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Questions and Answers
Which type of cells are the most abundant in the anterior pituitary gland?
What is the primary function of vasopressin (ADH) in the posterior pituitary?
What is the primary function of oxytocin in the posterior pituitary?
What is the primary function of the zona glomerulosa in the adrenal cortex?
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What is the primary function of the zona fasciculata in the adrenal cortex?
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What is the primary function of the zona reticularis in the adrenal cortex?
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What is the primary function of chromaffin cells in the adrenal medulla?
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What is the primary function of corticotrophs in the anterior pituitary gland?
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What is the primary function of gonadotrophs in the anterior pituitary gland?
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What is the primary function of thyrotrophs in the anterior pituitary gland?
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What is the primary function of the parathyroid hormone (PTH)?
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What is the main function of the pineal gland?
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What is the primary function of thyroid hormones T3 and T4?
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What is the primary function of norepinephrine?
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What is the primary function of epinephrine?
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What is the main component of the thyroid follicle lumen?
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What is the primary function of principal cells in the parathyroid gland?
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What is unique about the pineal gland?
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What type of cells are found in the parathyroid gland, aside from principal cells?
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What is the function of thyrocytes in the thyroid gland?
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Which of the following is a characteristic of steroid hormones?
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What is the primary mechanism of hormone release in response to changing levels of ions or nutrients in the blood?
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Which of the following types of hormone secretion involves the stimulation of neighboring cells through short loops of blood vessels?
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What is the name of the part of the pituitary gland that grows down from the diencephalon?
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Which of the following is a type of cell found in the pars distalis of the adenohypophysis?
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What is the name of the structure that forms the pituitary gland during embryonic development?
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Which of the following types of hormone secretion involves the stimulation of cells that are in direct contact with each other?
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What is the name of the part of the pituitary gland that develops from the oral cavity?
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Which of the following is a characteristic of peptide hormones?
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What is the name of the structure that forms the posterior part of the pituitary gland?
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Study Notes
Endocrine Glands
- Secretory cells of endocrine glands release hormones into capillaries for distribution throughout the body.
- Hormones can target cells with receptors at a distance away from the site of secretion.
- Paracrine secretion: cells produce hormones that stimulate or inhibit their neighbors through short loops of blood vessels or localized dispersal in intestinal fluid.
- Autocrine secretion: cells produce hormones that stimulate or inhibit themselves.
- Juxtacrine: cells sit side by side, one with a hormone on the surface and the other with a receptor.
Mechanisms of Hormone Release
- Humoral: in response to changing levels of ions or nutrients in the blood.
- Neural: stimulated by nerves.
- Hormonal: stimulation received from other hormones.
Classification of Hormones
- Peptides: stored in granules and released via exocytosis.
- Amino-acids.
- Steroids: lipid soluble and diffuse freely through the plasma membrane.
Pituitary Gland (Hypophysis)
- Lies below the brain in a small cavity.
- Develops from ectoderm and diencephalon during embryonic development.
- Consists of posterior neurohypophysis and anterior hypophysis (Rathke pouch).
Adenohypophysis (Anterior Pituitary)
- Derived from embryonic hypophyseal pouch.
- Has three parts: pars distalis, pars tuberalis, and pars intermedia.
- Pars distalis:
- Has a thin fibrous capsule.
- Main components: cords of endocrine cells, fenestrated capillaries, and supporting reticular CT.
- Contains two types of cells: chromophobes and chromophils.
- Chromophils are secretory cells divided into basophils and acidophils.
- Acidophils: secrete either somatotrophs (GH) or lactotrophs (PRL).
- Basophils: corticotropes (ACTH), gonadotrophs (LH and FSH), and thyrotropes (TSH).
- Pars tuberalis: mostly gonadotroph cells.
- Pars intermedia:
- Contains basophils (corticotrophs), chromophobes, and colloid-filled cysts.
- Corticotrophs of pars intermedia express POMC, but cleave it differently, producing mainly smaller peptide hormones.
Control of Hormone Secretion in the Anterior Pituitary
- Controlled primarily by peptide-related hypothalamic hormones.
- Most of the hormones are releasing hormones.
- Inhibiting hormones: block hormone secretion in specific cells of adenohypophysis.
- Negative feedback: by hormones from the target organ.
Neurohypophysis (Posterior Pituitary)
- Composed of pars nervosa and infundibulum.
- Does not contain cells that synthesize hormones, instead, it contains neural tissue made of unmyelinated axons.
- Contains glial cells called pituicytes.
- Hormones found in the pars nervosa: vasopressin (ADH) and oxytocin.
- Both bound to neurophysin I and II.
- Hormone release: nerve impulses trigger the release of ADH and oxytocin from neurosecretory bodies.
Vasopressin (ADH)
- Releases in response to body tonicity.
- Promotes water reabsorption and restoring osmotic balance.
Oxytocin
- Stimulates uterine smooth muscle contractions during childbirth.
- Induces contraction of myoepithelial cells in mammary glands, facilitating milk ejection.
- Promotes psychological effects such as pair bonding.
Adrenal Glands
- Consist of stroma and parenchyma.
- Stroma: reticular fibers.
- Parenchyma: dense CT and trabeculae.
- Each gland has two regions: a medulla and a cortex.
- Cortex: mesoderm and medulla: ectoderm/nural crest.
Adrenal Cortex
- Responsible for synthesizing and secreting steroid hormones.
- Cells of the adrenal cortex have acidophilic cytoplasm, are rich in lipid droplets, and have mitochondria involved in both ATP production and steroid synthesis.
- Organized into three zones, each responsible for producing a specific type of steroid hormone:
- Zona glomerulosa: produces aldosterone.
- Zona fasciculata: secretes glucocorticoids, especially cortisol, and small amounts of androgens.
- Zona reticularis: produces cortisol, but primarily weak androgens, including DHEA that converts to testosterone.
Adrenal Medulla
- Composed of large polyhedral cells arranged in cords and clumps, supported by a reticular fiber network.
- Chromaffin cells are innervated by preganglionic sympathetic neurons.
- The innervation triggers:
- Catecholamines: during stress and intense emotional reactions.
- Epinephrine: increases heart rate and dilates lobules and arteries in muscle.
- Norepinephrine: increases blood flow to the heart, muscle, and brain.
Thyroid Gland
- Consists of two lobes united by isthmus.
- Synthesizes thyroid hormones T4 and T3.
- Helps control the basal metabolic rate in cells throughout the body as well as maintaining the hormone calcitonin.
- Stroma: capsule, septa, reticular CT.
- Parenchyma: simple epithelial thyroid follicles with a central lumen densely packed with gelatinous acidophilic colloid.
- Contain a large glycoprotein called thyroglobin.
- Follicular cells (thyrocytes) range from squamous to low columnar, controlled by TSH, and function to synthesize T3 and T4.
Parathyroid Glands
- Contained within a thin capsule from which septa extends into the gland.
- A sparse reticular CT stroma.
- Principal cells: granules containing polypeptide.
- Main cells responsible for synthesis and secretion of PTH.
- Parathyroid hormone (PTH): an important regulator of blood calcium levels.
- Has three major targets: osteoblast and osteoclasts (bone), kidneys (calcium and phosphate reabsorption), and intestine (vitamin D activation).
Pineal Gland
- Regulates daily rhythms of bodily activities.
- Covered by CT of pia mater.
- Pinalocytes: contain serotonin and produce melatonin.
- Converts sensory input regarding light and darkness into variations in hormonal functions.
- Feature of the pineal gland: presence of salts called corpora arenacea.
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Description
Learn about the functions of endocrine glands, how hormones are released and transported, and the different types of hormone secretion, including paracrine and autocrine secretion.
