9. Lectures 20 Flashcards
What is the simple stepwise picture of homeostasis?
- Stimulus- produces change in variable
- Receptor- detects change
- Input- information sent along afferent pathway to control center
- Output- information sent along efferent pathway to effector
- Response- of effector feeds back to reduce the effect of stimulus and returns variable to homeostatic level
System is always trying to get to set point where body is happy
Slide 3-4 lecture 20
What is neuroendocrinology?
Study of reciprocal interaction between the nervous system and the endocrine system that regulate physiological processes and maintain homeostasis
Nervous system and endocrine system work together to keep you in perfect health
How does the nervous and endocrine systems compare?
Nervous system
Uses neurons as cells and neurotransmitters as chemical signal, receptors on post synaptic cell specify the response
Takes seconds for reaction, action is brief
Endocrine system
Uses epithelial and others as cells and hormones as chemical signal, hormones bind to receptors on target cell for specificity and the speed of onset can be seconds to hours
The action can be brief or last for days
Slides 5-6 lecture 20
What are the important hormones secreted from;
Adrenal medulla
Hypothalamus
Anterior pituitary gland
Adrenal medulla- epinephrine and norepinephrine
Hypothalamus- dopamine, somatostatin, CRG, TRH, etc
Anterior pituitary gland- growth hormone (somatotropin)
What are the 3 classes of hormones?
Amines
Peptides and proteins
Steroids
What are amine hormones?
Derivatives of amino acid tyrosine
Include catecholamines epinephrine, norepinephrine (adrenal medulla), dopamine (hypothalamus), and the thyroid hormones (thyroid gland)
Slides 10-11 lecture 20
Compare the parasympathetic, sympathetic, and endocrine systems of transport on slides 12-13 lecture 20
Endocrine system starts with sympathetic division of ANS!!!
What are peptide and protein hormones?
Most hormones are poly peptides
Synthesized on ribosomes of endocrine cells as larger preprohormones, then cleaved to prohormones by proteolytic enzymes in the rough ER
Prohormone is packaged into secretory vesicles by Golgi apparatus, then it is cleaved to yield active hormone and other peptide chains found in prohormone
Peptides and hormones in prohormone are secreted together when stimulated to release
Slides 14-15 lecture 20
What are the 6 steps in the typical synthesis and secretion of peptide hormones?
- Messenger RNA on ribosome binds amino acids into a peptide chain called a preprohormone, chain is directed into ER lumen by signal sequence of amino acids
- Enzymes in ER chop off signal sequence creating inactive prohormone
- The prohormone passed from the ER through the Golgi complex
- Secretory vesicles with enzymes and prohormone bud off Golgi, the enzymes chop the prohormone into one or more active peptides plus additional peptide fragments
- Secretory vesicle releases its contents by exocytosis into the extracellular space
- Hormone moves into the circulation for transport to target
Slide 15 lecture 20
What are steroid hormones?
Primarily produced by adrenal cortex and testes and ovaries
All steroid hormones are derived from cholesterol
Final hormone product depends upon the cell type and the types and amounts of the enzymes it expresses
Slide 16 lecture 20
What is the adrenal cortex in the adrenal gland and it’s 3 layers?
Adrenal gland is above kidney
Zona glomerulosa- express enzymes required to synthesize the mineralocorticoid aldosterone (effects salt balance)
Zona fasciculata- produces glucocorticoid cortisol (effects metabolism of glucose)
Zona reticularis- produces the androgens dehydroepiandrosterone and androstenedione
Slide 17 lecture 20
How are hormone producing cells stimulated?
Binding if an anterior pituitary gland hormone to the hormone producing cells plasma membrane receptor
The receptors are linked to Gs proteins which activate adenylyl cyclase and cAMP production (activates PKA)
One formed, steroid hormones freely diffuse across lipid bilayers into the circulation since most catecholamines and most peptides are water soluble (lipophilic)
Slide 18-19 lecture 20
What are the 2 things a hormones concentration in plasma depends on?
- Rate of secretion by the endocrine gland
- Rate of removal from the blood
Removal (clearance) occurs by excretion if metabolic transformation
Enzymes in blood also rapidly break down catecholamine and peptide hormones
Liver and kidney are major organs that metabolize or excrete hormones
We want controlled amount of hormones not too much not too little
What is receptor modulation?
What is up and down regulation?
Hormones can influence response if target cells by regulating hormone receptors
Up regulation- increase in receptor number, increases responsiveness to the hormone, prolonged exposure to a low concentration hormone, cell wants to response to hormone better by making more receptors
Down regulation- decrease in receptor number, decreases responsiveness to hormone, prevents over stimulation, high concentrations of hormone
Slide 21 lecture 20
What is permissiveness?
A hormone-hormone interaction in which the effectiveness of a second hormone is increased from a first
Hormones can up and down regulate their own receptors and the receptors of other hormones
Ex: ability of thyroid hormone to permit epinephrine induced release of fatty acids from adipose tissue cells (thyroid hormone causes increase in number of beta-adrenergic receptors on the cell)
Slide 22 lecture 20
What are the 5 steps of hormone-receptor binding for nonsteroid water soluble hormones?
Water soluble (peptide and catecholamine) hormones
- A nonsteroid hormone reaches a target cell
- Nonsteroid hormone bind receptor molecules on the cell membrane
- Hormone binding activates molecules of adenylate cyclase
- Adenylate cyclase catalyzes conversion of ATP into cyclic adenosine monophosphate (cAMP)
- cAMP activates existing proteins, causing a series of reactions leading to the cellular changes associated with the hormones action
Slide 23 lecture 20
What are the 5 steps of hormone-receptor binding for steroid lipid-soluble (steroid and thyroid) hormones?
Lipid soluble (steroid and thyroid) hormones
- Steroid hormone reaches target cell and crosses the cell membrane
- Hormone combines with a protein receptor usually in nucleus
- Hormone-receptor complex activates synthesis of mRNA molecules
- mRNA molecules leave nucleus into cytoplasm
- Translation of mRNA molecules leads to synthesis of the encoded proteins associated with the hormones action
Slide 24 lecture 20
What are the 3 types of inputs that control hormone secretion?
- Changes in concentrations of mineral ions or organic nutrients
- Neurotransmitters released from neurons
- Another hormone acting on the endocrine cell
Slide 25 lecture 20
Study how neurotransmitters releases from neurons control hormone secretion on slide 26 lecture 20
Ok
What is a tropic hormone?
A hormone that stimulated the secretion if another hormone
Main job is to cause release of hormone in next stage
Anterior pituitary gland secreted hormones that stimulate other endocrine glands to secrete hormones
Slide 27 lecture 20
What are the 4 types of encoring disorders?
- Hyposecretion- too little hormone
- Hypersecretion- too much hormone
- Hyporesponsiveness- decreased responsiveness of the target cells to hormone
May be caused by a deficiency of receptors or abnormal receptors - Hyperrresponsiveness- increased responsiveness of the target cells to hormone
What is primary and secondary hyposecretion?
Primary hyposecretion- endocrine gland secreting too little hormone because it is not functioning normally
Secondary hyposecretion- endocrine gland is not damaged but is receiving too little stimulation by its tropic hormone
Slide 29 lecture 20
What is primary and secondary hypersecretion?
Primary hypersecretion- endocrine gland secreting too much hormone (endocrine-cell tumour)
Secondary hypersecretion- excessive stimulation of the gland by its tropic hormone
Slide 30 lecture 20
