UNIT 3 TISSUES
SUBOBJECTIVES
3.1 I can describe the structures and functions of epithelial tissues.
3.2 I can describe the structures and functions of the types of glands.
3.3 I can describe the components of connective tissue and their functions.
3.4 I can describe the structures and functions of the connective tissues.
3.5 I can describe the structures and functions of cartilage tissue.
3.6 I can describe the structure and function of bone tissue.
3.7 I can describe the structure and function of blood tissue.
3.8 I can describe the structures and functions of muscle tissue.
3.9 I can describe the structure and function of nervous tissue.
3.10 I can describe the structure and function of the major types of epithelial membranes.
Evolution Connection
3.11 I can describe the evidence for, and explain how mammary glands evolved from epithelia involved in the innate
immune response.
Breast beginnings
http://scienceblogs.com/pharyngula/2006/05/19/breast-beginnings/
Four of my favorite things are development, evolution, and breasts,
and now I have an article that ties them all together in one pretty
package. It’s a speculative story at this point, but the weight of the
evidence marshaled in support of the premise is impressive: the
mammalian breast first evolved as an immunoprotective gland that
produced bacteriocidal secretions to protect the skin and secondarily
eggs and infants, and that lactation is a highly derived kind of
inflammation response. That mammary glands may have had their
origin as inflamed glands suppurating mucus may not be the most
romantic image to arise in a scientific study, but really—they got better
and better over the years.
Vorbach et al. have carried out a descriptive analysis of the elements of
breast milk and lactation and come to this conclusion on the basis of
three general lines of evidence.



Immunoprotective proteins are a significant component of
breast milk.
The nutritional components of milk are synthesized by enzymes that are derived from immunoprotective proteins.
Many of the molecular regulators of lactation are shared with inflammation pathways.
My previous article on mother’s milk gave a highly abbreviated list of the components found in milk, but there’s more detail in
the list below. Milk is much, much more than baby food—it’s an incredible cocktail of interesting proteins, and 1) many of them
are shared with mucus secretions produced by other secretory epithelia, and 2) many of them are elements of the innate
immune system. Milk is actually a kind of anti-microbial snot mixed in with a lot of fat and sugar.
(click for larger image)
Molecules that play a dual role in immunity and
nutrition. Proposed origin of milk as an antimicrobial
mucus secretion containing many evolutionarily
conserved, protective molecules, which today
comprise part of the whey proteins of milk (blue). Two
of these molecules, xanthine oxidoreductase and
lysozyme, evolved due to gene sharing and gene
duplication additional functions in the ancient
mammary epithelium such as milk fat droplet
secretion and the unique synthesis and secretion of alactalbumin as well as the milk sugar lactose. The
secretion of these calorie-rich components markedly
increased the nutritional value to milk (green). The
nutritional and protective importance of milk was
further expanded by serum-derived proteins that
comprise part of the whey proteins of milk (red). In
particular, lactose and its derivatives are osmotically
active and draw water into milk. Caseins are the major
protein source of milk in higher mammals. While the
calcium-sensitive α1 α2, β, γ, δ-caseins presumably
originated de novo, the calcium-insensitive κ-casein
shows structural and sequence similarities to
fibrinogen (purple). Abbreviation: Ab, antibody; Ig,
Immunoglobulin; PRM, Pattern Recognition Molecule;
PRR, Pattern Recognition Receptor; XOR, Xanthine
oxidoreductase.
The innate immune system is a primitive defense system that uses peptides that recognize various common microbial surface
molecules, and also uses enzymes that produce chemical agents lethal to bacteria. It’s a first line of defense that differs from the
more specific immune system in that it doesn’t require specialized immune system cells and also doesn’t acquire the kind of
highly refined specificity we see in antibodies (note, too, that antibodies are also secreted in milk—they are the IgG, IgE, and IgM
molecules listed above.)
One key element in milk is XOR, xanthine oxidoreductase. This enzyme mediates purine catabolism and, for instance, the
synthesis of uric acid, but also generates reactive oxygen species and reactive nitrogen species, compounds that can be
voraciously reactive and interact destructively with bacteria. You may have heard of one reactive nitrogen species, the nitrites
that hot dogs are loaded with as preservatives. Reactive oxygen species are chemicals like hydrogen peroxide, which is often
used as a disinfectant, and superoxide anions and hydroxyl radicals.
Another is lysozyme, a protein that hydrolyzes the polysaccharides (sugars) that make up bacterial cell walls. This is a very
common component of the innate immune system of many animals: you ooze this protein out of your skin, your mucus is loaded
with it, and it’s also found in high concentrations in other places, such as egg whites. It’s simply generally useful protection to be
able to chemically strip bacteria of their protective coats.
Other proteins also have bacteriocidal functions, and are found in other glandular secretions: lactoferrin and transferrin,
lactoperoxidase (which as you might guess from the name, synthesizes reactive oxygen species), defensins (which disrupt
bacterial membranes), and pattern recognition molecules (PRMs), which bind to certain common molecular motifs on bacterial
surfaces. It’s so sweet and tasty, yet so deadly to microbes!
Now wait, you may be wondering…how is this evidence that milk’s original function was immunoprotective? If you’re secreting a
sweet and fatty nutritious substance for your young, it would definitely be advantageous to load it up with antimicrobials to keep
the nasty beasties from growing in it. XOR and lysozyme and all those others could have been added secondarily.
One reason to think otherwise is that those protective molecules are universal to vertebrates—lizards and birds have them, too.
These enzymes and other proteins came first.
Those of you wise in the ways of evolution are saying to yourselves, “So what? It’s another example of cooption, taking a protein
used for one function and adapting it to another.” And you’d be right: that’s only suggestive. Another good reason, though, is to
look at the enzymes responsible for generating the nutritive components of milk, the lactose sugars and the fat droplets.
Breaking up fat into droplets and enveloping them with some kind of coat to promote suspension in water is an essential
function in the production of milk. The protein that is responsible for this structural function, and which if knocked out prevents
lactation and actually leads to collapse of the mammary gland, is…XOR! This is a wonderful example of a protein doing double
duty, as an enzyme responsible for bacteriocidal action and as a structural protein involved in solubilizing fats. It almost certainly
had the enzymatic function first, and if any cooption was going on, it was to recruit an immunoprotective protein to secondarily
assist in a nutritive function.
The other essential nutritive component of milk is lactose, the milk sugar. Lactose is an odd and unusual sugar—that’s actually
it’s advantage, that it is a sugar that many bacteria have difficulty digesting (it’s not just people that can be lactose intolerant!)—
and it requires a specific synthetic complex consisting of β-1,4 galactosyltransferase and α-lactalbumin for its production. Where
did α-lactalbumin come from? It’s sequence makes the homologies clear: the α-lactalbumin gene is a modified copy
of…lysozyme!
I think that’s remarkable. The two primary nutritive components of milk, the sugars and fats, are the product of novel activity by
proteins that are clearly primitively associated with innate immunity.
To further the similarities, the authors give a long list of components of signaling pathways that are typically associated with
inflammatory and immune system responses and are also essential in lactation. For instance, the transcription factor NF-kB,
which is also a hot candidate molecule in cancer research, is involved in regulating the expression of various cytokines and
antimicrobial agents; transgenic mice that knock out this pathway also exhibit developmental failures in the differentiation of the
mammary gland. They’ve modified other elements of this pathway (RANKL, C/EBPβ, TNF-α) which act in inflammation responses,
and they all also induce developmental problems in mammary gland tissue and reduce or shut down lactation.
I’ve just finished teaching a human physiology course in which we learned the basics of endocrinology, and I gave my students
the usual story on the pituitary hormone prolactin: it regulates milk production. It’s too bad I hadn’t read this paper earlier,
because it makes the story much, much more complicated (my students are probably relieved, though—the class was
complicated enough as it was).
Prolactin is known as a key lactogenic hormone but, depending on the cellular context, prolactin can also act as an antiinflammatory or proinflammatory cytokine. Interestingly, it has been demonstrated that prolactin is involved in the protective as
well as the nutritional role of milk. Prolactin participates in regulating the secretion of immunoglobin A (IgA), the prominent Ig in
mucus and milk that inhibits the colonization of pathogenic bacteria on mucosal surfaces. Changes in the secretion of IgA are
associated with the anti-inflammatory potential of epithelial tissues. In addition, prolactin stimulates the uptake of some amino
acids and glucose, as well as the synthesis of casein, α-lactalbumin, lactose and milk fat droplets in the lactating mammary
epithelium. Finally, prolactin and IFN-γ also stimulate the expression of XOR in mammary epithelial cells via the Jak/Stat signaling
pathway. Thus, multiple small molecules and ligandreceptor systems that have critical roles in
inflammatory responses exert dual and, in many
cases, essential functions in immunity and mammary
gland biology.
Gee, I’m going to have to revise and add some stuff in
that class next time I teach it. Very cool.
Their model for the evolution of the mammary gland
is illustrated below. It’s reasonable, and the
molecular evidence is persuasive. Basically, the
process began as the secretion of antimicrobials
agents from the skin of the early mammal (something
we still do) as a protective function. This function was
elaborated by infoldings of epithelia to increase surface area and generate reservoirs of mucus and the antimicrobials. Eggs and
infants would have benefitted from more copious secretions from the mother, coating them as well with this immunoprotective
substance. The young would have also lapped up the tasty rich goo, and infant survival would have been promoted by changes
that caused the secretion of ever-richer substances.
Proposed evolution of the mammary gland from a mucus-secreting epithelial gland. Mammary glands presumably evolved as
mucus-secreting skin glands that similar to many mucus surface epithelia secreted antimicrobial enzymes such as XOR and
lysozyme. The evolution of additional functions of XOR and lysozyme in the ancient mammary epithelium resulted in the
secretion of fat droplets, α-lactalbumin and lactose. Consequently, the mammary gland evolved from a protective immune organ
into a reproductive organ unique to the class mammalia.
One question not addressed by the paper is why only females lactate—you’d think the young would have benefitted if Papa
Proto-mammal was also slathering them with immunoprotective slime. I’d guess that this supports the idea that those ancient
males weren’t particularly involved in caring for their progeny, so it made little difference in infant survival if the father turned
these secretions down to a level sufficient to selfishly protect just himself. These secretions are also expensive—I’ve seen figures
that suggest that a third to half of the energy budget of nursing small mammals may be leaking out their lactating teats—so it
would have been advantageous for those slacking males to shut down the production so necessary for female reproductive
success.
Vorbach C, Capecchi MR, Penninger JM (2006) Evolution of the mammary gland from the innate immune system? BioEssays
28:606-616.
READINGS: SUBHEADINGS
1)
All of chapter 5
MORPHEMES TO MEMORIZE
http://quizlet.com/_et7ui
1)
2)
3)
4)
5)
6)
Adipfat
Chondrcartilage
–cyt
cell
EpiUpon, after, in adition
–glia
glue
Hist-
Web, tissue
7) HyalResemblance to glass
8) Interamong
9) Macrlarge
10) Neurnerve
11) Osbone
12) PhagTo eat
13) Pseudfalse
14) Squamscale
15) Stratlayer
16) Striagroove
STRUCTURES TO MEMORIZE
http://quizlet.com/_f77o7
Figure 5.1 page 134 memorize all structures
Figure 5.2 page 134 memorize all structures
Figure 5.3 page 135 memorize all structures
Figure 5.5 page 136 memorize all structures
Figure 5.7 page 137 memorize all structures
Figure 5.6 page 136 memorize all structures
Figure 5.8 page 137 memorize all structures
Figure 5.9 page 138 memorize all structures
Figure 5.11 page 140 memorize all structures
Figure 5.18 page 144 memorize all structures
Figure 5.20 page 145 memorize all structures
Figure 5.19 page 145 memorize all structures
Figure 5.21 page 121 memorize all structures
Figure 5.22 page 146 memorize all structures
Figure 5.24 page 147 memorize all structures
Figure 5.26 page 149 memorize all structures
Figure 5.28 page 150 memorize all structures
Figure 5.30 page 151 memorize all structures
Figure 5.25 page 148 memorize all structures
Figure 5.27 page 149 memorize all structures
Figure 5.29 page 151 memorize all structures
Figure 5.31 page 152 memorize all structures
OTHER VOCABULARY TO MEMORIZE
http://quizlet.com/_f77dx
3.1
1)
2)
Tissue
similar cells of the same origin that perform a specific function
Epithelial tissue
lines cavities and covers the surfaces of structures throughout the body
3) Basement membrane
a thin sheet of fibers that lines epithelium. It sticks the epithelium to its loose connective tissue.
4) Simple squamous epithelium
involved in filtration and diffusion. Found in air sacs of lungs, walls of capillaries, and the linings of blood and lymph
vessels
5) Simple cuboidal epithelium
involved in secretion and absorption. Found in kidney tubules, surface of ovaries, and the linings of kidneys
6) Simple columnar epithelium
involved in protection, secretion, and absorption. Found in linings of uterus, stomach, and intestines
7) Cilia
projections of epithelial cells into a lumen that move substances
8) Microvilli
hair-like processes of cells that wisp substances in one direction. They are also involved with secretion and absorption
9) Goblet cells
single celled glands found in epithelia that secrete mucin, which mixes with water forming mucus
10) Mucus
a slippery fluid mostly of glycoproteins. Also contains lysozymes and antibodies
11) Pseudostratified columnar epithelium
_____ cells that appear layered because the nuclei are at different levels, but each cell reaches the basement
membrane. They line repiratory passages, protect, secrete and move mucus
12) Stratified squamous epithelium
involved in protection. Found in the outer layer of skin, linings of oral cavity, throat, vagina, and anal canal
13) Keratin
a fibrous protein type that is the main structural unit of hair, nails, and the outer layer of skin
14) Stratified cuboidal epithelium
involved in protection. Found in the larger ducts of mammary gland, salivary glands, sweat glands, and the pancreas
15) Stratified columnar epithelium
involved in protection and secretion. Located in the Vas deferens, part of the male urethra, and parts of the pharynx
16) Transitional epithelium
multiple layers of epithelial cells which can contract and expand
17) Glandular epithelium
The type of epithelium that secretes into ducts that open onto surfaces like skin or into body fluids is
3.2
18) Exocrine gland
excretes product through a duct into a cavity or out of the body
19) Endocrine gland
a gland that secretes its product directly into the blood stream
20) Merocrine gland
an exocrine gland that secretes its product into a duct via exocytosis. Found in salivary glands, pancreatic glands, and
sweat glands
21) Apocrine gland
An exocrine gland that secretes bits of the cell in the form of vesicles. Examples include a few types of sweat glands like
those of the arm pits and mammary glands.
22) Holocrine gland
an exocrine gland that secretes by the disintigration of hole cells filled with the secretory product. Found in sabaceous
glands
3.3
23) Connective tissue
tissue that supports, connects, or separates different tissues and organs of the body
24) Matrix
The gelatinous extracellular material that includes ground substance and fibrous proteins. It sticks tissue cells and cell
layers together
25) Ground substance
a gel-like material that surrounds connective tissue cells
26) Fibroblast
a cell that synthesizes the extracellular matrix and collagen
27) Macrophage
Amoeboid cells that roam connective tissue and engulf foreign particles and debris of dead cells.
28) Mast cell
a cell found in various tissues that produces histamine and heparin which cause inflammation. They are involved in
allergic responses and defense against pathogens
29) Collagenous fibers
fibers made of the most abundant protein found in animals. They have diverse functions including tension resistance.
3.4
30) Connective tissue proper
unspecialized connective tissue found throughout the body that has various functions
31) Areolar tissue
loose connective tissue that binds different tissue types together while providing cushioning. It has loosely organized
fibers and significant vascularization. It is found throughout the body.
32) Adipose tissue
loose connective tissue specialized for storage of fat. It protects vital organs, insulates, and stores energy.
33) Reticular connective tissue
Loose connective tissue dominated by _____ fibers. Provides structural support for lymphatic organs, the spleen, and
liver
34) Dense connective tissue
parallel collagen fibers that connect different tissues and resists tension well in one direction. Found in ligaments, and
tendons
35) Elastic connective tissue
connective tissue that can stretch. It is found in hollow organs such as the bladder and arteries
3.5
36) Cartilage
flexible connective tissue with extensive extracellular matrix and no direct blood supply. Found throughout the body.
37) Chondrocyte
a cell found in cartilage tissue types that produces and maintains the matrix of cartilage
38) Lacunae
a tiny cavity found in bone and cartilage tissue where osteocytes and chondrocytes are located
39) Hyaline cartilage
composed mostly of extracellular matrix. Has a glassy appearance and is found on the ends of bone and the supporting
rings of respiratory passages
40) Elastic cartilage
cartilage composed of collagen and elastic fibers that support and provide shape. Found in the outer ear, Eustachian
tubes, and epiglottis
41) Fibrocartilage
cartilage with many large cartilage fibers. Supports, protects, and provides framework. Located between vertebral disks,
pelvic girdle, and knee
3.6
42) Bone
dense connective tissue that supports and protects organs, produces red and white blood cells, and stores minerals
43) Osteocyte
bone cells that regulate the cell types that form bone and reabsorb bone. They also regulate phosphate metabolism.
44) Lamellae
cylindrical sheets of bone matrix
45) Haversian canals
the channel formed by lamellae where blood vessels and nerves travel through bone
46) Osteon
the structural unit of bone consisting of concentric layers of lamellae surrounding a channel (Haversian canal) that
contains blood vessels and nerves
47) Canaliculi
tiny spaces where the processes of an osteocyte extend through and connect to other osteocytes. The membranes of
the cells are fastened by gap junctions.
3.7
48) Plasma
the noncellular, watery portion of blood that suspends the other components of blood
49) Red blood cell
cells without a nucleus packed with hemoglobin, which carries oxygen
50) White blood cell
a cell that defends against pathogens and foreign materials
51) Platelets
cell fragments that cause clotting and produce growth factors involved in tissue repair
3.8
52) Muscle tissue
soft tissue composed of myofibrils that may be smooth or striated. They are involved in both voluntary and involuntary
movement
53) Skeletal muscle tissue
striated _____ tissue that is under voluntary control. Moves and supports bone
54) Smooth muscle tissue
non-striated _____ tissue under involuntary control. Involved in organ movements
55) Cardiac muscle tissue
involuntary _____ tissue, single nucleated, and striated with intercalated discs. Self-contracting
56) Intercalated disc
structures with specialized gap junctions that connect heart muscle and allow for coordinated muscle contractions
3.9
57) Nervous tissue
soft tissue composed of neurons and glial cells that transmit electrical messages that control body function
58) Neuron
an electrically excitable cell that transmits electrical messages to and from organs and tissues
3.10
59) Organ
two or more tissues grouped together performing the same function
60) Synovial membrane
A membrane between a joint capsule and joint cavity that secretes a lubricating fluid
61) Cutaneous membrane
protects the organism from pathogens and desiccation. Insulates, regulates body temperature, and produces vitamin D