4.4 - STRUCTURE OF BLOOD VESSELS, FUNCTION AND CIRCULATORY ROUTE

10. Explain the role of the Cardiovascular Center in regulation of blood receptor below; (a) Baroreceptors (4m) (b)Chemoreceptor Reflexes (4m)

(a) Baroreceptors (4m) A group of blood pressure-sensitive neurons in the arch of the aorta & carotid artery. When blood pressure increases, the baroreceptors are stretched more tightly and initiate action potentials at a higher rate. At lower blood pressures, the degree of stretch is lower and the rate of firing is slower. When the cardiovascular center in the medulla oblongata receives this input, it triggers a reflex that maintains homeostasis. (b)Chemoreceptor Reflexes (4m) Chemoreceptor Reflexes are monitoring blood chemistry changes (CO2, O2, H + concentrations). Peripheral chemoreceptors (carotid and aortic bodies) and central chemoreceptors (medullary neurons) primarily function to regulate respiratory activity. This is an important mechanism for maintaining arterial blood PO2, PCO2, and pH within appropriate physiological ranges. For example, a fall in arterial PO2 (hypoxemia) or an increase in arterial PCO2 (hypercapnia) leads to an increase in the rate and depth of respiration through activation of the chemoreceptor reflex.

12. Explain Regulation of venous return ; (a) contraction of the heart (2m) (b) Skeletal muscle pump (3m) (c) Respiratory pump (2m)

(a) contraction of the heart (2m) The Heart must be working efficiently to pump blood out of the veins and maintain CVP. Rate the heart pumps blood out are linked to the cardiac output of the heart. (b) Skeletal muscle pump (3m) Peripheral veins work in concert with the muscular contraction to increase venous return to the heart. When muscles (such as the quadriceps) contract (during walking, running etc), the valves are forced open to increase the venous return. (c) Respiratory pump (2m) During inspiration, venous return increases as the pressure in the thoracic cavity becomes more negative. This reduced intrathoracic pressure draws more blood into the right atrium.

7. Describe the Blood Circulatory Routes below; (a) systemic circulation (2m) (b) pulmonary circulation (2m) (c) hepatic portal circulation (1m)

(a) systemic circulation (2m) · Oxygenation of blood from the left ventricle through the aorta directly to the body tissue & the deoxygenated blood returns from the body tissue through the vein to the right atrium (b) pulmonary circulation (2m) · Oxygen circulation from the right ventricle to the lungs through the pulmonary artery & Oxygen return from the lungs to the left atrium through the pulmonary vein (c) hepatic portal circulation (1m) · Oxygenated blood circulation, rich in nutrients from the gastrointestinal (GIT) organs.

1. All arteries carry oxygenated blood except for the pulmonary artery. Describe the structure and function of Elastic Arteries. (6m)

Largest; conducting arteries. -Characteristics: · Large Diameter, Thin wall · More elastic fiber less smooth muscle · Connecting heart to medium · Easily expand: cope with blood pressure pumped from the heart. . Function: helps transport blood throughout the body. Ø Structure : Elastic arteries contain larger numbers of collagen and elastin filaments in their tunica media than muscular arteries do, giving them the ability to stretch in response to each pulse. Elastic arteries include the largest arteries in the body, those closest to the heart, and give rise to the smaller muscular arteries. Ø Function : maintain continuous flow of blood away from the heart.

11. Explain hormonal regulation of blood pressure below; a) Renin angiotensin aldosteron system (4m) b) Epinephrine and Norepinephrine (3m) c) Antidiuretic hormoen (ADH) (2m)

a) Renin angiotensin aldosteron system (4m) The renin-angiotensin-aldosterone system (RAAS) plays an important role in regulating blood volume and systemic vascular resistance, which together influence cardiac output and arterial pressure. As the name implies, there are three important components to this system: 1) renin, 2) angiotensin, and 3) aldosterone. Renin, which is released primarily by the kidneys, stimulates the formation of angiotensin in blood and tissues, which in turn stimulates the release of aldosterone from the adrenal cortex. b) Epinephrine and Norepinephrine (3m) Norepinephrine generally results in increased vasoconstriction while epinephrine results in the dilation of vessels adjacent to muscle cells. Both epinephrine and norepinephrine increase heart rate. During a bout of exercise, epinephrine exerts a significant vasodilatory effect on the blood vessels associated with the skeletal muscles. Corticosteroids, including cortisol, also have an effect on blood pressure. Without the presence of cortisol, the influence of epinephrine and norepinephrine upon vascular c) Antidiuretic hormoen (ADH) (2m) ADH constantly regulates and balances the amount of water in your blood. Higher water concentration increases the volume and pressure of your blood. Osmotic sensors and baroreceptors work with ADH to maintain water metabolism

8. Blood Pressure is Hydrostatic pressure that is applied by the blood to the blood vessel wall. Describe a) Systolic Blood Pressure (2m) b) Diastolic Blood Pressure (2m)

a) Systolic Blood Pressure (2m) · Peak pressure (highest) on artery during systolic; the heart contracted. · The normal systolic BP value for adults under rest is 120mmHg b) Diastolic Blood Pressure (2m) · Low arterial pressure during diastol (heart rest) · The normal diastolic BP value for adults under rest is 80mmHg.

2. Describe the structure and function of Muscular arteries. (5m)

Ø Structure : A muscular artery (or distributing artery) is a medium-sized artery that draws blood from an elastic artery and branches into "resistance vessels" including small arteries and arterioles. Their walls contain larger number of smooth muscles, allowing them to contract and expand depending on peripheral blood demand. Ø Function : helps carry & distribute blood throughout the body

3. Describe the structure and function of Arterioles.(4m)

Ø Structure : Arterioles have muscular walls and are the primary site of vascular resistance, which reduces the pressure and velocity of flow for gas and nutrient exchange to occur within the capillaries. Ø Function : regulates blood flow from artery to capillary by controlling resistance

4. Capillaries is the smallest blood vessels. Describe the structure and function of Capillaries. (7m)

Ø Structure : Capillaries are very tiny blood vessels. It is so small that a single red blood cell can barely fit through them. Capillaries are composed of only two layers of cells, an inner layer of endothelial cells and an outer layer of epithelial cells. They are so small that red blood cells need to flow through them single file. Ø Function : Exchanges of gas, nutrients & metabolic waste

5. Veins is the blood vessels that enter the heart. Describe the structure and function of vein. (4m)

Ø Structure : Structure of a vein, which consists of three main layers. The outer layer is connective tissue, called tunica adventitia or tunica externa, a middle layer of smooth muscle called the tunica media, and the inner layer lined with endothelial cells called the tunica intima. Ø Function : Transport blood to the heart from all body parts.

6. Describe the structure and function of venules. (3m)

Ø Structure : Venule walls have three layers: An inner endothelium composed of squamous endothelial cells that act as a membrane, a middle layer of muscle and elastic tissue and an outer layer of fibrous connective tissue. The middle layer is poorly developed so that venules have thinner walls than arterioles. Ø Function : Transport blood from the capillaries to the veins to return it to the heart

9. Explain 3 factors affecting blood pressure. (6m)

• Cardiac Output It is the volume of blood pumped from the left ventricle to the right ventricle @ pulmonary artery in one minute. If cardiac output increases, blood pressure also increases. • Blood Volume The volume of blood in the body can decrease & increase. Volume decreases - hemorrhage. - Increased volume - water retention - As blood volume increases, blood pressure increases. • Vascular resistance Obstruction to blood flow due to friction between blood & blood vessels. Depending on: The size of the lumen of the blood vessels, Blood viscosity, Length of blood vessels.