Hormones / Target Cells
A. Chemical Signals — Chemoreception
1. Food, Pheromones, Hormones, Neurotransmitter
2. Earliest organisms (single celled prokaryotes)
a. mechanisms for detecting external signals for food, for sex.
b. sensory transduction:
external signal >> cell curface Receptor >> internal signal
3. Multicellular organisms…
a. elaborate mechanisms for detecting and responding to sigals
b. external signal detection (organismic)
c. “internal” signal detection
– internal is “external” to individual cells, tissues, organs, etc.
4. Evolutionary origins of hormones / pheromones…
a. Cells / organisms leak out specialized metabolites.
b. other cells “pick up” / detect metabolites >>> “respond”
c. Evolutionary Selection
d. e.g. fish pheromones are steroid sex hormones / hormone metabolites
– males opportunistically monitor for presence of hormones in water
– male physiology and behavior responds…
A. Hormones come from secretory cells
1. endocrine glands
a. loosely associated secretory cells intermingling with capillaries
b. hormone secreted, diffuses to capillary, travels blood to target
c. chemically stimulated
2. neurohemal organ
a. neurosecretory cells – neurons
b. terminate at capillary (instead of another neuron)
c. neuronally stimulated (stimulated by other neurons)
B. Hormones: chemical diversity –
1. peptides (gene products)
generally small.. few to 30 amino acids (Eckert p.296)
some proteins (200 amino acids or more; e.g. insulin, GH, TSH)
2. modified amino acids
epinephrine (adrenaline), norepinephrine (noradrenaline)
thyroid hormone (thyroxine – tyrosine dimer)
3. steroids – cholesterol-like
progesterone, estrogen, testosterone, aldosterone
4. modified fatty acids
prostaglandins
C. Synthesis and release – triggered
1. Secretory Cells
a. synthesize and release chemicals
b. hydrophilic chemicals – vesicle storage and release
c. lipophilic chemicals – move through membranes / binding proteins
2. Gland and Cell Types
a. Exocrine Glands
– secretion into lumen
– duct allows release to outside of body (e.g. skin / digestive tract)
b. Endocrine Glands
– cells in close association with capillaries