Human Physiology and Immunology Midterm Exam - Prof. Par Towb, Exams of Biology

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• BILD 2 Spring
  • Midterm #

Section I: Answer all of these questions (10 points each).

1. MHC Class II molecules_________ are used found on the surface of dendritic cells and other antigen presenting cells. They display peptides from ingested pathogens.
2. Which type of differentiated lymphocyte acts to secrete large amounts of antibody proteins? plasma cells
3. ___T-cell receptors________ recognize MHC protein / peptide complexes.
4. Lymphocytes that are responsible for the more rapid, prolonged and effective response to a second encounter with an antigen are called by the general term, memory cells.
5. The HIV virus attacks helper T-cells___ and is responsible for the disease known as __AIDS______.
6. The three major classes of chemicals that serve as hormones in the human body are:____amines_________, _proteins (peptides)_______ and _____steroids________.
7. The __anterior pituitary_______ responds to releasing hormones sent from the hypothalamus _______________. It then proceeds to release hormones such as TSH.
8. An example of an exocrine gland is ____________________________________.
9. A ___saltwater______________________fish needs to actively transport solutes out of its body through its gills.
10. Approximately 99 % of the water in the initial filtrate is reabsorbed by the kidney.
11. This region of a nephron is always impermeable to water: ascending limb of the Loop of Henle_________.
12. Epinephrine binding to liver cells stimulates glycogen breakdown______.
13. The adrenal glands _____(endocrine glands) sit on top of the kidneys.
14. The target cells for PTH reside in the _________bones and ___kidneys_________.
15. Human body cells are (hyper / hypo / iso) osmotic to seawater (circle one).
16. Lymph nodes often become swollen during an infection due to leukocyte proliferation within them.
17. Differences in MHC molecules______ between humans lead to the phenomenon of tissue transplant rejection.

Section II. Answer 8 (out of 12) of the following questions. Write OMIT in large letters on the questions you don’t want to be graded. (40 points each) 18A) What are the three major forms in which animals excrete nitrogenous wastes? Ammonia (NH 4 ) Urea Uric acid 18B) For each of the animals listed below, which compound would that animal probably use as its form of nitrogenous waste? What is one advantage and one disadvantage for that animal to use that compound as its nitrogenous waste molecule? Tiger -- Compound: Urea Advantage: much less toxic than ammonia, requires less water to dilute and excrete Disadvantage: high metabolic energy cost to convert ammonia to urea Eel -- Compound: Ammonia Advantage: requires no additional metabolic energy cost to create Disadvantage: very toxic, have to dilute it and excrete it using a large amount of water (or no real disadvantage, since the eel lives in water) Seagull -- Compound: Uric acid Advantage: non-toxic, can be excreted with almost no associated water loss Disadvantage: very high metabolic energy cost to convert nitrogenous wastes to uric acid

19. Why does each human kidney contain about a million small diameter nephrons, instead of a smaller number of larger diameter nephrons (or just one big nephron)? (1- 2 sentences) The large number of nephrons lead, in aggregate, to a huge surface area through which water and solutes can be reclaimed from, or excreted into, the filtrate.

20. Why do many physiological systems, such as the ones that control blood sugar or calcium levels, contain negative feedback mechanisms? (Don’t assume I understand what “negative feedback” means.) (2 – 3 sentences) Most living creatures need to maintain these parameters within a fairly narrow range of permissible values (this is referred to as maintaining homeostasis). A negative feedback system ensures that if some biological parameter starts to deviate from optimal conditions, sensing systems will trigger a counteracting response that will restore the parameter to the proper range.
21. If a person had an abnormally low level of pancreatic alpha cells, what sort of medical problems might they experience? Explain why and when they’d be most likely to experience these problems. (3 – 4 sentences) They would have low levels of blood glucose, especially in between meals. This is because they could not produce enough glucagon to release stored glucose from the liver when blood glucose levels fall. They would probably experience dizziness or confusion, could faint, etc.
22. If a person had defective MHC Class I molecules, which types of infectious challenge would his/her immune cells not be able to recognize? Explain. (2 – 3 sentences) Since the MHC Class I molecule displays peptides from virus infected or cancerous cells, and presents them to T cell receptors, the immune system cells (notably helper T cells and cytotoxic T cells) of that person’s immune system would be unable to recognize those threats.

23. What gets included in the filtrate that starts out in Bowman’s capsule in the mammalian kidney? (just give 3 things) What gets excluded? (just give 2 things) Included: water, ions, urea, glucose, amino acids Excluded: cells, proteins
24. How does the regulation of oxytocin release illustrate the interplay between the nervous system and the endocrine system? (1-2 sentences) Suckling sends a nervous system stimulus to the brain, where it triggers neurosecretory cells in the hypothalamus to release oxytocin from the posterior pituitary.
25. Glucagon and insulin are both protein hormones, but each have largely different cellular targets and both cause differing cellular responses. How can this be so? (1 sentence) These two different hormones bind to different receptors at the surface of their respective target cells, and thus trigger different responses.

26. Every year new flu viruses arise in the world, and yet most of the time we have one or more lymphocytes that can respond to these new viruses. How is this so? ( 2 – 3 sentences) The genes for the B cell and T cell receptors are rearranged randomly in individual lymphocytes, and they produce proteins that recognize random epitopes. Millions of lymphocytes are present in the body, so most microorganisms contain an epitope that is recognized by at least one of the lymphocytes.
27. When feeding, a vampire bat offloads most of the weight of its blood meal by excreting large volumes of dilute urine. Assuming its kidney is regulated by the same mechanisms that regulate human kidney function, give two ways (in some detail) the vampire bat kidney can regulate and thus produce dilute urine. In the proximal tubule, distal tubule and loop of Henle the amount of solutes that are actively pumped back into the interstitial fluid may be decreased. This will decrease the amount of water that follows (is reclaimed) by osmosis. Aquaporins may be removed from the membrane of the collecting duct, so that water will not be reabsorbed (reclaimed) from the filtrate at this point.

28. Draw a diagram of a B-cell receptor, and indicate what the component parts do. Which parts are identical to each other, and which are different? See the appropriate figure in the book. You needed to indicate where the antigen binding sites are located, and what the “stem” of the receptor does (transmembrane domain). Both heavy chains and both light chains are identical to one other; conversely, the light chains and the heavy chains are different from each other.
29. What do helper T-cells do? How do they become activated? (3-4 sentences) T-cell receptors, on the surface of helper T cells, recognize peptide antigens bound by MHC Class II molecules on the surface of antigen presenting cells (phagocytic cells like dendritic cells). This causes the helper T cells to proliferate and secrete several different cytokines that stimulate other lymphocytes.