blood pressure

Arteries

carry blood away from the heart

Veins

carry blood toward the heart

Arteries

carry blood away from the heart

Veins

carry blood toward the heart

tunica intima

- Innermost layer

- Made up of endothelium = simple squamous epithelial attached to the basement layer

- Needs epithelial because it touches blood

- Capillaries ONLY have a tunica interna to allow for gas exchange

1. Endothelium: continuous with the endocardium of the heart

2. Basement membrane

3. Lamina propria (CT)

4. Internal elastic membrane: fenestrated layer of elastic fibers

tunica media

- Smooth muscle organized in a ring

- Makes BVs bioconstrict (get smaller) when contracted

- Controlled by the sympathetic nervous system

- Epi or NE

• middle layer of smooth muscle fibers arranged circularly around the BV

  • Regulates blood flow through:

□ Vasoconstriction: smooth muscle contraction → decrease in BV diameter

□ Vasodilation: smooth muscle relaxation → increase in BV diameter

• Elastic and collagen fibers

  • External elastic membrane: separates tunica media from the tunica externa

tunica externa

- Outermost layer

- Collagen fibers - mechanical properties

- Integrates vessel into surrounding tissue

- Protects from kinetic energy inside BV

- Big BVs have a thick tunica externa because they need their own circulatory system

Elastin/conducting blood vessels

- Biggest arteries

- High blood pressure - need elastin to stretch and absorb the kinetic energy

- Thick walls

- Close to heart - take the blood away from heart

- Big lumens

Muscular/distributing Vessels

- Distribute blood into different body regions

- Thicker tunica media

- Can control the tunica media to control the amount of blood entering the region

Arterioles

- Smallest

- Distribute blood within and organ to a specific capillary bed

- Almost exclusively smooth muscle

Arteriovenous anastomoses

• specialized vascular connections that allow blood to flow from arterioles to small veins directly → without passing through the capillaries

  • Glomus: consists of arterioles with lots of smooth muscle in their walls

    • Vessels are branched/coiled 

    • Surrounded by CT

    • Located in the sole of the foot, palm of the head, terminal phalanges, and nail beds

    • Regulate body temperature

      • Body temp decrease → constrict → less blood flows → reduce rate of heat loss

      • Body temp increase → dilate → more blood flows → increase rate of heat loss

Venules

• Venules: smallest veins

  • Similar to capillaries

  • Tubes of endothelium resting on a basement membrane

  • Small veins: vessels that are increased in diameter and smooth muscle fibers form a continuous layer

    • Tunica externa composed of collagenous CT

  • Collect blood from the capillaries → transport it to small veins

  • Nutrient exchange occurs across venule wall

    • But thicker walls = less exchange

Medium and large veins

• Medium veins: collect blood from small veins and deliver it to large veins

• Large veins: transport veins from the medium veins to the heart

• Tunica intima: thin endothelial cells, thin collagenous CT

• Tunica media is thin as well → BUT CAN HOLD A LARGE VOLUME OF BLOOD

• Tunica externa is the predominant layer → collagenous CT

Portal vein

• connects one capillary network to another

  • Begin in a primary capillary network → extend → then end in a secondary capillary 

  • No pumping mechanism between the networks

  • Hepatic portal veins: from the gastrointestinal tract and spleen to sinusoidal capillaries in the liver

  • Hypothalamohypophysial portal veins: from the hypothalamus to the anterior pituitary

  • Renal nephron portal systems: associated with the urine forming structures of the kidneys

Valves

• allow blood to flow toward the heart, but not the opposite direction

  • Veins that have diameters greater than 2 mm

  • Folds in the tunica intima → form flaps that overlap to stop flow in the opposite direction

  • Many valves in the medium valves

Vasa vasorum

• small BVs that supply nutrients to the BV walls

  • Penetrate from the exterior to form a capillary network in the tunica externa/tunica media

Systemic pathway

heart -> arteries -> arterioles -> capillary bed -> venules -> veins -> capacitance vessels -> vena cava

Arterial system

heart -> start of venous system in capillary bed

Venous system

capillary bed -> right atrium

Capillary beds

- functional units of the CV system

- Collection of arteries and veins

- Enters through arterioles, leaves through venules

- ONLY place where exchange of materials can take place; capillaries only have a tunica interna which allows for gas exchange

Pericapillary cells

• fibroblasts, macrophages, undifferentiated smooth muscle fibers

  • Scattered along the length of the capillary

• Branch without changing in diameter

Metarteriole

- brings blood from the arteriole to capillary

- Once bypassed or entered, blood not entered into the capillary will return to arteriole

Thoroughfare channel

allows blood to travel from the metarteriole directly into the venule, a bypass

Precapillary sphincter

smooth musucular rings, determine if blood can enter the capillary bed, at base of true capillaries

Sinusoid Capillaries

- Typical capillary beds , 90%

- Designed to be leaky; spaces between the desmosomes allow fluid to leave relatively easily

Continuous Capillaries

- Tight junctions

- Nothing can pass between the cells

- Continuos means NOT permeable

- Ex: BBB

- However: gases like ethanol can still pass through

Fenestrated Capillaries

- Open pores in the endothelial cells

- Highly permeable

- Ex: glomerulus in kidney, urinary system

- Very uncommon

- Still have desmosomes because theyre modified sinusoid

Pressure

- allows for blood flow to occur

- as pressure goes up, blood flow goes up

resistance

- Resistance opposes blood flow

- As resistance goes up, blood flow goes down

Viscosity

- As viscosity goes up, resistance goes up

- Can be regulated if you change locations but not short term

Length of vessels

- More length = more resistance

- Can't be regulated

diameter

- As diameter goes down, resistance goes up

- Only factor that the body can regulate

how arterial pressure changes throughout the systemic circuit

- Heart -> arteries -> arterioles -> capillaries -> venules -> veins -> vena cava

- As you move further down the circuit, pressure goes from 120 mL Hg when leaving the heart to about 20 mL at venules; meaning it loses 100 mL of pressure

- Once you get passed the arterioles, the difference in pressure between systolic and diastolic is no longer percievable

- At the starting point (heart) its 120/80

So, blood pressure will taken at the elbow because there are arterioles present

mean arterial pressure (MAP)

- MAP = Diastolic Pressure + ⅓ Pulse Pressure

- Pulse Pressure = Systolic pressure - Diastolic Pressure

- Diastolic pressure and systolic pressure CANNOT be equally weighted because the heart spends more time in diastole than in does systole (diastole = 0.5 of 0.8 seconds in the cardiac cycle)

- A weighted average

Pulse pressure

the difference between your systolic and diastolic BP

venous return

- Blood has 120 mL Hg when it leaves the heart, but about 20 mL by capillaries

- This is not enough pressure to bring the blood back to the heart

Muscular pump

- Primary method of return

- Most veins are intergrated or on the surface of muscles

- When contracted, it compressed the vessel which pressurizes its fluid

- Ensures the movement of blood towards the heart

- Leading valve = opened

- Trailing valve = closed

- Valves = one way, opened towards the heart

Respiratory pump

- Not very active when you're sedentary, usually activated when you're breathing heavy from exercising

- Heart is above the diaphragm

- Diaphragm us above the abdominal cavity

- When you inhale, your diaphragm contracts and pushes down on your abdominal cavity which causses the muscles of the abdominal cavity to pressurize the fluid inside of it

- Your inferior vena cava runs down from your heart to your abdominal cavity

- Inferior vena cava become squeezed by the pressurized fluid

- Meanwhile, as you inhale your rib cage gets bigger and so pressure of this region goes down

- This creates a pressure gradient where blood wants to move from high pressure to low pressure

- Allows blood from your abdominal cavity to have enough pressure to travel to your heart

Venous valves

- Allow for one way blood flow

- Only open towards the heart

Relationship between CO and BP

- BP = CO X PR

- Any variable that affects CO will affect BP

- PR = peripheral resistance, the resistance within the vessels of the CV system

BP and SV

- CO = SV x HR and BP = CO x PR

- So, SV and BP are directly related

- Higher SV = higher BP

resistance and BP

- more resistance = higher PR

- higher PR = higher BP

Vasomotor center

- Within the medulla

- Vasoconstriction: making the blood vessels smaller

- Vasoconstriction -> increases resistance -> increases PR -> increases BP

- Sympathetic NS

- Releases NE which causes vasoconstriction

Baroreceptors

- Detect changes in arterial blood pressure

- Within large vessels (like the aorta)

- needed to make sure high blood pressure doesn't reach the brain

- parasympathetic

- Stretching increases signaling to vasomotor center (inhibits)

- Causes dilation of arteries and veins (bigger)

-. Reduces peripheral resistance

- Inhibits sympathetic NS (HR and contractile force decrease)

- vasodilation = less resistance

Chemoreceptor

- O2 and CO2

- Blood borne chemicals

Adrenal medulla hormones

- NE and EPI are agonists (same function)

- Released by vasomotor center in the medulla

- NE is a vasoconstrictor

- EPI increases cardiac output by increasing cardiac muscle contractility

Atrial natriuretic peptide (ANP)

- Atrial peptide hormone

- Reduces blood pressure by antagonizing aldosterone

- Triggered if blood pressure is too high

- Acts on right atria

- Increases water excretion from kidney - so there is less in blood stream (lower SV = lower BP)

Nephrons

- functional units of the kidney

- Nephrons receive blood from the arterioles

- Arterioles become glomerulus - a complex capillary

- Glomerulus connects to the capsule

- Blood entering the kidney becomes filtrate

PCT

area in kidney where water can be recovered (leave nephrons and enter blood stream) PASSIVELY

Loop of Henley

area in kidney where water can be recovered PASSIVELY

DCT (Distal Convoluted Tube)

area in kidney that has to be regulated to be made more permeable so that water can be recovered

Collecting duct

area in kidney that has to be regulated to be made more permeable so that water can be recovered

JGA

sensory structure just before the arteriole enters the capillary bed that detect stretch in the arteriole walls

Antidiuretic hormone (ADH)

- Posterior pituitary hormone

- Increases blood pressure by increasing water absorption by distal tubule (DCT): this means more water is being released into the blood stream meaning EDV is higher = SV is higher = - - - CO is higher = BP is higher

- At high concentrations, causes vasoconstriction

- Vasoconstriction = smaller

- Smaller radius = more PR = higher BP

Angiotensin II

- Mediated by release of renin by JGA of kidney tubule

- When amount of blood entering kidney tubule is too low, renin is released

- Renin catalyzes the conversion of angiotensinogen into angiotensin II

- Angitoensinogen -> angiotensin I

- Angiotensin travels to lungs

- Angiotensin I is converted to Angiotensin II on the type II pneumocytes on the lungs

- Angiotensin II = the actual hormone, angiotensinogen and angiotensin I are just precursors/catalyst

direct effect angiotensin II

- causes vasoconstriction of systemic arterioles

- Increases BP by increasing the PR

indirect effect of angiotensin II

BP DECREASES (TRIGGER EVENT) -> Angitoensin II -> JGA is triggered -> JGA releases renin -> renin acts as a catalyst that riggers angiotensinogen to be converted into angiotensin I -> angiotensin I travels to the lungs where it is converted into angiotensin II on type II pneumocytes -> angiotensin II acts on the zona glomerulosa of the adrenal cortex -> stimulates release of aldosterone -> aldosterone acts on the DCT -> DCT reabsrobs Na+ into the blood -> Na+ increases solute concentration in blood -> increase in solute concentration acts on SON -> causes SON to release ADH -> ADH acts on DCT to increase H20 absorption out of nephron and into blood stream -> blood volume increases -> EDV increases -> SV increases -> CO increases -> BP INCREASES

Hydrostatic pressure (or just pressure)

- pressure within the capillary

- Pressure within the capillary is always greater than pressure within the intersitial space

Osmotic pressure

- the ability to oppose the movement of water

- Greater within than interstitial space than in the capillary

- Remains constant on both ends of the capillary; is based on what is dissolved into the capillary which does not change

Arterial end

- Hydrostatic pressure is greater than osmotic pressure

- So, the net movement of fluid is OUT of the capillary

Lymph Capillaries

- Have very low lymph pressure (inside capillary)

- More pressure in the interstitial space

- So, fluid moves into the capillary

- Lymph capillaries have one way valves that only open towards the heart

- Need lymph capillary so that pressure does not get to high within the interstitial space

Venule end

- Osmotic pressure is greater than hydrostatic pressure

- This is because lots of fluid within the capillary is lost by the lymph capillary

- So, net movement of fluid is out of the venule end