Chapter 21 Lecture 5 Flashcards
The Cardiovascular System involves:
Structure and function of blood vessels (Pt. 1)
Hemodynamics
forces involved in circulating blood (Pt. 2)
Major circulatory routes (Pt. 3)
Artery:
These muscular, elastic vessels carry blood under pressure from the heart. They branch many times before they become arterioles
Arterioles
Microscopic, thin-walled but still muscular vessels that regulate blood flow into the Capillaries
Capillaries
Single layer of epithelial cells that allow exchange of fluids, gasses, and nutrients in tissues. They then pass on to Venuoles
Venuoles
Thin-walled vessels that intersect others to begin returning blood to the heart. Eventually they merge to become larger veins
Veins
Similar structure to arteries, but much thinner walls, wider diameter, and less elastic
Inner layer =
tunica interna. Very thin inner lining in contact with blood. Three layers:
- squamous cell epithelium
- epithelial basement membrane
- internal elastic lamina
Middle Layer =
Muscular, elastic layer that varies considerably in thickness between the vessel types. Composition:
- smooth muscle cells
- elastic fibers
Outer layer =
tunica externa. Three primary elements: 1. external elastic lamina 2. nerves 3. vascular system 4/ connections/anchorage
Sympathetic Innervation:
Vascular smooth muscle is innervated by sympathetic nervous system
increase in stimulation causes
muscle contraction or vasoconstriction
injury to artery or arteriole causes
muscle contraction reducing blood loss (vasospasm)
decrease in stimulation or presence of certain chemicals causes
vasodilation
Structure of Arteries:
thick-walled elastic, muscular vessels that take blood from the heart under pressure
Two types of arteries:
- Elastic (connecting) arteries: thick tunica media and both elastic lamina. Ex.: pulmonary, aorta. Stretches, then pushes blood away from the heart.
- Muscular (distributing) arteries: thick muscle, low elastic, high collagen = regulation of blood pressure & direction, but do not aid in propelling flow.
Structure of Arterioles
Small arteries delivering blood to capillaries
Metarterioles form branches into capillary bed
Structure of Capillaries:
endothelial cell layer only; no tunica media or externa. Desmosomes, tight jcns, but also intercellular clefts between cells.
Types of capillaries:
- continuous: complete basement membrane. Most capillaries.
- fenestrated: pores in basement membrane. Increase fluid exchange in kidneys, sm. intestine, and choroid plexes.
- sinusoid: gaps in basement membrane. Allow cell crossing in bone marrow, liver, spleen.
Structures of Venules:
Essentially the reverse of arterioles, but no bordering muscular sphincter.
Two types of venules:
- post capillary venule: larger than capillary but very loose intercellular endothelial connections allow continued exchange of nutrients, gasses, wastes, etc. No sphincter.
- muscular venules: muscle fibers surround thickened endothelium; exchange no longer occurs
Structure of Veins:
Like arteries, 3 tunics, but
tunica interna and tunica media are much thinner
elastic layers missing
blood with little pressure
veins in extremities have valves to aid return
more veins than arteries, often with interconnected superficial and deep or paired, connected veins following artery
venous sinuses =
no tunica media & externa; bordered by connective tissue.
Vein valve function:
movement against gravity
Varicose Veins:
- Twisted, dilated superficial veins (caused by leaky venous valves, allow backflow and pooling)
- Deeper veins not susceptible because of support of surrounding muscles
Capillary Exchange
1.Movement of materials in and out of a capillary
2.Oxygen, carbon dioxide, nutrients,
and metabolic wastes diffuse
between the blood and interstitial
fluid along concentration gradients
3. 3 Mechanisms
3 mechanisms
Diffusion
Transcytosis
Filtration and Reabsorption
Diffusion
- Most important mechanism
- Substances move down concentration gradient
- Lipid soluble substances
- Insoluble substances
Transcytosis
Passage of material across endothelium in tiny vesicles by endocytosis and exocytosis
Bulk Flow: Filtration and Reabsorption
- Movement of large amount of dissolved or suspended material in same direction
- Move in response to pressure - from area of high pressure to area of low
- Regulates relative volumes of blood & interstitial fluid
- Comprised of: filtration (movement of material into interstitial fluid) + reabsorption
