Tissues, Glands, &

Membranes1

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• Tissue - group of cells similar structure and function along with similar extracellular substances between the cells

• Histology – microscopic study of tissue structure

• Histo- = tissue, -ology = study

Epithelial tissues◦ Epi = on + thele = covering or lining

Connective tissues Muscle tissues Nervous tissues

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1. Very little extracellular material between cells.

2. Free surface – layer of cells not in contact with other cells.

3. Basement membrane – attaches the epithelial cells to underlying tissues.

4. Avascular – capillaries do not extend from the underlying tissues, so gases, nutrients, & wastes must diffuse across the basement membrane.

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• Classified based on number of cell layers and cell shape

• Layers:• Simple epithelium – 1 layer of cells• Stratified epithelium - >1 layer of cells

• Note: When epithelium is stratified, it is named according to the shape of the cells at the free surface.

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• Shape:• Squamous (flat and scale-like)• Cuboidal (cube shaped)• Columnar (tall and thin)

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Layers or “Arrangement”

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Shapes

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• Single layer of thin, flat cells

• Line blood vessels, lymphatic vessels, heart, alveoli, kidney tubules, serous membranes

• Diffusion, filtration, anti-friction, secretion, absorption

Single layer of cube-shaped cells, some with microvilli or cilia

Kidney tubules, glands/ducts, brain, bronchioles, ovary surface

Secretion, absorption, movement of particles

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Single layer of tall, narrow cells, some with cilia/microvilli

Lining of stomach, intestines, glands, ducts, bronchioles, auditory tubes, uterus, uterine tubes

Secretion, absorption, movement of particles/oocytes

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Single layer of cells, some tall and thin, others not, nuclei at different levels, appear stratified, almost always ciliated

Lining of nasal cavity, nasal sinuses, auditory tubes, pharynx, trachea, bronchi

Synthesis/ secretion/ movement of mucus

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Stratified cells appear cuboidal when not stretched and squamous when stretched

Lining of bladder, ureters, superior urethra

Deals with changing volume of fluid in an organ, protects from urine contact

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Simple Columnar Epithelium

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Simple Squamous Epithelium

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Stratified Squamous Epithelium

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Simple Cuboidal Epithelium

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Stratified Columnar Epithelium

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Pseudostratified Epithelium

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[bladder]

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Transitional Epithelium

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Stratified Cuboidal Epithelium

Cell Layers & Cell Shapes◦ Single layers – control passage of materials

through epithelium Gas diffusion across lung alveoli Fluid filtration across kidney membranes Gland secretion Nutrient absorption in intestines

◦ Multiple layers – protect underlying tissues Damaged cells replaced by underlying cells Protect from abrasion (ex: skin, anal canal, vagina)

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Cell Layers & Cell Shapes, continued◦ Flat/thin (squamous) – diffusion, filtration

Diffusion in lung alveoli Fluid filtration in kidney tubules

◦ Cuboidal/columnar – secretion, absorption; contain more organelles Secretory vesicles (mucus) in stomach lining

Mucus protects against digestive enzymes and acid Secretion/absorption in kidney tubules made

possible by ATP production by multiple mitochondria Active transport of molecules into/out of kidney

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Free Cell Surfaces◦ Smooth – reduces friction

blood vessel lining – smooth blood flow◦ Microvilli – increase cell surface area; cells

involved in absorption or secretion Small intestine lining

◦ Cilia – propel materials along cell’s surface Nasal cavity/trachea – moves dust and other

materials to back of throat (swallowed/cough up) Goblet cells secrete mucus to entrap the “junk”

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Cell Connections◦ Tight junctions – bind adjacent cells together

Permeability layers – prevent passage of materials Intestinal lining and most simple epithelia

◦ Desmosomes – anchor cells to one another Hemidesmosomes – anchor cells to basement

membrane Epithelia subject to stress (skin stratified squamous)

◦ Gap Junctions – allow passage of molecules/ions between adjacent cells (communication) Most epithelia

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Gland – multicellular structure secreting substance onto a surface, into a cavity, or into the blood. There are two types:◦Exocrine gland (exo-outside + krino-to separate):

glands with ducts; secretions pass through ducts onto a surface or into an organ Simple – ducts w/o branches Compound – ducts w/ branches Tubular – tubes Acinus/alveolus – saclike

◦Endocrine gland (endo-within): glands w/o ducts that secrete into blood Hormones are secreted into blood

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*Goblet cells are the onlyunicellular gland.

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Merocrine: FLUID is released (Most glands are in this group)◦ Serous cells = produce a watery secretion w/enzymes◦ Mucous cells = produce thicker secretions

Apocrine: Small portions of the cell break off & are released◦ Mammary glands, Ceruminous (ear wax), and some sweat

glands

Holocrine: ENTIRE CELLS are released-Sebaceous Glands: oil in the skin)

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Connective Tissue

• The most abundant and widely distributed tissue in the body

• Multiple types, appearances and functions• Relatively few cells in extracellular

matrix (think: fruit “cells” floating or suspended in Jell-O).

• Matrix is made up of:• Protein fibers• Ground substance• Fluid

Three types of protein fibers : Collagen fibers:

◦ Rope-like; resist stretching Reticular fibers:

◦ Fine, short collagen fibers; branched for support Elastic fibers:

◦ Coiled; stretch and recoil to original shape

Ground substance – combination of proteins and other molecules◦ Varies from fluid to semisolid to solid

Proteoglycans – protein/polysaccharide complex that traps water

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Based on function:◦ Blast (germ) – produce (build) matrix◦ Cyte (cell) – cells maintain it ◦ Clast (break) – cells break down for remodeling

Osteoblast (osteo-bone) – form bone Osteocyte – maintain bone Osteoclast – break down bone

◦ Cells associated with the immune system are also found in connective tissue: Macrophage (makros-large + phago-to eat) – large,

mobile cells that ingest foreign substances found in connective tissue

Mast Cells – nonmotile cells that release chemicals that promote inflammation

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1. Enclose & Separate organs and tissues from one another • Liver, kidney; (capsules form around) • muscles, blood vessels, nerves

2. Connect tissues to each other • Tendons – muscles to bone

• Remember: TTT (tendons 2 types)

• Ligaments – bone to bone • Remember: LLL (ligaments like to like)

3. Support and movement • Bones, cartilage, joints

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4. Storage • Fat stores energy; bone stores calcium

5. Cushion and insulation • Fat cushions/protects/insulates (heat)

6. Transportation • Blood transports gases, nutrients,

enzymes, hormones, immune cells7. Protection

• Immune & blood cells protect against toxins/tissue injury; bones protect underlying structures

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Composition: ECM has fibroblasts, other cells, collagen, fluid-filled spaces

Functions: forms thin membranes between organs and binds them (loose packing material)

Locations: widely distributed, between glands, muscles, nerves, attaches skin to tissues, superficial layer of dermis

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Composition: very little ECM (has collagen and elastic fibers); large adipocytes filled with lipid

Functions: Stores fat, energy source, thermal insulator, protection/ packing material

Locations: Beneath the skin, in breasts, within bones, in loose connective tissues, around organs (kidneys and heart)

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Composition: ECM mostly collagen (made by fibroblasts), orientation varies

Functions: withstands pulling forces, resists stretching in direction of fibers orientation

Locations: tendons, ligaments, dermis of skin, organ capsules

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Composition: ECM collagen and elastic fibers; orientation varies

Functions: stretches and recoils; strength in direction of fiber orientation

Locations: arterial walls, vertebral ligaments, dorsal neck, vocal cords

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Chondrocytes (cartilage cells) inside lacunae (small spaces)

No blood vessels – slow healing, can’t bring cells/nutrients necessary for tissue repair

Three types:◦ Hyaline cartilage◦ Elastic cartilage ◦ Fibrocartilage

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Composition: solid matrix, small evenly distributed collagen fibers, transparent matrix, chondrocytes in lacunae

Functions: supports structures, some flexibility, forms smooth joint surfaces

Locations: costal cartilages of ribs, respiratory cartilage rings, nasal cartilages, bone ends, epiphyseal (growth) plates, embryonic skeleton

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Composition: similar to hyaline, numerous collagen fibrous arranged in thick bundles

Functions: somewhat flexible, withstands great pressure, connects structures under great pressure

Locations: intervertebral disks, pubic symphysis, articulating cartilage of some joints (knee, TMJ)

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Composition: similar to hyaline cartilage, abundant elastic fibers

Functions: rigidity, more flexibility than hyaline (elastic fibers recoil to original shape)

Locations: external ears, epiglottis, auditory tubes

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Composition: hard, mineralized matrix, osteocytes inside lacunae, lamellae layers

Functions: strength, support, protects organs, muscle/ligament attachments, movement (joints)

Locations: all bones of body

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Composition: blood cells in a fluid matrix (plasma)

Functions: transportation (O2, CO2, hormones, nutrients, waste, etc.), protect from infection, temperature regulation

Locations: in blood vessels and heart, produced by red bone marrow, WBCs leave blood vessels and enter tissues

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General features: ◦ Can contract

Contractile proteins◦ Enables movement of the structures that are

attached to them◦ Muscle fibers = cells

Three (3) types of muscle tissue:◦ skeletal◦ smooth◦ cardiac

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Composition: striated muscle fibers, large, cylindrical cells that have many nuclei near periphery

Functions: body movement, voluntary control

Locations: attached to bone

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Composition: cylindrical cells, striated, single nucleus, branched and connected with intercalated disks

Functions: pump blood, involuntary control

Locations: heart

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Composition: cells tapered at each end, not striated, single nucleus

Functions: regulates organ size, forces fluid through tubes, regulates amount of light entering eye, “goose bumps”, involuntary control

Locations: walls of hollow organs and tubes (stomach, intestine, blood vessels), eye

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Forms brain, spinal cord, peripheral nerves Functions:

◦ Conscious control of skeletal muscles◦ Unconscious control of cardiac muscles◦ Self and environmental awareness◦ Emotions◦ Reasoning skills◦ Memory

Action potentials = electrical signals responsible for communication between neurons and other cells

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Neurons = conducts action potentials (a.p.’s)◦ Cell body = contains

nucleus, site of general cell functions

◦ Dendrite = conduct a.p.’s toward cell body

◦ Axon = conducts a.p.’s away from cell body

Neuroglia = support cells: nourish, protect, insulate neurons

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In response to tissue damage◦ Viral/bacterial infections◦ Trauma

Functions:◦ Mobilize body’s defenses ◦ Destroy microorganisms, foreign materials,

damaged cells◦ “Pave way” for tissue repair

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Redness Heat Swelling Pain Disturbance of function

* Inflammation is beneficial, though painful!

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Mediators of inflammation cause dilation permeability of blood vessels (redness/heat)◦ Bring blood and important substances to site

Edema = swelling (water, proteins, etc.) of tissues

Fibrin = protein that “walls off” site; keeps infection from spreading

Neutrophils ingest bacteria (phagocytic WBC)

Macrophage ingest tissue debris Pus = mixture of dead neutrophils, cells, fluid

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Inflammation warns person from further injury:◦Pain◦Limitation of movement

(edema)◦Tissue destruction Fibroclast migrate to

damaged tissue and digest

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Substitution of viable cells for dead cells◦ Regeneration = same type of cells takes place

of previous cells; same function◦ Replacement = different type of tissue

develops; forms scars; loss of some function◦ Fibroclast lays down fibrin and forms scar tissue◦ Type of tissue repair is determined by:

Wound severity Tissue types involved

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Labile cells (not fixed)◦ Divide continuously through life◦ Skin, mucous membranes

Stable cells◦ Don’t actively divide, but can after injury◦ Connective tissue, glands (liver, pancreas)

Permanent cells◦ Little to no ability to divide◦ Neurons, skeletal muscle

If killed, replaced by connective tissue Recover from limited damage (axon of neuron)

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1. Clot (fibrin)2. Scab (seal)3. Blood vessel

dilation Fibroclast-clean up

4. Fibrin “walls off”

5. Epithelium replaced

6. Scab sloughs7. Fibroblasts

form granulation tissue

8. Wound contracture 73

Tissue changes with age:◦ neurons and muscle cells◦ visual acuity, smell, taste, touch◦ in functional capacities of respiratory and

cardiovascular systems◦ Slower cell division means slower healing◦ flexibility (irregular collagen fibers in tendons

& ligaments)◦ elasticity (elastic fibers bind to Ca2+,

becoming brittle) – makes skin wrinkled too ◦ Atherosclerosis – plaques in blood vessels

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