Week 4 Flashcards
Hormones secreted where
Into extracellular fluid; circulates in blood, hemolymph
Role of hormones
Communicates regulatory responses through interaction with a specific receptor
- Reproduction
- Development
- Energy metabolism
- Growth
- Behavior
Endocrine system
Chemical signaling by hormones
Levels of cellular regulation
Intracellular, local environment, systematic regulation
Intracellular regulation
Within the individual cells themselves (positive or negative regulation)
- Covalent modification
- Phosphorylation
Local environment regulation
Cells response to the immediate environment, including presence of other cells
- Local factors secreted by other cells
- Extracellular matrix
Systematic regulation
Provides integration of activities of cells distant from each other
- Endocrine system
- Nervous system
- Overlap between endocrine and nervous system
Endocrine signaling
Hormone enters the blood
Paracrine signaling
Hormone works on a neighboring cell
Autocrine signaling
Hormone works on itself
Neuroendocrine signaling
Neurons release hormone that then acts on a receptor on a cell
Hormones
- Chemical substance (many diverse substances)
- Produced in one organ
- Transported via blood to a distant organ
- Modifies organ function
Types of hormones
Steroids (lipids)- derivatives of cholesterol, derivatives of arachidonic acids (lipids), proteins/peptides, catecholamines, glycoproteins
Which hormones act via membrane receptor
- Proteins
- Glycoproteins
-Prostaglandin (derived from arachidonic acid) - Catecholamines (aa derivative)
Which hormones act via nuclear receptor
- Steroids
- Thyroxine (aa derivative)
Hormone classification
-Amines
- Peptides
- Steroids
- Prostaglandins
Amines
- Derived from tyrosine
- Thyroid hormone
- Epinephrine/norepinephrine
Peptides
- Peptides: short proteins (1-9 amino acids)
- Polypeptides (long unbranched peptide chain)
- Proteins (one or more polypeptides arranged together)
Steroid hormones
- Derivative of cholesterol (fat soluble)
- Have a direct action on target cell
- Pass through cell membrane (phospholipid bilayer) and have intracellular receptors
- Binds to receptor in cytoplasm or nucleus of target cell
Prostaglandins
Derived from arachidonic acid
Examples of steroid hormones
- Progesterone (female sex hormone)
- Testosterone (male sex hormone)
- Aldosterone (adrenal cortex hormone)
- Cortisol (adrenal cortex hormone)
-Estradiol (female sex hormone)
Plasma membrane receptors
- B adrenergic receptor (GPCR)
- EGF receptor ( RTKs)
-Insulin receptor (RTKs) - Growth hormone receptor (JAK/STA)
RTK signaling (EGF-EGFR)
-hormone binds to receptor and induces receptor dimerization with other nearby RTK
- Cytoplasmic kinase domains are activated
- Receptor becomes autophorsphorylated on tyrosine residues
- Results in creation of binding sites for an addutional factor which activates the subsequent signaling pathway (2nd messenger system)
JAK/STAT signaling (Growth hormone)
- GH binds receptor, then STAT binds –> JAK talks to STAT
- STAT then delivers message to nucleus and triggers a reaction
G-Protein Coupled Receptor signaling
- Guanine nucleotide-binding proteins
- 7 transmembrane domains; integral membrane proteins, the extracellular part of the receptor can be glycosylated
- Ligand binds to receptor outside of cell
- Intracellular domain then activates G protein (2nd messenger system)
Posterior Pituitary
-Neuron terminals in posterior pituitary (release vasopressin and oxytocin into systemic blood)
-neuron terminals connect to neurosecretory cell bodies that produce oxytocin and vasopressin in paraventricular nucleus and Supraoptic nucleus
Anterior Pituitary
- Neurosecretory neurons in hypothalamus (secrete releasing and inhibiting hormones into portal system)
- Neurons and anterior pituitary communicate via Hypothalamic-hypophyseal portal system
- Endocrine cells of anterior pituitary secrete hormones into blood
Hormones of Anterior Pituitary
- TSH
- ACTH
- Prolactin
- Growth hormone
- LH and FSH (sex hormones)
TSH
-Acts on thyroid gland
- promotes thyroid hormone T3 and T4
- leads to increased metabolic rate
ACTH
- Acts on adrenal cortex
- Promotes cortisol
- causes stress response
Growth hormone
- Acts on liver (and adipose tissue, and muscle)
- Promotes IGF-1 which causes growth of bone and soft tissue
Prolactin
- Acts on mammary glands
- Causes breast growth and milk secretion
Regulation of Anterior Pituitary
- Hypothalamic releasing and inhibiting hormones
- These hormones reach anterior pituitary via hypothalamic-hypophyseal portal system
- Neural input
- Negative-feedback effects of anterior pituitary or target gland hormones (can be applied to all hormones that are in the hypothalamic- anterior pituitary gland axis)
Positive Feedback
-Process of labor
-Occurs during milk letdown
Pineal gland
- Secretes melatonin (produced by seratonin)
- Maintains circadian rhythm (melatonin secretion increases x10 in darkness)
- Seasonal changes in melatonin secretin patterns trigger reproduction
- In mammals, melatonin output is controlled by the suprachiasmatic nucleus (SCN) of the hypothalamus (SCN receives light info from eyes)
Long day breeders
Breed during summer
Short day breeders
Breed during fall/winter
Melatonins affect on reproduction
- LH pulse frequency influenced by concentration of melatonin which is dependent on light being received by eyes
Direct effects of Growth Hormone
Enhances immune system
Metabolic effects:
- Target organs are adipose tissue skeletal muscle and liver
- Mobilizes fat stores as a major energy source
- Conserves glucose for use by the brain (Decreases glucose uptake by muscles and increases glucose output by liver)
Mediation of GH’s actions
Mediated by insulin-like growth factors (IGFs)- indirect effects
- Stimulates production of IGF-1 by the liver
- Critical for long bone growth in young animals
Thyroid hormones
- Derived from tyrosine
- contains iodine
- T4 has 4 iodine
- T3 has 3 iodine (this is the active form)
-Functions include increase internal heat/oxygen consumption, stimulate metabolic tissues, and ATP
Mechanism of thyroid hormone action
- T3 is the major biologically active form of thyroid hormone
- Most secreted T4 is activated by conversion to T3 by deiodinase enzyme
- T3 binds with nuclear receptors attached to thyroid-response elements of DNA
- Alters transcription of specific mRNAs and synthesis of specific proteins
Pathway for Thyroid hormone
- Stress is inhibitor and cold in infants is a promoter
- Hypothalamus releases Thyrotropin-releasing hormone
- This stimulates anterior pituitary to produce Thyroid-stimulating hormone (TSH)
- THis produces thyroid gland to produce T3 and T4
- T3 causes metabolic rate and heat production to increase and enhances sympathetic activity
- T3 and T4 negatively regulate TSH in anterior pituitary
Calcitonin
- Secreted by parafollicular (C) cells of thyroid gland
-Polypeptide - 32 amino acids long
- Stimulated by hypercalcemia and hypermagnesia
- Inhibits osteoclast activity
Parathyroid gland
-Embedded in thyroid glands
- One or two pairs depending on animal
Parathyroid hormone
- Polypeptide, 84 amino acids long
- Stimulated by low blood calcium concentrations (hypocalcemia)
- Bones: increases osteolysis
- Kidneys: increases calcium absorption from tubular fluid
- Intestine: increases calcium and phosphorous absorption by increased formation of active form of vitamin D
Adrenal glands
Adrenal cortex:
- 3 distinct layers
Adrenal medulla
- homogenous
- contains secretory granules
- supplied by preganglionic sympathetic neurons
Adrenal hormones
steroid hormones of the adrenal cortex
- Derived from cholesterol
- Mineralocorticoids (aldosterone): influence mineral (electrolyte) balance) and produced in zona glomerulosa
- Glucocorticoids (cortisol): Role in metabolism of glucose, proteins, and lipids. Produced in zona fasciculata
- Sex steroids: androgenic effects
Glucocorticoids effects (cortisol)
- Metabolic effects: increase blood glucose, while reducing proteins and fat stores
- permissive actions
- enhanced memory
- adaption to long term stress
- Anti-inflammatory and immunosuppressive effects at high doses
Mineralocorticoids effects
- Aldosterone enhances sodium reabsorption and potassium excretion by kidney
- Promote membrane transport in sweat glands, salivary glands, and intestinal mucosa
Catecholamines
- Chromaffin cells in the adrenal medulla are modified postganglionic sympathetic neurons
- Secrete NE and E (both are catecholamines derived from tyrosine), stored in chromaffin granules
- Secretion is by exocytosis
- Secretion stimulated by the sympathetic system
Pancreas
- Composed of both exocrine (digestive system) and endocrine tissue
- Exocrine portion secretes digestive enzymes through pancreatic duct into digestive tract
- Islets of langerhans are integrators of endocrine regulatory responses and secrete hormones (pancreatic hormones are the dominant hormonal regulators of glucose homeostasis)
