enzymes

• Qualitative and Quantitative Attributes


  In biology, qualitative attributes describe characteristics that can be ranked as present or absent, whereas quantitative attributes are measurable, with numerical values.
• Gene Expression


  Cells respond to environmental changes through gene expression, regulation of gene transcription, and translation, allowing them to adapt and survive in different conditions.
• Haploid and Diploid Cells

  Haploid cells have only one set of chromosomes, while diploid cells have two sets of chromosomes. Examples of haploid cells include gametes, while body cells are typically diploid.
• DNA and Nucleotides


  DNA (deoxyribonucleic acid) is the molecule containing the genetic instructions for an organism. Nucleotides are the building blocks of DNA, composed of a sugar molecule, a phosphate group, and a nitrogenous base.
• Genotype and Phenotype


  The genotype is the genetic makeup of an organism, describing the specific combination of genes an individual possesses. The phenotype is the physical and behavioral traits observed in an organism, influenced by its genotype and environment.
• Meiosis


  Meiosis is a type of cell division that leads to the formation of gametes (sperm and egg cells). It reduces the number of chromosomes by half, resulting in haploid cells.
• Negative feedback


  The majority of homeostatic control mechanisms in organisms use negative feedback to maintain homeostatic balance, i.e. to keep certain physiological factors, such as internal temperature or blood glucose concentration, within certain limits
• Negative feedback control loops

  1. Receptor detects a stimulus

  2. Coordination system transfers information

  3. Effector carries out a response

  
• If there is an increase in the factor


  The body responds to make the factor decrease
• If there is a decrease in the factor


  The body responds to make the factor increase
• Negative feedback systems


  • Work by reversing a change in the body to bring it back within normal limits
• Negative feedback systems


  • If body temperature rises, a negative feedback system will act to lower body temperature, bringing it back to normal
  • If blood glucose levels drop, a negative feedback system will act to raise blood glucose, bringing it back to normal
• Positive feedback


  In positive feedback loops the original stimulus produces a response that causes the factor to deviate even more from the normal range
• Positive feedback


  • Dilation of the cervix during labour
  • Blood clotting to close up a wound
• Positive feedback loops are not involved in homeostasis as they do not maintain a constant internal environment
• Homeostasis


  Physiological control systems that maintain the internal environment within restricted limits
• Homeostasis


  • Keeps the internal environment of the body fluctuating around a specific normal level, in a state of dynamic equilibrium
• Receptors


  Sensory cells that can detect information about the conditions inside and outside the body

  
• Importance of homeostasis


  • Ensures the maintenance of optimal conditions for enzyme action and cell function
  • Ensures a constant supply of energy in the form of ATP
  • Ensures the amount of water in the blood remains constant
• Thermoregulation


  1. Cooling mechanisms: vasodilation, sweating, flattening of hairs

  2. Warming mechanisms: vasoconstriction, boosting metabolic rate, shivering, erection of hairs, less sweating

  
• Hypothalamus


  Area of the brain responsible for controlling many functions including hormones, sleep, growth, body temperature, blood pressure
• Role of hypothalamus in thermoregulation

  1. Detects external temperatures via thermoreceptors

  2. Sends impulses along motor neurons to effectors to bring about physiological responses

  3. Monitors temperature of blood flowing through it and initiates homeostatic responses

  
• Topics covered


  • Hormones
  • Sleep
  • Growth
  • Body temperature
  • Blood pressure
• Mammals detect external temperatures


  • Via thermoreceptors found in the skin and mucous membranes
  • There are receptors for both heat and cold
• Communication of thermoreceptors


  1. Communicate with the hypothalamus along sensory neurons

  2. The hypothalamus will send impulses along motor neurons to effectors to bring about a physiological response to changing external temperatures

  
• Hypothalamus


  Helps to regulate body temperature by monitoring the temperature of the blood flowing through it and initiating homeostatic responses when it gets too high or too low

  
• The regulation of body temperature involves communication between thermoreceptors, the hypothalamus and effectors to respond to change

  
• Vasoconstriction and vasodilation occur in the arterioles that supply the skin capillaries, not the skin capillaries themselves; capillary walls are only one cell thick and do not contain any muscle fibres capable of contracting or relaxing
• Muscles contract, arterioles constrict
• Kidneys


  • Humans have two kidneys
  • They are responsible for carrying out two very important functions: regulating the water content of the blood and enabling the excretion of toxic waste products of metabolism

  
• Location and structure of the kidneys

  1. The kidneys are located above the bladder, supplied with blood by the renal artery and connect to the bladder via the ureter

  2. The kidney itself is surrounded by an outer layer known as the fibrous capsule

  3. Beneath the fibrous capsule, the kidney has three main regions: the cortex, the medulla, and the renal pelvis

  
• Nephrons


  • Each kidney contains thousands of tiny tubes, or tubules, known as nephrons
  • Nephrons are the functional unit of the kidney and are responsible for the formation of urine
  • Different parts of the nephron are found in different regions of the kidney

  
• Regions of the kidney where parts of the nephron are found

  • Cortex: glomerulus, Bowman's capsule, proximal convoluted tubule, distal convoluted tubule
  • Medulla: loop of Henle, collecting duct
  • Renal pelvis: all kidney nephrons drain into this structure, which connects to the ureter

  
• Types of nephrons


  • Cortical nephrons: occur mainly in the renal cortex, have a short loop of Henle
  • Juxtamedullary nephrons: have long loops of Henle that span across the entire medulla, very efficient at conserving water

  
• Blood vessels associated with each nephron


  • There is a network of blood vessels associated with each nephron
• Structure and function of the glomerulus

  1. Within the Bowman's capsule of each nephron is a structure known as the glomerulus

  2. Each glomerulus is supplied with blood by an afferent arteriole which carries blood from the renal artery

  3. The afferent arteriole splits into a ball of capillaries that forms the glomerulus itself

  4. The capillaries of the glomerulus rejoin to form the efferent arteriole

  5. Blood flows from the glomerulus into a network of capillaries that run closely alongside the rest of the nephron and eventually into the renal vein

  
• Formation of urea


  1. Liver cells, or hepatocytes, are responsible for removing the amino group from excess amino acids in a process called deamination

  2. During deamination the amino group (-NH2) of an amino acid is removed, together with an extra hydrogen atom, forming ammonia (NH3)

  3. Ammonia is quickly converted into less toxic urea in a series of steps known as the ornithine cycle
• Ultrafiltratio


  The process of filtering small molecules from the blood at high pressure, occurring between the glomerulus and the Bowman's capsule

  
• Ultrafiltratio


  1. The blood in the glomerulus is at high pressure due to the afferent arteriole being wider than the efferent arteriole

  2. This high pressure forces small molecules in the blood out of the capillaries of the glomerulus and into the Bowman's capsule

  3. The resulting fluid in the Bowman's capsule is called the glomerular filtrate

  4. Large molecules such as proteins remain in the blood and do not pass into the filtrate

  
• Structures within the glomerulus and Bowman's capsule


  • The blood in the glomerular capillaries is separated from the lumen of the Bowman's capsule by two cell layers with a basement membrane in between them
  • The first cell layer is the endothelium of the capillary; gaps between the cells allow fluid to pass through
  • The next layer is the mesh-like basement membrane
  • The second cell layer is the epithelium of the Bowman's capsule; gaps between the cells allow the passage of small molecules