Blood vessels are ___
Dynamic anatomical structures that maintain efficient blood flow via a variety of fascinating physiological processes
Sort these vessel types in the order of blood flow, starting with those that first carry blood away from the heart and finishing with those that eventually return blood to the heart
- Arteries
- Arterioles
- Capillaries
- Venules
- Veins
Arteries
Carry blood away from the heart and branch into progressively smaller structures
Arterioles
The smallest of the structures and deliver blood to capillaries
Capillaries
Gets blood from arterioles which serve the organs and tissues of the body (systemic circuit) or the lungs (pulmonary circuit)
Venules
Collect blood from capillary networks and then converge to form progressively larger structures, the veins
Veins
Eventually return blood to the heart
Arteries carry oxygenated blood, veins carry deoxygenated blood
Systemic circuit
Arteries carry deoxygenated blood, veins carry oxygenated blood
Pulmonary circuit
Arteries and arterioles carry blood ___ from the heart
Away
Veins and venules carry blood ___ the heart
Toward
Which blood vessels carry oxygenated blood?
- Pulmonary veins
- Systemic arteries
Arrange the layers of a blood vessel wall, from superficial to deep
- Tunica externa
- Tunica media
- Tunica intima
What is the likely problem the patient is suffering from (pain is excruciating and tearing)?
Aortic dissection (tearing)
Tunica intima (tissue type)
Simple squamous endothelium
Tunica media (tissue type)
Smooth muscle and elastic connective tissue
Tunica externa (tissue type)
Collagenous connective tissue
Aorta and its principle branches are considered to be
Elastic arteries and conducting arteries
Why must the aorta and its branches be able to stretch and recoil so readily?
The arteries must be able to stretch when pressure rises during the ventricular systole and then recoil when the pressure stops during ventricular diastole.
If vessels were to harden and lose the ability to stretch and recoil, resistance to blood flow would be much greater.`
Elastic arteries-
- The largest
- Contains the highest proportion of elastic connective tissue
Muscular arteries-
- Medium sized arteries
- Have a greater proportion of smooth muscle than the other arteries
Arterioles-
- Smallest of the three
- Have all three tunics
Which arteries are most directly responsible for controlling the amount of blood entering individual capillary beds?
Arterioles
Autoregulation
Occurs through mechanisms that are activated in response to changes in local tissue demands
2 categories: metabolic and myogenic responses
Metabolic respones
- Adjust blood flow based on the specific demands of local tissue
Ex: endothelial cells of tunica intima produce and release strong vasodilators and vasoconstrictors. NO and endothelins are constantly produced and released; metabolic demands occur by adjusting the balance between the two mediators.
Myogenic responses
- Occur reflexively within the smooth muscle of the tunica media
- Prevents over or under delivery of blood to the tissues
Ex: stretch, associated with increased pressure, causes vascular smooth muscle to contract, while decreased pressure and stretch causes it to relax. Arterioles avoid large changes to their diameter as systemic blood pressure fluctuates
Elastic arteries
These arteries are closest to the heart and have relatively larger lumens than other arteries
Muscular arteries
These arteries have the thickest tunica media of any vessel type
Arterioles
These arteries can be so small that their wall is only an endothelium and a thin layer of smooth muscle fibers
What would be the effect of capillaries with diameters less than 5 micrometers?
The capillaries would quickly plug with red blood cells, making them ineffective in delivering nutrients to tissues.
Only the tunica intima is present in ___
- Tunica media and tunica externa are absent
Capillaries
Capillaries have ___ ___ that make them even more permeable, facilitating the movement of fluid and small solutes between the blood and interstitial fluid
Intercellular clefts
Continuous capillaries
- The most common and widely distributed type of capillary
- Completeness of their endothelial lining
- Do not contain pores, have tight junctions
- Have pinocytotic vesicles that increase the permeability of continuous capillaries by allowing the movement of fluid and solutes across the capillary wall through endothelial cells
- Specialized to be less permeable
Fenestrated capillaries
- Endothelial cells are dotted with pores, or fenestrations that more readily allow the passage of fluid and larger molecules
- More permeable
- Fenestrations
- Small intestine, kidney glomeruli, certain endocrine organs
Sinusoid capillaries
- Permeability exceeds that of the fenestrated type
- Serve bone marrow, spleen, and liver
- Large fenestrations and a discontinuous basement membrane
- Tight junctions are more incomplete, creating larger intercellular clefts
Arrange the capillary tubes in order from the most to least permeable
- Sinusoid capillaries
- Fenestrated capillaries
- Continuous capillaries
Portal system
An arrangement of vessels through which blood collected from one set of capillaries passes through a large vessel (or vein) to a second set of capillaries before returning to the systemic circulation and passing through the heart
GI tract to liver- portal system
Capillary blood from GI tract passes through the hepatic portal vessel vein to a second capillary bed in the liver
- Portal blood flow allows the liver to immediately monitor, detoxify, and adjust the materials absorbed in the intestine prior to release into the general venous circulation
Hypothalamus to the anterior pituitary- portal system
Hypothalamaic neurons secrete releasing hormones into a capillary bed of the infundibulum that drains into a portal vessel that carries this blood to the anterior pituitary, which itself is drained by a second capillary bed into the general systemic circulation
- Provides intimate and specific chemical signaling between these two important homeostatic regulatory structures
Glomerulus capillary bed with the nephron of a kidney to the peritubular/vasa recta capillary beds also within the kidney- portal system
Blood is filtered by a capillary bed inside the glomerulus and then the same blood passes through the peritubular/vasa recta capillary bed surrounding nephrons
Maternal placenta capillaries to the capillaries of the developing fetus-portal system
Maternal placental capillaries exchange nutrients with blood that then passes through fetal capillaries
How does the presence of large fenestrations within sinusoids affect the movement of cancerous cells or bacteria?
It makes the movement of bacteria or cancer cells easier throughout the body. This is one of the drawbacks of this type of arrangement.
Continuous capillary location
Skin
Fenestrated capillary location
Small intestine
Sinusoid capillary location
Bone marrow
Capillaries are typically organized as branching networks of vessels called ___ ___
Capillary beds
Arterial capillaries
True capillaries arising from the metarterioles
Venous capillaries
True capillaries emptying into the thoroughfare channel
Microcirculation
Flow of blood from a terminal arteriole to a postcapillary venule through the capillary bed, is regulated by the precapillary sphincters in response to nervous input and local metabolic demands
Which feature of the capillary wall results from incomplete tight junctions?
Intercellular clefts
Venules
The smallest of the vessels carrying blood back toward the heart after it has passed through capillary networks
- Have very thin walls; walls of postcapillary venules are thin enough to allow passage of fluids and to readily permit the movement of leukocytes by diapedesis
Venules converge to form larger vessels called ___
Veins
- They have larger lumens and thinner walls than are arteries
Thickest layer of a vein is ___
Tunica externa
Veins can be though of as ___ ___ and are often called ___ ___
Blood reservoirs; capacitance vessels
Which vessel types may be porous enough to allow diapedesis?
Capillaries and venules
- Capillaries are the most permeable type of blood vessel. Postcapillary venules have walls that are thin enough to allow diapedesis.
Venous valves
Ensure a undirectional flow of blood
What would be the impact on venous physiology if the tunica media had many smooth muscle cell layers?
You would lose venous compliance and the ability of the veins to store extra blood. This would increase the amount of blood within the arterial side of the circulatory system, and hence blood pressure.
Varicose veins
Result from failure of the venous valves, which allows blood to back-up and pool in the peripheral veins of the legs
Explain the function of venous valves
In veins, valves ensure that blood flow is unidirectional despite being under low pressure
Are the effects of gravity the same in the body when a person is swimming compared with standing or with lying down?
No, when swimming, people are at neutral buoyancy, minimizing the effects of gravity
What is the likely problem the patient is suffering from (lips blue, no pulse in right leg, hairdresser)?
Deep vein thrombosis
Anastosomes
Specialized connections between blood vessels that permit alternate routes of blood flow
Arterial anastosomes create ___ ___ that provide multiple, additional pathways for blood delivery
Collateral channels
Arteriovenous anastosomes
Direct connections between arterioles and venules, which are primarily controlled by the sympathetic nervous system
Blood flow (F)
The volume of blood per unit of time moving through a vessel, tissue, organ, or the entire circulation, F is the same as cardiac output (CO), which is the amount of blood pumped by either ventricle each minute
- Blood flow between two points in the circulation is directly proportional to the difference in pressure
Blood pressure (BP)
- Form of hydrostatic pressure
- Is the force exerted onto a given area of the vessel wall by the blood contained within the vessel, and is measured in mmHG
Resistance (R)
Friction encountered by blood that impedes its flow
Briefly describe the relationship between blood flow, blood pressure, and resistance using the formula discussed. What is the relationship between flow and pressure? What is the relationship between flow and resistance?
Flow (F) varies directly with the difference in pressure (delta P) and inversely with resistance (R). As delta P increases, F increases; as R increases, F decreases.
If the viscosity (thickness) of a fluid moving through a tube were to decrease, what would happen to the value of delta P?
Delta P would decrease
Peripheral resistance is ___
- Directly proportional to blood vessel length
- Directly proportional to blood viscosity
Total peripheral resistance
Used to describe the forces impeding blood flow through the systemic circulation
Laminar flow
Under normal conditions, with a constant blood vessel diameter, blood flows with laminar flow
- Blood moving within different sections of a vessel's cross-sectional diameter moves witht he same relative velocity
Turbulent flow
Abrupt change to the diameter of the vessel disrupts this continuity and causes turbulent flow
- Blood will flow at varying relative velocities in different sections of the vessel, thereby increasing resistance