Cardiovascular overview dentistry hb2 dr magdi

Cardiovascular system

overview

Presented 2011 / 2012 by: Dr Magdi El Sersi

Assistant Prof of Medical Physiology

Basic Medical Sciences Department

Ext. 7243 E mail:

[email protected]

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MAIN FUNCTIONS OF THE

CIRCULATORY SYSTEM

• Transport and distribute essential substances

to the tissues.

• Remove metabolic byproducts.

• Adjustment of oxygen and nutrient supply

in different physiologic states.

• Regulation of body temperature.

The system has two major

divisions:

v A pulmonary circuit :

which carried blood to the

lungs for gas exchange and

returns it to the heart.

v A systemic circuit :

which supplies blood to

every organ of the body.

The right

side of the

heart serves

the

pulmonary

circuit

The left side

serves the

systemic

circuit.

has a tough, superficial fibrous layer of dense

irregular connective tissue and a deep, thin

serous layer.

The heart is enclosed in a

double-walled sac called the

pericardium.

The outer wall,

called the parietal

pericardium

(pericardial sac).

The serous layer turns inward at the base of the

heart and forms the visceral pericardium (epicardium)

covering the heart surface .

The pericardial sac is anchored by ligaments to the

diaphragm below and the sternum anterior to it.

Between the parietal and visceral membranes

is a space called the pericardial cavity . It

contains 5 to 30 mL of pericardial fluid.

The pericardium

The pericardial fluid

lubricates the membranes

and allows the heart to

beat almost without

friction.

Pathophysiology : Pericardial

disease manifest itself by the

accumulation of fluid in the

pericardial space (pericardial

effusion) and /or inflammation

of the pericardium (pericarditis).

The pericardial cavity can fill with up to

2 litters of serous fluid

(hydropericardium ) or blood

(hemopericardium) that prevent

normal diastolic filling and thereby

reduces cardiac output.

PUMP

DISTRIBUTING

TUBULES THIN

VESSELS

COLLECTING

TUBULES

THE MAIN CIRCUIT

There are 3 primary blood vessel

types:

1. Arteries : which carry blood

away from the heart.

2. Veins : which carry blood

towards the heart.

3. Capillaries : tiny blood

vessels that function in the

exchange of gases, nutrients,

and wastes between the blood

and the interstitial fluid.

The walls of both arteries and veins have 3

layers that surround the lumen:

1. Tunica externa

Outermost layer. Made primarily of loose

connective tissue. Anchors the blood

vessel to the surrounding tissue.

2. Tunica Media

Consists primarily of smooth muscle and

is responsible for vasoconstriction and

vasodilatation. Usually the thickest layer

in arteries.

3. Tunica Interna (Endothelium) Acts as a

selectively permeable barrier to blood

solutes.

Secretes vasoconstrictors and

vasodilators.

Provides a smooth surface that repels

blood cells and platelets.

They are constructed to withstand

surges of blood pressure associated with

ventricular systole.

•They're more muscular than veins and appear

relatively round in tissue sections.

• They retain their round shape even when empty.

There are 3 basic categories of arteries

Conducting (or Elastic) Arteries

Distributing (or Muscular) Arteries

Arterioles

1. Conducting (or Elastic) Arteries

The largest

Examples include the aorta, pulmonary arteries,

and the common carotid arteries.

Their tunica media contains a

great deal of elastic tissue.

The elastic tissue allows for

expansion during ventricular

systole and recoil during

ventricular diastole.

This helps create continuous

flow from a discontinuous

pump.

Conducting arteries expand during ventricular systole to

receive blood, and recoil during diastole:

*Their expansion takes some of the pressure off the blood so that

smaller arteries downstream are subjected to less systolic stress .

•* Their recoil between heart beats prevents t he blood

pressure from dropping too low while the heart is relaxing

and refilling.

Lessen the fluctuations in blood pressure

2. Distributing (or Muscular) Arteries

Smaller branches ,distribute blood to individual organs.

They have 25-40 layers of smooth muscle cells

constituting about three quarters of the wall thickness.

Examples include the brachial, femoral, and splenic arteries

3. Arterioles

•Smallest of the three.

• They are heavily innervated .

• The primary points at which the body controls the

relative amounts of blood directed to specific organs.

Linking the arterioles

to the capillaries are

short vessels known

as metarterioles.

Part of their wall surrounded

by smooth muscle

These muscle cells form precapillary sphincters which

encircle the entrance to a capillary bed.

These sphincters regulate how much blood will flow

through particular capillary beds.

Certain major arteries above

the heart have sensory

structures in their walls that

monitor blood pressure and

chemistry.

They transmit information to

the brain stem that is used to

regulate the heart beat,

vasomotion and respiration.

:Arterial sense organs

The sensory receptors are of three kinds

1. Carotid sinuses. These are

baroreceptors (pressure sensors) that

respond to changes in blood pressure.

* Thin tunica media

* An abundance of glossopharyngeal

nerve fibers in the tunica externa.

A rise in blood pressure stretches the

thin media and stimulates the nerve

fibers which transmits signals to the

vasomotor and cardiac centers of the

brainstem, which responds by lowering

the heart rate and dilating the blood

vessels, thereby lowering the blood

pressure.

The carotid sinuses

are located in the

wall of the internal

carotid artery

2. Carotid bodies: located near the

branch of the common carotid

arteries.

They are chemoreceptors that monitor changes in

blood composition.

They primarily transmit

signals to the brainstem

respiratory centers, which

adjust breathing to stabilize

the blood pH and its CO2 and

O2 levels

3. Aortic bodies: These are one

to three chemoreceptors

located in the aortic

arch

They are structurally similar to

the carotid bodies and have

the same function.

Capillaries There are approximately 1 billion of them in the human body.

Capillaries are organized into groups of 10-100 in capillary beds

There are 3 separate types of capillaries:

1. Continuous Capillaries

2. Fenestrated Capillaries

3. Sinusoidal Capillaries

1. Continuous Capillaries

Endothelial cells are joined by tight junctions.

but contain intercellular clefts through which small molecules

(e.g., glucose, but not albumin) can pass.

Most common.

Abundant in skin and muscle.

Cerebral capillaries lack these clefts and have far more

numerous tight junctions forming the blood brain barrier which

helps protect the delicate brain tissue from blood-borne toxins

and pathogens.

Some continues capillaries

exhibit cells called pericytes

that lie external to the

endothelium

Pericytes are contractile,

have elongated tendrils that

wrap around the capillary

It thought that they contract and regulate blood flow

through the capillaries.

They also can differentiate into endothelial and smooth

muscle cells and thus contribute to vessel growth and

repair.

. Fenestrated capillaries2

Similar to

continuous

capillaries but

some of the

endothelial cells

has filtration pores

fenestrations.

These pores allow for

the rapid passage of

molecules, even

proteins , through the

capillary wall.

Found in sites of active

absorption (small intestine),

secretion (endocrine

organs) and capillary

filtration (kidneys).

3. Sinusoidal Capillaries

Highly modified, extremely

leaky, fenestrated capillaries

Found in sites where large stuff needs to

exit/enter the bloodstream.

Such sites include bone marrow (for

passage of nascent blood cells), lymphoid

organs (for easy entry/exit by WBCs) and

the liver (for large plasma proteins, e.g.,

albumin).

Contain irregularly shaped lumen and large intercellular clefts

In the liver and the spleen , the

endothelium is intimately

associated with macrophages.

In these locations the sinusoids

are twisty and tortuous,

conformed to the shape of the

surrounding tissue. . The

twistiness makes blood flow

extra slowly which gives time

for splenic and hepatic

macrophages to monitor and

assess its contents.

Just by looking at this image, can you identify the

different capillary types?

Veins

The capacitance vessels of the cardiovascular system

because :

They are relatively thin-walled and flaccid.

Expand easily to accommodate an

increased volume of blood.

At rest, about 54% of

the blood is found in

the systemic veins as

compared with only

11% in the systemic

arteries

Being distant from the ventricles of the heart,

they are subjected to relatively low blood

pressure.

In large arteries, blood pressure averages 90 to

100 mm Hg (millimeters of mercury) and

surges to 120 mm Hg during systole, whereas

in veins it averages about 10 mm Hg.

Considering the relatively low pressure in

the veins.

how blood is forced through them to get back to the

heart????

It's a combination of 3 separate things:

1.Skeletal Muscle Pump .

2. Respiratory Pump .

3. Venous Valves

1. Skeletal Muscle

Pump :- the

contraction/relaxation

cycles of skeletal

muscles squeeze the

veins forcing the

contained blood

towards the heart.

It's a combination of 3 separate

things:

1.Skeletal Muscle Pump .

2. Respiratory Pump .

3. Venous Valves

2. Respiratory Pump : as we inhale,

our thoracic cavity expands while

our abdominal cavity compresses.

pressure within veins of the

thoracic cavity drops.

Meanwhile, pressure in the

abdominal veins increases.

This combination results in

increased blood flow towards that

heart.

3. Venous Valves: - one-way

valves (similar to the

semilunars of the heart) made

of flaps of endothelium are

found in medium veins

(mostly in the legs and the

arms) where they help prevent

backflow.

Pathophysiology: varicose

veins:

In people who stand for long

periods, blood tends to pool in the

lower limbs and stretch the veins.

This is especially true of superficial

veins, which are not surrounded by

supportive tissue.

Stretching pulls the cusps of the

venous valves farther apart until the

valves become incompetent to

prevent the backflow of blood

As the veins become further

distended, their walls grow

weak and they develop into

varicose veins with irregular

dilations and twisted pathways.