General Anatomy -Cardiovascular System
Q. What are the components of the cardiovascular system?
A. Cardiovascular system includes heart and blood vessels i.e. arteries, arterioles, capillaries, venules and veins.
Q. What are the different types of circulation?
A. a. Systemic circulation: It is responsible for transporting oxygenated blood through arteries to the entire body and then returns deoxygenated blood to the heart via veins. The circulation of blood flow is as follows:
b. Pulmonary circulation: It consist of that part of circulatory system which pumps deoxygenated blood to the lungs and returns oxygenated blood to the heart. The circulation of blood flow is as follows:
c. Portal circulation : It is part of systemic circulation. The blood passes through two sets of capillaries,the circulation begins with capillaries and ends with capillaries. The vessel between the two sets of capillaries is known as portal vein. Portal circulation is found at the following sites:
a. Hepatic portal system – between intestines and liver.
b. Renal portal system – in the kidney.
c. Hypothalamo-hypophyseal system – between hypothalamus and hypophysis cerebri.
d. Suprarenal portal system – between the cortex and medulla of adrenal gland.
Q. Enumerat the:
a. types of arteries and write examples of each.
b. avascular tissues or structures.
c. structures/organs supplied by end arteries.
d. types of capillaries with examples of each.
e. sites where sinusoids are found.
f. factors responsible for venous return.
g. sites where arterial pulsation is felt.
h. sites where arteriovenous anastomoses are found.
i. end arteries.
A. a. Types of arteries:
• Elastic /conducting arteries. e.g. aorta, pulmonary trunk.
• Muscular/distributing arteries . e.g. radial artery, femoral artery etc.
b. Avascular tissues/structures:
• Epidermis of skin
c. Structures or organs supplied by end arteries:
d. Types of capillaries:
a. Continuous capillaries : e.g. in muscle, brain, connective tissue, skin, lung.
b. Fenestrated capillaries . e.g. in endocrine glands, intestinal villi, renal glomeruli.
e. Sites where sinusoids are found:
• Bone marrow
• Anterior pituitary gland
f. Factors responsible for venous return:
• Contraction of muscles
• Presence of valves in the veins
• Negative intrathoracic pressure
• Pulsation of arteries
g. Sites where arterial pulsations can be felt:
• Carotid artery – along the anterior border of sternocleidomastoid muscle at the level of cricoids cartilage.
• Brachial artery – In front of the elbow medial to the tendon of biceps brachii.
• Radial artery – lateral side of front of forearm at wrist
• Femoral artery – below the inguinal ligament at midinguinal point
• Popliteal artery – in the popliteal fossa
• Dorsalis pedis artery – on the dorsum of foot between the tendon of extensor hallucis longus and extensor digitorum longus.
h. Sites where arteriovenous anastomoses are found
- Skin of nose,lips, external ear
- Nasal mucosa
- Erectile tissue of sex organs.
i. End arteries.
Q. Describe in brief the characteristic features and functions of the arteries,arterioles, capillaries venules and veins.
|Arteries||The walls of arteries contain smooth muscle fibers that contract and relax under the control of the sympathetic nervous system.||Transport blood away from the heart Transport oxygenated blood only (except in the case of the pulmonary arteries).|
|Arterioles||Arterioles are smaller branches (diameter < 1mm.) of arteries that lead to capillaries. These are also under the control of the sympathetic nervous system, and constrict and dilate, to regulate blood flow (Also known as resistance vessels).||Transport blood from arteries to capillaries. Are the main regulators of blood flow and pressure.|
|Capillaries||There is network of capillaries in most of the organs and tissues of the body. They receive blood from the arterioles and are drained by venules. Capillary walls are only one cell thick (endothelium), (Also known as exchange vessels)||Exchange of oxygen, carbon dioxide, water, salts, etc., between the blood and the surrounding body tissues.|
|Venules||Venules are the vessels that drain blood from capillaries and into veins. Many venules unite to form a vein.||Drains blood from capillaries into veins.|
|Veins||The walls of veins are thinnerand less elastic than the corresponding layers of aerteries. They contain valves that aid the return of blood to the heart by preventing blood from flowing in the reverse direction.||Transport blood towards the heart. Transport deoxygenated blood only (except in the case of the pulmonary vein).|
Q. Enumerate the differences between the arteries and veins.
|Transport blood away from the heart||Transport blood towards the heart;|
|Carry Oxygenated Blood (except in the case of the Pulmonary Artery)||Carry De-oxygenated Blood (except in the case of the Pulmonary Vein)|
|Have relatively narrow lumens;||Have relatively wide lumens .|
|Have relatively more muscle/elastic tissue||Have relatively less muscle/elastic tissue;|
|Transports blood under higher pressure (than veins)||Transports blood under lower pressure (than arteries);|
|Do not have valves .||Have valves to prevent blood flowing in the reverse direction.|
A. Differences between the arteries and veins
Q. Explain the following terms.
a. End arteries
b. Functional arteries
d. Collateral circulation
A. a. End arteries : End arteries are those arteries that do not anastomose with their neighbouring arteries. In case of blockage of an end artery due to a thrombus, the part supplied by it undergoes ischemia and later avascular necrosis. e.g. in kidneys, brain and retina.
b. Functional end arteries: Functional arteries are those arteries whose terminal branches do anastomose, but the anastomosis is not sufficient to maintain the blood supply to the part they supply in case of any blockage in the artery. e.g. coronary arteries.
c. Anastomosis : Anastomosis is defined as communication between the neighbouring blood vessels. It is of two types:
i. Arterial anastomosis : The branches of an artery are connected to the branches of another neighbouring artery. The anastomosis provide collateral channel for circulation when one of the arteries is blocked. e.g. labial branches of facial arteries, intercostals arteries, uterine and ovarian arteries, arterial arcades in the mesentery of intestine etc. They are of two types:
- Actual anastomosis: In actual arterial anastomosis the arteries meet end to end, e.g. palmar and plantar arches, circle of Willis, intestinal arcades, labial branches of facial arteries.
- Potential anastomosis: In potential arterial anastomosis the communication occurs between the terminal arterioles. On sudden occlusion of a main artery such anastomosis may not provide sufficient collateral circulation these anastomoses dilate gradually over a period of time for collateral circulation,e.g e coronary arteries.
ii. Arteriovenous anastomosis: The direct connection between the arteries and veins without the intervention of capillaries is termed arteriovenous anastomosis. Their function is to regulate temperature and regional blood flow. When the organ is active these shunts are closed and the blood passes through the capillaries. However, when the organ is not active, the blood bypasses the capillary bed and is shunted through the arteriovenous anastomosis. They are found in the lip, ear, nose, nasal mucosa, kidney , intestine etc.
d. Collateral circulation: Collateral circulation is possible when an area of tissue or an organ has a number of different pathways for blood to reach it. This is as a result of anastomosis formed between adjacent blood vessels. In this process small (normally closed) arteries open up and connect two larger arteries or different parts of the same artery and serve alternate route of blood supply.