9.1, 9.2 Homeostasis and chem. ctrl in mammals

Question 1

define homeostasis

Answer 1

The maintenance of the state of a dynamic equilibrium through the responses of the body to external and internal stimuli

Question 2

why must the pH level in the body be controlled

Answer 2

so the structures of protein molecules remain stable, this allows enzymes to function at their optimum activity and allows the structure of cell membranes to be maintained

Question 3

why does the core temperature of the body need to be maintained

Answer 3

• to maintain optimum activity of enzymes that control the rate of cellular reactions
• to maintain the integrity of the membranes so they can control the movement of substances into and out of the cells

Question 4

why must the water potential of body fluids remain within narrow limits

Answer 4

• to avoid osmotic effects that could damage or destroy (lyse) cells

Question 5

what is the most common type of feedback system in mammals

Answer 5

• negative feedback systems

Question 6

describe a negative feedback system if the factor drops below the norm

Answer 6

1. factor falls to a lower level
2. receptor detects change
3. communication via hormones/ nervous system via control centre
4. effector carries out response which brings about corrective change
5. factor rises to normal level

Question 7

give two examples of a negative feedback system

Answer 7

• the production of many hormones
• temperature regulation in mammals

Question 8

give an example of a positive feedback loop

Answer 8

• the contractions of the uterus lining during labour

Question 9

describe the positive feedback loop of the contractions of the uterus lining

Answer 9

1. brain stimulates the pituitary gland to release oxytocin
2. oxytocin makes the uterus lining contract harder, pushing the baby’s head against the surface
3. baby’s head is pushed against the cervix
4. stretch receptors in the cervix send impulses to the brain

Question 10

give an example of long term stimulation of tissues

Answer 10

growth and sexual development

Question 11

what are the effectors of the feedback loop if:
- the communication is hormonal
- the communication is nervous

Answer 11

hormonal: effectors are the various target organs

nervous: effectors are the muscle glands

Question 12

define hormone

Answer 12

organic chemicals produced in the endocrine glands and released into the blood

Question 13

what type of molecules are hormones usually

Answer 13

• proteins
• peptides
• steroids

Question 14

how do hormones facilitate a response

Answer 14

• they are made by the endocrine glands
• once it enters the blood stream, it is carried in the blood until it reaches the target organ
• the cells of the target organ have specific receptor molecules on the surface of their membranes that bind to the hormone
• this brings about a change in the cell membrane and elicits a response

Question 15

what are the conditions of an endocrine gland like and why ?

Answer 15

• they have a rich blood supply with plenty of capillaries in the glandular tissue because they secrete hormones directly into the blood

Question 16

name all of the endocrine glands and their positions in the human body

Answer 16

1. hypothalamus - behind the eyes, roughly at the base of the brain
2. pituitary gland - just under the hypothalamus
3. thyroid gland - in the middle of your chest and throat
4. parathyroid gland - in the thyroid gland
5. pancreas - between belly and boobs/ chest
6. kidneys - at the sides of your belly button
7. adrenal glands - at the top of the kidneys
8. ovaries - spherical structure at the side of your uterus
9. testes - balls

Question 17

what must happen in order for a hormone to be released from a gland

Answer 17

• the gland must be stimulated

Question 18

which gland is referred to as the ,master gland and why

Answer 18

the pituitary gland because it secretes hormones that stimulate other glands

Question 19

what controls the pituitary gland

Answer 19

• hypothalamus

Question 20

define negative feedback system

Answer 20

bodily system that provides a way of maintaining a condition, such as concentration of a substance, within a narrow range. A change in conditions is registered by receptors and as a result effectors are stimulated to restore the equilibrium

Question 21

define positive feedback system

Answer 21

a fluctuation triggers changes that causes effectors to cause an even greater deviation from the normal level

Question 22

how do hormones have their effect

Answer 22

• they act by binding to specific receptor sites on the membranes of their target cells
• hormones affect the target cell by a mode of action to bring about desired change

Question 23

what are the two modes of action by hormones

Answer 23

1. release of a second messenger
2. hormone enters the cell

Question 24

describe mode of action 1, and state an examples

Answer 24

1. release of a second messenger
   - it can’t cross the membrane because it isn’t lipid soluble
   - binds to a receptor in the cell membrane
   - triggers a series of membrane bound reactions that result in the formation of a second messenger from ATP
   - second messenger activates a number of enzymes (usually cyclic AMP, cAMP)
   - this triggers a number of responses e.g. increased muscle contraction, increased cellular respiration, glycogenesis
   - e.g. adrenaline

Question 25

describe mode of action 2, and state some examples

Answer 25

• lipid soluble hormones pass through the cell membrane and acts as the internal messenger
• hormone binds to receptor, newly formed complex passes through pores of nuclear membrane into nucleus
• hormone bound to the receptor acts as a transcription factor, regulating gene expression
• e.g. oestrogen and testosterone

Question 26

what are plants sensitive to

Answer 26

light, gravity, water, temperature

Question 27

what are meristems

Answer 27

• the main areas of cell division in a plant
• they occur just behind the tip of a root or shoot
• these areas are particularly sensitive to plant growth substances

Question 28

what is the mode of action of oestrogen

Answer 28

• steroid hormone diffuses into the cell membrane
• forms a hormone receptor complex with ER a receptor in the cytoplasm
• complex enters the nucleus and acts a transcription factor