Lecture 18: Blood Vessels and Circuits Flashcards
What is the structure of blood vessel walls?
Walls of arteries and veins:
Inner layer = tunica intima
Middle layer = tunica media
Outer layer = tunica externa
Arteries: Receive blood from the heart are elastic; they branch into muscular.
Walls of capillaries: Endothelium (simple squamous epithelia)
Lumen: Central blood containing space.
What is the difference between arteries and veins?
- Tunica media is thicker in arteries compared to veins.
- Veins are thinner walled but larger lumens.
- Veins also have valves not seen in arteries.
What is tunica media made up of? How does it maintain normal blood pressure?
The smooth muscle can alter the diameter of blood vessels by contracting (vasoconstriction) or relaxing (vasodilation). Elastic fibers allow blood arteries to stretch and recoil.
What controls the vessel’s diameter?
Modified by the sympathetic NS through the release of norepinephrine at synapses. Causes vasoconstriction in the body which increases BP.
What are the classification of arteries?
- Elastic arteries (pressure reservoirs)
- Muscular arteries (distributing vessels)
- Arterioles (resistance vessels)
What is the function of elastic arteries?
Expand due to increased volume of blood during ventricular contraction. The walls can passively recoil during ventricular relaxation.
What is the function of muscular arteries?
Receives blood from elastic arteries and delivers blood to specific body organs. Thickest tunica media and contains the most smooth muscle.
What is the function of arterioles?
Act as resistance vessels because they regulate blood flow into the capillary beds through vasoconstriction and dilation.
What is the function of capillaries?
Blood cells must pass through one at a time. Site of exchange with interstitial fluid of body tissues. Facilitates transport of gases, nutrients, hormones and wastes.
What are the three types of capillaries?
- Continuous
- Fenestrated
- Sinusoid
What are continuous capillaries?
Least permeable. Endothelial cells continuous except for small intercellular clefts. Abundant in skin, muscles and lungs and only allows small molecules like water, ions and respiratory gases.
What are fenestrated capillaries?
Contains large pores that allow rapid passage to water, solutes and small peptides. (Ex. kidneys, small intestines and thyroid gland).
What are sinusoid capillaries?
Most permeable. Has an incomplete basement membrane and allows free passage of water, solutes and plasma proteins. (Ex. liver, bone marrow and spleen).
What are vascular shunts?
Directly connect the arteriole to the venule. Bypasses exchange with tissue cells.
What are precapillary sphincter’s?
Controls blood flow by opening or closing. Ex. when concentration of dissolved oxygen drops in interstitial fluid, the sphincters will open allowing for exchange.
What is a property of post capillary venules?
Porous. Endothelium allows movement of fluid and white blood cells.
What are veins also known as?
They are known as blood reservoirs. 60% of blood volume is contained within veins and venules.
What are the two venous valves which prevent backflow of blood in veins?
- Muscular Pumps
- Respiratory Pumps
What are muscular pumps?
When skeletal muscles contract, they squeeze veins which propels the blood back toward the heart.
What are respiratory pumps?
During inhalation, the diaphragm moves downward, causing decrease in pressure in thoracic cavity and increase in abdominal cavity. This causes, greater volume of blood to move from compressed abdominal veins to decompressed thoracic veins and into the right atrium.
What are varicose veins?
Veins that have become dilated due to faulty valves. (Can be caused by prolonged standing, obesity or pregnancy).
How is the myocardium nourished with coronary vessels?
- Coronary arteries: Branch from aorta to supply oxygen rich blood to coronary capillaries.
- Coronary capillaries: Exchange occurs between heart tissue and blood.
- Cardiac veins: Drain oxygen poor blood from capillaries to coronary sinus.
- Coronary sinus: A large vein on the posterior of the heart.
What is atherosclerosis?
Plaques composed mostly of lipids between tunica media and externa. May cause myocardial infraction. (Heart attack)
