Blood vessels

3 major types of blood vessels

1. *arteries* (carry blood away from the heart); 2. *veins* (carry blood towards the heart); 3. *capillaries* (transfer station between arteries and veins).

How blood reaches your thumb

1. Blood leaves your *aorta* and travels along the elastic *subclavian artery*, which gives way to a series of muscular arteries - brachial artery in your upper arm, and the radial artery in your lower arm. 2. These arteries keep tapering down until they turn into the nearly microscopic *arterioles* that feed into the smallest of your blood vessels - tiny and thin-walled *capillaries*, which serve as a sort of a bridge between your arterial and venous systems.

How blood flow, blood pressure and resistance are tied together

Blood flow = Difference in blood pressures/Resistance F = deltaP/R When one of the variables change, your body tries to compensate for it to maintain homeostasis by using neurons, hormones and kidneys.

What are capillary walls made of?

Capillary walls are made of just a single layer of epithelial tissue, which form only the *tunica intima*, so they are able to deliver the oxygen and other nutrients in your blood to their cellular destinations through diffusion. The capillaries are also where those cells can dump their carbon dioxide and other waste back into the blood and send it away through the veins to the lungs and kidneys.

Blood resistance

It can be the result of increased *viscosity* - the thicker your blood is, the more difficult it is to move - or it could be because of increased vessel length, since longer vessels are more resistant to flow in general. But for most people, the biggest factor that affects resistance has to do with *vessel diameter*. Changes in the diameter can be temporary, but an excess of low-density lipoprotein (*LDL*) - bad cholesterol - in the blood can build up to form fatty plague on the inside of your arteries, permanently increasing the resistance, and hindering blood flow.

The danger of chronic high blood pressure (hypertension)

It can cause serious damage to both the heart that creates the hight pressure, and to the blood vessels that have to withstand that extra pressure. Over time, the increased force of blood against the arterial walls can make them stiffen, leak, or rupture, while the heart itself may simply wear out from all the exra work it's doing to keep blood moving.

How does the excess sodium used in processed foods and salty snacks affect you?

It causes your body to retain water, which creates higher blood volume and leads to higher blood pressure.

How many layers are in a blood vessel?

Most of your *blood vessels* share a similar structure consisting of 3 layers of tissue surrounding the open space (*lumen*) that actually holds the blood.

Cardiac output (formula)

Stroke volume (ml/beat) * Heart rate (beats/min)

How does blood pressure work?

The heart is the pump, the arteries are pressure reservoirs, the arteries control distribution, the capillaries are the exchange sites, and the veins are blood reservoirs. Blood pressure is the circulatory system's way of getting your 5L of blood flowing throughout your body, so that your tissues can get the oxygen and nutrients they need.

What is the long-term control of blood pressure?

The way to get more control of blood pressure is to *alter its blood volume*. For that you need the *kedneys*. They produce hormones like *renin* and *angiotensin*, which help regulate levels of sodium and fluids in your body. And also help expand and constrict blood vessels. When your blood pressure grts too high, your kidneys will try to reduce the volume of blood by getting rid of any extra water. Basically, they make you pee.

Why are your fingers stiff and numb in the cold?

They are not getting as much warm blood, because your blood vessels are trying to conserve heat.

What do *beta-blockers* do?

They are used to reduce the risk of heart disease by *blocking the beta receptors for epinephrine and norepinephrine*. When these hormones bind to beta receptors, it causes *vasoconstriction* and causes the heart to produce more forceful and faster contractions. Therefore, blocking beta receptors leads to more dilated blood vessels and a slower heart even under stress.

What does NS and ES do to create homeostatic balance to your blood pressure?

They try to balance blood pressure when it gets too high or low in an effort to create homeostatic balance. If your BP stays out of balance long enough, things will start going wrong.

Things that contribute to high blood pressure

Things that can in some way affect how efficiently your blood flows: - emotional stress; - physical exertion; - dehydration; - too much salt; - saturated fat.

The outermost layer of a blood vessel

Tunica externa. It is like an overcoat made of loosely woven collagen fiber. It protects and reinforces the whole blood vessel.

The innermost layer of a blood vessel

Tunica intima. It contains the *endothelium*, which is made uo of simple squamous epithelium tissue. These cells form a slick surface that helps the blood move without friction.

The middle layer of a blood vessel

Tunica media. It is made of smooth muscle tissue and sheets of the protein *elastin*. The tunica media is usually the thicket layer in arteries, which plays a much bigger role in maintaining blood pressure and circulation than veins. That smooth muscle tissue is regulated in part by the nerve fibers of the ANS, which can decrease the diameter of the lumen by contracting this middle layer during *vasoconstriction*, or expand it by relaxing during *vasodilation*. The tunica media plays a key role in blood flow and blood pressure, because the smaller the diameter of the blood vessel, the harder it is for blood to move through it.

How do capillaries operate?

Unlike arteries and veins, capillaries don't opearte on their own, but rather form interweaving groups called *capillary beds*. Besides exchanding nutrients and gases, your capillary beds also help regulate blood pressure and play a role in thermoregulation.

What is a short-term effect on your blood pressure coming from your hormones?

When your body needs a little high blood pressure, like when it has to get ready to fight or flee, the *adrenal medulla* starts flooding your blood with epinephrine and norepinephrine. These hormones raise both the heart rate and the blood volume, and therefore *cardiac output*, while also constricting vessels in less essential regions, increasing the overall resistance, and therefore pressure. These hormonal controls work by changing *vessel resistance* and *cardiac output*.

What is a major short-term solution to stabilize high blood pressure (from your brain)?

Your brain targets both cardiac output and resistance by altering the distribution of blood flow around the body, or by changing the diameter of certain blood vessels. The vessels feeding your digestive organs constrict, which increases resistance there, so more blood goes to your organs which need it more. Most neural connections use *baroreceptors*, special nerve endings found in the carotid arteries, the aorta, and other larger arteries in the neck. When blood pressure stretches arterial walls, that opens mechanically-gated sodium channels in these little receptors. The higher the blood pressure is, the more frequently they send action potentials to the midbrain informing it just how much pressure the artery is feeling. When the brain learns what is happening, it can do any number of things to correct the situation - like dilate some arterioles to reduce resistance, or reduce the heart rate to lower cardiac output. But baroreceptors are not effective for long-term pressure changes, in part because they end up adapting, essentially reprogramming themselves to read a high blood pressure as the new normal.

Heart failure

a chronic condition in which the heart is unable to pump out all of the blood that it receives.

Arteriosclerosis

abnormal hardening of the walls of an artery or arteries (from flexible to stiff).

Aneurysm

an excessive localized enlargement of an artery caused by weakening of the artery wall.

Blood vessels

are active, dynamic organs, capable of contracting and expanding as they: 1. deliver oxygen and nutrients to cells throughout the body; 2. carry away waste products; 3. partly maintain blood pressure.

Heart attack (myocardial infarction)

damage or death of cardiac muscle tissue resulting from blockage of one or more coronary arteries.

Arterioles

mini-arteries that branch out into capillaries.

Venules

the smallest vein components that suck blood out of the capillaries.

Blood flow

the volume of blood flowing through any given vessel, or through the circulatory system as a whole, per minute. It is also called *cardiac output* and it is determined by the blood volume pumped during one beat and the number of beats per minute.