21)Signal Transduction is a process by which an extracellular signal molecule, called the first messenger activates a membrane receptor that in turn alters intracellular molecules, called the secondary messenger, to create a response.
22) Antagonists are moleculres that bind to the receptor in such a way that they block competing ligands from binding and prevents the receptor from responding.B) Osteoblasts are responsible for bone deposition while Osteoclasts are responsible for bone break down.
23) Compare and contrast hormones, neurotransmitters, and neurohormones--> Hormones: produced in and secreted from endocrine glands or in scattered cells distributed in another organ; found in circulation(Epinephrine). Neurotransmitters: chemical messengers released from neuron terminals onto other neurons, muscle cells, or gland cells; not present in circulation(serotonin). Neurohormones: a chemical signal produced by cells of the nervous system and secreted in to the circulatory system(Oxytocin,ADH)
24) The 4 major tissue types are nervous, epithelial, muscle, and connective. An example of nervous tissue would be found in the spinal cord. An example of epithelial tissue would be found in the lumen of an organ. An example of muscle tissue, which has 3 different types is cardiac muscle which can be found in the heart. An example of connective tissue is actually blood
25) What are two benefits of having a portal system that connects the hypothalamus with the anterior pituitary gland? --> One benefit of the portal system is that it connects the hypothalamus and the anterior pituitary gland through capillaries. This allows the hormones to go directly to their target cells without first passing general circulation and they are not diluted. The hypothalamus can control the cells of the anterior lobe of the pituitary glands with much smaller amounts of releasing and inhibiting hormones than would be necessary if they had to first go through the circulatory pathway before reaching the pituitary. Another benefit is that the portal system also allows for possible secretion which releases hormones in rapid succession.
27)A) Diffusion is a form of passive transport that requires no energy in put. Diffusion transports solutes down the gradient, from higher concentration to lower concentration. Facilitated diffusion is also a form of passive transport but makes use of ion channels that are in the plasma membrane; it still goes with the gradient. B) Primary active transport directly uses energy from ATP hydrolysis in order to transport solutes against the concentration gradient, in an epithelial fashion. An example of this is the Na+/K+ pump. Secondary active transport is different in that it does not use the energy from ATP hydrolysis and instead uses a pre-existing gradient created by a primary active transport earlier. Secondary active transport does not go against the gradient like primary active transport.
28)A solution may have the same osmolarity as normal body fluids yet it may not be isotonic. Why? --> A solution may have the same osmolarity as normal body fluids but that does not mean it is isotonic. Without knowing the amount of nonpenetrating vs penetrating solute in solution, one would not know for certain. For example, if the nonpenetrating solute was greater than 300mOsM/L then that would be considered a hypertonic solution. If the solution had less than 300mOsM/L of nonpenetrating solute then it would be hypotonic. Knowing this we can say that a solution that is isoosmotic is not necessarily isotonic as it can also be hypotonic at less than 300mOsM/L