Unit 3 - Homeostasis (1)

Question 1

Homeostasis

Answer 1

the maintenance of a relatively steady internal environment within an organism or its cells
importance
enzymes only function properly under certain conditions (temp, pH)
buildup of waste products can inhibit the progress of metabolic reactions by Le Chatelier principle
lack of necessary substrate molecules shuts down metabolic processes, perhaps leading to tissue death

Question 2

Regulatory systems

Answer 2

receptors = sense a stimulus (eg. blood, temperature, blood pressure)
control centre (central nervous system) = receives signals from receptors and makes a suitable response
effectors (muscles or glands) = initiates an action to reduce the stress and sends a signal to reset the receptor
muscles = contract, go through peristalsis, constrict blood vessels
glands = secrete hormones

Question 3

Negative feedback

Answer 3

most common strategy
a stimulus initiates a series of events that counteracts the stimulus
eg. furnace control, thermoregulation

Question 4

Positive feedback

Answer 4

a stimulus initiates a series of events which amplifies the stimulus
rather than regaining homeostasis, positive feedback does the opposite, so it is rarely used

Question 5

Example of positive feedback

Answer 5

uterine contraction:
fetus’ head pushes against cervix
stretch receptors in cervix send signals to the brain
pituitary gland secretes oxytocin
the bloodstream carries oxytocin to the uterus, stimulating uterine contractions, pushing fetus’ head against cervix

Question 6

Exocrine glands

Answer 6

not a part of the endocrine system
secretions released outside of the body
some exocrine glands release digestive enzymes, bile, acid and sodium bicarbonate into the digestive system
others release secretions directly to the outside (sweat glands, mammary glands)

Question 7

Endocrine glands

Answer 7

release hormones into the bloodstream
hormones = molecules made in a gland that are carried to and affect cells in another part of the body, creates a cascade effect
glands = hypothalamus, pituitary, thyroid, parathyroid, adrenals, pancreas, ovaries, testes

Question 8

Peptide and protein hormones

Answer 8

do not enter their target cells, and do not affect genes
interact with a receptor on the cell surface and induce the formation of a second messenger in the cell
this activates a specific enzyme to produce a product
eg. hypothalamus hormones, pituitary hormones, insulin

Question 9

Steroid hormones

Answer 9

developed from cholesterol
enter the cell and combine with a receptor in the cytoplasm
enter the nucleus, turning specific genes on or off, altering the genes
eg. estrogen, progesterone, testosterone

Question 10

Pancreas

Answer 10

areas in the pancreas called the Islets of Langerhans contain two different cells
alpha cells produce glucagon
beta cells produce insulin

Question 11

Normal glucose regulation

Answer 11

the pancreas beta cells produce insulin when blood glucose is too high
this causes the glucose to be stored as glycogen in the liver and muscles
when blood sugar is too low, the pancreas alpha cells release glucagon, which breaks down glycogen into glucose

Question 12

Life threatening glucose regulation

Answer 12

the sympathetic nervous system controls the flight/fight response using epinephrine and norepinephrine released by the adrenal medulla
this response causes a variety of effects designed to prepare you for an intense effort in times of extreme danger
one effect is breakdown of glycogen to glucose in bloodstream

Question 13

Long term-stress response glucose regulation

Answer 13

the adrenal cortex releases glucocorticoids as a long-term, inflammatory stress response
these include cortisol, which causes gluconeogenesis, the conversion of amino acids and triglycerides to glucose

Question 14

Blood pressure regulation - when pressure is too low

Answer 14

kidneys release renin, which leads to the production of angiotensin
this causes the adrenal cortex to produce aldosterone, which causes the kidneys to retain sodium ions rather than putting them in your urine
you retain water, so blood volume increases as well as blood pressure

Question 15

Blood pressure regulation - when pressure is too high

Answer 15

causes the distension of stretch receptors in the heart walls and causes the release of natriuretic peptide
this hormone relaxes the blood vessels and inhibits the production of renin and aldosterone
it also increases the elimination of sodium ions with the urine, causing water to follow and diluting the urine
the blood volume decreases, lowering blood pressure
ACE inhibitors are a drug that prevent conversion of angiotensin 1 to angiotensin 2, which lowers blood pressure

Question 16

Blood calcium regulation - when too low

Answer 16

the parathyroid glands release parathyroid hormone which causes the bones to release calcium ions
this causes the kidneys to withdraw more calcium ions from the urine and causes the intestines to absorb more calcium

Question 17

Blood calcium regulation - when too high

Answer 17

the thyroid gland releases calcitonin, which does the opposite of the parathyroid hormone
bones absorb calcium ions, kidneys do not withdraw calcium from urine, intestines release calcium

Question 18

Thyroid system

Answer 18

thyroid hormones (T3 and T4 (thyroxine)) increase your metabolic rate
their production is increased due to thyroid stimulating hormone from the anterior pituitary
they self-regulate by inhibiting the production of TSH

Question 19

Thyroid disesase

Answer 19

thyroid hormones require iodine, which is now put in salt to prevent deficiency
thyroid problems cause goiters or excessively high or low metabolism
an overactive thyroid can be trimmed back using radioisotopes of iodine and an underactive one can be supplemented by thyroxine pills
eg. hypothyroidism, hyperthyroidism (Grave’s disease)

Question 20

Male reproductive cycle

Answer 20

hypothalamus releases gonadotropin-releasing hormone (GnRH) which stimulates the anterior pituitary to release FSH and LH
FSH (follicle stimulating hormone) affects the Sertoli cells which influence sperm production
LH (luteinizing hormone) affects the interstitial cells which release testosterone, which also influence sperm production
testosterone and the Sertoli cells then turn off the hypothalamus

Question 21

Female reproductive cycle

Answer 21

hypothalamus releases GnRH which stimulates the anterior pituitary to release FSH, which stimulates the ovarian follicle, producing estrogen which develops the endometrium
the rise in estrogen deactivates the release of FSH, and LH is now released, and ovulation occurs
after ovulation, the follicle becomes a corpus luteum, which secretes estrogen and progesterone, further developing the endometrium
the ovum lasts for two days, if fertilized, it becomes a zygote and releases chorionic gonadotrophin, which keeps the corpus luteum and the endometrium
if not fertilized, the corpus luteum lasts for 7 days, then is broken down
the estrogen and progesterone then inhibit the release of FSH and LH, signaling the beginning of menstruation