Topic 12 – Rhythms, Stress, and Associated Hormones

Rhythms and Hormones

10.1 Endocrine function shows rhythmic variation over time (Part 1)

• Chronobiology is a field of biology that examines periodic (cyclic) actions in living organisms. These cycles are known as biological rhythms.

• Chronobiology comes from the ancient Greek word “chrónos” which means "time“

• Chronobiological studies are important in many fields of biology, but especially in anatomy, physiology, endocrinology, developmental biology, genetics, ecology, molecular biology and behavioral biology.

Hourly fluctuations in LH secretion.

10.1 Endocrine function shows rhythmic variation over time (Part 2)

Daily fluctuations in LH secretion

10.1 Endocrine function shows rhythmic variation over time (Part 3)

Yearly fluctuations in LH secretion

Special Note: Notice how we can see different rhythms that are seen in these hamster LH levels depending upon the sampling frequencies. There are actually three different cyclic patterns observable.

Jean Jacques Dortous De Mairan (1678-1771) – a french astronomer that is credited with identifying

the internal biological clock.

10.3 De Mairan’s experiment

The plant shown is heliotropic, meaning it typically responds to sunlight for opening and closing. Yet, the researcher found this species would open & close cyclically in the absence of sunlight.

The cyclicity was not due to light intensity but instead due to an INTERNAL CLOCK in an organism.

Note that entrainment is the alignment of a circadian system's period and phase to the period and phase of an external rhythm.

10.4 The diversity of biological rhythms (Part 2)

10.5 The collection of data on behavioral biological rhythms (Part 1)

• Each turn of the wheel creates a mark on the chart.

• Black bands indicate long periods of running.

• The running pattern can be correlated with time of day (see C).

10.5 The collection of data on behavioral biological rhythms (Part 2)

10.8 Ultradian rhythms in human plasma glucose level and insulin secretion rate

• Ultradian rhythms are shorter rhythms than circadian (shown).

• Sometimes the term “infradian rhythms” is used to describe rhythms close to but longer than circadian (not shown).

10.14 Circadian rhythms in human physiology and behavior

Optic Chiasm shown as the “X”

The Suprachiasmatic Nucleus (SCN) is important in rhythms.

10.22 SCN damage disrupts the daily sleep–wake cycle in humans

• The suprachiasmatic nucleus or nuclei (abbreviated SCN) is a small region of the brain found directly above the optic chiasm. It is responsible for controlling circadian rhythms.

• The neuronal and hormonal activities it generates regulate many different body functions in a 24-hour cycle, using around 20,000 neurons.

• The SCN interacts with many other regions of the brain. It contains several cell types and produces several different peptides (including vasopressin and vasoactive intestinal peptide) and a variety of neurotransmitters.

10.23 The three main components of a mammalian biological clock system

Notice how the SCN exerts effects both neurally and hormonally.

The SCN sends information to other hypothalamic nuclei and the pineal gland to modulate body temperature and production of hormones such as cortisol and melatonin.

• The US Food and Drug Administration (FDA) has approved tasimelteon (Hetlioz, Vanda Pharmaceuticals Inc) for the treatment of non–24-hour sleep-wake disorder (non-24), in January 2014.

• Non-24 is a chronic circadian rhythm disorder that disrupts the sleep-wake cycle and affects the majority of totally blind individuals. Without input from the eyes, information about environmental light levels fails to reach the suprachiasmatic nuclei in the hypothalamus to synchronize the internal clock.

• As a result, levels of the hormone melatonin, produced by the pineal gland and playing a key role as a feedback regulator of the master circadian clock, peak at later and later times each day, disrupting the sleep-wake cycle.

10.30 Melatonin measures night length

Stress & Hormones

11.2 Catecholamine concentrations peaked on the day of a Ph.D. exam (Part 1)

Does this secretion pattern seem familiar?

11.2 Catecholamine concentrations peaked on the day of a Ph.D. exam (Part 2)

11.3 Hypothalamic–pituitary–adrenal (HPA) axis releases several hormones in response to stress

11.4 Blood hormone concentrations are altered by the stress of parachute jumps (Part 1)

11.4 Blood hormone concentrations are altered by the stress of parachute jumps (Part 2)

11.7 Prolactin inhibits reproductive function (Part 1)

11.7 Prolactin inhibits reproductive function (Part 2)

11.8 Wound healing is impaired in stressed caregivers

11.11 Stress responses are reduced in offspring that received maternal attention as pups

11.12 Epigenetic influences of maternal behavior on offspring

11.17 Dominant male rats have lower corticosterone and higher testosterone when stressed

11.18 Exercise elevates testosterone in men

11.26 Leg-swinging displacement activity reduces heart rate

Hyperparathyroidism produces considerable osseous erosion and the development of brown tumors (osteoclastomas) and also osteoporosis.