1.The internal environment and blood
Cells live in a enviroment tht provides nutrients they  need,in the same enviroment allows cells to release waste substances resulting from their metabolism.
Multicellular organism have an internal environment formed by interstitial plasma:a liquid that fills the existing spaces between cells,this needs to be renewed continuosly,blood renews interstinal plasma given that it circulates around the whole organism carryng nutrients and removing waste products.If the blood stops circulating,interstitial plasma isn’t renewed and the cells die.
The circulatory system connects the digestive,respiratory and excretory.
*Blood provides cells with the nutrients they need*Blood removes waste products produced during cell metabolism*Tissue cells exchange subst with the int plasma.
1.2.Blood composition.
Blood plasma:Water with minerals(90)nutrients(gluc,amino,vit)waste prod.(urea)protens and hormones.
Blood cells:Erythrocyted/red blood clls:Don´t have a nucleus,contain hemoglobin,red pigment that carries oxygen from pulmonary alveoly to all the cells.Leukocytes/white bloo. clls.:Hve a nucleus,Granlocytes-Neutrophils,eosinophils,basophils.Monocytes,Lymphocytes.Thrombocytes/platelets:Fragments of cells,substances that allow the blood to coagulate.
1.3.Functions of the blood.
*Transport nutrients and oxygen to cells and collects waste products produced by cell metabolism,it carries hormones.*Regulation of body temp.*Fight against infections.
2.Blood circulation
Multicellular orgsm, needs blood to reach all of their organs,blood needs a closed circuit.
2.1.Blood vessels.
Responsible fcarryng blood around the body.
*Arteries:Carry blood from the heart to other organs,have muscular walls are elastic.*Capillaries:Microscopid bood vesssels,in organism’s tissues,formed by walls have one layer of cells,allows the entry and exit of molecules.*Veins:Carry blood from tissues to the heart,they have valves,formed many venules.
2.2The heart.
Hollow muscular orga.Divided left and right.
Subs 2 chambers:atrium8upper smaller cham)ventricle(larger lower chamb)
Constant movement.Pumps the blood fron the veins into the atriums,goes inti the ventrickes and relased into the arteries.Heart rate:Number of times the heart beat per unit of time.
*Atrial systole:The atriums contranc and blood is propelled through the opened arrioventricular valves into the ventricles.*Ventricular systole:Ventricles contract,the sigmoud valves open,blood exits through  the pulmonary artery and the aorta,valves connect with ventricles close.*Diastole:The heart relaxes and sucks blood comming from the cava and pulmonary veins into the atriums .
2.3.Blood circuits.
*Systematic circuit*Pulmonary circuit
-Circulation is double:blood has to travel twice though the heart in order to comolete the whole circuit-Is comolete:oxygenated blood proceding fron the lungs never mixes with deoxygenated blood coming from the rest of the body.-Is closed:The blood or the cells gound in blood,never leaves the blood vessels. 
3.The lymphatic system
Is composed of lymph,Lymphatic vesseks,lymphatic organs and lymph nodes.
*Lymph:Transparent liquid composed of lymphocytes and intersititial plasma*Lymphatic vessels::Made of beads and in their interior they have half-moon shaped valves,end when they reach blood veins.*Lymphatic organs and tissues:Producing and maturing lymphocytes and purifying blood.*Lymph nodes:are made up of lymphatic tissue,they maje lymphocytes and rekease lymph plasma.
3.1.Functions of the lymphatic system.
*It mantains a liquid balance in the internal enviroment*Protecting the body*Collects products from fat digestion.

4. Excretory system
 is the group of organs facilitate the elimination of wast produced by cells after cell metabolism.  *Carbon dioxide it’s formed during the metabolic reactions that produce energy. *Urea and uric acid it’s formed when the body breaks down proteins and nucleic acids respectively. *Toxic substances: these have to beingested. Examples of them are alcohol, drugs, medicine  contributes to the adequate functioning of the body’s vital signs by regulating: the quantity of water in tissues, the concentration of minerals, the blood’s pH levels… By doing this, it participates in the body’s homeostasis. 
Liver: It eliminates products resulting from the destruction of hemoglobin found in old red blood cells.  The liver also eliminates a small quantity of cholesterol and certain toxic substances that can affect the body. Urinary system This is the most important excretory system and eliminates waste products through the urine. Respiratory system: It blood releases it to the exterior. removes and Sweat glands: They produce sweat that, when evaporated, cools the skin when temperatures are high. Sweat also releases certain waste products to the exterior. 
4.1.1. Kidneys 
They are two organs that are of behind the abdomen, one on each side the S Each of them has an external interna which is called the renal cortex, section known as the renal and cavity, known as the pelvis. The renal elvis collects urine, formed in the renal cortex and medulla that contains waste products. Nephons are the structural and functional units kidneys. They are esponsible for filtering blood and forming ur we regulating water and mineral content in the blood. Different parts: Bowman’s capsule it’s the initial zone (spherical), inside is a capillary that folds into a ball called the glomerulus of Malpighi. Convolut tube: it’s a long twisted tube that has two main parts: proximal and distal. ILoop of Henle: this is the section located between the proximal convoluted tube and the distal one. Nephrons end in collecting conduits that end in the renal pelvis leading to the ureter. n addition, kidneys perform other physiological functions: They actively intervene in the regulation of the internal environment. They secrete substances that stimulate the production of red blood cells (erythropoietin) and substances that regulate blood pressure (renin)
4.1.2. Urinary tract for urine. They connect the kidneys with the exterior 
*Ureters: they are thin tubes approximately 28 cm long,that start from kiney and ends in the bladder. When the bladder contains a large quantity of urine, it produces a nervous reflex (micturition reflex)*uurethra is the duct that connects with the exterior. At its end it has a sphincter that remains closed except for when the micturition reflex occurs. 
4.2. Urine formation the function of the kidneys is to form urine, using the nephrons, and to then release it to the exterior urine is a liquid obtained from blood composed of water, minerals and diverse waste products (mostly urea and uric acid.The process of urine formation has two stages: u Glomerular filtration:  Tubular reabsorption