INTS 11: The Hypothalamic-Pituitary Axes Flashcards
Read and understand the learning objectives of this session
Define endocrinology
- it is the study of endocrine glands and their hormonal products
- these are released directly into the bloodstream
What are the body’s two principal communication systems?
- the endocrine glands
- the nervous system
Define endocrine gland
- a group of cells which secrete ‘messenger’ molecules (hormones) directly into the bloodstream
Define hormone
- the bioactive ‘messenger’ molecule secreted by an endocrine gland into the blood
- i.e. not simply a metabolite or energy substrate
Define the endocrine system
- the endocrine system is comprised of the endocrine glands and their hormonal products
- it is often also used to describe the cells which respond to these hormones
Give examples of some of the endocrine organs
Where are endocrine cells found?
- they are often grouped together in particular endocrine organs
- e.g. thyroid gland or pituitary gland
- some cells can also be found in other tissues that are not primarily endocrine tissues
Discuss the properties of endocrine cells
What about protein hormone-secreting cells?
- endocrine cells are highly metabolically active
- therefore, they typically have many mitochondria
- they have a rich blood supply to allow their secreted products to be effectively transported into the blood stream
- often, secretory granules will be positioned in a cell adjacent to a nearby capillary
- protein hormone-secreting cells will have a lot of RER for protein sysnthesis
- will also contain secretory granules where protein hormones are stored
What are neurosecretory cells?
Briefly descirbe their function and morphology
- a subset of endocrine cells
- they are neurons which release hormones
- so they will have typical neuronal morphology
- hormones are stored in granules at the axonal terminals
- these terminals release their contents into capillaries, allowing the hormone to enter the circulation
Describe this micrograph
What are the three ways hormones can act?
- endocrine:
- a hormone acting on target cells at a distnace from source
- via the bloodsteam
- paracrine:
- a hormone acting on nearby target cells
- i.e. within immediate area around source
- autocrine:
- a hormone acting on its own immediate source
- i.e. on the cell that released it
What are the three classes of hormones?
- protein or peptide hormones
- steroid hormones
- amino acid derived hormones
Describe the synthesis of protein hormones, their properties and hence their function
- synthesised by the same pathways that synthesise other proteins within the cell
- they are subsequently packaged into secretory granules where they are stored until required
- they are typically easy to dissolve in water, so can circulate in the bloodstream without the need for binding proteins
- they do not easily cross cell membranes and act on cell surface receptors instrad
- the conformation of the receptors are altered when they bind a hormone
- this stimulates intracellular signal pathways which then drive the effects of the hormone within the cell
Describe the synthesis of steroid hormones, their properties and hence their function
- synthesised from cholesterol in the mitochondria when required
- usually not stored within the cell
- they are hydrophobic
- so require binding proteins to carry them through the circulation
- due to their hydrophobicity, they can cross cell membranes relatively easily
- then they bind to and activate intracellular or nuclear receptors
- receptor-steroid hormone complexes can then relocate to the nucleus and influence gene transcription
Describe the synthesis of amino acid derived hormones, their properties and hence their function
- they are a more diverse group
- some display properties like steroid, other more like protein hormones
Describe the hypothalamus
- Location
- Function
- Structure
Location:
- found at the base of the brain, below the thalamus
Function:
- forms part of the limbic system: involved in processes such as learning, emotion and behaviousr
- regulates many homeostatic processes:
- heart rate, body temperature, metabolic rate and food intake
- received neuronal input from a number of other brain regions, particularly the brainstem
- hypothalamic neurons themseles signal to other brain regions to regulate behavious
- can regulate the autonomic nervous system and the pituitary gland
Structure:
- composed of individual nuclei and some less well define subregions which are integrated, but can regulate different physiological functions
Describe the pituitary gland
- Alternate name
- Location
- What it is
- also known as the hypothysis
- it is an endocrine organ that sits within a bony pocket underneath the hypothalamus
- composed of anterior, intermediate and posterior lobes