Principles of Organization of Organs- Histology Flashcards
What are ‘hollow’ organs?
These are the body tubes that connect with the outside of the body (the digestive, respiratory, and urogenital tracts)
Hollow organs are all lined by what?
a mucosa or mucus membrane
What do mucous membranes consist of?
consists of the surface epithelium, the underlying connective tissue (called the lamina propria).
NOTE: In the GI tract, there is also a layer of smooth muscle, which is called the muscularis mucosa.
T or F. Muscularis externa lies external to the mucosa in the GI tract
T
What does muscularis externa consist of?
1-3 layers of smooth muscle. (typically 2 in GI tract)
External to muscularis externa in hollow organs is what?
loose connective tissue.
For organs not situated within a body cavity, the outer layer outside the connective tissue is called the adventitia and attaches the organ to adjacent structures.
For organs situated within a body cavity, this connective tissue is covered by mesothelium (i.e. simple squamous epithelium); together they are called the serosa.
Some organs have an additional layer of connective tissue between lamina propria & muscularis externa, which is termed the submucosa.
a collection of tissues joined in a structural unit to perform a common function is called what?
an organ
What are three main architectural types of organs?
hollow (tubular)
glands
solid
Name 5 examples of tubular organs
- Digestive tract – esophagus, stomach, small intestine, large intestine
- Respiratory tract – trachea, bronchi, bronchioles
- Urinary tract – ureters, urinary bladder, urethra
- Female reproductive tract – oviduct, uterus, cervix, vagina
- Male reproductive tract – ductus deferens, urethra
What are the four layers of most hollow organs? Note that some others have additional layers
epithelium
lamina propria
muscularis externa
adventitia or serosa
Note that some others have additional layers
What is mucosa?
the lining of the body tubes that connect with the outside of the body (i.e. digestive, respiratory, and urogenital tracts).
What two layers make up the mucosa?
epithelium and lamina propia (term used for the underlying connective tissue)
Some organs have an additional submucosa layer. Where is this layer?
between lamina propia and muscular external
it is connective tissue
T or F. All hollow organs have muscularis externa
T
T or F. All hollow organs have muscularis mucosa
F. Only present in the GI tract
For organs situated within a body cavity, this outer layer is comprised of loose connective tissue covered by mesothelium (i.e. simple squamous epithelium). What is this layer called?
serosa
Adventitia – for organs not situated within a body cavity, the outer layer is made up of connective tissue that attaches the organ to adjacent structures.
In the GI, the muscular externa typically exists as how many layers? What are those layers?
2 layers
inner circular and outer longitudinal
NOTE: can exist as 1,2, or 3 layers
contraction of circularly-arranged muscle in the GI results in what?
narrowing of the lumen
contraction of longitudinally-arranged muscle in the GI results in what?
shortening of the tube
In the GI tract, contraction of smooth muscle is controlled by what?
Post-synaptic sympathetic fibers & parasympathetic ganglion neurons present and modulate the contraction of smooth muscle
What kind of neurons modulate smooth muscle contraction in the GI tract?
enteric neurons
Where are enteric neurons typically found in the GI tract?
typically grouped in small clusters, mostly in submucosa and between smooth muscle layers of muscularis externa.
the submocusa contains of what kind of tissue?
dense irregular CT
Sometimes contains glands – e.g. esophagus, duodenum, trachea
What are the layers of mucosa?
epithelium
lamina propria
(also muscularis mucosa in GI tract)
T or F. Mucosa varies extensively in different organs
T.
Differences in:
architecture – presence of folds, projections, and/or invaginations
cellular composition – types of cells present & variations in their relative abundance
What kind of epithelium is present in the esophagus?
stratified squamous non-keratinized
What kind of epithelium is present in the trachea?
pseudostratified ciliated columnar
What kind of epithelium is present in the urinary bladder?
transitional
What kind of epithelium is present in the stomach, small intestine, and large intestine?
all are simple columnar, but differences in the cell types present and their relative abundance
What is Celiac disease?
immune reaction to gluten; inflammation & shortening of microvilli & villi, with their eventual loss
What is Crohn’s disease?
chronic inflammation of uncertain etiology, perhaps autoimmunity
What is epithelial metaplasia?
Adaptive response whereby original type of epithelial cells is replaced by a type more resistant to chronic inflammation, environmental conditions, stress, etc
Epithelial stem cells change their patterns of gene expression.
What is the most common epithelial cell type ‘change’ as part of epithelial metaplasia?
columnar to stratified squamous
- in trachea & bronchi, in response to prolonged exposure to cigarette smoke
- in cervix, associated with chronic infections
If not reversed (e.g. by removing pathogenic stimulus), cells can become cancerous
What other type of transition of cell type can occur as part of epithelial metaplasia?
‘Squamous-to-columnar’ transformation can also occur
What is Barrett’s esophagus?
lower part of esophagus transforms into intestinal-like epithelium after repeated exposure to stomach acid.
How do glands form?
Form by invagination of an epithelium
Notes on the route of endocrine glands from epithelium to bloodstream
Secretory product -> diffuses into nearby connective tissue -> enters the bloodstream
What are the mechanisms of secretion of exocrine glands?
merocrine
apocrine
holocrine
Describe merocrine secretion
exocytosis from membrane-bounded vesicles
most exocrine glands are merocrine
e.g. salivary glands and pancreas
the term ‘eccrine’ refers specifically to merocrine sweat glands
Describe apocrine secretion
apical part of cell pinches off, releasing lipid droplet e.g. milk from mammary gland
Describe apocrine secretion
secretory product is released as cell dies & disintegrates e.g. sebaceous glands of hair follicle
What are the two types of organization of exocrine glands?
tubular or acinar/alveolar
simple or compound
What are some examples of solid organs?
liver
kidneys
ovaries
endocrine glands – e.g. adrenal, pituitary
exocrine glands – e.g. salivary glands
pancreas – has both endocrine and exocrine glandular components lymphoid organs – e.g. lymph node, spleen
What are the types of organization of solid organs?
lobes and lobules
cortex and medulla
What kinds of organs have a cortex/medulla organization?
kidney, lymph nodes, adrenal gland, ovary
What kinds of organs have lobes and lobules?
liver, pancreas, many glands
What is the parenchyma?
functional part of an organ
What makes up the parenchyma in the Liver, kidney, pancreas, and various glands?
epithelial cells
What makes up the parenchyma in lymphoid organs?
lymphocytes
