Chapter 19 - Blood Vessels Flashcards
Closed System
The blood never directly bathes the tissues, a small amount of fluid is forced across the walls of the capillaries and that is what bathes the tissues.
Dual Circulatory System
Two different circuits. The pulmonary circuit and the systemic circuit.
Pattern of Flow
Arteries carry blood away from the heart, they then divide into smaller arteries and then arterioles. The arterioles supply the capillaries and the capillaries are then drained by venules which join to form veins, which return the blood to the heart.
Structure of a blood vessel
Three layers, or tunics. The tunica intima, tunica media, and tunica adventitia
Tunica Intima
The innermost layer of the blood vessels. A simple layer of squamous epithelium, or endothelium. It is continuous throughout the heart and all the way to the capillary walls.
Tunica Media
Layer of smooth muscle and elastic fibers.
Tunica Adventitia (Externa)
A thin outer layer of connective tissue. It contains collagen and elastic fibers.
Elastic Arteries
Largest arteries in the body. Have a thick tunica media rich in elastic fibers, actually have more elastic tissue than muscle. The main arteries leaving the heart: the aorta, pulmonary trunk, pulmonary arteries, etc.
Muscular Arteries
Medium sized arteries. They distribute blood to the organs. They have more smooth muscle than elastic tissue. They constitute most of the named arteries.
Arterioles
Smallest arteries, their main function is to regulate the blood flow into the capillaries
Capillaries
Consist of nothing more than an endothelium, because of that they are able to move material across their walls.
Continuous Capillaries
Found in most parts of the body. The epithelial cells are held together by tight junctions
Fenestrated Capillaries
They have pores, which means they can have extensive filtration. Found in sites of heavy filtration, like the kidneys.
Sinusoidal Capillaries
Have wide flat channels through which blood flows very slowly. A special type of fenestrated capillary, found in the liver because of the extensive exchange.
Vasomotion
Blood flow through the capillaries is not a continuous flow, but a series of impulses. It can be controlled by a change in the concentrations of chemicals and gasses dissolved in the interstitial fluid.
Venules
Consist of endothelium surrounded by a small amount of connective tissue. As they get larger, they begin to have a tunica media.
Veins
They have all 3 layers, but the tunica media is very thin, only a few muscle cells, and the tunica adventitia is the thickest layer. THey are thin walled and more distensible than arteries. The tunica intima will form valves which prevent the backflow of blood.
Blood Flow
Represents the volume of blood passing though an area per unit of time.
Blood Velocity
The larger the cross-sectional area, the slower the flow.
Factors Which Affect Flow
Pressure- the energy imparted by the pumping of the heart
Resistance - The friction that blood has to overcome while traveling through the vessels
Types of Resistance
Blood viscosity - The blood’s internal resistance to flow
Vessel resistance - Vessel length, diameter, and turbulence.
Relationship between flow, pressure, and resistance
Flow is equal to pressure divided by resistance. In order for blood to flow, the pressure at the end of the vessel must be loss that at the beginning of the vessel.
Mean Arterial Pressure
The average between the two different blood pressure, systolic and diastolic.
Blood Pressure
Essential for blood flow. Refers to the arterial blood pressure. Two different values, systolic and diastolic, and expressed in mmHg. Ex: 120/80mmHg
Pulse Pressure
The difference between systolic and diastolic pressure. Responsible for what we perceive as our pulse. A large difference means a strong pulse, a small difference creates a weak pulse.
Factors That Affect Blood Pressure:
Blood Volume
The higher the volume, the greater the pressure
Factors That Affect Blood Pressure:
Viscosity of Blood
The more viscous, the greater the pressure. Due mostly to the formed elements. The higher hematocrit, the higher viscosity.
Factors That Affect Blood Pressure:
Elasticity
The elasticity of vessels buffers the blood pressure from having extreme systolic and diastolic numbers
Factors That Affect Blood Pressure:
Gravity
Blood moving upwards has to work against the pull of gravity
Factors That Affect Blood Pressure:
Cardiac Output
The more blood put into the arterial tree per minute, the greater the pressure
Factors That Affect Blood Pressure:
Peripheral Resistance
The total resistance offered by the vascular network.
Central Regulation of Blood Pressure
Nervous control. Precise homeostatic controls exist to maintain proper pressure and flow. Mainly regulate cardiac output and peripheral resistance.
Vasomotor Center
Regulates the sympathetic activity of the ANS. Maintains adequate flow to the tissues. Innervates the smooth muscle layer of the vessels.
Pressoreceptors
Detect any change in arterial pressure
Chemoreceptors
If H+ levels are too high or O2 levels are too low, an impulse is sent to get the body to increase blood pressure. This speeds up the blood going to the heart and lungs to increase O2.
Hypothalamus
Mediates the distribution of blood
Hormonal Regulation by the Kidney
The kidney is very sensitive to reductions in blood flow. When flow drops below normal, the kidney releases Renin. Renin acts on Angiotensinogen to convert it to Angiotensin I and then Angiotensin II.
Angiotensin
Increases blood flow by:
- Causing vasoconstriction of the arterioles to increase peripheral resistance
- Activating Aldosterone, which increases fluid volume by making the kidney retain salt and therefore water.
Atrial Natriuretic Factor (ANF)
Hormone released by the atrial myocardial cells, it reduces aldosterone secretion and therefore increases the loss of salt and water. Resulting in a drop in blood pressure.
Adrenal Medulla Hormones
Epinephrine and Norepinephrine increase cardiac output and vasoconstriction resulting in an increase in blood pressure.
Antidiuretic Hormone (ADH)
Released by the hypothalamus. It regulates the fluid balance in the body. It promotes intense vasoconstriction and fluid retention when blood pressure drops.
Autoregulation of Blood Pressure
Necessary to increase blood flow to selected tissues without changing the central blood pressure. Determined by the concentration of metabolic end products in the cells.
Venous Blood Pressure
Much less uniform than arterial pressure, and much lower.
Venous Blood Return
Brought about by two mechanisms:
- Contraction of skeletal muscles
- Siphon action
Effects of Standing for Long Periods
Varicose veins - distended surface veinds due to blood pooling due to gravity.
Hemorrhoids - distended veins in the rectum.
Fainting - Loss of blood pressure to the brain due to pooling in the lower extremities.
Distribution of Blood
- Venous side - 64%
- Systemic arteries - 17%
- Heart - 7%
- Systemic capillaries - 5%
- Pulmonary Veins - 9%
Blood Reservoir
Because of their large capacity and small amount of contraction, the veins serve as a blood reservoir.
Net Filtration Pressure
The capillaries are the site of exchange. Fluid is forced out of the capillaries by hydrostatic pressure and then into the capillaries by osmotic pressure. The difference between the two pressure is the net filtration pressure
Hypertension
A blood pressure of 140/90 or higher. Leads to heart attacks, and strokes.
Primary Hypertension
Dietary or exercise related
Secondary Hypertension
Kidney tumors may lead to hyper aldosterone production. Tumors on the adrenal glands lead to higher epinephrine and norepinephrine production.
Atherosclerosis
Narrowing of the arteries due to a build up of plaque. The major cause of strokes.
Cholesterol
An essential lipid, part of membranes and a precursor for vitamin D. It’s insoluble in a water plasma so it must be combined with a lipoprotein to become soluble.
LDL (Low Density Lipoprotein)
Most common, it functions to transport cholesterol to the cells. It must interact with a receptor on the cell. If there are too few receptors or if there are the correct amount of receptors, but a high fat diet, the receptors will be overcome, and LDL will build up in the blo.
VLDL (Very Low Density Lipoprotein)
Transport triglycerides and a small amount of cholesterol
HDL (High Density Lipoprotein)
The good kind! THey remove cholesterol from circulation and take it to the liver to be eliminated.
Shock
Reduced cardiac output, or not getting enough blood to the tissues. Can be caused by heart failure, hemorrhage, reduced venous return due to massive vasodilation, etc.
Edema
Accumulation of excess tissue fluid. Results in swelling and may impair transfer of materials.
Hypotension
Extremely low blood pressure. In patients being treated for hypertension, who go overly aggressive. Anything below 100 mmHg systolic.
