Chapter 12

• Circulatory system works together with respiratory system to give cells a constant supply of oxygen for cellular respiration and constant removal of carbon dioxide
• Circulatory system delivers oxygen to cell and takes away the carbon dioxide so that the body can remove it
• Main function of the circulatory system is the transport of materials within the internal environment for exchange with all cells

  • Nutrients and gases are exchanged for wastes
• Circulatory system consists of three components :

  1. a fluid on which materials are transported, such as blood
  2. a system of interconnected blood vessels or spaces throughout the body in which the fluid moves
  3. a muscular pump, usually the heart, that pushes the fluid through the blood vessels or spaces
• Open circulatory system

  • Fluid circulates freely in the body cavity by bathing the cells -> substances then enter cells by diffusion
  • Fluid in open circulatory is haemolymph -> this blood is mixed with interstitial fluid
  • muscular heart contraction pumps heamolymph through spaces surrounding organs, it is then drawn back through pores by relaxation of muscular heart
  • pore valves close preventing back flow of circulating fluid and ensure one way flow
  • arthropods (grasshoppers) have open circulatory
• Gastrovascular cavity: is a central cavity with a single opening that functions to transport substances efficiently
• A combination of gastrovascular cavity and flat body, along with the process of diffusion is enough to provide the substances needed for insects
• Closed circulatory

  • Fluid is blood and it flows through enclosed vessels called arteries, veins and capillaries
  • One or more hearts pump blood into large vessels that branch into smaller vessels that wind through tissues
  • network of smaller vessels exchanges gases and nutrients with interstitial fluid and body cells
  • earthworms, squids and all vertebrates have closed circulatory
• Contact with cells

  • Open: Direct -- fluid directly bathes cells, gases are directly exchanged between haemolymph and cells
  • Closed: Indirect -- fluid travels inside vessels which is transported to cells
• Pathways of blood

  • Open: From heart through a blood vessel to an open body cavity, then returns to heart via openings
  • Closed: From heart to lungs and back to heart through closed vessels
• Advantages: Pressure

  • Open: Outside of arteries, there is no pressure; less energy is required
  • Closed: Arteries are thick-walled to enable high blood pressure for faster delivery of blood but more energy is required because of this
• Advantages: Body size

  • Open: Advantageous for small animals due to having lower energy needs
  • Closed: Advantageous for larger animals who are active and need a fast rate of oxygen supply
• Advantages: Efficiency of blood flow

  • Open: Slow flow and limited supply inhibits rate of metabolic activity and limits size of animals
  • Closed: Fast flow and steady supply facilitates higher rate or metabolic activity and larger size of animals
• Single circulatory system 


  • Contain one circuit
  • Found in bony fish and sharks
  • Heart pumps to the gills to be re-oxygenated -> blood then flows to rest of the body and back the heary
  • fish have two-chambered heart with one atrium (heart chamber that receives blood from body) and one ventricle (heart chamber that receives blood from atrium and pumps it out to body)
• Double circulatory system 


  • contain two circuits: pulmonary circuit -- which transports blood to the lung and back to heart and systemic circuit -- which transports oxygenated blood around the body and back to the heart
  • found in all vertebrates (birds, reptiles, amphibians)
• Oxygenated blood -- blood that has just returned from picking up oxygen from lungs

  Deoxygenated blood -- blood that has just returned from dropping off oxygen to body cells
• Digestive system

  Main function of digestion in all animals is to:

  • acquire nutrients in the form of large molecules
  • break down these macromolecules into small molecules
  • allow absorption in the bloodstream for body to use
• Animals may have a gastrovascular cavity with one opening or a specialised alimentary canal with two openings; specialisation of alimentary canals is related to diet -> shown by difference between herbivores and carnivores
• Digestion takes two forms


  1. Mechanical Digestion (physical digestion): is when large pieces of food are broken down into smaller pieces of food through chewing or muscular movement in the stomach
  2. Chemical Digestion: is when enzymes break down complex substances into their simplest forms, such as carbohydrates to glucose
• Digestion 


  Is the process by which animals break down nutrients acquired in the form of large molecules into molecules that are small enough to be absorbed by bloodstream

  • By moving them across cell membrane and into internal environment
• Digestive system (gastrointestinal tact) roles

  1. Ingestion: the acquisition of nutrients
  2. Digestion: the breakdown of complex organic molecules into smaller components by mechanical and chemical means
  3. Absorption: the taking up of digested molecules into the internal environment of the cells of the digestive tract
  4. Egestion: the removal (elimination) of undigested waste food materials from the body
• The gastrovascular cavity 


  • has one opening for both food intake and waste elimination
  • found in simple animals like cnidarians (jellyfish, corals)
• Alimentary canal in humans

  • It has two openings; one for food entry and the other for waste elimination
• 1. Mouth -> ingestion, mechanical and chemical digestion
  2. Oesophagus
  3. Stomach -> mechanical and chemical digestion
  4. Small intestine -> chemical digestion and absorption
  5. Large intestine -> absorption of water, egestion
• Ingestion

  • most animals ingest food through the mouth
  • once food enter through mouth, mechanical and chemical digestion commence
  • amalyse enzyme secreted from salivary glands -> it chemically breaks down of complex carbohydrates to simpler carbohydrates
• Complex molecule to simple molecule after digestion

  Protein -> Amino acids

  Lipids -> Glycerol and fatty acids

  Carbohydrates -> Glucose)

  Nucleic Acids -> Nucleotides
• Digestion and secretion

  • Food moves to the back of the mouth after it is ready for swallowing -> tongue pushes it to oesophagus
  • food moves down with the aid of unidirectional muscular contraction known as peristalsis
• Chemical digestion of starch continues until food reaches stomach
• • Mechanical digestion increases the surface area across which digestive enzymes may act
  • Chemical digestion describes the action of the digestive enzymes on the nutrients, chemically breaking then down until they are of molecular form and size that can be absorbed by cells in the body
• Specialisation of alimentary canal

  Diet type determines the features animals use to obtain food

  • Carnivores have sharp gripping teeth for grabbing prey , pointed incisors, canines, and jagged molars to tear flesh
  • Herbivores have broad molars with ridged surfaces for grinding tough plant material, incisors and canines for biting off vegetation
  • Omnivores have blade-like incisors for biting, pointed canines for tearing, and molars for grinding
• The alimentary canal is the passage along which food passes from mouth to anus during digestion. 


  Herbivores have a longer alimentary canal than carnivores -- Herbivores take a longer time to digest and absorb nutrients while carnivores readily absorb nutrients
• Omnivore alimentary canal

  • Omnivore alimentary canal breaks down both plant and animals nutrients into simpler forms that can be absorbed into cells
  • Omnivores have simpler stomach and an intestine that is longer than that of carnivores
  • Size ratio of small intestine to large intestine varies greatly among omnivores
• Animals with no digestive system

  • They have a high surface area to volume ratio, allowing nutrients and gases to move efficiently across their cell membrane
  • These animals rely on diffusion for oxygen and carbon dioxide exchange which is sufficient due to their small size
• Blood Components

  • Plasma: pale, yellow fluid component of blood where nutrients, wastes and hormones are transported around the body
  • Red blood cells: contain haemoglobin, a molecule that enables the cell to bind oxygen molecules
  • White blood cells: protects body against invading toxins by engulfing them or producing antibodies
  • Platelets: initiates blood clotting
• Major circulatory system organs: heart, arteries, arterioles, veins, venules, and capillaries
• Blood vessels

  • The heart drives blood flow through the body, connecting all blood vessels

  Three main types of blood vessels

  • Arteries -- carry blood away from heart
  • Veins -- carry blood towards the heart
  • Capillaries -- found between arteries and veins
  • Arterioles (small arteries) and venules (small veins) act as bridges between larger vessels and capillaries
• Heart structure and function

  Heart has four chambers

  • Two atria (thin-walled)
  • Two ventricles (more muscular)
• The excretory system helps maintain the important balance between the amount of water in blood and the concentration of solutes dissolved in it
• Human kidneys


  The main organs of the excretory system

  • each kidney contains about one million nephrons -> responsible for filtering water and solutes from the blood and adjusting what gets reabsorbed
  • nephrons consist of: glomerulus (ball of capillaries) inside Bowman's capsule
  • Nephron is basic functional unit of the kidney
• Part of the nephron

  1. Glomerulus --filtration: small solutes are filtered out glomerulus to Bowman's capsul
  2. Bowman's capsule -- filtration: filtrate diffuses and passes on to tubule
  3. Proximal tubule -- reabsorption: some solutes are pumped back
  4. Loop of Henle (descending) -- reabsorption: urea stays inside tubule
  5. Loop of Henle (ascending) -- reabsorption: sodium pumped out of tubule
  6. Distal tube -- reabsorption and secretion: dilutes urine that leaves the body
  7. Collecting ducts -- urine collection