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dr weiss....wearing all black today, and shades too. teehee.

back to the mammary gland - we saw them in lab the other day. 

what we have structurally is a duct which pierces the nipple/teat and 
opens to the outside. the duct expands and branches into delicate 
alveolar system. 

the mammary gland is derived from either sweat or sebaceous gland.

the gland is divided into lobules, so there are intralobular and 
interlobular ducts.

large ducts: interlobular. an epithelium- cells have the plicated lateral 
surface and folding at the base, where mitochondria are located. these 
cells are on a basement membrane and are connected to eachother via 
desmosomes and tight junctions so fluids don't get between the cells. you 
get a belt/branching of tight junctions. beneath the basement membrane 
are blood and lymph vessels.

in addition to these larger cells are smaller cells which serve as stem 
cells to replace these larger cells. also present are myoepithelial cells 
which serve a contractile purpose. they are filled w/actin and myosin and 
can contract.

in the smaller ducts, the myoepithelial cells are apart from one another 
and they encircle the glands but won't fully line the duct as they do in 
th larger ducts.

in the smaller ducts the epi cells are very similar but cuboidal instead 
of columnar, and the myoepithelial cells have additional processes which 
kind of wrap around the epi cells. it's likely that the myoepi cells in 
the smaller ducts can contract and force the milk out of the ducts into 
the larger ducts and into the cisternae (dilated portions near the 
opening), where it waits to be sucked out. suckling results in release of 
milk from mammary gland. this is due to oxytocin, coming from 
hypothalamus to posterior pituitary to stimulate gland to release milk. 
also stimulated by mom seeing baby or hearing cry...

several hormones are important in milk production: 

PROLACTIN: produced by the hypothalamus and causes milk letdown
GROWTH HORMONE: somatotropin. as an individual grows, mammary gland needs 
to grow. 
OXYTOCIN also important.

for gland growth:
estrogen and progesterone also important early in ovarian cycles during 
puberty and they become less important with succeeding cycles. 
estrogen builds large/intermediate ducts
progesterone builds the acinar parts of the duct system.

later they can have diminishing effect on milk production that's  
countered by prolactin.

one thing about mammary gland; it has an array of hormones that is 
extraordinary. ACTH and insulin also important with sugar metabolism. 
during lactation prolactin is constant concomitant of lactation, and 
oxytocin activates the contractile part of duct system.

mamm gland also noteworthy for making distinctive protein: casein, 
lactalbumen, lactoglobulin. also lipids: fatty acids that show a lot of 
pleomorphism. the fatty acids tend to have long and short fats associated 
with them, and lots of double bonds: unsaturated fats. so the fats in 
milk stay liquid under most circumstances, there is no tendency for them 
to congeal. carbohydrates: lactose: dissacharide of galactose and glucose 
which again is distinctive of this organ.

one characteristic of milk is that there is another element associated 
with it at the outset of lactation, milk comes out as serous yellowish 
fluid aka COLOSTRUM - this comes out for the first few days, and is very 
rich in antibody. mother is making Ab from plasma cells, and it's added 
to the milk. this is IgA, secretory antibody. even when conventional milk 
is being made there's a lot of antibody in it which is handled by the 
newborn - what happens is that the baby taking the milk, something 
amazing happens...the baby treats the IgA as SELF, and does not degrade 
it. so the IgA serves to protect the baby. this Ab also coats the GI 
tract of the infant, protecting it from all that crap babies put in their 
mouths....

the last point to emphasize here is the extraordinarily important 
flexibility of this gland re: secretion. when it is stimulated to secrete 
milk, initially cells forming acini secrete milk. as production increases 
and continues, more of the ducts become involved in production until, 
depending on species, but generally only the LARGER ducts stay 
nonproductive. so all these ducts become transformed into milk production 
structures. with SUSTAINED lactation, even major ducts may become 
partially involved in milk production. 

so these are the points of note of the mammary gland. the character of 
the epi, its responsiveness, the columnar and cuboidal cells and the 
myoepithelial cells. the extraordianry # of hormones influencing growth 
development and secretion, and the inclusion of IgA which isn't broken 
down by the infant.

--

now. if we can sort of just pause for a moment and turn to the liver and 
the liver of course is connected to eerything so i'd just like to 
reinforce what i told you earlier about the liver.

i won't tell you about an old anatomical characterization of the liver: 
is life worth living? depends upon the liver. (HA!)

liver is metabolic factory of great proportions. points will be made by 
series of slides. 

don't underestimate the importance of the lobule, seen well in bears and 
pigs. each lobule surrounded by CT and we find these hexagonal structures 
clearly demarcated. the hepatocytes form a wall of sorts at the periphery 
of the lobule. from the hepatocytes there are other hepatocytes arranged 
in a radial way toward the center of the lobule, in kind of cord or 
chainlike structure. 

at the center is the central vein which carries blood out of the liver. 
at the periphery of the lobule is what was called the hepatic trinity.. 
branch of hepatic artery, portal vein, and bile duct are present. also 
lymphatics and nerves. what happens is the outer wall is pierced by the 
vessels and the artery will send its blood into the space between the 
cords of hepatocytes. the portal vein will do likewise. so blood from 
hepatic artery full of nutrients comes into liver, bringing what liver 
needs to keep working, and blood from portal vein, draining intestine and 
stuff, rich in nutrients from there, and also brings drainage from liver, 
including antibody, and this flows into the venous sinusoids between the 
cords of hepatocytes. the venous sinusoids are made of an endothelium : 
in ruminants it is intact w/few holes, most other animals it is quite 
fenestrated. between the endothelium and hepatocytes is CT space called 
the space of DISSE which is not usually noticable but is seen during 
inflammation etc.

also, monocyte cell line KUYPFER cells are within the endothelium, and 
are phagocytic and transient. they come in as monocytes from bone marrow, 
intercolate themselves w/in endothelium, and become phagocytic, then are 
swept away to the lung. these cells are not like most macrophages. what 
happens is in the liver this population of phagocytic cells is almost 
self sufficent. they can proliferate and maintain themselves without 
constant replacement. they pick up fat droplets and things.

so blood enters sinusoid and leaves through central vein, drains to right 
heart. as far as bile ducts go, they start as canaliculi between the 
liver cells, getting larger and larger and feeding into larger 
canaliculus, finally draining out of a duct. this is countercurrent to 
bloodflow.

slides....

liver lobule showing delicate reticular framework under silver stain. the 
lobule has this extensive structural reticular support .

section showing hepatocytes: large, large nuclei, and kuypfer cells 
protruding into lumen of venous sinusoid. they look more fusiform or just 
smaller.

plastic embedded tissue section of central vein receiving sinusoids. 
kuypfer cells are seen. hepatocytes are large, polyploid cells. recall 
that they undergo chromosomal replication w/o cell division because they 
need to maintain their proximity to sinusoids, bile ducts. but they need 
to work hard so they need more genes. older cells may have two nuclei. 
the nuclei become polyploid

hepatocytes have smooth ER (lipids, CHO, detox, steroids), nuclei, 
mitochondria
rough ER makes peptides. the bileducts run like little channels between 
the hepatocytes.

bile ducts reinforced by tonofilaments, and at their periphery as you go 
from bile duct between hepatocytes to ordinary junctional complexes 
between hepatocytes there aretight junctions, desmosomes, etc reinforcing 
the wall of the bile duct. near the duct is a lot of smooth ER because 
bile is being produced.




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