- Pulmonary circulation: blood pumped from right ventricle flowing through pulmonary arteries to capillaries of lungs; returns to heart via pulmonary
Systemic circulation: blood from left ventricle flows through aorta to major arteries of the body; blood flows through capillary beds of the organs to the veins; blood collected in superior and inferior vena cava and transported to right atrium.
- Arteries: Large, muscular, elastic vessels, carry blood away from heart
Arterioles: smaller vessels connecting arteries to capillaries; generate
the greatest resistance to blood flow; diameter can be changed to
control blood to organs.
Capillaries: microscope; thin walled vessels; transport of nutrients, gasses,
and fluid across walls to the tissues.
Venules: small vessels that collect blood from capillary beds
Veins: large vessels that return blood to heart; very elastic to act as reservoirs
for blood; low pressure; valves to prevent back flow; muscular contractions
drive blood back to heart.
- Capillary blood flow: capillary beds arranged in parallel; blood does not flow from one organ to another; this allows blood flow to one capillary bed to be restricted without restricting the blood flow to other organs.
- Capillary filtration: blood volume is dependent on how much fluid leaks out of the capillaries into the tissues.
- Filtration pressure: pressure in the capillaries favors movement of fluid out of capillaries into tissues; pressure is higher at arterial end of capillary and lower at the venous end.
6. Colloid osmotic pressure; small molecules will leak out of the capillaries with the fluid; proteins are too large to leave the capillary; proteins create an osmotic pressure that draws fluid into capillary.
- Net filtration: filtration pressure is higher at arterial end of capillary than at venous end with its osmotic pressure; therefore, fluid leaks out; at venous end, filtration pressure is less than the osmotic pressure allowing fluid to be drawn back in.
- Lymphatic drainage: 15% of the fluid remains in the tissues; it is drained from the tissues by the lymphatic system that returns it back to the venous system.
- Kidney filtration: kidneys filter blood (about 1% of blood volume lost per day to urine); changes in the amount of urine produced have an effect on blood volume.
- Antidiuretic hormone-osmoreceptors: in hypothalamus: monitor concentration of
solutes in the blood; ↑salt causes posterior pituitary to release ADH causing the kidneys to reabsorb more water, raising blood volume.
- Aldosterone: ↓salt, adrenal cortex secretes aldosterone causing kidney to reabsorb more Na+; this increases absorbtion of more water
- Renin-Angiotensin system: ↓blood flow to kidneys, juxtaglomerular apparatus
releases enzyme renin into blood; renin cleaves a protein (angiotensinogen) into angiotensin I. This is converted into angiotensin II which activates thirst centers in the hypothalamus and stimulates release of aldosterone.
- Atrial natriuretic factor: ↑blood volume causes stretching of right atria; it releases atrial natriuretic factor (ANF) causing kidneys to excrete more Na+; when Na+ is excreted, water is excreted also, lowering blood volume.
- Maintaining blood pressure: resistance to blood flow
- Control of resistance: the smaller the diameter of blood vessels, the larger the resistance to blood flow; resistance most easily controlled in the arterioles due to their small diameter; the smooth muscles of the arterioles can be contracted to increase resistance.
- Blood shunting effect; increased resistance in one set of arterioles will shunt blood from the capillary bed served by that arteriole to other capillary beds; Decreasing the resistance to blood flow in one capillary bed can reduce the total blood pressure on the body.
- Angiotensin II: will cause contraction in vascular smooth muscle causing
Vasoconstriction= ↑ in blood pressure.
- Flight or fight: sympathetic stimulation causes vasoconstriction of arterioles feeding the capillaries of the skin and viscera to shunt blood away from skin and viscera to skeletal muscles
Calm state: sympathetic stimulation sets the tone of the smooth muscle of the arterioles helping maintain blood pressure
19. Parasympathetic division: causes vasodilation in arterioles of digestive tract, external genitalia, and salivary glands; has little effect in regulating blood pressure.
- Intrinsic regulation of blood flow: individual organs can control the amount of blood that reaches their capillary beds.
- Metabolic control mechanisms: ↓blood flow to an organ will experience decreased oxygen concentration, increased CO2 concentration, lower pH and release of adenosine or K+; these factors will cause the smooth muscles of the arterioles to dilate increasing blood flow
- Calculation of blood pressure:
Arterial blood pressure= cardiac output x total peripheral resistance
- Vasoconstriction: this event in arterioles raises blood pressure upstream of the vasoconstriction while lowering the pressure downstream of the constriction.
- Baroreceptors: stretch receptors located in the aortic arch and carotid sinuses.
- Effect of high pressure: arteries stretch and cause baroreceptors to send more action potentials to the vasomotor control center in the medulla oblongata; the center then causes the smooth muscles of the arteries to dilate, reducing resistance and blood pressure and heart rate.
stretch reflex: over stretching of receptors in atria cause:
- Decrease in heart rate
- Inhibition in ADH
- ↑ release of atrial naturetic factor