• Types of Circulation

A. Systemic – carries blood throughout the body

B. Pulmonary – carries blood to and from the lungs

C. Coronary – carries blood to and from the heart itself

D. Special Types

1. Hepatic Portal – unique blood route through the liver

a. A vein – the hepatic portal vein – exists between two capillary beds.

b. Veins from the spleen, stomach, pancreas, gallbladder, and intestines do not pour their blood directly into the vena cava as other abdominal organs do.

c. Blood from these organs enters the hepatic portal vein and passes through the liver before entering the inferior vena cava.

d. Assists with homeostasis of blood glucose by removing excess glucose and storing it as glycogen.

2. Fetal – circulation that exists before birth.

a. Modifications required for fetus to efficiently secure oxygen and nutrients from maternal blood.

b. Unique structures include:

1. placenta – actual place of exchange for oxygen, nutrients, and waste

2. umbilical arteries (2) and vein (1) – located inside the umbilical cord.

- vein carries oxygenated blood

- arteries carry deoxygenated blood

3. ductus venosus – continuation of the umbilical vein

- allows blood to bypass liver

4. ductus arteriosus – connects aorta and pulmonary artery

5. foramen ovale – shunts the blood from the right atrium directly into the left atrium

c. Upon infants first breaths the circulatory system is subjected to increased pressure. The result is the closure of the foramen ovale, collapse of the umbilical vessels, ductus venosus, and ductus arteriosus (which becomes the ligamentum arteriosum – between left pulmonary artery and aorta).

3. Circle of Willis – arterial anastomosis (connection between tubular structures) of the two posterior and single anterior communicating arteries of the brain.

a. encircles the pituitary gland and optic chiasma and unites the brain’s anterior and posterior blood supplies.

b. acts to equalize blood pressure in the two brain areas.

c. provides alternate routes for blood if carotid or vertebral artery becomes occluded.

• Blood Pressure – push or force of blood in the vessels

A. highest in arteries, lowest in veins

B. blood pressure gradient causes blood to circulate

- aorta = 100 mm Hg to 0 mm Hg at the termination of the vena cava

C. blood volume, heartbeat, and viscosity are the main factors that produce blood pressure changes.

E. pressure varies within normal ranges

- average arteriole BP is 120/80 (120 mm Hg systolic pressure as the ventricles contract over 80 mm Hg diastole pressure as ventricles relax)

F. mechanisms that keep venous blood moving through the system and back to the right atrium.

1. strongly beating heart

2. adequate arteriole blood pressure

3. valves in veins

4. “milking action” of skeletal muscles

5. changing pressures in the chest cavity caused by breathing

• Pulse – alternate expansion & recoil of vessel wall

• Circulatory Shock – failure of the circulatory system to deliver oxygen to the tissues adequately, results in cell impairment.

A. cardiogenic shock – caused by heart failure

B. hypovolemic shock – caused by a drop in blood volume that causes blood pressure and blood flow to drop

C. neurogenic shock – caused by nerve condition (spinal cord/medulla injury, depressive drugs, emotional stress) that dilates blood vessels & reduces blood flow

D. anaphylactic shock – caused by a type of severe allergic reaction characterized by vessel dilation

E. septic shock – results from complications of septicemia (toxins in blood resulting from infection)

- toxic shock syndrome –stapholococcal infection that begins in vagina of menstruating women and spreads to blood