BIO210 Weekly Guide #3
EPITHELIUM; INTEGUMENT;
MEMBRANE TRANSPORT
After completing this laboratory you should be able to:
1) Recognize, fully classify, and functionally characterize samples of epithelia in microscopic sections
2) For any sample of epithelia, state where in the body it could be found
3) Recognize and functionally characterize the various surface modifications found in epithelia
4) Distinguish between the hypodermis, dermis, and epidermis in histological models and slides
5) Be able to distinguish thick and thin skin and state where in the body each could be found
6) Identify the layers of the dermis and epidermis
7) Recognize hair follicles, dermal papillae, arrector pili, sebaceous glands, and sweat glands in histological models and slides
8) Distinguish between thick and thin skin and state where in the body each is found
9) Identify and distinguish the major fingerprint patterns
10) Identify Meissner's and Pacinian corpuscles and describe the sensory function of each
11) Characterize the various mechanisms of passive and active movement of materials through cell membranes.
Guide to Gross Anatomy Guide to Histology Guide to Physiology
Outline
I. Epithelium {AP 4-2; APL Exercise 5.1}
A. Properties
cellular - tight cell apposition
polarity - apical and basal surfaces
basement membrane
avascular
B. Locations
lining surfaces, glands
C. Functions
boundaries, sealing, protection, absorption, excretion, transport, secretion, sensory
reception
D. Classification
cell shape
squamous
cuboidal
columnar
transitional
arrangement
simple
stratified
pseudostratified
surface modifications and accessory cells
cilia
microvilli
stereocilia
keratinization
goblet cells
naming conventions
named for apical layer
order - arrangement, cell shape, "with", modification and accessory cells
special types of epithelium
endothelium (simple squamous)
mesothelium (simple squamous)
transitional (stratified transitional)
functional considerations
how epithelial type matches function
why not all combinations are possible
E. Actual Epithethelial Types
simple squamous
esp. endothelium and mesothelium
simple cuboidal
w/wo brush border (microvilli)
glandular
simple columnar
w/wo brush border, ciliated, goblet cells
stratified squamous moist (nonkeratinizing)
stratified squamous keratinizing
stratified cuboidal
stratified columnar
pseudostratified columnar ciliated w goblet cells (respiratory epithelium)
transitional
II. Integument {AP Ch 5; APL Unit 6}
A. General features:
largest organ of body
3 layers:
epidermis, dermis, hypodermis
B. Epidermis
stratified squamous epithelium, keratinized
epidermal ridges
5 layers:
stratum basale (stratum geminativum)
stratum spinosum
stratum granulosum
stratum lucidum
stratum corneum
melanocytes
thick vs. thin skin
C. Dermis
dense irregular C.T.
2 layers:
papillary layer
dermal papillae
Meissner's corpuscles - fine touch
capillary loops
reticular layer
Pacinian corpuscles - deep pressure
hair follicles
arrector pili
sweat glands - simple coiled tubular
sweat
merocrine glands - open to surface
apocrine glands - open to hair follicle
sebaceous glands - branched acinar
sebum
holocrine glands
open to hair follicles
D. Hypodermis
loose CT
adipose tissue
E. Skin coloration
melanin in melanocytes - black
carotene in subcutaneous fat - yellow
hemoglobin in dermal capillaries - red
F. Wound Repair
G. Effects of Aging
III. Membrane Transport {FAP 3-6, Figs 3-18 - 3-22}
A. Facilitated diffusion
channels
channel selectivity
channel gating - voltage and ligand
relative conductances
carrier molecules
aquaporins
B. Active transport
the sodium/potassium pump
proton pumps
metabolic requirements
consequences for cells
Na+, K+ Cl- gradients
the membrane resting potential
C. Cotransport and countertransport mechanisms
cotransport - e.g. Na+/glucose; Na+/aa's
countertransport - e.g. Na+/H+; Cl-/HCO3-
Gross Anatomy List
Locations in the body for each type of epithelium (not an exhaustive index):
simple squamous:
lungs (alveoli)
kidneys (parts of Loops of Henle)
endothelium - lining blood vessels and heart
mesothelium - ling true body cavities
simple cuboidal:
kidneys
parts of repiratory tree
glands and ducts
simple columnar:
lower GI tract - enteron and colon
appendix
gall bladder
parts of respiratory tree
parts of urinary tract
stratified squamous moist
upper digestive and shared digestive/respiratory tracts
lower urogenital tracts
rectum
glans and clitoris
stratified squamous keratinized
skin
stratified cuboidal (2 layers)
larger ducts - e.g. salivary, pancreas, liver
stratified columnar (2 layers)
conjunctiva of eye
pseudostratified columnar w cilia and goblet cells (respiratory)
upper respiratory passages (e.g. nasopharynx, trachea, bronchi)
transitional
renal calyces, ureters, urinary bladder
Thick and thin skin locations:
thick skin:
plantar, palmar, volar surfaces
thick skin:
everywhere else
Guide to Gross Anatomy
Integument
A) Locate the following structures on the integument models {APL Fig 6.3, 6.4}:
Dermis
reticular and papillary layers
dermal papillae
hair follicle
hair shaft
hair root
hair bulb
hair papilla
sebaceous gland
arrector pili muscle
sweat gland
Meissner's corpuscle
cutaneous blood vessels
Epidermis
stratum corneum
stratum lucidum
deeper epidermal strata (granulosum, spinosum, basale/germinativum)
B) Locate the following structures on the distal end of one of your fingers {APL Fig 6.5}:
nail
lateral, medial, and proximal nail folds
hyponychium
lunula
eponychium
Fingerprints
Follow APL Exercise 6-4 to make your own fingerprint card and to practice "dusting", "lifting", classifying, and matching fingerprints.
Guide to Histology
Epithelium {APL Exercise 5.1; Fig. 5.3}
This tissue is found covering the outer body surface and lining the inner body surfaces, including hollow organs, ducts, vessels, body cavities, etc. Epithelium has the following structural properties:
1) It is predominantly cellular, having very little intercellular (extracellular) material.
2) Characteristically, epithelium is avascular - blood vessels are not found within the epithelium proper, so oxygen and nutrients must diffuse to the epithelium from adjacent tissues.
3) Epithelium has a polarity; it has an apical surface (usually facing a lumen or the outside world) and a basal surface (usually bordering on underlying connective tissue [C.T.]).
4) All epithelium is bound to a fibrous basement membrane (basal lamina). Epithelia are classified according to the number of cell layers and the cell shape of the surface layer. In addition, the classification includes any specialized surface modifications (such as cilia, microvilli, or stereocilia) and specialized cells (such as goblet cells) in the epithelium. There are three basic layering patterns - simple, pseudostratified, and stratified. There are four basic cell shapes - squamous, cuboidal, columnar, and transitional. This would seem to imply twelve (3 x 4) possible epithelial combinations, however, only seven basic types of epithelium are found in the body.
For each of these basic epithelial types you should be able to:
recognize it
correctly classify it
state for what function(s) it is specialized
state where in the body it might be found.
1) Simple Squamous Epithelium
This consists of a single layer of flattened cells, specialized for diffusion, typical of thellining of blood and lymph vessels (which is given the specialized name "endothelium"), of the lining of the pleural (lung exterior), cardiac, and abdominal body cavities ("mesothelium"), the alveolar air sacs of the lungs, and portions of each kidney nephron.
2) Simple Cuboidal Epithelium
Simple cuboidal epithelium consists of a single layer of cells as tall as they are broad. It is specialized for secretion/absorption and is found in the ducts of many glands, in the kidney, on the ovary, and in the ciliary body of the eye.
3) Simple Columnar Epithelium
This epithelium has a single layer of cells, taller than they are broad. It is specialized for secretion aand/or absorption and is found in the stomach, small and large intestines, gall bladder, oviducts, and the secretory cells of many glands.
4) Pseudostratified Columnar Epithelium
This is like a simple epithelium, in that each cell is in contact with the basement membrane, but it appears stratified because the cell nuclei lie at multiple levels, giving the superficial appearance of multiple layers of cells. It is found in the upper respiratory system (nasal cavity, pharynx, trachea, and large bronchi), in the vas deferens, and in portions of the male and female urethra.
5) Stratified Squamous Epithelium
This is an epithelium of multiple layers, with the cells at the apical surface being flattened and squamous. It is specialized for protection, resistance to friction, and waterproofing. The surface layer may be keratinized or nonkeratinized (moist); no other cell surface modifications are present. This epithelium forms the skin and lines the nostrils, lips, mouth, parts of the pharynx, esophagus, anus, distal urethra, and vagina.
6) Stratified Cuboidal or Columnar Epithelium
This epithelium is relatively rare. Stratified columnar or stratified cuboidal epithelia are found in the larger ducts of some glands (sweat and sebaceous glands of the skin, salivary and mammary glands), in the Graafian follicle of the ovary, in the conjunctiva of the eye, and occasionally in the male urethra. It provides a tougher lining than would a simple epithelium.
7) Transitional Epithelium
This is formally a "stratified transitional epithelium", which is specialized for stretching. It is found in the renal calyces, ureters, and bladder. The large rounded transitional, or "dome" cells of the apical surface, often spreading across several lower cells, distinguish it from stratified squamous, which it superficially resembles. As the organs expand, these dome cells undergo a transition from a cuboidal to a squamous shape, to accommodate the increase in surface area.
Surface Modifications and Specializations
There are five possible kinds of modifications of the apical surface layer(s) of cells.
1) Cilia
Cilia are motile surface structures which propel substances along the walls of the organ lumen. They are found in the respiratory tree and the oviduct. What gets moved in each structure? They are also never found on squamous cells. Why? Under high magnification cilia can be distinguished from other surface extensions by the dark line at the base. This dark line is formed by the optically-dense basal bodies which anchor the cilia.
2) Microvilli
Microvilli are outfoldings or extensions of the luminal cell membrane. They increase the surface area of the cell and are especially adapted for absorption and secretion. Under light microscopy the individual projections may not be visible, but their presence blurs the cell surface, giving it a "cuticular" or "brush" border. Microvilli may be found in simple cuboidal or columnar epithelia and are present in portions of the gut and in the kidney tubules, among other places.
3) Stereocilia
Stereocilia are sparse, extremely long microvilli (hence, the name "stereocilia" is really a misnomer; stereocilia are not related to cilia). They give the surface cells a feathery, wispy, or comb-like appearance. They are nonmotile. They are found in the pseudostratified cuboidal epithelium of the epididymis and ductus deferens, as well as in some sensory cells.
4) Goblet Cells
Goblet cells are goblet-shaped cells which are found interspersed among the "regular" columnar cells of the upper respiratory epithelium, lining of the intestines, and conjunctiva of the eye. Their function is to produce mucus, which lubricates and protects the epithelial surface.
5) Keratinization
Keratinization is a surface modification of the epidermis of skin. The most apical cells become filled with the protein keratin, then die. This forms a rough, abrasion resistant, and water-proof layer of stacked, flattened, dead cells at the surface of the skin.
- In what regions of the body surface do you think that this keratin layer is the thickest?
Integument
Work through the skin slides and models to observe and recognize the following:
a) Skin {APL Fig 6.3}
The epidermis is easily recognized as stratified squamous keratinizing epithelium. The dermis may be recognized by the dense irregular C.T., characteristic sebaceous and sweat glands, specialized sensory nerve endings, and appendages, such as hair follicles.
- In each of the skin slides and in the models distinguish the dermis from the epidermis.
- In the epidermis, identify the following strata: stratum basale (or stratum germinativum), stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum. In which stratum are melanocytes located and what is their function?
- Identify the superficial papillary and deeper reticular layers of the dermis. Identify dermal papillae. Locate a merocrine sweat gland and try to trace its spiral path up through the dermis and epidermis to the surface. In what regions of the body surface are apocrine sweat glands concentrated? What distinguishes apocrine, merocrine, and holocrine glands?
- Locate a hair follicle. Identify the hair shaft, surrounding sebaceous glands, and the arrector pili muscle. Where do sebaceous glands empty? What is the function of the arrector pili?
- In the dermis try to locate arteries, veins, and peripheral nerves. What part of the autonomic nervous system controls sweat and sebaceous glands? Describe the role of the skin and its appendages in thermoregulation.
- Compare the slides of thin and thick skin. Where do you find each in the body? What dermal structures are missing from thick skin?
b) Somatosensory Organs {APL Fig 6.4A}
We will study two specialized sensory endings of the skin. Meissner's corpuscles are small, dense, oval whorls of flattened cells located in the dermal papillae. Pacinian corpuscles are larger and more circular, resemble onions in cross section, and are typically found much deeper in the dermis.
- Try to identify Pacinian (lamellated) and Meissner's (tactile) corpuscles. What is the function of each? Why is it more important for Meissner's corpuscles to be located just beneath the epidermis?
Guide to Physiology
Active Transport
We will study active transport via a video of active transport in the frog skin. Take careful notes and be prepared to ask questions for any points or procedures which you do not understand. Be sure to record all measurements which are made during the video. Try to answer the accompanying questions, based on your observations from the video experiment.
Experiment 1
Data Table:
Condition:
Sac Fluid (Inside)
Bath Fluid (Outside)
Inside Out Skin
Outside Out Skin
Control
Q1.1 What are the principal ions being actively "pumped" across the frog skin?
Q1.2 Which ion is being tracked and how is this done in video experiment #1?
Q1.3 Based on this experiment do individual sodium ions move in one direction or in both directions across the frog skin?
Q1.4 Based on this experiment is the net flux of sodium into or out of a live frog?
Q1.5 What is the point of the control measurement?
Experiment 2
Data Table:
Time after Application
Ouabain to Skin Outside
Ouabain to Skin Inside
t = 0 min (baseline)
t = .45 min
t = 1.5 min t = 2.5 min t = 5 min t = 7.5 min t = 10 min t = 15 min t = 30 min t = 60 min
Q2.1 What measure is used as evidence of sodium flux in this experiment?
Q2.2 Given that sodium ions are positively charged and that the baseline electrical potential is positive inside the skin relative to outside the skin, in which direction are sodium ions being actively transported? Does this agree with your conclusions from experiment 1?
Q2.3 What is the physiological action and cellular mechanism of ouabain?
Q2.4 Based on this experiment are the sodium pumps nearer to the inner or outer surface of the frog skin?
Experiment 3
Data Table:
Time After Application:
Arginine Vasotocin
to Skin Inside
t = 0 min (baseline)
t = 5 min
t = 10 min t = 15 min t = 20 min t = 25 min t = 30 min
Q3.1 What measure is used as evidence of sodium flux in this experiment?
Q3.2 Based on this experiment, does arginine vasotocin increase or decrease the rate of sodium active transport across the frog skin?
Q3.3 Why is the frog skin pumping sodium in the first place? I.e. what is the physiological benefit or necessity to the frog of pumping sodium across the skin?
Q3.4 Can you think of one organ or location in your body where net transport of sodium across an epithelium might be crucial to its function?