Bsci202 lab practical 2

Blood Vessels

Overview

The circulatory system is a closed transport system that consists of the heart, arteries, arterioles, capillary beds, venules, veins, and back to the heart. Nutrients and oxygen diffuse from the blood into the tissues, while waste products like carbon dioxide diffuse from the tissues back into the blood.

Microscopic Structure of Blood Vessels

Blood vessels are composed of three tunics that surround the lumen:

  1. Tunica intima/interna

    • Innermost layer

    • Consists of a thin layer of endothelial cells with a connective tissue (CT) basement membrane.

  2. Tunica media

    • Middle layer

    • Made of circularly arranged smooth muscle and elastic connective tissue, allowing for changes in lumen diameter.

  3. Tunica adventitia/externa

    • Outermost layer

    • Protects and anchors the vessels, consists of areolar or fibrous connective tissue.

Types of Blood Vessels

  • Arteries: Transport blood away from the heart. They expand during systole and recoil passively during diastole. There are three main types of arteries:

    • Elastic arteries: Largest, located close to the heart; serves as conducting vessels that are highly expandable.

    • Muscular arteries: Medium-sized and distribute blood to specific body areas.

    • Arterioles: Smallest arteries that act as resistance vessels.

  • Capillaries: The smallest blood vessels. They are composed of a single layer of endothelial cells, facilitating the exchange of materials such as oxygen, nutrients, and waste products.

  • Veins: Transport blood toward the heart and contain about 65% of the total blood volume. They operate at low pressure and have thinner walls with large lumens. Adaptations for venous return include:

    • Valves: Formed by folds of the tunica intima to prevent backflow, particularly concentrated in the limbs.

    • Skeletal muscle pump: Skeletal muscle contractions help squeeze veins and assist venous return.

    • Respiratory pump: Inhalation decreases intrathoracic pressure and increases intra-abdominal pressure, promoting blood flow from abdominal veins to thoracic veins.

The Aorta

The aorta is the largest artery in the body, originating from the left ventricle of the heart. It can be divided into several regions:

  • Ascending aorta: Leaves the left ventricle.

  • Aortic arch: Arches to the left.

  • Thoracic aorta: Descends through the thorax.

  • Abdominal aorta: Passes through the diaphragm into the abdominopelvic cavity.

Arterial Branches of the Aorta

  • Ascending aorta:

    • Right and left coronary arteries supply blood to the heart.

  • Aortic arch:

    • Brachiocephalic trunk: Splits into right common carotid artery and right subclavian artery.

    • Left common carotid artery: Splits into left internal and external carotid arteries.

    • Left subclavian artery: Becomes the axillary artery, then branches into the brachial artery, further dividing into radial and ulnar arteries.

  • Descending thoracic aorta:

    • Intercostal arteries supply the thorax wall.

    • Bronchial arteries supply the lungs.

    • Esophageal arteries serve the esophagus.

    • Phrenic arteries serve the diaphragm.

  • Abdominal aorta:

    • Celiac trunk: First branch, splits into left gastric, splenic, and common hepatic arteries.

    • Superior mesenteric artery: Supplies most of the small intestine and the first half of the large intestine.

    • Renal arteries: Serve the kidneys.

    • Gonadal arteries: Ovarian in females and testicular in males.

    • Lumbar arteries: Supply the abdominal wall and trunk muscles.

    • Inferior mesenteric artery: Supplies the second half of the large intestine.

    • Common iliac arteries: Final branches of the aorta, subdividing into internal and external iliac arteries, leading into the thigh via the femoral artery.

Special Circulations

Coronary Circulation

  • The heart has its own circulatory system consisting of coronary arteries that branch from the aorta, supplying oxygenated blood to the myocardium. Cardiac veins drain the myocardium, converging into the coronary sinus (a large vein) that empties into the right atrium.

Pulmonary Circulation

  • Involves the capillary beds around alveoli for CO2 and O2 exchange, with bronchial arteries providing nourishment to lung tissue.

Hepatic Portal System

  • Veins from the digestive organs and spleen drain into the hepatic portal vein which carries nutrient-rich blood to the liver for processing and detoxification. Key vessels include:

    • Inferior and superior mesenteric veins

    • Splenic vein

    • Left gastric vein

Cerebral Circulation

  • Known as the circle of Willis, it includes anterior and middle cerebral arteries from the internal carotid arteries and posterior cerebral