32.Properties of circulation in the coronaries, the skin, the brain, splanchnic circulation, and the fetal circulation.

Question 1

In this topic:

Answer 1

Coronary circulation (heart)
Circulation of the brain
Circulation of the skin
Splanchnic (portal) circulation
Fetal circulation

Question 2

Coronary circulation

Answer 2

The coronary arterial system consists of the right and left coronary arteries. The coronary arteries arises from the aorta artery.

• The right coronary give vessels that supply the right atrium and the right ventricle. Continues as the posterior descending coronary artery which supplies the posterior part of interventricular septum and the posterior left ventricular wall.
• The left coronary artery. The first part is known as the left main. It then divides into left anterior descending and the left circumflex arteries. The left anterior descending artery runs in the anterior interventricular groove and supplies the anterior septum and the anterior left ventricular wall. The left circumflex supplies to the left atrium and the left ventricle ( lateral wall).
• The conduction system is supplied by the coronary artery as well. Therefore, disease of this artery may cause bradycardia . The majority of left ventricle is supplied by the left coronary artery, so that stenosis in the left main is extremely dangerous; total obstruction of this vessel is rarely compatible with life.

Question 3

Cornaria circulation

Answer 3

Systole:
In the phase of fast ejection the pressure is so high that it can ensure the coronary flow inspite of the very large wall tension of the left chamber.

During slow ejection the wall tension is still high, but the aortic pressure drops. This results in slower coronary perfusion

Diastole

• Maximal coronary flow
• More blood enters the coronaries in diastole then in systole!

Question 4

Circulation of the brain -basics

Answer 4

• Closed cerebral cavity: the arterial blood flow entering the cavity and venous blood flow leaving it have to be equal.
• The whole brain has a constant blood flow
• The relative blood flow shows significant differences in brain areas with different metabolism

Question 5

Circulation of the brain

Answer 5

• The intravasal volume to EC volume ratio in the brain is also constant. If the ratio was not constant the brain tissue could suffer from overpressure.
• The brain tissue is the most sensitive one to hypoxia. There are local reflex mechanisms, which keep the blood flow constant despite of altering peripheral circulatory situations. As an example in case of brain tumor, when the intracranial pressure increases, the peripheral blood pressure also increases in order to maintain the constant blood flow in the brain (Cushing-effect, most probably elicited by the hypoxia in the compressed vasomotor center).
• The sympathetic innervation of brain vessels is secondary, while local regulation based on the myogenic tone is dominant.
• The facial nerve provides considerable parasympathetic innervation for brain vessels.

Question 6

Circulation of skin

Answer 6

• Heat balance regulation.
• Flow rate varies a lot.
• vasoconstrictor (narrowing of the blood vessels) tone is of major importance.
• Thermoregulation

Question 7

Splanchnic circulation

Answer 7

• Double capillary system
• Main regulator is the sympathetic tone.
• metabolic autoregulation is less developed
• In liver myogenic autoreg occur.
• The splanchic area(liver) serves as reservoir. (15% of circulation blood volume resides here in resting conditions.)

Question 8

Fetal circulation

Answer 8

In a fetus the lungs are not functioning:
Most of the blood bypasses the lungs by a natural opening, the foramen ovale, between the left and right atrium.

Fetal Heart
-At birth, the pressure in the left atrium becomes slightly larger causing a flap valve closing over the opening. In the first year the opening is closed completely. The remnant structure of the valve is called the Fossa Ovalis.

• In about 30% of the population the foramen ovale is not completely closed
• Ductus Botallo (vessel between aorta and a. pulmonalis) will also be closed ±4 weeks postpartum.
• The fetus receives the oxygenated blood through the umbilical vein.

Circulation:

• Most of the blood reaches the fetal liver, while a small part of it reaches the heart directly through the v. cava caudalis.
• Finally blood goes from the liver to the right ventricle. Left and right atria communicate with each other through the foramen ovale.
• In the fetus the left and right ventricles work as a parallely coupled system.
• Blood goes through the ductus arteriosus into the aorta and is then added to the systemic circulation. This way the pressure in the a. pulmonalis is higher that in the aorta. The left ventricle has only a 20 % larger volume than the right one.
• One third of the blood from the aorta goes to the cranial part of the body, while the rest is delivered to the caudal one. Half of this latter blood volume goes through the placenta.
• After delivery a sudden increase of the pulmonary circulation sets in. The pulmonary resistance decreases because of the appearance of surfactant factors after breathing. More and more blood goes through the lung.
• Pressure decreases in the right atrium as compared to the left one, which leads to the closure of the foramen ovale.
• Pressure decreases in both the arteria pulmonaris and the ductus arteriosus. The pressure drop , which closes the ductus arteriosus. Muscles of the left ventricle develop rapidly and finally the serially coupled pulmonary and systemic circulation evolves.