Hormones: Defintions and processes

Question 1

What are hormones?

Answer 1

Chemical messenger released into blood stream / tissue fluid system to affect function of target cell ⇒ secreted by endocrine system

• bind receptors on target cells -> act as/ degrade/ synthesise neurotransmitters, alter gene expression, signalling cascade
• slower than neuronal action potentials
• can be sustained over minutes / days / months

First study: Arnold Berthold
- Castrated male chicks displayed few male morphological traits and behaved like females

Question 2

Key groups of hormones, glands

Answer 2

Amine derived (e.g. melatonin), peptides (e.g. Insulin), lipids (e.g. testosterone)

Endocrine (blood) or exocrine (duct -> blood stream)

Brain hormonal glands:
- Hypothalamus hormones
- Pituitary hormones
- pineal hormones (third eye)
- > Control circadium rythms by releasing melatonin (from seratonin)
- > cells derived from photo receptors (remain as photoreceptors in fish, both in replites, and gland in mammals)

Other glands: thyroid / parathyroid (metabolism + growth / differentiation), pancreatic (sugar metabolism), adrenal (arousal + stress), gastrointestinal, gonadal (repro + development

Question 3

Homeostasis

Answer 3

Ability to regulate one’s internal state/environment to a stable or optimum condition (nutrients, temperature, water balance)

Relies on feedback:

Positive: Gland -> hormone -> target -> product induces hormone release

child pushes on cervix -> pituirtary gland releases oxytocin -> uterus contractions -> child usges on cervix

Negative: Gland -> hormone -> target -> product inhibits hormone release

decrease Ca2+ in blood plasma → parathyroid gland secretes hormone → releases Ca2+ from bone into blood and increases blood Ca2+ conc → inhibits parathyroid gland to prevent leaching all bones into blood

Question 4

Sensation -> integration -> action

Answer 4

Sensation -> integration -> action

hormones effect all three processes

sensation: hormones can make individuals more sensitive to stimuli

integration: hormones effect the processing of stimuli (e.g. speed of impulses)

Action: hormones effect the output (e.g. strength of muscles)

They influence these three systems so that specific stimuli are more likely to elicit certain responses in the appropriate behavioural or social context.

Question 5

Hormones and behavior feedback

Answer 5

Hormones -> behavior

behavior -> hormones

Question 6

What effects hormone secretion?

Answer 6

1) Age
a. Juvenile vs adult

2) Genetic sex
a. male, female, hermaphrodite

3) Metabolic/emotional state
a. hungry, thirsty, tired, afraid

4) Behaviour/experience
a. winning/losing, escape, social
interaction

5) Environment
a. Social group, temperature

6) Biological/circadian rhythm
a. time of year, time of day

7) Reproductive state
a. pregnant, nursing, in heat

Question 7

What do hormones effect?

Answer 7

Nervous system
e.g. Songbird HVC (higher vocal centre) development in males associated w/ testosterone. May lose HVC in autumn (non-breeding season)

**Sensory perception **
e.g. Ovulating women more sensitive to visual / auditory stimuli + least sensitive during menstruation

**Tissue development **
e.g. Anatomical + physiological during development from kid to adult

Sex-specific traits
e.g. High estrogen causes dull plumage in female birds

Metabolism
e.g. Low thyroxin = low basal metabolic rate

**Biological/circadian rhythms **
e.g. Melatonin affects circadian rhythm via action on hypothalamus

**Reproduction **
e.g. Steroids, peptides, monoamines effect repro + parenting

Question 8

Circadium rhythms

Answer 8

Physical, mental, and behavioral changes an organism experiences over a 24-hour cycle controlled by solar day -> regulation of gene expression
-> Controls metabolism, sleep, body temperature, blood pressure, endocrine, immune, cardiovascular, and renal function.

Mechanisms
- Light -> Retinohypothalamic tract (RHT) receive info and signals to SCN-> SCN secretes humoral signal which controls gene expression. E.g. secretes neurone inhbitor stopping synapse signal transduction to pineal gland -> stops seratonin conversion to melatonin thus no release
- Dark -> Retinohypothalamic receive info -> SCN signals to pineal gland -> Melatonin released
- SCN signals are controlled by the levels of PER and and CRY proteins which vary throughout the period

Hamster Tau mutant:
- BMAL1 and CLOCK are transcription factors of PER and CRY
- PER and CRY move to cytoplasm and are degraded or form complex which acts as negative repressor
- Mutation in Casein Kinase 1 stops the degredation of PER meaning more complexes form and PER CRY return to nucleus and negatively feedback on their production.
- Less PER and CRY production shortens the circadium rhythm

Plamsa hormones level follow the cycle -> pattern reversed in nocturnal animals

Question 9

Blood sugar homeostasis

Answer 9

Hypathalamum monitors signals from the blood, pituirtary and body fat-> sends hormonal signals to hind brain -> releases hormones to control feeding

Hormones prepare body to eat/ digest and increase motivation to eat -> ensure blood sugar remains constant

Hormones vary around when we eat:
Ghrelin/ GLP-1 – peaks before eat
Insulin – peaks at consumptions

Nutritional state affected by:
- when last ate
- how much
- parasite load
- if making eggs, hunting etc.

Question 10

Motivation

Answer 10

Motivation = biological, social + cognitive forces that activate behaviours

Example: male guppies
- Motivation / interest in breeding depends on age + testosterone + time to last breeding event
- Older, more developed males more motivated so will court small females too