Biology A&P- Blood Vessels

Describe how blood pressure differs in the arteries, capillaries, and veins.

Arteries - must be able to endure high pressure of blood, from the aorta to the ends of the arterioles is about 60 mm Hg. Capillaries - fragile and high pressures would rupture them, and most capillaries are extremely permeable and thus even the low capillary pressure forces solute. Venous blood pressure is steady and changes very little during the cardiac cycle. The pressure gradient in the veins, from venules to the termini of the venae cavae, is only about 15 mm Hg.

Trace the pathway of blood through the pulmonary circuit, and state the importance of this special circulation.

Iron poor blood returns from the systemic circuit to the right atrium, pumped through the tricuspid valve into the right ventricle. The right ventricle pumps the blood through the pulumonary valve into the pulmonary trunk to the lungs. Carbon dioxide is exchanged is released and oxygen is picked up in the lungs. The blood then moves through the pulmonary veins and into the left atrium to be pumped through the systemic system.

Describe the general functions of the systemic circuit.

The general function of the systemic system is to pump oxygenated blood to all the tissues of the body. Pick up cell waste in the tissue and return it to the heart.

Describe the structure and special function of the hepatic portal system.

The hepatic portal system carries nutrient-rich blood (which may also contain toxins and microorganisms) from the digestive organs to the liver; where it can be "treated" before it reaches the rest of the body. As the blood percolates slowly through the liver sinusoidal capillaries, hepatocytes process nutrients and toxins, and phagocytic cells rid the blood of bacteria and other foreign matter.

Describe the structure and function of veins, and explain how veins differ from arteries.

Tunica Adventitia: This is the strong outer covering of arteries and veins which consists of connective tissues, collagen and elastic fibres. Tunica Media: This is the middle layer and consists of smooth muscle and elastic fibres. This layer is thinner in veins. Tunica Intima: This is the inner layer which is in direct contact with the blood flowing through the vein. It consists of smooth endothelial cells. The hollow centre through which blood flows is called the lumen. Veins also contain valves which prevent the backflow of blood and aid venous return.

Define vasoconstriction and vasodilation.

•Vasoconstriction - reduction in lumen diameter as the smooth muscle contracts. •Vasodilation - increase in lumen diameter as the smooth muscle relaxes.

List and explain the factors that influence blood pressure, and describe how blood pressure is regulated.

-Heart, blood vessels and kidneys work together to regulate blood pressure. Brain supervises and regulates as well. -Short term BP regulation: neural and hormonal controls; when there are fluctuations in BP, PR and CO are altered as a response. -Long term BP regulation: renal controls; the kidneys alter blood volume when there are changes in BP. -Factors that influence blood pressure = Cardiac Output (CO), peripheral resistance (PR), and blood volume.

Compare and contrast the structure and function of the three types of arteries.

1. Elastic Arteries: largest in diameter, most elastic. Larger lumens --> low resistance pathways --> conduct blood from heart to med-sized arteries. "pressure reservoirs"; expand/recoil as blood is pumped from the heart. 2. Muscular Arteries: "distributing arteries"; medium sized lumens (smaller than elastic but larger than arterioles), largest tunica media of the 3 artery types. Active in vasoconstriction. 3. Arterioles: "resistance vessels". Smallest of all the arteries; small arterioles lead into capillary beds and is composed of smooth muscle (use vasodilation and vasoconstriction to control flow into capillary beds).

Provide examples of changes that often occur in blood vessels as a person ages.

As you age, so do your blood vessels. They become less flexible, making it harder for blood to move through them easily. Fatty deposits called plaques also collect along your artery walls and slow the blood flow from the heart.

Define blood flow, blood pressure, and resistance, and explain the relationships between these factors.

Blood flow - is the volume of blood flowing through a vessel, an organ, or the entire circulation in a given period (ml/min). Blood pressure (BP)- the force per unit area exerted on a vessel wall by the contained blood, is expressed in millimeters of mercury (mm Hg). Resistance - is opposition to flow and is a measure of the amount of friction blood encounters as it passes through the vessels. Blood flow (F) is directly proportional to the difference in blood pressure (ΔP) between two points in the circulation, that is, the blood pressure, or hydrostatic pressure, gradient. Thus, when ΔP increases, blood flow speeds up, and when ΔP decreases, blood flow declines. Blood flow is inversely proportional to the peripheral resistance (R) in the systemic circulation; if R increases, blood flow decreases. These relationships are expressed by the formula F=∆P/R.

Define circulatory shock. List several possible causes.

Circulatory shock is defined as an inadequate blood flow throughout the body. In the absence of mechanisms that function to maintain blood pressure within a normal range of values, blood pressure decreases dramatically. Consequently, tissues can suffer from damage as a result of too little delivery of oxygen to cells. Severe circulatory shock can damage vital body tissues to the extent that death of the individual occurs.

Describe the three layers that typically form the wall of a blood vessel, and state the function of each.

Tunica Intima - the innermost tunic, in intimate contact with the blood in the lumen. This tunic contains the endothelium, the simple squamous epithelium that lines the lumen of all vessels.lium. forms a slick surface that minimizes friction as blood moves through the lumen. Tunica Mediais - the middle tunic, mostly circularly arranged smooth muscle cells and sheets of elastin, the bulkiest layer in arteries chief responsibility for maintaining blood pressure and continuous blood circulation. The activities of the tunica media are critical in regulating circulatory dynamics because small changes in vessel diameter greatly influence blood flow and blood pressure. Tunica Externa - the outermost layer, is composed largely of loosely woven collagen fibers that protect and reinforce the vessel and anchor it to surrounding structures.

Explain how blood flow is regulated in the body in general and in specific organs.

•Autoregulation is the automatic adjustment of blood flow to each tissue in proportion to its needs and is controlled intrinsically by modifying the diameter of local arterioles. •Metabolic controls of autoregulation are most strongly stimulated by a shortage of oxygen at the tissues. •Myogenic control involves the localized response of vascular smooth muscle to passive stretch. •Long-term autoregulation develops over weeks or months and involves an increase in the size of existing blood vessels and an increase in the number of vessels in a specific area, a process called angiogenesis.

Explain how blood vessels develop in the fetus.

•Blood vessels begin to form from the embryonic mesoderm.

Describe the structure and function of a capillary bed.

•Capillaries Continuous Capillaries - abundant in the skin and muscles, are most common. They are continuous in the sense that their endothelial cells provide an uninterrupted lining, adjacent cells being joined laterally by tight junctions Fenestrated Capillaries - similar to the continuous variety, except that some of the endothelial cells in fenestrated capillaries are riddled with oval pores, or fenestrations. Sinusoids Capillaries - are highly modified, leaky capillaries found only in the liver, bone marrow, spleen, and adrenal medulla. •Terminal Arteriole - feeds the capillary bed •Metarteriole - a vessel structurally intermediate between an arteriole and a capillary •True Capillaries number 10 to 100 per capillary bed, depending on the organ or tissues served. They usually branch off the metarteriole. •Precapillary Sphincter - surrounds the root of each true capillary at the metarteriole and acts as a valve to regulate blood flow into the capillary. •Thoroughfare Channel - intermediate between a capillary and a venule. •Venules - are formed when capillaries unite. Postcapillary Venules - the smallest venules, consist entirely of endothelium around which pericytes congregate. They are extremely porous and fluid and white blood cells move easily from the bloodstream through their walls. The larger venules have one or two layers of smooth muscle cells (a scanty tunica media) and thin externa as well.

Define hypertension. Describe its manifestations and consequences.

•Hypertension - high blood pressure, a condition of sustained arterial pressure of 140/90 or higher, and the higher the pressure, the greater the risk for serious cardiovascular problems. Causes: Hereditary, diet, age, and stress. Consequences: Untreated hypertension can lead to various organ damage (so-called end-organ damage). Heart, brain, kidneys, blood vessels and eyes are particularly vulnerable.

Define and hypotension. Describe its manifestations and consequences.

•Hypotension- low blood pressure - Systolic pressure below 100 mm Hg - Often associated with long life and lack of cardiovascular illness •Orthostatic hypotension: temporary low BP and dizziness when suddenly rising from a sitting or reclining position. - Chronic hypotension: hint of poor nutrition and warning sign for Addison's disease or hypothyroidism. - Acute hypotension: important sign of circulatory shock.

Name and give the location of the major arteries and veins in the systemic circulation.

•Major Arteries Aorta - supplies the upper body, arches and descends past the diaphragm into the abdominal aorta supplying the lower body. Common Carotid Arteries - supplies the head Subclavian Arteries - supplies the upper limb Internal Iliac Arteries - branches into the femoral arteries that supply the lower limb. •Major Veins Femoral Veins - drains into the External Iliac veins to drain the lower limbs. Inferior Vena Cava - drains the lower body Cephalic Veins and the Basilic Veins - drain into the subclavian veins to drain the upper limb. Internal and External jugular veins drain the head Superior Vena Cava - drains the upper body into the heart.

Outline factors involved in capillary dynamics, and explain the significance of each.

•Vasomotion, the slow, intermittent flow of blood through the capillaries, reflects the action of the precapillary sphincters in response to local autoregulatory controls. •Capillary exchange of nutrients, gases, and metabolic wastes occurs between the blood and interstitial space through diffusion. •Hydrostatic pressure (HP) is the force of a fluid against a membrane. •Colloid osmotic pressure (OP), the force opposing hydrostatic pressure, is created by the presence of large, nondiffusible molecules that are prevented from moving through the capillary membrane. •Fluids will leave the capillaries if net HP exceeds net OP, but fluids will enter the capillaries if net OP exceeds net HP.