Week 1
Mar 24: Endocrine Overview
Pituitary Gland
Overview
- Master organ of the endocrine system
- Composed of two distinct parts:
1. Anterior Pituitary (Adenohypophysis)
- Histo: Glandular epithelium
- Derived from ectoderm
2. Posterior Pituitary (Neurohypophysis)
- Histo: Neural secretory tissue
- Derived from neuroectoderm
Anterior Lobe (Adenohypophysis)
- Structural Components
- Derived from Rathke's pouch: outpouching of the roof of pharynx
- Consists of: glandular epithelium
- Pars anterior: Largest part, responsible for hormone secretion
- Pars intermedia: Thin epithelial layer between anterior and posterior lobes
- Pars tuberalis: Upward extension surrounding infundibulum
- Hormone Regulation
- Release controlled by hypothalamus
- Communication via neurotransmitters in hypophyseal portal vessels
Posterior Lobe (Neurohypophysis)
- Originates from embryonic forebrain, essentially an extension of the hypothalamus
- Consists of Nervous tissue
- Infundibulum stalk: hypothalamus connection
- Pars Nervosa: hormone storage
Embryological Development
Dual Origin
- Epithelial Portion: pharyngeal roof and Rathke's pouch detaches→ anterior pituitary
- Neural: extension of forebrain/hypothalamus via infundibulum → posterior pituitary
Developmental Process
- Week 3:
- Proximal infundibulum develops in 3rd ventricle floor→ ventral growth
- Ectodermal placode→ forms Rathke's pouch→ loses stomodeum connection
- Differentiates into adenohypophysis
Anatomical Characteristics
- Small, ovoid body (500mg), located in sphenoid bone's pituitary fossa
- Covered by diaphragm sellae, near optic chiasm
- Vasculature
, - Superior Hypophyseal A→ Anterior Pituitary
- Unique portal system allows hypothalamic communication
- Posterior Pituitary: multiple arteries
- Superior Hypophyseal A, Infundibular A, Inferior Hypophyseal A
- Anterior Pituitary
- Pars Distalis: makes up bulk of anterior pituitary
- Contains acidophiles, basophils, chromophobes
- Pars Intermedia: between pars distalis and pars nervosa
- Contains Rathke Cysts and secretory cells → Melanocyte-Stimulating H(MSH)
- Pars Tuberalis: surrounds the infundibulum
- Contains parenchymal cells and squamous/cuboidal cells
- Shows immunoreactivity to ACTH, FSH, LH
Cellular Composition
Anterior Pituitary
1. Acidophils (40%): stain red
- Somatotrophs: Somatotropin(GH)
- Stimulated by GHRH, Inhibited by Somatostatin
- Increase metabolic rate via Insulin-GF(IGF-1) → bone and muscle growth
- Lactotropes: Prolactin
- Stimulated by PRH and Oxytocin, Inhibited by Dopamine/PIF
- Increase mammary gland development and lactation
2. Basophils (10%): stain blue
- Corticotrophs: ACTH precursor
- Stimulated by CRH, Inhibited by high plasma cortisol
- Increases release of hormones from adrenal cortex
- Thyrotrophs: Thyrotropin (TSH)
- Stimulated by TRH, Inhibited by blood T4/T3
- Increases synthesis and release of thyroid hormones
- Gonadotrophs: FSH and LH
- Stimulated by GnRH, Inhibited by ovarian/testes hormones
- Increases ovarian follicle growth, estrogen/testosterone secretion
3. Chromophobes (50%): stain weakly
- Stem cells and undifferentiated progenitors
Posterior Pituitary
- Characteristics
- Not a true endocrine gland, storage and release site for hypothalamic neurosecretions
- Cell bodies in hypothalamus, unmyelinated axons terminating in posterior lobe
- Pars Nervosa: Neurosecretory axon endings
- Features Herring bodies: accumulation of axons with granules(oxytocin/ADH)
- Supported by Pituicytes (glial-like cells)
- Infundibulum: Neurosecretory tract
Adrenal Glands
Overview
, - Location: Paired organs on superior poles of each kidney
- Structure:
- Covered by dense connective tissue capsule
- Stroma consists of reticular fibers and microvasculature
- Composed of two regions: adrenal cortex and adrenal medulla
Neurovasculature
Arterial Supply
- 50-60 branches penetrate the gland's capsule
- Sources:
- Inferior Phrenic AA→ Superior Suprarenal AA→ superior portion
- Abdominal Aorta → Middle Suprarenal AA → middle portion
- Renal A → Inferior Suprarenal AA → inferior portion
Venous Drainage
- Right Suprarenal V→ drains into IVC
- Left suprarenal V→ drains into L Renal V
- Often joined by Inferior Phrenic V
Innervation
- Adrenal Cortex: mainly responds to hormonal input (ACTH)
- Secrete mineralocorticoids, glucocorticoids, sex hormones
- Adrenal Medulla: direct sympathetic innervation, produces steroids
- Preganglionic Symp. fibers → pass thru paravertebral ganglia→ Greater Splanchnic N
- Can synapse directly on adrenal medulla or pass thru celiac ganglion→ Chromaffin cells
- Produces catecholamines (norepinephrine/epinephrine)
Adrenal Cortex
- Mesenchyme origin
- Functional Zones (outer→inner)
1. Zona Glomerulosa (15% of cortex)
- Histo:: Small columnar/pyramidal shaped cells
- Hormone: Mineralocorticoids(Aldosterone)
- Regulates Na+ and K+ homeostasis→ fluid and electrolyte balance
- Feedback from renin-angiotensin system
2. Zona Fasciculata (80% of cortex)
- Histo: Long cords of large, polyhedral cells
- Hormones: Glucocorticoids (Cortisol, Corticosterone)
- Regulates gluconeogenesis and glycogenesis
3. Zona Reticularis (5-7% of cortex)
- Histo: Smaller cells with dark nuclei
- Hormones: Dehydroepiandrosterone (DHEA)
- Secretes weak androgens(masculinizing)
Adrenal Medulla
- Neural crest origin
- Functions as modified sympathetic ganglion
1. Chromaffin Cells:
- Large epithelioid cells arranged in clusters or cords surrounded by capillaries
, - Two populations of cells called pheochromocytes
- Secrete either epinephrine/norepinephrine depending on cortisol levels (high→epi)
- Stimulated by ACh from preganglionic sympathetic terminals
Adrenal Gland Development
- Cortex: Develops from mesenchyme
- Medulla: Develops from neural crest cells
Developmental Stages:
- Neural crest cells form mass on medial side of embryonic cortex
- Zona glomerulosa and fasciculata present at birth
- Zona reticularis recognizable by end of third year
- Fetal glands 10-20x larger relative to body weight compared to adult glands
Thyroid Gland
Overview
- Largest endocrine gland, 2 lobes connected by an isthmus
- Located anteriorly to the 2nd tracheal ring, surrounded by a thin fibrous capsule
- Hormones Produced
1. Thyroid hormones(T3/T4): Control metabolism rate
2. Calcitonin: decreases blood calcium
Neurovasculature
- Arterial Supply
- L side: Common Carotid A→ superior part, L Subclavian A → inferior part
- R: Brachiocephalic trunk→ External Carotid → Superior Thyroid A and Thyroid ima A
- Superior part and isthmus
- Venous Drainage
- Similarly named veins → L and R brachiocephalic V→ SVC
- Innervation
- Sympathetic: superior, middle & inferior sympathetic cervical ganglia
- Parasympathetic: Vagus N (CN X)
Thyroid Gland Development
- Origin: endoderm
- Forms at the apex of foramen cecum on developing tongue
- Key Developmental Stages:
- Forms late in week 4
- Descends through neck via thyroglossal duct
- Duct breaks down by end of fifth week
- Reaches final position below cricoid cartilage by seventh week
- Begins hormone secretion as early as week 10
- Cell Composition:
- Invested with neural crest cells and ultimobranchial bodies → form parafollicular cells
- Pharyngeal Pouches
- 1st: tympanic cavity and mastoid(ear part)
- 2nd: palatine/tonsillar fossa
- 3rd: inferior parathyroid and thymus
- 4th: superior parathyroid and parafollicular cells of thyroid
Mar 24: Endocrine Overview
Pituitary Gland
Overview
- Master organ of the endocrine system
- Composed of two distinct parts:
1. Anterior Pituitary (Adenohypophysis)
- Histo: Glandular epithelium
- Derived from ectoderm
2. Posterior Pituitary (Neurohypophysis)
- Histo: Neural secretory tissue
- Derived from neuroectoderm
Anterior Lobe (Adenohypophysis)
- Structural Components
- Derived from Rathke's pouch: outpouching of the roof of pharynx
- Consists of: glandular epithelium
- Pars anterior: Largest part, responsible for hormone secretion
- Pars intermedia: Thin epithelial layer between anterior and posterior lobes
- Pars tuberalis: Upward extension surrounding infundibulum
- Hormone Regulation
- Release controlled by hypothalamus
- Communication via neurotransmitters in hypophyseal portal vessels
Posterior Lobe (Neurohypophysis)
- Originates from embryonic forebrain, essentially an extension of the hypothalamus
- Consists of Nervous tissue
- Infundibulum stalk: hypothalamus connection
- Pars Nervosa: hormone storage
Embryological Development
Dual Origin
- Epithelial Portion: pharyngeal roof and Rathke's pouch detaches→ anterior pituitary
- Neural: extension of forebrain/hypothalamus via infundibulum → posterior pituitary
Developmental Process
- Week 3:
- Proximal infundibulum develops in 3rd ventricle floor→ ventral growth
- Ectodermal placode→ forms Rathke's pouch→ loses stomodeum connection
- Differentiates into adenohypophysis
Anatomical Characteristics
- Small, ovoid body (500mg), located in sphenoid bone's pituitary fossa
- Covered by diaphragm sellae, near optic chiasm
- Vasculature
, - Superior Hypophyseal A→ Anterior Pituitary
- Unique portal system allows hypothalamic communication
- Posterior Pituitary: multiple arteries
- Superior Hypophyseal A, Infundibular A, Inferior Hypophyseal A
- Anterior Pituitary
- Pars Distalis: makes up bulk of anterior pituitary
- Contains acidophiles, basophils, chromophobes
- Pars Intermedia: between pars distalis and pars nervosa
- Contains Rathke Cysts and secretory cells → Melanocyte-Stimulating H(MSH)
- Pars Tuberalis: surrounds the infundibulum
- Contains parenchymal cells and squamous/cuboidal cells
- Shows immunoreactivity to ACTH, FSH, LH
Cellular Composition
Anterior Pituitary
1. Acidophils (40%): stain red
- Somatotrophs: Somatotropin(GH)
- Stimulated by GHRH, Inhibited by Somatostatin
- Increase metabolic rate via Insulin-GF(IGF-1) → bone and muscle growth
- Lactotropes: Prolactin
- Stimulated by PRH and Oxytocin, Inhibited by Dopamine/PIF
- Increase mammary gland development and lactation
2. Basophils (10%): stain blue
- Corticotrophs: ACTH precursor
- Stimulated by CRH, Inhibited by high plasma cortisol
- Increases release of hormones from adrenal cortex
- Thyrotrophs: Thyrotropin (TSH)
- Stimulated by TRH, Inhibited by blood T4/T3
- Increases synthesis and release of thyroid hormones
- Gonadotrophs: FSH and LH
- Stimulated by GnRH, Inhibited by ovarian/testes hormones
- Increases ovarian follicle growth, estrogen/testosterone secretion
3. Chromophobes (50%): stain weakly
- Stem cells and undifferentiated progenitors
Posterior Pituitary
- Characteristics
- Not a true endocrine gland, storage and release site for hypothalamic neurosecretions
- Cell bodies in hypothalamus, unmyelinated axons terminating in posterior lobe
- Pars Nervosa: Neurosecretory axon endings
- Features Herring bodies: accumulation of axons with granules(oxytocin/ADH)
- Supported by Pituicytes (glial-like cells)
- Infundibulum: Neurosecretory tract
Adrenal Glands
Overview
, - Location: Paired organs on superior poles of each kidney
- Structure:
- Covered by dense connective tissue capsule
- Stroma consists of reticular fibers and microvasculature
- Composed of two regions: adrenal cortex and adrenal medulla
Neurovasculature
Arterial Supply
- 50-60 branches penetrate the gland's capsule
- Sources:
- Inferior Phrenic AA→ Superior Suprarenal AA→ superior portion
- Abdominal Aorta → Middle Suprarenal AA → middle portion
- Renal A → Inferior Suprarenal AA → inferior portion
Venous Drainage
- Right Suprarenal V→ drains into IVC
- Left suprarenal V→ drains into L Renal V
- Often joined by Inferior Phrenic V
Innervation
- Adrenal Cortex: mainly responds to hormonal input (ACTH)
- Secrete mineralocorticoids, glucocorticoids, sex hormones
- Adrenal Medulla: direct sympathetic innervation, produces steroids
- Preganglionic Symp. fibers → pass thru paravertebral ganglia→ Greater Splanchnic N
- Can synapse directly on adrenal medulla or pass thru celiac ganglion→ Chromaffin cells
- Produces catecholamines (norepinephrine/epinephrine)
Adrenal Cortex
- Mesenchyme origin
- Functional Zones (outer→inner)
1. Zona Glomerulosa (15% of cortex)
- Histo:: Small columnar/pyramidal shaped cells
- Hormone: Mineralocorticoids(Aldosterone)
- Regulates Na+ and K+ homeostasis→ fluid and electrolyte balance
- Feedback from renin-angiotensin system
2. Zona Fasciculata (80% of cortex)
- Histo: Long cords of large, polyhedral cells
- Hormones: Glucocorticoids (Cortisol, Corticosterone)
- Regulates gluconeogenesis and glycogenesis
3. Zona Reticularis (5-7% of cortex)
- Histo: Smaller cells with dark nuclei
- Hormones: Dehydroepiandrosterone (DHEA)
- Secretes weak androgens(masculinizing)
Adrenal Medulla
- Neural crest origin
- Functions as modified sympathetic ganglion
1. Chromaffin Cells:
- Large epithelioid cells arranged in clusters or cords surrounded by capillaries
, - Two populations of cells called pheochromocytes
- Secrete either epinephrine/norepinephrine depending on cortisol levels (high→epi)
- Stimulated by ACh from preganglionic sympathetic terminals
Adrenal Gland Development
- Cortex: Develops from mesenchyme
- Medulla: Develops from neural crest cells
Developmental Stages:
- Neural crest cells form mass on medial side of embryonic cortex
- Zona glomerulosa and fasciculata present at birth
- Zona reticularis recognizable by end of third year
- Fetal glands 10-20x larger relative to body weight compared to adult glands
Thyroid Gland
Overview
- Largest endocrine gland, 2 lobes connected by an isthmus
- Located anteriorly to the 2nd tracheal ring, surrounded by a thin fibrous capsule
- Hormones Produced
1. Thyroid hormones(T3/T4): Control metabolism rate
2. Calcitonin: decreases blood calcium
Neurovasculature
- Arterial Supply
- L side: Common Carotid A→ superior part, L Subclavian A → inferior part
- R: Brachiocephalic trunk→ External Carotid → Superior Thyroid A and Thyroid ima A
- Superior part and isthmus
- Venous Drainage
- Similarly named veins → L and R brachiocephalic V→ SVC
- Innervation
- Sympathetic: superior, middle & inferior sympathetic cervical ganglia
- Parasympathetic: Vagus N (CN X)
Thyroid Gland Development
- Origin: endoderm
- Forms at the apex of foramen cecum on developing tongue
- Key Developmental Stages:
- Forms late in week 4
- Descends through neck via thyroglossal duct
- Duct breaks down by end of fifth week
- Reaches final position below cricoid cartilage by seventh week
- Begins hormone secretion as early as week 10
- Cell Composition:
- Invested with neural crest cells and ultimobranchial bodies → form parafollicular cells
- Pharyngeal Pouches
- 1st: tympanic cavity and mastoid(ear part)
- 2nd: palatine/tonsillar fossa
- 3rd: inferior parathyroid and thymus
- 4th: superior parathyroid and parafollicular cells of thyroid
