21 - Circulation

What is the circulatory system made of?

BVs that carry blood to tissues of body

• allow for exchange of substances (O2, CO2, nutrients, waste) to maintain homeostasis

What are pulmonary vessels?

transport from RV, pulmonary trunk, through lungs, get CO2 & O2, to LA

What are systemic vessels?

transport blood from LV, aortic arch & extras → through all parts of body to RA

What are the functions of the circulatory system?

• carry blood

• handle nutrients

• manages BP

• directs blood flow

How does the circulatory system in carrying blood?

carries blood to body tissues & back to heart

• go to distal tissues

• need to bring back from lungs w/ O2

How does the circulatory system handle nutrients?

exchange nutrients, waste products, gases

• bring to kidneys, liver conjugates waste

How does the circulatory system transport?

transports substances → hormones, immune components, coag mols, enzymes, nutrients, gases, waste products

How does the circulatory system manage BP?

helps regulate BP → uses chemo & baroreceptors

How does the circulatory system direct blood flow?

directs blood flow to tissues by controlling degree/volume of blood flow

• controls vessel diameter → constrict/dilate

What connects passageways to & from the heart?

3 types of BVs → form a continuous passageway

• from heart → tissues → heart

Which blood vessels form a continuous passageway?

arteries, capillaries, veins

• heart → arteries → capillaries → veins → heart

What are arteries?

Blood vessels that carry oxygenated blood away from the heart to tissues. They have thick, elastic walls to accommodate high pressure.

• higher pressure system, kick off O2 & pick up CO2 later

• get smaller further away from heart

What are capillaries?

Tiny blood vessels that connect arteries and veins, facilitating the exchange of oxygen, nutrients, and waste between blood and tissues. They have thin walls to allow for easy diffusion.

• oxy & deoxy exchange

What are veins?

Blood vessels that carry deoxygenated blood back to the heart from tissues. They have thinner walls than arteries and contain valves to prevent backflow.

What are the tissue layers of blood vessels?

tunica → intima, media, externa

What is the tunica intima?

tunica interna

• endothelium → direct contact w/ blood

• basment memb

• lamina propria (CT layer)

• internal elastic memb

What is unique about the tunica intima’s internal elastic membrane?

fenestrated layer of elastic fibers

• holes to allow for movement

What is unique about the tunica intima?

gives bounce & elasticity, accounts for pressure mechanism

• continuous w/ inside of heart

• gets damaged w/ clots

What is the tunica media?

middle layer, smooth muscle cells in circ arrangement around BV

• also has elastic & collagen fibers depending on vessel size

• work around circumference to allow for squeeze/rest

What are the functions of the tunica media?

regulate BV diameter & blood flow, structural support, elasticity for pressure changes

• vasoconstriction

• vasodilation

What is vasoconstriction?

smooth muscles of tunica media contract → decrease in blood flow

• go to inner organs w/ cold/conserve

What is vasodilation?

smoot muscles of tunica media relax → increase in blood flow

• less back pressure

• diff in diff areas

• ex → in fight or flight, muscle VDs, kidneys X

What is tunica externa?

outermost layer,, CT, varies based on area

• helps to anchor to surrounding areas

• still flexible → X want too rigid

How does the CT of the tunica externa vary?

• dense reg near vessel

• loose CT merges w/ surrounding CT

List the sublayers of the tunica intima (external to internal).

• internal elastic memb

• lamina propria

• basement memb

• endothelium

List the sublayers of the tunica media (external to internal).

• external elastic memb

• smooth muscle

What are the classifications of arteries?

• elastic/conducting arteries

• muscular/distributing arteries

• arterioles

What happens to arteries’ structures as they get smaller?

further from heart → go from lots of elastic fibers & less smooth muscle to less elastic & more smooth muscle

• less muscle = bigger

• more muscle = smaller (need to shunt/control more w/ vasodil/const)

What are elastic/conducting arteries?

largest diameters, high pressure, fluctuate b/w systolic & diastolic

• elastic tissue > muscle

• thick tunica intima, thin tunica externa

• most of named arteries

Why do elastic/conducting arteries have a thick tunica intima?

To accommodate high pressure and ensure efficient blood flow

• X want blood to burst through, 1st wall

• open AV & pushing blood on aorta → want more elasticity for the pressure

What are muscular/medium arteries?

distributing arteries → smooth muscles lets vessels to partially regulate blood supply to diff regions of body

What are smaller muscular arteries?

adapted for vasodilation & vasoconstriction to regulate blood flow effectively in targeted areas

What are arterioles?

transport blood from small arteries to capillaries/beds

• O2, waste products → deliver/pickup

• smallest arteries → 3 tunics can be differentiated

Why are the 3 tunics differentiated in arterioles?

The three tunics in arterioles are differentiated to allow for localized control of blood flow, enabling the regulation of blood pressure and distribution to various tissues through changes in vessel diameter.

What is a capillary wall made of?

simple endothelium surrounded by loose CT

• endothelium → simple squamous

• BM

• delicate layer of loose CT

• scattered pericapillary cells

What are pericapillary cells?

in the capillary wall

• fibroblasts → help w/ rebuilding

• macrophages

• undiff smooth muscle cells

What are the functions of capillaries?

vessels for exchange b/w blood & interstitial fluid/spaces

• collateral flow → block 1, can be sign of other areas w/ issues

• thin & delicate → pulling ions, water

• fluid → intra/extracellular

• work way to cells w/ diffusion collection from blood

What are the types of capillaries?

continuous, fenestrated, sinusoidal

What are continuous capilllaries?

no gaps b/w endothelial cells, X fenestrae → X leak

• less permeable to large mols

• large/many floating things = damage

What are fenestrated capillaries?

pores → X cytoplasm, thin & porous diaphragm for PM

• highly permeable

Where are continuous capillaries found?

Continuous capillaries are found in tissues such as muscle, nervous tissue, and lungs, where they help regulate the passage of substances due to their low permeability.

Where are fenestrated capillaries found?

• intestinal villi

• ciliary process of eye → change lens

• choroid plexus → CSF filter, highly pressurized system

• glomeruli of kidney

What is the purpose of the diaphragm in fenestrated capillaries?

helps hold t/g even w/ openness

What are sinusoidal capillaries?

large diameter w/ large fenestrae

• less BM

• X strong walls to help leak out/in

• room w/o door

Where are sinusoidal capillaries found?

• endocrine glands → large mols cross walls

• liver

How does diffusion in capillaries occur?

• through or b/w endothelial cells

• through fenestrae

What do capillaries form?

branching networks

Where does blood flow from arterioles to?

through metarterioles, then → capillary network

How does blood flow in capillary network compare?

• thoroughfare channel → venule fairly consistent (direct shot through tissue, w/o = go to backroads)

• through arterial capillaries → intermittent

Why might substances leave blood & enter other tissue in capillary network movement?

Substances may leave blood and enter tissues due to diffusion, allowing nutrients and gases to exchange, and due to osmotic and hydrostatic pressure differences across the capillary wall.

• higher capacity tissues use blood more → give away things earlier

What regulates blood flow into capillary network?

precapillary sphincters, smooth muscle in metarterioles

• shrink diameters, decide where/what to allow in

What is the flow of blood from arterioles to venule?

arteriole → metarteriole → arterial capillaries → venule capillaries → venule

How does blood flow occur in hypoxia?

Blood flow increases to hypoxic tissues as vasodilation occurs in response to low oxygen levels, allowing for improved oxygen delivery.

What is unique about tissues with high metabolism?

have more capillary networks

• lungs, liver, kidneys, skeletal muscle, cardiac muscle

What do skin capillary networks do?

function in thermoregulation → have more thoroughfare channels

What is the major function of capillaries?

nutrient & waste product exchange (CO2, tissue metabolites)

What are arteriovenous anastomoses?

specialized vascular connxns

• allow blood flow directly from arterioles → small veins (SKIP capillaries)

• good for heat

What is a glomus?

arteriovenous anastomosis w/ abundant smooth muscle in walls

• help regulate body temp → adjust blood flow through them

• can sacrifice CO2/O2, just let pass through internal areas

Where can a glomus be found?

abundant → sole of foot, palm of hand, terminal phalanges, nail beds

What are pathologic arteriovenous anastomoses?

form from injury/tumors, abnormal

• very large, can lead to heart failure

• shunting of blood b/w arteries & veins, only thoroughfare

How does vein size alternate?

vessels get larger as they approach heart, tiny away from heart

What are the classifications of veins?

venules, small veins, med/large veins

• get larger from venule → to become S/M/L veins

What are venules?

drain capillary network

• endothelial cells, few smooth muscle cells

• inc diameter → more smooth muscle

What are small veins?

smooth muscle cells form continuous layer

• tunica adventitia → collagenous CT (EXTRA layer)

• smaller layer → more smooth muscle cells

What are medium veins?

go b/w small & large veins

• have a more prominent smooth muscle layer and valves to prevent backflow.

What are large veins?

• thin tunica intima → endothelial cells, thin CT layer, few scattered elastic fibers

• tunica media → circ arranged smooth muscle cells

• tunica externa → PREDOM layer

  • lower BP compared to arterioles

What are portal veins?

start in primary capillary network, extend some distance

• end in secondary capillary network w/o pumping mechanism

What are the 3 portal vein systems?

• hepatic

• hypothalamo-hypophyseal portal system (HPS)

• renal nephron portal system

What are hepatic portal veins?

carry nutrient rich blood from GI capillaries → liver

• dilate & are sinusoidal capillaries in liver

What is the HPS?

b/w hypothalamus & ant pit gland

• 2 capillary beds connected

What is the renal nephron portal system?

w/in urine producing structures of kidneys

• absorb nutrients & spread to kidneys → detoxify

What are valves?

flap-like structures in veins that prevent backflow of blood.

How big are valves?

valves found in all veins greater than 2 mm in diameter

How are valves structured?

Valves consist of two or three thin, flap-like cusps that open and close to regulate blood flow, ensuring it moves toward the heart and preventing backflow.

• folds in intima form 2 flaps that overlap

Where are the majority of valves found?

more valves in veins of lower extremities than in veins of upper extremities

• blood drains w/ hand over head, X as much pressure to move, need more to move from foot to heart

How does valve movement occur?

muscle contracting, pushes in on both sides

• take blood & push up, come back down, gets caught behind valves & closes in on itself

• close escape route, work way back to heart

What might arterial turbulence cause?

blood works way around valves to try & get back through

• non-laminar flow constantly = hear squirt sound

• X valves there = flap of tunica intima sticking out, can catch some cells & form a clot

What is the vasa vasorum?

BVs supply walls of arteries & veins

• penetrate vessel walls from exterior

• branches of arteries into tunica externa & media

How is vasoconstriction neurally controlled?

unmyelinated sympathetic nerve fibers → form plexi in tunica adventitia

Which vascular structures are the most innervated?

small arteries & arterioles innervated the most

How are vessels of reproductive organs innervated?

parasympathetic

What detects stretch & BP changes in BVs?

some BVs innervated by myelinated fibers

• act as baroreceptors → monitor stretch, detect BP changes

How is deoxygenated blood transported?

from RV into pulmonary trunk

What does the pulmonary trunk divide into?

L/R pulmonary arteries

How is oxygenated blood transported?

2 pulmonary veins carry oxygenated blood

• exit each lung & enter LA

What is the aorta?

The aorta is the largest artery in the body, responsible for carrying oxygenated blood from the LV to distribute it throughout the entire body.

What are the 3 parts of the aorta?

ascending aorta, aortic arch, descending aorta

What is the ascending aorta?

R/L coronary arteries branch from here

What is the aortic arch?

arch posteriorly & to L, has 3 branches

What are the 3 branches of the aortic arch?

brachiocephalic artery, L common carotid, L subclavian artery

What is the descending aorta?

The portion of the aorta that travels downward through the thorax and abdomen, supplying blood to the lower body.

• includes thoracic & abdominal aorta

What is the thoracic aorta?

portion of descending aorta in thorax

What is the abdominal aorta?

part of descending aorta, inferior to diaphragm

• ends as 2 common iliac arteries

How can blood flow change in the inferior vena cava?

speed up a bit in IVC, wider but lose velocity due to system’s resistance

Why is the aorta strong & thick?

high pressure blood inside

• 1 inch diameter

What is the brachiocephalic artery?

branches off aortic arch supplying blood to the right arm & head

• R common carotid artery

• R subclavian artery

What is the right common carotid artery?

serves R side of neck & head

• branches off brachiocephalic artery

What is the right subclavian artery?

serves R upper limb

• branches off brachiocephalic artery

What is the left common carotid artery?

serves L side of neck & head

• branches off aortic arch

What is the left subclavian artery?

serves L upper limb

• branches off aortic arch