Endocrine System: Pituitary Gland Flashcards
Homeostasis = ?
- What is responsible for maintaining this ?
Endocrine System
Homeostasis:
- A state of balance among all the body systems needed for the body to survive and function correctly.
- Endocrine system + nervous system = responsible for homeostasis.
Mechanism of Peptide Hormone Action and Second Messengers = ?
Endocrine System
Mechanism of Peptide Hormone Action and Second Messengers:
- Hormone
- Receptor
- G proteins
- Effector proteins/enzymes (adenylyl cyclase, phospholipase C)
- Second messenger (cAMP, IP3)
- Phosphorylates protein-physiologic actions
Steroid Hormone Mechanism = ?
Endocrine System
Steroid Hormone Mechanism:
(1) Steroid hormone enters the cell:
- Steroid hormones are lipid-soluble, which means they can easily pass through the cell membrane. In this step, the steroid hormone enters the target cell by passive diffusion.
(2) Binding to receptor:
- Once inside the cell, the steroid hormone binds to a specific receptor protein in the cytoplasm or nucleus.
- This receptor protein is called a steroid hormone receptor.
(3) Dimerization and binding to SRE:
- After binding to the hormone, the receptor protein undergoes a conformational change and dimerizes. This means that two receptor molecules come together to form a dimer.
- The dimer then binds to a specific DNA sequence called a steroid response element (SRE) in the promoter region of a target gene.
(4) Transcription:
- Binding of the receptor-hormone complex to the SRE activates RNA polymerase, an enzyme that transcribes DNA into messenger RNA (mRNA).
(5) Translation and physiologic actions:
- The mRNA produced in step 4 is then translated into protein in the ribosomes.
- These newly synthesized proteins are responsible for the physiological effects of the steroid hormone.
Note:
- Overall, the mechanism of action of steroid hormones is a complex process that involves several steps.
- However, the basic idea is that steroid hormones enter the cell, bind to a receptor protein, and then activate the transcription of target genes.
- The proteins produced from these genes are responsible for the hormone’s effects on the cell.
Regulation of Hormone Receptors:
- Dose-response relationship = ?
- Down-regulation = ?
- Up-regulation = ?
Endocrine System
Regulation of Hormone Receptors:
(a) Dose-response relationship:
- Magnitude of response is correlated with hormone concentration.
- (Ex.) Analgesic medications, such as opioids, demonstrate a dose-response relationship in pain relief. As the dose of the analgesic increases, there is a corresponding increase in pain relief.
(b) Down-regulation:
- Mechanism in which a hormone decreases the number or affinity of its receptors in a target tissue.
- May occur by decreasing the synthesis of new receptors, increasing the degradation of existing receptors, by inactivating receptors.
- (Ex.) In individuals with type 2 diabetes, there is often down-regulation of insulin receptors on target cells, such as muscle and adipose tissue. Prolonged elevated levels of insulin, which occur in insulin resistance, can lead to reduced responsiveness of these cells to insulin, contributing to impaired glucose uptake.
(3) Up-regulation:
- Number or affinity of the receptors for the hormone had increased.
- Increasing the synthesis of new receptors, decreasing the degradation of existing receptors, by activating receptors.
- (Ex.) In cases of testosterone deficiency, there can be up-regulation of androgen receptors in target tissues. This adaptation aims to increase the responsiveness of cells to the available testosterone, compensating for the lower hormone levels.
Eight Endocrine Glands = ?
Endocrine System
Endocrine Glands :
- Hormones are synthesized and secreted by endocrine cells usually found in endocrine glands:
- Hypothalamus
- Adrenal
- Pituitary
- Thyroid
- Parathyroid
- Pancreas
- Pineal
- Thymus
Regulation of Hormone Secretion:
Negative feedback = ?
Endocrine System
Regulation of Hormone Secretion:
(a) Negative feedback:
- When hormone levels are judged to be adequate or high, further secretion of the hormone is inhibited.
- Also called self limiting
- Common mechanism
Regulation of Hormone Secretion:
- Explain this what is happening in this graph.
Endocrine System
Regulation of Hormone Secretion:
(A) It shows a negative feedback loop between the hypothalamus, the pituitary gland, the testes, and target tissues. Here’s how it works:
(1) Hypothalamus:
- The hypothalamus is a part of the brain that produces GnRH (gonadotropin-releasing hormone).
- GnRH travels to the pituitary gland through blood vessels.
(2) Pituitary gland:
- The pituitary gland releases LH (luteinizing hormone) in response to GnRH.
- LH travels through the bloodstream to the testes.
(3) Testes:
- The testes produce testosterone in response to LH.
- Testosterone travels through the bloodstream to the target tissues.
(4) Target tissues:
- Testosterone has a variety of effects on target tissues, such as muscle and bone. These effects include promoting growth and development, and increasing sex drive.
(5) Negative feedback:
- When testosterone levels in the blood reach a certain level, they send a signal back to the hypothalamus and pituitary gland.
- This signal tells the hypothalamus and pituitary gland to decrease the production of GnRH and LH, respectively.
(6) Decrease in hormone production:
- As a result of the decreased production of GnRH and LH, testosterone production in the testes also decreases.
Note:
- This negative feedback loop helps to keep testosterone levels in the blood within a normal range.
- If testosterone levels were to become too high, it could have harmful effects, such as an increased risk of prostate cancer.
Here are some additional details about the diagram:
- The short loop refers to the direct feedback from testosterone to the hypothalamus.
- The long loops refer to the indirect feedback from testosterone to the hypothalamus and pituitary gland via the target tissues.
- The hormone shown in the diagram is testosterone, but this negative feedback loop can also apply to other hormones, such as cortisol and estrogen.
Endocrine System
Hypothalamic-pituitary axis = ?
Endocrine System
Hypothalamic-Pituitary Axis:
- The hypothalamic-pituitary axis (HPA axis), also sometimes called the hypothalamic-pituitary-adrenal (HPA) axis, is a major neuroendocrine system that plays a crucial role in maintaining homeostasis (internal balance) within our bodies.
- It’s a complex system involving three key players:
(1) Hypothalamus:
- This part of the brain acts as the control center, monitoring internal and external stimuli and sending signals to the pituitary gland.
(2) Pituitary gland:
- Often called the “master gland,” it sits at the base of the brain and produces various hormones in response to signals from the hypothalamus.
- These hormones then regulate other endocrine glands and various bodily functions.
(3) Adrenal glands:
- These glands sit atop the kidneys and have two parts; the medulla and the cortex.
- The medulla produces adrenaline and noradrenaline (stress hormones).
- While the cortex produces cortisol (another stress hormone) and other hormones regulating metabolism, blood pressure, and electrolyte balance.
(a) How it works:
- The hypothalamus monitors your body’s state through various factors like stress, blood pressure, blood sugar levels, and sleep patterns.
- Based on this information, the hypothalamus releases releasing hormones (CRH for cortisol, for example) to stimulate the pituitary gland.
- The pituitary gland, in turn, releases tropic hormones (ACTH for cortisol, for example) into the bloodstream.
- The tropic hormones travel to their target organs, in this case, the adrenal glands.
- Upon receiving the tropic hormone, the adrenal glands produce and release specific hormones (like cortisol) into the bloodstream to help your body adapt to the perceived need.
- Once the desired effect is achieved (e.g., increased energy during stress), rising hormone levels send feedback signals back to the hypothalamus and pituitary gland, inhibiting their further release. This negative feedback loop helps maintain balance and prevents hormone overproduction.
(b) Functions of the HPA axis:
- Stress response: This is the most well-known function. During stress, the HPA axis activates, releasing cortisol to increase energy, focus, and blood sugar levels to help you deal with the situation.
- Regulation of metabolism: Cortisol affects how your body uses carbohydrates, proteins, and fats for energy.
- Regulation of blood pressure and electrolyte balance: Cortisol and other hormones released by the adrenal glands help maintain balance in these crucial areas.
- Regulation of the immune system: Cortisol can modulate the immune system’s response to inflammation and infection.
- Regulation of mood and sleep: Cortisol levels influence mood and sleep patterns.
(c) Dysfunction of the HPA axis: If the HPA axis malfunctions, it can lead to various disorders, including:
- Cushing’s syndrome: Overproduction of cortisol due to HPA axis overactivity.
- Addison’s disease: Underproduction of cortisol due to HPA axis underactivity.
- Stress-related disorders: Chronic stress can lead to HPA axis overactivity and contribute to anxiety, depression, and other conditions.
- Tropic hormones = Hormones that stimulate other endocrine glands to produce their hormones.
Explain the Hypothalamic-Pituitary relationship
Endocrine System
Hypothalamic Pituitary Relationship:
(a) Pituitary gland:
- Also called hypophysis, pea size, is located at the base of the brain; referred to as Master Gland, releases several hormones.
- Anterior pituitary (adenohypophysis)
- Posterior pituitary (neurohypophysis).
(b) Hypothalamus:
- Almond size, located below the thalamus.
- Primary function is to maintain homeostasis (stability in the internal body).
- It links nervous and the endocrine system by the way of pituitary gland.
- Connects to pituitary gland by a thin stalk of tissue called infundibulum.
Hypothalamus and Posterior Pituitary:
- Another name for posterior pituitary gland = ?
Endocrine System
Hypothalamus and Posterior Pituitary:
Posterior lobe (neurohypophysis):
- Posterior lobe is a neural tissue.
- Posterior pituitary is a collection of nerve axons whose cell bodies are located in the hypothalamus.
- Hormones are synthesized in cell bodies, hormones are transported down the axons in the neurosecretory vesicles and stored in bulbous nerve terminals in the posterior pituitary.
- When these neurons receive signals, hormone is released by exocytosis into the blood.
Hypothalamus and Anterior Pituitary:
- ____ regulate the secretion of other hormones = ?
Endocrine System
Hypothalamus and Anterior Pituitary:
(a) Anterior lobe (adenohypophysis):
- Anterior lobe is primarily collection of endocrine cells.
- Trophic hormones regulate the secretion of other hormones.
- Trophic hormones can be stimulating or inhibiting.
- Trophic hormones are secreted into the surrounding hypothalamic tissue and enter the nearby capillary plexus.
- Blood from these capillaries drain into the anterior lobe.
- Hormones act on cells of anterior lobe, they stimulate / inhibit the release of anterior pituitary hormones.
- Anterior pituitary hormones then enters the systemic circulation which delivers them to the target tissues.
Anterior Pituitary Hormones = ?
6
Endocrine System
Anterior Pituitary Hormones:
(1) Somatotropin (Growth Hormone):
- Stimulates growth synthesis and overall growth.
(2) Thyroid stimulating hormone (TSH):
- Stimulates synthesis and secretion of thyroid hormones.
(3) Follicle stiulating hormone (FSH):
- Ovaries and seminiferous tubule.
- Development of ovarian follicle.
- Secretes estrogen and maturation of sperm.
(4) Luteinizing hormone (LH):
- Promotes ovulation
- Synthesis of estrogen and progesterone and testosterone.
(5) Prolactin:
- Stimulates milk production and secretion in breast.
(6) Adrenocorticotrophic hormone (ACTH):
- Stimulates synthesis and secretion of adrenal cortical hormones.
Posterior Pituitary Hormones = ?
2
Endocrine System
Posterior Pituitary Hormones:
(1) Antidiuertic hormone (ADH):
- Kidneys
- Reabsorbs water
(2) Oxytocin:
- Uterus
- Stimulates contraction
Gland / Hormone / Target-Action:
- Stimulates growth synthesis and overall growth.
Endocrine System
Gland / Hormone / Target-Action:
(a) Somatotropin (Growth Hormone):
- Stimulates growth synthesis and overall growth.
(b) Anterior pituitary (adenohypophysis)
Gland / Hormone / Target-Action:
- TSH = ?
Endocrine System
Gland / Hormone / Target-Action:
(a) Thyroid stimulating hormone (TSH):
- Stimulates synthesis and secretion of thyroid hormones.
(b) Anterior pituitary (adenohypophysis)
Gland / Hormone / Target-Action:
- Follicle stiulating hormone = ?
Endocrine System
Gland / Hormone / Target-Action:
(a) Follicle stiulating hormone (FSH):
- Ovaries and seminiferous tubule.
- Development of ovarian follicle.
- Secretes estrogen and maturation of sperm.
(b) Anterior pituitary (adenohypophysis)
Gland / Hormone / Target-Action:
- ADH = ?
Endocrine System
Gland / Hormone / Target-Action:
(a) Antidiuertic hormone (ADH):
- Kidneys
- Reabsorbs water
(b) Posterior pituitary (neurohypophysis)
Gland / Hormone / Target-Action:
- Oxytocin = ?
Gland / Hormone / Target-Action:
(a) Oxytocin:
- Uterus
- Stimulates contraction
(b) Posterior pituitary (neurohypophysis)
Hormones released by Hypothalamus = ?
Endocrine System
Hormones released by Hypothalamus:
(a) Thyrotropin-releasing hormone (TRH)
- Simulates production of TSH and prolactin
(b) Corticotrophin- releasing hormone (CRH)
- Stimulates production of ACTH
(c) Gonadotrophin- releasing hormone
(GnRH)
- Stimulates secretion of LH and FSH
(d) Somatotropin Release inhibiting hormone (SIRF)
- Inhibits secretion of growth hormone
(e) Growth hormone-releasing hormone (GHRH)
- Stimulates secretion of growth hormone
(f) Dopamine or prolactin inhibiting hormone (PIF)
- Inhibits secretion of prolactin
Anti Diuretic Hormone:
Endocrine System
Anti Diuretic Hormone:
- ADH (vasopressin) is the major hormone concerned with regulation of body fluid osmolarity.
- ADH is secreted by posterior pituitary in response to an increase in the serum osmolarity.
- Acts on the cells of the late distal tubule and collecting duct to increase water reabsorption thus and decreasing body fluid osmolarity back towards normal.
Factors that stimulate the secretion of ADH by the posterior pituitary:
- Increased plasma osmolarity (the concentration of a solution expressed as the total number of soluteparticles per litre
- Hypovolemia
- Hemorrhage
- Decrease in ECF volume - decrease in arterial pressure-sensed by baroreceptors in carotid and aortic arch - increase in ADH secretion - stimulates water reabsorption in the collecting ducts.
Regulation of Growth Hormone Secretion:
- Explain this picture = ?
Endocrine System
Regulation of Growth Hormone Secretion:
(1) GHRH release:
- The hypothalamus releases GHRH in response to a variety of stimuli, including sleep, exercise, low blood sugar, and certain hormones.
(2) Growth hormone release:
- When GHRH reaches the anterior pituitary gland, it binds to GHRH receptors on the surface of somatotroph cells. This triggers the release of growth hormone into the bloodstream.
(3) IGF production:
- Growth hormone stimulates the production of IGFs in the liver and other tissues. IGFs are responsible for many of the growth-promoting effects of growth hormone, such as increasing bone and muscle mass and promoting tissue repair.
(4) Negative feedback:
- IGFs also act on the hypothalamus and anterior pituitary gland to inhibit the release of GHRH and growth hormone, respectively. This creates a negative feedback loop that helps to keep growth hormone levels within a normal range.
Growth Promoting and Anti-Insulin Effects:
- Two hormones regulate GH secretion = ?
Endocrine System
Growth Promoting and Anti-Insulin Effects:
(a) Two hypothalamic hormones regulate GH secretion:
- GHRH = Increases GH release
- Somatostatin = Inhibits GH release
Diabetes Insipidus:
- What is it = ?
- Causes = ?
- Pathophysiology = ?
Endocrine System
Diabetes Insipidus:
(a) Introduction:
- Condition of deficient antidiuretic hormone (ADH)
- Inability of the body to concentrate or retain water.
(b) Causes:
(b.1) Central diabetes insipidus
- Injury to hypothalamus.
(b.2) Central diabetes insipidus
- Injury to neurohypophyseal tract
- Injury to posterior pituitary gland
(b.3) Nephrogenic diabetes insipidus
- Inadequate kidney response to the presence of ADH
(b.4) Primary polydipsia
- Excessive consumption of fluids secondary to damage of thirst-regulating mechanism within the hypothalamus.
(c) Pathophysiology:
- Polyuria is excessive urination
- Polydipsia is excessive thirst.
- These symptoms can be caused by a condition called diabetes insipidus (DI), which is caused by a lack of antidiuretic hormone (ADH).
- ADH is a hormone that is produced by the hypothalamus and stored in the pituitary gland.
- It helps the kidneys to reabsorb water from the urine, which helps to keep the body hydrated.
- When there is not enough ADH, the kidneys cannot reabsorb water as effectively, and this leads to polyuria and polydipsia.
- The diagram shows that there are two main types of DI: central DI and nephrogenic DI.
- Central DI is caused by damage to the hypothalamus or pituitary gland.
- Nephrogenic DI is caused by damage to the kidneys.
- The diagram also shows that there are other causes of polyuria and polydipsia, such as excessive fluid intake, diuretic use, and some medications.
- Prevalence: 3 per 100,000 population
SIADH:
- What is it = ?
- Diagnosis = ?
- Treatment = ?
Endocrine System
Syndrome of Inappropriate Antidiuretic Hormone (SIADH):
(a) Excessive release of ADH- water intoxication due to fluid retention.
(b) Hyponatremia
- Mild hyponatremia (125-130mEq/L)
- Severe hyponatremia (sodium < 115 mEq/L)- life threating condition
- Lethargy, nausea, weakness, increased thirst, muscle cramps, headache, irritability, seizures, coma.
(c) Diagnosis
- Hyponatremia (serum sodium < 135mEq/L)
- Plasma osmolality < 280 mOsm/kg
- Decreased urine output
- Concentrated urine
(d) Treatment
- Removal of the cause
- Patient at risk should be monitored for weight gain/ changes in urination/ fluid intake
- With mild symptoms (Fluid restrictions, sodium restrictions)
- Severe hyponatremia(Hypertonic IV solution)
- Medications to increase the urine output
