Pituitary gland and hypothalamus Flashcards
Antidiuretic hormone
Stimulates the kidneys to reabsorb water
Oxytocin
- stimulates the contraction of uterine muscles during childbirth (an example of positive feedback) - stimulates milk release in breastfeeding
Mechanism for posterior pituitary hormone secretion
1) stimulus: neural input to hypothalamus 2) hypothalamus signals posterior pituitary to release stored hormones by neural stimulation 3) ADH or oxytocin released into blood
How the hypothalamus communicates with the posterior pituitary
- hypothalamus is connected to the posterior lobe by neurons - PP hormones are made in hypothalamus, travel down axon and stored at axon ending until required
How the hypothalamus communicates with the anterior pituitary
- hypothalamus communicates with the anterior lobe by hormones in blood vessel - AP hormones are made in AP by specific cells
Mechanism for anterior pituitary hormone secretion
1) stimulus: neural input into hypothalamus 2) hypothalamus signals the anterior pituitary to release hormones by hormonal stimulation, releasing hormones (or inhibiting hormones) 3) hormone binds to receptor on membrane of a specific cell type and a specific peptide hormone is secreted
Growth hormone secretion sequence
1) Stimulus - stress, sleep, exercise, fasting 2) Hypothalamus - releases GHRH into bloodstream 3) Anterior pituitary - secretes growth hormone into bloodstream 4) Liver and other cells - increase in IGF-1 (growth factor) secretion 5) Metabolic effects
metabolic effects of GH
increased protein synthesis and decreased glucose uptake in muscle, increased glucose synthesis in liver, increased fat breakdown by mobilising fatty acids
GH disorders
- hyposecretion (too little) - dwarfism - hypersecretion (too much) - gigantism - Hyposensitivity (little or no response) - Hypersensitivity (respond too much)
GH function
promotes the growth of bones, muscles and other tissues by stimulating cell division
pituitary gland location
base of brain, attached to hypothalamus
hormone
chemical messengers produced in one location and transported to a second location where they cause a response in those cells
functions of endocrine system
Regulates our internal environment by secreting hormones into the bloodstream.
Endocrine gland
secrete hormones
major endocrine glands
hypothalamus, pituitary, thyroid, thymus, adrenal, testes
Specificity of Hormone action
Target cells have specific receptors proteins that allows for specific and close hormone-target cell interaction
hormone receptors for peptides and catecholamines
located on plasma membrane of target cell because they are water-soluble to cannot cross lipid bilayer
hormone receptors for lipid-soluble hormones
located in cytoplasm (steroid hormones) or nucleus (thyroid hormones) because can diffuse across the cell membrane into target cell
response to receptor activation of water-soluble hormones
- Water-soluble hormone binds to cell surface receptor
- Hormone binding allows activation of associated (G-) protein
- G- protein activates adenylyl cyclase
- Second messenger production e.g. cyclic AMP (cAMP)
- cAMP activates protein kinase
- Protein kinase activates specific enzyme Enzyme converts specific substrate to product (cell’s specific response)
what determines amount of hormone in blood
- Rate of production – controlled by negative feedback loops (usually)
- Rate of removal – controlled by enzymes in the bloodstream
response to receptor activation for lipid-soluble hormones (steroid and thyroid hormones)
- Lipid-soluble hormone dissociates from carrier protein
- Hormone diffuses across cell membrane
- Hormone binds to INTRACELLULAR receptor
- Hormone-receptor complex acts as a specific transcription factor
- New mRNA is generated
- New protein is generated by translation of mRNA
- New protein mediates cell’s specific response (SLOW PROCESS)
lipid soluble vs water soluble hormones
comparison of endocrine and neural control systems
Neuronal (action potentials in axons and neurotransmitter release at synapse)
- Targeting achieved by specific wiring
- Fastest transmission speed to minimise response delays
- Good for brief responses
Hormonal (hormones released into blood)
- Targeting by expression of specific receptors on target cells
- Relatively slow, but long-lasting action
- Good for widespread and sustained responses
pancreas and islets
- Head and neck in the C-shaped curve of the duodenum and the body extends behind the stomach
- Endocrine tissues called pancreatic islets are dispersed throughout the pancreas (~2% of mass)
- Beta cells secrete insulin
- Alpha cells secrete glucagon
