Endocrine System
Endocrine Function
1. regulate organic metabolism and H2O and electrolyte balance
2. induce adaptive changes to help body cope with stress
3. promote smooth growth
4. controls reprod
5. regulate RBC prod
6. Control and integrate cirulation with digestion and absorption of food
Hormones
- nervous system coordinates rapid, precise responses
- mediating bodies interactions with ext environment
- endocrine system acts require duration vs speed
Tropic Hormones
-regulate hormoen secretion by other glands
-stims and maintains endocrine target tissues
- TSH secreted from anterior pituitary stims thyroid hormone secretion by thyroid gland
Complexity of Endocrine Function
- single gland can produce multiple hormones
- single hormone can be secreted by multiple glands
- secretion rate varies
- target cell can be influenced by multiple hormones
- chem msger can be hormone or NT
- not all endorcrine organs involve endocrine function
Plasma Concentration
controlled by :
1. hormone secretion rate
2. metabolic activation rate
3. binding of plasma proteins (lipophilic hormones)
4. rate of removal
Inputs that influence secretion:
- neural input
- hormonal input
Negative-Feedback Control
- exits wheb output counteracts change input
- maintains plasma concen of horm
- given level referred to set point
- maj of endocrine feedback are neg
- some pos feedback are oxtocin in childbirth
Neuroendocrine Reflexes
- includes neural and hormonal components
- prod sudden increase in horm secretion responsing to spef stim
e.g: increase cortisol secretion in stress response
Transport, Metabolism and Excretion
- alterations influenced by hormones plasma concen
- horms metabolized by enzyme mediated reactions
- elim from blood by urinary excretion
Endocrine Disorders
- commonly results from abnormal plasma concentrations of horm
Hyposecretion
Primary: too little horm secreted due to abnormality in glands
Secondary: gland is normal but too little hormone is secreted due tropic hormone deficiency
Cause: Genetics, diet , chemicals, immunologic, diseases (cancer), iatrogenic or idiopathic
Hypersecretion
Primary: too much horm secreted due to abnormality in glands
Secondary: Excessive stim from outside gland causes oversecretion
Causes: Tumors, immunologic factors
Target Cells
- receptors for particular hormone can be altered by control mechs
- reponse to give plasma concen of horm can be fine tuned by varying number of receptors available
- number of receptors doesnt remain constant
Hormone Classifications
Peptide Hormones: made from AA (insulin)
Catecholamines: made from tyrosine derivative (epinephrine)
Thyroid: made from tyrosine derivative (T3)
Steroids: made from lipids (estrogen)
Hydrophilic Hormones
- highly water soluble
- low lipid solubility
- insulin
- peptides and catecholamines bind with spef receptors located on outer plasma membrane
- change cells permeability upon binding
2 pathways:
cAMP, Calcium
Lipophilic Hormones
- high lipid solubility
- poor water soluble
- thyroid hormone
- Sterioids and thyroid hormones bind with receptors inside target cells
- activates specific genes in target cells
Hydrophilic Hormones Mech cAMP
1)
binding hormone to receptor activating G-protein
activates enzyme adenylate cyclase
2)
adenylate cyclase converts ATP to cAMP
3)
cAMP 2nd msger activates protein kinase A (PKA)
4)
PKA phosphorylates inactive target protein, trigs activation
5)
phosphorylates changes shape of protein to desired response
Hydrophilic Hormone Mech Ca and DAG
1)
bings of hormone to receptor activated G-protein of enzyme phospholipase C
2)
Phospholipase C breaks down phosphatidylinositol bisphosphate (PIP2) to inositol triphosphate (IP3) and diacylglycerol (DAG)
IP3 and DAG pathway
3.
a) IP3 mobilizes intracellular Ca stores
b) DAG activates protein kinase C
4.
a) Ca then activates calmodulin Sa. Activating calmodulin-dependent protein kinase (CaMK)
b) PKC phosphorylates target protein activation
5.
a) Calmodulin activates calmodulin-dependent protein kinase (CaMK)
b) active target protein brings desired response
6.
a) CaMK phosphorylates target protein activation
7.
a) active target protein brings desired response
Activation of Genes by Lipophilic Hormones
1. lipophilic hormone diffuses through target CM
2. hormone binds to receptor in nucleus or cytoplasm forming hormone receptor complex
2. hormone receptor complex binds on DNA (hormone reponse element
3. HRE binding to DNA turns on spef gene, code of activated gene transcribed to msger RNA
4. mRNA leaves nucleus
5. cytoso mRNA binds to ribssome starting assembly of new proteins
6. new enzymatic or structural portein prods desired response
Pituitary Gland
-small gland on base of brain
- connected to hypothalamus by thin connecting stalk
Posterior pituitary gland
- nervous tissue
neurohypothysis
Anterior pituitary gland
- glandular epithelial tissue
adenohypophysis
Neuroendocrin System
- formed by posteruor pituitary and hypothalamus
- neurosecretory neurons cell bodies lie in supraoptic nuclei and paraventricular nuclei in hypothalamus
- posterior pituitary stores and releases vasopressin and oxytocin
Anterior Pituitary Hormones
1. Thyroid-stimulating hormone (TSH)
- tropic hormone
- stims secretion of thryroid hormone
2. Adrenocorticotrpic hormone (ACTH)
- tropic hormone
- stims rsecretion of cortisol by adrenal cortex
3. Follicle-stimulating hormone (FSH)
- trpoic hormone
- stims growth of ovarian follicles
- promos secretion ofestrogen by overies
- required for sperm prod
4. Luteinizing hormone
- trpoic hormone
- ovulation and luteinization
- regs secretion of fem sex horms
- stims test secretion
5. Growth hormone (GH)
- not tropic hormone
- regs overall body growth
- intermediary metabolism
6. Prolactin (PRL)
- not tropic hormone
- enhacnes breast development and milk prod
Hypothalamic Releasing and Inhibiting Hormones
finish this
Growth Hormone
1. genetic determination of individuals max growth capacity
2. adequate diet
3. free from chronic disease and stress
4. norm lvls of growth-influencing horms
Growth
- 2 periods of rapid growth
- factors arent the same
1. fetal growth
- promo largely by horms from placenta
2. postnatal growth spurt
- 1st 2 years of life
3. pubertal growth spurt
- adolescence
Metabolic Actions of GH Unrelated to Growth
1. increase rate of protein and collagen synthesis
- sparring AA
- increase trnasport of AA across CM
2. increased fatty acid mobilization and use
- increase lipolysis
3. decreased rate of glucose/glycogen use
- sparring of glucose
Growth-Promoting Actions of GH on Soft Tissues
1. increase carilage growth
2. hyperplasia
3. hypertrophy
4. increase number of cells by stim cell division and preventing apoptosis
Growth hormone deficiency and excess
Deficeincy
- Due to pituitary defect or hypothalamic dysfunction
- Hyposecretion of GH in child is one cause of dwarfism
- Deficiency in adults produces relatively few symptoms
Excess
Caused by tumor of GH-producing cells of anterior pituitary
Symptoms depend on age of individual when abnormal secretion begins
Gigantism (right) caused by overproduction of GH in childhood before epiphyseal plates close.
Acromegaly (below) occurs when GH hypersecretion occurs after adolescence.