Lecture #15 - Chemical Signals in Animals
* CD-Rom activity 45.3 highly recommended
I. Chemical Signaling
A. Terms
1. Hormone - a chemical signal secreted by an endocrine gland or neurosecretory cell which travels through body fluids to a target cell where it elicits a specific response
a. Steroids - lipid based molecules (cholesterol), include sex hormones
b. Amino acid derived hormones - derived from amino acids, peptide hormones, glycoproteins
2. Endocrine glands - ductless gland (interface at capillaries within the organ) which secretes hormones in to the blood for distribution to target cells, may produce more that one type of hormone
Exocrine gland - has a duct, gall bladder, etc.
3. Target cell - a cell with a receptor for a specific type of hormone, capable of responding to a signal from that hormone
4. Neurosecretory cell - a neuron which secrets a hormone into blood or into a storage area after receiving a signal from another neuron
B. Signal Pathways - potential pathways that chemical signals might take to deliver a message from one tissue (location) to another
1. Systemwide pathways (system may be whole body or a given organ)
a. Endocrine gland pathway - Secretory vessicles from endocrine cell within the organ into the bloodstream, travels to target tissue
b. Neurosecretory cell pathway - as above, from a specialized neuron
c. Pheromones - loosely considered in this group, functions between animals of the same species, small volatile substances
2. Local regulators effect target cells adjacent to or very near the point of secretion, no travel through blood stream.
a. Synaptic signaling - direct, signal travels across a narrow space between neurons called a synapse, normal neuronal function
b. Paracrine signaling - transfer to signal via diffusion to nearby cells, less directed, but very localized
c. Gases - (paracrine signaling) many cell types produce gasses that can act as local regulators (both types) - recent discover, they are everywhere
i. Nitric Oxide (NO)
ii. Carbon Monoxide (CO)
C. Control systems
1. Cascades
a. Hypothalamus
b. Pituitary
c. Endocrine gland
d. Tissues
2. Negative feedback loop (Fig 45.9) - hormone products feed back to producing gland or higher levels in the cascade to show or stop their own continued release.
3. Antagonistically paired (Fig 45.1) to have opposite effects
a. glucagon - raises blood glucose level
insulin - lowers blood glucose level
b. calcitonin - decreases calcium levels
parathyroid hormone - increases calcium levels
II. Signal Receptors & Transduction Pathways (Transduction = changing a signal from one form to another)
A. Steroid hormones (Fig. 45.3a, 45.14)
1. Receptor - within the cytoplasm, lipid hormone can pass through the cell membrane
2. Hormone-receptor complex - then binds to genome and induces or suppresses the expression of specific genes
3. Protein synthesis - initiates or shuts down protein synthesis
B. Protein hormones (Fig. 41.3b)
1. Receptors - binds to specific receptor on surface of cell (can't pass through), then initiates a 2nd messenger system to effect a change in cell
2. Second messengers systems - deliver the message from the surface receptor into the metabolic machinery of the in the cytoplasm
a. Cyclic AMP (adenosine monophosphate) - surface proteins turn the production of CAMP on or off, it has specific role inside specific cells
b. Cytoplasmic calcium - IP3 initiates an increase in intracellular Ca2+
3. Enzymes/protein activity - increases or decreases the activity of proteins already present in the cell
III. Hypothalamic/pituitary axis
A. Hypothalamus/pituitary relationship
1. Hypothalamus - region of lower brain, receives info from throughout body and brain and initiates many endocrine signals, tip of endocrine pyramid
a. Neurosecretory cells - two sets - affect two regions of pituitary
2. Pituitary - dual gland, anterior and posterior portions made of different tissues and producing different hormones. Major hub in hormone cascades.
a. Anterior - develops from out-pocketing of roof of mouth - epithelial origin
b. Posterior - develops from out-pocketing of brain - nervous origin
B. Posterior pituitary (Neuophypophysis) (Fig. 45.7a)
1. Structure - made of nervous tissue, signals from hypothalamus travels directly to these neurosecretory cell, which produce hormones and dump them in to circulation
a. Neurosecretory
b. Stores and secretes two hormones made by hypothalamus
2. Oxytocin - muscles of uterus, milk production
3. Antidiuretic hormone - allows for the production of concentrated urine by increasing water reabsorption at the collecting duct of the nephron in the kidney
C. Anterior pituitary (Adenohypophysis) (Fig. 45.7b) - controlled by releasing (or inhibiting) factors produced by the hypothalamus and delivered by the portal system
1. Structure - non-nervous tissue, receives neurosecretory input from hypothalamus via a portal system (of blood vessels).
a. Non- neuronal
b. Portal system
c. Releasing and inhibiting hormones = trophic hormones
2. Growth hormone - promotes growth of tissue directly and indirectly
3. Prolactin - milk synthesis in mammals
4. Trophic hormones - released to control the release of hormones from other glands
a. FSH - follicle stimulating hormone, affects gametogenesis in gonads & induce the release of steroid hormones from the gonads
b. LH - leutenizing hormone, as above
c. TSH - Thyroid stimulating hormone, induced T3 & T4 production
d. ACTH - adrenocorticotropin, stimulates adrenal glands to production
IV Endocrine glands and functions (Fig 45.6)
A. Thyroid gland
1. Location - two lobes, ventral surface of trachea
2. Hormones/function
a. T2, T3 - from amino acid tyrosine, both bear iodine
b. metabolic rate in mammals, metamorphosis in amphibians
3. Disfunction
a. hypertyroidism - high body temp, weight loss etc.
b. hypothyroidism, weight gain lethargy, cold-intolerance
B. Parathyroid gland
1. Location - 4 glands embedded in surface of thyroid
2. Hormones/function - parathyroid hormone/calcitonin - Ca control, bone formation
C. Pancreas
1. Location - in abdominal cavity, primarily a duct-bearing exocrine gland important in digestion, but there are some true endocrine tissues in the pancreas as well
2. Exocrine gland - Digestive enzymes produced and released through a duct to the duodenum of the small intestine
3. Endocrine gland - two cells types produce hormones responsible for control of blood sugar level, released directly into the blood.
a. alpha cells = glucagon
b. beta cells = insulin
4. Disfunction
a. lacking glucagon leads to hypoglycemia (low blood sugar levels)
b. lacking insulin leads to diabetes (hyperglycemia)
D. Adrenal glands (Fig. 45.15) - responds to stress
1. Location - on top of the kidneys, back of abdominal cavity
2. Adrenal medulla (inner core) - responds to direct innervation from the hypothalamus, rapid response, fight or flight reflex
a. catecholamines released - epinephrine, & norepinephrine
b. have rapid and dramatic effects on energy mobilization, heart rate, blood pressure, blood delivery, oxygen delivery
3. Adrenal cortex (outer shell) - responds to ACTH released by anteriror pituitary, long term stress response
a. cortisosteroids produced (mineralocorticoids, glucocorticoides)
b. production of glucose from non-carbohydrate sources, salt and water balance, important in handling swelling
E. Gonads
1. Location - lower abdominal cavity (women), outside of body in scrotum (men)
2. Ovaries
a. estrogens - stimulates the development & maintenance of reproductive system, production of gametes
b. progesterone - preparing & maintaining uterus
3. Testes
a. testosterone - stimulates the development & maintenance of reproductive system, production of gametes
F. Pineal gland
1. Location - center of brain, closer to skull in some other animals
2. Hormones/function- light sensitive cells, or connected to eye
a. melatonin - regulates functions related to daily light/dark cycles, or to seasonal changes in light level