Tissues

Tissue

a group of similar cells and cell products working together to perform a specific role in an organ

Organ

structure with discrete boundaries that is composed of two or more tissue types

Histology

the study of tissues and how they are arranged into organs

4 categories of tissues

1. Epithelial
2. Connective
3. Nervous
4. Muscular

what is the Matrix composed of?

Fibrous proteins and clear gel called ground substance (tissue fluid, extracellular fluid (ECF), interstitial fluid, or tissue gel)

three primary germ layers

1. ectoderm- gives rise to the epidermis and nervous system
2. endoderm- gives rise to mucous membrane lining digestive and respiratory tracts, digestive glands
3. mesoderm- becomes gelatinous tissue called mesenchyme (made of wispy collagen fibers and fibroblasts in gel matrix), gives rise to cartilage, bone, blood

What are these?


1. Histological sections
2. Stains
3. Longitudinal section
4. Cross section
5. Oblique section

1. tissue is sliced into thin sections one or two cells thick
2. tissue is mounted on slides and artificially colored with histological stain. stain bind to different cellular components
3. tissue cut on its axis
4. tissue cut perpendicular to long axis of organ
5. tissue cut at angle between cross and longitudinal sections

Smear

tissue is rubbed across a slide

* ex: blood

Spread

some membranes and cobwebby tissues are laid out on a slide

* ex: areolar tissue

Epithelial Tissue

sheets of closely adhering cells one or more thick, cover body surface and lines cavities, avascular (no blood vessels), nourished by underlying connective tissue

Basement membrane

layer between the epithelium and underlying connective tissue

* collagen, reticular proteins, glycoproteins, other protein-carbohydrate complexes
* anchors the epithelium to the connective tissue below

Basal surface

cell surface facing the basement membrane

Apical surface

cell surface that faces away from the basement membrane

Lateral surface

cell surface between the basal and apical surface, “sidewall”

Functions of Epithelial Tissue

* protect deeper tissue from injury and infection
* produce and release chemical secretions
* excrete wastes
* absorb chemicals including nutrients
* selectively filter substances
* senes stimuli

2 ways epithelial tissue is classified

1. layers of cells
2. shape of cells

Simple epithelia

contain one layer of cells with all cells touching basement membrane

* named by number of layers was well as shape of cells

Stratified epithelia

contain more than one layer with some cells resting on top of others and do not at all touch the basement membrane

* named by shape of apical cells and layers of cells

Pseudostratified columnar

falsely appears stratified, as some cells are taller than others. Every cell reaches the basement membrane (but not all cells reach cell surface)

Goblet cells

wineglass-shaped mucus-secreting cells in simple columnar and pseudostratified epithelia

Simple Squamous Epithelium

Appearance: single row of thin flat cells

Function: absorption and diffusion

Location: glomeruli, alveoli, endothelium, and serosa

Simple Cuboidal Epithelium

Appearance: single layer of cube cells with round nucleus

Function: secretion and absorption

Location: mammary and salivary glands, liver, thyroid, kidney tubules

Simple Columnar Epithelium

Appearance: single row of tall narrow cells, oval nuclei in basal half of cell, apical layer may have brush border of microvilli, possible goblet cells, ciliated in some organs

Function: secretion and absorption

Location: small and large intestine, uterus

Pseudostratified Epithelium

Appearance: looks multilayed, but all cells touch the basement membrane, nuclei at several layers with cilia at apical layer, contains goblet cells

Function: secretion and propels mucus

Location: respiratory tract and portions of male urethra

where is simple squamous located?

glomeruli and alveoli

where is simple cuboidal located?

mammary and salivary glands, thyroid, liver

where is simple columnar located?

small and large intestine, uterus

where is pseudostratified epithelium located?

respiratory tracts

2 types of Stratified Squamous Epithelia

Keratinized and Nonkeratinized

Keratinized

found on skin surface, abrasion resistant

Nonkeratinized

lacks surface layer of dead cells

Keratinized Stratified Squamous Epithelium

Appearance: multilayer of cells, flat and scaly towards the surface

Function: retards water loss, abrasion resistant, resist penetration of pathogenic organisms

Location: palms and soles of feet

Nonkeratinized Stratified Squamous Epithelium

Appearance: same as Keratinized but lacks dead layer of cells

Function: protect from pathogenic organisms, resist abrasion

Location: esophagus, vaginal canal

Stratified Cuboidal Epithelium

Appearance: multilayer of cells square shaped

Function: produce ovarian hormones, sperm, secretes sweat

Location: sweat ducts, mammary ducts, salivary ducts

Stratified Columnar Epithelium

Appearance: multilayer long cells

Function: protection

Location: epiglottis, anus, mammary glands

Transitional Epithelium

Appearance: multilayer with surface cells changing from round to flat when stretched

Function: expansion without distortion, filling of urinary tract

Location: urinary bladder

Connective Tissue

a diverse, abundant type of tissue in which cells occupy less space than the matrix. most cells in direct contact with each other. highly variable vascularity with some connective tissue with more vessels than others

* supports, connects, and protects organs

Cells of fibrous connective tissue

Fibroblast, Macrophages, Leukocytes, Plasma cells, Mast cells, Adipocytes

Fibroblasts

produce fibers and ground substance of matrix

Macrophages

arise from monocytes; phagocytize foreign material and activate immune system when they sense foreign matter (antigens)

Leukocytes

white blood cells: Neutrophils attack bacteria, Lymphocytes react against bacteria, toxins, and other foreign agents

Plasma cells

arise from lymphocytes and synthesize antibodies (proteins)

Mast cells

secrete heparin to inhibit clotting and histamine to dilate blood vessels

Adipocytes

store triglycerides(fat molecules)

Fibers of fibrous connective tissue

Collagenous fibers, reticular fibers, elastic fibers

Collagenous fibers

* most abundant of the body’s proteins(25%)
* tough, flexible, and stretch-resistant
* tendons, ligaments, and deep layers of the skin are mostly collagen; it is less visible in the matrix of cartilage and bone

Reticular fibers

* thin collagen fibers coated with glycoprotein
* form framework of lymphatic organs such as spleen and lymph nodes

Elastic fibers

* thinner than collagenous fibers, made of protein elastin
* allows for stretch and recoil

3 parts of the ground substance

Glycosaminoglycans (GAGs), Proteoglycans, Adhesive glycoproteins

Glycosaminoglycans (GAGs)

* long polysaccharide composed of amino sugars and uronic acid
* regulates water and electrolyte balance of tissues
* ex: chondroitin sulfate, heparin, and hyaluronic acid

Proteoglycans

* gigantic molecules shaped like bottle brushes
* form gravy-like colloids and hold tissues together

Adhesive glycoproteins

* protein-carbohydrate complexes
* bind components of a tissue together

what is Loose connective tissue and what are the 3 types of Loose Connective Tissue?

gel-like ground substance between cells, fewer fibers

* Areolar, Reticular, Adipose

Embryonic connective tissues not found in adults

Mesenchyme

* first connective tissue in embryos

Mucous connective tissue

* loose embryonic connective tissue

What is Dense connective tissue and what are the 3 types of Dense Connective Tissue?

fibers fill spaces between cells. types vary in fiber orientation. more fibers and less ground substance

* Dense regular connective tissue, Dense irregular connective tissue, Elastic connective tissue

Areolar Tissue

Appearance: loosely organized fibers, abundant blood vessels, a lot of empty space

Function: supports internal organs

Location: underlies epithelia, in serous membrane, between muscles, passageways for nerves and blood vessels

Reticular Tissue

Appearance: mesh of reticular fibers and fibroblasts

Function: forms supportive framework for lymphatic organs

Location: lymph nodes, spleen, thymus, bone marrow

2 types of fat

White:

* only in adults, provides thermal insulation and cushions organs such as eyeballs, and kidneys. contributes to body contours- female breasts and hips

Brown:

* in fetuses, infants, children. color comes from blood vessels and mitochondrial enzymes. functions as a heat-generating tissue

Adipose Tissue

Appearance: empty-looking cells with thin margins, nucleus pressed against the membrane

Function: energy storage, insulation, cushioning

Location: beneath the skin, breasts, eye sockets kidney

Dense Regular Connective Tissue

Appearance: densely packed, parallel collagen fibers with compressed fibroblast nuclei. elastic tissue forms wavy sheets in some locations

Function: tendons attach muscle to bone and ligaments hold bone together

Location: tendons and ligaments

Dense Irregular Connective Tissue

Appearance: densely packed, randomly arranged, collagen fibers with few visible cells

Function: strength and resist forces from multiple directions

Location: deeper layer of skin, capsules around organs

Elastic Connective Tissue

Appearance: elastic fibers with interspersed fibroblasts

Function: allows for expansion and recoil

Location: elastic arteries and vertebrae

Cartilage

* supporting stiff connective tissue and flexible matrix
* gives shape to ear, tip of nose, and larynx
* no blood vessels (avascular) depends on diffusion to bring nutrients and remove wastes
* heals slowly because avascular
* matrix rich in GAGs and contains collagen fibers

Chondroblasts

cartilage cells that produce the matrix that will trap them

Chondrocytes

cartilage cells that are trapped in lacunae (cavities)

Perichondrium

sheath of dense irregular connective tissue that surrounds elastic and most hyaline cartilage (not articular cartilage). contains a reserve population of chondroblasts that contribute to cartilage growth throughout life

3 types of Cartilage

Hyaline, Fibrocartilage, Elastic

Hyaline Cartilage

Appearance: clear and glassy because of the fineness of collagen fibers

Function: ease joint movement, holds airways open, moves vocal cords

Location: articular cartilage, costal cartilage, trachea, larynx, fetal skeleton

Elastic cartilage

Appearance: containing an abundance of elastic fibers, covered with perichondrium

Function: Provide flexible, elastic support

Location: external ear and epiglottis

Fibrocartilage

Appearance: containing large, coarse bundles of collagen fibers

Function: resist compression and absorb shock

Location: pubic symphysis, menisci, intervertebral discs

2 types of bone

Spongey and Compact

Spongey bone

Appearance: bone trabeculae with spaces filled with blood vessels

Function: reduce weight of bone

Location: ends of long bone and middle of flat bones

Compact bone

Appearance: arranged in cylinders that surround central (osteonic) canals that run longitudinally through shafts of long bone. blood vessels and nerves travel through the central canal. bone matrix deposited in concentric lamellae

Function: strength and support

Location: diaphysis of long bones and outside of flat bones

Osteon

central canal and its surrounding lamellae

Osteocytes

mature bone cells within lacunae

Canaliculi

delicate canals radiating from each lacuna to its neighbors, allowing osteocytes to contact each other

Periosteum

tough fibrous connective tissue covering the whole bone

Blood

fluid connective tissue, transports cells and dissolved matter from place to place. made up of Plasma (blood’s ground substance") and blood cells

What are these and their function?


1. Erythrocytes
2. Leukocytes
3. Platelets

1. red blood cells (RBCs): transport O2 and CO2
2. white blood cells (WBCs) (Neutrophils, eosinophils, basophils, lymphocytes, monocytes): defend against infection and disease
3. cell fragments involved in clotting

Excitability

ability to respond to stimuli by changing membrane potential

* developed to highest degree in nervous and muscular tissue

Membrane potential

electrical charge difference (voltage) that occurs across the cell membrane

* in nerve cells, changes in voltage result in the rapid transmission of signals to other cells
* in muscle cells, changes in voltage result in contraction, shortening of the cell

Nervous tissue

specialized for communication by electrical and chemical signals

2 cells of the Nervous tissue

neurons (nerve cells) and neuroglia (glial cells)

Neuroglia

protect and assist neurons, are the “housekeepers” of nervous system

What are the parts of the Neuron and their functions?

1. Neurosoma (cell body)- houses nucleus and other organelles; controls protein synthesis
2. Dendrites- short branched processes that recieve signals from other cells and transmit messages to the neurosoma
3. Axon (nerve fibers)- sends outgoing signals to other cells

Muscular Tissue

* elongated cells that are specialized to contract in response to stimulation
* primary job is to exert physical force on other tissues and organs
* creates movements involved in body and limb movement, digestion, waste elimination, breathing, speech, and blood circulation
* important source of body heat

Skeletal Muscle Tissue

Appearance: made of muscle fibers, long thin cells with multiple nuclei adjacent to plasma membrane, striated, alternating dark and light bands

Function: voluntary- conscious control over skeletal muscle to allow for movement

Location: most skeletal muscle attach to bone

Cardiac Muscle Tissue

Appearance: Cardiomyocytes are short and branched with one centrally located nucleus, intercalated discs, striated

Function: involuntary (not under conscious control) contracts to pump blood to organs of the body

Location: heart wall

Smooth Muscle Tissue

Appearance: fusiform cells lacking striations, one central nucleus

Function: involuntary contraction to propel movement through hollow organs

Location: visceral muscle, respiratory, digestive, reproductive organs

4 cell junctions

Gap, Desmosome, Hemidesmosome, Tight

Tight junction

* zipper-like, interlocking linkage between two adjacent cells by transmembrane cell-adhesion proteins
* seals off intercellular space, making it difficult for substances to pass between cells

Desmosome

* patch that holds cells together (like a clothing snap)
* made of Hook like, J-shaped proteins which arise from cytoskeleton
* keeps cell from pulling apart- resit mechanical stress

Hemidesmosome

* half-desmosome that anchors basal cell of epithelium to an underlying basement membrane
* prevents epithelium from easily peeling away from the underlying tissues

Gap junction

* communicating junction are formed by ring-like connexons
* connexons consist of six transmembrane proteins arranged like segments of an orange around water-filled pore which allows ions, nutrients, and other small solutes to pass between cells
* located in cardiac and smooth muscle, embryonic tissue, lens and cornea

Gland

* cell or organ that secretes substances for use in the body or releases them for elimination from the body
* usually composed of epithelial tissue in a connective tissue framework and capsule
* secretion- product useful to the body
* excretion- waste product

2 types of glands

exocrine and endocrine

* some organs have both endocrine and exocrine functions, ex: liver, gonads, pancreas

Exocrine glands

* gland that maintain their contact with the surface of epithelium by way of a duct
* can be external (sweat, tear glands) or internal (pancreas, salivary glands)
* release their products into ducts

3 exocrine gland structures

1. Capsule- connective tissue covering exocrine gland. extensions of capsule that divide interiro of gland into compartments (lobes and lobules) is known as the septa or trabeculae
2. Stroma- connective tissue framework of the gland that supports and organizes glandular tissue
3. Parenchyma- typically cuboidal or simple columnar epithelium are made up of cells that perform the task of synthesis and secretion

Endocrine Glands

no ducts, instead secrete their products- hormones directly into the blood stream

* hormones: chemical messengers that stimulate cells elsewhere in the body (ex: thyroid, adrenal, and pituitary glands)

Unicellular glands

* found in an epithelium that is predominantly non-secretor


* can be exocrine or endocrine
* ex: mucus-secreting goblet cells in trachea or endocrine cells of stomach