20110112 04 circulatory notes.txt

From Iusmhistology

(Difference between revisions)

Revision as of 21:34, 3 February 2011

  • started here on 01/12/11


Contents

Circulatory

  • First time we'll see tissues put together into tissues and organs.

Objectives

  • At the conclusion ofthe unit on the circulatory system, each student should be able to:
    • Sketch from memory the histologic structure of all ofthe vessels. Label the tunicae.
    • Distinguish the relative functions of the parts ofthe vascular system, and correlate these with their structures.
    • Describe the physical relationship ofpericytes to endothelial cells.
    • List the four types of capillary and describe their similarities and differences. How do these differences relate to function?
    • Describe the function of precapillary sphincters and arteriovenous anastomoses.
    • List the metabolic functions ofendothelial cells, as described in the text.
    • List the layers ofthe heart and distinguish between atrium and ventricle in the structures ofthese layers.
    • Describe the specialized cells ofthe heart.
    • Compare and contrast lymphatic vessels with blood vessels with regard to structure and function.

Components

  • Heart
    • Pumps to two systmes at once
    • Has variable output and speed
      • Yes, output, asin the volume
  • Artieries
    • Low capacity: hold little of the total blood
    • Carry at high hydrostatic pressure
  • Capillaries
    • Low hydrostatic pressure
    • High cross-sectional area
    • Low flow velocity
    • Good chance for diffusion with fluid around caps
  • Veins
    • Very Low hydrostatic pressure
    • High and variable capacity
      • Can hold 75% or can contract to hold less volume (if dehydrated) or expand (if well hydrated).

Functions

  • Draw a heart, divide with two lines to make four sections.
    • Atria and ventricles
  • Blood goes out left ventrical to systemic capillaries (everything but the lungs)
  • Blood comes back into venules and veins and right atrium.
  • Then to right ventricle and to the pulomonary system (the lungs)
    • We won't talk about pulmonary vessels this lecture.
    • Theya re different because their pressure is different.
  • Back into left atria and ventricle

Histology of vessels

  • The vessels have layers, called tunics.
    • Tunics were garmets, tight-fitting shirts.
  • Layer closest to the blood is tunica intima.
  • Outside most layer is called tunica adventitia or tunica externa.
    • The layer that comes to the outside of the vessel.
  • In between is the tuica intermedia
    • Contains muscle
  • Vessels can have vessels in them: vasa vesorum (vessels of the vessels)
    • This is to supply the outer cells of the bigger vessels.
  • When we see smooth muscle in the vessels, there is probably innervation
    • We usually won't see the nerves, though, because they are so small.

Capillaries

  • Capillaries are about 10 microns, so blood cells just barely fit thorugh.
    • In smaller capillaries, RBCs even have to change their shape and squeeze through.
  • Not all capillaries are the same
    • Different degree of permeability depending on where they are in the body.
    • Thinner, more holes = more permeability
  • Recall that a cell membrane is about 10 nm with proteins in it.
  • Recall that we can see about 1 micron things as points via LM.
  • Capilarries are usually 7-10 microns in diameter.
  • They only have the tunica intima.
  • Sometimes have pericytes with them
    • Can replace other cells
    • Can form new blood vessels
    • Can undergo division
  • Caps are simple squamous epithelium
  • Continuous capilarries:
    • Have a relatively thick (though very thin) extension of cytoplasm
    • Found in muscle, nerve, connective tissue, and exocrine glands
      • Like salivary glands seen on monday.
  • Fenestrated capilarries
    • Have windows = fenetre in french
    • Found in kidney, GI, and endocrine glands (pit, thryroid)
    • More leaky than continuous
  • Fenestrated capilarries without diaphragm
    • Have windows
    • The windows do not have diaphragms that are like a piece of glass in the window
    • Found in the renal glomerulus
    • More leaky than fenestrated with
  • Sinusoidal capilarries
    • Bone marrow, liver, lymphod tissue
    • Where lots of proteins move in and out of blood
    • usually cells can move in and out pretty easily as well.

Structures

  • Continuous
    • Tight jxns with endothelial cells
    • Have lots of penocytoic vesicles
      • Looks like material is brought into cell from outside
    • Not fenestri
    • No diaphram
    • BM is always present in continuous caps
    • Tightest of caps
  • Fenestrated with diaphragm
    • A little leakier
    • Have tight jxns with endothelial cells
    • Have some pinocytotic vesicles
    • Have fenestri, diaphragm, and bm.
  • Fenestrated without diaphragm
    • Tight jxns
    • Pinocytoics
    • Fenestri
    • BM
  • Sinusoidal
    • Some tight jxns, but some of the endothelial cells don't form tight jxns with their neighbor.
    • No pinocytoic vesicles
    • Have fenestri, without diaphragm
    • Discontinuous BM
    • Leakiest.

Image examples

  • Epithelial cells can wrap all the way around a vessel.
  • Fenestrations:
    • They are arranged in little collections.
  • Pinocytotic vessles are much like the fenestra.
    • Also called caveoli
    • Can fuse to cause little diaphrams
  • Diaphragm of fenestra
    • Has spokes
    • Made of PB1 and other proteins
    • PB1 forms fibrilar spokes across the fenestra.

Facts

  • Entrance to the capillary bed is controlled by the pre-capilarry sphincter.
    • controls whether and how much blood flows into the capillary bed.
  • Capillaries function to keep cells and protine in the blood.
    • BBB exists to
    • BBB is made up by continuous capillaries and the cellular barriers on the outside. 
*Read 188-189 on function of endothelial cells
**A quesiton will coem from this for exam.

Arteries and veins

  • The smalles arteries carrying blood away from heart are called arterioles.
    • We'll define these as the smallest arteries with 1-5 layers.
  • The venules are the smallest veins.
  • Larger arteries are median arteries and median veins.
  • Then we talk about larger arteries and large veins.
  • This is all a continuous spectrum, though.
  • We can see arterioles and their layers in lab.
    • CT on the outside
    • Venules accompany them
      • Venules have much larger lumen compared to the thickness of the wall.
      • That is, arteries have thicker walls relative to the luman than do venules. 


Be able to fill out the table from scratch as it indicates you know your vessels.


  • Tunica intima:
    • In healthy tissue, all vessels contain only simple squamous epithelium called endothelium.
    • large elastic artery:
    • medium (muscular) artery:
    • arteriole:
    • capillary:
    • venule:
    • medium vein:
    • large vein: the exception
      • tunica intima of the large veins is a thicker layer as it includes connective tissue and smooth muscle.


  • Tunica media:
    • Manifests itself as smooth muscle in all vessles (except caps and venules where it does not exist)
    • Some layers consist of additional materials
    • large elastic artery: has elastic layers (lamini)
    • medium (muscular) artery: has elastic fibers not layers
    • arteriole: not much eleastic fiber
    • capillary: no tunica media at all
    • venule: no tunica media at all
    • medium vein:
    • large vein:


  • Tunica adventitia:
    • On the outside
    • Found on all larger vessels
    • More on veins (that is, larger walls) than on arteries
    • large elastic artery:
    • medium (muscular) artery:
    • arteriole:
    • capillary:
    • venule:
    • medium vein:
    • large vein: the exception
      • has connective tissue
      • has longitudinal bundles of smooth muscle

Medium vessels

  • Comparison of medium (muscular) artery and medium vein.
    • Muscular artery is on the left
    • Medium vein is on the right.
  • In general, the thickness of the artery wall looks greather than the vein wall.
    • Tends ot be the case in most pairs of analogous artery and vein strcutreus.
  • The relative thickness of the tunica adventitia of the vein is greater than the thickness of the tunic adventitia of the artery.
  • The muscular artery
    • Muscular layer is from tunica media
    • Connective tissue = tunica adventitia
    • Wiggly thing is internal elastic membrane common in medium arteries.
  • More on tunica adventitia of muscular artery.
    • Endothelial cells cover the surface (tunica intima)
    • Internal elastic membrane is at the top part of the smooth muscle of the tunica media.
    • Smooth muscle cells make the internal elastic membrane.
      • So we consider it part of the tunica media (though some books disagree)
  • Medium vein
    • Endothelium on inside
    • A bit of tunica media
    • Tunica adventitia on outside
  • There can also be external elastic membrane, too.

Large vessels

  • Large elastic fibers have many elastic layers in the tunica media.
    • Medium fibers only have internal elastic layer and maybe an external elastic layer.
  • Large veins are the complicated one
    • Longitudinal bundles of smooth muscle in tunica adventitia
    • Longitudinal muslce in tunica intima, too.
  • Large arteries have elastic lamini
  • A healthy tunica intima of large vessels is hard to see because it is one cell thick.
  • Large vein:
    • Specimens don't stain well
    • Find the muscle that runs around the vessel, this will be the tunica media.
    • There is lots of connective tissue near the lumen, with the endothelium.
    • Look for vasa vasorum, too.

Topics

  • Arteriole-venus anastamosis
    • Used them when we played in the snow.
    • Blood flow to skin shuts down.
    • This is achieved by connecting artery and vein so the capillary bed is bypassed.
    • This maintains normal blood flow in arteries and veins.

Heart

  • has three tunics: endocardium, myocardium, epicardium
    • differ in the atrium and ventricle.
  • Endocardium:
    • Atrium: Endothelium and connective tissue
    • Ventricle: Only endothelium
  • Myocardium:
    • Atrium: Cardiac muscle
    • Ventricle: Thick layer of cardiac muscle
  • Epicardium:
    • Atrium: Connective tissue and mesothelium
    • Ventricle: Connective tissue and lots of larger vessels (coronary arteries), and mesothelium.
  • Specialized cells:
    • Nodal cells
      • Set pace of heart
    • Perkinje cells
      • Modified cardiac muscle cells
      • Carry signal from one part of the heart to another.
Observation
  • Endocardium layer of atrium is thicker than the epicardium.
    • Makes sense because the atrium may get stretched an endocardium will sustain the structure.
  • Epicardium:
    • Mesothelium on the outside is often simple squamous epithelium.
  • Perkinje cells:
    • Looke very diff
    • Multiple nuclei and some myofibers
    • But not packed full of contractile apparatus

Lymphatics

  • Lymphatics drain ECF.
    • Blood vessels leak
    • Lymph vessels recover the fluid that has escaped the blood circulation
    • Also impt for lymphatic cells
  • Lymphatic capillaries:
    • blind ended capillaries
    • exist out in tissue
    • Have incomplete fenestri
    • have very few tight junctions
    • have very little bm
    • They are super leaky
  • The cells of the lymph capillaries are anchored to the connective tissue around them by collagen fibrils.
    • So when pressed, they are squished but open up upon freedom from pressure and as connective tissue spreads.
    • This pulls fluid into it.
  • Caps form larger vessels
    • These have thinner walls than veins of similar size.

Observations

  • Lymphatics sometimes have valves that keep lymph flowing in one direction.
  • The walls may not be apparent; they can look like open space with endothelium lining it.

Lab 6: Cardiovascular tissue

  • There are three layers to cardiac tissue:
    • Tunica intima
    • Tunica media
    • Tunica adventitia
  • In some parts of the cardiovascular tissues, one of these three tissues dominates over the others:
    • The tunica media is dominant in all arteries (small to large).
    • The tunica adventitia is dominant in most if not all veins.
  • See Basic Histology 11-7.

SMALL VESSELS

  • Arterioles and venules are the smallest of the arteries and veins, respectively.
  • They are often seen as paired structures in connective tissue.
  • Note that the arterioles will have a thick wall composed mostly of tunica media; venules will have a much thinner wall.
  • Capillaries are very difficult to see in light microscopy because they are a single endothelial cell thick.
  • Note that we use H&E as well as orcein to stain vessels.
    • Orcein generates brown stains.

Slide 10: Mesentery, human

  • This is an orcein and H&E stain.
  • The arterioles and venules are easily seen to be paired.
  • Arteriole observations:
    • A thin tunica intima exists as a deep, purple, smooth band.
    • A thick tunica media clearly distinguishes between arteriole and venule.
    • The tunica adventitia is about half as thick as the tunica media and stains as a jagged band of cells.
  • Venules
    • The tunica intima stains a deep purple as in the arteriole but is not as smooth; each cell seems to jut out into the lumen.
    • The tunica media is thinner than in the artiole with a more speckled pattern--less homogenous.
    • The tunica abventitia of the venule gives a similar jagged stain but is slightly lighter.
      • The two tunica adventitia are often adjacent.

Slide 25: Lymph node, monkey

  • This is an orcein and H&E stain.
  • Similar to slide 10.
  • In this section, the venules tunica intima does not show the same jagged pattern as seen in the mesentery.
  • Another difference is that in this section the arteriole's tunica adventitia has a definite wavy pattern as opposed to a jagged homogeneity.

Slide 15: peripheral nerve

  • This is an H&E stain.
  • Wavy pattern of arteriole tunica adventitia seen again.

MUSCULAR (MEDIUM) ARTERIES AND MEDIUM VEINS

  • Medium arteries are also called muscular arteries because of the prominent smooth muscle found in the tunic media.
    • However, in muscular arteries, the tunica adventitia is often thicker than the tunic media.
  • Muscular arteries also have eleastic fibers running through them.
    • These fold over themselves as contraction occurs.
  • Some medium arteries show a prominent external elastic lamina in the tunica media.
  • Elastic fibers can also be found running in the tunica adventitia.

Slide 16: Aorta and mesenteric artery, human

  • This is an orcein and H&E stain.
  • The elstic fibers of the tunica media are seen as blue-purple, folded, ghostly, fibers.
  • A fairly continuous external elastic lamina can be seen in the transition between tunica media and tunica adventitia.
  • Elastic fibers are visible in the tunica adventitia as pink connective tissue.

Slide 25: Lymph node, monkey

  • This is an H&E stain.
  • Elastic fibers of the tunica media are readily seen.

Slide 10: Mesentery, human

ELASTIC (LARGE) ARTERIES

  • Note that this section is specific to arteries.
  • We have seen elastic fibers as blue-purple in orcein + H&E; they will appear as read or brown with just orcein.
  • In large vessels, vasa vasorum should be visible in the tunica adventitia

Slide 16: Aorta

  • This is an orcein stain so elastic fibers will be red / brown.
  • There is a definite border between the tunica media and the tunica adventitia.
  • Though there is a distinction between the tunica media and the tunic intima, there isn't really a solid border.

Slide 37: Aorta

  • This is an H&E stain so elastic fibers will be blue-purple.
  • Again there is a definite border between tunica media and tunica adventitia but not between the tunica media and tunica intima.


  • stopped here


LARGE VEINS

  • Large veins like the vena cava have longitudinal bundles of muscle cells in the adventitia.
  • Large veins also have thin tunica media.

Slide 38: Vena cava

  • This is an H&E stain.
  • Note that because the vena cava is a large vein, the media is thin and there are smooth muscle cells in the adventitia.
  • The vasa vesorum are readily apparent, also.

THE HEART

Atrium

  • The ventricle is easily identified as the tissue with epicardium (which has a high fat content) at the border.
  • Note that coronary arteries are also visible, supplying oxygenated blood to the cardiac tissue.

Ventricle

Slide 19: Heart, ventricle and auricle
  • Note that the epi, myo, and endo cardium of the atrium and the ventricle are visible.
    • The epicardium of the atrium is especially thick.
Slide 20: Heart ventricle moneky
  • In the ventricle, Perkinje fibers are visible but difficult to find.
    • These fibers conduct the electricity of the heart.


  • stopped here on 01/12/11.
Retrieved from "http://72.14.177.54/iusmhistology/20110112_04_circulatory_notes.txt"
Personal tools