Exam 3

Question 1

Define homeostasis and its importance.

Answer 1

The maintenance of a dynamic equilibrium in the body; keeps the internal environment of an organism in a tolerable range. Stable internal environments maximize enzyme efficiency and membrane permeability.

Question 2

What are the factors that can be control by homeostasis? Explain.

Answer 2

Factors can be maintained in a physiological range. Some include blood pressure, blood glucose levels, blood pH, blood osmolarity, core body temperature, and levels of memorabilia waste like, CO2.

Question 3

Compare and contrast regulators and conformers.

Answer 3

Conformers allow their internal conditions to become similar to the external conditions. They have lower energy expenditure, but they are less functional in certain environments. Regulators maintain a stable internal environment. They have higher energy expenditure but can function in more environments.

Question 4

What are the functions of the 3 components of a homeostatic system?

Answer 4

1. Sensor: detects the value of what is being measured
2. Integrator: evaluates sensory information to determine if the measurement is too high, low, or just right
3. Effector: mechanism that returns the condition to a normal range

Question 5

What are the four mechanisms of heat exchange?

Answer 5

Conduction: heat transfer between two touching solids
Convention: heat transfers between a touching solid and liquid/gas
Radiation: heat transfer between two objects that are not in direct contact (the sun)
Evaporation: heat transfer when a liquid become a gas; no heat gain

Question 6

What is endothermic, ectothermic, homeothermic, and poikilothermic strategies?

Answer 6

Endotherms receive heat as a byproduct of internal chemical reactions. Ectotherms receive heat from their environment.

Homeotherms keeps their body heat constant in a narrow range. Poikilotherms allow their body temperature to rise/fall based on environmental conditions.

Question 7

Compare and contrast adaptive advantages/disadvantages of endothermic and ectothermy.

Answer 7

Endotherms are able to maintain enzymes at a constant temperature, remain active in winter and during the night, and have high levels of aerobic activity thanks to their high metabolic rate. However, they must consume large quantities of energy-rich food and the energy used to produce heat is unavailable for other things.

Ectotherms can survive on much less food and devote more of their energy to reproduction. However, temperature-dependent chemical reactions slow as body temperature drops, molecule activity slows which makes them more vulnerable to predators, and they are less successful at inhabiting cold environments.

Question 8

Define osmolarity and osmoregulation.

Answer 8

Osmolarity is the concentration of all the solutes in a solution. Higher solute concentration have higher osmolarity. Osmoregulation maintains homeostasis by regulating water and solute levels.

Question 9

What is the difference between osmolarity and tonicity?

Answer 9

Osmolarity refers to solutions while tonicity always refers to cells.

Question 10

Define hyper-, hypo-, and isosmotic; define hyper-, hypo-, and isotonic

Answer 10

Hyper: higher osmolarity/concentration
Hypo: lower osmolarity/concentration
Isosmotic: same osmolarity
Isotonic: same concentration

Question 11

Explain the difference between osmoconformers and osmoregulators.

Answer 11

Osmoconformers are in osmotic equilibrium with their environment. The extracellular fluids outside the cells but inside the body are isosmotic to seawater. Osmoregulators actively maintain a constant blood osmolarity that is different from the surrounding environment.

Question 12

Explain the adaptations that freshwater and marine (saltwater) fishes use to osmoregulate.

Answer 12

Freshwater fish live in a hypoosmotic environment where the water has a lower solute concentration. They gain water by osmosis and lose electrolytes through diffusion. They drink little water, excrete large amounts of dilute urine, and activity take up ions though gills.

Saltwater fish live in a hyper osmotic environment where the water has a higher solute concentration. They lose water by osmosis and Gian electrolytes by diffusion. they drink a lot of seawater, excrete concentrated urine, and actively excrete ions through gills.

Question 13

List the major parts of the kidney.

Answer 13

The renal corpuscle, proximal tubule, loop of henle, distal tubule, and the collecting duct.

Question 14

What is the function of the renal corpuscle?

Answer 14

Filtration occurs and urine formation begins. Blood enters the glomerulus, which is a cluster of capillaries that bring blood to the nephron from the renal artery.
Blood pressure from the heart pushes water and solutes through capillary pores and into the lumen of Bowman’s capsule, which surrounds the glomerulus. the filtered pre-urine will enter the renal tubule.

Question 15

What is the function of the proximal/renal tubule?

Answer 15

The renal tube reabsorbs the filtrate from the renal corpuscle (75%). Microvilli in the lumen of the tubule increase absorption. Active transport moves solutes from the proximal tubule and into epithelial cells (water follows osmotic gradient) and the solutes/water are reabsorbed.

Question 16

What is the function of the Loop of Henle?

Answer 16

The Loop of Henle continues reabsorption. As fluid goes down the descending limb, water passively diffuses out and down its osmotic gradient. In the thin acceding limb, solutes passively diffuses out according to the solute gradient.
In the thick ascending limb, the osmolarity of the surrounding interstitial fluid is low and the solutes are actively transported out of the nephron.

Question 17

What is the function of the distal tubule?

Answer 17

The distal tubule connects the ascending limb to the collecting duct and deals with secretion. When aldosterone is present, Na+ is reabsorbed. When it is not present, Na+ is not reabsorbed.

Question 18

What is the function of the collecting duct?

Answer 18

It regulates water retention. When ADH is present, the duct is permeable to water. Water leaves the filtrate, causing a smaller amount of urine to be produced that is hyperosmotic to blood.

When ADH is not present, the duct is not permeable to water. Water stays int eh filtrate, causing a larger volume of urine that is hypoosmotic to blood.

Urea leaks out by passive transport, establishing high osmolarity of inner medulla.

Question 19

Articulate the mechanisms of secondary active transport observed in the proximal tube—
how does it promote reabsorption of water and other solutes?

Answer 19

Na+/K+ ATPase ejects Na+ into interstitial fluid, creating a gradient that encourages Na+ to diffuse from the lumen of the proximal tubule.

Na+ cotransporters use the Na+ gradient to selectively remove ions & nutrients from the filtrate (secondary active transport).

Solutes moved into the cell with Na+ diffuse across membranes and into nearby blood vessels through facilitated diffusion.

Water follows the ions from the proximal tubule, through the cell, and into the blood vessels through facilitated diffusion.

Filtrate reduced to 1/4 volume.

Question 20

Explain what molecules (water or Na/Cl) diffuse in which direction in the loop of Henle
and the interstitial fluid/blood vessels surrounding it. Explain how these osmolarity
differences are self-sustaining.

Answer 20

As fluid goes down the descending limb, water passively diffuses out and down its osmotic gradient. In the thin acceding limb, solutes passively diffuses out according to the solute gradient.
In the thick ascending limb, the osmolarity of the surrounding interstitial fluid is low and the solutes are actively transported out of the nephron. The descending limb provides an electrochemical gradient for the ascending limb while the ascending limb provides an osmolarity gradient for the descending limb.

Question 21

Explain the purpose and function of ADH.

Answer 21

ADH regulates water retention by determining if the collecting duct is permeable to water.

Question 22

What are hormones?

Answer 22

They are chemical signals that regulate and coordinate metabolism, growth, development, and homeostasis.

Question 23

Define transduction.

Answer 23

The conversion of a signal from outside the cell to inside the cell.

Question 24

What is a ligand?

Answer 24

A signaling molecule (hormone). it binds to the ligand binding site on the receptor.

Question 25

What is a kinase?

Answer 25

An enzyme that helps phosphorylate (attach a phosphate) to a molecule.

Question 26

Distinguish between lipid-soluble (hydrophobic) and lipid-insoluble (hydrophilic) mechanisms of signal processing.

Answer 26

Hydrophobic ligands use extracellular receptors for signal processing. Since the hydrophobic molecule cannot cross the plasma membrane, it must rely on cell-surface receptors. Hydrophilic ligands use intracellular receptors because the small, non polar molecules can pass through the membrane.

Question 27

Explain the differences between two common signal transduction systems: G-protein coupled receptors and enzyme-linked receptors. Focus on the outcomes (what does each trigger?)

Answer 27

G-Protein: production of second messengers; amplification Enzyeme: directly triggers phosphorylation cascade; each kinase phosphorylates a different one untila response is triggered.

Question 28

List and contrast the five categories of chemical signals.

Answer 28

Autocrine signals act on the same cell that secretes them. Paracrine signals diffuse locally and act on nearby cells. Endocrine signals are hormones carried between cells by blood/bodily fluids. Neural signals (neurotransmitters) diffuse a short distance between neurons. Neuroendocrine signals (neurohormones) are hormones released from neurons that travel in the bloodstream.

Question 29

Explain the mechanisms of the three main signaling pathways.

Answer 29

Endocrine pathway: A stimulus acts on an endocrine cells, causing it to secret a hormone into the bloodstream. The hormone reaches the effector cell and a response is initiated. Neuroendocrine pathway: A stimulus acts on a sensory cell, which sends the information to a neurotransmitter. A neurohormone is released into the bloodstream, which will reach an effector cell and initiate a response. Neuroendocrine-to-endocrine pathway: A stimulus acts on a sensory cell, which sends the information to a neurotransmitter. A neurohormone is released into the bloodstream and reaches an endocrine cell. The cell releases a hormone into the bloodstream. The hormone reaches the effector cell and a response is initiated.

Question 30

Explain the epinephrine response as an example of a G protein-coupled receptor.

Answer 30

Epinephrine binds to an extracellular receptor. The receptor activates a G protein, which then activates Adenyly Cyclase. This activates cAMP, which triggers the activation of kinases and phosphorylase. Phosporylase is an enzyme that triggers glycogen to break down into glucose. Glucose is eventually released. This is an example of a GPCR because it involves a G protein and a second messenger, cAMP.

Question 31

Explain how blood glucose levels are maintained (the role of insulin and glucagon).

Answer 31

When blood glucose levels rise, the pancreas secretes insulin. It stimulates liver and muscle cells to convert glucose to glycogen to be stored in cells. The blood glucose level will then fall. When blood glucose levels drop, the pancreas secretes glucagon. It stimulates liver cells to convert glycogen to glucose, releasing it into the bloodstream and raising blood glucose levels.

Question 32

Explain how blood osmolarity is maintained (the role of ADH as a G protein-coupled receptor).

Answer 32

ADH is a neurohormone that is produce in the brain and transported to the kidneys. When our brain perceives changes in the blood osmolarity that we are dehydrated and do not have enough water, ADH is produced. It binds to a receptor, which activates a G protein. The G protein will then release GDP and bind GTP, which stimulates aquaporin production to reabsorb water in the collecting duct.

Question 33

Contrast negative and positive feedback.

Answer 33

Negative feedback reduces or counteracts in initial change to bring the system back to homeostasis. Positive feedback amplifies the initial change (childbirth, blood clotting).

Question 34

Explain the difference between phosphorylase (fight-or-flight) and glucagon (daily homeostasis).

Answer 34

Phosporylase quickly releases large amount of glucose while glucagon release smaller amounts slower.

Question 35

What are the symptoms of diabetes insipidis? Discuss water reabsorption.

Answer 35

The symptoms are extreme thirst, excessive increase of urination, and nighttime urination. The extreme thirst and frequent urination is due to a lack of proper water reabsorption.

Question 36

Explain the action of desmopressin; articulate how desmopressin is distinct from ADH (vasopressin).

Answer 36

Desmopressin is similar to ADH and used to treat diabetes insipidus. It is more resistant to enzymatic breakdown, so its effects last longer.

Question 37

Explain how ABA functions in water homeostasis.

Answer 37

ABA inhibits the growth of plants. It closes the stomata to prevent water loss and gas exchange. it maintains dormancy insides and closes stomate in response to water stress. It promotes the elongation of primary roots and suppress lateral root growth.

Question 38

Explain how gibberellins promote seed germination.

Answer 38

When an embryo swells with water, gibberellins is secreted and triggers the synthesis of hydrolytic enzymes. The enzymes move into the endosperm and hydrolyze protein and starch for the developing embryo to use for energy.

Question 39

Distinguish between dendrites and axons.

Answer 39

Dendrites are the branches off of the cell body that receive signals and convert them from chemical signals to electrical signals. more dendrites increase the ability to detect sensory inputs. Axons are where the signal travels and is conducted.

Question 40

Explain how resting membrane potential is achieved, including the locations of sodium and potassium ions. Explain the role of the NA+/K+ pump and the K+ leak channels. Identify the resting potential (in millivolts) in humans.

Answer 40

Membrane potential is the charge difference between the inside and outside of a cell due to differences in charge voltage. When a neuron is not active, the resting membrane potential is negative. There is more K+ inside the cell and more Na+ outside the cell. A sodium/potassium pump pumps 3 Na+ out the cell and 2 K+ in. K+ leak channels let K+ leak down the [K+] until equilibrium (-65 mV). This results in negative membrane potential.

Question 41

List the three steps of an action potential, and explain what happens at each stage (which ions are moving where, in what direction is the signal moving). Be sure to incorporate refractory states into your explanation.

Answer 41

1. Depolarization During depolarization, Na+ flows in while K+ flows out. At threshold potential (-55 mV), voltage-gated Na+ channels open as a result of a shape change when the membrane is depolarized and allow Na+ inside the cell. They remain open until the potential is 40 mV. The gate then closes and stays closed for a refractory period. This ensures it only goes in one direction. When Na+ enter the axon, it repels positive charges and depolarizes nearby areas, causing more gates to open. 2. Repolarization The Na+ gates are closed and K+ channels open. K+ leaves the cell and causes the membrane to repolarize. 3. Hyperpolarization As K+ exits, the membrane become hyper polarized, but eventually goes back to normal after the K+ channels close.

Question 42

How do myelin sheaths propagate a signal?

Answer 42

Myelin sheaths speed up signal transmission by acting as an insulator, allowing electrical signals (action potentials) to "jump" between gaps in the myelin.