Blood Vessels

Blood flow

Heart to arteries to arterioles to blood capillaries to venues to veins

How do red blood cells travel in capillaries?

Single file line

Capillaries

Structure: Thin walls

Function: Gas exchange

Capillary beds

Network of interconnected capillaries

What exists in the middle of blood vessels?

Lumen

3 layers of vessels

1. Tunica intima

2. Tunica media

3. Tunica externa

Turnica intima

Structure:

4 sublayers:

1. Endothelium

2. Basement membrane

3. Subendothelial layer

4. Internal elastic lamina

Location: closest to lumen. Inner most layer.

Endothelium

Structure: simple squamous ET

Function: secrete vasodilators and vasoconstrictors

Basement membrane

Function: connect endothelium layer to subendothelial layer

Subendothelial layer

Structure: areolar CT

Location: turnica intima layer between the basement membrane and the internal elastic lamina

Function: metabolic support

Internal elastic laminate

Structure: looks like Swiss cheese. Elastic fibers

Location: most superficial layer in the trunica intima layer

Function: contributes to elasticity of blood vessel. Stretch and recoil.

Turnica media

Structure: smooth muscle tissue

Location: middle layer of blood vessel

Function: vasoconstriction and vasodilation. Sphincter.

External elastic lamina

Structure: elastic fibers

Location: the layer between the turnica media and turnica externa

Function: provides elasticity, stretch, and recoil

Turnica externa

Structure: areolar connective tissue and dense irregular connective tissue

Location: most superficial layer of blood vessels

Function: metabolic and structural support, and anchor blood vessels to surrounding tissues and organs

Vasa vasorum

Structure: blood vessels, capillaries

Location: found in the turnica externa layer

Function: provide metabolic support to large blood vessels

2 types of arteries

1. Elastic arteries

2. Muscular arteries

Elastic artery

Structure: lots of elastic fibers especially in tunica media. Largest arteries. AKA conducting arteries. Able to withstand strong pulsations of ejected blood

Location: aorta, pulmonary, brachiocephalic

Function: conduct blood away from the heart to smaller muscular arteries

Muscular arteries

Structure: AKA distributing arteries. Thicker tunica media composed of smooth muscle tissue

Location: brachial, anterior tibial, coronary, and inferior mesenteric arteries

Function: most effective vasoconstriction and vasodilation

Arterioles

Structure: Smallest arteries. Lack elastic laminae. Well innervated. Sympathetic innervation controls vasoconstriction.

Location: throughout the body

Function: control blood flow

How do arterioles contribute to blood flow during exercise?

Arterioles dilate in the active skeletal muscles and constrict in less active and nonessential organs such as the digestive organs

Venules

Structure: No elastic laminae. Larger lumen and thinner walls than arterioles. Porous. Some have valves..

Location: throughout the body

Function: store more blood

Veins

Structure: larger lumen. Store more blood. Thinner walls. Blood pressure is reduced.

Location: throughout the body

Function: drain capillaries and return blood to the heart

Venous valves

Structure: composed of tunica intima and strengthened by elastic and collagen fibers. Fold to create semilunar valve leaflets. As muscle contracts, blood is squeezed up the vein

Location: inside veins. More prominent in lower limbs because blood is farther from the heart and close to the ground

Function: maintain one way blood flow. Unidirectional.

What happens when valves fail?

Blood pools and dilates.

Varicose veins

Venous sinuses

Structure: lack tunica media layer. Not capable of vasoconstriction or validity. Irregular lumen

Location: cranial cavity. Coronary sinus, superior sagittal sinus

Function: drain deoxygenated blood from the brain

Capillaries

Structure: smallest blood vessel. Erythrocytes must travel single file inside. Very thin. Composed of tunica intima only with 2 sublayers, endothelium and basement membrane. Simple squamous ET. Leaky. Things can go though very fast.

Location: connect arterioles to venules

Function: gas exchange

Intercellular cleft

Gaps between cells that cause leaks

3 types of capillaries based on how leaky

1. Continuous capillaries

2. Fenestrated capillaries

3. Sinusoid capillaries

Continuous capillaries

Structure: least leaky. Basement membrane is intact. No holes or gaps. Really small intercellular clefts. Most common. Have tight junctions between cells.

Location: found in the brain. Skeletal muscle, and skin

Fenestrated capillaries

Structure: middle for leakiness. Basement membrane is continuous but has fenestrations or pores within endothelial cells .

Location: kidneys, small intestine, endocrine glands

Sinusoidal capillaries

Structure: most leaky. Intercellular clefts large. Basement membrane discontinuous. Large fenestrations. Larger and wider.

Location: liver, red bone marrow, spleen

Capillary bed

Structure: Network of capillaries between an arteriolr and a Venice. May contain precapillary sphincters

Function: regulates blood flow into capillaries

Portal system

2 capillary beds between arteries and veins

Hepatic portal system

Structure: part of the circulatory system. Main vessel is the hepatic portal vein.

Location: digestive tract

Function: nutrient processing, detoxification, bacterial clearance

What type of blood does the hepatic portal vein carry?

O2 poor dirty blood

What type of blood does the hepatic vein carry?

O2 poor clean blood

Blood flow in the Hepatic portal system

Left ventricle to aorta to hepatic artery to liver to hepatic vein to inferior vena cava to right atrium

Capillaries of digestive system

Stomach

Intestines

Pancreas

Spleen

Other option for blood flow

Left ventricle to aorta to arteries if abdominal organs to hepatic portal vein to liver to hepatic vein to inferior vena cava