Vascular System

A&P 335 Exam 3

Characteristics of arteries

Thick elastic connective tissue, smooth muscle, endothelium

Large radius, low resistance

Characteristics of arterioles

Thick smooth muscle, endothelium, have greatest resistance to flow

Characteristics of capillaries

Endothelium

Characteristics of veins

Thin connective tissue, endothelium

Characteristics of veins

Thin connective tissue, endothelium, wide and floppy

Explain the dicrotic notch

A result of SL valve closing, a bounce in pressure

Function of arteries

Maintains pressures and continues to push out blood even during diastole

Is a pressure reservoir and keeps pressure high by storing blood in stretched areas of artiers

Due to elastic recoil and compliance

Define compliance

How easy it is to stretch blood vessels

Define elastic recoil

Ability to return to original size after change, can snap back

Pulse pressure formula

= Systolic P - Diastolic P

Mean arterial pressure formulas

= Diastolic P + 1/3 Pulse pressure
= CO x TPR

How does age affect the arteries

The arteries get stiff which decreases…

Compliance - ↑ volume in lumen → ↓ volume stored → ↑ SP

Elasticity - ↓ volume in lumen (not stored → ↓ DP

Explain how sphygmomanometry is used to measure arterial pressure

The cuff compresses the brachial artery to above the systolic pressure, blocking flow (no sound).

As the cuff delates, turbulent sound is heard. First sound = systolic blood pressure

When sound disappears and flow is laminar = diastolic blood pressure

Functions of arterioles

Match blood flow to local tissue/cellular metabolic demand by changing the radius due to the smooth muscle

Maintain mean arterial pressure by determining the total peripheral resistance

Arterioles and resistance

All blood vessels contribute resistance to blood flow but arterioles are the site of greatest vascular resistance and are the main contributors to TPR

Describe conditioning organs

Ex. kidneys, intestines, skin

Receive blood flow in excess of needs

Tolerant of blood flow reduction so can be constricted to protect others

Describe Flow-depending organs

Ex. brain, heart

Critically dependent on blood flow

No tolerance for low blood flow, will constrict other areas so these get blood

What is a local environment with local factors?

Individual arteriole with one capillary bed. Local factors are things that influence arteriole (O2, metab waste, CO2)

Define and list local controls

They match blood flow to demand. Involves metabolites or factors in local ISF surrounding capillaries

Active hyperemia, flow autoregulation, reactive hyperemia

Describe active hyperemia

When metabolic activity ↑ —> ↑ metabolites and ↓ O2 —> arteriolar dilation to allow more O2 into organ —> ↑ blood flow

More metabolic activity leads to more blood flow

Describe flow autoregulation

Maintains blood pressure in specific organs

Will vasoconstrict when there’s greater arterial pressure to protect capillary beds

Involves myogenic response mechanism

Describe myogenic response

Increase of BP stretches the walls of the arteries → activates stretch-sensitive Ca channels → enter smooth muscles and leads to vasoconstriction

Describe reactive hyperemia

Involves a rebound of high blood flow after a period of deprivation and its metabolic changes

Describe extrinsic controls of arterioles

Purpose is to protect MAP. Involves ONLY the sympathetic

Explain sympathetic controls of arterioles

Sympathetic ganglionic neurons release NE → binds to A1 receptors on smooth muscle → vasoconstriction and decreased blood fow

Adrenal medulla secretes E → binds to B2 (low doses) → vasodilation

With high dose of E → binds to A1 receptors

List neural controls of arterioles

Vasoconstrictors - NE on A1

Vasodilators - nitric oxide

List hormonal controls of arterioles

Vasoconstrictors - E (high), angiotensin II, vasopressin (ADH)

Vasodilators - E (low), atrial natrieuretic peptide (ANP)

Function of capillaries

Exchange of nutrients, oxygen, hormones, signals, removal of metabolic products. Only 5% of total circulating blood is in the capillaries

Describe the structure of capillaries

Thin wall and sizable pores for increased diffusion, no smooth muscle

Single layer of endothelial cells maximizes exchange with RBCs and ISF compartment

Define precapillary sphincters

Bands of smooth muscle where arterioles branch into capillaries, open and close perfusion

Define metartioles

Blood vessels with some smooth muscle that allow blood to bypass capillaries straight form arterioles to venules

What is the continuity of flow principle

Flow rate must remain constant. If cross-sectional area changes, velocity of fluid changes inversely

Capillaries and velocity

Capillaries have the slowest velocity to allow for exchange of substances

Define filtration

Movement of fluid out of the blood

Define absorption

Movement of fluid into the blood

Two ways of moving material in capillaries

Diffusion and bulk flow

Define bulk flow in the capillary

Movement of fluid across the capillary wall due to pressure differences

Explain 4 Starling forces

Hydrostatic pressures - built up pressure that pushes water out

• Capillary (Pc) → filtration, interstitial (Pif) → reabsorption

Osmotic force due to protein concentration - proteins draw water to them

• Plasma (πP) → reabsorption, interstitial (πif) → filtration

Describe the lymphatic system

The lymphatic system takes up water that comes out of the capillaries and back into CV system

4 L/day of mismatch in lymphatic fluid

Prevents edema/swelling and doesn’t accumulate fluid (no Pif)

4 mechanisms that enhance lymph flow

1. Increased filtration at capillaries (more filtration → more pressure → more flow)

2. Smooth muscle contraction

3. Sympathetic stimulation via NE binding to A1 receptors

4. Skeletal muscle pump and respiratory pump

Disease states and lymph

Lymph nodes enlarge when fighting infection

Cancer cells can spread through lymph

Blockage of lymph occurs when filaria worms invade body, causes lymphedema

Net filtration pressure formula

Pc + πif - Pif - πC

Function of veins

Return blood to heart by being a big radius, low resistance blood vessel

Act as storage vessels

List the factors that assist in venous return

Sympathetic innervation, skeletal muscle pump, inhalation movements, blood volume

Explain sympathetic innervation in promoting venous return

Releases NE on A1 receptors → contracts veins → increases venous return

Doesn’t change resistance because the veins are so floppy

Explain skeletal muscle pump in promoting venous return

Contracting muscles squeeze large veins, which increases venous return

One-way valves prevents flow from flowing backward, reduces blood pooling due to gravity

Explain inhalation movements in promoting venous return

Inhaling creates lower pressures in thoracic cavity. Blood moves from veins outside thorax w high pressure to veins in thorax with lower pressure

Explain blood volume in promoting venous return

Volume equates with pressure. More volume → more pressure

Explain baroreceptors

Receptors that are sensitive to stretch and monitors MAP

Stretch → sends afferent signals through afferent axons of 9th and 10th cranial nerves → send APs to brainstem nuclei —> change in pressure

Always active, only inactive when dead

Pressure goes up when there’s lots of stretching

Short-term regulation of BP

Describe medullary cardiovascular center

Info is carried to cardiovascular control center, contains these nuclei

APs to parasympathetic are always exitatory, APs to sympathetic are always inhibitory

List the 3 neuronal centers in the medullary cardiovascular center

The cardioinhibitory center (CI), the cardioacceleratory center (CA), and the vasomotor center (VM)

Explain the cardioinhibitory center (CI)

Parasympathetic

Releases ACh onto M-AChR at SA node → lowers HR

Explain the cardioacceleratory center (CA)

Sympathetic

Releases NE + E onto B1 receptors on SA node → increases HR

Releases NE + E onto B1 receptors on contractile cells in ventricles → increases SV

Explain the vasomotor center (VM)

Sympathetic

Releases NE onto A1 receptors on arterioles → decreases radius and increases TPR

Releases NE onto A1 receptors on veins → decreases radius and increases VR and SV

MAP and medullary cardiovascular center response

If MAP ↑, then want ↓ symp and ↑ parasymp

If MAP ↓, then want ↑ symp and ↓ parasymp

What does long term regulation of arterial pressure depend on

Blood volume

Examples of long term regulation of arterial pressure

• Regulating kidney function - ↑ arterial pressure → ↓ hormone secretion → ↑ urinary output and filtration → ↑ water, ↓ plasma and blood volume

• Peripheral chemoreceptors - near aortic and carotid bodies and detect O2, CO2, and pH

  • Low O2, high CO2 and lots of acid → vasoconstriction

Explain Cushing’s phenomenon

Elevated intracranial pressure resulting in large increases in systemic MAP.

Head trauma → intracranial bleeding and swelling → pressure and metabolite build up → stimulates central chemoreceptors → constricts arterioles and increases TPR → temporarily fixes it but makes swelling worse by raising MAP