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Questions and Answers
What is the primary role of the hypothalamus within the hypothalamic-pituitary axis?
What is the primary role of the hypothalamus within the hypothalamic-pituitary axis?
- Serving as a relay station for sensory information to the cerebral cortex.
- Regulating the anterior pituitary gland's secretion through releasing and inhibiting hormones. (correct)
- Directly secreting hormones into the bloodstream to affect peripheral tissues.
- Producing digestive enzymes to aid in nutrient absorption.
Which of the following best describes the anatomical relationship between the hypothalamus and the pituitary gland?
Which of the following best describes the anatomical relationship between the hypothalamus and the pituitary gland?
- The hypothalamus communicates with the anterior pituitary via the hypophyseal portal system, and the posterior pituitary via direct neuronal projections. (correct)
- They are directly connected through a series of gap junctions allowing for rapid electrical communication.
- They are completely separate structures with no direct communication, relying solely on systemic hormone circulation.
- The hypothalamus physically encapsulates the pituitary gland, providing structural support.
Which of the following hormones is NOT produced by the anterior pituitary (adenohypophysis)?
Which of the following hormones is NOT produced by the anterior pituitary (adenohypophysis)?
- Adrenocorticotropic Hormone (ACTH)
- Thyroid-Stimulating Hormone (TSH)
- Antidiuretic Hormone (ADH) (correct)
- Growth Hormone (GH)
What is the functional significance of the hypophyseal portal system?
What is the functional significance of the hypophyseal portal system?
Which of these best describes the role of the posterior pituitary?
Which of these best describes the role of the posterior pituitary?
Which of the following endocrine glands is NOT directly regulated by the Hypothalamic-Pituitary Axis?
Which of the following endocrine glands is NOT directly regulated by the Hypothalamic-Pituitary Axis?
Which of the following is a function regulated by the coordinated activity of the hypothalamus and pituitary gland?
Which of the following is a function regulated by the coordinated activity of the hypothalamus and pituitary gland?
The hypothalamus controls the secretion of the anterior pituitary through which mechanism?
The hypothalamus controls the secretion of the anterior pituitary through which mechanism?
What is the origin of the anterior hypophysis during development?
What is the origin of the anterior hypophysis during development?
Which cell type constitutes approximately 50% of the adenohypophysis and is responsible for producing growth hormone (GH)?
Which cell type constitutes approximately 50% of the adenohypophysis and is responsible for producing growth hormone (GH)?
When anterior pituitary cells are stained for microscopic examination, which type stains with an acid dye?
When anterior pituitary cells are stained for microscopic examination, which type stains with an acid dye?
Which of the following hormones is produced by corticotropes in the anterior pituitary?
Which of the following hormones is produced by corticotropes in the anterior pituitary?
Which of the following hormones is NOT released by the hypothalamus to control the anterior pituitary?
Which of the following hormones is NOT released by the hypothalamus to control the anterior pituitary?
What distinguishes the endings of neurosecretory neurons in the hypothalamus from typical nerve endings?
What distinguishes the endings of neurosecretory neurons in the hypothalamus from typical nerve endings?
What structural characteristic of the capillaries within the hypophyseal portal system facilitates rapid hormone exchange?
What structural characteristic of the capillaries within the hypophyseal portal system facilitates rapid hormone exchange?
Which hormone primarily regulates water excretion in the urine?
Which hormone primarily regulates water excretion in the urine?
Which peptide hormone is known for promoting mammary gland development and milk production?
Which peptide hormone is known for promoting mammary gland development and milk production?
Which of the following is the correct term for gonadotropic hormones?
Which of the following is the correct term for gonadotropic hormones?
Which portion of the pituitary gland originates from neural tissue?
Which portion of the pituitary gland originates from neural tissue?
What are the names of the nuclei where the cell bodies of magnocellular neurons reside?
What are the names of the nuclei where the cell bodies of magnocellular neurons reside?
In the context of hormone action, what does 'fenestrated capillaries' refer to, specifically within the hypothalamic-hypophyseal portal system?
In the context of hormone action, what does 'fenestrated capillaries' refer to, specifically within the hypothalamic-hypophyseal portal system?
If a researcher selectively ablates corticotropes in the anterior pituitary, what hormonal change would be expected?
If a researcher selectively ablates corticotropes in the anterior pituitary, what hormonal change would be expected?
In a patient with a tumor affecting the hypothalamus, which of the following symptoms would NOT be expected?
In a patient with a tumor affecting the hypothalamus, which of the following symptoms would NOT be expected?
What is the functional consequence of delivering a drug that blocks the action of growth hormone-releasing hormone (GHRH) to the hypophyseal portal system?
What is the functional consequence of delivering a drug that blocks the action of growth hormone-releasing hormone (GHRH) to the hypophyseal portal system?
What is the primary role of the sella turcica in relation to the hypophysis?
What is the primary role of the sella turcica in relation to the hypophysis?
Which two hormones are synthesized by the hypothalamus but stored and released by the posterior pituitary?
Which two hormones are synthesized by the hypothalamus but stored and released by the posterior pituitary?
In which specific region of the hypothalamus are the cell bodies of neurons that produce vasopressin primarily located?
In which specific region of the hypothalamus are the cell bodies of neurons that produce vasopressin primarily located?
What would be the expected outcome of a lesion that severs the pituitary stalk?
What would be the expected outcome of a lesion that severs the pituitary stalk?
Why are the capillaries in the hypophyseal portal system described as ‘fenestrated’?
Why are the capillaries in the hypophyseal portal system described as ‘fenestrated’?
Which mechanism allows oxytocin to facilitate milk ejection from the mammary glands?
Which mechanism allows oxytocin to facilitate milk ejection from the mammary glands?
What distinguishes magnocellular neurons from other neurons in the hypothalamus?
What distinguishes magnocellular neurons from other neurons in the hypothalamus?
In what manner do hormones produced by the hypothalamus reach the anterior pituitary?
In what manner do hormones produced by the hypothalamus reach the anterior pituitary?
Which cellular characteristic is used to classify anterior pituitary cells as either acidophilic or basophilic?
Which cellular characteristic is used to classify anterior pituitary cells as either acidophilic or basophilic?
A patient presents with increased levels of cortisol due to a pituitary adenoma. Which type of anterior pituitary cell is most likely affected?
A patient presents with increased levels of cortisol due to a pituitary adenoma. Which type of anterior pituitary cell is most likely affected?
Which of the following is the correct sequence of the HPA axis?
Which of the following is the correct sequence of the HPA axis?
What is the functional relationship between the hypothalamus and the anterior pituitary?
What is the functional relationship between the hypothalamus and the anterior pituitary?
Which cellular mechanism most directly couples increased plasma osmolality or decreased blood volume to the release of vasopressin (ADH) from the posterior pituitary?
Which cellular mechanism most directly couples increased plasma osmolality or decreased blood volume to the release of vasopressin (ADH) from the posterior pituitary?
Flashcards
What is the Hypothalamus?
What is the Hypothalamus?
The main connection point for neurological and endocrine signals in the brain, impacting autonomic, endocrine, and limbic systems.
What is the Hypophysis (Pituitary Gland)?
What is the Hypophysis (Pituitary Gland)?
A small gland in the brain's sella turcica, connected to the hypothalamus by the pituitary stalk, and divided into anterior and posterior parts.
What is the Anterior Pituitary (Adenohypophysis)?
What is the Anterior Pituitary (Adenohypophysis)?
Originates from Rathke's pouch, contains five major cell types, and produces various hormones.
What do somatotropes produce?
What do somatotropes produce?
Growth hormone (GH); about 50% of the adenohypophysis gland.
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What do Corticotropes produce?
What do Corticotropes produce?
Adrenocorticotropic hormone (ACTH); 15 to 20% of gland.
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What do Lactotropes produce?
What do Lactotropes produce?
Prolactin; 15 to 20% of gland.
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What do Thyrotropes produce?
What do Thyrotropes produce?
Thyroid-stimulating hormone (TSH); 5% of gland.
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What do Gonadotropes produce?
What do Gonadotropes produce?
Gonadotropic hormones like LH and FSH (10-15% of gland); control reproductive functions.
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What is the Hypothalamic-Pituitary Axis?
What is the Hypothalamic-Pituitary Axis?
The hypothalamus regulates the endocrine system by working with the pituitary gland and is a connection to the nervous sytem by using hormones.
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What does the hypothalamus control?
What does the hypothalamus control?
Releasing and inhibiting hormones that effect the secretion of the anterior pituitary.
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What is the Hypothalamic-Hypophysial Portal System?
What is the Hypothalamic-Hypophysial Portal System?
A system that carries hormones from the hypothalamus directly to the anterior pituitary gland.
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What is the function of the anterior pituitary hormones?
What is the function of the anterior pituitary hormones?
The peptide hormones secreted from the anterior pituitary play a major role in the control of metabolic functions throughout the body.
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List some controls of the anterior pituitary
List some controls of the anterior pituitary
Growth, cortisol/androgen production, thyroid hormone synthesis, prolactin production, and gonadotropins release. These are released by the anterior pit.
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What effect does oxytocin have?
What effect does oxytocin have?
Released in response to copulation, pregnancy, and nursing and helps with milk expression and labor.
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- The Hypothalamic-Pituitary (HP) Axis is discussed.
- Clara Camargo, DVM, Cert AqV, presents VP 2025.
Learning Objectives
- Understand the relationship between the hypothalamus and the pituitary gland.
- Describe the structures and characteristics of the anterior (adenohypophysis) and posterior (neurohypophysis) pituitary.
- Describe the functions of hormones produced by the hypothalamus and pituitary gland.
- List the endocrine glands regulated by the Hypothalamic-Pituitary Axis.
Hypothalamic-Pituitary Axis
- The HPA axis involves the hypothalamus, anterior pituitary, and adrenal cortex.
- The hypothalamus releases Corticotropin Releasing Hormone (CRH).
- The anterior pituitary releases Adrenocorticotropic Hormone (ACTH).
- The adrenal cortex releases Cortisol (CORT).
- Negative feedback loops regulate the hormone release.
Hypothalamus
- The hypothalamus is a neurological and endocrine connection.
- It has more than 12 nuclei that regulate the autonomic, endocrine, and limbic systems.
- The autonomic system includes sympathetic and parasympathetic functions.
- The limbic system covers instincts, emotions, memories, and behaviors like feeding, pleasure, and sex.
Hypophysis
- The hypophysis (pituitary gland) is located in the sella turcica and connected to the hypothalamus through the pituitary stalk (infundibulum).
- It is divided into the anterior pituitary (adenohypophysis) and posterior pituitary (neurohypophysis).
Anterior pituitary (Adenohypophysis)
- The anterior hypophysis originates from the Rathke's pouch.
- It contains 5 major types of cells with epithelioid nature, each producing a different hormone.
Adenohypophysis
- The adenohypophysis has 5 major cell types: somatotropes, corticotropes, lactotropes, thyrotropes, and gonadotropes.
- Somatotropes produce growth hormone (GH), about 50% of the total adenohypophysis gland.
- Corticotropes produce adrenocorticotropic hormone (ACTH), 15-20%.
- Lactotropes produce prolactin, 15-20%.
- Thyrotropes produce thyroid-stimulating hormone (TSH), 5%.
- Gonadotropes produce gonadotropic hormones (LH and FSH), 10-15%.
- Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH).
Anterior Pituitary Cells
- When stained, anterior pituitary cells show different appearances under a light microscope.
- Acidophilic cells:
- Include somatotropes and lactotropes.
- Stain with an acid dye like Eosin, appearing pink.
- Basophilic cells:
- Include corticotropes, thyrotropes, and gonadotropes.
- Stain with a basic dye like Haematoxylin, appearing dark purple.
- Chromophobic cells:
- Are non-secretory and do not stain.
- Include stem cells that can differentiate into hormone-producing cells.
Hypothalamic Pituitary Axis Regulation
- The endocrine system is regulated when the hypothalamus works in close connection with the pituitary gland.
Hypothalamus and Pituitary Gland Function
- The hypothalamus and pituitary gland function in a coordinated way to affect the endocrine system.
- This system regulates thyroid glands, adrenal glands, reproductive glands, growth, milk production/ejection, and osmoregulation.
Hypothalamus Control of Anterior Pituitary
- The hypothalamus controls the anterior pituitary (adenohypophysis) secretion via releasing and inhibiting hormones.
- Releasing hormones include thyrotropin-releasing hormone (TRH), corticotropin-releasing hormone (CRH), gonadotropin-releasing hormone (GnRH), and growth hormone-releasing hormone (GHRH).
- Inhibiting hormones include growth hormone-inhibiting hormone (GHIH/Somatostatin) and prolactin-inhibiting hormone (PIH/Dopamine).
Neurosecretory Neurons
- Neurosecretory neurons in the hypothalamus synthesize and secrete hypothalamic releasing and inhibiting hormones.
- Neurons originate in various parts of the hypothalamus (nuclei).
- The endings of these fibers (axon terminal) are different from most nerve endings in the CNS.
- They secrete hormones into the ECF (extra cellular fluid).
- The hypothalamic-hypophysial portal system carries hormones from the hypothalamus directly to the sinuses of the anterior pituitary gland.
Hypothalamic-Hypophyseal Portal System
- The hypothalamic-hypophyseal portal system is a microcirculation system of blood vessels at the base of the brain connecting the hypothalamus with the anterior pituitary.
- Its main function is to quickly transport and exchange hormones between the hypothalamus and anterior pituitary gland.
- The capillaries in the portal system are fenestrated, allowing a rapid exchange between the hypothalamus and the pituitary.
Anterior Pituitary Hormones
- Peptide hormones of the anterior pituitary control metabolic functions throughout the body.
- Growth hormones (GH) promote growth by affecting protein formation, cell multiplication, and cell differentiation.
- Corticotropin (adrenocorticotropic hormone ACTH) controls the secretion of adrenocortical hormones (cortisol and androgen) and affects metabolism, blood pressure, and reproduction.
- Thyrotropin (thyroid stimulating hormone TSH) controls the HPT axis and influences the synthesis and secretion of thyroxine (T4) and triiodothyronine (T3) by the thyroid gland.
- Prolactin (PRL) promotes mammary gland development and milk production.
- Gonadotropins (FSH and LH) control the growth of the ovaries and testes and impact hormonal and reproductive activities.
Posterior Pituitary (Neurohypophysis)
- The neurohypophysis originates from a neural tissue outgrowth from the hypothalamus.
- It is composed of glial-like cells and axons of large neurons called magnocellular neurons.
- The cell bodies are located in the hypothalamus.
- Hormones are produced in the hypothalamus and transported in the axoplasm to the posterior pituitary.
- Axon terminals contain many secretory vesicles and lie on the surface of terminal capillaries, where they secrete 2 hormones.
Neurohypophysis Peptide Hormones
- Two important peptide hormones are produced in the hypothalamus and secreted by the neurohypophysis: antidiuretic hormone (ADH) or vasopressin and oxytocin.
- Antidiuretic hormone (ADH) controls the rate of water excretion into the urine, helping to control the concentration of water in the body fluids.
- Oxytocin is released during copulation, pregnancy, and nursing and affects smooth muscles.
- It helps with the delivery of the baby at the end of gestation and helps express milk from the mammary gland to the nipples during suckling.
- Oxytocin is released in response to low-intensity stimulation of the skin.
Feedback Loops in the HP Axis
- Releasing hormones from the hypothalamus act on the hypophysis.
- Trophic hormones from the hypophysis act on the target gland.
- Target hormones from the target gland feed back to the hypothalamus and hypophysis.
ADH Production and Release
- ADH is produced in the neuron's cell body and transported through the axon using a specific protein called neurophysin.
- Production of mature peptide takes place as the secretory granules move down the axon.
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