Circulatory System of a Mammal

The Blood System The general pattern of blood circulation in a mammal. Names are required only of the coronary arteries and of blood vessels entering and leaving the heart, liver and kidneys. The structure of arteries, arterioles and veins in relation to their function. The structure of capillaries and their importance in metabolic exchange. The formation of tissue fluid and its return to the circulatory system.

Learning Objectives: How do large organisms move substances around their bodies? What are the features of the transport systems of large organisms? How is blood circulated in mammals?

Why do large organisms need a transport system? Increasing size = decrease in the SA to Volume ratio. Can no longer rely on simple diffusion and need to develop specialist exchange surfaces these are linked to transport systems.

Features of Transport Systems: A suitable medium in which to carry materials. A form of mass transport in which the transport medium is moved around in bulk over large distances. A closed system of tubular vessels that contains the transport medium.

Features of Transport Systems: A mechanism for moving the transport medium within vessels. Muscular contraction of the heart or body muscles. Passive processes such as evaporation in plants (see later lessons). A mechanism to maintain the mass flow in one direction. A mechanism of controlling the flow of the transport medium.

Transport System in Mammals: A suitable medium in which to carry materials - Blood A form of mass transport in which the transport medium is moved around in bulk over large distances. A closed system of tubular vessels that contains the transport medium – Blood vessels (arteries, veins and capillaries)

Transport System in Mammals: A mechanism for moving the transport medium within vessels - Muscular contraction of the heart A mechanism to maintain the mass flow in one direction – valves A mechanism of controlling the flow of the transport medium – heart rate, vasodilation, vasoconstriction

Single Circulation – e.g. fish Blood passes through heart ONCE per complete circuit Blood pressure reduced as blood passes through the gill capillaries - slows down flow to the rest of the body Limits the rate of delivery of O2 and nutrients to cells and removal of waste Efficient for the level of activity of fish but not mammals – also fish do not maintain their body temperature – need to respire relatively less compared to mammals Double Circulation – more efficient - e.g. mammals Heart is composed of two separate pumps – right side pumps blood to the lungs to pick up oxygen; the blood is returned to the left side; the left side pumps oxygenated blood rapidly and at high pressure to the body; the blood is returned to the right side Higher level of activity (energy) and need to maintain their body temperature at 370C – through respiration Need to deliver and remove materials to and from cells rapidly – achieved by delivering blood at high pressure to tissues. Pulmonary – oxygenates blood & removes CO2 Systemic – oxygenated blood from lungs pumped rapidly at an increased pressure by the heart Blood passes through heart TWICE per complete circuit

Questions: Name the blood vessel in each of the following descriptions: Joins the right ventricle to the capillaries of the lungs Carries oxygenated blood away from the heart Carries deoxygenated blood away from the liver The first main blood vessel that an oxygen molecule reaches after being absorbed from an alveolus Has the highest blood pressure

Questions: State two factors that make it more likely that an organism will have a circulatory pump such as the heart. What is the main advantage of the double circulation system found in mammals?

Blood Vessels and their Functions

Learning Objectives: What are the structures of arteries, arterioles and veins? How is the structure of each of the blood vessels related to its function? What is the structure of capillaries and how is it related to their function?

Blood Vessels Arteries: Carry blood away from the heart Arterioles: Control blood flow from arteries to capillaries Capillaries: Link arterioles to veins Veins: Carry blood towards the heart

Structure of Blood Vessels Tough outer layer – resists pressure Muscle layer – can contract and control the flow of blood Elastic layer – can stretch and recoil to maintain blood pressure Endothelium – smooth layer to prevent friction Lumen – not a layer – a cavity

Structure of Arteries Thick muscle layer – control the flow of blood Thick elastic layer – smooth surges from the heart No valves

Structure of Arterioles Thicker muscle layer than arteries Thinner elastic layer than arteries No valves

Structure of Veins Thin muscle layer Thin elastic layer Valves

Structure of Capillaries No muscle No elastic No valves Thin layer of cells only

Capillary Structure to Function Thin layer of cells – short diffusion distance. Numerous and highly branched – large SA for diffusion. Narrow diameter – keep all cells close by. Narrow lumen – bring RBC close to the cells = short diffusion distance. Spaces between cells – allow WBC to escape.

Capillary – endothelium – large number – large surface area for exchange Wall - one cell thick – short diffusion distance Endothelium is continuous throughout circulatory system Capillary Artery Vein Narrow lumen; High pressure Highly elastic – expand and recoil Thick muscular wall – to withstand force; more elastic fibres (recoil) No valves (except aortic and pulmonary semilunar at the start) Oxygenated blood from heart – except pulmonary artery to lungs Pulsatile blood flow (expansion + recoil) Pulse can be felt – e.g. wrist Wide lumen; Low pressure Thin wall - less elastic and less muscular Valves (semilunar) – prevent backflow Deoxygenated blood to heart from tissues - except pulmonary vein from lungs Non pulsatile – smooth flow of blood

Tissue Fluid

Tissue Fluid What is the role of tissue fluid? It is the fluid which allows the exchange of substances between the blood and cells What substances are found in tissue fluid? glucose, amino acids, fatty acids, salts and oxygen = all delivered to the cells. carbon dioxide and other waste substances = removed from the cells.

Hydrostatic pressure

Hydrostatic Pressure As the capillaries are narrower than the arterioles, a pressure builds up which forces tissue fluid out of the blood plasma = hydrostatic pressure. This pressure is resisted by: Pressure of the tissue fluid on the capillaries (from the outside) The lower water potential of the blood (caused by plasma proteins – too large to leave the blood) Overall, pressure pushes tissue fluid and small molecules out of the capillary, leaving cells and large proteins behind = ultrafiltration.

Return of tissue fluid Most tissue fluid is returned to the blood plasma via the capillaries. Hydrostatic pressure at the venule end of the capillary is higher outside the capillary and tissue fluid is forced back in. Osmotic forces (resulting from the proteins in the plasma) pull water back into capillaries. Remaining tissue fluid enters the lymph vessels – drain back into the veins close to the heart.

Lymph System

Lymph Lymph is moved by: Hydrostatic pressure Contraction of body muscles (aided by valves in the lymph vessels)