CHAPTER SIXTEEN: ENDOCRINE SYSTEM Flashcards
DESCRIBE THE MAJOR DIFFERENCES BETWEEN HORMONAL AND NEURAL REGULATION OF BODILY FUNCTIONS
→ neural: initial response happens very quickly, however the response itself is short. Communicates via action potentials and neurotransmitters. Targets are limited to the axon pathway. Neurotransmitters act through very short distances.
→ hormonal: initial response happens slowly, however the response in itself is long. Communicates via hormones in the bloodstream. Targets are at diffuse locations and can be anywhere where the blood travels. Hormones act through very long distances.
IDENTIFY AND LOCATE THE MAJOR ENDOCRINE GLANDS
The major endocrine glands are the pituitary, pineal glands, adrenal glands, thyroid and parathyroid.
Pituitary and the pineal gland are located in the diencephalon, the adrenal glands are located on the kidneys and the thyroid is in the neck, the parathyroid is the distal aspect.
DISTINGUISH BETWEEN HORMONES, PARACRINES, AND AUTOCRINES
→ hormones: are long distance chemical messengers that travel through the blood or lymph.
→ autocrines: are chemicals that only exert effects on the signalling cells (itself)
→ paracrines: are locally acting chemicals that exert effects on cells other than the signalling one (itself)
EXPLAIN AMINO ACID BASED HORMONES
→ amino-acid based hormones: these hormones are derived from peptides and proteins. They are polar which means they are water soluble. Blood is also polar and water soluble, so amino-acid based proteins have no trouble travelling through the blood. However the issue arises when the hormone reaches the lipid bilayer. The lipid bilayer is aggressively non-polar and not water soluble, so amino-acid proteins will not be able to enter. This is when the G-protein second messenger activation system is used. There are 2 methods: cyclic AMP and PIP2-calcium methods.
EXPLAIN CYCLIC AMP METHOD
→ cyclic AMP
Amino-acid based hormone will bind onto peripheral protein receptor
This receptor will then activate the G-protein
The G-protein will either activate or inhibit the enzyme adenylate cyclase
Adenylate cyclase will then convert ATP into cyclic AMP
Cyclic AMP will activate protein kinases, and cause phosphorylation of other proteins
Cyclic AMP is rapidly degraded by an enzyme called phosphodiesterase
Cascades cause huge amplitude effects
EXPLAIN PIP2-CALCIUM METHOD
→ PIP2-calcium
The hormone activated G-protein will activate a different enzyme called phospholipase 3
Phospholipase 3 will split protein PIP2 into 2 second messengers: DAG also known as diacylglycerol, which will activate protein kinases, and IP3 also known as inositol triphosphate, which will release calcium from intracellular storage spaces
Calcium will act as another 2nd messenger that will either alter enzyme or channel activities or bind to calmodulin that will activate enzymes that increase cellular response.
EXPLAIN STEROID BASED HORMONES
→ steroid based hormones: steroid based hormones are derived from cholesterol, which makes it lipid soluble and non-polar. However because the blood is polar, it will have a hard time travelling in the bloodstream. This is when transport proteins come into play, they will help steroid based hormones travel in the bloodstream. When it reaches the lipid bilayer it can easily diffuse in because it is lipid soluble. The hormone will then bind to receptors in the cell, which will then enter the nucleus and bind onto specific parts of DNA, aid in DNA transcription to make Mrna, and then the Mrna is translated into the specific protein.
EXPLAIN AND GIVE EXAMPLES TO THREE TYPES OF STIMULI THAT TRIGGER HORMONE SECRETION
→ humoral stimuli: hormone secretion stimulated by different ion levels detected in blood, ex, calcium
→ neural stimuli: hormone secretion is stimulated by nerve fibers, ex. Sympathetic fibers triggering adrenal medulla to release epinephrine into the bloodstream.
→ hormonal stimuli: hormones targeting other endocrine organs to release their own hormones, very common between the hypothalamus and pituitary.
DESCRIBE THE STRUCTURAL RELATIONSHIP BETWEEN THE HYPOTHALAMUS AND THE PITUITARY GLAND AND DESCRIBE HOW THE HYPOTHALAMUS AFFECTS THE SECRETION OF HORMONES BY THE ANTERIOR AND POSTERIOR PITUITARY.
The hypothalamus is connected to the pituitary gland by a stalk called the infundibulum. The hypothalamus secretes releasing and inhibiting hormones to regulate hormone secretion.
→ posterior pituitary: it is composed of neural tissue and releases neurohormones like oxytocin (love and labour contraction hormone), as well as antidiuretic hormone which regulates water levels in the body.
Alongside the infundibulum, the posterior pituitary is part of the neurohypophysis
The posterior pituitary is neurally connected to the hypothalamus by the hypothalamic- hypophyseal tract
→ anterior pituitary: is composed of glandular tissue and releases 6 different types of hormones
Is vascularly connected to the hypothalamus by the hypophyseal portal system, which makes sure hormones from the hypothalamus directly get to the anterior pituitary.
LIST HORMONES SECRETED BY ANTERIOR PITUITARY AND THEIR EFECTS
→ anterior pituitary
Growth hormone: is the main hormone that causes growth and development in children. It is regulated by growth hormone-releasing hormone which is triggered by low glucose levels and high amino acid levels, and growth hormone-inhibiting hormone which is triggered by low growth hormone levels. Too much growth hormone can cause gigantism in children which causes them to be very tall, acromegaly in adults which causes large hands and feet. Too little growth hormone can cause dwarfism.
Adrenocorticotropic hormone: this hormone is regulated by corticotropin releasing hormone. It triggers the long term stress response in the adrenal cortex.
Thyroid stimulating hormone: is regulated by thyroid releasing hormone. From there it will target the thyroid glands to release their hormones (T3 and T4)
Follicle stimulating hormone:
Luteinizing hormone
^^ Both of the hormones above are regulated by gonadotropin releasing hormones. Follicle stimulating hormone causes follicles to mature in the ovaries, luteinizing hormone triggers ovulation in females and testosterone production in males.
Prolactin: causes lactation and is regulated by prolactin inhibiting hormone.
EXPLAIN HORMONES RELEASED BY THE POSTERIOR PITUITARY AND THEIR EFFECTS
→ posterior pituitary
Oxytocin: is the main love hormone and the hormone that induces labour contractions, it has a positive feedback mechanism. Uses the PIP2-calcium method.
Antidiuretic hormone: essentially controls the amount of water in our bodies. Lack of antidiuretic hormone or its inability to work can cause diabetes insipidus.
EXPLAIN HORMONES RELEASED BY THE ADRENAL GLANDS AND THIER EFFECTS
Adrenal glands: adrenal medulla
→ mineralocorticoids: contains electrolyte (ion) levels in the blood. Most important glucocorticoid is aldosterone. It changes the permeability of sodium in the kidneys. Some things that affect aldosterone release are the renin-angiotensin-aldosterone system, plasma concentration of K+, adrenocorticotropic hormone and many more.
→ glucocorticoids: regulate blood glucose levels in the blood. Most prominent glucocorticoid is cortisol. Cortisol will encourage the breakdown of fatty acids and amino acids into glucose for the brain as well as suppress the immune system. Too much cortisol causes cushing’s disease.
→ gonadocorticoids: gonadocorticoids are responsible for estrogen for women in menopause, secondary sex characteristics in women, sex drive, etc.
Adrenal gland: adrenal cortex
Releases epinephrine and norepinephrine
DESCRIBE THE REGULATION OF ALDOSTERONE SECRETION (RENIN-ANGIOTENSIN-ALDOSTERONE SYSTEM)
Decreased blood pressure stimulates special cells in the kidneys
Those cells release renin into the blood
Renin splits from plasma protein angiotensinogen, this causes a cascade of events to occur, which results in the conversion to angiotensin II
Angiotensin II is a potent stimulant of aldosterone.
DESCRIBE THE SHORT TERM AND LONG TERM STRESS RESPONSES MEDIATED BY THE ADRENAL GLANDS
Hypothalamus releases corticotropin releasing hormone → anterior pituitary releases adrenocorticotropic hormone → adrenal glands release aldosterone and cortisol
Preganglionic fiber releases acetylcholine into adrenal medulla → adrenal medulla releases epinephrine and norepinephrine into bloodstream
LIST AND DESCRIBE THE EFFECTS OF THE TWO MAJOR PANCREATIC HORMONES, DESCRIBE THE NEGATIVE FEEDBACK REGULATION OF SECRETION OF THESE HORMONES
→ glucagon: released to increase blood glucose levels and is triggered by lower blood glucose levels, is also triggered by high amino acid levels and the sympathetic nervous system. made by alpha cells
→ insulin: triggered by high blood glucose levels and promotes conversion from glucose to glycogen, inhibiting amino acid and fatty acid conversion to glucose, and increases glucose uptake by cells. made by beta cells.
