S1M3 Circulatory System Histology

• 1.) Heart: the muscle to pump into the two systems
• 2.) Two Systems: a Pulmonary Circuit (carrying blood to/from lungs) and a Systemic Circuit (delivering blood to and from all the organs!)

The pulmonary circuit to the lungs and back to the left side of the heart.

Left side of heart pumps into the systemic circuit to all the body tissues and then deoxy blood comes back to the right side of the heart.

• Loses: CO₂
• Gains: O₂

• 1.) tunica intima (it's intimate with the blood)
• 2.) tunica media
• 3.) tunica adventitia

• Single layer of endothelial cells
• In contact with the blood
• Made of LCT & scattered Smooth Muscle.

Concentric layers of smooth muscle cells

***smooth muscle has interspered elastic fibers, type III collagen and proteoglycans

Regulation of blood pressure because of the smooth muscle cells that are present in the tunica media.

it is the outer-most layer of the BV and is made of just CT.

**composed of fibroblasts, type I collagen, and longitudinal elastic fibers

Can tell where it begins (against the tunica media) but not where it ends because it becomes continuous with the surrounding vessels and CT.

a system of vessels called the vasa vasorum that supply blood to the vascular walls themselves because the tunica adventitia is too thick!

Elastic arteries or conducting arteries (ie., aorta) which are the biggest arteries closest to the aorta and its branches)

They're so close to the heart and they have to handle the HIGH BP coming from the heart.

• 1.) Elastic Arteries (largest)
• 2.)Muscular Arteries (next largest)
• 3.)Arterioles (and metarterioles) smallest arteries

Smallest arteries that regulate blood flow into capillary beds.

When the heart contracts duh.

when the heart relaxes

Windkessel effect

when you aorta can't take the pressure from expansion and as a results rips through the inner t. intima layer and can even rip the t. media. You get a seperation of the layers, and blood flowing through the other layers.

• Rips all the way? Du bist schnell tot.
• Rips partially? Blood ends up in the t. media which needs to be fixed.

• They have less elastic fibers in the middle of the t.media
• Also have Inner/external elastic lamina that seperates external media from adventitia

TRUE: the largest muscular arteries have both layers--

As the artery gets smaller you lose the external elastic lamina first and the internal elastic lamina last.

• The INTERNAL ELASTIC LAMINA!
• Seperates the tunica intima from the tunica media.

muscle.

If it has muscle around the vessel it is called a metarteriole not a capillary.

2-3 layers of SMOOTH MUSCLE cells.

up to 40 LAYERS of SMOOTH MUSCLE

tunica media

• *instead veins can have more smooth muscle in the adventitia, to help blood move along

Smooth Muscle!

Smooth muscle bundles are present in the tunica adventitia which contract and cause parastaltic motion that moves the blood along

• large VEINS!
• because veins carry deoxy blood, to compensate, the larger veins typically contain more vasa vasorum to provide metabolites to the thick t. adventitia

LOOK at the size of the WALL

• Veins have thinner walls than arteries
• Lumen of vein is much larger relative to the size of the tunics

• Valves!
• Used to regulate blood flow, prevent backflow of blood

• tunica intima jutting out into the lumen
• Reinforced with collagen and elastic fibers
• Purpose: PREVENT BACKFLOW :(

• If the one-way valves in your veins fail to close, blood will pool in the vein
• Over time, the pooling will force the vein walls outward resulting in enlargement and ugly bulging of the vein, making to look rope-like.

MORE COMMON IN WOMEN--less developed skeletal muscle, being overweight can also contribute to this as well.

• Junction between arteries and veins
• Major place for exchange of gases and nutrients btw. bloodstream and extravesicular tissue
• ***THIS is WHY we need a circulatory system.
• The heart is just a pump, A/Vs are just transporters, the capillaries are where the action is

• Called Thoroughfare channels

• Continuous (least leaky)
• Fenestrated
• Discontinuous (most leaky)

SINGLE layer.

• Associated closely with capillaries and post-capillary venules, they have contractile function (contain actin & myosin, tropomyosin
• WHY? because remember capillaries lack a tunica media and muscle and pericytes take the place of the muscle in the tunica media.
• Allows blood to continuously flow though capillaries

Continuous (or somatic) capillaries

Capillaries provide the oxygen & nutrients to the muscles in order to contract!

• Tissues where rapid interchange of substances occus between the tissues and the blood
• Kidney
• Intestine (for nutrients)
• Endocrine glands (for secretions)

• Have PORES or "windows" bridged by an ultrathin diaphragm! (allows movement of substances across capillaries)

A fenestrated capillary of the glomerulus of the kidney.

Each arrow is a Fenestration with a diaphragm, picture is then of a fenestrated capillary.

• Sinusoidal (discontinuous) capillaries
• Have HUGE gaps btw endothelial cells
• Incomplete basal lamina

• Liver
• Hematopoietic organs (megakaryocytes send their projections through these holes)
• Bone Marrow
• Spleen
• ***Whole CELLS will pass through these large holes

Shuttle material across the endothelial wall!!

The side of a vessel facing the lumen

• The side of a vessel directed away from the lumen
• b for beyond!!!!

A special type of capillary which lets essential metabolites (O2, glucose) pass from blood to brain and CNS but blocks molecules bigger than 500 daltons.

Tight tight tight tight tight junctions.

the PINEAL GLAND which secretes hormone melatonin directly into the systemic circulation.

• 1.) Normal: Arteriole --> metarteriole-->capillary-->venule and vein
• 2.) Arteriovenous anastomosis (direct communic. btw arterioles and venules, no capillaries --> ie, penis clitoris
• 3.)Arterial portal system: arteriole-->capillary-->arteriole (ie., kidney glomerulus)
• 4.)Venous portal system: present in liver (venule-->capillary-->venule

arteriole-->capillary-->arteriole

Penis & Clitoris (normally closed off with a sphincter!

Venule-->capillary-->venule

ie: liver

• Endocardium: continuous with tunica intima of blood vessels entering heart
• Myocardium (middle and thickest layer)
• Epicardium: the outer most layer of the heart, called the visceral layer of the pericardium

• Cardiac muscle tissue, dark red is myocardium
• Endocardium is above it and is stained purple
• Pale fibers are the PURKINJE FIBERS in the endocardium

• These are purkinje cells
• The light area around the nuclei of the conducting cells is caused by local accumulation of glycogen

Arteriosclerosis

Atherosclerosis

the tunica intima

• lipid deposits in the tunica intima of arteries, porducing a yellow swelling on the endothelial surface.
• Characteristic of artherosclerosis!

• any damage to the cells lining the arteries
• a result of high BP
• Smoking
• Toxic Substances

• 1.) Monocyte migrate through endothelial wall and into the intima, where they differentiate into macrophages
• 2.)Macrophages take up excess LDL (lipid) forming FOAM cells. These foam cells release GF (growth factors, cytokines that act on smooth muscle, so smooth muscle cells migrate secrete collagen and fibrous tissue to heal damage and form a fibrous cap.

When macrophages that have migrated to a atherosclerotic plaque forming area, and take up lots of LDL (lipid) and take on a different "Foamy" appearance

It is a bunch of lipid (fat) that has forms UNDER the endothelial cells, that will become calcified, brittle and could crack and expose collagen, jumpstarting the clotting cascade that can cause a heart attack.