BLG111 Quiz 2: Chapters 19, 20, 21 Flashcards
Compare and contrast arteries, veins, and capillaries
Arteries: carry (mostly oxygenated) blood away from the heart; non-oxygenated blood is carried through the arteries during pulmonary circulation
Capillaries: have direct contact with tissue cells and directly serve cellular needs
Veins: carry (mostly deoxygenated) blood toward the heart; deoxygenated except for the pulmonary circulation and umbilical vessels of fetus
What are the forces acting across the capillary wall
See slide #49
Define Blood Vessels
Blood vessels consist of three layers: a smooth inner layer, a muscular layer, and a connective tissue layer. They deliver blood around the body and work very closely with the lymphatic system. Working together, they redistribute the fluids of the body.
All blood vessels consist of a central blood-containing space called a..?
Lumen
All walls of vessels, except capillaries, have three layers known as…?
Tunics.
1. Tunica intima: simple squamous epithelium that lines lumen of all vessels (great for diffusion)
2. Tunica media: middle layer composed of mostly smooth muscle and sheets of elastin (innervated by the sympathetic nervous system for constriction and dilation)
3. Tunica externa: composed mostly of loose collagen fibers that protect and reinforce wall and anchor it to surrounding structures
Arteries are divided into three groups, based on size and function - what are these three groups?
- Elastic arteries: thick-walled with large, low-resistance lumen (i.e., aorta)
- Muscular arteries: have thickest tunica media with more smooth muscle, but less elastic tissue (i.e., active vasoconstriction)
- Arterioles: smallest of all arteries, also called resistance arteries
Most capillary endothelial cells are joined by tight junctions with gaps called…?
Intercellular clefts that allow for passage of fluids and small solutes
What are the three types of capillaries?
- Continuous: least permeable and most common (i.e., skin, muscles, lungs, CNS, and brain)
- Fenestrated: endothelial cells contain swiss-cheese-like pores called fenestrations that allow for increased permeability; found in areas involved in active filtration (kidneys), absorption (intestines), or endocrine hormone secretion
- Sinusoidal: fewer tight junctions, usually fenestrated with larger intercellular cleft - blood flow is sluggish so allows time for modification of large molecules and blood cells (i.e., liver, bone marrow, spleen, adrenal medulla)
Why are veins called capacitance vessels?
Otherwise known as blood reservoirs, because they contain up to 65% of blood supply
Dilated and painful veins due to incompetent (leaky) valve are known as…?
Varicose veins
What is blood flow?
Volume of blood flowing through a vessel, organ, or entire circulation in a given period and is measured in ml/min; it is equivalent to cardiac output for entire vascular system
Define blood pressure
The force per unite area exerted on the wall of a blood vessel by blood
Define peripheral resistance
Is a measurement of the amount of friction blood encounters with vessel walls, generally in peripheral (systemic) circulation. There are three important sources of resistance: blood viscosity, total blood vessel length, and blood vessel diameter.
Blood flow (F) is directly proportional to _______; blood flow is inversely proportional to _______.
blood pressure gradient (P); peripheral resistance (R)
F = P/R
The blood pressure near the heart is considered…?
Pulsatile, it rises and falls with each heartbeat
Why is systemic pressure highest in the aorta?
- Elasticity of arteries close to the heart
- Volume of blood forced into them at any time
Define pulse pressure
The difference between systolic and diastolic pressure. 0.5 is diastole, 0.3 is systole of the 0.8 seconds in a heart beat.
What is the systolic pressure?
The pressure exerted in aorta during ventricular contraction. The left ventricle pumps blood into the aorta, imparting kinetic energy that stretches aorta which averages 120 mm Hg in a normal adult.
Define Mean Arterial Pressure (MAP)
The pressure that propels blood to the tissues. The heart, however, spends more time in diastole, so it is not just a simple average of diastole and systole.
Why is a low capillary pressure desirable?
- High BP would rupture fragile, thin-walled capillaries
- Most capillaries ae very permeable, so low pressure forces filtrate into interstitial spaces
Low venous blood pressure requires adaptations to help with venous return, what are these adaptations/
- Muscular pump: the contraction of skeletal muscles “milks” blood back toward the heart; valves prevent backflow
- Respiratory pump: pressure changes during breathing move blood toward the hear by squeezing abdominal veins as thoracic veins expand
- Sympathetic venoconstriction: under sympathetic control, smooth muscles constrict, pushing blood back toward the heart
How do neural controls impact blood pressure regulation?
- Cardiovascular center of the medulla: sympathetic innervation controls vasomotor tone and dilation
- Baroreceptors: sense changes in blood vessels and therefore blood pressure
- Chemoreceptor reflexes: sensitive to changes in blood gas measurements (i.e. increase in CO2, or decrease in pH or O2)
- Influence of higher brain centers (i.e., hypothalamus)
How do hormonal controls impact blood pressure regulation?
Hormones regulate BP in short term via changes in peripheral resistance or long term via changes in blood volume.
1. Adrenal medulla hormones (epinephrine and norepinephrine) increase CO and vasoconstriction
2. Angiotensin II stimulates vasoconstriction
3. ADH in high levels can cause vasoconstriction
4. Atrial natriuretic peptide decreases BP by antagonizing aldosterone, causing decreases in blood volume
How do the kidneys regulate arterial blood pressure independently of hormones?
- Increase in BP or blood volume causes the elimination of more urine, thus reducing BP
- Decreased BP or blood volume causes kidneys to conserve water, and BP rises
What is tissue perfusion and what is it involved in?
Blood flow through body tissues; involved in:
1. Delivery of O2 and nutrients to, and removal of wastes from, tissue cells
2. Gas exchange (lungs)
3. Absorption of nutrients (digestive tract)
4. Urine formation (kidneys)
What is an extrinsic control?
sympathetic nervous system and hormones control blood flow through the whole body. controls how quickly fluid gets to certain tissues
What is an intrinsic control?
Blood flow is adjusted locally to meet specific tissue requirements (i.e., organs regulate their own blood flow by varying resistance of their own arterioles)
What are the four ways molecules use to travel across capillaries?
- Diffuse directly through endothelial membranes
- Pass through clefts
- Pass through fenestrations
- Active transport via pinocytotic vesicles or caveolae