Chapter 5 : The Endocrine System

Question 1

What is inter-cellular fluid? State examples.

Answer 1

Inter-cellular fluid is the fluid located inside the cells, mainly the cytosol.

Question 2

True or False.

The internal environment of a multicellular organism is mostly made of tissue fluid.

Answer 2

True.

Question 3

What is the internal environment of a multicellular organism made of?

Answer 3

Extracellular fluid.

Question 4

Define homeostasis.

Answer 4

Homeostasis is the condition of a relatively stable internal environment, maintained within narrow limits.

Question 5

Name some of the variables maintained under homeostasis.

Answer 5

Blood pH level, blood glucose level, blood volume and pressure, body temperature, ion concentration, etc.

Question 6

Define negative feedback.

Answer 6

Negative feedback is a response mechanism in which a response produced in the opposite direction counteracts the effect of the stimulus (either by raising or lowering the stimulus), returning the body back to its normal state.

Question 7

State the sequence for negative feedback.

Answer 7

Stimulus (an object or event that causes a change) - receptor - control center - effector - response.

Question 8

State the (detailed) process for negative feedback.

Answer 8

A change in a key variable is detected (stimulus), and a signal is produced. The signal is detected by a receptor (sensor) and is transmitted to the control center. The control center sends another signal to the target organ, gland or muscle (effector). The effector responds to the signal by producing a response in the opposite direction to counteract the effect of the stimulus. The original signal decreases and the process continues until it is switched off.

Question 9

Name an example of negative feedback.

Answer 9

For example, bright light (stimulus) falls onto your eyes (sensor). The muscle in the eyes (effector) constricts (response), so that less light can get into your eye, and vice versa.

Question 10

How is homeostasis maintained?

Answer 10

Through negative feedback systems, which are mainly the endocrine and nervous systems.

Question 11

What is the hypothalamus?

Answer 11

The hypothalamus is a small gland located at the base of the brain. It detects changes in blood passing through it, and is involved in water balance in blood, temperature regulation and blood pressure regulation. The hypothalamus can send messages through nerves or produce hormones.

Question 12

Define positive feedback.

Answer 12

Positive feedback is a response mechanism that increases the effect of the stimulus, moving the body further away from its normal state.

Question 13

Name the hormones that control blood glucose regulation.

Answer 13

Insulin (increases blood glucose level) and glucagon (decreases blood glucose level).

Question 14

Where is the hormone glucagon produced?

Answer 14

Glucagon is secreted by alpha cells in the pancreas.

Question 15

Name examples of positive feedback.

Answer 15

Contractions during childbirth, the production of clotting factors in blood after an injury, etc.

Question 16

Where is the hormone insulin produced?

Answer 16

Insulin is secreted by beta cells in the pancreas.

Question 17

What happens when blood glucose level reduces below normal?

Answer 17

Glucagon is secreted by alpha cells in the pancreas, and released into the bloodstream, where it targets mainly the liver and muscle cells. Glucagon binds to receptors located on the surface of the plasma membrane, and uses cAMP as a second messenger. cAMP activates a range of other proteins. Responses include the inhibition of the secretion of insulin by beta cells, resulting in the decrease uptake of glucose by the cells, glycogen in the liver being converted into glucose and released into the bloodstream and stored fat being converted into carbohydrates.

Question 18

What happens when blood glucose level rises above normal?

Answer 18

Insulin is secreted by beta cells in the pancreas, and released into the bloodstream, where it targets mainly liver and muscle cells. Insulin binds to kinase receptor located on the surface of the plasma membrane, which also acts as a second messenger. The kinase receptor activates a range of other proteins. Responses include increasing the rate of glucose uptake by cells, converting glucose into glycogen to be stored in the liver, glucose and glycogen being converted into fat and the inhibition of the secretion of glucagon, resulting in the decrease conversion of stored glycogen into glucose.

Question 19

What is extracellular fluid? State examples.

Answer 19

Extracellular fluid is the fluid located outside the cells, such as tissue fluid (interstitial fluid) and blood plasma.

Question 20

Define signalling molecules.

Answer 20

Signalling molecules are molecules that enable cell communication, such as hormones, neuro-hormones and neurotransmitters.

Question 21

Name the types of cell signalling.

Answer 21

Autocrine, paracrine, endocrine and contact dependent signalling.

Question 22

What is autocrine signalling?

Answer 22

Cell signalling from neighboring cells of the same type or within the cell itself, such as immune signalling.

Question 23

What is paracrine signalling?

Answer 23

Cell signalling from nearby cells of different types. It has short-lived local effects and the signal molecule will diffuse through the extracellular fluid into the other cell, such as neurotransmitter signalling.

Question 24

What is endocrine signalling?

Answer 24

Cell signalling from cells in distant parts of the body travelling through the bloodstream to the target cell.

Question 25

What is contact-dependent signalling?

Answer 25

Cell signalling that targets a cell that is connected by gap junctions.

Question 26

Define signal transduction.

Answer 26

Signal transduction involves getting a signal from a target cells exterior to the cells interior during which the cell converts one kind of signal into another, by a series of relay molecules and other proteins. Within a cell, signal transduction amplifies the signal that the original hormone molecule produced.

Question 27

Name examples of the results of signal transduction in cells.

Answer 27

• Altering gene expression, which influences the production of proteins, including enzymes (mainly steroid hormones).
• Altering the permeability of the cell membrane.
• Activating/deactivating enzymes, which affects cellular metabolism.

Question 28

Define hormone.

Answer 28

A hormone is a chemical that is produced in one part of an organism and transported in the bloodstream to another part where it exerts its effect.

Question 29

True or False.

Hormones always enter the bloodstream, and act on cells that are in another part of the body.

Answer 29

False.

They can act on the cell that produced the hormone, or act on nearby cells.

Question 30

If hormones travel through the bloodstream, why don’t all cells of the body respond to that hormone?

Answer 30

Only cells with specific receptors for that hormone will respond to the hormone signal.

Question 31

Name the three main types of hormones.

Answer 31

Amino acid derivatives, protein (over 200 amino acids) and peptide (under 200 amino acids) hormones, and steroid hormones.

Question 32

Describe protein based hormones in as much detail as possible.

Answer 32

Protein based hormones, such as insulin and thyroid gland hormone, are hydrophilic in nature, which means that they travel in the bloodstream but are unable to pass through the cell membrane. Their receptors are located on the surface of the cell membrane, and the response produced is rapid, as the enzymes being activated are already present. However, the duration of the response is relatively short. Transduction method includes the generation of second messenger that alters the activity of enzymes already in the target cell.

Question 33

Describe steroid based hormones in as much detail as possible.

Answer 33

Steroid based hormones, such as testosterone, are hydrophobic in nature, which means that they are transported in blood by carrier proteins and are able to pass through the cell membrane. Their receptors are located inside the cytosol of the cell, and the response produced is longer, as the hormone/receptor complex has to interact with DNA to alter the rate of protein synthesis. However, the duration of the response is longer. Transduction method includes altering the rate of gene transcription thereby altering the rate of protein synthesis.

Question 34

True or False.

Hormones last forever.

Answer 34

False.
Once their effect has been exerted they are no longer needed. They are degraded by cell enzymes and excreted via the kidneys or faeces.

Question 35

Define pheromones.

Answer 35

Pheromones are chemical signalling molecules that are produced by animals, usually insects. They are often used as sex attractants and influence the behavior of members of the same species.

Question 36

True or False.

Pheromones are species-specific.

Answer 36

True.

Question 37

True or False.

The action of pheromones is external, and not internal.

Answer 37

True.

Question 38

True or False.

Plants lack a nervous system, so their responses are governed by hormones or chemical regulators.

Answer 38

True.

Question 39

Name the five main groups of hormones.

Answer 39

Auxins (IAA), gibberellins, cytokinins, abscisic acid and ethylene.

Question 40

What is the effect of auxins?

Answer 40

Stimulate cell elongation, cell division in the cambium and differentiation of the phloem and xylem. Suppress growth of lateral buds (apical dominance), and mediate trophic responses to light and gravity. Suppress fruit ripening, stimulate growth of flower parts.

Question 41

What is the effect of gibberellins?

Answer 41

Promote cell division and cell elongation in plant shoots.

Question 42

What is the effect of cytokinins?

Answer 42

Stimulate cell division in the middle layer of cells in leaves.

Question 43

What is the effect of abscisic acid?

Answer 43

Generally acts as an inhibitor, promotes stomata closure, particularly during times of water stress. Also stimulates dormancy in seeds and buds.

Question 44

What is the effect of ethylene?

Answer 44

Promotes fruit ripening, leaf fall, stress responses.

Question 45

Define tropism.

Answer 45

The growth of a plant in response to a specific stimulus, such as light or gravity.

Question 46

Define phototropism.

Answer 46

Phototropism is the growth of a plant in response to light.

Question 47

Define geotropism.

Answer 47

Geotropism is the growth of a plant in response to gravity.

Question 48

Which part of the plant shows positive geotropism?

Answer 48

The roots.

Question 49

Which part of the plant shows negative geotropism?

Answer 49

The shoots.

Question 50

Why does a coleoptile bend towards the light?

Answer 50

Growing coleoptiles bend toward the light as auxin is more concentrated in the side of the plant that is not exposed to the sunlight, resulting in the elongation of one side of the plant, causing the plant to bend towards the light.

Question 51

Define thighmotropism.

Answer 51

Thighmotropism is the growth of a plant in response to touch.

Question 52

Define photoperiodism.

Answer 52

Photoperiodism is the growth of a plant in response to seasonal changes in day length.