chapter 11 part 1 endocrine glands: secretion and action of hormones
TRANSCRIPT
Chapter 11 Part 1
Endocrine Glands:
Secretion and Action of Hormones
Classic Definition of a Hormone
• Hormone - Chemical messenger produced by a ductless gland or tissue and carried in the blood/lymph to a target organ where it effects a change in cellular activity.
EffectorCell 1
TargetCell 2
Capillary
Endocrine Glands
Located at base of brain
Testis in Male
Adrenal Gland Ovary
KidneyPituitary
Hypothalamus
ThyroidParathyroid
Higher Centers of Brain Control All Hormonal Functions
Cerebrum
Cerebellum
MedullaOblongata
ThirdVentricle
PinealBody
Anterior & PosteriorPituitary
Hypothalamus
Pituitary Stalk
Anatomy of Cow Brain
Spenoid Bone
Pituitary
Diaphragma sellae
Infundibular Stalk
Control of Endocrine Gland FunctionHypothalamic-Pituitary Interrelationships
Pituitary Stalk
Nerve cells which releasepeptide hormones:Oxytocin, ADH
NeurohypophysisNerve endings comedirectly from hypothalamus
Adenohypophysisnon-neural tissue
HypothalamusSecreting neurons: GnRH,
CRH, TRH, GHRH
Hypophyseal Portal Vessels
Posterior Pituitary:
Release of Oxytocin or ADHinto circulation
Release of LH, FSH, ACTH, PRL, GH, TSH
Anterior Pituitary
Superior HypophysealArtery
Endocrine Glands and Hormones
• Secrete biologically active molecules into the blood.– Lack ducts.
• Carry hormones to target cells that contain specific receptor proteins for that hormone.
• Target cells can respond in a specific fashion.
• Different from nervous system – – Nervous system is fast, short-term reactions– Endocrine – longer duration, adaptation response.
Endocrine Glands and Hormones (continued)
• Neurohormone:– Specialized neurons that secrete chemicals into
the blood rather than synaptic cleft.• Chemical secreted is called neurohormone.
• Hormones:– Affect metabolism of target organs.
• Help regulate total body metabolism, growth, and reproduction.
1) Paracrine - released from effector cell (E) interact with a different target cell (T1).2) Autocrine - secreted by E interact with original E cell or similar cell types. 3) Juxtacrine -expressed on surface of E and interacts with target cell (T2) via direct cell-cell contact. 4) Intracrine - is not secreted by E and interacts with an intercellular receptor.
Other forms of endocrine action
E T
E
E T
• Pheromones: A chemical substance that is liberated by one animal and causes a relatively specific behavior modification in a recipient animal following its chemoreception• Lee-Boot effect: Crowded female mice become anestrous when no males are present.• Bruce effect: A newly mated female mouse will abort if placed with a strange male (not the previous mate).• Dormitory effect: menstrual synchrony in all-females living groups
EctocrineFlehmen
Common Aspects of Neural and Endocrine Regulation
• APs are chemical events produced by diffusion of ions through neuron plasma membrane.
• Action of some hormones are accompanied by ion diffusion and electrical changes in the target cell.– Nerve axon boutons release NTs.– Some chemicals are secreted as hormones, and also are
NTs.• In order for either a NT or hormone to function in
physiological regulation:– Target cell must have specific receptor proteins.– Combination of the regulatory molecule with its receptor
proteins must cause a specific sequence of changes.– There must be a mechanism to quickly turn off the action of
a regulator.
Most hormones belong to one of 4 structural classes
• Peptides & Amines (E, NE % DA) are hyrophilic
• Steroids and eicosanoids are hydrophobic
Structural Classes• Amines:
– Hormones derived from tyrosine and tryptophan.• NE, Epi, T4.
• Peptides, Polypeptides and Proteins– Polypeptides
• Chains of < 100 amino acids in length.– ADH.
• Ex: Adrenalcorticotropic Hormone (ACTH) – 39 amino acids
– Peptide - Few - Several amino acids• Ex: Gonadotropin Releasing Hormone (GnRH) - 10 amino acids• Oxytocin - 8 amino acids
– Protein hormones:• Polypeptide chains with > 100 amino acids.
– Growth hormone, Insulin, ACTH.– Prolactin - 198 amino acids
Structural Classes
• Glycoprotein - Protein hormone with carbohydrate molecules- Some have large amount of sialic acid – FSH
- Steroids- Lipids derived from cholesterol– Are lipophilic (fat loving; can diffuse through
plasma membrane) hormones.- Ex – testosterone, estradiol, progesteone, and
cortisol
Effects of [Hormone] on Tissue Response
• [Hormone] in blood reflects the rate of secretion.• Half-life:
– Time required for the blood [hormone] to be reduced to ½ reference level.
• Minutes to days.
• Normal tissue responses are produced only when [hormone] are present within physiological range.
• Varying [hormone] within normal, physiological range can affect the responsiveness of target cells.
Percent of Carbohydrate and Size of Protein Effects Half-Life in Blood
% inBloodAfterInjection
Human ChorionicGonadotropin -30% Carbohydrate
eCG
Equine ChorionicGonadotropin -45% Carbohydrate
Follicle Stimulating Hormone 8% Carbohrydrate
Luteinizing Hormone little sialic acid
GnRHOxytocin
Time required to remove or clear half of the dose from the blood
Chemical Classification of Hormones (continued)
Δ5Δ4
Δ5: Primates, Sheep, CattleΔ4: Pigs, rats, mice(Conley and Bird 1997)
Hormone Synthesis
• Protein Hormones – Synthesized at ribosomes as large precursor proteins – Preprohomrone converted to prohormone within
rough ER– Golgi apparatus – packages prohormone and
converts it to hormone– Stored in secretory granules– Upon stimulation – get exocytosis
• Requires: – 1. ATP
– 2. Ca
The flow of
genetic information in a typical
cell
Anterior Pituitary Hormones Such as LH, FSH andTSH (Thyroid Stimulating Hormone) have Two Chains Alpha - Beta -
chain is identical between FSH, LH and TSH. chain gives the hormone its specific action.Need both chains together for biological activity
S S
LHmRNA
Transcription
Translation
FSH
TSH
hCG
TSH, LH and FSH: Pituitary Glycoprotiens
hCG: placental
Synthesis of Steroid Hormones
• Ex: glucocorticoids, mineralocorticoids, sex steroids• Formed from cholesterol – which is used
immediately or stored in cell– Type of steroid hormone produced depends on presence
of specific enzymes– EX: adrenal cortex cell – contain enzymes needed for
production of glucocorticoids or mineralocorticoids
• Steroid hormones secreted immediately from cell after formation– Rate of steroid hormone secretion controlled by rate of
production
Mineralocorticoids, glucocorticoids and steroids are synthesized from
cholesterol
Cholesterol C27
Pregnenolone C21
Glucocorticoids C21
Mineralocorticoids C21
Androgens C19
Estrogens C18
Chemical Classification of Hormones (continued)
• Hormones can also be divided into:– Polar:
• H20 soluble.
– Nonpolar (lipophilic):• H20 insoluble.
– Can gain entry into target cells.
– Steroid hormones and T4.
– Pineal gland secretes melatonin:• Has properties of both H20 soluble and lipophilic
hormones.
Prohormones and Prehormones
• Prohormone:– Precursor is a longer chained polypeptide that is
cut and spliced together to make the hormone.• Proinsulin.
• Preprohormone:– Prohormone derived from larger precursor
molecule.• Preproinsulin.
• Prehormone:– Molecules secreted by endocrine glands that are
inactive until changed into hormones by target cells.
• T4 converted to T3.
Prohormones and Prehormones
• Synergistic:– Two hormones work together to produce a
result.– Additive:
• Each hormone separately produces response, together at same concentrations stimulate even greater effect.
– NE and Epi.
– Complementary:• Each hormone stimulates different step in the
process.– FSH and testosterone.
Hormonal Interactions
Hormonal Interactions (continued)
– Permissive effects:• Hormone enhances the responsiveness of a
target organ to second hormone.– Increases the activity of a second hormone.
» Prior exposure of uterus to estrogen induces formation of receptors for progesterone.
– Antagonistic effects:• Action of one hormone antagonizes the
effects of another.– Insulin and glucagon.
Effects of [Hormone] on Tissue Response (continued)
• Priming effect (upregulation):– Increase number of receptors formed on target
cells in response to particular hormone.– Greater response by the target cell.
• Desensitization (downregulation):– Prolonged exposure to high [polypeptide
hormone].• Subsequent exposure to the same [hormone]
produces less response.– Decrease in number of receptors on target cells.
» Insulin in adipose cells.» Type 2 diabetes
– Pulsatile secretion may prevent down regulation.
Mechanisms of Hormone Action• Hormones of same chemical class have
similar mechanisms of action.– Similarities include:
• Location of cellular receptor proteins depends on the chemical nature of the hormone.
• Events that occur in the target cells.• GH and Prolactin (Trophic hormones - increase in
growth)
• To respond to a hormone:– Target cell must have specific receptors for that
hormone (specificity).• Hormones exhibit:
– Affinity (bind to receptors with high bond strength).– Saturation (low capacity of receptors).