Gross Anatomy of the Circulation

Blood circulatory systems:

  • systemic

  • pulmonary

  • specialised circulatory systems

    • Portal system - double layer set of capillary beds. Lymphatic and Endocrine.

    • Coronary

    • Foetal

Function:

transport oxygen, nutrients, metabollic waste, hormones etc

Systematic Circulation:

  • high pressure system

  • takes oxygen rich blood from the left side of the heart to body tissues and returns oxygen poor blood to right side of the heart

  • most veins take the same name as corresponding artery with some exceptions eg vena cava

Finding a pulse: radial in the wrist, carotid in the neck, brachial, femoral in groin, popliteal, posterior tibial, dorsalis pedis…

Pulmonary circulation:

  • lower pressure system

  • takes blood low in oxygen from the right side of heart to lung

  • oxygen rich from lungs to left

  • pulmonary arteries are oxygen poor

  • pulmonary veins are oxygen rich

Lymphatic system

  • network of lymph vessels

  • lymph

  • lymphatic tissues and organs

Functions:

  • involved in defence mechanism

  • provides a mechanism for the drainage of interstitial fluid

Interstitial fluid:

  • fluid moves from arterial end of the capillary into the interstitial space and fluid moves from interstitial space back into the capillary at the venous end

  • capillary fluid is plasma, in interstitial fluid it is interstitial fluid

  • hydrostatic pressure moves the fluid out, taking nutrients and gases etc

  • blood colloid osmotic pressure draws the fluid back in, bringing wastes, gases etc - mainly due to plasma proteins

  • capillary blood pressure will decrease along the capillary

  • blood colloid osmotic pressure remains constant because of the plasma proteins

  • movement of fluid is due to net pressure

  • arterial end cbp > bcop so filtration

  • venous end bcop>cbp so reabsorption

85% of fluid is reabsorbed…

  • remainder must be removed - drained through lymph capillaries and is then called lymph

  • oedema is when this fluid is not drained

  • lymph passes through lymphatic circulation and returns to the blood system

  • lymph capillaries → lymph vessels → (lymph nodes filter the lymph along the way) → lymph trunks → drain into right lymphatic duct or thoracic duct

right lymphatic duct - lymph from the right side of head, thorax and right upper limb into right subclavian vein

thoracic duct drains lymph from the remainder of body into left subclavian vein

lymph re-enters the blood vascular circulation !

Lymphoid organs include the lymph nodes, thymus and spleen, fibrous connective tissue separates these organs from surrounding tissues

Tonsils - found in throat are small masses of lymphoid tissue - 4 in total, play an important role in immunity

Thymus - small organ under the sternum in the anterior of the chest composed of immature T cells

Spleen - located in the upper left of the abdomen which filters pathogens from the blood, also recycles old red blood cells

Inguinal lymph nodes - located in upper thigh that receive lymph fluid from nodes in the knee and surrounding regions

Popliteal lymph nodes - seven small nodes embedded in the popliteal fossa (behind the knee) drain lymphatic fluid from the knee to the lower leg. sends lymph to the inguinal lymph nodes in the groin through pumping action

Lymph Nodes

Lymphoid cells

  • immune system cells found in lymphoid tissues and the cells that support those tissues

  • phagocytes and lymphocytes

Lymphoid tissues

  • connective tissues dominated by lymphocytes

  • lymphoid nodule - lymphocytes are densely packed together in the area of areolar tissue

  • lymphoid nodes occur in connective tissue

  • tonsils are large lymphoid nodules in the walls of the pharynx (most ppl have 5) example of MALT

  • MALT - mucosa-associated lymphoid tissue - protect the epithelia of the digestive, respiratory, urinary and reproductive systems

  • dense connective tissue covers the lymph node

Lymph Nodes

  • kidney bean shaped

  • blood vessels and nerves reach the lymph node at the hilum

  • afferent lymphatics bring lymph to the lymph node from peripheral tissues

    • penetrate the capsule of the lymph node opposite to the hilum

  • efferent lymphatics exit the lymph node at the hilum and carry lymph away towards venous circulation

Lymph flow through nodes

  • first enters subcapsular space

  • flows through cortex of the node - contains B cells

  • continues through lymph sinuses towards paracortex - T cell domination

    • lymphocytes leave blood stream here and enter lymph node by crossing blood vessel walls

  • lymph follows through medulla - B cells and macrophages

  • dense lymphoid tissue is known as medullary cords between sinuses and medulla

Functions:

  • purifies the lymph before reaching the veins

  • early defense system

Thymus

primary lymphoid organ, atrophies later in life and becomes inactive by involution

Structure:

  • capsule that covers the thymus is divided into two thymic lobes, separated by fibrous partitions called septa - creating the two lobules

  • each lobule has an outer cortex densely packed with lymphocytes and paler central medulla

  • lymphocytes in the cortex are surrounded by epithelial reticular cells

  • in the medulla they create thymic corpuscles due to the concentric layers

Function:

  • contains actively dividing T cells

  • epithelial reticular cells maintain the blood-thymus barrier - separating T cells from the general circulation

  • mature T cells will leave the thymus cortex and enter the medulla

  • then can enter the bloodstream

Thymic hormones:

  • thymosin promotes development and maturation of T cells - contains several complementary hormones

  • thymosins is used to refer to all thymic hormones

  • thymopoietin stimulates production of T cells and stimulates the pituitary gland to release hormones

The Spleen

largest collection of lymphoid tissue in the body

Functions:

  1. removing abnormal blood cells by phagocytosis

  2. storing iron recycled from red blood cells

  3. initiating immune responses by B cells and T cells in response to antigens in circulating blood

Anatomy

  • attached to the lateral border of the stomach by the gastrosplenic ligament

  • splenic blood vessels and lymphatic vessels communicate with the spleen on the surface of the hilum

  • surrounded by a capsule containing collagen and elastic fibres

  • spleens of most mammals including cats and dogs have smooth muscle to allow contraction to pump blood around the body but human spleen lacks this

Pulp

  • red pulp contains large quantities of red blood cells - filtering the blood of antigens, microorgansims and worn out cells

    • metwork of reticular fibres

    • macrophages are scattered throughout

  • white pulp is composed of lymphatic tissue and lymphoctyes around arteries

    • resmbles lymphoid nodules

Passage of blood

  1. blood passes through reticular fibres of the red pulp

  2. enters large sinusoids

  3. sinusoid empty into small veins

  4. collect into trabecular veins that continue toward the hilum

Gives phagocytes the opp to identify and engulf damaged or infected cells

Rupture of the spleen

  • can tear easily

  • serious intern bleeding