Homeostasis And Cell Function

Question 1

Define homeostasis.

Answer 1

• Refers to the maintenance of nearly constant conditions in the internal environment
• it is the condition in which the body’s internal environment remain relatively constant within limits

Question 2

A homeostatic mechanism is made up of which types of responses?

Answer 2

Adaptive responses

Question 3

An organism is said to be in homeostasis when its internal environment is?

Answer 3

• contains the optimum concentration of gases, nutrients, ions, and water
• has an optimal temperature
• has an optimal pressure for the health of the cells

Question 4

Define stress.

Answer 4

• stress is any stimulus that creates an imbalance in the internal environment

Question 5

Which cation is the most abundant in the extracellular fluid?

Answer 5

• Na+ (sodium)

Question 6

Which cation is the most abundant int the intracellular fluid?

Answer 6

• K+ (potassium)

Question 7

Which anion is the most abundant in the extracellular fluid?

Answer 7

• Cl- (chloride)

Question 8

Define a feedback system.

Answer 8

• Circular situation in which the information about the status of something is continually reported to a central control region

Question 9

Define a negative feedback loop (Fig. 1-3).

Answer 9

• A change in some parameter (I.e., blood pressure) that causes a response that results in a return of that parameter to normal (baseline)
• The response reverses the direction of the initial condition

Question 10

What are the characteristics of a a negative feedback loop?

Answer 10

• Diminishes the original change

- Stabilizing

Question 11

Give an example of a negative feedback loop.

Answer 11

Regulation of arterial blood pressure:
> baroreceptors (type of stretch receptor located in arterial walls) associated with the carotid system sense an increase in arterial pressure

> baroreceptors send inhibitory signals to vasomotor receptors in medulla

> heart pumping capacity is reduced and blood vessels dilate

> arterial pressure decreases

Question 12

Review figure 1-4 : Recovery of heart pumping caused by negative feedback

Answer 12

Pic

Question 13

Define a positive feedback loop.

Answer 13

> A change in some parameter causes a responses that continues to change that parameter in the same direction as before

> The input is intensified

Question 14

What are the characteristics of a positive feedback loop?

Answer 14

> enhance the original change

> destabilizing and can lead to runaway effects

Question 15

Give an example of a positive feedback loop.

Answer 15

Childbirth
> stretch of the cervix during delivery sends signals that increase the force of uterine contractions which then increase the stretch on the cervix

> NOTE that in this example, there is a natural end to the initial stretch in the form of childbirth, which then terminates the feedback loop

> in most instances, there is no natural end to the feedback, and the process exceeds limits conducive to life

Question 16

An increase in the production of TSH releasing facto results in an increase in the release of thyroid stimulating hormone, which results in the release of mere thyroxine, which results in a decrease in the production of TSH releasing factor. Is this a negative or positive feedback loop?

Answer 16

This is an example of a negative feed back loop

Question 17

What is gain?

Answer 17

Gain is the effectiveness with which a control system maintains constant conditions

Question 18

How is gain calculated?

Answer 18

Gain = correction/ error

> error is the amount of uncorrected increase

> correction is the amount of counteracted increase

Question 19

Baroreceptors (pressure receptors) in the carotid system sense changes (increases) in the arterial pressure. These baroreceptors send signals to the brainstem where the cardiac centers are located. A feedback system then activates a number of responses that result in a lowering of arterial pressure. Two dogs are used in a study to test the effects of a drug that causes hypertension as a possible side effect. In one of the dogs the baroreceptor feedback system has been inactivated. In the dog with the intact feedback system the arterial pressure increases Fromm 100-110. In the animal with the inactivated control system, the pressure increases from 100-150. What is the effectiveness with which the baroreceptor system controls increase in blood pressure?
A.  -1
B.  -2
C.  -4
D.  -5

Answer 19

C. -4

Question 20

Describe the structure of a typical cell membrane with respect to phospholipids and proteins.

Answer 20

Structure:
> All cell membranes (plasma as well as those around organelles) have the same basic structure, referred to as the “unit membrane”

> the unit membrane is a phospholipid bilayer with cholesterol inserted among the phospholipids

> proteins are associated with the membrane
» integral proteins
» peripheral proteins

Question 21

How are integral proteins associated with the cell membrane?

Answer 21

> Integral proteins are either inserted into the membrane on one side or the other or pass all the way through and are exposed on either side of the membrane

Question 22

How are peripheral proteins associated with the cell membrane?

Answer 22

> Peripheral proteins are loosely attached to one surface of the membrane or the other and are easily removed

Question 23

Many peripheral proteins are attached to the membrane via what?

Answer 23

> Glycophosphatidylinositol

Question 24

What is the purpose of cholesterol in the cell membrane?

Answer 24

> Cholesterol is relatively inflexible and REDUCES MEMBRANE FLUIDITY

Question 25

List some of the basic functions of the plasma membrane.

Answer 25

> serves as a selective filter and limits what can pass from one side to the other
» lipid soluble substances can general pass readily across the membrane

> plays an integral role in defining the intracellular and extracellular fluid composition

> plays a role in information exchange between the cell and its environment

> intimately involved in exocytosis and endocytosis (pinocytosis and phagocytosis). (Refer to fig. 2-11)

Question 26

List the major functions of each of the membrane-bound organelles

Answer 26

Nucleus
ER
Golgi
Mitochondria
Lysosomes
Peroxisomes and endosomes

Question 27

With which function is clathrin associated? (Fig. 2-11)

Answer 27

> endocytosis (pinocytosis and phagocytosis)
» coated pits (with clathrin) with or without receptors
» form phagocytic vesicles

Question 28

Describe the characteristics of lysosomes.

Answer 28

Involved in cellular digestion:

> contain hydrolytic enzymes at a low pH
» result in a hydrogen-ion pump

> primary lysosomes fuse with phagocytic vesicles to form secondary lysosomes

> undigested material is left behind within residual bodies

> residual bodies may be eliminated via exocytosis

Question 29

What organelles are associated with protein synthesis?

Answer 29

> involves ribosomes and endoplasmic reticulum (ER)
» proteins bound for lysosomes or secretion are synthesized on rough ER (RER) to which the ribosomes attach
» proteins bound for the cytoplasm, nucleus, mitochondria, or to other cell membranes are synthesized on free ribosomes

Question 30

What is the role of the Golgi apparatus?

Answer 30

> plays a role in packaging proteins for secretion:
»I.e., O-glycosylation

> forms lysosomes

> modifies proteins from the RER

Question 31

What are the ways in which energy is produced?

Answer 31

> glycolysis (anaerobic respiration)

> kreb’s cycle and ETC (aerobic respiration)

Question 32

Summarize glycolysis.

Answer 32

> glycolysis (anaerobic respiration)
>>> begins with glucose
>>> occurs in the cytoplasm of all cells
>>> does not require oxygen
>>> produces pyruvic acid (lactic acid) and a small amount of ATP

Question 33

Summarize the kreb’s cycle and ETC.

Answer 33

> Kreb’s cycle and ETC (aerobic respiration):
» utilizes pyruvic acid from glycolysis
» can only occur in the mitochondria
» requires oxygen as the final electron acceptor
» produces carbon dioxide and water
» produces much more ATP than glycolysis

Question 34

What are the types of ways in which cells are able to move?

Answer 34

> ameboid movement
cilia and flagella
microtubules

Question 35

Summarize ameboid movement.

Answer 35

> ameboid movement (fig. 2-16):

|&raquo_space;> used by macrophages and some other leukocytes

Question 36

Summarize locomotion via cilia and flagella.

Answer 36

> cilia and flagella (figs. 2-17 and 2-18)
» flagella move cells (The only flagellated cells in humans and other mammals are sperm cells.)
» cilia move other material, usual through a layer of mucous that coats a layer of ciliated cells
» the cells remain stationary

Question 37

What are the only flagellated cells in humans and other mammals?

Answer 37

> the only flagellated cells in humans and other mammals are sperm cells

Question 38

Summarize movement via microtubules.

Answer 38

> provide tracks on which motor molecules can move cargos