3.1.2 Transport in Animals

• What is the function of veins?

  • return blood to the heart
  • mostly carries deoxygenated blood
• What is the function of venules?

  • return blood to the heart
  • connect the capillaries to veins
• What is the function of capillaries?

  • connect arterioles and venules
  • allow the exchange of substances with cells
• What is the function of arterioles?

  • carry blood from the heart
  • connect arteries to capillaries
• What is the function of arteries?

  • carry blood from the heart
  • mostly carry oxygenated blood
• What are the four types of tissue in a blood vessel?

  • endothelium
  • smooth muscle
  • elastic fibres
  • connective tissue with collagen fibres
• What is the structure and function of endothelium tissue in a blood vessel?

  Structure:

  • single layer of thin squamous cells

  Properties:

  • smooth- minimises friction
  • thin- can be a good exchange surface
  • can be gaps between cells for filtration and to allow white blood cells to exit

  Function:

  • line the circulatory system allowing blood flow
  • exchange of substances into fluid surrounding cells
• What is the structure and function of smooth muscle in a blood vessel?

  Structure:

  • overlapping muscle cells (not striated like skeletal muscle)

  Properties:

  • contracts or relaxes, which alters the lumen size

  Function:

  • particularly important in arterioles to adjust blood flow through vasoconstriction or vasodilation
• What is the structure and function of elastic fibres in a blood vessel?

  Structure:

  • made of elastin proteins

  Properties:

  • can stretch coping with high blood pressure
  • can recoil, maintaining blood pressure

  Function:

  • flexibility in vessel walls
  • particularly important in arteries, to even out surges in blood flow
• What is the structure and function of connective tissue with collagen fibres in a blood vessel?

  Structure:

  • a few cells embedded into a matrix containing collagen fibres

  Properties:

  • inelastic
  • flexible
  • high tensile strength

  Function:

  • prevents blood vessels increasing in diameter too much when blood pressure is high
  • protects blood vessels from physical damage (e.g. rubbing against other organs)
• What types of tissues are in arteries?

  • endothelium
  • smooth muscle
  • elastic fibres
  • connective tissue with collagen fibres
• What types of tissue are in capillaries?

  • endothelium
• What types of tissue are in veins?

  • endothelium
  • smooth muscle
  • elastic fibres
  • connective tissue with collagen fibres
• What is the role of arteries?

  arteries carry blood away from the heart (high pressure, pulsing). they need to be able to withstand pressure so that they maintain the flow and direction of blood.
• What is the role of arterioles?

  arterioles can alter blood flow to particular tissues by vasoconstriction or vasodilation by contracting or relaxing the smooth muscle to change the diameter of the lumen.
• What is vasoconstriction and vasodilation caused by?

  Vasoconstriction:

  • high oxygen concentration
  • low carbon dioxide concentration
  • cold

  Vasodilation:

  • low oxygen concentration
  • high carbon dioxide concentration
  • heat
• What is the role of capillaries?

  capillaries link arterioles to venules and are the exchange surface where substances move by diffusion from the blood into surrounding cells or from surrounding cells into the blood.
• What is the role of veins?

  veins carry low pressure blood towards the heart. veins have valves to prevent the backflow of low pressure blood. valves are not actively controlled by muscles and they work by relative pressure differences. contraction of skeletal muscles squeezes veins forcing blood through. a negative pressure in the chest cavity from breathing also aids blood flow back to the heart.
• Artery

  • blood flows away from the heart to body tissues (oxygenated) and to the lungs (deoxygenated)
  • lumen diameter is smaller than in veins
  • high pressure and pulsating, due to the pumping action of the heart and lumen diameter
  • wall structure consists of large amounts of elastic tissue and smooth muscle
  • wall function: elastic tissue stretches under pressure. elastic recoil evens out the pulses of blood from heart beating
• Arteriole

  • blood flow is variable, as it is dependent on smooth muscle
  • relatively small lumen diameter
  • has high pressure at the artery end and relatively low pressure approaching the capillaries; the greatest drop in pressure
  • wall structure consists of very large amounts of smooth muscle tissue and less elastic tissue
  • wall function: smooth muscle controls blood flow to specific tissues through vasodilation or vasoconstriction
• Vein

  • blood flows from the capillary beds back towards the heart (deoxygenated except in pulmonary circuit)
  • lumen diameter in veins is larger than arteries, in order to return blood to the heart despite a slower flow
  • low pressure
  • unidirectional flow aided by valves, working skeletal muscles and inspiration
  • wall structure contains little elastic tissue and smooth muscle tissue and has thin muscular wall
  • wall function: maintain blood pressure and flow to return blood to the heart
• Capillary.

  • blood flows through tissue slowly allowing exchange of nutrients and gases with the surrounding tissues
  • lumen diameter is small to ensure short diffusion distance
  • has relatively low pressure, which is important for the creation of tissue fluid
  • walls of the capillary are one cell thick, which is made of squamous epithelium
  • wall function: endothelium provides a large surface area and short diffusion distance for exchange of substances with cells
• What are the three functions of blood in the body?

  • helps to maintain a steady body temperature
  • helps to maintain a steady pH, by acting as a buffer
  • blood is the transport medium of the circulatory system
• What is transported in the blood?

  • digested food
  • nitrogenous waste
  • hormones
  • white blood cells and antibodies
  • platelets
  • food molecules from storage compounds
  • oxygen
  • carbon dioxide
• Composition of blood: Plasma

  • plasma is a straw-coloured liquid
  • makes up 55% of blood
  • plasma made up of:
  • 91% water: for transport
  • 8% plasma proteins: maintains osmotic potential of the blood, has a role in blood clotting
  • <1% salts, dissolved gases, nutrients, etc: being transported to various locations
• What is the structure and function of red blood cells?

  • 44% of blood are composed of red blood cells

  Structure:

  • biconcave disc
  • no nucleus or organelles
  • flexible shape
  • contains haemoglobin

  Function:

  • maximum surface and volume for transport of oxygen and to aid in transport of carbon dioxide
• What is the structure and function of white blood cells?

  • less than 1% of the blood is composed of white blood cells

  Structure:

  • white blood cells made up of neutrophils and monocytes
  • neutrophils and monocytes have multi-lobed nuclei
  • has many lysosomes
  • white blood cells also consists of lymphocytes
  • lymphocytes are spherical with round nuclei

  Function:

  • neutrophils and monocytes: phagocytosis
  • lymphocytes: specific immunity- production of antibodies
• What is the structure and function of platelets?

  • less than 1% of the blood is composed of platelets

  Structure:

  • disc-shaped cell fragments
  • no nucleus

  Function:

  • clotting mechanism of the blood
• Outline the formation of lymph and Explain the importance of lymph.

  • some tissue fluid drains into the lymphatic vessels becoming lymph
  • lymph is similar to tissue fluid but more leucocytes and waste, and fewer nutrients
  • lymphatic system includes: lymph nodes, tonsils, thymus gland and spleen
  • lymph from lymphatic system drains excessive tissue fluid and has a role in defence against infection
  • lymph rejoins the circulatory system in the subclavian veins
• What is the purpose of tissue fluid?

  tissue fluid carries dissolved substances to the tissue cells.
• What is tissue fluid?

  tissue fluid is the solution that surrounds/bathes the cells of multicellular animals and allows exchange of substances with cells.
• Define ultrafiltration.

  ultrafiltration is the process by which blood plasma is filtered through the walls of the endothelium under pressure.
• What is oncotic pressure and How is it important in the formation of tissue fluid?

  Oncotic pressure is the tendency of water to move into the blood by osmosis as a result of the plasma protein concentration.

  The osmotic pressure (solute potential) created by an increased concentration of plasma proteins, i.e. albumin, in the plasma is called oncotic pressure.
• Calculating direction of flow: Filtration

  • arterial end net filtration pressure: +10 mm Hg
  • fluid exits capillary since hydrostatic pressure (35 mm Hg) is greater than blood colloidal osmotic pressure (25 mm Hg)
• Calculating direction of flow: No Net Movement

  • mid capillary net filtration pressure: 0 mm Hg
  • no net movement of fluid since the capillary hydrostatic pressure (25 mm Hg) is equal to the colloidal osmotic pressure (25 mm Hg)
• Calculating the direction of flow: Reabsorption

  • venous end net filtration pressure: -7 mm Hg
  • fluid re-enters the capillary since capillary hydrostatic pressure (18 mm Hg) is less than blood colloidal osmotic pressure (25 mm Hg)
• What is hydrostatic pressure and How is it involved in the formation of tissue fluid?

  Hydrostatic pressure is the pressure created by fluid within an enclosed system.

  When the blood reaches a capillary bed, it still has pressure from the contraction (systole) of the heart. The pressure of blood against vessel walls, generated by the heart is called hydrostatic pressure.
• Outline the process of the formation of tissue fluid. (Part one)

  • as blood flows into the arterial end of a capillary bed, it still has some pressure from the systole (contraction) of the heart
  • blood enters capillaries, hydrostatic pressure forces plasma out of capillaries through the endothelium by filtration
  • plasma (containing dissolved substances) passes out of small gaps in the endothelium of capillaries to become tissue fluid
  • substances dissolved in plasma diffuse to cells through the tissue fluid, but red blood cells and plasma proteins are too large to leave the capillaries
• Outline the process of the formation of tissue fluid. (Part two)

  • as blood flows towards the venous end of a capillary bed, the flow of water from plasma into tissue fluid means the plasma proteins are concentrated
  • concentration of plasma proteins increases osmotic potential and decreases water potential of blood compared to tissue fluid
  • this increases oncotic pressure, or tendency of water to move from tissue fluid into blood by osmosis
  • as oncotic pressure exceeds the hydrostatic pressure at the venous end of a capillary bed, the net movement of water by osmosis is back into capillary
• Outline the process of the formation of lymph.

  • remaining 10% of tissue fluid drains into lymph capillaries, then larger lymph vessels
  • lymph vessels have valves to prevent backflow
  • within the lymphatic system, there are lymph nodes at which phagocytosis occurs, and lymphocytes accumulate and produce antibodies during infection by a pathogen
  • lymph rejoins the circulatory system under the clavicle returning fluids and proteins to the blood