**A&P 2 Unit 17 & 18 (Lab) [Blood Vessels] Flashcards
The Blood Flow of the Brain
The arterial supply of the brain comes primarily from the internal carotid arteries & the basilar artery.
Basilar Artery
Located on the base of the brainstem & is derived from the fusion of 2 branches off of the subclavian arteries called the vertebral arteries.
Cerebral Arterial Circle
Once the internal carotid arteries & basilar artery enter the brain, they contribute to a structure called the circle of Willis or Cerebral Arterial Circle
Cerebral Arterial Circle (Composition)
- This circle is composed of branches of these vessels & a set of anterior & posterior communicating arteries.
- These vessels are connected to provide alternate routes of circulation to the brain if one of the arteries supplying the brain becomes blocked.
Veins that Drain into the Hepatic Portal Vein
- Splenic Vein
- Gastric Veins
- Superior Mesenteric Vein
- Inferior Mesenteric Vein
DO NOT drain directly into the Inferior Vena Cava.
Splenic Vein
Drains the Spleen
Gastric Veins
Darin the Stomach
Superior Mesentric Vein
Drains the Small Intestine & much of the Large Intestine
Inferior Mesentric Vein
Drains the remainder of the Large Intestine
Renal Veins
- Drain the Kidneys
- Empties into the Inferior Vena Cava
Hepatic Portal Vein
- Here, the nutrient-rich blood percolates through the liver, where it is processed & detoxified.
- In this way, everything we ingest (except lipids) must travel through the liver before entering the systemic circulation.
- Once the blodd has filtered through the hepatic portal system, it exits via Hepatic Veins & drains into the Inferior Vena Cava
- Blood glucose (absorbed during digestion) is converted to glycogen for storage in the liver. We’ll breakdown that glycogen between meals. Environmental toxins (e.g. pesticides, drugs) can be broken down by liver cells as a means of detoxification. Pathogens (e.g. bacteria) are phagocytosed by macrophages in the liver. The blood, now “cleaner” and “detoxed” leaves the liver through the hepatic veins which drain into the inferior vena cava.
Three Layers of the Walls of Arteries & Veins
- Tunica Interna
- Tunica Media
- Tunica Externa
Tunica Interna
- The innermost lining of the blood vessel.
- It consists of a specialized type of simple squamous epithelium called endothelium.
- It rests on top of a thin layer of connective tissue.
Tunica Media
- The middle layer of the blood vessel wall & consists of smooth muscle & elastic fibers.
- The smooth muscle, innervated by the sympathetic nervous system, controls the diameter of the vessel & plays an important role in tissue perfusion & blood pressure.
- The elastic fibers allow the vessel to expand with changing pressure & return to its original shape & diameter.
Tunica Externa
- Also known as Tunica Adventitia
- The outermost layer of the blood vessel, which consists of dense irregular collagenous connective tissue with abundant collagen fibers. The collagen fibers reinforce the blood vessel & prevent it from rupturing when the pressure in the vessel increases.
Artery (Mean Diameter)
4.0 mm
Artery (Mean Wall Thickness)
1.0 mm
Arteriole (Mean Diameter)
30.0 µm
Arteriole (Mean Wall Thickness)
6.0 µm
Capillary (Mean Diameter)
8.0 µm
Capillary (Mean Wall Thickness)
0.5 µm
Venule (Mean Diameter)
20.0 µm
Venule (Mean Wall Thickness)
1.0 µm
Vein (Mean Diameter)
5.0 mm
Vein (Mean Wall Thickness)
0.5 mm
Arteries (Composition) [Most to Least]
- Smooth Muscle
- Elastic Tissue
- Fibrous Tissue
- Endothelium
Capillaries (Composition) [Most to Least]
- Endothelium
Veins (Composition) [Most to Least]
- Smooth Muscle
- Elastic Tissue & Fibrous Tissue
- Endothelium
Three Types of Capillaries
- Continuous Capillary
- Fenestrated Capillary
- Sinusoid
Continuous Capillary
Are continuous in the sense that the endothelial cells provide an uninterrupted lining, and they only allow smaller molecules, such as water and ions to diffuse through tight junctions, leaving gaps of unjoined membrane called intercellular clefts.