Chapter 4: The Tissue Level of Organization Flashcards
1
Q
Define a tissue.
Types of Tissues
A
- A group of cells, usually have common origin in an embryo and function together to carry out specialized activities.
Types of Tissues
2
Q
What is histology?
Types of Tissues
A
- The science that deals with the study of tissues.
Types of Tissues
3
Q
What is a pathologist?
Types of Tissues
A
- Physician who examines cells and tissues to help other physicians make accurate diagnoses.
- Examines tissues for any changes that may indicate disease.
Types of Tissues
4
Q
What are the four basic types of body tissues?
Types of Tissues
A
- Epithelial.
- Connective.
- Muscular.
- Nervous.
Types of Tissues
5
Q
What is epithelial tissue?
Types of Tissues
A
- Covers body surfaces and lines hollow organs, body cavities, and ducts.
- Forms glands.
- Allows body to interact with both its internal and external environments.
Types of Tissues
6
Q
What is connective tissue?
Types of Tissues
A
- Protects and supports body and organs.
- Various types bind organs together, store energy reserves as fat and help provide body with immunity to disease-causing organisms.
Types of Tissues
7
Q
What is muscular tissue?
Types of Tissues
A
- Composed of cells specialized for contraction and generation of force.
- Generates heat that warms the body.
Types of Tissues
8
Q
What is nervous tissue?
Types of Tissues
A
- Detects changes in variety of conditions inside/ outside body.
- Responds by generating electrical signals called nerve action potentials (nerve impulses) that activate muscular contractions and glandular secretions.
Types of Tissues
9
Q
What are cell junctions?
Cell Junctions
A
- Contact points between the plasma membranes of tissue cells.
Five most important types of cell junctions:
1. Tight junctions.
2. Adherens junctions.
3. Desmosomes.
4. Hemidesmosomes.
5. Gap junctions.
Cell Junctions
10
Q
What are tight junctions?
Cell Junctions
A
- Weblike strands of transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes to seal off passageways between adjacent cells.
- Inhibit passage of substances between cells, prevent contents of these ograns from leaking into blood/surrounding tissues.
- Examples: Stomach, intestines, urinary bladder.
Cell Junctions
11
Q
What are adherens junctions?
Cell Junctions
A
- Contain plaque, dense layer of proteins on inside of plasma membrane that attaches both to membrane proteins and to microfilaments of cytoskeleton.
- Each cadherin inserts into plaque from opposite side of plasma membrane, partially crosses intercellular space and connects to cadherins of adjacent cell.
- Help epithelial surfaces resist separation during various contractile activities (food moving through intestines).
Cell Junctions
12
Q
What are cadherins?
Cell Junctions
A
- Transmembrane glycoproteins that join cells.
Cell Junctions
13
Q
What are adhesion belts?
Cell Junctions
A
- Occur in adherens junctions of epithelial cells.
- Extensive zones encircle the cell similar to how a belt encircles your waist.
Cell Junctions
14
Q
What are desmosomes?
Cell Junctions
A
- Contain plaque and transmembrane glycoproteins (cadherins) that extend into intercellular space between adjacent cell membranes and attach cells to one another.
- Plaque attaches to elements of cytoskeleton (intermediate filaments).
- Intermediate filaments extend from desmosomes on one side of cell across cytosol to desmosomes on opposite side of cell.
- Structural arrangement contributes to stability of cells and tissues.
- Spot weld-like junctions.
- Common among cells of epidermis and cardiac muscle cells.
- Prevents epidermal cells from separating under tension and cardiac muscle cells from pulling apart during contraction.
Cell Junctions
15
Q
What are hemidesmosomes?
Cell Junctions
A
- Look like half of a desmosome.
- Transmembrane glycoproteins in hemidesmosomes are integrins.
- On inside of plasma membrane, integrins attach to intermediate filaments made of protein keratin.
- On outside of plasma membrane, integrins attach to protein laminin.
- Hemidesmosomes anchor cells to basement membrane.
Cell Junctions
16
Q
What are gap junctions?
Cell Junctions
A
- Membrane proteins (connexins) form tiny fluid-filled tunnels called connexons that connect neighboring cells.
- Plasma membranes of gap junctions are are separated by very narrow intercellular gap.
- Transfer of nutrients and wastes, takes place through gap junctions in avascular tissues.
- Allow cells in tissue to communicate with one another.
- Enable nerve or muscle impulses to spread rapidly among cells.
Cell Junctions
17
Q
What is one difference between an epithelial tissue and connective tissue?
Comparison between Epithelial and Connective Tissues
A
- Difference in number of cells in relation to extracellular matrix.
- Epithelial tissue, many cells are tightly packed together with little/ no extracellular matrix.
- Connective tissue, large amount of extracellular material separates cells that are usually widely scattered.
Comparison between Epithelial and Connective Tissues
18
Q
What is another difference between epithelial tissue and connective tissue?
Comparison between Epithelial and Connective Tissues
A
- Epithelial tissue has no blood vessels.
- Connective tissues have significant networks of blood vessels.
Comparison between Epithelial and Connective Tissues
19
Q
What is epithelial tissue?
Epithelial Tissue
A
- Cells arranged in continuous sheets, single or multiple layers.
- Closely packed, held tightly together by many cell junctions with little intercellular space between adjacent plasma membranes.
- Avascular, although has own nerve supply.
Arranged in 2 general patterns in body:
1. Covering/lining various surfaces.
2. Forming secreting portions of glands.
Epithelial Tissue
20
Q
What is the four most important functions of epithelial tissue?
Epithelial Tissue
A
- Protects.
- Secretes (mucus, hormones and enzymes).
- Asorbs (nutrients in GI tract).
- Excretes (various substances in urinary tract).
Epithelial Tissue
21
Q
What is the apical (free) surface of an epithelial cell?
Epithelial Tissue
A
- The most superficial layer of cells.
- Faces body surface, a body cavity, the lumen (interior space) of an internal organ, or a tubular duct that receives cell secretions.
- May contain cilia or microvilli.
Epithelial Tissue
22
Q
What are the lateral surfaces of an epithelial cell?
Epithelial Tissue
A
- Face the adjacent cells on either side.
- May contain tight junctions, adherens junctions, desmosomes, and/or gap junctions.
Epithelial Tissue
23
Q
What is the basal surface of an epithelial cell?
Epithelial Tissue
A
- The deepest layer of cells.
- Opposite the apical surface.
- Basal surfaces of deepest layer of epithelial cells adhere to extracellular materials such as basement membrane.
- Hemidesmosomes in basal surfaces of deepest layer of epithelial cells anchor epithelium to basement membrane.
Epithelial Tissue
24
Q
What is the basement membrane?
Epithelial Tissue
A
A thin extracellular layer that consists of two layers:
1. Basal lamina.
2. Reticular lamina.
Epithelial Tissue
25
What is the **basal lamina** of the **basement membrane**?
## Footnote
Epithelial Tissue
* Closer to-and secreted by-the epithelial cells.
* Contains proteins (laminin, collagen), glycoproteins and proteoglycans.
* Laminin molecules in basal lamina adhere to integrins in hemidesmosomes, attach epithelial cells to basement membrane.
## Footnote
Epithelial Tissue
26
What is the **reticular lamina** of the **basement membrane**?
## Footnote
Epithelial Tissue
* Closer to underlying connective tissue.
* Contains proteins such as collagen produced by connective tissue cells called fibroblasts.
## Footnote
Epithelial Tissue
27
What are the functions of the **basement membrane**?
## Footnote
Epithelial Tissue
1. Attaching to and anchoring epithelium to its underlying connective tissue.
2. Form a surface along which epithelial cells migrate during growth/wound healing.
3. Restrict passage of large molecules between epithelium and connective tissue.
4. Participate in filtration of blood in kidneys.
## Footnote
Epithelial Tissue
28
Why does **epithelial tissue** have a high rate of cell division?
## Footnote
Epithelial Tissue
* Repeatedly subjected to physical stress/ injury as it forms boundaries between bodys organs or between body and external environment.
* High rate of cell division allows epithelial tissue to constantly renew/repair itself by sloughing off dead/injured cells and replacing with new ones.
## Footnote
Epithelial Tissue
29
What are all the functions of **epithelial tissue** in the body?
## Footnote
Epithelial Tissue
1. **Protection**.
2. **Secretion**.
3. **Filtration**.
4. **Absorption**.
5. **Excretion**.
Also combines with nervous tissue to form special organs for:
1. **Smelling**.
2. **Hearing**.
3. **Vision**.
4. **Touch**.
## Footnote
Epithelial Tissue
30
What are the two types of **epithelial tissue**?
## Footnote
Epithelial Tissue
1. Covering and lining epithelium (Surface epithelium)
2. Glandular epithelium
## Footnote
Epithelial Tissue
31
What is **covering and lining epithelium**?
## Footnote
Epithelial Tissue
* Forms outer covering of skin and some internal organs.
* Forms inner lining of blood vessels, ducts, body cavaties, and interior of respiratory, digestive, urinary and reproductive systems.
## Footnote
Epithelial Tissue
32
What is **glandular epithelium**?
## Footnote
Epithelial Tissue
* Makes up secreting portion of glands such as the thyroid gland, adrenal glands, sweat glands, and digestive glands.
## Footnote
Epithelial Tissue
33
What is characteristic of **the arrangement of cells in layers** of **epithelial tissue**?
## Footnote
Epithelial Tissue
The cells are arranged in one or more layers depending on function:
1. **Simple epithelium**.
2. **Pseudostratified epithelium**.
3. **Stratified epithelium**.
## Footnote
Epithelial Tissue
34
What is the characteristic of **cell shapes** of **epithelial tissue**?
## Footnote
Epithelial Tissue
Epithelial cells vary in shape depending on their function:
1. **Squamous cells**.
2. **Cuboidal cells**.
3. **Columnar cells**.
4. **Transitional Cells**.
## Footnote
Epithelial Tissue
35
What is **simple epithelium**?
## Footnote
Epithelial Tissue
* Single layer of cells, functions in diffusion, osmosis, filtration, secretion or absorption.
* Secretion is production and release of substances (mucus, sweat or enzymes).
* Absorption is intake of fluids or other substances (digested food from the intestinal tract).
## Footnote
Epithelial Tissue
36
What is **pseudostratified epithelium**?
## Footnote
Epithelial Tissue
* Simple epithelium as all its cells rest on basement membrane.
* Appears to have multiple layers of cells as cell nuclei lie at different levels and not all cells reach apical surface.
* Cells that do extend to apical surface may contain cilia; others (**goblet cells**) secrete mucus.
## Footnote
Epithelial Tissue
37
What is **stratified epithelium**?
## Footnote
Epithelial Tissue
* Consists of two or more layers of cells that protect underlying tissues.
* Located where there is considerable wear and tear.
## Footnote
Epithelial Tissue
38
What is **squamous cells**?
## Footnote
Epithelial Tissue
* Cells that are thin, allows for the rapid passage of substances through them.
## Footnote
Epithelial Tissue
39
What are **cuboidal cells**?
## Footnote
Epithelial Tissue
* As tall as they are wide.
* Shaped like cubes or hexagons.
* May have microvilli at apical surface and function in either secretion/absorption.
## Footnote
Epithelial Tissue
40
What are **columnar cells**?
## Footnote
Epithelial Tissue
* Much taller than they are wide, like columns.
* Protect underlying tissues.
* Apical surfaces may have cilia or microvilli, and often are specialized for secretion and absorption.
## Footnote
Epithelial Tissue
41
What are **transitional cells**?
## Footnote
Epithelial Tissue
* Change shape, from squamous to cuboidal and back.
* Organs such as urinary bladder stretch to larger size and then collapse to smaller size.
## Footnote
Epithelial Tissue
42
What are the different types of **epithelial tissues**?
## Footnote
Epithelial Tissue
**Simple epithelium**
A. Simple squamous epithelium
1. *Endothelium (lines heart, blood vessels, lymphatic vessels)*
2. *Mesothelium (forms epithelial layer of serous membranes)*
B. Simple cuboidal epithelium
C. Simple columnar epithelium
1. *Nonciliated (lacks cilia)*
2. *Ciliated (contain cilia)*
D. Pseudostratified columnar epithelium
1. *Nonciliated (lacks cilia)*
2. *Ciliated (contain cilia)*
**Stratified epithelium**
A. Stratified squamous epithelium +
1. *Nonkeratinized (lacks keratin)*
2. *Keratinized (contains keratin)*
B. Stratified cuboidal epithelium +
C. Stratified columnar epithelium +
D. Transitional epithelium or urothelium (lines most of urinary tract)
(+) **This classification is based on the shape of the cells at the apical surface**.
## Footnote
Epithelial Tissue
43
**Simple squamous epithelium**
## Footnote
Epithelial Tissue
**Description**:
* Single layer, flat cells. Centrally located nucleus that is flattened and oval/spherical in shape.
**Location**:
* Lines cardiovascular, lymphatic system (heart, blood vessels), called **endothelium**.
* Forms epithelial layer of serous membranes (peritoneum, pleura, pericardium), called **mesothelium**.
* Found in air sacs of lungs, glomerular (Bowman's) capsules of kidneys, inner surface of tympanic membrane (eardrum).
**Function**:
* Sites of filtration (blood filtration in kidneys) or diffusion (diffusion of oxygen into blood vessels of lungs), at site of secretion in serous membranes.
* Not found in body areas subject to mechanical stress.
## Footnote
Epithelial Tissue
44
**Simple cuboidal epithelium**
## Footnote
Epithelial Tissue
**Description**:
* Single layer of cube-shaped cells; round, centrally located nucleus.
* These cuboidal cells are more pie-shaped, nearly as high as they are wide at base.
**Location**:
* Covers surface of ovary; lines anterior of capsule of lens of eye; forms pigmented epithelium at posterior surface of retina; lines kidney tubules and smaller ducts of glands; makes up secreting portion of some glands such as thyroid gland and ducts of some glands such as pancreas.
**Function**:
* Secretion and absorption.
## Footnote
Epithelial Tissue
45
**Nonciliated simple columnar epithelium**
## Footnote
Epithelial Tissue
**Description**:
* Single layer of nonciliated columnlike cells, oval nuclei near base of cells.
* Contains columnar epithelial cells with microvilli at apical surface and goblet cells.
**Location**:
* Lines GI tract (stomach to anus), ducts of many glands, and gallbladder.
**Function**:
* Secretion and absorption.
* Capable of higher level of secretion and absorption than are cuboidal cells.
* Secreted mucus lubricates linings of digestive, respiratory, and reproductive tracts, most of urinary tract.
* Helps prevent destruction of stomach lining by acidic gastric juice.
## Footnote
Epithelial Tissue
46
**Ciliated simple columnar epithelium**
## Footnote
Epithelial Tissue
**Description**:
* Single layer of ciliated columnlike cells, oval nuclei near base of cells. Goblet cells are usually interspersed.
**Location**:
* LInes some bronchioles of respiratory tract, uterine tubes, uterus, some paranasal sinuses, central canal of spinal cord, and ventricles of brain.
**Function**:
* Cilia beat in unison, moving mucus and foreign particles toward throat, where they can be coughed up, swallowed or spit out.
* Cilia help move oocytes expelled from ovaries through fallopian tubes into uterus.
## Footnote
Epithelial Tissue
47
**Nonciliated pseudostratified columnar epithelium**
## Footnote
Epithelial Tissue
**Description**:
* Appears to have many layers as nuclei of cells are at various levels.
* All the cells are attached to basement membrane in a single layer.
* Some cells do not extend to apical surface.
* Contains cells without cilia and lacks globlet cells.
**Location**:
* Lines epididymis, larger ducts of many glands, parts of male urethra.
**Function**:
* Absorption and secretion.
## Footnote
Epithelial Tissue
48
**Ciliated pseudostratified columnar epithelium**
## Footnote
Epithelial Tissue
**Description**:
* Appears to have many layers as cell nuclei are at various levels.
* All cells are attached to basement membrane in a single layer.
* Some cells do not extend to apical surface.
* Contains cells that extend to surface and secrete mucus (globlet cells) or bear cilia.
**Location**:
* Lines airways of most upper respiratory tract.
**Function**:
* Secretes mucus, traps foreign particles, cilia sweep away mucus for elimination from body.
## Footnote
Epithelial Tissue
49
**Stratified squamous epithelium**
## Footnote
Epithelial Tissue
**Description**:
* 2 or more layers of cells.
* Cells in apical layer and several layers deep to it are squamous.
* Cells in deep layers vary from cuboidal to columnar.
* As basal cells divide, daughter cells push up to apical layer.
* Move toward surface, away from blood supply, become dehydrated, less metabolically active.
* Cells become tough, hard structures, eventually die.
* Replaced continuously, new cells emerge from basal cells.
*Keratinized stratified squamous epithelium*: Develops tough layer of keratin apical layer and deep layers. Amount of keratin increases in cells as move away from blood supply, organelles die.
*Nonkeratinized stratified squamous epithelium*: Does not contain large amounts of keratin. Constantly moistened by mucus from salivary and mucous glands; organelles not replaced.
**Location**:
* Keratinized forms superficial layer of skin.
* Nonkeratinized lines wet surfaces (lining of mouth, esophagus, part of epiglottis, part of pharynx, vagina), covers tongue.
**Function**:
* Protection against abrasion, water loss, UV radiation, and foreign invasion.
* Both types form first line of defense against microbes.
## Footnote
Epithelial Tissue
50
**Stratified cuboidal epithelium**
## Footnote
Epithelial Tissue
**Description**:
* 2 or more layers of cells.
* Cells in apical layer cube-shaped; fairly rare type.
**Location**:
* Ducts of adult sweat glands, esophageal glands, part of male urethra.
**Function**:
* Protection; limited secretion and absorption.
## Footnote
Epithelial Tissue
51
**Stratified columnar epithelium**
## Footnote
Epithelial Tissue
**Description**:
* Basal layers usually consist of shortened, irregularly shaped cells.
* Only apical layer has columnar cells; uncommon.
**Location**:
* Lines part of urethra; large excretory ducts of some glands, such as esophageal glands;
* Small areas in anal mucous membrane.
* Part of conjunctiva of eye.
**Function**:
* Protection and secretion.
## Footnote
Epithelial Tissue
52
**Transitional epithelium (urothelium)**
## Footnote
Epithelial Tissue
**Description**:
* Variable appearance (transitional).
* Relaxed/unstretched state, looks stratified cuboidal epithelium, apical layer cells tend to be large and rounded.
* As tissue stretched, cells become flatter, appearance of stratified squamous epithelium.
* Multiple layers, elasticity make it ideal for lining hollow structures subject to expansion from within.
**Location**:
* Lines urinary bladder and portions of ureters and urethra.
**Function**:
* Allows urinary organs to stretch, maintain protective lining while holding variable amounts of fluid without rupturing.
## Footnote
Epithelial Tissue
53
What is the function of **glandular epithelium**?
## Footnote
Epithelial Tissue
* **Secretion**, accomplished by glandular cells that often lie in clusters deep to the covering and lining epithelium.
## Footnote
Epithelial Tissue
54
What is a **gland**?
## Footnote
Epithelial Tissue
* Epithelium that secretes substances into ducts (tubes), onto a surface, or into blood in absence of ducts.
* All glands of body are either **endocrine** or **exocrine**.
## Footnote
Epithelial Tissue
55
What is an **endocrine gland**?
## Footnote
Epithelial Tissue
* Secretions (hormones), enter interstitial fluid, then diffuse into bloodstream without flowing through duct.
* Endocrine secretions have far-reaching effects as they are distributed throughout body by bloodstream.
## Footnote
Epithelial Tissue
56
What is an **exocrine gland**?
## Footnote
Epithelial Tissue
* Secretes products into ducts that empty onto surface of a covering and lining epithelium (skin surface or lumen of hollow organ).
* Secretions of exocrine glands have limited effects, some would be harmful if entered bloodstream.
## Footnote
Epithelial Tissue
57
What are the different classifications of **exocrine glands**?
## Footnote
Epithelial Tissue
1. **Unicellular glands**.
2. **Multicellular glands**.
## Footnote
Epithelial Tissue
58
What are **unicellular glands**?
## Footnote
Epithelial Tissue
* Single-celled glands.
* Goblet cells are important unicellular exocrine glands that secrete mucus directly onto apical surface of lining epithelium.
## Footnote
Epithelial Tissue
59
**Endocrine Glands**
## Footnote
Epithelial Tissue
**Description**:
* Secretions (hormones) enter interstitial fluid, then diffuse into bloodstream without flowing through duct.
**Location**:
* Pituitary gland at base of brain, pineal gland in brain, thyroid and parathyroid glands near larynx (voice box), adrenal glands superior to kidneys, pancreas near stomach, ovaries in pelvic cavity, testes in scrotum, thymus in thoracic cavity.
**Function**:
* Hormones regulate many metabolic and physiological activities to maintain homeostasis.
## Footnote
Epithelial Tissue
60
**Exocrine Glands**
## Footnote
Epithelial Tissue
**Description**:
* Secretory products, released into ducts that empty onto surface of covering and lining epithelium (skin surface or lumen of hollow organ).
**Location**:
* Sweat, oil, earwax glands of skin; digestive glands such as salivary glands (secrete into mouth cavity) and panreas (secretes into small intestine).
**Function**:
* Produce substances such as sweat to help lower body temperature, oil, earwax, saliva or digestive enzymes.
## Footnote
Epithelial Tissue
61
What are **multicellular glands**?
## Footnote
Epithelial Tissue
* Most exocrine glands are multicellular glands.
* Many cells, form distinctive microscopic structure/macroscopic organ.
* Examples include sudoriferous (sweat), sebaceous (oil), and salivary glands.
Categorized according to two criteria:
1. Whether ducts are branched or unbranched.
2. Shape of the secretory portions of the gland.
* Duct does not branch, it is a **simple gland**.
* Duct branches, it is a **compound gland**.
* Glands with tubular secretory parts are **tubular glands**.
* Glands with rounded secretory portions are **acinar glands**.
* **Tubuloacinar glands** have both tubular and more rounded secretory parts.
## Footnote
Epithelial Tissue
62
What are the structural classification schemes for **multicellular exocrine glands**?
## Footnote
Epithelial Tissue
1. **Simple glands**
A. *Simple branched tubular*: Tubular secretory part is straight, attached to single unbranched duct (glands in large intestine).
B. *Simple branched tubular*: Tubular sedretory part is branched, attached to single unchanged duct (gastric glands).
C. *Simpled coiled tubular*: Tubular secretory part is coiled, attached to single unbranched duct (sweat glands).
D. *Simple acinar*: Secretory portion is rounded, attaches to single unbranched duct. (glands of penile urethra).
E. *Simple branched acinar*: Rounded secretory part is branched, attaches to single unbranched duct (sebaceous glands).
2. **Compound glands**
A. *Compound tubular*: Secretory portion in tubular, attaches to branched duct (bulbourethral (Cowper's) glands).
B. *Compound acinar*: Secretory portion in rounded, attaches to branched duct (mammary glands).
C. *Compound tubuloacinar*: Secretory portion is both tubular and rounded, attaches to branched duct (acinar glands of the pancreas).
## Footnote
Epithelial Tissue
63
How are **multicellular exocrine glands** structurally classified?
## Footnote
Epithelial Tissue
* Based on branching pattern of the duct and the shape of the secreting portion.
## Footnote
Epithelial Tissue
64
How do **simple** multicellular exocrine glands differ from **compound** ones?
## Footnote
Epithelial Tissue
* Simple multicellular exocrine glands have nonbranched duct.
* Compound multicellular exocrine glands have branched duct.
## Footnote
Epithelial Tissue
65
What is the functional classification of **exocrine glands**?
## Footnote
Epithelial Tissue
* Based on how secretions are released.
* Each of secretory processes begins with endoplasmic reticulum and Golgi complex working together to form intracellular secretory vesicles that contain secretory product.
Consists of:
1. **Merocrine glands**.
2. **Apocrine glands**.
3. **Holocrine glands**.
## Footnote
Epithelial Tissue
66
What are **merocrine glands**?
## Footnote
Epithelial Tissue
* Secretions are synthesized on ribosomes attached to rough ER.
* Processed, sorted, packed by Golgi complex.
* Released from cell in secretory vesicles via exocytosis.
* Most exocrine glands of body are merocrine glands.
* Example: Salivary glands and pancreas.
## Footnote
Epithelial Tissue
67
What are **apocrine glands**?
## Footnote
Epithelial Tissue
* Accumulate secretory products at apical surface of the secreting cell.
* That portion of cell pinches off by exocytosis from rest of cell to release secretion.
* Cell repairs itself and repeats process.
* Example: Mammary glands.
## Footnote
Epithelial Tissue
68
What are **holocrine glands**?
## Footnote
Epithelial Tissue
* Cells accumulate a secretory product in their cytosol.
* Secretory cell matures, ruptures and becomes the secretory product.
* Because cell ruptures, secretion contains large amounts of lipids from plasma membrane and intracellular membranes.
* Sloughed off cell is replaced by new cell.
* Example: Sebaceous gland of the skin.
## Footnote
Epithelial Tissue
69
How are **multicellular exocrine glands** classified by function?
## Footnote
Epithelial Tissue
* Based on whether a secretion is a product of a cell or consists of an entire or a partial glandular cell.
## Footnote
Epithelial Tissue
70
What is **connective tissue**?
## Footnote
Connective Tissue
* One of most abundant, widely distributed tissues in body.
* Various forms, a variety of functions.
* Binds together, supports, strengthens other body tissues.
* Protects, insulates internal organs.
* Compartmentalizes structures such as skeletal muscles.
* Serves as major transport system (blood, a fluid connective tissue).
* Primary location of stored energy reserves (adipose/fat, tissue) and is main source of immune responses.
## Footnote
Connective Tissue
71
What are the general features of **connective tissue**?
## Footnote
Connective Tissue
Connective tissue consists of two basic elements:
**Extracellular matrix**:
* Material located between widely spaced cells.
* Consists of protein fibers and ground substances.
* Extracellular fibers are secreted by connective tissue cells, account for many functional properties of tissue and controlling surrounding watery environment via specific proteoglycan molecule.
* Structure determines much of tissues qualities.
**Cells**:
* Embryonic cells (mesenchymal cell) give rise to cells of connective tissue.
* Each major type of connective tissue contains immature class of cells with name ending in "blast".
## Footnote
Connective Tissue
72
What are the different types of **connective tissue cells**?
## Footnote
Connective Tissue
* Connective tissue cells vary according to type of tissue:
1. **Fibroblasts**.
2. **Macrophages**.
3. **Plasma cells** (plasmocytes).
4. **Mast cells** (mastocytes).
5. **Adipocytes**.
6. **Leukocytes**.
## Footnote
Connective Tissue
73
What are **fibroblasts**?
## Footnote
Connective Tissue
* Large, flat cells with branching processes.
* Present in all the general connective tissues.
* Usually are the most numerous.
## Footnote
Connective Tissue
74
What are **macrophages**?
## Footnote
Connective Tissue
* Phagocytes that develop from monocytes, (type of white blood cell).
**Fixed macrophages**:
* Reside in a particular tissue; (alveolar macrophages in lungs or splenic macrophages in spleen).
**Wandering macrophages**:
* Ability to move throughout tissue and gather at sites of infection or inflammation to carry on phagocytosis.
## Footnote
Connective Tissue
75
What are **plasma cells (plasmocytes)**?
## Footnote
Connective Tissue
* Found in many places in the body.
* Most reside in connective tissue, especially gastrointestinal and respiratory tracts.
76
What are **mast cells (mastocytes)**?
## Footnote
Connective Tissue
* Involved in inflammatory response, the body's reaction to injury or infection.
* Can also bind to, ingest or kill bacteria.
## Footnote
Connective Tissue
77
What are **adipocytes**?
## Footnote
Connective Tissue
* Fat cells or adipose cells.
* Connective tissue cells that store triglycerides (fats).
* Found deep to skin and around organs (heart, kidney).
## Footnote
Connective Tissue
78
What are **leukocytes**?
## Footnote
Connective Tissue
* White blood cells.
* Response to certain conditions, they migrate from blood into connective tissue.
* Example: neutrophils gather at sites of infection, eosinophils migrate to sites of parasitic invasions and allergic responses.
## Footnote
Connective Tissue
79
What are the two major components of the **extracellular materials** between cells?
## Footnote
Connective Tissue
Extracellular matrix consists of two major components:
1. **The ground substance**.
2. **The fibers**.
## Footnote
Connective Tissue
80
What are the **ground substances** of connective tissue?
## Footnote
Connective Tissue
* Component of connective tissue between cells and fibers.
* May be fluid, semifluid, gelatinous, or calcified.
* Supports cells, binds together, stores water, provides medium for exhange of substances between blood and cells.
* Active role in how tissues develop, migrate, proliferate, and change shape, and how they carry out metabolic functions.
* Contains water and assortment of large organic molecules, (many complex combinations of poly-saccharides and proteins).
## Footnote
Connective Tissue
81
What is **hyaluronic acid**?
## Footnote
Connective Tissue
* Viscous, slippery substance, binds cells together, lubricates joints, helps maintain shape of eyes.
* White blood cells, sperm cells, some bacteria produce *hyaluronidase* (enzyme breaks apart hyaluronic acid).
* Hyaluronidase causes ground substance of connective tissue to become more liquid.
## Footnote
Connective Tissue
82
What are the **fibers** of connective tissue?
## Footnote
Connective Tissue
* 3 types of fibers are embedded in extracellular matrix between cells.
* Function to strengthen, support connective tissues:
1. **Collagen fibers**.
2. **Elastic fibers**.
3. **Reticular fibers**.
## Footnote
Connective Tissue
83
What are **collagen fibers**?
## Footnote
Connective Tissue
* Very strong, resist pulling/stretching, not stiff, allows tissue flexibility.
* Properties vary from tissue to tissue.
* Often occur in parallel bundles.
* Chemically, consist of protein collagen, most abundant protein in body.
* Found in most types of connective tissues, especially bone, cartilage, tendons, ligaments.
## Footnote
Connective Tissue
83
What are **elastic fibers**?
## Footnote
Connective Tissue
* Small in diameter, branch and join together to form a fibrous network within a connective tissue.
* Consists of molecules of protein **elastin** surrounded by a glycoprotein named **fibrillin** (adds strength and stability).
* Strong, can be stretched to 150% of relaxed length without breaking.
* Ability to return to original shape after being stretched (elasticity).
* Plentiful in skin, blood vessel walls and lung tissue.
## Footnote
Connective Tissue
84
What are **reticular fibers**?
## Footnote
Connective Tissue
* Collagen arranged in fine bundles with coating of glycoprotein.
* Provide support in walls of blood vessels, form network around cells in some tissues, such as areolar connective tissue, adipose tissue, nerve fibers and smooth muscle tissue.
* Produced by fibroblast, much thinner than collagen fibers and form branched networks.
* Provide support and strength.
* Plentiful in reticular connective tissue, which forms stroma (supporting framework) of many soft organs, (spleen, lymph nodes).
* Helps form the basement membrane.
## Footnote
Connective Tissue
85
What is the classification scheme of **connective tissue**?
## Footnote
Connective Tissue
1. **Embryonic connective tissue**
A. Mesenchyme
B. Mucous (mucoid) connective tissue
2. **Mature connective tissue**
A. Connective tissue proper
1. Loose connective tissue
a. Areolar connective tissue
b. Adipose tissue
c. Reticular connective tissue
2. Dense connective tissue
a. Dense regular connective tissue
b. Dense irregular connective tissue
c. Elastic connective tissue
B. Supporting connective tissue
1. Cartilage
a. Hyaline cartilage
b. Fibrocartilage
c. Elastic cartilage
2. Bone tissue
a. Compat bone
b. Spongy bone
C. Liquid connective tissue
1. Blood
2. Lymph
## Footnote
Connective Tissue
86
What are the overall basis for the classification scheme of **connective tissue**?
## Footnote
Connective Tissue
**Embryonic connective tissue**:
* Connective tissue present in an embryo or fetus.
**Mature connective tissue**:
* Connective tissue, present at birth, presists throughout life.
Consists of 3 categories.
1. **Connective tissue proper**: Flexible, contains a viscous ground substance with abundant fibers.
2. **Supporting tissue proper**: Protects and supports soft tissues of the body.
3. **Liquid connective tissue**: Means that the extracellular matrix is liquid.
## Footnote
Connective Tissue
87
What is **embryonic connective tissue**?
## Footnote
Connective Tissue
Consists of two types:
1. **Mesemchyme**.
2. **Mucous connective tissue**.
## Footnote
Connective Tissue
88
**Mesenchyme**
(Embryonic connective tissue)
## Footnote
Connective Tissue
**Description**:
* Irregularly shaped mesenchymal cells embedded in semifluid ground substance that contains delicate reticular fibers.
**Location**:
* Almost exclusiely under skin and along developing bones of embryo; some in adult connective tissue, especially along blood vessels.
**Function**:
* Forms almost all other types of connective tissue.
## Footnote
Connective Tissue
89
**Mucous (mucoid) connective tissue**
(Embryonic connective tissue)
## Footnote
Connective Tissue
**Description**:
* Widely scattered fibroblasts embedded in viscous, jellylike ground substance that contains fine collagen fibers.
**Location**:
* Umbilical cord of fetus.
**Function**:
* Support.
## Footnote
Connective Tissue
90
What is **connective tissue proper**?
## Footnote
Connective Tissue
* Type of mature connective tissue.
* Flexible, has viscous ground substance with abundant fibers.
Consists of:
1. **Loose connective tissue**
A. *Areolar connective tissue*
B. *Adipose tissue*
C. *Reticular connective tissue*
2. **Dense connective tissue**
A. *Dense regular connective tissue*
B. *Dense irregular connective tissue*
C. *Elastic connective tissue*
## Footnote
Connective Tissue
91
**Areolar connective tissue**
(Loose connective tissue)
## Footnote
Connective Tissue
**Description**:
* One of most widely distributed connective tissues.
* Consists of fibers (collagen, elastic, reticular) arranged randomly and several kinds of cells (fibroblasts, macrophages, plasma cells, adipocytes, mast cells, few white blood cells) embedded in semifluid ground substance.
**Location**:
* In/around nearly every body structure ("packing material" of body).
* In subcutaneous layer deep to skin.
* Papillary (superficial) region of dermis of skin.
* Lamina propria of mucous membranes.
* Around blood vessels, nerves, and body organs.
**Function**:
* Strength, elasticity, support.
## Footnote
Connective Tissue
92
**Adipose tissue**
(Loose connective tissue)
## Footnote
Connective Tissue
**Description**:
* Cells derived from fibroblasts (adipocytes), are specialized for storage of triglycerides (fats) as a large, centrally located droplet.
* Cells fill up with single, large triglyceride droplet. Cytoplasm, nucleus are pushed to periphery of cell.
Weight gain, amount of adipose tissue increases, new blood vessels form.
* Most adipose tissue in adults is white adipose tissue.
* Brown adipose tissue (BAT) is darker, very rich blood supply, numerous pigmented mitochondria that participate in aerobic cellular respiration.
* BAT is widespread in fetus and infant; adults only have small amounts.
**Location**:
* Wherever areolar connective tissue is located: subcutaneous layer deep to skin, around heart and kidneys, yellow bone marrow, padding around joints, behind eyeball.
**Function**:
* Reduces heat loss through skin; serves as energy reserve.
* Supports and protects organs.
* BAT generates heat to maintain body temperature.
* Adipose tissue source of stem cells, used in rejuvenation medicine to repair/replace damaged tissue.
## Footnote
Connective Tissue
93
**Reticular connective tissue**
(Loose connective tissue)
## Footnote
Connective Tissue
**Description**:
* Fine interlacing network of reticular fibers (thin form of collagen fiber) and reticular cells.
**Location**:
* Stroma (supporting framework) of liver, spleen, lymph nodes; red bone marrow; reticular lamina of basement membrane; around blood vessels and muscles.
**Function**:
* Forms stroma of organs; binds smooth muscle tissue cells; filters and removes worn-out blood cells in spleen and microbes in lymph nodes.
## Footnote
Connective Tissue
94
What is **loose connective tissue**?
## Footnote
Connective Tissue
* Fibers of loose connective tissue are loosely arranged between cells.
The types of loose connective tissue are:
1. **Areolar connective tissue**.
2. **Adipose tissue**.
3. **Reticular connective tissue**.
## Footnote
Connective Tissue
95
What is **dense connective tissue**?
## Footnote
Connective Tissue
* Second type of connective tissue proper, contains more fibers, are thicker, more densely packed.
* Have considerably fewer cells than loose connective tissue.
There are 3 types:
1. **Dense regular connective tissue**.
2. **Dense irregular connective tissue**.
3. **Elastic connective tissue**.
## Footnote
Connective Tissue
96
**Dense regular connective tissue**
(Dense connective tissue)
## Footnote
Connective Tissue
**Description**:
* Forms shiny white extracellular matrix; mainly collagen fibers regularly arranged in bundles with fibroblasts in rows between them.
**Location**:
* Forms tendons (attach muscle to bone), most ligaments (attach bone to bone), aponeuroses (sheetlike tendons that attach muscle to muscle or muscle to bone).
**Function**:
* Provides strong attachment between various structures.
* Tissue structure withstands pulling (tension) along long axis of fibers.
## Footnote
Connective Tissue
97
**Dense irregular connective tissue**
(Dense connective tissue)
## Footnote
Connective Tissue
**Description**:
* Made up of collagen fibers.
* Usually irregularly arranged with few fibroblasts.
**Location**:
* Occurs in sheets, such as fasciae (tissue beneath skin and around muscles and other organs), reticular (deeper) region of dermis of organs (kidneys, liver, testes, lymph nodes); also in heart valves.
**Function**:
* Provides tensile (pulling) strength in many directions.
## Footnote
Connective Tissue
98
**Elastic connective tissue**
(Dense connective tissue)
## Footnote
Connective Tissue
**Description**:
* Elastic fibers with fibroblasts between them; unstained tissue is yellowish.
**Location**:
* Lung tissue, walls of elastic arteries, trachea, bronchial tubes, true vocal cords, suspensory ligaments of penis, some ligaments between vertebrae.
**Function**:
* Allows stretching of various organs.
* Strong, can recoil to original shape after being stretched.
* Elasticity is important to functioning of lung tissue (recoils in exhaling) and elastic arteries (recoil between heartbeats to help maintain blood flow).
## Footnote
Connective Tissue
99
What is **supporting connective tissue**?
## Footnote
Connective Tissue
* Type of mature connective tissue that includes cartilage and bone.
## Footnote
Connective Tissue
100
What is **cartilage**?
## Footnote
Connective Tissue
* Consists of dense network of collagen fibers and elastic fibers firmly embedded in chondroitin sulfate (gel-like component of ground substance).
* Can endure more stress than loose and dense connective tissues.
* Strength is due to collagen fibers, resilience is due to chondroitin sulfate.
* Has few cells and large quantities of extracellular matrix.
There are 3 types of cartilage:
1. **Hyaline cartilage**.
2. **Fibrocartilage**.
3. **Elastic cartilage**.
## Footnote
Connective Tissue
101
**Hyaline Cartilage**
(Supporting connective tissue-cartilage)
## Footnote
Connective Tissue
**Description**:
* Contains resilient gel as ground substance.
* Appears in body as bluish-white, shiny substance.
* Prominent chondrocytes are found in lacunae surrounded by perichondrium (exceptions: articular cartilage in joints and cartilage of epiphyseal plates, where bones lengthen during growth).
**Location**:
* Most abundant cartilage in body.
* Ends of long bones, anterior ends of ribs, nose, parts of larynx, trachea, bronchi, bronchial tubes, embryonic and fetal skeleton.
**Function**:
* Provides smooth surfaces for movement at joints, flexibility, support.
* Weakest type of cartilage, can be fractured.
## Footnote
Connective Tissue
102
**Fibrocartilage**
(Supporting connective tissue-cartilage)
## Footnote
Connective Tissue
**Description**:
* Chondrocytes among clearly visible thick bundles of collagen fibers within extracellular matrix.
* Lacks perichondrium.
**Location**:
* Pubic symphysis (hip bones join anteriorly), intervertebral discs, menisci (cartilage pads) of knee, portions of tendons that insert into cartilage.
**Function**:
* Support and joining structures together.
* Strength, rigidity make it strongest type of cartilage.
## Footnote
Connective Tissue
103
**Elastic cartilage**
(Supporting connective tissue-cartilage)
## Footnote
Connective Tissue
**Description**:
* Chondrocytes in threadlike network of elastic fibers within extracellular matrix.
* Perichondrium present.
**Location**:
* Lid on top of larynx (epiglottis), part of external ear (auricle), auditory (eustachian) tubes.
**Function**:
* Provides strength and elasticity.
* Maintains shape of certain structures.
## Footnote
Connective Tissue
104
What is the growth of **cartilage**?
## Footnote
Connective Tissue
Follows two basic patterns:
1. **Interstitial growth**: Growth from within tissue. Cartilage increases rapidly in size due to division of existing chondrocytes and continuous deposition of increasing amounts of extracellular matrix by chondrocytes. As chrondrocytes synthesize new matrix, they are pushed away from each other. Cause cartilage to expand from within. Growth pattern occurs while cartilage is young, pliable, during childhood and adolescence.
2. **Appositional growth**: Growth at outer surface of tissue. Cells in inner cellular layer of perichondrium differentiate into chondroblasts. As differentiation continues, chondroblast surround themselves with extracellular matrix, become chondrocytes. As result, matrix accumulates beneath perichondrium on outer surface of cartilage, causing it to grow in width. Starts later than interstitial grown, continues through adolescence.
## Footnote
Connective Tissue
105
What are **chondrocytes**?
## Footnote
Connective Tissue
* Cells of mature cartilage.
* Occur singly or in groups within spaces called lacunae in the extracellular matrix.
## Footnote
Connective Tissue
106
What is **perichondrium**?
## Footnote
Connective Tissue
* Protective layer of dense irregular connective tissue that surrounds the surface of most cartilage.
* Contais blood vessels and nerves and is source of new cartilage cells.
## Footnote
Connective Tissue
107
What is **bone tissue**?
## Footnote
Connective Tissue
* Classified as **compact** or **spongy**.
* Bones store calcium and phosphorus.
* House red bone marrow, (produces blood cells).
* Contains yellow bone marrow, (storage for triglycerides).
* Bones are organs composed of several different connective tissues, including bone or osseous tissue, the periosteum, red and yellow bone marrow, and the endosteum.
## Footnote
Connective Tissue
108
**Bone tissue-Compact and Spongy**
(Supporting connective tissue)
## Footnote
Connective Tissue
**Description**:
* *Compact bone tissue* consists of osteons (haversian systems) thay lamellae, lacunae, osteocytes, canaliculi, central (haversian) canals.
* *Spongy bone tissue* consists of thin columns called trabeculae; spaces between trabeculae filled with red bone marrow.
**Location**:
* Both compact and spongy bone make up various parts of bones of the body.
**Function**:
* Support, protection, storage.
* Houses blood-forming tissue.
* Serves as levers that act with muscle tissue to enable movement.
## Footnote
Connective Tissue
109
What is **compact bone**?
## Footnote
Connective Tissue
Basic unit of compact bone is an **osteon** (haversian system).
Each osteon has four parts:
1. **Lamellae**: Concentric rings of extracellular matrix, consist of mineral salts. Give bones its hardness and compressive strength. Collagen fibers, give bone tensile strength. Responsible for compact nature of bone tissue.
2. **Lacunae**: Small spaces between lamellae that contain mature bone cells called osteocytes.
3. **Canaliculi**: Project from the lacunae, networks of minute canals containing processes of osteocytes. Provide routes for nutrients to reach osteocytes, wastes to leave them.
4. **Central canal**: Haversian canal contains blood vessels and nerves.
## Footnote
Connective Tissue
110
What is **spongy bone**?
## Footnote
Connective Tissue
* Lacks osteons.
* Consists of columns of bone called trabeculae, which contain lamellae, osteocytes, lacunae, and canaliculi.
* Spaces between trabeculae are filled with red bone marrow.
## Footnote
Connective Tissue
111
What is **liquid connective tissue**?
## Footnote
Connective Tissue
* Type of mature connective tissue.
* Liquid connective tissue has a liquid as its extracellular matrix.
* Consists of blood and lymph.
## Footnote
Connective Tissue
112
What is **blood tissue**?
## Footnote
Connective Tissue
* One of liquid connective tissues.
* Has liquid extracellular matrix called blood plasma and formed elements.
* Blood plasma is pale yellow fluid, consists mostly of water with variety of dissolved substances (nutrients, wastes, enzymes, plasma proteins, hormones, respiratory gases, and ions).
* Formed elements in blood plasma include RBCs, WBCs, platelets.
## Footnote
Connective Tissue
113
**Blood**
(Liquid connective tissue)
## Footnote
Connective Tissue
**Description**:
* Consists of blood plasma and formed elements: red blood cells (erythrocytes), white blood cells (leukocytes), platelets (thrombocytes).
**Location**:
* Within blood vessels (arteries, arterioles, capillaries, venules, veins), within chambers of heart.
**Function**:
* RBCs: transport oxygen and some carbon dioxide.
* WBCs: carry on phagocytosis, mediate allergic reactions and immune system responses.
* Platelets: essential for blood clotting.
## Footnote
Connective Tissue
114
What is **lymph**?
## Footnote
Connective Tissue
* Extracellular fluid that flows in lymphatic vessels.
* Liquid connective tissue consists of several types of cells in clear liquid extracellular matrix similar to blood plasma, with less protein.
* Composition varies from one part of body to another.
## Footnote
Connective Tissue
115
What are **membranes**?
## Footnote
Membranes
* Flat sheets of pliable tissue, cover or line part of body.
* Majority of membranes consist of epithelial layer and an underlying connective tissue layer.
* Are called epithelial membranes.
Types of membranes include:
1. **Mucous membranes**: Line body cavities that open to the outside.
2. **Serous membranes**: Line cavities that do not open directly to outside.
3. **Cutaneous (skin) membranes**: Skin covers the surface of the body.
4. **Synovial membranes**: Line the joints.
## Footnote
Membranes
116
What are **mucous membranes**?
## Footnote
Membranes
* Lines body cavity that opens directly to the exterior.
* Lines entire digestive, respiratory, and reproductive tracts and most of urinary tract.
* Consist of lining layer of epithelium and underlying layer of connective tissue.
* Connective tissue layer is areolar connective tissue called **lamina propria**:
* Supports epithelium, binds it to underlying structures.
* Allows some flexibility of membrane, some protection for underlying structures.
* Holds blood vessels in place, vascular source for overlying epithelium.
## Footnote
Membranes
117
What are **serous membranes**?
## Footnote
Membranes
* Lines a body cavity that does not open directly to exterior.
* Covers the organs that are within cavity.
* Consist of areolar connective tissue covered by **mesothelium** (simple squamous epithelium).
* Mesothelium of serous membrane secretes serous fluid.
Have two layers:
1. *Parietal layer*: Attached to and lining the cavity wall.
2. *Visceral layer*: Layer that covers and adheres to organs within the cavity.
## Footnote
Membranes
118
What are **cutaneous membranes**?
## Footnote
Membranes
* Skin covers entire surface of body, consists of superficial portion called epidermis and deeper portion called dermis.
* **Epidermis** consists of keratinized stratified squamous epithelium (protects underlying tissues).
* **Dermis** consists of dense irregular connective tissue and areolar connective tissue.
## Footnote
Membranes
119
What are **synovial membranes**?
## Footnote
Membranes
* Lines cavities of freely moveable joints (joint cavities).
* Lines structures that do not open to the exterior.
* Lack an epithelium, not epithelial membranes.
* Composed of discontinuous layer of cells called synoviocytes, which are closer to synovial cavity, and a layer of connective tissue deep to synoviocytes.
* **Synoviocytes** secrete some of components of synovial fluid.
* Synovial fluid lubricates, nourishes cartilage covering bones at movable joints, contains macrophages that remove microbes and debris from joint cavity.
## Footnote
Membranes
120
What is **muscular tissue**?
## Footnote
Muscular Tissue
* Enlongated cells (muscle fibers) or myocytes that can use ATP to generate force.
* Produces body movements, maintains posture, generates heat.
* Provides protection.
* Based on location and certain structural and functional features, muscle tissue is classified into three types:
1. **Skeletal**.
2. **Cardiac**.
3. **Smooth**.
## Footnote
Muscular Tissue
121
**Skeletal muscle tissue**
(Muscular tissue)
## Footnote
Muscular Tissue
**Description**:
* Long, cylindrical, striated fibers (striations are alternating light and dark bands within fibers).
* Skeletal muscle fibers vary greatly in length, few centimeters in short muscles to 30-40cm in longest muscles.
* Muscle fiber is roughly cylingrical, multinucleated cell with nuclei at the periphery.
* Voluntary, can contract /relax by conscious control.
**Location**:
* Usually attached to bones by tendons.
**Function**:
* Motion, posture, heat production, protection.
## Footnote
Muscular Tissue
122
**Cardiac muscle tissue**
(Muscular tissue)
## Footnote
Muscular Tissue
**Description**:
* Branched, striated fibers, usually one centrally located nucleus (occasionally two).
* Attach end to end by transverse thickenings of plasma membrane called intercalated discs (contain desmosomes and gap junctions).
* Desmosomes strengthen tissue, hold fibers together during vigorous contractions.
* Gap junctions provide route for quick conduction of electrical signals (muscle action potentials) throughout heart.
* Involuntary control.
**Location**:
* Heart wall.
**Function**:
* Pumps blood to all parts of body.
## Footnote
Muscular Tissue
123
**Smooth muscle tissue**
(Muscular tissue)
## Footnote
Muscular Tissue
**Description**:
* Nonstriated fibers (lacks striations).
* Small spindle-shaped cell, thickest in middle, tapering at each end, containing a single, centrally located nucleus.
* Gap junctions connect many individual fibers in some smooth muscle tissue (example, in wall of intestines).
* Usually involuntary; produce powerful contractions as muscle fibers contract in unison.
* Where gap junctions are absent, (iris of eye), smooth muscle fibers contract individually, like skeletal muscle fibers.
**Location**:
* Iris of eyes; walls of hollow internal structures such as blood vessels, airways to lungs, stomach, intestines, gallbladder, urinary bladder, and uterus.
**Function**:
* Motion (constriction of blood vessels and airways, propulsion of foods through GI tract, contraction of urinary bladder, and gallbladder).
## Footnote
Muscular Tissue
124
What is **nervous tissue**?
## Footnote
Nervous Tissue
Consists of only two principle types of cells:
1. **Neurons**: Sensitive stimuli. Converts stimuli into electrical signals (nerve impulses) and conduct these action potentials to other neurons, to muscle tissue, or glands. Consist of 3 basic parts: cell body, dendrites and axons.
2. **Neuroglia**: Do not generate or conduct nerve impulses, although do have many important supportive functions.
## Footnote
Nervous Tissue
125
What are the three basic parts of a **neuron**?
## Footnote
Nervous Tissue
1. **Cell body**: Contains the nucleus and other organelles.
2. **Dendrites**: Tapering, highly branched, usually short cell processes (extensions). Major receiving/input portion of a neuron.
3. **Axons**: Single, thin, cylindrical process, may be very long. Output portion of a neuron, conducting nerve impulses toward another neuron or to other tissue.
## Footnote
Nervous Tissue
126
**Nervous Tissue**
## Footnote
Nervous Tissue
**Description**:
* Consists of:
1: **Neurons** (nerve cells): Consists of cell body and processes extending from cell body (one to multiple dendrites and single axon).
2. **Neuroglia**: Do not generate/conduct nerve impulses, have other important supporting functions.
**Location**:
* Nervous system.
**Function**:
* Exhibits sensitivity to various types of stimuli.
* Converts stimuli into nerve impulses (action potentials).
* Conducts nerve impulses to other neurons, muscle fibers, or glands.
## Footnote
Nervous Tissue
127
What are **excitable cells**?
## Footnote
Excitable Cells
* Cells that exhibit electrical excitability (ability to respond to certain stimuli by producing electrical signals such as action potentials.).
* Action potentials can propagate (travel) along plasma membrane of a neuron or muscle fiber due to presence of specific voltage-gated ion channels.
## Footnote
Excitable Cells
128
What are **neurotransmitters**?
## Footnote
Excitable Cells
* When an action potential forms in a neuron, neuron releases chemicals called neurotransmitters.
* Allows neurons to communicate with other neurons, muscle fibers, or glands.
* When action potential occurs in muscle fiber, muscle fiber contracts, resulting in activities such as movement of limbs, propulsion of food through small intestine, and movement of blood out of heart and into blood vessels.
## Footnote
Excitable Cells
