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Tema 3: Biología (The lymphatic system (6.1. The internal environment,…

- - - - Interstitial fluid surrounds the cells and directly exchanges with them the substances that they need and produce
      - Lymph is a clear liquid which forms from the interstitial fluid. It circulates through a second circulatory system: the lymphatic system
  - - - Lymph capillaries are very small tubes which flow into most of the tissues in the body
      - Lymph vessels are similar to veins. They collect lymph from the capillaries and flow into the blood circulatory system
      - Lymph nodes are small swellings which are found along the lymph vessels. Their function is to filter lymph and produce white blood cells
- - - - It consists of the digestive tract and the digestive glands
      - The digestive tract
        
        The mouth is a cavity containing the tongue and the teeth (tear and grind up food)
        
        The pharynx is a tube shared with the respiratory system. Food travels along the pharynx towards the stomach, and air travels towards the larynx. The pharynx contains the epiglotis, a cartilaginous membrane which stops food from getting into the larynx
        
        The oesophagus is a tube surrounded by a layer of muscle. When it contracts it helps to carry food to the stomach
        
        The stomach is an organ which is connected to the oesophagus (cardiac orifice) and the intestine (pyloric orifice). The opening of each orifice is regulated by a muscle called a sphincter
        
        The small intestine is a very long tube connecting the stomach to the large intestine. Its walls have folds called intestinal villi which increase the absorption surface area and are surrounded by blood capillaries and lymphatic capillaries. The small intestine has three parts: the duodenum, the jejunum and the ileum
        
        The large intestine is a wide tube which surrounds the small intestine and reaches the anus. It is divided into three parts: the caecum, the colon and the rectum. The caecum has an extension without an exit called the appendix
      - The digestive glands
        
        They secrete substances into the digestive tract
        
        The salivary glands are three pairs of glands which secrete saliva into the mouth
        
        The liver is an organ which produces bile, the substance which is stored in the gallbladder before being released into the duodenum
        
        The pancreas is a gland which secretes pancreatic juice and releases it into the duodenum
        
        The gastric glands are cells in the gastric mucosa which secrete gastric juice and protective mucus
        
        The intestinal glands are cells in the intestinal mucosa which secrete intestinal juice and protective mucus
- - - - It involves mechanically reducing the size of food and moving it along the digestive tract
        
        Mastication and insalivation. It forms the bolus.
        
        Deglutition involves using the tongue to move the bolus towards the pharynx. From there the bolus is moved with the peristaltic movements
    - - It involves a chemical reaction which transforms large molecules into smaller molecules
        
        Saliva contains water and enzymes, which break down carbohydrates into simpler substances
        
        Gastric juice in the stomach mainly consists of hydrochloric acid and enzymes, which break down proteins into small fragments of various amino acids
        
        Bile helps to digest fats by converting them into small droplets which can then be acted on by enzymes
        
        Intestinal juice contains enzymes which transform proteins and carbohydrates into nutrients
        
        Pancreatic juice contains many enzymes which digest fats by converting them into fatty acids and other substances
    - - It is the process by which nutrients obtained through digestion cross the intestinal wall into the circulatory system. From there, they are distributed to all of the body's cells
        
        Most organic nutrients are absorbed in the small intestine. They cross the plasma membrane of the cells in the intestinal mucosa and travel towards the intestinal villi, which are surrounded by a network of capillaries. Nutrients then reach the capillaries into the circulatory system
        
        In the large intestine water and minerals continue to be absorbed and faeces are formed. A number of bacteria live in this portion of the intestine and decompose food which has not been digested or absorbed by the small intestine (intestinal flora). They synthesise amino acids and vitamins which are absorbed by the blood capillaries
    - - Faeces accumulate in the rectum until the defecation reflex is triggered. That is, the expulsion of faeces through the anus
- - - - The respiratory tract is a network of tubes which carry air to the lungs. They become more branching and narrower as they move closer to the lungs
        It is made up of the nasal passages, pharynx, larynx, trachea, bronchi and bronchioles. The bronchioles end inside the lungs in sacs called pulmonary alveoli. These have very thin walls made up of a single layer of cells which are surrounded by a network of capillaries
      - The lungs are two spongy organs located in the rib cage and separated from the abdomen by the diaphragm. They are protected by the ribs and the pleural membrane which is full of pleural fluid
    - - Inhalation takes place when the muscles that raises the ribs and the diaphragm contract. The combined action of these muscles causes the rib cage to expand. As a result, air enters through the nose where it warms up, becomes moist and travels trough the respiratory tract towards the lungs
      - Gas exchange takes place in the pulmonary alveoli and in tissues. It's carried out by diffusion (gases move naturally across the cell membranes from areas of higher concentration to areas of lower concentrantion)
      - Exhalation takes place when the muscles that raise the rib cage and the diaphragm relax, the rib cage reduces in volume and the lungs squeeze the air passively into the respiratory tract
- - - - Arteries are vessels with a circular cross-section. They have thick, elastic walls and carry blood from the heart to the organs. They branch into thinner vessels called arterioles
      - Veins have an oval cross-section and thin, less elastic walls. They carry blood from the organs to the heart. They are formed by the joining together of small veins called venules. They have valves which prevent reverse blood flow.
      - Capillaries are very thin vessels which connect the arteries and the veins. They enable exchange of nutrients, waste and gases between the blood and the cells
    - - It's a viscous, red and slightly salty liquid. It is made up of plasma and blood cells
        
        Blood plasma is a yellowish solution made up mainly of water. It contains dissolved inorganic substances (gases, mineral salts) and organic substances (glucose, proteins, hormones)
        
        Blood cells
        
        Red blood cells (erythrocytes or red blood corpuscles) are the most numerous cells in the blood, they are small and don't have a nucleus. They are disc-shaped, elastic and can become deformed, which helps them to circulate through the thinnest blood capillaries. They transport oxygen thanks to haemoglobin in their cytoplasm
        
        White blood cells (leucocytes) have nucleus and are larger than red ones although there are fewer of them. They can actively move around by means of pseudopodia. They defend the body against infections and tumour cells. There are different types: lymphocytes, macrophages...
        
        Platelets are fragments of cytoplasm. They are quite numerous and their function is to participate in blood clotting, thanks to proteins on its surface which favour agglutination
        
        Function of the blood
        
        It transports substances, suplying cells with the nutrients and oxygen that they need and removes CO2 and waste
        
        It defends the body thanks to different types of leucocytes and antibodies and other protective substances defend the body against infections and lesions
        
        It regulates body temperature, maintaining and distributing body heat while it circulates
    - - It's a muscular organ located in the rib cage between the lungs
        
        Inside the heart there are 4 cavities. The upper 2 cavities are called atria and receive blood. The lower 2 are called ventricles, pump blood away from the heart and have thicker walls. The heart is split in half lenghtwise by a dividing wall which stops the blood on either side from mixing together
        
        In the right half deoxygenated blood enters the atrium through the venae cavae. From the atrium it moves to the ventricle through the tricuspid valve, which opens to let blood through and then closes again to prevent backflow. Blood leaves the ventricle through the pulmonary artery
        
        Inside the left half oxygenated blood from the lungs enters the atrium through the pulmonary veins. Then it moves to the ventricle through the mitral valve. Blood leaves the ventricle through the aorta and from there is distributed throughout the whole body
        
        The exit of blood from the ventricles through the main arteries is regulated by the semilunar valves which prevent reverse blood flow
- - - - It runs between the heart and the lungs and its purpose is to oxygenate the blood
        
        Blood leaves the right ventricle through the pulmonary artery which, further along, branches in two, one for each lung
        
        After gas exchange has taken place in the lungs the oxygenated blood returns to the left atria through four pulmonary veins
    - - It runs between the heart and the different organs in the body. Its purpose is to provide oxygen and nutrients to the cells and, from there, to remove CO2 and other waste products
        
        Blood leaves the left ventricle through the aorta
        
        The aorta branches into smaller arteries and arterioles, which are spread throughout the body and reach all organs and tissues through the capillaries
        
        Once substances exchange has taken place in the tissues the blood returns through veins. These come together into the superior and inferior venae cavae, which flow into the right atrium
- - - - The kidneys are two bean-shaped organs located in the lumbar region on either side of the spine. They filter and clean the blood and produce urine.
        
        The cortex or outer region has a reddish, grainy appearance
        
        The medulla, divided into pyramid-shaped sections
        
        The renal pelvis is a funnel-shaped cavity which the **pyramid-shaped sections of the medulla flow into. It's responsible for collecting urine** produced by the kidney
      - Nephrons are microscopic structures (there are more than a million in each kidney). Each one consists of a glomerulus (ball of blood capillaries), which is surrounded by the Bowman's capsule. This leads into the renal tubule which flows into a collecting duct along with the tubules from other nephrons
      - The urinary tract is responsible for transporting urine outside of the body from the kidneys
        
        The ureters are tubes which flow from the renal pelvis and carry urine continuously to the urinary bladder, the muscular organ which stores it. When the bladder is full the body feels the urge to urinate. The urethra is the tube through which urine is expelled
    - - Urine is a liquid formed by water and waste substances.
        
        Filtration takes place in the glomerulus, where water and small dissolved molecules are filtered through the capillary walls. All these substances form primary urine which is collected in the Bowman's capsule before moving through the renal tube
        
        Reabsorption. Along the renal tube most of the substances in primary urine are reabsorbed and returned to the blood. 98% of the water is reabsorbed, along with all of the glucose and amino acids, and a large part of the mineral salts
        
        Secretion takes place in the last part of the renal tubule. It involves the transfer of some minerals from the capillaries to the inside of the tubule, forming urine, which empties into the collecting duct
        
        Urine moves from the nephrons to the renal pelvis, then to the ureter, to the bladder and then it's expelled
    - - The lungs, which expel CO2 produced during cellular respiration
      - The sweat glands, distributed all over the skin and excrete sweat through the pores. Sweat is similar to diluted urine and is produced by filtering the blood in the capillaries which are close to the gland. It has a role in temperature regulation
      - The liver acts as an excretory organ of some substances, such as bile pigments produced from the breakdown of red blood cells or certain medicines, which are excreted with the bile