goblet cells are a unicellular exocrine gland and

are epithelial

Goblet Cells – a type of epithelial cell (Unicellular gland)

Figure 4.5

Multicellular Exocrine Glands

Have two basic parts Epithelium-walled duct Secretory unit

Classified by structure of duct Simple Compound

Categorized by secretory unit Tubular Alveolar Tubuloalveolar

Types of Multicellular Exocrine Glands

Figure 4.6

For information only!

Endocrine Glands

Endocrine glands are ductless glands Secrete substances directly into extracellular space

to be picked up by the bloodstream by diffusion Produce molecules called hormones

Special Characteristics of Epithelia1) Cellularity - cells separated by minimal extra cellular material

2) Specialized contacts - cells joined by specialized cell junctions

3) Polarity - cell regions of the apical surface differ from the basal surface

Special Contacts (Lateral Surface Features) – Cell Junctions

Think about the function of epithelial tissues and what characteristics it would have to have to perform that function.

Since exposure to digested food would be very dangerous if exposed to the contents of the abdominal cavity, the intestinal tissue needs to be a barrier.

Therefore, cells need to be tightly held together Factors holding epithelial cells together

Adhesion proteins link plasma membranes of adjacent cells Contours of adjacent cell membranes

(Like puzzle pieces)

Special cell junctions

A) Tight Junction

Figure 4.7aTight junctions (zona occludens) – close off intercellular space

B) Desmosome

Figure 4.7b

Desmosomes – two disclike plaques connected across intercellular space

C) Gap Junction

Figure 4.7c

Gap junctions – passageway between two adjacent cells

D) Adherens Junctions

Has linker proteins;

Important for the skin

Zonula adherens

Special Characteristics of Epithelia4) Support by connective tissue

5) Avascular but innervated - Epithelia receive nutrients from underlying connective tissue

6) Regeneration - Lost cells are quickly replaced by cell division

Basal Feature: The Basal Lamina

Noncellular supporting sheet between the ET and the CT deep to it

Consists of proteins secreted by ET cells

Basal Lamina

Damage to the basal lamina due to untreated diabetes may lead to kidney failure and blindness.

Basal Feature: The Basal Lamina

Functions Acts as a selective filter, determining which

molecules from capillaries enter the epithelium Acts as scaffolding along which regenerating ET

cells can migrate

Basal lamina and reticular layers of the underlying CT deep to it form the basement membrane

Epithelial Apical Surface Features Apical surface features

1) Microvilli – fingerlike extensions of plasma membraneAbundant in ET of small intestine and kidneyMaximize surface area across which small

molecules enter or leaveAct as stiff knobs that resist abrasion

2) Cilia – whiplike, highly motile extensions of apical surface membranesContains a core of nine pairs of microtubules

encircling one middle pairEach pair of microtubules – arranged in a

doublet Movement of cilia – in coordinated waves

Cilia – found in upper respiratory passageways

Figure 4.8

For information only

Simple Squamous Epithelium

Description – single layer – flat cells with disc-shaped nuclei

Specialized types Endothelium (inner covering) – slick lining of

hollow organs Mesothelium (middle covering)

Lines peritoneal, pleural, pericardial cavities Covers visceral organs of those cavities

Simple Squamous Epithelium

Figure 4.3a

Simple Cuboidal Epithelium

Figure 4.3b

Simple Columnar Epithelium

Figure 4.3c

Pseudostratified Ciliated Columnar Epithelium

Figure 4.3d

Stratified Epithelia

Properties Contain two or more layers of cells Regenerate from below (basal layer) Major role is protection Named according to shape of cells at apical layer

Stratified Squamous Epithelium

Description Many layers of cells – squamous in shape Deeper layers of cells appear cuboidal or columnar Thickest epithelial tissue

Adapted for protection from abrasion

Stratified Squamous Epithelium

Two types Keratinized and nonkeratinized

KeratinizedLocation – epidermis Contains the protective protein keratinWaterproof Surface cells are dead and full of keratin

Nonkeratinized Forms moist lining of body openings

Stratified Squamous Epithelium

Figure 4.3e

Stratified Cuboidal Epithelium

Figure 4.3f

Stratified Columnar Epithelium

Figure 4.3g

Transitional Epithelium

Figure 4.3h

Classes of Connective Tissue

Most diverse and abundant tissue Main classes

Connective tissue proper Cartilage Bone tissue Blood and fat!

Cells separated by large amount of extracellular matrix Common embryonic origin – mesenchyme Extracellular matrix is composed of ground substance

Classes of Connective Tissue

Figure 4.9

Connective Tissue Proper

Has two subclasses Loose connective tissue

Areolar, adipose, and reticular

Dense connective tissueDense irregular, dense regular, and elastic

This cell type is the most divers and abundant type of tissue

Areolar Connective Tissue – A Model Connective Tissue

Areolar connective tissue Underlies epithelial tissue Surrounds small nerves and blood vessels Has structures and functions shared by other CT Borders all other tissues in the body Is a “model” connective tissue – why?

It has all 3 fiber types: Reticular, elastic and collagen fibers

Major Functions of Connective Tissue

Structures within areolar CT and function Support and binding of other tissues Holding body fluids (interstitial fluid lymph) Defending body against infection Storing nutrients as fat

Areolar Connective Tissue

Fibers provide support Three types of protein fibers in extracellular matrix

Collagen fibersReticular fibersElastic fibers

Fibroblasts produce these fibers

Areolar Connective Tissue

Figure 4.12b

Areolar Connective Tissue

Tissue fluid (interstitial fluid) Watery fluid occupying extracellular matrix Tissue fluid derives from blood

Ground substance Viscous, spongy part of extracellular matrix Consists of sugar and protein molecules Made and secreted by fibroblasts

Areolar Connective Tissue

Main battlefield in fight against infection Defenders gather at infection sites

Macrophages Plasma cells Mast cells White blood cells

Neutrophils, lymphocytes, and eosinophils

Adipose Tissue

Figure 4.12c

Reticular Connective Tissue

Figure 4.12d

Dense Connective Tissue

Dense irregular connective tissue Dense regular connective tissue Elastic connective tissue

Dense Irregular Connective Tissue

Figure 4.12e

Dense Regular Connective Tissue

Figure 4.12f

Elastic Connective Tissue

Figure 4.12g

Other Connective Tissues

Cartilage Bone Blood

Cartilage

Firm, flexible tissue Contains no blood vessels or nerves Matrix contains up to 80% water Cell type – chondrocyte

Types of Cartilage

Hyaline cartilage Elastic cartilage Fibrocartilage

Hyaline Cartilage

Figure 4.12h

collagen fibers (hyaline = glassy); Chodroblasts produce matrix; Chondrocytes lie in lacunae

Elastic Cartilage

Figure 4.12i

Fibrocartilage

Figure 4.12j

Bone Tissue

Description Calcified matrix containing many collagen fibers Osteoblasts – secrete collagen fibers and matrix Osteocytes – mature bone cells in lacunae Well vascularized

Bone Tissue

Figure 4.12k

Blood Tissue

An atypical connective tissue Develops from mesenchyme Consists of cells surrounded by nonliving matrix

Blood Tissue

Figure 4.12l

Muscle Tissue

Skeletal muscle tissue Cardiac muscle tissue Smooth muscle tissue

Skeletal Muscle Tissue

Figure 4.14a

Cardiac Muscle Tissue

Figure 4.14b

Smooth Muscle Tissue

Figure 4.14c

Nervous Tissue

Description Main components are brain, spinal cord, and nerves Contains two types of cells

Neurons – excitatory cells Supporting cells (neuroglial cells)

Nervous Tissue

Figure 4.15

The Tissues Throughout Life

With increasing age Epithelia thin Collagen decreases Bones, muscles, and nervous tissue begin to

atrophy Poor nutrition and poor circulation – poor health of

tissues

Covering and Lining Membranes

Combine epithelial tissues and connective tissues Cover broad areas within body Consist of epithelial sheet plus underlying

connective tissue

Three Types of Membranes

Cutaneous membrane – skin Mucous membrane

Lines hollow organs that open to surface of body An epithelial sheet underlain with layer of lamina

propria

Three Types of Membranes

Serous membrane – slippery membranes Simple squamous epithelium lying on areolar

connective tissue Line closed cavities

Pleural, peritoneal, and pericardial cavities

Covering and Lining Membranes

Figure 4.13a, b

Covering and Lining Membranes

Figure 4.13c

HOMEWORK What are the four tissue types, where are they found in the

body and what are their general functions? Name the 3 shapes of epithelial tissue and their subtypes

and where they would be found on the body What are the features of the basal surface, the apical surface

and the lateral surfaces of epithelial tissues? What are the various cell junctions and in which tissues

(specifically, where in the body) would they be found? What is a gland? How many types of glands are there and

what do they secrete? What type of tissue is bone, tendon, ligaments, blood, fat,

nerves, muscles? What is the simple squamous layer that lines blood vessels

called?

HOMEWORK

What are the types of connective tissues, where would they be found in the body and what are their functions?

What are the filaments (fibers) which are secreted by CT? What are the contents of loose areolar tissue? What is the difference between DICT and DRCT? What type of tissue is a tendon made of? What are the three types of muscle tissue? How do you distinguish cardiac from skeletal muscle? How do you distinguish smooth muscle from skeletal

muscle? What is the last tissue type? What is it’s function? Elastic fibers are composed of? IVD are made of? (intervertebral discs)

Name all cell junction types and what are their distinguishing features?

How many layers is pseudostratified epithelium?