circulatory system

• The cardio-vascular system is a closed system of tubes which consist of heart and blood vessels.
• Heart is a muscular pump which propels the blood through the blood vessels up to a network of capillaries where gaseous exchange occurs.
• The blood vessels carry:

  1. Blood to the lungs for oxygenation
  2. Blood to the intestines for absorption
  3. Blood to the endocrine glands – hormones
  4. Blood to the kidneys, lungs and skin for excretion.
• 2 circuits

  Pulmonary Circulation:

  • Heart → Pulmonary Arteries (CO2) → Lungs → Pulmonary Veins (O2) → Heart.
  • Oxygenation and CO2 removal in the lungs.

  Systemic Circulation:

  • Heart → Arteries → Body Tissues and Organs → Superior/Inferior Vena Cava, Cardiac Veins → Heart.
  • Supplies oxygenated blood to the body and collects deoxygenated blood for reoxygenation.
• Fill in the blank (circuit)

  A) Pulmonary

  B) Systemic

  
• TYPES OF BLOOD VESSELS

  A) Artery

  B) Vein

  C) Capillary

  
• Fill in the blank

  A) oxygenated

  B) deoxygenated

  C) deeply

  D) superficial

  E) thick

  F) thin

  G) narrow

  H) wide

  I) low

  J) empty

  K) fountain

  
• Arteries

  • carry oxygenated blood away from the heart.
  • They have a smaller diameter and lumen compared to veins.
  • Arteries do not collapse after death due to thicker walls.
  • Blood spurts out when cut due to higher pressure.
  • Arteries lack valves.
• Types of Arteries:

  1. Elastic Arteries:

  • Arise directly from the heart and their main branches.

  1. Muscular Arteries:

  • most arteries in the body.

  1. Arterioles:

  • Smallest division of arteries.
  • Diameter is < 100 µm.
• Veins

  • carry deoxygenated blood to the heart.
  • They are more numerous than arteries.
  • Dark blue in color and do not pulsate.
  • Blood oozes out when cut.
  • Larger diameter and lumen compared to arteries.
  • Thinner walls and collapse after death.
  • Veins contain valves.
  • Venules collect blood from capillaries.
• Fill in the blank

  A) Elastic

  B) Muscular

  C) Arteriole

  D) venule

  
• Elastic Arteries includes:

  • Aorta and its three main branches (brachiocephalic, left common carotid, and left subclavian arteries).
  • Pulmonary trunk and right/left pulmonary arteries.
  • Its walls contain large amount of elastic fibers which permits elastic recoil
• Muscular Arteries

  • are branches and continuations of elastic arteries.
  • They end as arterioles.
  • Walls have a lower amount of elastic fibers.
  • Relatively more smooth muscle.
  • Examples include branches arising from the main arterial trunk.
• Arterioles

  • are the smallest division of arteries.
  • Diameter is < 100 µm (0.1 mm), similar to a thin thread.
  • Walls are relatively thick, and mostly composed of smooth muscle.
• Metarterioles

  • A vessel that emerges from an arteriole.
  • Traverses the capillary bed.
  • Empties into the venule.
• Capillaries

  • Form the communicating link between arterioles and venules.
  • Act as semi-permeable membranes.
  • Permit the exchange of small molecules.
  • Impermeable to large molecules.
• Capillaries

  Types:

  1. Continuous Capillaries:

  • Found in muscles.

  1. Fenestrated Capillaries:

  • Present in kidney, endocrine glands, and intestines.

  1. Discontinuous Capillaries or Sinusoids:

  • Located in the liver, spleen.
• Capillaries

  • Present in the greatest number in active tissues (muscles, glands, kidneys, and lungs).
  • Fewer in number in inactive tissues (tendons and ligaments).
  • Absent in cornea, epidermis, and hyaline cartilage.
• Fill in the blank

  A) Continuous

  B) Fenestrated

  C) Sinusoids

  
• 2 types of Veins:

  1. Superficial veins : run in the subcutaneous tissues.
  2. Deep veins : Medium sized arteries below the elbow and knees are accompanied by paired veins called venae commitantes
• Venous return to the heart

  1. The azygos system drains body walls.
  2. The portal system drains GIT
  3. The vertebral system vertebral column and its contents
• Valves are present in many veins.

  • When closed they prevent the reverse flow of blood.
  • are numerous in veins of the limbs; absent in most veins of the trunk (SVC, IVC) including the portal and vertebral systems.
• Communication between the neighboring vessels is called anastomoses.
• Circulation through the anastomosis is called collateral circulation.
• Arterial Anastomoses

  • Communication between arteries or branches of arteries.
  • Ex: Circle of Willis in the brain, coronary arteries in the heart.
• Venous Anastomoses

  • Communication between veins or tributaries of veins.
  • Ex: Dorsal venous arches of the hand and foot.
• Arteriovenous (A-V) Anastomosis (Shunt)

  • Communication between an artery and a vein.
  • Arterioles communicate directly with venules, bypassing the capillary bed.
• Arteriovenous (A-V) Anastomosis (Shunt)

  Function:

  • Prevents heat loss.
  • Increases the venous return.

  Sites:

  1. Palm, terminal phalanges, and nail bed.
  2. Skin of nose, lips, and eyelids.
  3. Tip of the tongue and intestines.
• Anatomical end artery

  • do not anastomose with neighbouring arteries.
  • Death of tissue occurs if this type of artery is occluded.
  • e.g central retinal artery of the eye.
• Functional end artery

  • An artery anastomosing so poorly with a neighboring artery that an adequate blood supply is not maintained after its occlusion.
  • E.g. Heart, kidney, brain, spleen and intestines
• Fill in the blank

  A) anatomical

  B) functional

  
• Varicose Veins in Weak Venous Valves:

  • Cause: Weak venous valves lead to blood backflow.
  • Effect: Increased venous pressure distends vein walls.
  • Result: Over time, walls lose elasticity, causing varicose veins.
  • Signs: Visible on skin, may cause discomfort.
  • Management: Includes lifestyle changes and medical interventions.
• Fill in the blank

  A) Heart

  B) Aorta

  C) Portal vein

  D) Brachial

  E) Radial

  F) Corotid

  G) retina

  H) Coronary

  
• Blood vessels have 3 layers

  1. The tunica intima (endothelium, subendothelial layer, internal elastic lamina )
  2. The tunica media
  3. The tunica adventiti
• Fill in the blank

  A) intima

  B) media

  C) adventitia

  
• The tunica intima →the elements of this layer lie longitudinally.

  • The endothelium : simple squamous epithelium, as a semipermeable barrier between the blood plasma and the interstitial fluid.
  • The subendothelial layer which is composed of fibroelastic tissue
  • The internal elastic lamina is the outermost covering of this layer.
• The tunica media

  • Vascular smooth muscle tissue is present in all vessels except capillaries and pericytic venules.
  • Smooth muscle cells are abundant.
  • Arranged in a circular pattern.
  • Often accompanied by elastic fibers.
• The tunica media

  Function:

  • Resists distension of the vessel.
  • Provides structural support.
• The tunica media

  Distribution:

  • Prominent in large arteries.
  • Elastic fibers distributed between muscle cells throughout the media.
• Tunica Adventitia in Blood Vessels:

  • Outermost layer of blood vessels.
  • Abundance of inextensible collagen fibers.
  • Collagen fibers are longitudinally arranged.