8. Body in Balance

Question 1

Homeostasis

Answer 1

Tendency of body to maintain a condition of balance. Depends on active regulation which often involves the hypothalamus

Question 2

Example of body’s internal clock

Answer 2

Faster pulses of peristaltic waves in gut during day and dip in blood pressure during night

Question 3

How are daily rhythms coordinated?

Answer 3

Clocks cannot detect daylight, so they can’t tell time on their own. Coordinated by suprachiasmatic nucleus (SCN), group of neurons in hypothalamus. Emits a steady stream of action potentials during day and does nothing at night.

Question 4

How is the shift between active and silent states of suprachiasmatic nucleus controlled?

Answer 4

Controlled by cyclic interactions between two sets of proteins encoded by clock genes

Question 5

How does the suprachiasmatic nucleus track time?

Answer 5

Via signals received from photoreceptors in retina

Question 6

Why is the nudge from the suprachiasmatic nucleus important for our internal clocks?

Answer 6

Because clock proteins take slightly more than 24 hours to complete a cycle. Studies of animals deprived of light have discovered that they go to sleep and wake up a bit later each day

Question 7

How is activity of SCN tied to other clocks in body?

Answer 7

Autonomic neural pathway ties daily activity of SCN to other clocks in body. Neurons in the SCN stimulate paraventricular nucleus (PVN) which sends signals down the spinal cord to the peripheral organs of the body

Question 8

Melatonin

Answer 8

Hormone that influences sleep behaviours. Electrical activity originating in SCN enters PVN and sends signals to pineal gland, which secretes melatonin into bloodstream at night. Melatonin binds to many different types of cells, has no direct effect on clock gene expression in SCN but reduces alertness and increases sleepiness. Light exposure stops melatonin secretion.

Question 9

What happens when your body prepares to wake?

Answer 9

Levels of cortisol peak in blood, releasing sugars from storage and increasing appetite. Core body temperature rises, raising metabolic rate

Question 10

Circadian rhythm disruptions

Answer 10

Jet lag, late-shift jobs, blindness

Question 11

Outline of neuroendocrine system

Answer 11

Hypothalamus oversees production and release of hormones through ties to pituitary gland. Paraventricular and supraoptic nuclei of hypothalamus send axons into posterior part of pituitary gland. Activation of specific neurons either releases vasopressin or oxytocin into capillaries. Two substances serve as both neurotransmitters and hormones.

Question 12

Vasopressin

Answer 12

Antidiuretic hormone, increases water retention in kidneys, constricts blood vessels.

Question 13

Oxytocin

Answer 13

Promotes uterine contractions during labour and milk release during nursing

Question 14

Activation of anterior pituitary

Answer 14

Other hypothalamic regions send axons to the median eminence (capillary-rich area above pituitary). When these neurons are activated, they release their hormones into the blood to anterior pituitary, where they trigger or inhibit the secretion of another hormone.

Question 15

Anterior pituitary hormones (7)

Answer 15

5 are trophic hormones (travel in bloodstream to stimulate activity in specific glands). Other 2 are non-endocrine tissues.

Growth hormone: stimulates growth of bone and soft tissues

Prolactin: stimulates milk production

Question 16

How are hormone levels regulated?

Answer 16

Negative feedback loops. Many hormones produced by the pituitary affect the amount of hormone released by the hypothalamus

Question 17

First three steps in hormone regulation of reproduction in mammals

Answer 17

Gonadotropin releasing hormone (GnRH) from hypothalamus makes anterior pituitary release luteinizing hormone (LH) and follicle stimulating hormone (FSH), which make the gonads secrete sex hormones and start development of egg/sperm. Sex hormones attach to receptors in hypothalamus and anterior pituitary and modify release of hypothalamic and pituitary hormones. How sex hormones regulate these feedback loops differs between males and females

Question 18

Regulation of reproduction in males

Answer 18

Simple negative feedback loops that reduce secretion of GnRH, LH, and FSH. interplay among hormones. Creates a repetitive pulse of GnRH that peaks every 90 minutes. Waxing and waning of GnRH keeps testosterone levels steady, maintains libido, and keeps testes making sperm each day

Question 19

Regulation of reproduction in females

Answer 19

More complex, over course of menstrual cycle, hormones exert both positive and negative feedback on 3 hormones. When circulating levels of estrogen and progesterone are low, rising FSH levels trigger egg maturation and estrogen production. Rising estrogen levels make LH levels rise. As levels of sex hormones rise, they exert negative feedback on FSH secretion, limiting number of eggs that mature each month, but positive feedback on LH, eventually producing th LH surge that triggers ovulation. After ovulation, high levels of sex hormones again exert negative feedback on 3 hormones, reducing ovarian activity. Levels of sex hormones therefore decrease, allowing cycle to restart

Question 20

Examples of hormones not regulated by pituitary gland

Answer 20

Released by specific tissues, brain contains receptors but doesn’t regulate secretion.

Leptin: helps maintain body weight within set range. Produced by fat cells, released when fat stores are large. Suppresses activity of hunger circuits

Ghrelin: keeps body fed. Released by wall of gastrointestinal tract when stomach is empty. Activates hunger circuits in hypothalamus

Question 21

Heat-shock proteins

Answer 21

In single-celled organisms/cells, heat-shock proteins guide damaged proteins to where they can be repaired/degraded, protecting the cell from toxicity

Question 22

Somatic nervous system in stress response

Answer 22

Voluntary nervous system, prime boy to fight or flee

Question 23

Autonomic nervous system in stress response

Answer 23

Involuntary nervous system, redirect nutrients and oxygen to muscle

Question 24

Sympathetic branch in stress response

Answer 24

Tells adrenal medulla to release epinephrine (adrenaline), making heart pump faster and relaxing arterial walls

Question 25

Parasympathetic branch in stress response

Answer 25

Restricts blood flow to other organs

Question 26

Glucocorticoid hormones

Answer 26

Adrenal cortex releases it. Bind to many tissues and produce widespread effects that prepare body for threat. Stimulate production and release of sugar from storage. Bind to areas that ramp up attention and learning. Inhibit nonessential functions like growth and immune responses until crisis ends

Question 27

Inhibition of immune system in stress response

Answer 27

Activation of hypothalamic-pituitary-adrenal axis. Increased production of corticotropin releasing factor (CRF) in hypothalamus, CRF travels to pituitary gland to release adrenocorticotropin releasing factor (ACTH) which travels to adrenal gland to release cortisol. Cortisol suppresses immune function

Question 28

Chronic stress

Answer 28

Adrenal glands keep secreting epinephrine and glucocorticoids. Causes muscles to atrophy, pushes body to store energy as fat, keeps blood sugar abnormally high.

Question 29

Mothers with high glucocorticoid levels during pregnancies often have babies with…

Answer 29

Lower birth weights, developmental delays, more sensitive stress responses. Stressful environments push fetuses to develop stress-sensitive metabolisms that store fat easily to deal with environment. However, this can backfire, especially if the child eventually grows up in a healthy environment with a lot of food

Question 30

Negative effects of chronic stress

Answer 30

Contributes to development of hypertension and atherosclerosis (hardening of arteries). Reduces resistance to infection and inflammation, sometimes pushes immune system to attack body. Inhibit neuron growth in hippocampus. Can speed deterioration of brain function caused by aging. Can lead to sleep disorders (cortisol is an important wakeful signal)

Question 31

Responses to disease regulated primarily by…

Answer 31

Hypothalamus

Question 32

Neural signals for immune system sent via…

Answer 32

C-fibres and vagus nerve from liver

Question 33

Cytokines

Answer 33

Important immune signals. Group of over 100 proteins. Normally produced at very low levels, but are switched on in response to disease/injury. Cause most of the responses to disease and infection, stimulating immune system and key parts of inflammation (swelling, changes to blood flow). Shown to also be active contributors to brain diseases (Alzheimer’s, stroke, multiple sclerosis)

Question 34

Examples of cytokines

Answer 34

Interferons, interleukins, tumour necrosis factors, and chemokines